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_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, offset)
  38                 if (insn->sec == sec && insn->offset == offset)
  39                         return insn;
  40
  41         return NULL;
  42 }
  43
  44 static struct instruction *next_insn_same_sec(struct objtool_file *file,
  45                                               struct instruction *insn)
  46 {
  47         struct instruction *next = list_next_entry(insn, list);
  48
  49         if (!next || &next->list == &file->insn_list || next->sec != insn->sec)
  50                 return NULL;
  51
  52         return next;
  53 }
  54
  55 static struct instruction *next_insn_same_func(struct objtool_file *file,
  56                                                struct instruction *insn)
  57 {
  58         struct instruction *next = list_next_entry(insn, list);
  59         struct symbol *func = insn->func;
  60
  61         if (!func)
  62                 return NULL;
  63
  64         if (&next->list != &file->insn_list && next->func == func)
  65                 return next;
  66
  67         /* Check if we're already in the subfunction: */
  68         if (func == func->cfunc)
  69                 return NULL;
  70
  71         /* Move to the subfunction: */
  72         return find_insn(file, func->cfunc->sec, func->cfunc->offset);
  73 }
  74
  75 #define func_for_each_insn(file, func, insn)                            \
  76         for (insn = find_insn(file, func->sec, func->offset);           \
  77              insn;                                                      \
  78              insn = next_insn_same_func(file, insn))
  79
  80 #define sym_for_each_insn(file, sym, insn)                              \
  81         for (insn = find_insn(file, sym->sec, sym->offset);             \
  82              insn && &insn->list != &file->insn_list &&                 \
  83                 insn->sec == sym->sec &&                                \
  84                 insn->offset < sym->offset + sym->len;                  \
  85              insn = list_next_entry(insn, list))
  86
  87 #define sym_for_each_insn_continue_reverse(file, sym, insn)             \
  88         for (insn = list_prev_entry(insn, list);                        \
  89              &insn->list != &file->insn_list &&                         \
  90                 insn->sec == sym->sec && insn->offset >= sym->offset;   \
  91              insn = list_prev_entry(insn, list))
  92
  93 #define sec_for_each_insn_from(file, insn)                              \
  94         for (; insn; insn = next_insn_same_sec(file, insn))
  95
  96 #define sec_for_each_insn_continue(file, insn)                          \
  97         for (insn = next_insn_same_sec(file, insn); insn;               \
  98              insn = next_insn_same_sec(file, insn))
  99
 100 static bool is_static_jump(struct instruction *insn)
 101 {
 102         return insn->type == INSN_JUMP_CONDITIONAL ||
 103                insn->type == INSN_JUMP_UNCONDITIONAL;
 104 }
 105
 106 static bool is_sibling_call(struct instruction *insn)
 107 {
 108         /* An indirect jump is either a sibling call or a jump to a table. */
 109         if (insn->type == INSN_JUMP_DYNAMIC)
 110                 return list_empty(&insn->alts);
 111
 112         if (!is_static_jump(insn))
 113                 return false;
 114
 115         /* add_jump_destinations() sets insn->call_dest for sibling calls. */
 116         return !!insn->call_dest;
 117 }
 118
 119 /*
 120  * This checks to see if the given function is a "noreturn" function.
 121  *
 122  * For global functions which are outside the scope of this object file, we
 123  * have to keep a manual list of them.
 124  *
 125  * For local functions, we have to detect them manually by simply looking for
 126  * the lack of a return instruction.
 127  */
 128 static bool __dead_end_function(struct objtool_file *file, struct symbol *func,
 129                                 int recursion)
 130 {
 131         int i;
 132         struct instruction *insn;
 133         bool empty = true;
 134
 135         /*
 136          * Unfortunately these have to be hard coded because the noreturn
 137          * attribute isn't provided in ELF data.
 138          */
 139         static const char * const global_noreturns[] = {
 140                 "__stack_chk_fail",
 141                 "panic",
 142                 "do_exit",
 143                 "do_task_dead",
 144                 "__module_put_and_exit",
 145                 "complete_and_exit",
 146                 "__reiserfs_panic",
 147                 "lbug_with_loc",
 148                 "fortify_panic",
 149                 "usercopy_abort",
 150                 "machine_real_restart",
 151                 "rewind_stack_do_exit",
 152                 "kunit_try_catch_throw",
 153         };
 154
 155         if (!func)
 156                 return false;
 157
 158         if (func->bind == STB_WEAK)
 159                 return false;
 160
 161         if (func->bind == STB_GLOBAL)
 162                 for (i = 0; i < ARRAY_SIZE(global_noreturns); i++)
 163                         if (!strcmp(func->name, global_noreturns[i]))
 164                                 return true;
 165
 166         if (!func->len)
 167                 return false;
 168
 169         insn = find_insn(file, func->sec, func->offset);
 170         if (!insn->func)
 171                 return false;
 172
 173         func_for_each_insn(file, func, insn) {
 174                 empty = false;
 175
 176                 if (insn->type == INSN_RETURN)
 177                         return false;
 178         }
 179
 180         if (empty)
 181                 return false;
 182
 183         /*
 184          * A function can have a sibling call instead of a return.  In that
 185          * case, the function's dead-end status depends on whether the target
 186          * of the sibling call returns.
 187          */
 188         func_for_each_insn(file, func, insn) {
 189                 if (is_sibling_call(insn)) {
 190                         struct instruction *dest = insn->jump_dest;
 191
 192                         if (!dest)
 193                                 /* sibling call to another file */
 194                                 return false;
 195
 196                         /* local sibling call */
 197                         if (recursion == 5) {
 198                                 /*
 199                                  * Infinite recursion: two functions have
 200                                  * sibling calls to each other.  This is a very
 201                                  * rare case.  It means they aren't dead ends.
 202                                  */
 203                                 return false;
 204                         }
 205
 206                         return __dead_end_function(file, dest->func, recursion+1);
 207                 }
 208         }
 209
 210         return true;
 211 }
 212
 213 static bool dead_end_function(struct objtool_file *file, struct symbol *func)
 214 {
 215         return __dead_end_function(file, func, 0);
 216 }
 217
 218 static void clear_insn_state(struct insn_state *state)
 219 {
 220         int i;
 221
 222         memset(state, 0, sizeof(*state));
 223         state->cfa.base = CFI_UNDEFINED;
 224         for (i = 0; i < CFI_NUM_REGS; i++) {
 225                 state->regs[i].base = CFI_UNDEFINED;
 226                 state->vals[i].base = CFI_UNDEFINED;
 227         }
 228         state->drap_reg = CFI_UNDEFINED;
 229         state->drap_offset = -1;
 230 }
 231
 232 /*
 233  * Call the arch-specific instruction decoder for all the instructions and add
 234  * them to the global instruction list.
 235  */
 236 static int decode_instructions(struct objtool_file *file)
 237 {
 238         struct section *sec;
 239         struct symbol *func;
 240         unsigned long offset;
 241         struct instruction *insn;
 242         unsigned long nr_insns = 0;
 243         int ret;
 244
 245         for_each_sec(file, sec) {
 246
 247                 if (!(sec->sh.sh_flags & SHF_EXECINSTR))
 248                         continue;
 249
 250                 if (strcmp(sec->name, ".altinstr_replacement") &&
 251                     strcmp(sec->name, ".altinstr_aux") &&
 252                     strncmp(sec->name, ".discard.", 9))
 253                         sec->text = true;
 254
 255                 for (offset = 0; offset < sec->len; offset += insn->len) {
 256                         insn = malloc(sizeof(*insn));
 257                         if (!insn) {
 258                                 WARN("malloc failed");
 259                                 return -1;
 260                         }
 261                         memset(insn, 0, sizeof(*insn));
 262                         INIT_LIST_HEAD(&insn->alts);
 263                         INIT_LIST_HEAD(&insn->stack_ops);
 264                         clear_insn_state(&insn->state);
 265
 266                         insn->sec = sec;
 267                         insn->offset = offset;
 268
 269                         ret = arch_decode_instruction(file->elf, sec, offset,
 270                                                       sec->len - offset,
 271                                                       &insn->len, &insn->type,
 272                                                       &insn->immediate,
 273                                                       &insn->stack_ops);
 274                         if (ret)
 275                                 goto err;
 276
 277                         hash_add(file->insn_hash, &insn->hash, insn->offset);
 278                         list_add_tail(&insn->list, &file->insn_list);
 279                         nr_insns++;
 280                 }
 281
 282                 list_for_each_entry(func, &sec->symbol_list, list) {
 283                         if (func->type != STT_FUNC || func->alias != func)
 284                                 continue;
 285
 286                         if (!find_insn(file, sec, func->offset)) {
 287                                 WARN("%s(): can't find starting instruction",
 288                                      func->name);
 289                                 return -1;
 290                         }
 291
 292                         sym_for_each_insn(file, func, insn)
 293                                 insn->func = func;
 294                 }
 295         }
 296
 297         if (stats)
 298                 printf("nr_insns: %lu\n", nr_insns);
 299
 300         return 0;
 301
 302 err:
 303         free(insn);
 304         return ret;
 305 }
 306
 307 /*
 308  * Mark "ud2" instructions and manually annotated dead ends.
 309  */
 310 static int add_dead_ends(struct objtool_file *file)
 311 {
 312         struct section *sec;
 313         struct rela *rela;
 314         struct instruction *insn;
 315         bool found;
 316
 317         /*
 318          * By default, "ud2" is a dead end unless otherwise annotated, because
 319          * GCC 7 inserts it for certain divide-by-zero cases.
 320          */
 321         for_each_insn(file, insn)
 322                 if (insn->type == INSN_BUG)
 323                         insn->dead_end = true;
 324
 325         /*
 326          * Check for manually annotated dead ends.
 327          */
 328         sec = find_section_by_name(file->elf, ".rela.discard.unreachable");
 329         if (!sec)
 330                 goto reachable;
 331
 332         list_for_each_entry(rela, &sec->rela_list, list) {
 333                 if (rela->sym->type != STT_SECTION) {
 334                         WARN("unexpected relocation symbol type in %s", sec->name);
 335                         return -1;
 336                 }
 337                 insn = find_insn(file, rela->sym->sec, rela->addend);
 338                 if (insn)
 339                         insn = list_prev_entry(insn, list);
 340                 else if (rela->addend == rela->sym->sec->len) {
 341                         found = false;
 342                         list_for_each_entry_reverse(insn, &file->insn_list, list) {
 343                                 if (insn->sec == rela->sym->sec) {
 344                                         found = true;
 345                                         break;
 346                                 }
 347                         }
 348
 349                         if (!found) {
 350                                 WARN("can't find unreachable insn at %s+0x%x",
 351                                      rela->sym->sec->name, rela->addend);
 352                                 return -1;
 353                         }
 354                 } else {
 355                         WARN("can't find unreachable insn at %s+0x%x",
 356                              rela->sym->sec->name, rela->addend);
 357                         return -1;
 358                 }
 359
 360                 insn->dead_end = true;
 361         }
 362
 363 reachable:
 364         /*
 365          * These manually annotated reachable checks are needed for GCC 4.4,
 366          * where the Linux unreachable() macro isn't supported.  In that case
 367          * GCC doesn't know the "ud2" is fatal, so it generates code as if it's
 368          * not a dead end.
 369          */
 370         sec = find_section_by_name(file->elf, ".rela.discard.reachable");
 371         if (!sec)
 372                 return 0;
 373
 374         list_for_each_entry(rela, &sec->rela_list, list) {
 375                 if (rela->sym->type != STT_SECTION) {
 376                         WARN("unexpected relocation symbol type in %s", sec->name);
 377                         return -1;
 378                 }
 379                 insn = find_insn(file, rela->sym->sec, rela->addend);
 380                 if (insn)
 381                         insn = list_prev_entry(insn, list);
 382                 else if (rela->addend == rela->sym->sec->len) {
 383                         found = false;
 384                         list_for_each_entry_reverse(insn, &file->insn_list, list) {
 385                                 if (insn->sec == rela->sym->sec) {
 386                                         found = true;
 387                                         break;
 388                                 }
 389                         }
 390
 391                         if (!found) {
 392                                 WARN("can't find reachable insn at %s+0x%x",
 393                                      rela->sym->sec->name, rela->addend);
 394                                 return -1;
 395                         }
 396                 } else {
 397                         WARN("can't find reachable insn at %s+0x%x",
 398                              rela->sym->sec->name, rela->addend);
 399                         return -1;
 400                 }
 401
 402                 insn->dead_end = false;
 403         }
 404
 405         return 0;
 406 }
 407
 408 /*
 409  * Warnings shouldn't be reported for ignored functions.
 410  */
 411 static void add_ignores(struct objtool_file *file)
 412 {
 413         struct instruction *insn;
 414         struct section *sec;
 415         struct symbol *func;
 416         struct rela *rela;
 417
 418         sec = find_section_by_name(file->elf, ".rela.discard.func_stack_frame_non_standard");
 419         if (!sec)
 420                 return;
 421
 422         list_for_each_entry(rela, &sec->rela_list, list) {
 423                 switch (rela->sym->type) {
 424                 case STT_FUNC:
 425                         func = rela->sym;
 426                         break;
 427
 428                 case STT_SECTION:
 429                         func = find_func_by_offset(rela->sym->sec, rela->addend);
 430                         if (!func)
 431                                 continue;
 432                         break;
 433
 434                 default:
 435                         WARN("unexpected relocation symbol type in %s: %d", sec->name, rela->sym->type);
 436                         continue;
 437                 }
 438
 439                 func_for_each_insn(file, func, insn)
 440                         insn->ignore = true;
 441         }
 442 }
 443
 444 /*
 445  * This is a whitelist of functions that is allowed to be called with AC set.
 446  * The list is meant to be minimal and only contains compiler instrumentation
 447  * ABI and a few functions used to implement *_{to,from}_user() functions.
 448  *
 449  * These functions must not directly change AC, but may PUSHF/POPF.
 450  */
 451 static const char *uaccess_safe_builtin[] = {
 452         /* KASAN */
 453         "kasan_report",
 454         "check_memory_region",
 455         /* KASAN out-of-line */
 456         "__asan_loadN_noabort",
 457         "__asan_load1_noabort",
 458         "__asan_load2_noabort",
 459         "__asan_load4_noabort",
 460         "__asan_load8_noabort",
 461         "__asan_load16_noabort",
 462         "__asan_storeN_noabort",
 463         "__asan_store1_noabort",
 464         "__asan_store2_noabort",
 465         "__asan_store4_noabort",
 466         "__asan_store8_noabort",
 467         "__asan_store16_noabort",
 468         /* KASAN in-line */
 469         "__asan_report_load_n_noabort",
 470         "__asan_report_load1_noabort",
 471         "__asan_report_load2_noabort",
 472         "__asan_report_load4_noabort",
 473         "__asan_report_load8_noabort",
 474         "__asan_report_load16_noabort",
 475         "__asan_report_store_n_noabort",
 476         "__asan_report_store1_noabort",
 477         "__asan_report_store2_noabort",
 478         "__asan_report_store4_noabort",
 479         "__asan_report_store8_noabort",
 480         "__asan_report_store16_noabort",
 481         /* KCOV */
 482         "write_comp_data",
 483         "__sanitizer_cov_trace_pc",
 484         "__sanitizer_cov_trace_const_cmp1",
 485         "__sanitizer_cov_trace_const_cmp2",
 486         "__sanitizer_cov_trace_const_cmp4",
 487         "__sanitizer_cov_trace_const_cmp8",
 488         "__sanitizer_cov_trace_cmp1",
 489         "__sanitizer_cov_trace_cmp2",
 490         "__sanitizer_cov_trace_cmp4",
 491         "__sanitizer_cov_trace_cmp8",
 492         "__sanitizer_cov_trace_switch",
 493         /* UBSAN */
 494         "ubsan_type_mismatch_common",
 495         "__ubsan_handle_type_mismatch",
 496         "__ubsan_handle_type_mismatch_v1",
 497         "__ubsan_handle_shift_out_of_bounds",
 498         /* misc */
 499         "csum_partial_copy_generic",
 500         "__memcpy_mcsafe",
 501         "mcsafe_handle_tail",
 502         "ftrace_likely_update", /* CONFIG_TRACE_BRANCH_PROFILING */
 503         NULL
 504 };
 505
 506 static void add_uaccess_safe(struct objtool_file *file)
 507 {
 508         struct symbol *func;
 509         const char **name;
 510
 511         if (!uaccess)
 512                 return;
 513
 514         for (name = uaccess_safe_builtin; *name; name++) {
 515                 func = find_symbol_by_name(file->elf, *name);
 516                 if (!func)
 517                         continue;
 518
 519                 func->uaccess_safe = true;
 520         }
 521 }
 522
 523 /*
 524  * FIXME: For now, just ignore any alternatives which add retpolines.  This is
 525  * a temporary hack, as it doesn't allow ORC to unwind from inside a retpoline.
 526  * But it at least allows objtool to understand the control flow *around* the
 527  * retpoline.
 528  */
 529 static int add_ignore_alternatives(struct objtool_file *file)
 530 {
 531         struct section *sec;
 532         struct rela *rela;
 533         struct instruction *insn;
 534
 535         sec = find_section_by_name(file->elf, ".rela.discard.ignore_alts");
 536         if (!sec)
 537                 return 0;
 538
 539         list_for_each_entry(rela, &sec->rela_list, list) {
 540                 if (rela->sym->type != STT_SECTION) {
 541                         WARN("unexpected relocation symbol type in %s", sec->name);
 542                         return -1;
 543                 }
 544
 545                 insn = find_insn(file, rela->sym->sec, rela->addend);
 546                 if (!insn) {
 547                         WARN("bad .discard.ignore_alts entry");
 548                         return -1;
 549                 }
 550
 551                 insn->ignore_alts = true;
 552         }
 553
 554         return 0;
 555 }
 556
 557 /*
 558  * Find the destination instructions for all jumps.
 559  */
 560 static int add_jump_destinations(struct objtool_file *file)
 561 {
 562         struct instruction *insn;
 563         struct rela *rela;
 564         struct section *dest_sec;
 565         unsigned long dest_off;
 566
 567         for_each_insn(file, insn) {
 568                 if (!is_static_jump(insn))
 569                         continue;
 570
 571                 if (insn->ignore || insn->offset == FAKE_JUMP_OFFSET)
 572                         continue;
 573
 574                 rela = find_rela_by_dest_range(file->elf, insn->sec,
 575                                                insn->offset, insn->len);
 576                 if (!rela) {
 577                         dest_sec = insn->sec;
 578                         dest_off = arch_jump_destination(insn);
 579                 } else if (rela->sym->type == STT_SECTION) {
 580                         dest_sec = rela->sym->sec;
 581                         dest_off = arch_dest_rela_offset(rela->addend);
 582                 } else if (rela->sym->sec->idx) {
 583                         dest_sec = rela->sym->sec;
 584                         dest_off = rela->sym->sym.st_value +
 585                                    arch_dest_rela_offset(rela->addend);
 586                 } else if (strstr(rela->sym->name, "_indirect_thunk_")) {
 587                         /*
 588                          * Retpoline jumps are really dynamic jumps in
 589                          * disguise, so convert them accordingly.
 590                          */
 591                         if (insn->type == INSN_JUMP_UNCONDITIONAL)
 592                                 insn->type = INSN_JUMP_DYNAMIC;
 593                         else
 594                                 insn->type = INSN_JUMP_DYNAMIC_CONDITIONAL;
 595
 596                         insn->retpoline_safe = true;
 597                         continue;
 598                 } else {
 599                         /* external sibling call */
 600                         insn->call_dest = rela->sym;
 601                         continue;
 602                 }
 603
 604                 insn->jump_dest = find_insn(file, dest_sec, dest_off);
 605                 if (!insn->jump_dest) {
 606
 607                         /*
 608                          * This is a special case where an alt instruction
 609                          * jumps past the end of the section.  These are
 610                          * handled later in handle_group_alt().
 611                          */
 612                         if (!strcmp(insn->sec->name, ".altinstr_replacement"))
 613                                 continue;
 614
 615                         WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
 616                                   insn->sec, insn->offset, dest_sec->name,
 617                                   dest_off);
 618                         return -1;
 619                 }
 620
 621                 /*
 622                  * Cross-function jump.
 623                  */
 624                 if (insn->func && insn->jump_dest->func &&
 625                     insn->func != insn->jump_dest->func) {
 626
 627                         /*
 628                          * For GCC 8+, create parent/child links for any cold
 629                          * subfunctions.  This is _mostly_ redundant with a
 630                          * similar initialization in read_symbols().
 631                          *
 632                          * If a function has aliases, we want the *first* such
 633                          * function in the symbol table to be the subfunction's
 634                          * parent.  In that case we overwrite the
 635                          * initialization done in read_symbols().
 636                          *
 637                          * However this code can't completely replace the
 638                          * read_symbols() code because this doesn't detect the
 639                          * case where the parent function's only reference to a
 640                          * subfunction is through a jump table.
 641                          */
 642                         if (!strstr(insn->func->name, ".cold.") &&
 643                             strstr(insn->jump_dest->func->name, ".cold.")) {
 644                                 insn->func->cfunc = insn->jump_dest->func;
 645                                 insn->jump_dest->func->pfunc = insn->func;
 646
 647                         } else if (insn->jump_dest->func->pfunc != insn->func->pfunc &&
 648                                    insn->jump_dest->offset == insn->jump_dest->func->offset) {
 649
 650                                 /* internal sibling call */
 651                                 insn->call_dest = insn->jump_dest->func;
 652                         }
 653                 }
 654         }
 655
 656         return 0;
 657 }
 658
 659 /*
 660  * Find the destination instructions for all calls.
 661  */
 662 static int add_call_destinations(struct objtool_file *file)
 663 {
 664         struct instruction *insn;
 665         unsigned long dest_off;
 666         struct rela *rela;
 667
 668         for_each_insn(file, insn) {
 669                 if (insn->type != INSN_CALL)
 670                         continue;
 671
 672                 rela = find_rela_by_dest_range(file->elf, insn->sec,
 673                                                insn->offset, insn->len);
 674                 if (!rela) {
 675                         dest_off = arch_jump_destination(insn);
 676                         insn->call_dest = find_func_by_offset(insn->sec, dest_off);
 677                         if (!insn->call_dest)
 678                                 insn->call_dest = find_symbol_by_offset(insn->sec, dest_off);
 679
 680                         if (insn->ignore)
 681                                 continue;
 682
 683                         if (!insn->call_dest) {
 684                                 WARN_FUNC("unsupported intra-function call",
 685                                           insn->sec, insn->offset);
 686                                 if (retpoline)
 687                                         WARN("If this is a retpoline, please patch it in with alternatives and annotate it with ANNOTATE_NOSPEC_ALTERNATIVE.");
 688                                 return -1;
 689                         }
 690
 691                         if (insn->func && insn->call_dest->type != STT_FUNC) {
 692                                 WARN_FUNC("unsupported call to non-function",
 693                                           insn->sec, insn->offset);
 694                                 return -1;
 695                         }
 696
 697                 } else if (rela->sym->type == STT_SECTION) {
 698                         dest_off = arch_dest_rela_offset(rela->addend);
 699                         insn->call_dest = find_func_by_offset(rela->sym->sec,
 700                                                               dest_off);
 701                         if (!insn->call_dest) {
 702                                 WARN_FUNC("can't find call dest symbol at %s+0x%lx",
 703                                           insn->sec, insn->offset,
 704                                           rela->sym->sec->name,
 705                                           dest_off);
 706                                 return -1;
 707                         }
 708                 } else
 709                         insn->call_dest = rela->sym;
 710         }
 711
 712         return 0;
 713 }
 714
 715 /*
 716  * The .alternatives section requires some extra special care, over and above
 717  * what other special sections require:
 718  *
 719  * 1. Because alternatives are patched in-place, we need to insert a fake jump
 720  *    instruction at the end so that validate_branch() skips all the original
 721  *    replaced instructions when validating the new instruction path.
 722  *
 723  * 2. An added wrinkle is that the new instruction length might be zero.  In
 724  *    that case the old instructions are replaced with noops.  We simulate that
 725  *    by creating a fake jump as the only new instruction.
 726  *
 727  * 3. In some cases, the alternative section includes an instruction which
 728  *    conditionally jumps to the _end_ of the entry.  We have to modify these
 729  *    jumps' destinations to point back to .text rather than the end of the
 730  *    entry in .altinstr_replacement.
 731  */
 732 static int handle_group_alt(struct objtool_file *file,
 733                             struct special_alt *special_alt,
 734                             struct instruction *orig_insn,
 735                             struct instruction **new_insn)
 736 {
 737         struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump = NULL;
 738         unsigned long dest_off;
 739
 740         last_orig_insn = NULL;
 741         insn = orig_insn;
 742         sec_for_each_insn_from(file, insn) {
 743                 if (insn->offset >= special_alt->orig_off + special_alt->orig_len)
 744                         break;
 745
 746                 insn->alt_group = true;
 747                 last_orig_insn = insn;
 748         }
 749
 750         if (next_insn_same_sec(file, last_orig_insn)) {
 751                 fake_jump = malloc(sizeof(*fake_jump));
 752                 if (!fake_jump) {
 753                         WARN("malloc failed");
 754                         return -1;
 755                 }
 756                 memset(fake_jump, 0, sizeof(*fake_jump));
 757                 INIT_LIST_HEAD(&fake_jump->alts);
 758                 INIT_LIST_HEAD(&fake_jump->stack_ops);
 759                 clear_insn_state(&fake_jump->state);
 760
 761                 fake_jump->sec = special_alt->new_sec;
 762                 fake_jump->offset = FAKE_JUMP_OFFSET;
 763                 fake_jump->type = INSN_JUMP_UNCONDITIONAL;
 764                 fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
 765                 fake_jump->func = orig_insn->func;
 766         }
 767
 768         if (!special_alt->new_len) {
 769                 if (!fake_jump) {
 770                         WARN("%s: empty alternative at end of section",
 771                              special_alt->orig_sec->name);
 772                         return -1;
 773                 }
 774
 775                 *new_insn = fake_jump;
 776                 return 0;
 777         }
 778
 779         last_new_insn = NULL;
 780         insn = *new_insn;
 781         sec_for_each_insn_from(file, insn) {
 782                 if (insn->offset >= special_alt->new_off + special_alt->new_len)
 783                         break;
 784
 785                 last_new_insn = insn;
 786
 787                 insn->ignore = orig_insn->ignore_alts;
 788                 insn->func = orig_insn->func;
 789
 790                 /*
 791                  * Since alternative replacement code is copy/pasted by the
 792                  * kernel after applying relocations, generally such code can't
 793                  * have relative-address relocation references to outside the
 794                  * .altinstr_replacement section, unless the arch's
 795                  * alternatives code can adjust the relative offsets
 796                  * accordingly.
 797                  *
 798                  * The x86 alternatives code adjusts the offsets only when it
 799                  * encounters a branch instruction at the very beginning of the
 800                  * replacement group.
 801                  */
 802                 if ((insn->offset != special_alt->new_off ||
 803                     (insn->type != INSN_CALL && !is_static_jump(insn))) &&
 804                     find_rela_by_dest_range(file->elf, insn->sec, insn->offset, insn->len)) {
 805
 806                         WARN_FUNC("unsupported relocation in alternatives section",
 807                                   insn->sec, insn->offset);
 808                         return -1;
 809                 }
 810
 811                 if (!is_static_jump(insn))
 812                         continue;
 813
 814                 if (!insn->immediate)
 815                         continue;
 816
 817                 dest_off = arch_jump_destination(insn);
 818                 if (dest_off == special_alt->new_off + special_alt->new_len) {
 819                         if (!fake_jump) {
 820                                 WARN("%s: alternative jump to end of section",
 821                                      special_alt->orig_sec->name);
 822                                 return -1;
 823                         }
 824                         insn->jump_dest = fake_jump;
 825                 }
 826
 827                 if (!insn->jump_dest) {
 828                         WARN_FUNC("can't find alternative jump destination",
 829                                   insn->sec, insn->offset);
 830                         return -1;
 831                 }
 832         }
 833
 834         if (!last_new_insn) {
 835                 WARN_FUNC("can't find last new alternative instruction",
 836                           special_alt->new_sec, special_alt->new_off);
 837                 return -1;
 838         }
 839
 840         if (fake_jump)
 841                 list_add(&fake_jump->list, &last_new_insn->list);
 842
 843         return 0;
 844 }
 845
 846 /*
 847  * A jump table entry can either convert a nop to a jump or a jump to a nop.
 848  * If the original instruction is a jump, make the alt entry an effective nop
 849  * by just skipping the original instruction.
 850  */
 851 static int handle_jump_alt(struct objtool_file *file,
 852                            struct special_alt *special_alt,
 853                            struct instruction *orig_insn,
 854                            struct instruction **new_insn)
 855 {
 856         if (orig_insn->type == INSN_NOP)
 857                 return 0;
 858
 859         if (orig_insn->type != INSN_JUMP_UNCONDITIONAL) {
 860                 WARN_FUNC("unsupported instruction at jump label",
 861                           orig_insn->sec, orig_insn->offset);
 862                 return -1;
 863         }
 864
 865         *new_insn = list_next_entry(orig_insn, list);
 866         return 0;
 867 }
 868
 869 /*
 870  * Read all the special sections which have alternate instructions which can be
 871  * patched in or redirected to at runtime.  Each instruction having alternate
 872  * instruction(s) has them added to its insn->alts list, which will be
 873  * traversed in validate_branch().
 874  */
 875 static int add_special_section_alts(struct objtool_file *file)
 876 {
 877         struct list_head special_alts;
 878         struct instruction *orig_insn, *new_insn;
 879         struct special_alt *special_alt, *tmp;
 880         struct alternative *alt;
 881         int ret;
 882
 883         ret = special_get_alts(file->elf, &special_alts);
 884         if (ret)
 885                 return ret;
 886
 887         list_for_each_entry_safe(special_alt, tmp, &special_alts, list) {
 888
 889                 orig_insn = find_insn(file, special_alt->orig_sec,
 890                                       special_alt->orig_off);
 891                 if (!orig_insn) {
 892                         WARN_FUNC("special: can't find orig instruction",
 893                                   special_alt->orig_sec, special_alt->orig_off);
 894                         ret = -1;
 895                         goto out;
 896                 }
 897
 898                 new_insn = NULL;
 899                 if (!special_alt->group || special_alt->new_len) {
 900                         new_insn = find_insn(file, special_alt->new_sec,
 901                                              special_alt->new_off);
 902                         if (!new_insn) {
 903                                 WARN_FUNC("special: can't find new instruction",
 904                                           special_alt->new_sec,
 905                                           special_alt->new_off);
 906                                 ret = -1;
 907                                 goto out;
 908                         }
 909                 }
 910
 911                 if (special_alt->group) {
 912                         if (!special_alt->orig_len) {
 913                                 WARN_FUNC("empty alternative entry",
 914                                           orig_insn->sec, orig_insn->offset);
 915                                 continue;
 916                         }
 917
 918                         ret = handle_group_alt(file, special_alt, orig_insn,
 919                                                &new_insn);
 920                         if (ret)
 921                                 goto out;
 922                 } else if (special_alt->jump_or_nop) {
 923                         ret = handle_jump_alt(file, special_alt, orig_insn,
 924                                               &new_insn);
 925                         if (ret)
 926                                 goto out;
 927                 }
 928
 929                 alt = malloc(sizeof(*alt));
 930                 if (!alt) {
 931                         WARN("malloc failed");
 932                         ret = -1;
 933                         goto out;
 934                 }
 935
 936                 alt->insn = new_insn;
 937                 alt->skip_orig = special_alt->skip_orig;
 938                 orig_insn->ignore_alts |= special_alt->skip_alt;
 939                 list_add_tail(&alt->list, &orig_insn->alts);
 940
 941                 list_del(&special_alt->list);
 942                 free(special_alt);
 943         }
 944
 945 out:
 946         return ret;
 947 }
 948
 949 static int add_jump_table(struct objtool_file *file, struct instruction *insn,
 950                             struct rela *table)
 951 {
 952         struct rela *rela = table;
 953         struct instruction *dest_insn;
 954         struct alternative *alt;
 955         struct symbol *pfunc = insn->func->pfunc;
 956         unsigned int prev_offset = 0;
 957
 958         /*
 959          * Each @rela is a switch table relocation which points to the target
 960          * instruction.
 961          */
 962         list_for_each_entry_from(rela, &table->sec->rela_list, list) {
 963
 964                 /* Check for the end of the table: */
 965                 if (rela != table && rela->jump_table_start)
 966                         break;
 967
 968                 /* Make sure the table entries are consecutive: */
 969                 if (prev_offset && rela->offset != prev_offset + 8)
 970                         break;
 971
 972                 /* Detect function pointers from contiguous objects: */
 973                 if (rela->sym->sec == pfunc->sec &&
 974                     rela->addend == pfunc->offset)
 975                         break;
 976
 977                 dest_insn = find_insn(file, rela->sym->sec, rela->addend);
 978                 if (!dest_insn)
 979                         break;
 980
 981                 /* Make sure the destination is in the same function: */
 982                 if (!dest_insn->func || dest_insn->func->pfunc != pfunc)
 983                         break;
 984
 985                 alt = malloc(sizeof(*alt));
 986                 if (!alt) {
 987                         WARN("malloc failed");
 988                         return -1;
 989                 }
 990
 991                 alt->insn = dest_insn;
 992                 list_add_tail(&alt->list, &insn->alts);
 993                 prev_offset = rela->offset;
 994         }
 995
 996         if (!prev_offset) {
 997                 WARN_FUNC("can't find switch jump table",
 998                           insn->sec, insn->offset);
 999                 return -1;
1000         }
1001
1002         return 0;
1003 }
1004
1005 /*
1006  * find_jump_table() - Given a dynamic jump, find the switch jump table in
1007  * .rodata associated with it.
1008  *
1009  * There are 3 basic patterns:
1010  *
1011  * 1. jmpq *[rodata addr](,%reg,8)
1012  *
1013  *    This is the most common case by far.  It jumps to an address in a simple
1014  *    jump table which is stored in .rodata.
1015  *
1016  * 2. jmpq *[rodata addr](%rip)
1017  *
1018  *    This is caused by a rare GCC quirk, currently only seen in three driver
1019  *    functions in the kernel, only with certain obscure non-distro configs.
1020  *
1021  *    As part of an optimization, GCC makes a copy of an existing switch jump
1022  *    table, modifies it, and then hard-codes the jump (albeit with an indirect
1023  *    jump) to use a single entry in the table.  The rest of the jump table and
1024  *    some of its jump targets remain as dead code.
1025  *
1026  *    In such a case we can just crudely ignore all unreachable instruction
1027  *    warnings for the entire object file.  Ideally we would just ignore them
1028  *    for the function, but that would require redesigning the code quite a
1029  *    bit.  And honestly that's just not worth doing: unreachable instruction
1030  *    warnings are of questionable value anyway, and this is such a rare issue.
1031  *
1032  * 3. mov [rodata addr],%reg1
1033  *    ... some instructions ...
1034  *    jmpq *(%reg1,%reg2,8)
1035  *
1036  *    This is a fairly uncommon pattern which is new for GCC 6.  As of this
1037  *    writing, there are 11 occurrences of it in the allmodconfig kernel.
1038  *
1039  *    As of GCC 7 there are quite a few more of these and the 'in between' code
1040  *    is significant. Esp. with KASAN enabled some of the code between the mov
1041  *    and jmpq uses .rodata itself, which can confuse things.
1042  *
1043  *    TODO: Once we have DWARF CFI and smarter instruction decoding logic,
1044  *    ensure the same register is used in the mov and jump instructions.
1045  *
1046  *    NOTE: RETPOLINE made it harder still to decode dynamic jumps.
1047  */
1048 static struct rela *find_jump_table(struct objtool_file *file,
1049                                       struct symbol *func,
1050                                       struct instruction *insn)
1051 {
1052         struct rela *text_rela, *table_rela;
1053         struct instruction *dest_insn, *orig_insn = insn;
1054         struct section *table_sec;
1055         unsigned long table_offset;
1056
1057         /*
1058          * Backward search using the @first_jump_src links, these help avoid
1059          * much of the 'in between' code. Which avoids us getting confused by
1060          * it.
1061          */
1062         for (;
1063              &insn->list != &file->insn_list && insn->func && insn->func->pfunc == func;
1064              insn = insn->first_jump_src ?: list_prev_entry(insn, list)) {
1065
1066                 if (insn != orig_insn && insn->type == INSN_JUMP_DYNAMIC)
1067                         break;
1068
1069                 /* allow small jumps within the range */
1070                 if (insn->type == INSN_JUMP_UNCONDITIONAL &&
1071                     insn->jump_dest &&
1072                     (insn->jump_dest->offset <= insn->offset ||
1073                      insn->jump_dest->offset > orig_insn->offset))
1074                     break;
1075
1076                 /* look for a relocation which references .rodata */
1077                 text_rela = find_rela_by_dest_range(file->elf, insn->sec,
1078                                                     insn->offset, insn->len);
1079                 if (!text_rela || text_rela->sym->type != STT_SECTION ||
1080                     !text_rela->sym->sec->rodata)
1081                         continue;
1082
1083                 table_offset = text_rela->addend;
1084                 table_sec = text_rela->sym->sec;
1085
1086                 if (text_rela->type == R_X86_64_PC32)
1087                         table_offset += 4;
1088
1089                 /*
1090                  * Make sure the .rodata address isn't associated with a
1091                  * symbol.  GCC jump tables are anonymous data.
1092                  *
1093                  * Also support C jump tables which are in the same format as
1094                  * switch jump tables.  For objtool to recognize them, they
1095                  * need to be placed in the C_JUMP_TABLE_SECTION section.  They
1096                  * have symbols associated with them.
1097                  */
1098                 if (find_symbol_containing(table_sec, table_offset) &&
1099                     strcmp(table_sec->name, C_JUMP_TABLE_SECTION))
1100                         continue;
1101
1102                 /*
1103                  * Each table entry has a rela associated with it.  The rela
1104                  * should reference text in the same function as the original
1105                  * instruction.
1106                  */
1107                 table_rela = find_rela_by_dest(file->elf, table_sec, table_offset);
1108                 if (!table_rela)
1109                         continue;
1110                 dest_insn = find_insn(file, table_rela->sym->sec, table_rela->addend);
1111                 if (!dest_insn || !dest_insn->func || dest_insn->func->pfunc != func)
1112                         continue;
1113
1114                 /*
1115                  * Use of RIP-relative switch jumps is quite rare, and
1116                  * indicates a rare GCC quirk/bug which can leave dead code
1117                  * behind.
1118                  */
1119                 if (text_rela->type == R_X86_64_PC32)
1120                         file->ignore_unreachables = true;
1121
1122                 return table_rela;
1123         }
1124
1125         return NULL;
1126 }
1127
1128 /*
1129  * First pass: Mark the head of each jump table so that in the next pass,
1130  * we know when a given jump table ends and the next one starts.
1131  */
1132 static void mark_func_jump_tables(struct objtool_file *file,
1133                                     struct symbol *func)
1134 {
1135         struct instruction *insn, *last = NULL;
1136         struct rela *rela;
1137
1138         func_for_each_insn(file, func, insn) {
1139                 if (!last)
1140                         last = insn;
1141
1142                 /*
1143                  * Store back-pointers for unconditional forward jumps such
1144                  * that find_jump_table() can back-track using those and
1145                  * avoid some potentially confusing code.
1146                  */
1147                 if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest &&
1148                     insn->offset > last->offset &&
1149                     insn->jump_dest->offset > insn->offset &&
1150                     !insn->jump_dest->first_jump_src) {
1151
1152                         insn->jump_dest->first_jump_src = insn;
1153                         last = insn->jump_dest;
1154                 }
1155
1156                 if (insn->type != INSN_JUMP_DYNAMIC)
1157                         continue;
1158
1159                 rela = find_jump_table(file, func, insn);
1160                 if (rela) {
1161                         rela->jump_table_start = true;
1162                         insn->jump_table = rela;
1163                 }
1164         }
1165 }
1166
1167 static int add_func_jump_tables(struct objtool_file *file,
1168                                   struct symbol *func)
1169 {
1170         struct instruction *insn;
1171         int ret;
1172
1173         func_for_each_insn(file, func, insn) {
1174                 if (!insn->jump_table)
1175                         continue;
1176
1177                 ret = add_jump_table(file, insn, insn->jump_table);
1178                 if (ret)
1179                         return ret;
1180         }
1181
1182         return 0;
1183 }
1184
1185 /*
1186  * For some switch statements, gcc generates a jump table in the .rodata
1187  * section which contains a list of addresses within the function to jump to.
1188  * This finds these jump tables and adds them to the insn->alts lists.
1189  */
1190 static int add_jump_table_alts(struct objtool_file *file)
1191 {
1192         struct section *sec;
1193         struct symbol *func;
1194         int ret;
1195
1196         if (!file->rodata)
1197                 return 0;
1198
1199         for_each_sec(file, sec) {
1200                 list_for_each_entry(func, &sec->symbol_list, list) {
1201                         if (func->type != STT_FUNC)
1202                                 continue;
1203
1204                         mark_func_jump_tables(file, func);
1205                         ret = add_func_jump_tables(file, func);
1206                         if (ret)
1207                                 return ret;
1208                 }
1209         }
1210
1211         return 0;
1212 }
1213
1214 static int read_unwind_hints(struct objtool_file *file)
1215 {
1216         struct section *sec, *relasec;
1217         struct rela *rela;
1218         struct unwind_hint *hint;
1219         struct instruction *insn;
1220         struct cfi_reg *cfa;
1221         int i;
1222
1223         sec = find_section_by_name(file->elf, ".discard.unwind_hints");
1224         if (!sec)
1225                 return 0;
1226
1227         relasec = sec->rela;
1228         if (!relasec) {
1229                 WARN("missing .rela.discard.unwind_hints section");
1230                 return -1;
1231         }
1232
1233         if (sec->len % sizeof(struct unwind_hint)) {
1234                 WARN("struct unwind_hint size mismatch");
1235                 return -1;
1236         }
1237
1238         file->hints = true;
1239
1240         for (i = 0; i < sec->len / sizeof(struct unwind_hint); i++) {
1241                 hint = (struct unwind_hint *)sec->data->d_buf + i;
1242
1243                 rela = find_rela_by_dest(file->elf, sec, i * sizeof(*hint));
1244                 if (!rela) {
1245                         WARN("can't find rela for unwind_hints[%d]", i);
1246                         return -1;
1247                 }
1248
1249                 insn = find_insn(file, rela->sym->sec, rela->addend);
1250                 if (!insn) {
1251                         WARN("can't find insn for unwind_hints[%d]", i);
1252                         return -1;
1253                 }
1254
1255                 cfa = &insn->state.cfa;
1256
1257                 if (hint->type == UNWIND_HINT_TYPE_SAVE) {
1258                         insn->save = true;
1259                         continue;
1260
1261                 } else if (hint->type == UNWIND_HINT_TYPE_RESTORE) {
1262                         insn->restore = true;
1263                         insn->hint = true;
1264                         continue;
1265                 }
1266
1267                 insn->hint = true;
1268
1269                 switch (hint->sp_reg) {
1270                 case ORC_REG_UNDEFINED:
1271                         cfa->base = CFI_UNDEFINED;
1272                         break;
1273                 case ORC_REG_SP:
1274                         cfa->base = CFI_SP;
1275                         break;
1276                 case ORC_REG_BP:
1277                         cfa->base = CFI_BP;
1278                         break;
1279                 case ORC_REG_SP_INDIRECT:
1280                         cfa->base = CFI_SP_INDIRECT;
1281                         break;
1282                 case ORC_REG_R10:
1283                         cfa->base = CFI_R10;
1284                         break;
1285                 case ORC_REG_R13:
1286                         cfa->base = CFI_R13;
1287                         break;
1288                 case ORC_REG_DI:
1289                         cfa->base = CFI_DI;
1290                         break;
1291                 case ORC_REG_DX:
1292                         cfa->base = CFI_DX;
1293                         break;
1294                 default:
1295                         WARN_FUNC("unsupported unwind_hint sp base reg %d",
1296                                   insn->sec, insn->offset, hint->sp_reg);
1297                         return -1;
1298                 }
1299
1300                 cfa->offset = hint->sp_offset;
1301                 insn->state.type = hint->type;
1302                 insn->state.end = hint->end;
1303         }
1304
1305         return 0;
1306 }
1307
1308 static int read_retpoline_hints(struct objtool_file *file)
1309 {
1310         struct section *sec;
1311         struct instruction *insn;
1312         struct rela *rela;
1313
1314         sec = find_section_by_name(file->elf, ".rela.discard.retpoline_safe");
1315         if (!sec)
1316                 return 0;
1317
1318         list_for_each_entry(rela, &sec->rela_list, list) {
1319                 if (rela->sym->type != STT_SECTION) {
1320                         WARN("unexpected relocation symbol type in %s", sec->name);
1321                         return -1;
1322                 }
1323
1324                 insn = find_insn(file, rela->sym->sec, rela->addend);
1325                 if (!insn) {
1326                         WARN("bad .discard.retpoline_safe entry");
1327                         return -1;
1328                 }
1329
1330                 if (insn->type != INSN_JUMP_DYNAMIC &&
1331                     insn->type != INSN_CALL_DYNAMIC) {
1332                         WARN_FUNC("retpoline_safe hint not an indirect jump/call",
1333                                   insn->sec, insn->offset);
1334                         return -1;
1335                 }
1336
1337                 insn->retpoline_safe = true;
1338         }
1339
1340         return 0;
1341 }
1342
1343 static void mark_rodata(struct objtool_file *file)
1344 {
1345         struct section *sec;
1346         bool found = false;
1347
1348         /*
1349          * Search for the following rodata sections, each of which can
1350          * potentially contain jump tables:
1351          *
1352          * - .rodata: can contain GCC switch tables
1353          * - .rodata.<func>: same, if -fdata-sections is being used
1354          * - .rodata..c_jump_table: contains C annotated jump tables
1355          *
1356          * .rodata.str1.* sections are ignored; they don't contain jump tables.
1357          */
1358         for_each_sec(file, sec) {
1359                 if (!strncmp(sec->name, ".rodata", 7) &&
1360                     !strstr(sec->name, ".str1.")) {
1361                         sec->rodata = true;
1362                         found = true;
1363                 }
1364         }
1365
1366         file->rodata = found;
1367 }
1368
1369 static int decode_sections(struct objtool_file *file)
1370 {
1371         int ret;
1372
1373         mark_rodata(file);
1374
1375         ret = decode_instructions(file);
1376         if (ret)
1377                 return ret;
1378
1379         ret = add_dead_ends(file);
1380         if (ret)
1381                 return ret;
1382
1383         add_ignores(file);
1384         add_uaccess_safe(file);
1385
1386         ret = add_ignore_alternatives(file);
1387         if (ret)
1388                 return ret;
1389
1390         ret = add_jump_destinations(file);
1391         if (ret)
1392                 return ret;
1393
1394         ret = add_special_section_alts(file);
1395         if (ret)
1396                 return ret;
1397
1398         ret = add_call_destinations(file);
1399         if (ret)
1400                 return ret;
1401
1402         ret = add_jump_table_alts(file);
1403         if (ret)
1404                 return ret;
1405
1406         ret = read_unwind_hints(file);
1407         if (ret)
1408                 return ret;
1409
1410         ret = read_retpoline_hints(file);
1411         if (ret)
1412                 return ret;
1413
1414         return 0;
1415 }
1416
1417 static bool is_fentry_call(struct instruction *insn)
1418 {
1419         if (insn->type == INSN_CALL &&
1420             insn->call_dest->type == STT_NOTYPE &&
1421             !strcmp(insn->call_dest->name, "__fentry__"))
1422                 return true;
1423
1424         return false;
1425 }
1426
1427 static bool has_modified_stack_frame(struct insn_state *state)
1428 {
1429         int i;
1430
1431         if (state->cfa.base != initial_func_cfi.cfa.base ||
1432             state->cfa.offset != initial_func_cfi.cfa.offset ||
1433             state->stack_size != initial_func_cfi.cfa.offset ||
1434             state->drap)
1435                 return true;
1436
1437         for (i = 0; i < CFI_NUM_REGS; i++)
1438                 if (state->regs[i].base != initial_func_cfi.regs[i].base ||
1439                     state->regs[i].offset != initial_func_cfi.regs[i].offset)
1440                         return true;
1441
1442         return false;
1443 }
1444
1445 static bool has_valid_stack_frame(struct insn_state *state)
1446 {
1447         if (state->cfa.base == CFI_BP && state->regs[CFI_BP].base == CFI_CFA &&
1448             state->regs[CFI_BP].offset == -16)
1449                 return true;
1450
1451         if (state->drap && state->regs[CFI_BP].base == CFI_BP)
1452                 return true;
1453
1454         return false;
1455 }
1456
1457 static int update_insn_state_regs(struct instruction *insn,
1458                                   struct insn_state *state,
1459                                   struct stack_op *op)
1460 {
1461         struct cfi_reg *cfa = &state->cfa;
1462
1463         if (cfa->base != CFI_SP)
1464                 return 0;
1465
1466         /* push */
1467         if (op->dest.type == OP_DEST_PUSH || op->dest.type == OP_DEST_PUSHF)
1468                 cfa->offset += 8;
1469
1470         /* pop */
1471         if (op->src.type == OP_SRC_POP || op->src.type == OP_SRC_POPF)
1472                 cfa->offset -= 8;
1473
1474         /* add immediate to sp */
1475         if (op->dest.type == OP_DEST_REG && op->src.type == OP_SRC_ADD &&
1476             op->dest.reg == CFI_SP && op->src.reg == CFI_SP)
1477                 cfa->offset -= op->src.offset;
1478
1479         return 0;
1480 }
1481
1482 static void save_reg(struct insn_state *state, unsigned char reg, int base,
1483                      int offset)
1484 {
1485         if (arch_callee_saved_reg(reg) &&
1486             state->regs[reg].base == CFI_UNDEFINED) {
1487                 state->regs[reg].base = base;
1488                 state->regs[reg].offset = offset;
1489         }
1490 }
1491
1492 static void restore_reg(struct insn_state *state, unsigned char reg)
1493 {
1494         state->regs[reg].base = initial_func_cfi.regs[reg].base;
1495         state->regs[reg].offset = initial_func_cfi.regs[reg].offset;
1496 }
1497
1498 /*
1499  * A note about DRAP stack alignment:
1500  *
1501  * GCC has the concept of a DRAP register, which is used to help keep track of
1502  * the stack pointer when aligning the stack.  r10 or r13 is used as the DRAP
1503  * register.  The typical DRAP pattern is:
1504  *
1505  *   4c 8d 54 24 08             lea    0x8(%rsp),%r10
1506  *   48 83 e4 c0                and    $0xffffffffffffffc0,%rsp
1507  *   41 ff 72 f8                pushq  -0x8(%r10)
1508  *   55                         push   %rbp
1509  *   48 89 e5                   mov    %rsp,%rbp
1510  *                              (more pushes)
1511  *   41 52                      push   %r10
1512  *                              ...
1513  *   41 5a                      pop    %r10
1514  *                              (more pops)
1515  *   5d                         pop    %rbp
1516  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1517  *   c3                         retq
1518  *
1519  * There are some variations in the epilogues, like:
1520  *
1521  *   5b                         pop    %rbx
1522  *   41 5a                      pop    %r10
1523  *   41 5c                      pop    %r12
1524  *   41 5d                      pop    %r13
1525  *   41 5e                      pop    %r14
1526  *   c9                         leaveq
1527  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1528  *   c3                         retq
1529  *
1530  * and:
1531  *
1532  *   4c 8b 55 e8                mov    -0x18(%rbp),%r10
1533  *   48 8b 5d e0                mov    -0x20(%rbp),%rbx
1534  *   4c 8b 65 f0                mov    -0x10(%rbp),%r12
1535  *   4c 8b 6d f8                mov    -0x8(%rbp),%r13
1536  *   c9                         leaveq
1537  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1538  *   c3                         retq
1539  *
1540  * Sometimes r13 is used as the DRAP register, in which case it's saved and
1541  * restored beforehand:
1542  *
1543  *   41 55                      push   %r13
1544  *   4c 8d 6c 24 10             lea    0x10(%rsp),%r13
1545  *   48 83 e4 f0                and    $0xfffffffffffffff0,%rsp
1546  *                              ...
1547  *   49 8d 65 f0                lea    -0x10(%r13),%rsp
1548  *   41 5d                      pop    %r13
1549  *   c3                         retq
1550  */
1551 static int update_insn_state(struct instruction *insn, struct insn_state *state,
1552                              struct stack_op *op)
1553 {
1554         struct cfi_reg *cfa = &state->cfa;
1555         struct cfi_reg *regs = state->regs;
1556
1557         /* stack operations don't make sense with an undefined CFA */
1558         if (cfa->base == CFI_UNDEFINED) {
1559                 if (insn->func) {
1560                         WARN_FUNC("undefined stack state", insn->sec, insn->offset);
1561                         return -1;
1562                 }
1563                 return 0;
1564         }
1565
1566         if (state->type == ORC_TYPE_REGS || state->type == ORC_TYPE_REGS_IRET)
1567                 return update_insn_state_regs(insn, state, op);
1568
1569         switch (op->dest.type) {
1570
1571         case OP_DEST_REG:
1572                 switch (op->src.type) {
1573
1574                 case OP_SRC_REG:
1575                         if (op->src.reg == CFI_SP && op->dest.reg == CFI_BP &&
1576                             cfa->base == CFI_SP &&
1577                             regs[CFI_BP].base == CFI_CFA &&
1578                             regs[CFI_BP].offset == -cfa->offset) {
1579
1580                                 /* mov %rsp, %rbp */
1581                                 cfa->base = op->dest.reg;
1582                                 state->bp_scratch = false;
1583                         }
1584
1585                         else if (op->src.reg == CFI_SP &&
1586                                  op->dest.reg == CFI_BP && state->drap) {
1587
1588                                 /* drap: mov %rsp, %rbp */
1589                                 regs[CFI_BP].base = CFI_BP;
1590                                 regs[CFI_BP].offset = -state->stack_size;
1591                                 state->bp_scratch = false;
1592                         }
1593
1594                         else if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1595
1596                                 /*
1597                                  * mov %rsp, %reg
1598                                  *
1599                                  * This is needed for the rare case where GCC
1600                                  * does:
1601                                  *
1602                                  *   mov    %rsp, %rax
1603                                  *   ...
1604                                  *   mov    %rax, %rsp
1605                                  */
1606                                 state->vals[op->dest.reg].base = CFI_CFA;
1607                                 state->vals[op->dest.reg].offset = -state->stack_size;
1608                         }
1609
1610                         else if (op->src.reg == CFI_BP && op->dest.reg == CFI_SP &&
1611                                  cfa->base == CFI_BP) {
1612
1613                                 /*
1614                                  * mov %rbp, %rsp
1615                                  *
1616                                  * Restore the original stack pointer (Clang).
1617                                  */
1618                                 state->stack_size = -state->regs[CFI_BP].offset;
1619                         }
1620
1621                         else if (op->dest.reg == cfa->base) {
1622
1623                                 /* mov %reg, %rsp */
1624                                 if (cfa->base == CFI_SP &&
1625                                     state->vals[op->src.reg].base == CFI_CFA) {
1626
1627                                         /*
1628                                          * This is needed for the rare case
1629                                          * where GCC does something dumb like:
1630                                          *
1631                                          *   lea    0x8(%rsp), %rcx
1632                                          *   ...
1633                                          *   mov    %rcx, %rsp
1634                                          */
1635                                         cfa->offset = -state->vals[op->src.reg].offset;
1636                                         state->stack_size = cfa->offset;
1637
1638                                 } else {
1639                                         cfa->base = CFI_UNDEFINED;
1640                                         cfa->offset = 0;
1641                                 }
1642                         }
1643
1644                         break;
1645
1646                 case OP_SRC_ADD:
1647                         if (op->dest.reg == CFI_SP && op->src.reg == CFI_SP) {
1648
1649                                 /* add imm, %rsp */
1650                                 state->stack_size -= op->src.offset;
1651                                 if (cfa->base == CFI_SP)
1652                                         cfa->offset -= op->src.offset;
1653                                 break;
1654                         }
1655
1656                         if (op->dest.reg == CFI_SP && op->src.reg == CFI_BP) {
1657
1658                                 /* lea disp(%rbp), %rsp */
1659                                 state->stack_size = -(op->src.offset + regs[CFI_BP].offset);
1660                                 break;
1661                         }
1662
1663                         if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1664
1665                                 /* drap: lea disp(%rsp), %drap */
1666                                 state->drap_reg = op->dest.reg;
1667
1668                                 /*
1669                                  * lea disp(%rsp), %reg
1670                                  *
1671                                  * This is needed for the rare case where GCC
1672                                  * does something dumb like:
1673                                  *
1674                                  *   lea    0x8(%rsp), %rcx
1675                                  *   ...
1676                                  *   mov    %rcx, %rsp
1677                                  */
1678                                 state->vals[op->dest.reg].base = CFI_CFA;
1679                                 state->vals[op->dest.reg].offset = \
1680                                         -state->stack_size + op->src.offset;
1681
1682                                 break;
1683                         }
1684
1685                         if (state->drap && op->dest.reg == CFI_SP &&
1686                             op->src.reg == state->drap_reg) {
1687
1688                                  /* drap: lea disp(%drap), %rsp */
1689                                 cfa->base = CFI_SP;
1690                                 cfa->offset = state->stack_size = -op->src.offset;
1691                                 state->drap_reg = CFI_UNDEFINED;
1692                                 state->drap = false;
1693                                 break;
1694                         }
1695
1696                         if (op->dest.reg == state->cfa.base) {
1697                                 WARN_FUNC("unsupported stack register modification",
1698                                           insn->sec, insn->offset);
1699                                 return -1;
1700                         }
1701
1702                         break;
1703
1704                 case OP_SRC_AND:
1705                         if (op->dest.reg != CFI_SP ||
1706                             (state->drap_reg != CFI_UNDEFINED && cfa->base != CFI_SP) ||
1707                             (state->drap_reg == CFI_UNDEFINED && cfa->base != CFI_BP)) {
1708                                 WARN_FUNC("unsupported stack pointer realignment",
1709                                           insn->sec, insn->offset);
1710                                 return -1;
1711                         }
1712
1713                         if (state->drap_reg != CFI_UNDEFINED) {
1714                                 /* drap: and imm, %rsp */
1715                                 cfa->base = state->drap_reg;
1716                                 cfa->offset = state->stack_size = 0;
1717                                 state->drap = true;
1718                         }
1719
1720                         /*
1721                          * Older versions of GCC (4.8ish) realign the stack
1722                          * without DRAP, with a frame pointer.
1723                          */
1724
1725                         break;
1726
1727                 case OP_SRC_POP:
1728                 case OP_SRC_POPF:
1729                         if (!state->drap && op->dest.reg == cfa->base) {
1730
1731                                 /* pop %rbp */
1732                                 cfa->base = CFI_SP;
1733                         }
1734
1735                         if (state->drap && cfa->base == CFI_BP_INDIRECT &&
1736                             op->dest.reg == state->drap_reg &&
1737                             state->drap_offset == -state->stack_size) {
1738
1739                                 /* drap: pop %drap */
1740                                 cfa->base = state->drap_reg;
1741                                 cfa->offset = 0;
1742                                 state->drap_offset = -1;
1743
1744                         } else if (regs[op->dest.reg].offset == -state->stack_size) {
1745
1746                                 /* pop %reg */
1747                                 restore_reg(state, op->dest.reg);
1748                         }
1749
1750                         state->stack_size -= 8;
1751                         if (cfa->base == CFI_SP)
1752                                 cfa->offset -= 8;
1753
1754                         break;
1755
1756                 case OP_SRC_REG_INDIRECT:
1757                         if (state->drap && op->src.reg == CFI_BP &&
1758                             op->src.offset == state->drap_offset) {
1759
1760                                 /* drap: mov disp(%rbp), %drap */
1761                                 cfa->base = state->drap_reg;
1762                                 cfa->offset = 0;
1763                                 state->drap_offset = -1;
1764                         }
1765
1766                         if (state->drap && op->src.reg == CFI_BP &&
1767                             op->src.offset == regs[op->dest.reg].offset) {
1768
1769                                 /* drap: mov disp(%rbp), %reg */
1770                                 restore_reg(state, op->dest.reg);
1771
1772                         } else if (op->src.reg == cfa->base &&
1773                             op->src.offset == regs[op->dest.reg].offset + cfa->offset) {
1774
1775                                 /* mov disp(%rbp), %reg */
1776                                 /* mov disp(%rsp), %reg */
1777                                 restore_reg(state, op->dest.reg);
1778                         }
1779
1780                         break;
1781
1782                 default:
1783                         WARN_FUNC("unknown stack-related instruction",
1784                                   insn->sec, insn->offset);
1785                         return -1;
1786                 }
1787
1788                 break;
1789
1790         case OP_DEST_PUSH:
1791         case OP_DEST_PUSHF:
1792                 state->stack_size += 8;
1793                 if (cfa->base == CFI_SP)
1794                         cfa->offset += 8;
1795
1796                 if (op->src.type != OP_SRC_REG)
1797                         break;
1798
1799                 if (state->drap) {
1800                         if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1801
1802                                 /* drap: push %drap */
1803                                 cfa->base = CFI_BP_INDIRECT;
1804                                 cfa->offset = -state->stack_size;
1805
1806                                 /* save drap so we know when to restore it */
1807                                 state->drap_offset = -state->stack_size;
1808
1809                         } else if (op->src.reg == CFI_BP && cfa->base == state->drap_reg) {
1810
1811                                 /* drap: push %rbp */
1812                                 state->stack_size = 0;
1813
1814                         } else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1815
1816                                 /* drap: push %reg */
1817                                 save_reg(state, op->src.reg, CFI_BP, -state->stack_size);
1818                         }
1819
1820                 } else {
1821
1822                         /* push %reg */
1823                         save_reg(state, op->src.reg, CFI_CFA, -state->stack_size);
1824                 }
1825
1826                 /* detect when asm code uses rbp as a scratch register */
1827                 if (!no_fp && insn->func && op->src.reg == CFI_BP &&
1828                     cfa->base != CFI_BP)
1829                         state->bp_scratch = true;
1830                 break;
1831
1832         case OP_DEST_REG_INDIRECT:
1833
1834                 if (state->drap) {
1835                         if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1836
1837                                 /* drap: mov %drap, disp(%rbp) */
1838                                 cfa->base = CFI_BP_INDIRECT;
1839                                 cfa->offset = op->dest.offset;
1840
1841                                 /* save drap offset so we know when to restore it */
1842                                 state->drap_offset = op->dest.offset;
1843                         }
1844
1845                         else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1846
1847                                 /* drap: mov reg, disp(%rbp) */
1848                                 save_reg(state, op->src.reg, CFI_BP, op->dest.offset);
1849                         }
1850
1851                 } else if (op->dest.reg == cfa->base) {
1852
1853                         /* mov reg, disp(%rbp) */
1854                         /* mov reg, disp(%rsp) */
1855                         save_reg(state, op->src.reg, CFI_CFA,
1856                                  op->dest.offset - state->cfa.offset);
1857                 }
1858
1859                 break;
1860
1861         case OP_DEST_LEAVE:
1862                 if ((!state->drap && cfa->base != CFI_BP) ||
1863                     (state->drap && cfa->base != state->drap_reg)) {
1864                         WARN_FUNC("leave instruction with modified stack frame",
1865                                   insn->sec, insn->offset);
1866                         return -1;
1867                 }
1868
1869                 /* leave (mov %rbp, %rsp; pop %rbp) */
1870
1871                 state->stack_size = -state->regs[CFI_BP].offset - 8;
1872                 restore_reg(state, CFI_BP);
1873
1874                 if (!state->drap) {
1875                         cfa->base = CFI_SP;
1876                         cfa->offset -= 8;
1877                 }
1878
1879                 break;
1880
1881         case OP_DEST_MEM:
1882                 if (op->src.type != OP_SRC_POP && op->src.type != OP_SRC_POPF) {
1883                         WARN_FUNC("unknown stack-related memory operation",
1884                                   insn->sec, insn->offset);
1885                         return -1;
1886                 }
1887
1888                 /* pop mem */
1889                 state->stack_size -= 8;
1890                 if (cfa->base == CFI_SP)
1891                         cfa->offset -= 8;
1892
1893                 break;
1894
1895         default:
1896                 WARN_FUNC("unknown stack-related instruction",
1897                           insn->sec, insn->offset);
1898                 return -1;
1899         }
1900
1901         return 0;
1902 }
1903
1904 static int handle_insn_ops(struct instruction *insn, struct insn_state *state)
1905 {
1906         struct stack_op *op;
1907
1908         list_for_each_entry(op, &insn->stack_ops, list) {
1909                 int res;
1910
1911                 res = update_insn_state(insn, state, op);
1912                 if (res)
1913                         return res;
1914
1915                 if (op->dest.type == OP_DEST_PUSHF) {
1916                         if (!state->uaccess_stack) {
1917                                 state->uaccess_stack = 1;
1918                         } else if (state->uaccess_stack >> 31) {
1919                                 WARN_FUNC("PUSHF stack exhausted",
1920                                           insn->sec, insn->offset);
1921                                 return 1;
1922                         }
1923                         state->uaccess_stack <<= 1;
1924                         state->uaccess_stack  |= state->uaccess;
1925                 }
1926
1927                 if (op->src.type == OP_SRC_POPF) {
1928                         if (state->uaccess_stack) {
1929                                 state->uaccess = state->uaccess_stack & 1;
1930                                 state->uaccess_stack >>= 1;
1931                                 if (state->uaccess_stack == 1)
1932                                         state->uaccess_stack = 0;
1933                         }
1934                 }
1935         }
1936
1937         return 0;
1938 }
1939
1940 static bool insn_state_match(struct instruction *insn, struct insn_state *state)
1941 {
1942         struct insn_state *state1 = &insn->state, *state2 = state;
1943         int i;
1944
1945         if (memcmp(&state1->cfa, &state2->cfa, sizeof(state1->cfa))) {
1946                 WARN_FUNC("stack state mismatch: cfa1=%d%+d cfa2=%d%+d",
1947                           insn->sec, insn->offset,
1948                           state1->cfa.base, state1->cfa.offset,
1949                           state2->cfa.base, state2->cfa.offset);
1950
1951         } else if (memcmp(&state1->regs, &state2->regs, sizeof(state1->regs))) {
1952                 for (i = 0; i < CFI_NUM_REGS; i++) {
1953                         if (!memcmp(&state1->regs[i], &state2->regs[i],
1954                                     sizeof(struct cfi_reg)))
1955                                 continue;
1956
1957                         WARN_FUNC("stack state mismatch: reg1[%d]=%d%+d reg2[%d]=%d%+d",
1958                                   insn->sec, insn->offset,
1959                                   i, state1->regs[i].base, state1->regs[i].offset,
1960                                   i, state2->regs[i].base, state2->regs[i].offset);
1961                         break;
1962                 }
1963
1964         } else if (state1->type != state2->type) {
1965                 WARN_FUNC("stack state mismatch: type1=%d type2=%d",
1966                           insn->sec, insn->offset, state1->type, state2->type);
1967
1968         } else if (state1->drap != state2->drap ||
1969                  (state1->drap && state1->drap_reg != state2->drap_reg) ||
1970                  (state1->drap && state1->drap_offset != state2->drap_offset)) {
1971                 WARN_FUNC("stack state mismatch: drap1=%d(%d,%d) drap2=%d(%d,%d)",
1972                           insn->sec, insn->offset,
1973                           state1->drap, state1->drap_reg, state1->drap_offset,
1974                           state2->drap, state2->drap_reg, state2->drap_offset);
1975
1976         } else
1977                 return true;
1978
1979         return false;
1980 }
1981
1982 static inline bool func_uaccess_safe(struct symbol *func)
1983 {
1984         if (func)
1985                 return func->uaccess_safe;
1986
1987         return false;
1988 }
1989
1990 static inline const char *call_dest_name(struct instruction *insn)
1991 {
1992         if (insn->call_dest)
1993                 return insn->call_dest->name;
1994
1995         return "{dynamic}";
1996 }
1997
1998 static int validate_call(struct instruction *insn, struct insn_state *state)
1999 {
2000         if (state->uaccess && !func_uaccess_safe(insn->call_dest)) {
2001                 WARN_FUNC("call to %s() with UACCESS enabled",
2002                                 insn->sec, insn->offset, call_dest_name(insn));
2003                 return 1;
2004         }
2005
2006         if (state->df) {
2007                 WARN_FUNC("call to %s() with DF set",
2008                                 insn->sec, insn->offset, call_dest_name(insn));
2009                 return 1;
2010         }
2011
2012         return 0;
2013 }
2014
2015 static int validate_sibling_call(struct instruction *insn, struct insn_state *state)
2016 {
2017         if (has_modified_stack_frame(state)) {
2018                 WARN_FUNC("sibling call from callable instruction with modified stack frame",
2019                                 insn->sec, insn->offset);
2020                 return 1;
2021         }
2022
2023         return validate_call(insn, state);
2024 }
2025
2026 static int validate_return(struct symbol *func, struct instruction *insn, struct insn_state *state)
2027 {
2028         if (state->uaccess && !func_uaccess_safe(func)) {
2029                 WARN_FUNC("return with UACCESS enabled",
2030                           insn->sec, insn->offset);
2031                 return 1;
2032         }
2033
2034         if (!state->uaccess && func_uaccess_safe(func)) {
2035                 WARN_FUNC("return with UACCESS disabled from a UACCESS-safe function",
2036                           insn->sec, insn->offset);
2037                 return 1;
2038         }
2039
2040         if (state->df) {
2041                 WARN_FUNC("return with DF set",
2042                           insn->sec, insn->offset);
2043                 return 1;
2044         }
2045
2046         if (func && has_modified_stack_frame(state)) {
2047                 WARN_FUNC("return with modified stack frame",
2048                           insn->sec, insn->offset);
2049                 return 1;
2050         }
2051
2052         if (state->bp_scratch) {
2053                 WARN_FUNC("BP used as a scratch register",
2054                           insn->sec, insn->offset);
2055                 return 1;
2056         }
2057
2058         return 0;
2059 }
2060
2061 /*
2062  * Follow the branch starting at the given instruction, and recursively follow
2063  * any other branches (jumps).  Meanwhile, track the frame pointer state at
2064  * each instruction and validate all the rules described in
2065  * tools/objtool/Documentation/stack-validation.txt.
2066  */
2067 static int validate_branch(struct objtool_file *file, struct symbol *func,
2068                            struct instruction *first, struct insn_state state)
2069 {
2070         struct alternative *alt;
2071         struct instruction *insn, *next_insn;
2072         struct section *sec;
2073         u8 visited;
2074         int ret;
2075
2076         insn = first;
2077         sec = insn->sec;
2078
2079         if (insn->alt_group && list_empty(&insn->alts)) {
2080                 WARN_FUNC("don't know how to handle branch to middle of alternative instruction group",
2081                           sec, insn->offset);
2082                 return 1;
2083         }
2084
2085         while (1) {
2086                 next_insn = next_insn_same_sec(file, insn);
2087
2088                 if (file->c_file && func && insn->func && func != insn->func->pfunc) {
2089                         WARN("%s() falls through to next function %s()",
2090                              func->name, insn->func->name);
2091                         return 1;
2092                 }
2093
2094                 if (func && insn->ignore) {
2095                         WARN_FUNC("BUG: why am I validating an ignored function?",
2096                                   sec, insn->offset);
2097                         return 1;
2098                 }
2099
2100                 visited = 1 << state.uaccess;
2101                 if (insn->visited) {
2102                         if (!insn->hint && !insn_state_match(insn, &state))
2103                                 return 1;
2104
2105                         if (insn->visited & visited)
2106                                 return 0;
2107                 }
2108
2109                 if (insn->hint) {
2110                         if (insn->restore) {
2111                                 struct instruction *save_insn, *i;
2112
2113                                 i = insn;
2114                                 save_insn = NULL;
2115                                 sym_for_each_insn_continue_reverse(file, func, i) {
2116                                         if (i->save) {
2117                                                 save_insn = i;
2118                                                 break;
2119                                         }
2120                                 }
2121
2122                                 if (!save_insn) {
2123                                         WARN_FUNC("no corresponding CFI save for CFI restore",
2124                                                   sec, insn->offset);
2125                                         return 1;
2126                                 }
2127
2128                                 if (!save_insn->visited) {
2129                                         /*
2130                                          * Oops, no state to copy yet.
2131                                          * Hopefully we can reach this
2132                                          * instruction from another branch
2133                                          * after the save insn has been
2134                                          * visited.
2135                                          */
2136                                         if (insn == first)
2137                                                 return 0;
2138
2139                                         WARN_FUNC("objtool isn't smart enough to handle this CFI save/restore combo",
2140                                                   sec, insn->offset);
2141                                         return 1;
2142                                 }
2143
2144                                 insn->state = save_insn->state;
2145                         }
2146
2147                         state = insn->state;
2148
2149                 } else
2150                         insn->state = state;
2151
2152                 insn->visited |= visited;
2153
2154                 if (!insn->ignore_alts) {
2155                         bool skip_orig = false;
2156
2157                         list_for_each_entry(alt, &insn->alts, list) {
2158                                 if (alt->skip_orig)
2159                                         skip_orig = true;
2160
2161                                 ret = validate_branch(file, func, alt->insn, state);
2162                                 if (ret) {
2163                                         if (backtrace)
2164                                                 BT_FUNC("(alt)", insn);
2165                                         return ret;
2166                                 }
2167                         }
2168
2169                         if (skip_orig)
2170                                 return 0;
2171                 }
2172
2173                 switch (insn->type) {
2174
2175                 case INSN_RETURN:
2176                         return validate_return(func, insn, &state);
2177
2178                 case INSN_CALL:
2179                 case INSN_CALL_DYNAMIC:
2180                         ret = validate_call(insn, &state);
2181                         if (ret)
2182                                 return ret;
2183
2184                         if (!no_fp && func && !is_fentry_call(insn) &&
2185                             !has_valid_stack_frame(&state)) {
2186                                 WARN_FUNC("call without frame pointer save/setup",
2187                                           sec, insn->offset);
2188                                 return 1;
2189                         }
2190
2191                         if (dead_end_function(file, insn->call_dest))
2192                                 return 0;
2193
2194                         break;
2195
2196                 case INSN_JUMP_CONDITIONAL:
2197                 case INSN_JUMP_UNCONDITIONAL:
2198                         if (func && is_sibling_call(insn)) {
2199                                 ret = validate_sibling_call(insn, &state);
2200                                 if (ret)
2201                                         return ret;
2202
2203                         } else if (insn->jump_dest) {
2204                                 ret = validate_branch(file, func,
2205                                                       insn->jump_dest, state);
2206                                 if (ret) {
2207                                         if (backtrace)
2208                                                 BT_FUNC("(branch)", insn);
2209                                         return ret;
2210                                 }
2211                         }
2212
2213                         if (insn->type == INSN_JUMP_UNCONDITIONAL)
2214                                 return 0;
2215
2216                         break;
2217
2218                 case INSN_JUMP_DYNAMIC:
2219                 case INSN_JUMP_DYNAMIC_CONDITIONAL:
2220                         if (func && is_sibling_call(insn)) {
2221                                 ret = validate_sibling_call(insn, &state);
2222                                 if (ret)
2223                                         return ret;
2224                         }
2225
2226                         if (insn->type == INSN_JUMP_DYNAMIC)
2227                                 return 0;
2228
2229                         break;
2230
2231                 case INSN_CONTEXT_SWITCH:
2232                         if (func && (!next_insn || !next_insn->hint)) {
2233                                 WARN_FUNC("unsupported instruction in callable function",
2234                                           sec, insn->offset);
2235                                 return 1;
2236                         }
2237                         return 0;
2238
2239                 case INSN_STACK:
2240                         if (handle_insn_ops(insn, &state))
2241                                 return 1;
2242                         break;
2243
2244                 case INSN_STAC:
2245                         if (state.uaccess) {
2246                                 WARN_FUNC("recursive UACCESS enable", sec, insn->offset);
2247                                 return 1;
2248                         }
2249
2250                         state.uaccess = true;
2251                         break;
2252
2253                 case INSN_CLAC:
2254                         if (!state.uaccess && func) {
2255                                 WARN_FUNC("redundant UACCESS disable", sec, insn->offset);
2256                                 return 1;
2257                         }
2258
2259                         if (func_uaccess_safe(func) && !state.uaccess_stack) {
2260                                 WARN_FUNC("UACCESS-safe disables UACCESS", sec, insn->offset);
2261                                 return 1;
2262                         }
2263
2264                         state.uaccess = false;
2265                         break;
2266
2267                 case INSN_STD:
2268                         if (state.df)
2269                                 WARN_FUNC("recursive STD", sec, insn->offset);
2270
2271                         state.df = true;
2272                         break;
2273
2274                 case INSN_CLD:
2275                         if (!state.df && func)
2276                                 WARN_FUNC("redundant CLD", sec, insn->offset);
2277
2278                         state.df = false;
2279                         break;
2280
2281                 default:
2282                         break;
2283                 }
2284
2285                 if (insn->dead_end)
2286                         return 0;
2287
2288                 if (!next_insn) {
2289                         if (state.cfa.base == CFI_UNDEFINED)
2290                                 return 0;
2291                         WARN("%s: unexpected end of section", sec->name);
2292                         return 1;
2293                 }
2294
2295                 insn = next_insn;
2296         }
2297
2298         return 0;
2299 }
2300
2301 static int validate_unwind_hints(struct objtool_file *file)
2302 {
2303         struct instruction *insn;
2304         int ret, warnings = 0;
2305         struct insn_state state;
2306
2307         if (!file->hints)
2308                 return 0;
2309
2310         clear_insn_state(&state);
2311
2312         for_each_insn(file, insn) {
2313                 if (insn->hint && !insn->visited) {
2314                         ret = validate_branch(file, insn->func, insn, state);
2315                         if (ret && backtrace)
2316                                 BT_FUNC("<=== (hint)", insn);
2317                         warnings += ret;
2318                 }
2319         }
2320
2321         return warnings;
2322 }
2323
2324 static int validate_retpoline(struct objtool_file *file)
2325 {
2326         struct instruction *insn;
2327         int warnings = 0;
2328
2329         for_each_insn(file, insn) {
2330                 if (insn->type != INSN_JUMP_DYNAMIC &&
2331                     insn->type != INSN_CALL_DYNAMIC)
2332                         continue;
2333
2334                 if (insn->retpoline_safe)
2335                         continue;
2336
2337                 /*
2338                  * .init.text code is ran before userspace and thus doesn't
2339                  * strictly need retpolines, except for modules which are
2340                  * loaded late, they very much do need retpoline in their
2341                  * .init.text
2342                  */
2343                 if (!strcmp(insn->sec->name, ".init.text") && !module)
2344                         continue;
2345
2346                 WARN_FUNC("indirect %s found in RETPOLINE build",
2347                           insn->sec, insn->offset,
2348                           insn->type == INSN_JUMP_DYNAMIC ? "jump" : "call");
2349
2350                 warnings++;
2351         }
2352
2353         return warnings;
2354 }
2355
2356 static bool is_kasan_insn(struct instruction *insn)
2357 {
2358         return (insn->type == INSN_CALL &&
2359                 !strcmp(insn->call_dest->name, "__asan_handle_no_return"));
2360 }
2361
2362 static bool is_ubsan_insn(struct instruction *insn)
2363 {
2364         return (insn->type == INSN_CALL &&
2365                 !strcmp(insn->call_dest->name,
2366                         "__ubsan_handle_builtin_unreachable"));
2367 }
2368
2369 static bool ignore_unreachable_insn(struct instruction *insn)
2370 {
2371         int i;
2372
2373         if (insn->ignore || insn->type == INSN_NOP)
2374                 return true;
2375
2376         /*
2377          * Ignore any unused exceptions.  This can happen when a whitelisted
2378          * function has an exception table entry.
2379          *
2380          * Also ignore alternative replacement instructions.  This can happen
2381          * when a whitelisted function uses one of the ALTERNATIVE macros.
2382          */
2383         if (!strcmp(insn->sec->name, ".fixup") ||
2384             !strcmp(insn->sec->name, ".altinstr_replacement") ||
2385             !strcmp(insn->sec->name, ".altinstr_aux"))
2386                 return true;
2387
2388         if (!insn->func)
2389                 return false;
2390
2391         /*
2392          * CONFIG_UBSAN_TRAP inserts a UD2 when it sees
2393          * __builtin_unreachable().  The BUG() macro has an unreachable() after
2394          * the UD2, which causes GCC's undefined trap logic to emit another UD2
2395          * (or occasionally a JMP to UD2).
2396          */
2397         if (list_prev_entry(insn, list)->dead_end &&
2398             (insn->type == INSN_BUG ||
2399              (insn->type == INSN_JUMP_UNCONDITIONAL &&
2400               insn->jump_dest && insn->jump_dest->type == INSN_BUG)))
2401                 return true;
2402
2403         /*
2404          * Check if this (or a subsequent) instruction is related to
2405          * CONFIG_UBSAN or CONFIG_KASAN.
2406          *
2407          * End the search at 5 instructions to avoid going into the weeds.
2408          */
2409         for (i = 0; i < 5; i++) {
2410
2411                 if (is_kasan_insn(insn) || is_ubsan_insn(insn))
2412                         return true;
2413
2414                 if (insn->type == INSN_JUMP_UNCONDITIONAL) {
2415                         if (insn->jump_dest &&
2416                             insn->jump_dest->func == insn->func) {
2417                                 insn = insn->jump_dest;
2418                                 continue;
2419                         }
2420
2421                         break;
2422                 }
2423
2424                 if (insn->offset + insn->len >= insn->func->offset + insn->func->len)
2425                         break;
2426
2427                 insn = list_next_entry(insn, list);
2428         }
2429
2430         return false;
2431 }
2432
2433 static int validate_section(struct objtool_file *file, struct section *sec)
2434 {
2435         struct symbol *func;
2436         struct instruction *insn;
2437         struct insn_state state;
2438         int ret, warnings = 0;
2439
2440         list_for_each_entry(func, &sec->symbol_list, list) {
2441                 if (func->type != STT_FUNC)
2442                         continue;
2443
2444                 if (!func->len) {
2445                         WARN("%s() is missing an ELF size annotation",
2446                              func->name);
2447                         warnings++;
2448                 }
2449
2450                 if (func->pfunc != func || func->alias != func)
2451                         continue;
2452
2453                 insn = find_insn(file, sec, func->offset);
2454                 if (!insn || insn->ignore || insn->visited)
2455                         continue;
2456
2457                 clear_insn_state(&state);
2458                 state.cfa = initial_func_cfi.cfa;
2459                 memcpy(&state.regs, &initial_func_cfi.regs,
2460                        CFI_NUM_REGS * sizeof(struct cfi_reg));
2461                 state.stack_size = initial_func_cfi.cfa.offset;
2462
2463                 state.uaccess = func->uaccess_safe;
2464
2465                 ret = validate_branch(file, func, insn, state);
2466                 if (ret && backtrace)
2467                         BT_FUNC("<=== (func)", insn);
2468                 warnings += ret;
2469         }
2470
2471         return warnings;
2472 }
2473
2474 static int validate_functions(struct objtool_file *file)
2475 {
2476         struct section *sec;
2477         int warnings = 0;
2478
2479         for_each_sec(file, sec)
2480                 warnings += validate_section(file, sec);
2481
2482         return warnings;
2483 }
2484
2485 static int validate_reachable_instructions(struct objtool_file *file)
2486 {
2487         struct instruction *insn;
2488
2489         if (file->ignore_unreachables)
2490                 return 0;
2491
2492         for_each_insn(file, insn) {
2493                 if (insn->visited || ignore_unreachable_insn(insn))
2494                         continue;
2495
2496                 WARN_FUNC("unreachable instruction", insn->sec, insn->offset);
2497                 return 1;
2498         }
2499
2500         return 0;
2501 }
2502
2503 static struct objtool_file file;
2504
2505 int check(const char *_objname, bool orc)
2506 {
2507         int ret, warnings = 0;
2508
2509         objname = _objname;
2510
2511         file.elf = elf_read(objname, orc ? O_RDWR : O_RDONLY);
2512         if (!file.elf)
2513                 return 1;
2514
2515         INIT_LIST_HEAD(&file.insn_list);
2516         hash_init(file.insn_hash);
2517         file.c_file = find_section_by_name(file.elf, ".comment");
2518         file.ignore_unreachables = no_unreachable;
2519         file.hints = false;
2520
2521         arch_initial_func_cfi_state(&initial_func_cfi);
2522
2523         ret = decode_sections(&file);
2524         if (ret < 0)
2525                 goto out;
2526         warnings += ret;
2527
2528         if (list_empty(&file.insn_list))
2529                 goto out;
2530
2531         if (retpoline) {
2532                 ret = validate_retpoline(&file);
2533                 if (ret < 0)
2534                         return ret;
2535                 warnings += ret;
2536         }
2537
2538         ret = validate_functions(&file);
2539         if (ret < 0)
2540                 goto out;
2541         warnings += ret;
2542
2543         ret = validate_unwind_hints(&file);
2544         if (ret < 0)
2545                 goto out;
2546         warnings += ret;
2547
2548         if (!warnings) {
2549                 ret = validate_reachable_instructions(&file);
2550                 if (ret < 0)
2551                         goto out;
2552                 warnings += ret;
2553         }
2554
2555         if (orc) {
2556                 ret = create_orc(&file);
2557                 if (ret < 0)
2558                         goto out;
2559
2560                 ret = create_orc_sections(&file);
2561                 if (ret < 0)
2562                         goto out;
2563
2564                 ret = elf_write(file.elf);
2565                 if (ret < 0)
2566                         goto out;
2567         }
2568
2569 out:
2570         if (ret < 0) {
2571                 /*
2572                  *  Fatal error.  The binary is corrupt or otherwise broken in
2573                  *  some way, or objtool itself is broken.  Fail the kernel
2574                  *  build.
2575                  */
2576                 return ret;
2577         }
2578
2579         return 0;
2580 }