tools/objtool/check.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * Copyright (C) 2015-2017 Josh Poimboeuf <jpoimboe@redhat.com>
   4  */
   5
   6 #include <string.h>
   7 #include <stdlib.h>
   8
   9 #include "builtin.h"
  10 #include "check.h"
  11 #include "elf.h"
  12 #include "special.h"
  13 #include "arch.h"
  14 #include "warn.h"
  15
  16 #include <linux/hashtable.h>
  17 #include <linux/kernel.h>
  18
  19 #define FAKE_JUMP_OFFSET -1
  20
  21 #define C_JUMP_TABLE_SECTION ".rodata..c_jump_table"
  22
  23 struct alternative {
  24         struct list_head list;
  25         struct instruction *insn;
  26         bool skip_orig;
  27 };
  28
  29 const char *objname;
  30 struct cfi_init_state initial_func_cfi;
  31
  32 struct instruction *find_insn(struct objtool_file *file,
  33                               struct section *sec, unsigned long offset)
  34 {
  35         struct instruction *insn;
  36
  37         hash_for_each_possible(file->insn_hash, insn, hash, sec_offset_hash(sec, offset)) {
  38                 if (insn->sec == sec && insn->offset == offset)
  39                         return insn;
  40         }
  41
  42         return NULL;
  43 }
  44
  45 static struct instruction *next_insn_same_sec(struct objtool_file *file,
  46                                               struct instruction *insn)
  47 {
  48         struct instruction *next = list_next_entry(insn, list);
  49
  50         if (!next || &next->list == &file->insn_list || next->sec != insn->sec)
  51                 return NULL;
  52
  53         return next;
  54 }
  55
  56 static struct instruction *next_insn_same_func(struct objtool_file *file,
  57                                                struct instruction *insn)
  58 {
  59         struct instruction *next = list_next_entry(insn, list);
  60         struct symbol *func = insn->func;
  61
  62         if (!func)
  63                 return NULL;
  64
  65         if (&next->list != &file->insn_list && next->func == func)
  66                 return next;
  67
  68         /* Check if we're already in the subfunction: */
  69         if (func == func->cfunc)
  70                 return NULL;
  71
  72         /* Move to the subfunction: */
  73         return find_insn(file, func->cfunc->sec, func->cfunc->offset);
  74 }
  75
  76 #define func_for_each_insn(file, func, insn)                            \
  77         for (insn = find_insn(file, func->sec, func->offset);           \
  78              insn;                                                      \
  79              insn = next_insn_same_func(file, insn))
  80
  81 #define sym_for_each_insn(file, sym, insn)                              \
  82         for (insn = find_insn(file, sym->sec, sym->offset);             \
  83              insn && &insn->list != &file->insn_list &&                 \
  84                 insn->sec == sym->sec &&                                \
  85                 insn->offset < sym->offset + sym->len;                  \
  86              insn = list_next_entry(insn, list))
  87
  88 #define sym_for_each_insn_continue_reverse(file, sym, insn)             \
  89         for (insn = list_prev_entry(insn, list);                        \
  90              &insn->list != &file->insn_list &&                         \
  91                 insn->sec == sym->sec && insn->offset >= sym->offset;   \
  92              insn = list_prev_entry(insn, list))
  93
  94 #define sec_for_each_insn_from(file, insn)                              \
  95         for (; insn; insn = next_insn_same_sec(file, insn))
  96
  97 #define sec_for_each_insn_continue(file, insn)                          \
  98         for (insn = next_insn_same_sec(file, insn); insn;               \
  99              insn = next_insn_same_sec(file, insn))
 100
 101 static bool is_static_jump(struct instruction *insn)
 102 {
 103         return insn->type == INSN_JUMP_CONDITIONAL ||
 104                insn->type == INSN_JUMP_UNCONDITIONAL;
 105 }
 106
 107 static bool is_sibling_call(struct instruction *insn)
 108 {
 109         /* An indirect jump is either a sibling call or a jump to a table. */
 110         if (insn->type == INSN_JUMP_DYNAMIC)
 111                 return list_empty(&insn->alts);
 112
 113         if (!is_static_jump(insn))
 114                 return false;
 115
 116         /* add_jump_destinations() sets insn->call_dest for sibling calls. */
 117         return !!insn->call_dest;
 118 }
 119
 120 /*
 121  * This checks to see if the given function is a "noreturn" function.
 122  *
 123  * For global functions which are outside the scope of this object file, we
 124  * have to keep a manual list of them.
 125  *
 126  * For local functions, we have to detect them manually by simply looking for
 127  * the lack of a return instruction.
 128  */
 129 static bool __dead_end_function(struct objtool_file *file, struct symbol *func,
 130                                 int recursion)
 131 {
 132         int i;
 133         struct instruction *insn;
 134         bool empty = true;
 135
 136         /*
 137          * Unfortunately these have to be hard coded because the noreturn
 138          * attribute isn't provided in ELF data.
 139          */
 140         static const char * const global_noreturns[] = {
 141                 "__stack_chk_fail",
 142                 "panic",
 143                 "do_exit",
 144                 "do_task_dead",
 145                 "__module_put_and_exit",
 146                 "complete_and_exit",
 147                 "__reiserfs_panic",
 148                 "lbug_with_loc",
 149                 "fortify_panic",
 150                 "usercopy_abort",
 151                 "machine_real_restart",
 152                 "rewind_stack_do_exit",
 153                 "kunit_try_catch_throw",
 154         };
 155
 156         if (!func)
 157                 return false;
 158
 159         if (func->bind == STB_WEAK)
 160                 return false;
 161
 162         if (func->bind == STB_GLOBAL)
 163                 for (i = 0; i < ARRAY_SIZE(global_noreturns); i++)
 164                         if (!strcmp(func->name, global_noreturns[i]))
 165                                 return true;
 166
 167         if (!func->len)
 168                 return false;
 169
 170         insn = find_insn(file, func->sec, func->offset);
 171         if (!insn->func)
 172                 return false;
 173
 174         func_for_each_insn(file, func, insn) {
 175                 empty = false;
 176
 177                 if (insn->type == INSN_RETURN)
 178                         return false;
 179         }
 180
 181         if (empty)
 182                 return false;
 183
 184         /*
 185          * A function can have a sibling call instead of a return.  In that
 186          * case, the function's dead-end status depends on whether the target
 187          * of the sibling call returns.
 188          */
 189         func_for_each_insn(file, func, insn) {
 190                 if (is_sibling_call(insn)) {
 191                         struct instruction *dest = insn->jump_dest;
 192
 193                         if (!dest)
 194                                 /* sibling call to another file */
 195                                 return false;
 196
 197                         /* local sibling call */
 198                         if (recursion == 5) {
 199                                 /*
 200                                  * Infinite recursion: two functions have
 201                                  * sibling calls to each other.  This is a very
 202                                  * rare case.  It means they aren't dead ends.
 203                                  */
 204                                 return false;
 205                         }
 206
 207                         return __dead_end_function(file, dest->func, recursion+1);
 208                 }
 209         }
 210
 211         return true;
 212 }
 213
 214 static bool dead_end_function(struct objtool_file *file, struct symbol *func)
 215 {
 216         return __dead_end_function(file, func, 0);
 217 }
 218
 219 static void init_cfi_state(struct cfi_state *cfi)
 220 {
 221         int i;
 222
 223         for (i = 0; i < CFI_NUM_REGS; i++) {
 224                 cfi->regs[i].base = CFI_UNDEFINED;
 225                 cfi->vals[i].base = CFI_UNDEFINED;
 226         }
 227         cfi->cfa.base = CFI_UNDEFINED;
 228         cfi->drap_reg = CFI_UNDEFINED;
 229         cfi->drap_offset = -1;
 230 }
 231
 232 static void init_insn_state(struct insn_state *state, struct section *sec)
 233 {
 234         memset(state, 0, sizeof(*state));
 235         init_cfi_state(&state->cfi);
 236
 237         /*
 238          * We need the full vmlinux for noinstr validation, otherwise we can
 239          * not correctly determine insn->call_dest->sec (external symbols do
 240          * not have a section).
 241          */
 242         if (vmlinux && sec)
 243                 state->noinstr = sec->noinstr;
 244 }
 245
 246 /*
 247  * Call the arch-specific instruction decoder for all the instructions and add
 248  * them to the global instruction list.
 249  */
 250 static int decode_instructions(struct objtool_file *file)
 251 {
 252         struct section *sec;
 253         struct symbol *func;
 254         unsigned long offset;
 255         struct instruction *insn;
 256         unsigned long nr_insns = 0;
 257         int ret;
 258
 259         for_each_sec(file, sec) {
 260
 261                 if (!(sec->sh.sh_flags & SHF_EXECINSTR))
 262                         continue;
 263
 264                 if (strcmp(sec->name, ".altinstr_replacement") &&
 265                     strcmp(sec->name, ".altinstr_aux") &&
 266                     strncmp(sec->name, ".discard.", 9))
 267                         sec->text = true;
 268
 269                 if (!strcmp(sec->name, ".noinstr.text") ||
 270                     !strcmp(sec->name, ".entry.text"))
 271                         sec->noinstr = true;
 272
 273                 for (offset = 0; offset < sec->len; offset += insn->len) {
 274                         insn = malloc(sizeof(*insn));
 275                         if (!insn) {
 276                                 WARN("malloc failed");
 277                                 return -1;
 278                         }
 279                         memset(insn, 0, sizeof(*insn));
 280                         INIT_LIST_HEAD(&insn->alts);
 281                         INIT_LIST_HEAD(&insn->stack_ops);
 282                         init_cfi_state(&insn->cfi);
 283
 284                         insn->sec = sec;
 285                         insn->offset = offset;
 286
 287                         ret = arch_decode_instruction(file->elf, sec, offset,
 288                                                       sec->len - offset,
 289                                                       &insn->len, &insn->type,
 290                                                       &insn->immediate,
 291                                                       &insn->stack_ops);
 292                         if (ret)
 293                                 goto err;
 294
 295                         hash_add(file->insn_hash, &insn->hash, sec_offset_hash(sec, insn->offset));
 296                         list_add_tail(&insn->list, &file->insn_list);
 297                         nr_insns++;
 298                 }
 299
 300                 list_for_each_entry(func, &sec->symbol_list, list) {
 301                         if (func->type != STT_FUNC || func->alias != func)
 302                                 continue;
 303
 304                         if (!find_insn(file, sec, func->offset)) {
 305                                 WARN("%s(): can't find starting instruction",
 306                                      func->name);
 307                                 return -1;
 308                         }
 309
 310                         sym_for_each_insn(file, func, insn)
 311                                 insn->func = func;
 312                 }
 313         }
 314
 315         if (stats)
 316                 printf("nr_insns: %lu\n", nr_insns);
 317
 318         return 0;
 319
 320 err:
 321         free(insn);
 322         return ret;
 323 }
 324
 325 /*
 326  * Mark "ud2" instructions and manually annotated dead ends.
 327  */
 328 static int add_dead_ends(struct objtool_file *file)
 329 {
 330         struct section *sec;
 331         struct rela *rela;
 332         struct instruction *insn;
 333         bool found;
 334
 335         /*
 336          * By default, "ud2" is a dead end unless otherwise annotated, because
 337          * GCC 7 inserts it for certain divide-by-zero cases.
 338          */
 339         for_each_insn(file, insn)
 340                 if (insn->type == INSN_BUG)
 341                         insn->dead_end = true;
 342
 343         /*
 344          * Check for manually annotated dead ends.
 345          */
 346         sec = find_section_by_name(file->elf, ".rela.discard.unreachable");
 347         if (!sec)
 348                 goto reachable;
 349
 350         list_for_each_entry(rela, &sec->rela_list, list) {
 351                 if (rela->sym->type != STT_SECTION) {
 352                         WARN("unexpected relocation symbol type in %s", sec->name);
 353                         return -1;
 354                 }
 355                 insn = find_insn(file, rela->sym->sec, rela->addend);
 356                 if (insn)
 357                         insn = list_prev_entry(insn, list);
 358                 else if (rela->addend == rela->sym->sec->len) {
 359                         found = false;
 360                         list_for_each_entry_reverse(insn, &file->insn_list, list) {
 361                                 if (insn->sec == rela->sym->sec) {
 362                                         found = true;
 363                                         break;
 364                                 }
 365                         }
 366
 367                         if (!found) {
 368                                 WARN("can't find unreachable insn at %s+0x%x",
 369                                      rela->sym->sec->name, rela->addend);
 370                                 return -1;
 371                         }
 372                 } else {
 373                         WARN("can't find unreachable insn at %s+0x%x",
 374                              rela->sym->sec->name, rela->addend);
 375                         return -1;
 376                 }
 377
 378                 insn->dead_end = true;
 379         }
 380
 381 reachable:
 382         /*
 383          * These manually annotated reachable checks are needed for GCC 4.4,
 384          * where the Linux unreachable() macro isn't supported.  In that case
 385          * GCC doesn't know the "ud2" is fatal, so it generates code as if it's
 386          * not a dead end.
 387          */
 388         sec = find_section_by_name(file->elf, ".rela.discard.reachable");
 389         if (!sec)
 390                 return 0;
 391
 392         list_for_each_entry(rela, &sec->rela_list, list) {
 393                 if (rela->sym->type != STT_SECTION) {
 394                         WARN("unexpected relocation symbol type in %s", sec->name);
 395                         return -1;
 396                 }
 397                 insn = find_insn(file, rela->sym->sec, rela->addend);
 398                 if (insn)
 399                         insn = list_prev_entry(insn, list);
 400                 else if (rela->addend == rela->sym->sec->len) {
 401                         found = false;
 402                         list_for_each_entry_reverse(insn, &file->insn_list, list) {
 403                                 if (insn->sec == rela->sym->sec) {
 404                                         found = true;
 405                                         break;
 406                                 }
 407                         }
 408
 409                         if (!found) {
 410                                 WARN("can't find reachable insn at %s+0x%x",
 411                                      rela->sym->sec->name, rela->addend);
 412                                 return -1;
 413                         }
 414                 } else {
 415                         WARN("can't find reachable insn at %s+0x%x",
 416                              rela->sym->sec->name, rela->addend);
 417                         return -1;
 418                 }
 419
 420                 insn->dead_end = false;
 421         }
 422
 423         return 0;
 424 }
 425
 426 /*
 427  * Warnings shouldn't be reported for ignored functions.
 428  */
 429 static void add_ignores(struct objtool_file *file)
 430 {
 431         struct instruction *insn;
 432         struct section *sec;
 433         struct symbol *func;
 434         struct rela *rela;
 435
 436         sec = find_section_by_name(file->elf, ".rela.discard.func_stack_frame_non_standard");
 437         if (!sec)
 438                 return;
 439
 440         list_for_each_entry(rela, &sec->rela_list, list) {
 441                 switch (rela->sym->type) {
 442                 case STT_FUNC:
 443                         func = rela->sym;
 444                         break;
 445
 446                 case STT_SECTION:
 447                         func = find_func_by_offset(rela->sym->sec, rela->addend);
 448                         if (!func)
 449                                 continue;
 450                         break;
 451
 452                 default:
 453                         WARN("unexpected relocation symbol type in %s: %d", sec->name, rela->sym->type);
 454                         continue;
 455                 }
 456
 457                 func_for_each_insn(file, func, insn)
 458                         insn->ignore = true;
 459         }
 460 }
 461
 462 /*
 463  * This is a whitelist of functions that is allowed to be called with AC set.
 464  * The list is meant to be minimal and only contains compiler instrumentation
 465  * ABI and a few functions used to implement *_{to,from}_user() functions.
 466  *
 467  * These functions must not directly change AC, but may PUSHF/POPF.
 468  */
 469 static const char *uaccess_safe_builtin[] = {
 470         /* KASAN */
 471         "kasan_report",
 472         "check_memory_region",
 473         /* KASAN out-of-line */
 474         "__asan_loadN_noabort",
 475         "__asan_load1_noabort",
 476         "__asan_load2_noabort",
 477         "__asan_load4_noabort",
 478         "__asan_load8_noabort",
 479         "__asan_load16_noabort",
 480         "__asan_storeN_noabort",
 481         "__asan_store1_noabort",
 482         "__asan_store2_noabort",
 483         "__asan_store4_noabort",
 484         "__asan_store8_noabort",
 485         "__asan_store16_noabort",
 486         /* KASAN in-line */
 487         "__asan_report_load_n_noabort",
 488         "__asan_report_load1_noabort",
 489         "__asan_report_load2_noabort",
 490         "__asan_report_load4_noabort",
 491         "__asan_report_load8_noabort",
 492         "__asan_report_load16_noabort",
 493         "__asan_report_store_n_noabort",
 494         "__asan_report_store1_noabort",
 495         "__asan_report_store2_noabort",
 496         "__asan_report_store4_noabort",
 497         "__asan_report_store8_noabort",
 498         "__asan_report_store16_noabort",
 499         /* KCOV */
 500         "write_comp_data",
 501         "__sanitizer_cov_trace_pc",
 502         "__sanitizer_cov_trace_const_cmp1",
 503         "__sanitizer_cov_trace_const_cmp2",
 504         "__sanitizer_cov_trace_const_cmp4",
 505         "__sanitizer_cov_trace_const_cmp8",
 506         "__sanitizer_cov_trace_cmp1",
 507         "__sanitizer_cov_trace_cmp2",
 508         "__sanitizer_cov_trace_cmp4",
 509         "__sanitizer_cov_trace_cmp8",
 510         "__sanitizer_cov_trace_switch",
 511         /* UBSAN */
 512         "ubsan_type_mismatch_common",
 513         "__ubsan_handle_type_mismatch",
 514         "__ubsan_handle_type_mismatch_v1",
 515         "__ubsan_handle_shift_out_of_bounds",
 516         /* misc */
 517         "csum_partial_copy_generic",
 518         "__memcpy_mcsafe",
 519         "mcsafe_handle_tail",
 520         "ftrace_likely_update", /* CONFIG_TRACE_BRANCH_PROFILING */
 521         NULL
 522 };
 523
 524 static void add_uaccess_safe(struct objtool_file *file)
 525 {
 526         struct symbol *func;
 527         const char **name;
 528
 529         if (!uaccess)
 530                 return;
 531
 532         for (name = uaccess_safe_builtin; *name; name++) {
 533                 func = find_symbol_by_name(file->elf, *name);
 534                 if (!func)
 535                         continue;
 536
 537                 func->uaccess_safe = true;
 538         }
 539 }
 540
 541 /*
 542  * FIXME: For now, just ignore any alternatives which add retpolines.  This is
 543  * a temporary hack, as it doesn't allow ORC to unwind from inside a retpoline.
 544  * But it at least allows objtool to understand the control flow *around* the
 545  * retpoline.
 546  */
 547 static int add_ignore_alternatives(struct objtool_file *file)
 548 {
 549         struct section *sec;
 550         struct rela *rela;
 551         struct instruction *insn;
 552
 553         sec = find_section_by_name(file->elf, ".rela.discard.ignore_alts");
 554         if (!sec)
 555                 return 0;
 556
 557         list_for_each_entry(rela, &sec->rela_list, list) {
 558                 if (rela->sym->type != STT_SECTION) {
 559                         WARN("unexpected relocation symbol type in %s", sec->name);
 560                         return -1;
 561                 }
 562
 563                 insn = find_insn(file, rela->sym->sec, rela->addend);
 564                 if (!insn) {
 565                         WARN("bad .discard.ignore_alts entry");
 566                         return -1;
 567                 }
 568
 569                 insn->ignore_alts = true;
 570         }
 571
 572         return 0;
 573 }
 574
 575 /*
 576  * Find the destination instructions for all jumps.
 577  */
 578 static int add_jump_destinations(struct objtool_file *file)
 579 {
 580         struct instruction *insn;
 581         struct rela *rela;
 582         struct section *dest_sec;
 583         unsigned long dest_off;
 584
 585         for_each_insn(file, insn) {
 586                 if (!is_static_jump(insn))
 587                         continue;
 588
 589                 if (insn->ignore || insn->offset == FAKE_JUMP_OFFSET)
 590                         continue;
 591
 592                 rela = find_rela_by_dest_range(file->elf, insn->sec,
 593                                                insn->offset, insn->len);
 594                 if (!rela) {
 595                         dest_sec = insn->sec;
 596                         dest_off = arch_jump_destination(insn);
 597                 } else if (rela->sym->type == STT_SECTION) {
 598                         dest_sec = rela->sym->sec;
 599                         dest_off = arch_dest_rela_offset(rela->addend);
 600                 } else if (rela->sym->sec->idx) {
 601                         dest_sec = rela->sym->sec;
 602                         dest_off = rela->sym->sym.st_value +
 603                                    arch_dest_rela_offset(rela->addend);
 604                 } else if (strstr(rela->sym->name, "_indirect_thunk_")) {
 605                         /*
 606                          * Retpoline jumps are really dynamic jumps in
 607                          * disguise, so convert them accordingly.
 608                          */
 609                         if (insn->type == INSN_JUMP_UNCONDITIONAL)
 610                                 insn->type = INSN_JUMP_DYNAMIC;
 611                         else
 612                                 insn->type = INSN_JUMP_DYNAMIC_CONDITIONAL;
 613
 614                         insn->retpoline_safe = true;
 615                         continue;
 616                 } else {
 617                         /* external sibling call */
 618                         insn->call_dest = rela->sym;
 619                         continue;
 620                 }
 621
 622                 insn->jump_dest = find_insn(file, dest_sec, dest_off);
 623                 if (!insn->jump_dest) {
 624
 625                         /*
 626                          * This is a special case where an alt instruction
 627                          * jumps past the end of the section.  These are
 628                          * handled later in handle_group_alt().
 629                          */
 630                         if (!strcmp(insn->sec->name, ".altinstr_replacement"))
 631                                 continue;
 632
 633                         WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
 634                                   insn->sec, insn->offset, dest_sec->name,
 635                                   dest_off);
 636                         return -1;
 637                 }
 638
 639                 /*
 640                  * Cross-function jump.
 641                  */
 642                 if (insn->func && insn->jump_dest->func &&
 643                     insn->func != insn->jump_dest->func) {
 644
 645                         /*
 646                          * For GCC 8+, create parent/child links for any cold
 647                          * subfunctions.  This is _mostly_ redundant with a
 648                          * similar initialization in read_symbols().
 649                          *
 650                          * If a function has aliases, we want the *first* such
 651                          * function in the symbol table to be the subfunction's
 652                          * parent.  In that case we overwrite the
 653                          * initialization done in read_symbols().
 654                          *
 655                          * However this code can't completely replace the
 656                          * read_symbols() code because this doesn't detect the
 657                          * case where the parent function's only reference to a
 658                          * subfunction is through a jump table.
 659                          */
 660                         if (!strstr(insn->func->name, ".cold.") &&
 661                             strstr(insn->jump_dest->func->name, ".cold.")) {
 662                                 insn->func->cfunc = insn->jump_dest->func;
 663                                 insn->jump_dest->func->pfunc = insn->func;
 664
 665                         } else if (insn->jump_dest->func->pfunc != insn->func->pfunc &&
 666                                    insn->jump_dest->offset == insn->jump_dest->func->offset) {
 667
 668                                 /* internal sibling call */
 669                                 insn->call_dest = insn->jump_dest->func;
 670                         }
 671                 }
 672         }
 673
 674         return 0;
 675 }
 676
 677 /*
 678  * Find the destination instructions for all calls.
 679  */
 680 static int add_call_destinations(struct objtool_file *file)
 681 {
 682         struct instruction *insn;
 683         unsigned long dest_off;
 684         struct rela *rela;
 685
 686         for_each_insn(file, insn) {
 687                 if (insn->type != INSN_CALL)
 688                         continue;
 689
 690                 rela = find_rela_by_dest_range(file->elf, insn->sec,
 691                                                insn->offset, insn->len);
 692                 if (!rela) {
 693                         dest_off = arch_jump_destination(insn);
 694                         insn->call_dest = find_func_by_offset(insn->sec, dest_off);
 695                         if (!insn->call_dest)
 696                                 insn->call_dest = find_symbol_by_offset(insn->sec, dest_off);
 697
 698                         if (insn->ignore)
 699                                 continue;
 700
 701                         if (!insn->call_dest) {
 702                                 WARN_FUNC("unsupported intra-function call",
 703                                           insn->sec, insn->offset);
 704                                 if (retpoline)
 705                                         WARN("If this is a retpoline, please patch it in with alternatives and annotate it with ANNOTATE_NOSPEC_ALTERNATIVE.");
 706                                 return -1;
 707                         }
 708
 709                         if (insn->func && insn->call_dest->type != STT_FUNC) {
 710                                 WARN_FUNC("unsupported call to non-function",
 711                                           insn->sec, insn->offset);
 712                                 return -1;
 713                         }
 714
 715                 } else if (rela->sym->type == STT_SECTION) {
 716                         dest_off = arch_dest_rela_offset(rela->addend);
 717                         insn->call_dest = find_func_by_offset(rela->sym->sec,
 718                                                               dest_off);
 719                         if (!insn->call_dest) {
 720                                 WARN_FUNC("can't find call dest symbol at %s+0x%lx",
 721                                           insn->sec, insn->offset,
 722                                           rela->sym->sec->name,
 723                                           dest_off);
 724                                 return -1;
 725                         }
 726                 } else
 727                         insn->call_dest = rela->sym;
 728         }
 729
 730         return 0;
 731 }
 732
 733 /*
 734  * The .alternatives section requires some extra special care, over and above
 735  * what other special sections require:
 736  *
 737  * 1. Because alternatives are patched in-place, we need to insert a fake jump
 738  *    instruction at the end so that validate_branch() skips all the original
 739  *    replaced instructions when validating the new instruction path.
 740  *
 741  * 2. An added wrinkle is that the new instruction length might be zero.  In
 742  *    that case the old instructions are replaced with noops.  We simulate that
 743  *    by creating a fake jump as the only new instruction.
 744  *
 745  * 3. In some cases, the alternative section includes an instruction which
 746  *    conditionally jumps to the _end_ of the entry.  We have to modify these
 747  *    jumps' destinations to point back to .text rather than the end of the
 748  *    entry in .altinstr_replacement.
 749  */
 750 static int handle_group_alt(struct objtool_file *file,
 751                             struct special_alt *special_alt,
 752                             struct instruction *orig_insn,
 753                             struct instruction **new_insn)
 754 {
 755         static unsigned int alt_group_next_index = 1;
 756         struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump = NULL;
 757         unsigned int alt_group = alt_group_next_index++;
 758         unsigned long dest_off;
 759
 760         last_orig_insn = NULL;
 761         insn = orig_insn;
 762         sec_for_each_insn_from(file, insn) {
 763                 if (insn->offset >= special_alt->orig_off + special_alt->orig_len)
 764                         break;
 765
 766                 insn->alt_group = alt_group;
 767                 last_orig_insn = insn;
 768         }
 769
 770         if (next_insn_same_sec(file, last_orig_insn)) {
 771                 fake_jump = malloc(sizeof(*fake_jump));
 772                 if (!fake_jump) {
 773                         WARN("malloc failed");
 774                         return -1;
 775                 }
 776                 memset(fake_jump, 0, sizeof(*fake_jump));
 777                 INIT_LIST_HEAD(&fake_jump->alts);
 778                 INIT_LIST_HEAD(&fake_jump->stack_ops);
 779                 init_cfi_state(&fake_jump->cfi);
 780
 781                 fake_jump->sec = special_alt->new_sec;
 782                 fake_jump->offset = FAKE_JUMP_OFFSET;
 783                 fake_jump->type = INSN_JUMP_UNCONDITIONAL;
 784                 fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
 785                 fake_jump->func = orig_insn->func;
 786         }
 787
 788         if (!special_alt->new_len) {
 789                 if (!fake_jump) {
 790                         WARN("%s: empty alternative at end of section",
 791                              special_alt->orig_sec->name);
 792                         return -1;
 793                 }
 794
 795                 *new_insn = fake_jump;
 796                 return 0;
 797         }
 798
 799         last_new_insn = NULL;
 800         alt_group = alt_group_next_index++;
 801         insn = *new_insn;
 802         sec_for_each_insn_from(file, insn) {
 803                 if (insn->offset >= special_alt->new_off + special_alt->new_len)
 804                         break;
 805
 806                 last_new_insn = insn;
 807
 808                 insn->ignore = orig_insn->ignore_alts;
 809                 insn->func = orig_insn->func;
 810                 insn->alt_group = alt_group;
 811
 812                 /*
 813                  * Since alternative replacement code is copy/pasted by the
 814                  * kernel after applying relocations, generally such code can't
 815                  * have relative-address relocation references to outside the
 816                  * .altinstr_replacement section, unless the arch's
 817                  * alternatives code can adjust the relative offsets
 818                  * accordingly.
 819                  *
 820                  * The x86 alternatives code adjusts the offsets only when it
 821                  * encounters a branch instruction at the very beginning of the
 822                  * replacement group.
 823                  */
 824                 if ((insn->offset != special_alt->new_off ||
 825                     (insn->type != INSN_CALL && !is_static_jump(insn))) &&
 826                     find_rela_by_dest_range(file->elf, insn->sec, insn->offset, insn->len)) {
 827
 828                         WARN_FUNC("unsupported relocation in alternatives section",
 829                                   insn->sec, insn->offset);
 830                         return -1;
 831                 }
 832
 833                 if (!is_static_jump(insn))
 834                         continue;
 835
 836                 if (!insn->immediate)
 837                         continue;
 838
 839                 dest_off = arch_jump_destination(insn);
 840                 if (dest_off == special_alt->new_off + special_alt->new_len) {
 841                         if (!fake_jump) {
 842                                 WARN("%s: alternative jump to end of section",
 843                                      special_alt->orig_sec->name);
 844                                 return -1;
 845                         }
 846                         insn->jump_dest = fake_jump;
 847                 }
 848
 849                 if (!insn->jump_dest) {
 850                         WARN_FUNC("can't find alternative jump destination",
 851                                   insn->sec, insn->offset);
 852                         return -1;
 853                 }
 854         }
 855
 856         if (!last_new_insn) {
 857                 WARN_FUNC("can't find last new alternative instruction",
 858                           special_alt->new_sec, special_alt->new_off);
 859                 return -1;
 860         }
 861
 862         if (fake_jump)
 863                 list_add(&fake_jump->list, &last_new_insn->list);
 864
 865         return 0;
 866 }
 867
 868 /*
 869  * A jump table entry can either convert a nop to a jump or a jump to a nop.
 870  * If the original instruction is a jump, make the alt entry an effective nop
 871  * by just skipping the original instruction.
 872  */
 873 static int handle_jump_alt(struct objtool_file *file,
 874                            struct special_alt *special_alt,
 875                            struct instruction *orig_insn,
 876                            struct instruction **new_insn)
 877 {
 878         if (orig_insn->type == INSN_NOP)
 879                 return 0;
 880
 881         if (orig_insn->type != INSN_JUMP_UNCONDITIONAL) {
 882                 WARN_FUNC("unsupported instruction at jump label",
 883                           orig_insn->sec, orig_insn->offset);
 884                 return -1;
 885         }
 886
 887         *new_insn = list_next_entry(orig_insn, list);
 888         return 0;
 889 }
 890
 891 /*
 892  * Read all the special sections which have alternate instructions which can be
 893  * patched in or redirected to at runtime.  Each instruction having alternate
 894  * instruction(s) has them added to its insn->alts list, which will be
 895  * traversed in validate_branch().
 896  */
 897 static int add_special_section_alts(struct objtool_file *file)
 898 {
 899         struct list_head special_alts;
 900         struct instruction *orig_insn, *new_insn;
 901         struct special_alt *special_alt, *tmp;
 902         struct alternative *alt;
 903         int ret;
 904
 905         ret = special_get_alts(file->elf, &special_alts);
 906         if (ret)
 907                 return ret;
 908
 909         list_for_each_entry_safe(special_alt, tmp, &special_alts, list) {
 910
 911                 orig_insn = find_insn(file, special_alt->orig_sec,
 912                                       special_alt->orig_off);
 913                 if (!orig_insn) {
 914                         WARN_FUNC("special: can't find orig instruction",
 915                                   special_alt->orig_sec, special_alt->orig_off);
 916                         ret = -1;
 917                         goto out;
 918                 }
 919
 920                 new_insn = NULL;
 921                 if (!special_alt->group || special_alt->new_len) {
 922                         new_insn = find_insn(file, special_alt->new_sec,
 923                                              special_alt->new_off);
 924                         if (!new_insn) {
 925                                 WARN_FUNC("special: can't find new instruction",
 926                                           special_alt->new_sec,
 927                                           special_alt->new_off);
 928                                 ret = -1;
 929                                 goto out;
 930                         }
 931                 }
 932
 933                 if (special_alt->group) {
 934                         if (!special_alt->orig_len) {
 935                                 WARN_FUNC("empty alternative entry",
 936                                           orig_insn->sec, orig_insn->offset);
 937                                 continue;
 938                         }
 939
 940                         ret = handle_group_alt(file, special_alt, orig_insn,
 941                                                &new_insn);
 942                         if (ret)
 943                                 goto out;
 944                 } else if (special_alt->jump_or_nop) {
 945                         ret = handle_jump_alt(file, special_alt, orig_insn,
 946                                               &new_insn);
 947                         if (ret)
 948                                 goto out;
 949                 }
 950
 951                 alt = malloc(sizeof(*alt));
 952                 if (!alt) {
 953                         WARN("malloc failed");
 954                         ret = -1;
 955                         goto out;
 956                 }
 957
 958                 alt->insn = new_insn;
 959                 alt->skip_orig = special_alt->skip_orig;
 960                 orig_insn->ignore_alts |= special_alt->skip_alt;
 961                 list_add_tail(&alt->list, &orig_insn->alts);
 962
 963                 list_del(&special_alt->list);
 964                 free(special_alt);
 965         }
 966
 967 out:
 968         return ret;
 969 }
 970
 971 static int add_jump_table(struct objtool_file *file, struct instruction *insn,
 972                             struct rela *table)
 973 {
 974         struct rela *rela = table;
 975         struct instruction *dest_insn;
 976         struct alternative *alt;
 977         struct symbol *pfunc = insn->func->pfunc;
 978         unsigned int prev_offset = 0;
 979
 980         /*
 981          * Each @rela is a switch table relocation which points to the target
 982          * instruction.
 983          */
 984         list_for_each_entry_from(rela, &table->sec->rela_list, list) {
 985
 986                 /* Check for the end of the table: */
 987                 if (rela != table && rela->jump_table_start)
 988                         break;
 989
 990                 /* Make sure the table entries are consecutive: */
 991                 if (prev_offset && rela->offset != prev_offset + 8)
 992                         break;
 993
 994                 /* Detect function pointers from contiguous objects: */
 995                 if (rela->sym->sec == pfunc->sec &&
 996                     rela->addend == pfunc->offset)
 997                         break;
 998
 999                 dest_insn = find_insn(file, rela->sym->sec, rela->addend);
1000                 if (!dest_insn)
1001                         break;
1002
1003                 /* Make sure the destination is in the same function: */
1004                 if (!dest_insn->func || dest_insn->func->pfunc != pfunc)
1005                         break;
1006
1007                 alt = malloc(sizeof(*alt));
1008                 if (!alt) {
1009                         WARN("malloc failed");
1010                         return -1;
1011                 }
1012
1013                 alt->insn = dest_insn;
1014                 list_add_tail(&alt->list, &insn->alts);
1015                 prev_offset = rela->offset;
1016         }
1017
1018         if (!prev_offset) {
1019                 WARN_FUNC("can't find switch jump table",
1020                           insn->sec, insn->offset);
1021                 return -1;
1022         }
1023
1024         return 0;
1025 }
1026
1027 /*
1028  * find_jump_table() - Given a dynamic jump, find the switch jump table in
1029  * .rodata associated with it.
1030  *
1031  * There are 3 basic patterns:
1032  *
1033  * 1. jmpq *[rodata addr](,%reg,8)
1034  *
1035  *    This is the most common case by far.  It jumps to an address in a simple
1036  *    jump table which is stored in .rodata.
1037  *
1038  * 2. jmpq *[rodata addr](%rip)
1039  *
1040  *    This is caused by a rare GCC quirk, currently only seen in three driver
1041  *    functions in the kernel, only with certain obscure non-distro configs.
1042  *
1043  *    As part of an optimization, GCC makes a copy of an existing switch jump
1044  *    table, modifies it, and then hard-codes the jump (albeit with an indirect
1045  *    jump) to use a single entry in the table.  The rest of the jump table and
1046  *    some of its jump targets remain as dead code.
1047  *
1048  *    In such a case we can just crudely ignore all unreachable instruction
1049  *    warnings for the entire object file.  Ideally we would just ignore them
1050  *    for the function, but that would require redesigning the code quite a
1051  *    bit.  And honestly that's just not worth doing: unreachable instruction
1052  *    warnings are of questionable value anyway, and this is such a rare issue.
1053  *
1054  * 3. mov [rodata addr],%reg1
1055  *    ... some instructions ...
1056  *    jmpq *(%reg1,%reg2,8)
1057  *
1058  *    This is a fairly uncommon pattern which is new for GCC 6.  As of this
1059  *    writing, there are 11 occurrences of it in the allmodconfig kernel.
1060  *
1061  *    As of GCC 7 there are quite a few more of these and the 'in between' code
1062  *    is significant. Esp. with KASAN enabled some of the code between the mov
1063  *    and jmpq uses .rodata itself, which can confuse things.
1064  *
1065  *    TODO: Once we have DWARF CFI and smarter instruction decoding logic,
1066  *    ensure the same register is used in the mov and jump instructions.
1067  *
1068  *    NOTE: RETPOLINE made it harder still to decode dynamic jumps.
1069  */
1070 static struct rela *find_jump_table(struct objtool_file *file,
1071                                       struct symbol *func,
1072                                       struct instruction *insn)
1073 {
1074         struct rela *text_rela, *table_rela;
1075         struct instruction *dest_insn, *orig_insn = insn;
1076         struct section *table_sec;
1077         unsigned long table_offset;
1078
1079         /*
1080          * Backward search using the @first_jump_src links, these help avoid
1081          * much of the 'in between' code. Which avoids us getting confused by
1082          * it.
1083          */
1084         for (;
1085              &insn->list != &file->insn_list && insn->func && insn->func->pfunc == func;
1086              insn = insn->first_jump_src ?: list_prev_entry(insn, list)) {
1087
1088                 if (insn != orig_insn && insn->type == INSN_JUMP_DYNAMIC)
1089                         break;
1090
1091                 /* allow small jumps within the range */
1092                 if (insn->type == INSN_JUMP_UNCONDITIONAL &&
1093                     insn->jump_dest &&
1094                     (insn->jump_dest->offset <= insn->offset ||
1095                      insn->jump_dest->offset > orig_insn->offset))
1096                     break;
1097
1098                 /* look for a relocation which references .rodata */
1099                 text_rela = find_rela_by_dest_range(file->elf, insn->sec,
1100                                                     insn->offset, insn->len);
1101                 if (!text_rela || text_rela->sym->type != STT_SECTION ||
1102                     !text_rela->sym->sec->rodata)
1103                         continue;
1104
1105                 table_offset = text_rela->addend;
1106                 table_sec = text_rela->sym->sec;
1107
1108                 if (text_rela->type == R_X86_64_PC32)
1109                         table_offset += 4;
1110
1111                 /*
1112                  * Make sure the .rodata address isn't associated with a
1113                  * symbol.  GCC jump tables are anonymous data.
1114                  *
1115                  * Also support C jump tables which are in the same format as
1116                  * switch jump tables.  For objtool to recognize them, they
1117                  * need to be placed in the C_JUMP_TABLE_SECTION section.  They
1118                  * have symbols associated with them.
1119                  */
1120                 if (find_symbol_containing(table_sec, table_offset) &&
1121                     strcmp(table_sec->name, C_JUMP_TABLE_SECTION))
1122                         continue;
1123
1124                 /*
1125                  * Each table entry has a rela associated with it.  The rela
1126                  * should reference text in the same function as the original
1127                  * instruction.
1128                  */
1129                 table_rela = find_rela_by_dest(file->elf, table_sec, table_offset);
1130                 if (!table_rela)
1131                         continue;
1132                 dest_insn = find_insn(file, table_rela->sym->sec, table_rela->addend);
1133                 if (!dest_insn || !dest_insn->func || dest_insn->func->pfunc != func)
1134                         continue;
1135
1136                 /*
1137                  * Use of RIP-relative switch jumps is quite rare, and
1138                  * indicates a rare GCC quirk/bug which can leave dead code
1139                  * behind.
1140                  */
1141                 if (text_rela->type == R_X86_64_PC32)
1142                         file->ignore_unreachables = true;
1143
1144                 return table_rela;
1145         }
1146
1147         return NULL;
1148 }
1149
1150 /*
1151  * First pass: Mark the head of each jump table so that in the next pass,
1152  * we know when a given jump table ends and the next one starts.
1153  */
1154 static void mark_func_jump_tables(struct objtool_file *file,
1155                                     struct symbol *func)
1156 {
1157         struct instruction *insn, *last = NULL;
1158         struct rela *rela;
1159
1160         func_for_each_insn(file, func, insn) {
1161                 if (!last)
1162                         last = insn;
1163
1164                 /*
1165                  * Store back-pointers for unconditional forward jumps such
1166                  * that find_jump_table() can back-track using those and
1167                  * avoid some potentially confusing code.
1168                  */
1169                 if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest &&
1170                     insn->offset > last->offset &&
1171                     insn->jump_dest->offset > insn->offset &&
1172                     !insn->jump_dest->first_jump_src) {
1173
1174                         insn->jump_dest->first_jump_src = insn;
1175                         last = insn->jump_dest;
1176                 }
1177
1178                 if (insn->type != INSN_JUMP_DYNAMIC)
1179                         continue;
1180
1181                 rela = find_jump_table(file, func, insn);
1182                 if (rela) {
1183                         rela->jump_table_start = true;
1184                         insn->jump_table = rela;
1185                 }
1186         }
1187 }
1188
1189 static int add_func_jump_tables(struct objtool_file *file,
1190                                   struct symbol *func)
1191 {
1192         struct instruction *insn;
1193         int ret;
1194
1195         func_for_each_insn(file, func, insn) {
1196                 if (!insn->jump_table)
1197                         continue;
1198
1199                 ret = add_jump_table(file, insn, insn->jump_table);
1200                 if (ret)
1201                         return ret;
1202         }
1203
1204         return 0;
1205 }
1206
1207 /*
1208  * For some switch statements, gcc generates a jump table in the .rodata
1209  * section which contains a list of addresses within the function to jump to.
1210  * This finds these jump tables and adds them to the insn->alts lists.
1211  */
1212 static int add_jump_table_alts(struct objtool_file *file)
1213 {
1214         struct section *sec;
1215         struct symbol *func;
1216         int ret;
1217
1218         if (!file->rodata)
1219                 return 0;
1220
1221         for_each_sec(file, sec) {
1222                 list_for_each_entry(func, &sec->symbol_list, list) {
1223                         if (func->type != STT_FUNC)
1224                                 continue;
1225
1226                         mark_func_jump_tables(file, func);
1227                         ret = add_func_jump_tables(file, func);
1228                         if (ret)
1229                                 return ret;
1230                 }
1231         }
1232
1233         return 0;
1234 }
1235
1236 static int read_unwind_hints(struct objtool_file *file)
1237 {
1238         struct section *sec, *relasec;
1239         struct rela *rela;
1240         struct unwind_hint *hint;
1241         struct instruction *insn;
1242         struct cfi_reg *cfa;
1243         int i;
1244
1245         sec = find_section_by_name(file->elf, ".discard.unwind_hints");
1246         if (!sec)
1247                 return 0;
1248
1249         relasec = sec->rela;
1250         if (!relasec) {
1251                 WARN("missing .rela.discard.unwind_hints section");
1252                 return -1;
1253         }
1254
1255         if (sec->len % sizeof(struct unwind_hint)) {
1256                 WARN("struct unwind_hint size mismatch");
1257                 return -1;
1258         }
1259
1260         file->hints = true;
1261
1262         for (i = 0; i < sec->len / sizeof(struct unwind_hint); i++) {
1263                 hint = (struct unwind_hint *)sec->data->d_buf + i;
1264
1265                 rela = find_rela_by_dest(file->elf, sec, i * sizeof(*hint));
1266                 if (!rela) {
1267                         WARN("can't find rela for unwind_hints[%d]", i);
1268                         return -1;
1269                 }
1270
1271                 insn = find_insn(file, rela->sym->sec, rela->addend);
1272                 if (!insn) {
1273                         WARN("can't find insn for unwind_hints[%d]", i);
1274                         return -1;
1275                 }
1276
1277                 cfa = &insn->cfi.cfa;
1278
1279                 if (hint->type == UNWIND_HINT_TYPE_RET_OFFSET) {
1280                         insn->ret_offset = hint->sp_offset;
1281                         continue;
1282                 }
1283
1284                 insn->hint = true;
1285
1286                 switch (hint->sp_reg) {
1287                 case ORC_REG_UNDEFINED:
1288                         cfa->base = CFI_UNDEFINED;
1289                         break;
1290                 case ORC_REG_SP:
1291                         cfa->base = CFI_SP;
1292                         break;
1293                 case ORC_REG_BP:
1294                         cfa->base = CFI_BP;
1295                         break;
1296                 case ORC_REG_SP_INDIRECT:
1297                         cfa->base = CFI_SP_INDIRECT;
1298                         break;
1299                 case ORC_REG_R10:
1300                         cfa->base = CFI_R10;
1301                         break;
1302                 case ORC_REG_R13:
1303                         cfa->base = CFI_R13;
1304                         break;
1305                 case ORC_REG_DI:
1306                         cfa->base = CFI_DI;
1307                         break;
1308                 case ORC_REG_DX:
1309                         cfa->base = CFI_DX;
1310                         break;
1311                 default:
1312                         WARN_FUNC("unsupported unwind_hint sp base reg %d",
1313                                   insn->sec, insn->offset, hint->sp_reg);
1314                         return -1;
1315                 }
1316
1317                 cfa->offset = hint->sp_offset;
1318                 insn->cfi.type = hint->type;
1319                 insn->cfi.end = hint->end;
1320         }
1321
1322         return 0;
1323 }
1324
1325 static int read_retpoline_hints(struct objtool_file *file)
1326 {
1327         struct section *sec;
1328         struct instruction *insn;
1329         struct rela *rela;
1330
1331         sec = find_section_by_name(file->elf, ".rela.discard.retpoline_safe");
1332         if (!sec)
1333                 return 0;
1334
1335         list_for_each_entry(rela, &sec->rela_list, list) {
1336                 if (rela->sym->type != STT_SECTION) {
1337                         WARN("unexpected relocation symbol type in %s", sec->name);
1338                         return -1;
1339                 }
1340
1341                 insn = find_insn(file, rela->sym->sec, rela->addend);
1342                 if (!insn) {
1343                         WARN("bad .discard.retpoline_safe entry");
1344                         return -1;
1345                 }
1346
1347                 if (insn->type != INSN_JUMP_DYNAMIC &&
1348                     insn->type != INSN_CALL_DYNAMIC) {
1349                         WARN_FUNC("retpoline_safe hint not an indirect jump/call",
1350                                   insn->sec, insn->offset);
1351                         return -1;
1352                 }
1353
1354                 insn->retpoline_safe = true;
1355         }
1356
1357         return 0;
1358 }
1359
1360 static int read_instr_hints(struct objtool_file *file)
1361 {
1362         struct section *sec;
1363         struct instruction *insn;
1364         struct rela *rela;
1365
1366         sec = find_section_by_name(file->elf, ".rela.discard.instr_end");
1367         if (!sec)
1368                 return 0;
1369
1370         list_for_each_entry(rela, &sec->rela_list, list) {
1371                 if (rela->sym->type != STT_SECTION) {
1372                         WARN("unexpected relocation symbol type in %s", sec->name);
1373                         return -1;
1374                 }
1375
1376                 insn = find_insn(file, rela->sym->sec, rela->addend);
1377                 if (!insn) {
1378                         WARN("bad .discard.instr_end entry");
1379                         return -1;
1380                 }
1381
1382                 insn->instr--;
1383         }
1384
1385         sec = find_section_by_name(file->elf, ".rela.discard.instr_begin");
1386         if (!sec)
1387                 return 0;
1388
1389         list_for_each_entry(rela, &sec->rela_list, list) {
1390                 if (rela->sym->type != STT_SECTION) {
1391                         WARN("unexpected relocation symbol type in %s", sec->name);
1392                         return -1;
1393                 }
1394
1395                 insn = find_insn(file, rela->sym->sec, rela->addend);
1396                 if (!insn) {
1397                         WARN("bad .discard.instr_begin entry");
1398                         return -1;
1399                 }
1400
1401                 insn->instr++;
1402         }
1403
1404         return 0;
1405 }
1406
1407 static void mark_rodata(struct objtool_file *file)
1408 {
1409         struct section *sec;
1410         bool found = false;
1411
1412         /*
1413          * Search for the following rodata sections, each of which can
1414          * potentially contain jump tables:
1415          *
1416          * - .rodata: can contain GCC switch tables
1417          * - .rodata.<func>: same, if -fdata-sections is being used
1418          * - .rodata..c_jump_table: contains C annotated jump tables
1419          *
1420          * .rodata.str1.* sections are ignored; they don't contain jump tables.
1421          */
1422         for_each_sec(file, sec) {
1423                 if (!strncmp(sec->name, ".rodata", 7) &&
1424                     !strstr(sec->name, ".str1.")) {
1425                         sec->rodata = true;
1426                         found = true;
1427                 }
1428         }
1429
1430         file->rodata = found;
1431 }
1432
1433 static int decode_sections(struct objtool_file *file)
1434 {
1435         int ret;
1436
1437         mark_rodata(file);
1438
1439         ret = decode_instructions(file);
1440         if (ret)
1441                 return ret;
1442
1443         ret = add_dead_ends(file);
1444         if (ret)
1445                 return ret;
1446
1447         add_ignores(file);
1448         add_uaccess_safe(file);
1449
1450         ret = add_ignore_alternatives(file);
1451         if (ret)
1452                 return ret;
1453
1454         ret = add_jump_destinations(file);
1455         if (ret)
1456                 return ret;
1457
1458         ret = add_special_section_alts(file);
1459         if (ret)
1460                 return ret;
1461
1462         ret = add_call_destinations(file);
1463         if (ret)
1464                 return ret;
1465
1466         ret = add_jump_table_alts(file);
1467         if (ret)
1468                 return ret;
1469
1470         ret = read_unwind_hints(file);
1471         if (ret)
1472                 return ret;
1473
1474         ret = read_retpoline_hints(file);
1475         if (ret)
1476                 return ret;
1477
1478         ret = read_instr_hints(file);
1479         if (ret)
1480                 return ret;
1481
1482         return 0;
1483 }
1484
1485 static bool is_fentry_call(struct instruction *insn)
1486 {
1487         if (insn->type == INSN_CALL &&
1488             insn->call_dest->type == STT_NOTYPE &&
1489             !strcmp(insn->call_dest->name, "__fentry__"))
1490                 return true;
1491
1492         return false;
1493 }
1494
1495 static bool has_modified_stack_frame(struct instruction *insn, struct insn_state *state)
1496 {
1497         u8 ret_offset = insn->ret_offset;
1498         struct cfi_state *cfi = &state->cfi;
1499         int i;
1500
1501         if (cfi->cfa.base != initial_func_cfi.cfa.base || cfi->drap)
1502                 return true;
1503
1504         if (cfi->cfa.offset != initial_func_cfi.cfa.offset + ret_offset)
1505                 return true;
1506
1507         if (cfi->stack_size != initial_func_cfi.cfa.offset + ret_offset)
1508                 return true;
1509
1510         for (i = 0; i < CFI_NUM_REGS; i++) {
1511                 if (cfi->regs[i].base != initial_func_cfi.regs[i].base ||
1512                     cfi->regs[i].offset != initial_func_cfi.regs[i].offset)
1513                         return true;
1514         }
1515
1516         return false;
1517 }
1518
1519 static bool has_valid_stack_frame(struct insn_state *state)
1520 {
1521         struct cfi_state *cfi = &state->cfi;
1522
1523         if (cfi->cfa.base == CFI_BP && cfi->regs[CFI_BP].base == CFI_CFA &&
1524             cfi->regs[CFI_BP].offset == -16)
1525                 return true;
1526
1527         if (cfi->drap && cfi->regs[CFI_BP].base == CFI_BP)
1528                 return true;
1529
1530         return false;
1531 }
1532
1533 static int update_cfi_state_regs(struct instruction *insn,
1534                                   struct cfi_state *cfi,
1535                                   struct stack_op *op)
1536 {
1537         struct cfi_reg *cfa = &cfi->cfa;
1538
1539         if (cfa->base != CFI_SP)
1540                 return 0;
1541
1542         /* push */
1543         if (op->dest.type == OP_DEST_PUSH || op->dest.type == OP_DEST_PUSHF)
1544                 cfa->offset += 8;
1545
1546         /* pop */
1547         if (op->src.type == OP_SRC_POP || op->src.type == OP_SRC_POPF)
1548                 cfa->offset -= 8;
1549
1550         /* add immediate to sp */
1551         if (op->dest.type == OP_DEST_REG && op->src.type == OP_SRC_ADD &&
1552             op->dest.reg == CFI_SP && op->src.reg == CFI_SP)
1553                 cfa->offset -= op->src.offset;
1554
1555         return 0;
1556 }
1557
1558 static void save_reg(struct cfi_state *cfi, unsigned char reg, int base, int offset)
1559 {
1560         if (arch_callee_saved_reg(reg) &&
1561             cfi->regs[reg].base == CFI_UNDEFINED) {
1562                 cfi->regs[reg].base = base;
1563                 cfi->regs[reg].offset = offset;
1564         }
1565 }
1566
1567 static void restore_reg(struct cfi_state *cfi, unsigned char reg)
1568 {
1569         cfi->regs[reg].base = initial_func_cfi.regs[reg].base;
1570         cfi->regs[reg].offset = initial_func_cfi.regs[reg].offset;
1571 }
1572
1573 /*
1574  * A note about DRAP stack alignment:
1575  *
1576  * GCC has the concept of a DRAP register, which is used to help keep track of
1577  * the stack pointer when aligning the stack.  r10 or r13 is used as the DRAP
1578  * register.  The typical DRAP pattern is:
1579  *
1580  *   4c 8d 54 24 08             lea    0x8(%rsp),%r10
1581  *   48 83 e4 c0                and    $0xffffffffffffffc0,%rsp
1582  *   41 ff 72 f8                pushq  -0x8(%r10)
1583  *   55                         push   %rbp
1584  *   48 89 e5                   mov    %rsp,%rbp
1585  *                              (more pushes)
1586  *   41 52                      push   %r10
1587  *                              ...
1588  *   41 5a                      pop    %r10
1589  *                              (more pops)
1590  *   5d                         pop    %rbp
1591  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1592  *   c3                         retq
1593  *
1594  * There are some variations in the epilogues, like:
1595  *
1596  *   5b                         pop    %rbx
1597  *   41 5a                      pop    %r10
1598  *   41 5c                      pop    %r12
1599  *   41 5d                      pop    %r13
1600  *   41 5e                      pop    %r14
1601  *   c9                         leaveq
1602  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1603  *   c3                         retq
1604  *
1605  * and:
1606  *
1607  *   4c 8b 55 e8                mov    -0x18(%rbp),%r10
1608  *   48 8b 5d e0                mov    -0x20(%rbp),%rbx
1609  *   4c 8b 65 f0                mov    -0x10(%rbp),%r12
1610  *   4c 8b 6d f8                mov    -0x8(%rbp),%r13
1611  *   c9                         leaveq
1612  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1613  *   c3                         retq
1614  *
1615  * Sometimes r13 is used as the DRAP register, in which case it's saved and
1616  * restored beforehand:
1617  *
1618  *   41 55                      push   %r13
1619  *   4c 8d 6c 24 10             lea    0x10(%rsp),%r13
1620  *   48 83 e4 f0                and    $0xfffffffffffffff0,%rsp
1621  *                              ...
1622  *   49 8d 65 f0                lea    -0x10(%r13),%rsp
1623  *   41 5d                      pop    %r13
1624  *   c3                         retq
1625  */
1626 static int update_cfi_state(struct instruction *insn, struct cfi_state *cfi,
1627                              struct stack_op *op)
1628 {
1629         struct cfi_reg *cfa = &cfi->cfa;
1630         struct cfi_reg *regs = cfi->regs;
1631
1632         /* stack operations don't make sense with an undefined CFA */
1633         if (cfa->base == CFI_UNDEFINED) {
1634                 if (insn->func) {
1635                         WARN_FUNC("undefined stack state", insn->sec, insn->offset);
1636                         return -1;
1637                 }
1638                 return 0;
1639         }
1640
1641         if (cfi->type == ORC_TYPE_REGS || cfi->type == ORC_TYPE_REGS_IRET)
1642                 return update_cfi_state_regs(insn, cfi, op);
1643
1644         switch (op->dest.type) {
1645
1646         case OP_DEST_REG:
1647                 switch (op->src.type) {
1648
1649                 case OP_SRC_REG:
1650                         if (op->src.reg == CFI_SP && op->dest.reg == CFI_BP &&
1651                             cfa->base == CFI_SP &&
1652                             regs[CFI_BP].base == CFI_CFA &&
1653                             regs[CFI_BP].offset == -cfa->offset) {
1654
1655                                 /* mov %rsp, %rbp */
1656                                 cfa->base = op->dest.reg;
1657                                 cfi->bp_scratch = false;
1658                         }
1659
1660                         else if (op->src.reg == CFI_SP &&
1661                                  op->dest.reg == CFI_BP && cfi->drap) {
1662
1663                                 /* drap: mov %rsp, %rbp */
1664                                 regs[CFI_BP].base = CFI_BP;
1665                                 regs[CFI_BP].offset = -cfi->stack_size;
1666                                 cfi->bp_scratch = false;
1667                         }
1668
1669                         else if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1670
1671                                 /*
1672                                  * mov %rsp, %reg
1673                                  *
1674                                  * This is needed for the rare case where GCC
1675                                  * does:
1676                                  *
1677                                  *   mov    %rsp, %rax
1678                                  *   ...
1679                                  *   mov    %rax, %rsp
1680                                  */
1681                                 cfi->vals[op->dest.reg].base = CFI_CFA;
1682                                 cfi->vals[op->dest.reg].offset = -cfi->stack_size;
1683                         }
1684
1685                         else if (op->src.reg == CFI_BP && op->dest.reg == CFI_SP &&
1686                                  cfa->base == CFI_BP) {
1687
1688                                 /*
1689                                  * mov %rbp, %rsp
1690                                  *
1691                                  * Restore the original stack pointer (Clang).
1692                                  */
1693                                 cfi->stack_size = -cfi->regs[CFI_BP].offset;
1694                         }
1695
1696                         else if (op->dest.reg == cfa->base) {
1697
1698                                 /* mov %reg, %rsp */
1699                                 if (cfa->base == CFI_SP &&
1700                                     cfi->vals[op->src.reg].base == CFI_CFA) {
1701
1702                                         /*
1703                                          * This is needed for the rare case
1704                                          * where GCC does something dumb like:
1705                                          *
1706                                          *   lea    0x8(%rsp), %rcx
1707                                          *   ...
1708                                          *   mov    %rcx, %rsp
1709                                          */
1710                                         cfa->offset = -cfi->vals[op->src.reg].offset;
1711                                         cfi->stack_size = cfa->offset;
1712
1713                                 } else {
1714                                         cfa->base = CFI_UNDEFINED;
1715                                         cfa->offset = 0;
1716                                 }
1717                         }
1718
1719                         break;
1720
1721                 case OP_SRC_ADD:
1722                         if (op->dest.reg == CFI_SP && op->src.reg == CFI_SP) {
1723
1724                                 /* add imm, %rsp */
1725                                 cfi->stack_size -= op->src.offset;
1726                                 if (cfa->base == CFI_SP)
1727                                         cfa->offset -= op->src.offset;
1728                                 break;
1729                         }
1730
1731                         if (op->dest.reg == CFI_SP && op->src.reg == CFI_BP) {
1732
1733                                 /* lea disp(%rbp), %rsp */
1734                                 cfi->stack_size = -(op->src.offset + regs[CFI_BP].offset);
1735                                 break;
1736                         }
1737
1738                         if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1739
1740                                 /* drap: lea disp(%rsp), %drap */
1741                                 cfi->drap_reg = op->dest.reg;
1742
1743                                 /*
1744                                  * lea disp(%rsp), %reg
1745                                  *
1746                                  * This is needed for the rare case where GCC
1747                                  * does something dumb like:
1748                                  *
1749                                  *   lea    0x8(%rsp), %rcx
1750                                  *   ...
1751                                  *   mov    %rcx, %rsp
1752                                  */
1753                                 cfi->vals[op->dest.reg].base = CFI_CFA;
1754                                 cfi->vals[op->dest.reg].offset = \
1755                                         -cfi->stack_size + op->src.offset;
1756
1757                                 break;
1758                         }
1759
1760                         if (cfi->drap && op->dest.reg == CFI_SP &&
1761                             op->src.reg == cfi->drap_reg) {
1762
1763                                  /* drap: lea disp(%drap), %rsp */
1764                                 cfa->base = CFI_SP;
1765                                 cfa->offset = cfi->stack_size = -op->src.offset;
1766                                 cfi->drap_reg = CFI_UNDEFINED;
1767                                 cfi->drap = false;
1768                                 break;
1769                         }
1770
1771                         if (op->dest.reg == cfi->cfa.base) {
1772                                 WARN_FUNC("unsupported stack register modification",
1773                                           insn->sec, insn->offset);
1774                                 return -1;
1775                         }
1776
1777                         break;
1778
1779                 case OP_SRC_AND:
1780                         if (op->dest.reg != CFI_SP ||
1781                             (cfi->drap_reg != CFI_UNDEFINED && cfa->base != CFI_SP) ||
1782                             (cfi->drap_reg == CFI_UNDEFINED && cfa->base != CFI_BP)) {
1783                                 WARN_FUNC("unsupported stack pointer realignment",
1784                                           insn->sec, insn->offset);
1785                                 return -1;
1786                         }
1787
1788                         if (cfi->drap_reg != CFI_UNDEFINED) {
1789                                 /* drap: and imm, %rsp */
1790                                 cfa->base = cfi->drap_reg;
1791                                 cfa->offset = cfi->stack_size = 0;
1792                                 cfi->drap = true;
1793                         }
1794
1795                         /*
1796                          * Older versions of GCC (4.8ish) realign the stack
1797                          * without DRAP, with a frame pointer.
1798                          */
1799
1800                         break;
1801
1802                 case OP_SRC_POP:
1803                 case OP_SRC_POPF:
1804                         if (!cfi->drap && op->dest.reg == cfa->base) {
1805
1806                                 /* pop %rbp */
1807                                 cfa->base = CFI_SP;
1808                         }
1809
1810                         if (cfi->drap && cfa->base == CFI_BP_INDIRECT &&
1811                             op->dest.reg == cfi->drap_reg &&
1812                             cfi->drap_offset == -cfi->stack_size) {
1813
1814                                 /* drap: pop %drap */
1815                                 cfa->base = cfi->drap_reg;
1816                                 cfa->offset = 0;
1817                                 cfi->drap_offset = -1;
1818
1819                         } else if (regs[op->dest.reg].offset == -cfi->stack_size) {
1820
1821                                 /* pop %reg */
1822                                 restore_reg(cfi, op->dest.reg);
1823                         }
1824
1825                         cfi->stack_size -= 8;
1826                         if (cfa->base == CFI_SP)
1827                                 cfa->offset -= 8;
1828
1829                         break;
1830
1831                 case OP_SRC_REG_INDIRECT:
1832                         if (cfi->drap && op->src.reg == CFI_BP &&
1833                             op->src.offset == cfi->drap_offset) {
1834
1835                                 /* drap: mov disp(%rbp), %drap */
1836                                 cfa->base = cfi->drap_reg;
1837                                 cfa->offset = 0;
1838                                 cfi->drap_offset = -1;
1839                         }
1840
1841                         if (cfi->drap && op->src.reg == CFI_BP &&
1842                             op->src.offset == regs[op->dest.reg].offset) {
1843
1844                                 /* drap: mov disp(%rbp), %reg */
1845                                 restore_reg(cfi, op->dest.reg);
1846
1847                         } else if (op->src.reg == cfa->base &&
1848                             op->src.offset == regs[op->dest.reg].offset + cfa->offset) {
1849
1850                                 /* mov disp(%rbp), %reg */
1851                                 /* mov disp(%rsp), %reg */
1852                                 restore_reg(cfi, op->dest.reg);
1853                         }
1854
1855                         break;
1856
1857                 default:
1858                         WARN_FUNC("unknown stack-related instruction",
1859                                   insn->sec, insn->offset);
1860                         return -1;
1861                 }
1862
1863                 break;
1864
1865         case OP_DEST_PUSH:
1866         case OP_DEST_PUSHF:
1867                 cfi->stack_size += 8;
1868                 if (cfa->base == CFI_SP)
1869                         cfa->offset += 8;
1870
1871                 if (op->src.type != OP_SRC_REG)
1872                         break;
1873
1874                 if (cfi->drap) {
1875                         if (op->src.reg == cfa->base && op->src.reg == cfi->drap_reg) {
1876
1877                                 /* drap: push %drap */
1878                                 cfa->base = CFI_BP_INDIRECT;
1879                                 cfa->offset = -cfi->stack_size;
1880
1881                                 /* save drap so we know when to restore it */
1882                                 cfi->drap_offset = -cfi->stack_size;
1883
1884                         } else if (op->src.reg == CFI_BP && cfa->base == cfi->drap_reg) {
1885
1886                                 /* drap: push %rbp */
1887                                 cfi->stack_size = 0;
1888
1889                         } else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1890
1891                                 /* drap: push %reg */
1892                                 save_reg(cfi, op->src.reg, CFI_BP, -cfi->stack_size);
1893                         }
1894
1895                 } else {
1896
1897                         /* push %reg */
1898                         save_reg(cfi, op->src.reg, CFI_CFA, -cfi->stack_size);
1899                 }
1900
1901                 /* detect when asm code uses rbp as a scratch register */
1902                 if (!no_fp && insn->func && op->src.reg == CFI_BP &&
1903                     cfa->base != CFI_BP)
1904                         cfi->bp_scratch = true;
1905                 break;
1906
1907         case OP_DEST_REG_INDIRECT:
1908
1909                 if (cfi->drap) {
1910                         if (op->src.reg == cfa->base && op->src.reg == cfi->drap_reg) {
1911
1912                                 /* drap: mov %drap, disp(%rbp) */
1913                                 cfa->base = CFI_BP_INDIRECT;
1914                                 cfa->offset = op->dest.offset;
1915
1916                                 /* save drap offset so we know when to restore it */
1917                                 cfi->drap_offset = op->dest.offset;
1918                         }
1919
1920                         else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1921
1922                                 /* drap: mov reg, disp(%rbp) */
1923                                 save_reg(cfi, op->src.reg, CFI_BP, op->dest.offset);
1924                         }
1925
1926                 } else if (op->dest.reg == cfa->base) {
1927
1928                         /* mov reg, disp(%rbp) */
1929                         /* mov reg, disp(%rsp) */
1930                         save_reg(cfi, op->src.reg, CFI_CFA,
1931                                  op->dest.offset - cfi->cfa.offset);
1932                 }
1933
1934                 break;
1935
1936         case OP_DEST_LEAVE:
1937                 if ((!cfi->drap && cfa->base != CFI_BP) ||
1938                     (cfi->drap && cfa->base != cfi->drap_reg)) {
1939                         WARN_FUNC("leave instruction with modified stack frame",
1940                                   insn->sec, insn->offset);
1941                         return -1;
1942                 }
1943
1944                 /* leave (mov %rbp, %rsp; pop %rbp) */
1945
1946                 cfi->stack_size = -cfi->regs[CFI_BP].offset - 8;
1947                 restore_reg(cfi, CFI_BP);
1948
1949                 if (!cfi->drap) {
1950                         cfa->base = CFI_SP;
1951                         cfa->offset -= 8;
1952                 }
1953
1954                 break;
1955
1956         case OP_DEST_MEM:
1957                 if (op->src.type != OP_SRC_POP && op->src.type != OP_SRC_POPF) {
1958                         WARN_FUNC("unknown stack-related memory operation",
1959                                   insn->sec, insn->offset);
1960                         return -1;
1961                 }
1962
1963                 /* pop mem */
1964                 cfi->stack_size -= 8;
1965                 if (cfa->base == CFI_SP)
1966                         cfa->offset -= 8;
1967
1968                 break;
1969
1970         default:
1971                 WARN_FUNC("unknown stack-related instruction",
1972                           insn->sec, insn->offset);
1973                 return -1;
1974         }
1975
1976         return 0;
1977 }
1978
1979 static int handle_insn_ops(struct instruction *insn, struct insn_state *state)
1980 {
1981         struct stack_op *op;
1982
1983         list_for_each_entry(op, &insn->stack_ops, list) {
1984                 int res;
1985
1986                 if (insn->alt_group) {
1987                         WARN_FUNC("alternative modifies stack", insn->sec, insn->offset);
1988                         return -1;
1989                 }
1990
1991                 res = update_cfi_state(insn, &state->cfi, op);
1992                 if (res)
1993                         return res;
1994
1995                 if (op->dest.type == OP_DEST_PUSHF) {
1996                         if (!state->uaccess_stack) {
1997                                 state->uaccess_stack = 1;
1998                         } else if (state->uaccess_stack >> 31) {
1999                                 WARN_FUNC("PUSHF stack exhausted",
2000                                           insn->sec, insn->offset);
2001                                 return 1;
2002                         }
2003                         state->uaccess_stack <<= 1;
2004                         state->uaccess_stack  |= state->uaccess;
2005                 }
2006
2007                 if (op->src.type == OP_SRC_POPF) {
2008                         if (state->uaccess_stack) {
2009                                 state->uaccess = state->uaccess_stack & 1;
2010                                 state->uaccess_stack >>= 1;
2011                                 if (state->uaccess_stack == 1)
2012                                         state->uaccess_stack = 0;
2013                         }
2014                 }
2015         }
2016
2017         return 0;
2018 }
2019
2020 static bool insn_cfi_match(struct instruction *insn, struct cfi_state *cfi2)
2021 {
2022         struct cfi_state *cfi1 = &insn->cfi;
2023         int i;
2024
2025         if (memcmp(&cfi1->cfa, &cfi2->cfa, sizeof(cfi1->cfa))) {
2026
2027                 WARN_FUNC("stack state mismatch: cfa1=%d%+d cfa2=%d%+d",
2028                           insn->sec, insn->offset,
2029                           cfi1->cfa.base, cfi1->cfa.offset,
2030                           cfi2->cfa.base, cfi2->cfa.offset);
2031
2032         } else if (memcmp(&cfi1->regs, &cfi2->regs, sizeof(cfi1->regs))) {
2033                 for (i = 0; i < CFI_NUM_REGS; i++) {
2034                         if (!memcmp(&cfi1->regs[i], &cfi2->regs[i],
2035                                     sizeof(struct cfi_reg)))
2036                                 continue;
2037
2038                         WARN_FUNC("stack state mismatch: reg1[%d]=%d%+d reg2[%d]=%d%+d",
2039                                   insn->sec, insn->offset,
2040                                   i, cfi1->regs[i].base, cfi1->regs[i].offset,
2041                                   i, cfi2->regs[i].base, cfi2->regs[i].offset);
2042                         break;
2043                 }
2044
2045         } else if (cfi1->type != cfi2->type) {
2046
2047                 WARN_FUNC("stack state mismatch: type1=%d type2=%d",
2048                           insn->sec, insn->offset, cfi1->type, cfi2->type);
2049
2050         } else if (cfi1->drap != cfi2->drap ||
2051                    (cfi1->drap && cfi1->drap_reg != cfi2->drap_reg) ||
2052                    (cfi1->drap && cfi1->drap_offset != cfi2->drap_offset)) {
2053
2054                 WARN_FUNC("stack state mismatch: drap1=%d(%d,%d) drap2=%d(%d,%d)",
2055                           insn->sec, insn->offset,
2056                           cfi1->drap, cfi1->drap_reg, cfi1->drap_offset,
2057                           cfi2->drap, cfi2->drap_reg, cfi2->drap_offset);
2058
2059         } else
2060                 return true;
2061
2062         return false;
2063 }
2064
2065 static inline bool func_uaccess_safe(struct symbol *func)
2066 {
2067         if (func)
2068                 return func->uaccess_safe;
2069
2070         return false;
2071 }
2072
2073 static inline const char *call_dest_name(struct instruction *insn)
2074 {
2075         if (insn->call_dest)
2076                 return insn->call_dest->name;
2077
2078         return "{dynamic}";
2079 }
2080
2081 static int validate_call(struct instruction *insn, struct insn_state *state)
2082 {
2083         if (state->noinstr && state->instr <= 0 &&
2084             (!insn->call_dest || !insn->call_dest->sec->noinstr)) {
2085                 WARN_FUNC("call to %s() leaves .noinstr.text section",
2086                                 insn->sec, insn->offset, call_dest_name(insn));
2087                 return 1;
2088         }
2089
2090         if (state->uaccess && !func_uaccess_safe(insn->call_dest)) {
2091                 WARN_FUNC("call to %s() with UACCESS enabled",
2092                                 insn->sec, insn->offset, call_dest_name(insn));
2093                 return 1;
2094         }
2095
2096         if (state->df) {
2097                 WARN_FUNC("call to %s() with DF set",
2098                                 insn->sec, insn->offset, call_dest_name(insn));
2099                 return 1;
2100         }
2101
2102         return 0;
2103 }
2104
2105 static int validate_sibling_call(struct instruction *insn, struct insn_state *state)
2106 {
2107         if (has_modified_stack_frame(insn, state)) {
2108                 WARN_FUNC("sibling call from callable instruction with modified stack frame",
2109                                 insn->sec, insn->offset);
2110                 return 1;
2111         }
2112
2113         return validate_call(insn, state);
2114 }
2115
2116 static int validate_return(struct symbol *func, struct instruction *insn, struct insn_state *state)
2117 {
2118         if (state->noinstr && state->instr > 0) {
2119                 WARN_FUNC("return with instrumentation enabled",
2120                           insn->sec, insn->offset);
2121                 return 1;
2122         }
2123
2124         if (state->uaccess && !func_uaccess_safe(func)) {
2125                 WARN_FUNC("return with UACCESS enabled",
2126                           insn->sec, insn->offset);
2127                 return 1;
2128         }
2129
2130         if (!state->uaccess && func_uaccess_safe(func)) {
2131                 WARN_FUNC("return with UACCESS disabled from a UACCESS-safe function",
2132                           insn->sec, insn->offset);
2133                 return 1;
2134         }
2135
2136         if (state->df) {
2137                 WARN_FUNC("return with DF set",
2138                           insn->sec, insn->offset);
2139                 return 1;
2140         }
2141
2142         if (func && has_modified_stack_frame(insn, state)) {
2143                 WARN_FUNC("return with modified stack frame",
2144                           insn->sec, insn->offset);
2145                 return 1;
2146         }
2147
2148         if (state->cfi.bp_scratch) {
2149                 WARN_FUNC("BP used as a scratch register",
2150                           insn->sec, insn->offset);
2151                 return 1;
2152         }
2153
2154         return 0;
2155 }
2156
2157 /*
2158  * Alternatives should not contain any ORC entries, this in turn means they
2159  * should not contain any CFI ops, which implies all instructions should have
2160  * the same same CFI state.
2161  *
2162  * It is possible to constuct alternatives that have unreachable holes that go
2163  * unreported (because they're NOPs), such holes would result in CFI_UNDEFINED
2164  * states which then results in ORC entries, which we just said we didn't want.
2165  *
2166  * Avoid them by copying the CFI entry of the first instruction into the whole
2167  * alternative.
2168  */
2169 static void fill_alternative_cfi(struct objtool_file *file, struct instruction *insn)
2170 {
2171         struct instruction *first_insn = insn;
2172         int alt_group = insn->alt_group;
2173
2174         sec_for_each_insn_continue(file, insn) {
2175                 if (insn->alt_group != alt_group)
2176                         break;
2177                 insn->cfi = first_insn->cfi;
2178         }
2179 }
2180
2181 /*
2182  * Follow the branch starting at the given instruction, and recursively follow
2183  * any other branches (jumps).  Meanwhile, track the frame pointer state at
2184  * each instruction and validate all the rules described in
2185  * tools/objtool/Documentation/stack-validation.txt.
2186  */
2187 static int validate_branch(struct objtool_file *file, struct symbol *func,
2188                            struct instruction *insn, struct insn_state state)
2189 {
2190         struct alternative *alt;
2191         struct instruction *next_insn;
2192         struct section *sec;
2193         u8 visited;
2194         int ret;
2195
2196         sec = insn->sec;
2197
2198         while (1) {
2199                 next_insn = next_insn_same_sec(file, insn);
2200
2201                 if (file->c_file && func && insn->func && func != insn->func->pfunc) {
2202                         WARN("%s() falls through to next function %s()",
2203                              func->name, insn->func->name);
2204                         return 1;
2205                 }
2206
2207                 if (func && insn->ignore) {
2208                         WARN_FUNC("BUG: why am I validating an ignored function?",
2209                                   sec, insn->offset);
2210                         return 1;
2211                 }
2212
2213                 visited = 1 << state.uaccess;
2214                 if (insn->visited) {
2215                         if (!insn->hint && !insn_cfi_match(insn, &state.cfi))
2216                                 return 1;
2217
2218                         if (insn->visited & visited)
2219                                 return 0;
2220                 }
2221
2222                 if (state.noinstr)
2223                         state.instr += insn->instr;
2224
2225                 if (insn->hint)
2226                         state.cfi = insn->cfi;
2227                 else
2228                         insn->cfi = state.cfi;
2229
2230                 insn->visited |= visited;
2231
2232                 if (!insn->ignore_alts && !list_empty(&insn->alts)) {
2233                         bool skip_orig = false;
2234
2235                         list_for_each_entry(alt, &insn->alts, list) {
2236                                 if (alt->skip_orig)
2237                                         skip_orig = true;
2238
2239                                 ret = validate_branch(file, func, alt->insn, state);
2240                                 if (ret) {
2241                                         if (backtrace)
2242                                                 BT_FUNC("(alt)", insn);
2243                                         return ret;
2244                                 }
2245                         }
2246
2247                         if (insn->alt_group)
2248                                 fill_alternative_cfi(file, insn);
2249
2250                         if (skip_orig)
2251                                 return 0;
2252                 }
2253
2254                 switch (insn->type) {
2255
2256                 case INSN_RETURN:
2257                         return validate_return(func, insn, &state);
2258
2259                 case INSN_CALL:
2260                 case INSN_CALL_DYNAMIC:
2261                         ret = validate_call(insn, &state);
2262                         if (ret)
2263                                 return ret;
2264
2265                         if (!no_fp && func && !is_fentry_call(insn) &&
2266                             !has_valid_stack_frame(&state)) {
2267                                 WARN_FUNC("call without frame pointer save/setup",
2268                                           sec, insn->offset);
2269                                 return 1;
2270                         }
2271
2272                         if (dead_end_function(file, insn->call_dest))
2273                                 return 0;
2274
2275                         break;
2276
2277                 case INSN_JUMP_CONDITIONAL:
2278                 case INSN_JUMP_UNCONDITIONAL:
2279                         if (func && is_sibling_call(insn)) {
2280                                 ret = validate_sibling_call(insn, &state);
2281                                 if (ret)
2282                                         return ret;
2283
2284                         } else if (insn->jump_dest) {
2285                                 ret = validate_branch(file, func,
2286                                                       insn->jump_dest, state);
2287                                 if (ret) {
2288                                         if (backtrace)
2289                                                 BT_FUNC("(branch)", insn);
2290                                         return ret;
2291                                 }
2292                         }
2293
2294                         if (insn->type == INSN_JUMP_UNCONDITIONAL)
2295                                 return 0;
2296
2297                         break;
2298
2299                 case INSN_JUMP_DYNAMIC:
2300                 case INSN_JUMP_DYNAMIC_CONDITIONAL:
2301                         if (func && is_sibling_call(insn)) {
2302                                 ret = validate_sibling_call(insn, &state);
2303                                 if (ret)
2304                                         return ret;
2305                         }
2306
2307                         if (insn->type == INSN_JUMP_DYNAMIC)
2308                                 return 0;
2309
2310                         break;
2311
2312                 case INSN_EXCEPTION_RETURN:
2313                         if (handle_insn_ops(insn, &state))
2314                                 return 1;
2315
2316                         /*
2317                          * This handles x86's sync_core() case, where we use an
2318                          * IRET to self. All 'normal' IRET instructions are in
2319                          * STT_NOTYPE entry symbols.
2320                          */
2321                         if (func)
2322                                 break;
2323
2324                         return 0;
2325
2326                 case INSN_CONTEXT_SWITCH:
2327                         if (func && (!next_insn || !next_insn->hint)) {
2328                                 WARN_FUNC("unsupported instruction in callable function",
2329                                           sec, insn->offset);
2330                                 return 1;
2331                         }
2332                         return 0;
2333
2334                 case INSN_STACK:
2335                         if (handle_insn_ops(insn, &state))
2336                                 return 1;
2337                         break;
2338
2339                 case INSN_STAC:
2340                         if (state.uaccess) {
2341                                 WARN_FUNC("recursive UACCESS enable", sec, insn->offset);
2342                                 return 1;
2343                         }
2344
2345                         state.uaccess = true;
2346                         break;
2347
2348                 case INSN_CLAC:
2349                         if (!state.uaccess && func) {
2350                                 WARN_FUNC("redundant UACCESS disable", sec, insn->offset);
2351                                 return 1;
2352                         }
2353
2354                         if (func_uaccess_safe(func) && !state.uaccess_stack) {
2355                                 WARN_FUNC("UACCESS-safe disables UACCESS", sec, insn->offset);
2356                                 return 1;
2357                         }
2358
2359                         state.uaccess = false;
2360                         break;
2361
2362                 case INSN_STD:
2363                         if (state.df)
2364                                 WARN_FUNC("recursive STD", sec, insn->offset);
2365
2366                         state.df = true;
2367                         break;
2368
2369                 case INSN_CLD:
2370                         if (!state.df && func)
2371                                 WARN_FUNC("redundant CLD", sec, insn->offset);
2372
2373                         state.df = false;
2374                         break;
2375
2376                 default:
2377                         break;
2378                 }
2379
2380                 if (insn->dead_end)
2381                         return 0;
2382
2383                 if (!next_insn) {
2384                         if (state.cfi.cfa.base == CFI_UNDEFINED)
2385                                 return 0;
2386                         WARN("%s: unexpected end of section", sec->name);
2387                         return 1;
2388                 }
2389
2390                 insn = next_insn;
2391         }
2392
2393         return 0;
2394 }
2395
2396 static int validate_unwind_hints(struct objtool_file *file, struct section *sec)
2397 {
2398         struct instruction *insn;
2399         struct insn_state state;
2400         int ret, warnings = 0;
2401
2402         if (!file->hints)
2403                 return 0;
2404
2405         init_insn_state(&state, sec);
2406
2407         if (sec) {
2408                 insn = find_insn(file, sec, 0);
2409                 if (!insn)
2410                         return 0;
2411         } else {
2412                 insn = list_first_entry(&file->insn_list, typeof(*insn), list);
2413         }
2414
2415         while (&insn->list != &file->insn_list && (!sec || insn->sec == sec)) {
2416                 if (insn->hint && !insn->visited) {
2417                         ret = validate_branch(file, insn->func, insn, state);
2418                         if (ret && backtrace)
2419                                 BT_FUNC("<=== (hint)", insn);
2420                         warnings += ret;
2421                 }
2422
2423                 insn = list_next_entry(insn, list);
2424         }
2425
2426         return warnings;
2427 }
2428
2429 static int validate_retpoline(struct objtool_file *file)
2430 {
2431         struct instruction *insn;
2432         int warnings = 0;
2433
2434         for_each_insn(file, insn) {
2435                 if (insn->type != INSN_JUMP_DYNAMIC &&
2436                     insn->type != INSN_CALL_DYNAMIC)
2437                         continue;
2438
2439                 if (insn->retpoline_safe)
2440                         continue;
2441
2442                 /*
2443                  * .init.text code is ran before userspace and thus doesn't
2444                  * strictly need retpolines, except for modules which are
2445                  * loaded late, they very much do need retpoline in their
2446                  * .init.text
2447                  */
2448                 if (!strcmp(insn->sec->name, ".init.text") && !module)
2449                         continue;
2450
2451                 WARN_FUNC("indirect %s found in RETPOLINE build",
2452                           insn->sec, insn->offset,
2453                           insn->type == INSN_JUMP_DYNAMIC ? "jump" : "call");
2454
2455                 warnings++;
2456         }
2457
2458         return warnings;
2459 }
2460
2461 static bool is_kasan_insn(struct instruction *insn)
2462 {
2463         return (insn->type == INSN_CALL &&
2464                 !strcmp(insn->call_dest->name, "__asan_handle_no_return"));
2465 }
2466
2467 static bool is_ubsan_insn(struct instruction *insn)
2468 {
2469         return (insn->type == INSN_CALL &&
2470                 !strcmp(insn->call_dest->name,
2471                         "__ubsan_handle_builtin_unreachable"));
2472 }
2473
2474 static bool ignore_unreachable_insn(struct instruction *insn)
2475 {
2476         int i;
2477
2478         if (insn->ignore || insn->type == INSN_NOP)
2479                 return true;
2480
2481         /*
2482          * Ignore any unused exceptions.  This can happen when a whitelisted
2483          * function has an exception table entry.
2484          *
2485          * Also ignore alternative replacement instructions.  This can happen
2486          * when a whitelisted function uses one of the ALTERNATIVE macros.
2487          */
2488         if (!strcmp(insn->sec->name, ".fixup") ||
2489             !strcmp(insn->sec->name, ".altinstr_replacement") ||
2490             !strcmp(insn->sec->name, ".altinstr_aux"))
2491                 return true;
2492
2493         if (!insn->func)
2494                 return false;
2495
2496         /*
2497          * CONFIG_UBSAN_TRAP inserts a UD2 when it sees
2498          * __builtin_unreachable().  The BUG() macro has an unreachable() after
2499          * the UD2, which causes GCC's undefined trap logic to emit another UD2
2500          * (or occasionally a JMP to UD2).
2501          */
2502         if (list_prev_entry(insn, list)->dead_end &&
2503             (insn->type == INSN_BUG ||
2504              (insn->type == INSN_JUMP_UNCONDITIONAL &&
2505               insn->jump_dest && insn->jump_dest->type == INSN_BUG)))
2506                 return true;
2507
2508         /*
2509          * Check if this (or a subsequent) instruction is related to
2510          * CONFIG_UBSAN or CONFIG_KASAN.
2511          *
2512          * End the search at 5 instructions to avoid going into the weeds.
2513          */
2514         for (i = 0; i < 5; i++) {
2515
2516                 if (is_kasan_insn(insn) || is_ubsan_insn(insn))
2517                         return true;
2518
2519                 if (insn->type == INSN_JUMP_UNCONDITIONAL) {
2520                         if (insn->jump_dest &&
2521                             insn->jump_dest->func == insn->func) {
2522                                 insn = insn->jump_dest;
2523                                 continue;
2524                         }
2525
2526                         break;
2527                 }
2528
2529                 if (insn->offset + insn->len >= insn->func->offset + insn->func->len)
2530                         break;
2531
2532                 insn = list_next_entry(insn, list);
2533         }
2534
2535         return false;
2536 }
2537
2538 static int validate_symbol(struct objtool_file *file, struct section *sec,
2539                            struct symbol *sym, struct insn_state *state)
2540 {
2541         struct instruction *insn;
2542         int ret;
2543
2544         if (!sym->len) {
2545                 WARN("%s() is missing an ELF size annotation", sym->name);
2546                 return 1;
2547         }
2548
2549         if (sym->pfunc != sym || sym->alias != sym)
2550                 return 0;
2551
2552         insn = find_insn(file, sec, sym->offset);
2553         if (!insn || insn->ignore || insn->visited)
2554                 return 0;
2555
2556         state->uaccess = sym->uaccess_safe;
2557
2558         ret = validate_branch(file, insn->func, insn, *state);
2559         if (ret && backtrace)
2560                 BT_FUNC("<=== (sym)", insn);
2561         return ret;
2562 }
2563
2564 static int validate_section(struct objtool_file *file, struct section *sec)
2565 {
2566         struct insn_state state;
2567         struct symbol *func;
2568         int warnings = 0;
2569
2570         list_for_each_entry(func, &sec->symbol_list, list) {
2571                 if (func->type != STT_FUNC)
2572                         continue;
2573
2574                 init_insn_state(&state, sec);
2575                 state.cfi.cfa = initial_func_cfi.cfa;
2576                 memcpy(&state.cfi.regs, &initial_func_cfi.regs,
2577                        CFI_NUM_REGS * sizeof(struct cfi_reg));
2578                 state.cfi.stack_size = initial_func_cfi.cfa.offset;
2579
2580                 warnings += validate_symbol(file, sec, func, &state);
2581         }
2582
2583         return warnings;
2584 }
2585
2586 static int validate_vmlinux_functions(struct objtool_file *file)
2587 {
2588         struct section *sec;
2589         int warnings = 0;
2590
2591         sec = find_section_by_name(file->elf, ".noinstr.text");
2592         if (sec) {
2593                 warnings += validate_section(file, sec);
2594                 warnings += validate_unwind_hints(file, sec);
2595         }
2596
2597         sec = find_section_by_name(file->elf, ".entry.text");
2598         if (sec) {
2599                 warnings += validate_section(file, sec);
2600                 warnings += validate_unwind_hints(file, sec);
2601         }
2602
2603         return warnings;
2604 }
2605
2606 static int validate_functions(struct objtool_file *file)
2607 {
2608         struct section *sec;
2609         int warnings = 0;
2610
2611         for_each_sec(file, sec) {
2612                 if (!(sec->sh.sh_flags & SHF_EXECINSTR))
2613                         continue;
2614
2615                 warnings += validate_section(file, sec);
2616         }
2617
2618         return warnings;
2619 }
2620
2621 static int validate_reachable_instructions(struct objtool_file *file)
2622 {
2623         struct instruction *insn;
2624
2625         if (file->ignore_unreachables)
2626                 return 0;
2627
2628         for_each_insn(file, insn) {
2629                 if (insn->visited || ignore_unreachable_insn(insn))
2630                         continue;
2631
2632                 WARN_FUNC("unreachable instruction", insn->sec, insn->offset);
2633                 return 1;
2634         }
2635
2636         return 0;
2637 }
2638
2639 static struct objtool_file file;
2640
2641 int check(const char *_objname, bool orc)
2642 {
2643         int ret, warnings = 0;
2644
2645         objname = _objname;
2646
2647         file.elf = elf_open_read(objname, orc ? O_RDWR : O_RDONLY);
2648         if (!file.elf)
2649                 return 1;
2650
2651         INIT_LIST_HEAD(&file.insn_list);
2652         hash_init(file.insn_hash);
2653         file.c_file = find_section_by_name(file.elf, ".comment");
2654         file.ignore_unreachables = no_unreachable;
2655         file.hints = false;
2656
2657         arch_initial_func_cfi_state(&initial_func_cfi);
2658
2659         ret = decode_sections(&file);
2660         if (ret < 0)
2661                 goto out;
2662         warnings += ret;
2663
2664         if (list_empty(&file.insn_list))
2665                 goto out;
2666
2667         if (vmlinux && !validate_dup) {
2668                 ret = validate_vmlinux_functions(&file);
2669                 if (ret < 0)
2670                         goto out;
2671
2672                 warnings += ret;
2673                 goto out;
2674         }
2675
2676         if (retpoline) {
2677                 ret = validate_retpoline(&file);
2678                 if (ret < 0)
2679                         return ret;
2680                 warnings += ret;
2681         }
2682
2683         ret = validate_functions(&file);
2684         if (ret < 0)
2685                 goto out;
2686         warnings += ret;
2687
2688         ret = validate_unwind_hints(&file, NULL);
2689         if (ret < 0)
2690                 goto out;
2691         warnings += ret;
2692
2693         if (!warnings) {
2694                 ret = validate_reachable_instructions(&file);
2695                 if (ret < 0)
2696                         goto out;
2697                 warnings += ret;
2698         }
2699
2700         if (orc) {
2701                 ret = create_orc(&file);
2702                 if (ret < 0)
2703                         goto out;
2704
2705                 ret = create_orc_sections(&file);
2706                 if (ret < 0)
2707                         goto out;
2708
2709                 ret = elf_write(file.elf);
2710                 if (ret < 0)
2711                         goto out;
2712         }
2713
2714 out:
2715         if (ret < 0) {
2716                 /*
2717                  *  Fatal error.  The binary is corrupt or otherwise broken in
2718                  *  some way, or objtool itself is broken.  Fail the kernel
2719                  *  build.
2720                  */
2721                 return ret;
2722         }
2723
2724         return 0;
2725 }