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