tools/objtool/builtin-check.c

   1 /*
   2  * Copyright (C) 2015 Josh Poimboeuf <jpoimboe@redhat.com>
   3  *
   4  * This program is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU General Public License
   6  * as published by the Free Software Foundation; either version 2
   7  * of the License, or (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, see <http://www.gnu.org/licenses/>.
  16  */
  17
  18 /*
  19  * objtool check:
  20  *
  21  * This command analyzes every .o file and ensures the validity of its stack
  22  * trace metadata.  It enforces a set of rules on asm code and C inline
  23  * assembly code so that stack traces can be reliable.
  24  *
  25  * For more information, see tools/objtool/Documentation/stack-validation.txt.
  26  */
  27
  28 #include <string.h>
  29 #include <stdlib.h>
  30 #include <subcmd/parse-options.h>
  31
  32 #include "builtin.h"
  33 #include "elf.h"
  34 #include "special.h"
  35 #include "arch.h"
  36 #include "warn.h"
  37
  38 #include <linux/hashtable.h>
  39
  40 #define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
  41
  42 #define STATE_FP_SAVED          0x1
  43 #define STATE_FP_SETUP          0x2
  44 #define STATE_FENTRY            0x4
  45
  46 struct instruction {
  47         struct list_head list;
  48         struct hlist_node hash;
  49         struct section *sec;
  50         unsigned long offset;
  51         unsigned int len, state;
  52         unsigned char type;
  53         unsigned long immediate;
  54         bool alt_group, visited;
  55         struct symbol *call_dest;
  56         struct instruction *jump_dest;
  57         struct list_head alts;
  58         struct symbol *func;
  59 };
  60
  61 struct alternative {
  62         struct list_head list;
  63         struct instruction *insn;
  64 };
  65
  66 struct objtool_file {
  67         struct elf *elf;
  68         struct list_head insn_list;
  69         DECLARE_HASHTABLE(insn_hash, 16);
  70         struct section *rodata, *whitelist;
  71         bool ignore_unreachables, c_file;
  72 };
  73
  74 const char *objname;
  75 static bool nofp;
  76
  77 static struct instruction *find_insn(struct objtool_file *file,
  78                                      struct section *sec, unsigned long offset)
  79 {
  80         struct instruction *insn;
  81
  82         hash_for_each_possible(file->insn_hash, insn, hash, offset)
  83                 if (insn->sec == sec && insn->offset == offset)
  84                         return insn;
  85
  86         return NULL;
  87 }
  88
  89 static struct instruction *next_insn_same_sec(struct objtool_file *file,
  90                                               struct instruction *insn)
  91 {
  92         struct instruction *next = list_next_entry(insn, list);
  93
  94         if (&next->list == &file->insn_list || next->sec != insn->sec)
  95                 return NULL;
  96
  97         return next;
  98 }
  99
 100 #define for_each_insn(file, insn)                                       \
 101         list_for_each_entry(insn, &file->insn_list, list)
 102
 103 #define func_for_each_insn(file, func, insn)                            \
 104         for (insn = find_insn(file, func->sec, func->offset);           \
 105              insn && &insn->list != &file->insn_list &&                 \
 106                 insn->sec == func->sec &&                               \
 107                 insn->offset < func->offset + func->len;                \
 108              insn = list_next_entry(insn, list))
 109
 110 #define sec_for_each_insn_from(file, insn)                              \
 111         for (; insn; insn = next_insn_same_sec(file, insn))
 112
 113
 114 /*
 115  * Check if the function has been manually whitelisted with the
 116  * STACK_FRAME_NON_STANDARD macro, or if it should be automatically whitelisted
 117  * due to its use of a context switching instruction.
 118  */
 119 static bool ignore_func(struct objtool_file *file, struct symbol *func)
 120 {
 121         struct rela *rela;
 122         struct instruction *insn;
 123
 124         /* check for STACK_FRAME_NON_STANDARD */
 125         if (file->whitelist && file->whitelist->rela)
 126                 list_for_each_entry(rela, &file->whitelist->rela->rela_list, list)
 127                         if (rela->sym->sec == func->sec &&
 128                             rela->addend == func->offset)
 129                                 return true;
 130
 131         /* check if it has a context switching instruction */
 132         func_for_each_insn(file, func, insn)
 133                 if (insn->type == INSN_CONTEXT_SWITCH)
 134                         return true;
 135
 136         return false;
 137 }
 138
 139 /*
 140  * This checks to see if the given function is a "noreturn" function.
 141  *
 142  * For global functions which are outside the scope of this object file, we
 143  * have to keep a manual list of them.
 144  *
 145  * For local functions, we have to detect them manually by simply looking for
 146  * the lack of a return instruction.
 147  *
 148  * Returns:
 149  *  -1: error
 150  *   0: no dead end
 151  *   1: dead end
 152  */
 153 static int __dead_end_function(struct objtool_file *file, struct symbol *func,
 154                                int recursion)
 155 {
 156         int i;
 157         struct instruction *insn;
 158         bool empty = true;
 159
 160         /*
 161          * Unfortunately these have to be hard coded because the noreturn
 162          * attribute isn't provided in ELF data.
 163          */
 164         static const char * const global_noreturns[] = {
 165                 "__stack_chk_fail",
 166                 "panic",
 167                 "do_exit",
 168                 "__module_put_and_exit",
 169                 "complete_and_exit",
 170                 "kvm_spurious_fault",
 171                 "__reiserfs_panic",
 172                 "lbug_with_loc"
 173         };
 174
 175         if (func->bind == STB_WEAK)
 176                 return 0;
 177
 178         if (func->bind == STB_GLOBAL)
 179                 for (i = 0; i < ARRAY_SIZE(global_noreturns); i++)
 180                         if (!strcmp(func->name, global_noreturns[i]))
 181                                 return 1;
 182
 183         if (!func->sec)
 184                 return 0;
 185
 186         func_for_each_insn(file, func, insn) {
 187                 empty = false;
 188
 189                 if (insn->type == INSN_RETURN)
 190                         return 0;
 191         }
 192
 193         if (empty)
 194                 return 0;
 195
 196         /*
 197          * A function can have a sibling call instead of a return.  In that
 198          * case, the function's dead-end status depends on whether the target
 199          * of the sibling call returns.
 200          */
 201         func_for_each_insn(file, func, insn) {
 202                 if (insn->sec != func->sec ||
 203                     insn->offset >= func->offset + func->len)
 204                         break;
 205
 206                 if (insn->type == INSN_JUMP_UNCONDITIONAL) {
 207                         struct instruction *dest = insn->jump_dest;
 208                         struct symbol *dest_func;
 209
 210                         if (!dest)
 211                                 /* sibling call to another file */
 212                                 return 0;
 213
 214                         if (dest->sec != func->sec ||
 215                             dest->offset < func->offset ||
 216                             dest->offset >= func->offset + func->len) {
 217                                 /* local sibling call */
 218                                 dest_func = find_symbol_by_offset(dest->sec,
 219                                                                   dest->offset);
 220                                 if (!dest_func)
 221                                         continue;
 222
 223                                 if (recursion == 5) {
 224                                         WARN_FUNC("infinite recursion (objtool bug!)",
 225                                                   dest->sec, dest->offset);
 226                                         return -1;
 227                                 }
 228
 229                                 return __dead_end_function(file, dest_func,
 230                                                            recursion + 1);
 231                         }
 232                 }
 233
 234                 if (insn->type == INSN_JUMP_DYNAMIC && list_empty(&insn->alts))
 235                         /* sibling call */
 236                         return 0;
 237         }
 238
 239         return 1;
 240 }
 241
 242 static int dead_end_function(struct objtool_file *file, struct symbol *func)
 243 {
 244         return __dead_end_function(file, func, 0);
 245 }
 246
 247 /*
 248  * Call the arch-specific instruction decoder for all the instructions and add
 249  * them to the global instruction list.
 250  */
 251 static int decode_instructions(struct objtool_file *file)
 252 {
 253         struct section *sec;
 254         struct symbol *func;
 255         unsigned long offset;
 256         struct instruction *insn;
 257         int ret;
 258
 259         list_for_each_entry(sec, &file->elf->sections, list) {
 260
 261                 if (!(sec->sh.sh_flags & SHF_EXECINSTR))
 262                         continue;
 263
 264                 for (offset = 0; offset < sec->len; offset += insn->len) {
 265                         insn = malloc(sizeof(*insn));
 266                         memset(insn, 0, sizeof(*insn));
 267
 268                         INIT_LIST_HEAD(&insn->alts);
 269                         insn->sec = sec;
 270                         insn->offset = offset;
 271
 272                         ret = arch_decode_instruction(file->elf, sec, offset,
 273                                                       sec->len - offset,
 274                                                       &insn->len, &insn->type,
 275                                                       &insn->immediate);
 276                         if (ret)
 277                                 return ret;
 278
 279                         if (!insn->type || insn->type > INSN_LAST) {
 280                                 WARN_FUNC("invalid instruction type %d",
 281                                           insn->sec, insn->offset, insn->type);
 282                                 return -1;
 283                         }
 284
 285                         hash_add(file->insn_hash, &insn->hash, insn->offset);
 286                         list_add_tail(&insn->list, &file->insn_list);
 287                 }
 288
 289                 list_for_each_entry(func, &sec->symbol_list, list) {
 290                         if (func->type != STT_FUNC)
 291                                 continue;
 292
 293                         if (!find_insn(file, sec, func->offset)) {
 294                                 WARN("%s(): can't find starting instruction",
 295                                      func->name);
 296                                 return -1;
 297                         }
 298
 299                         func_for_each_insn(file, func, insn)
 300                                 if (!insn->func)
 301                                         insn->func = func;
 302                 }
 303         }
 304
 305         return 0;
 306 }
 307
 308 /*
 309  * Warnings shouldn't be reported for ignored functions.
 310  */
 311 static void add_ignores(struct objtool_file *file)
 312 {
 313         struct instruction *insn;
 314         struct section *sec;
 315         struct symbol *func;
 316
 317         list_for_each_entry(sec, &file->elf->sections, list) {
 318                 list_for_each_entry(func, &sec->symbol_list, list) {
 319                         if (func->type != STT_FUNC)
 320                                 continue;
 321
 322                         if (!ignore_func(file, func))
 323                                 continue;
 324
 325                         func_for_each_insn(file, func, insn)
 326                                 insn->visited = true;
 327                 }
 328         }
 329 }
 330
 331 /*
 332  * Find the destination instructions for all jumps.
 333  */
 334 static int add_jump_destinations(struct objtool_file *file)
 335 {
 336         struct instruction *insn;
 337         struct rela *rela;
 338         struct section *dest_sec;
 339         unsigned long dest_off;
 340
 341         for_each_insn(file, insn) {
 342                 if (insn->type != INSN_JUMP_CONDITIONAL &&
 343                     insn->type != INSN_JUMP_UNCONDITIONAL)
 344                         continue;
 345
 346                 /* skip ignores */
 347                 if (insn->visited)
 348                         continue;
 349
 350                 rela = find_rela_by_dest_range(insn->sec, insn->offset,
 351                                                insn->len);
 352                 if (!rela) {
 353                         dest_sec = insn->sec;
 354                         dest_off = insn->offset + insn->len + insn->immediate;
 355                 } else if (rela->sym->type == STT_SECTION) {
 356                         dest_sec = rela->sym->sec;
 357                         dest_off = rela->addend + 4;
 358                 } else if (rela->sym->sec->idx) {
 359                         dest_sec = rela->sym->sec;
 360                         dest_off = rela->sym->sym.st_value + rela->addend + 4;
 361                 } else {
 362                         /* sibling call */
 363                         insn->jump_dest = 0;
 364                         continue;
 365                 }
 366
 367                 insn->jump_dest = find_insn(file, dest_sec, dest_off);
 368                 if (!insn->jump_dest) {
 369
 370                         /*
 371                          * This is a special case where an alt instruction
 372                          * jumps past the end of the section.  These are
 373                          * handled later in handle_group_alt().
 374                          */
 375                         if (!strcmp(insn->sec->name, ".altinstr_replacement"))
 376                                 continue;
 377
 378                         WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
 379                                   insn->sec, insn->offset, dest_sec->name,
 380                                   dest_off);
 381                         return -1;
 382                 }
 383         }
 384
 385         return 0;
 386 }
 387
 388 /*
 389  * Find the destination instructions for all calls.
 390  */
 391 static int add_call_destinations(struct objtool_file *file)
 392 {
 393         struct instruction *insn;
 394         unsigned long dest_off;
 395         struct rela *rela;
 396
 397         for_each_insn(file, insn) {
 398                 if (insn->type != INSN_CALL)
 399                         continue;
 400
 401                 rela = find_rela_by_dest_range(insn->sec, insn->offset,
 402                                                insn->len);
 403                 if (!rela) {
 404                         dest_off = insn->offset + insn->len + insn->immediate;
 405                         insn->call_dest = find_symbol_by_offset(insn->sec,
 406                                                                 dest_off);
 407                         if (!insn->call_dest) {
 408                                 WARN_FUNC("can't find call dest symbol at offset 0x%lx",
 409                                           insn->sec, insn->offset, dest_off);
 410                                 return -1;
 411                         }
 412                 } else if (rela->sym->type == STT_SECTION) {
 413                         insn->call_dest = find_symbol_by_offset(rela->sym->sec,
 414                                                                 rela->addend+4);
 415                         if (!insn->call_dest ||
 416                             insn->call_dest->type != STT_FUNC) {
 417                                 WARN_FUNC("can't find call dest symbol at %s+0x%x",
 418                                           insn->sec, insn->offset,
 419                                           rela->sym->sec->name,
 420                                           rela->addend + 4);
 421                                 return -1;
 422                         }
 423                 } else
 424                         insn->call_dest = rela->sym;
 425         }
 426
 427         return 0;
 428 }
 429
 430 /*
 431  * The .alternatives section requires some extra special care, over and above
 432  * what other special sections require:
 433  *
 434  * 1. Because alternatives are patched in-place, we need to insert a fake jump
 435  *    instruction at the end so that validate_branch() skips all the original
 436  *    replaced instructions when validating the new instruction path.
 437  *
 438  * 2. An added wrinkle is that the new instruction length might be zero.  In
 439  *    that case the old instructions are replaced with noops.  We simulate that
 440  *    by creating a fake jump as the only new instruction.
 441  *
 442  * 3. In some cases, the alternative section includes an instruction which
 443  *    conditionally jumps to the _end_ of the entry.  We have to modify these
 444  *    jumps' destinations to point back to .text rather than the end of the
 445  *    entry in .altinstr_replacement.
 446  *
 447  * 4. It has been requested that we don't validate the !POPCNT feature path
 448  *    which is a "very very small percentage of machines".
 449  */
 450 static int handle_group_alt(struct objtool_file *file,
 451                             struct special_alt *special_alt,
 452                             struct instruction *orig_insn,
 453                             struct instruction **new_insn)
 454 {
 455         struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump;
 456         unsigned long dest_off;
 457
 458         last_orig_insn = NULL;
 459         insn = orig_insn;
 460         sec_for_each_insn_from(file, insn) {
 461                 if (insn->offset >= special_alt->orig_off + special_alt->orig_len)
 462                         break;
 463
 464                 if (special_alt->skip_orig)
 465                         insn->type = INSN_NOP;
 466
 467                 insn->alt_group = true;
 468                 last_orig_insn = insn;
 469         }
 470
 471         if (!next_insn_same_sec(file, last_orig_insn)) {
 472                 WARN("%s: don't know how to handle alternatives at end of section",
 473                      special_alt->orig_sec->name);
 474                 return -1;
 475         }
 476
 477         fake_jump = malloc(sizeof(*fake_jump));
 478         if (!fake_jump) {
 479                 WARN("malloc failed");
 480                 return -1;
 481         }
 482         memset(fake_jump, 0, sizeof(*fake_jump));
 483         INIT_LIST_HEAD(&fake_jump->alts);
 484         fake_jump->sec = special_alt->new_sec;
 485         fake_jump->offset = -1;
 486         fake_jump->type = INSN_JUMP_UNCONDITIONAL;
 487         fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
 488
 489         if (!special_alt->new_len) {
 490                 *new_insn = fake_jump;
 491                 return 0;
 492         }
 493
 494         last_new_insn = NULL;
 495         insn = *new_insn;
 496         sec_for_each_insn_from(file, insn) {
 497                 if (insn->offset >= special_alt->new_off + special_alt->new_len)
 498                         break;
 499
 500                 last_new_insn = insn;
 501
 502                 if (insn->type != INSN_JUMP_CONDITIONAL &&
 503                     insn->type != INSN_JUMP_UNCONDITIONAL)
 504                         continue;
 505
 506                 if (!insn->immediate)
 507                         continue;
 508
 509                 dest_off = insn->offset + insn->len + insn->immediate;
 510                 if (dest_off == special_alt->new_off + special_alt->new_len)
 511                         insn->jump_dest = fake_jump;
 512
 513                 if (!insn->jump_dest) {
 514                         WARN_FUNC("can't find alternative jump destination",
 515                                   insn->sec, insn->offset);
 516                         return -1;
 517                 }
 518         }
 519
 520         if (!last_new_insn) {
 521                 WARN_FUNC("can't find last new alternative instruction",
 522                           special_alt->new_sec, special_alt->new_off);
 523                 return -1;
 524         }
 525
 526         list_add(&fake_jump->list, &last_new_insn->list);
 527
 528         return 0;
 529 }
 530
 531 /*
 532  * A jump table entry can either convert a nop to a jump or a jump to a nop.
 533  * If the original instruction is a jump, make the alt entry an effective nop
 534  * by just skipping the original instruction.
 535  */
 536 static int handle_jump_alt(struct objtool_file *file,
 537                            struct special_alt *special_alt,
 538                            struct instruction *orig_insn,
 539                            struct instruction **new_insn)
 540 {
 541         if (orig_insn->type == INSN_NOP)
 542                 return 0;
 543
 544         if (orig_insn->type != INSN_JUMP_UNCONDITIONAL) {
 545                 WARN_FUNC("unsupported instruction at jump label",
 546                           orig_insn->sec, orig_insn->offset);
 547                 return -1;
 548         }
 549
 550         *new_insn = list_next_entry(orig_insn, list);
 551         return 0;
 552 }
 553
 554 /*
 555  * Read all the special sections which have alternate instructions which can be
 556  * patched in or redirected to at runtime.  Each instruction having alternate
 557  * instruction(s) has them added to its insn->alts list, which will be
 558  * traversed in validate_branch().
 559  */
 560 static int add_special_section_alts(struct objtool_file *file)
 561 {
 562         struct list_head special_alts;
 563         struct instruction *orig_insn, *new_insn;
 564         struct special_alt *special_alt, *tmp;
 565         struct alternative *alt;
 566         int ret;
 567
 568         ret = special_get_alts(file->elf, &special_alts);
 569         if (ret)
 570                 return ret;
 571
 572         list_for_each_entry_safe(special_alt, tmp, &special_alts, list) {
 573                 alt = malloc(sizeof(*alt));
 574                 if (!alt) {
 575                         WARN("malloc failed");
 576                         ret = -1;
 577                         goto out;
 578                 }
 579
 580                 orig_insn = find_insn(file, special_alt->orig_sec,
 581                                       special_alt->orig_off);
 582                 if (!orig_insn) {
 583                         WARN_FUNC("special: can't find orig instruction",
 584                                   special_alt->orig_sec, special_alt->orig_off);
 585                         ret = -1;
 586                         goto out;
 587                 }
 588
 589                 new_insn = NULL;
 590                 if (!special_alt->group || special_alt->new_len) {
 591                         new_insn = find_insn(file, special_alt->new_sec,
 592                                              special_alt->new_off);
 593                         if (!new_insn) {
 594                                 WARN_FUNC("special: can't find new instruction",
 595                                           special_alt->new_sec,
 596                                           special_alt->new_off);
 597                                 ret = -1;
 598                                 goto out;
 599                         }
 600                 }
 601
 602                 if (special_alt->group) {
 603                         ret = handle_group_alt(file, special_alt, orig_insn,
 604                                                &new_insn);
 605                         if (ret)
 606                                 goto out;
 607                 } else if (special_alt->jump_or_nop) {
 608                         ret = handle_jump_alt(file, special_alt, orig_insn,
 609                                               &new_insn);
 610                         if (ret)
 611                                 goto out;
 612                 }
 613
 614                 alt->insn = new_insn;
 615                 list_add_tail(&alt->list, &orig_insn->alts);
 616
 617                 list_del(&special_alt->list);
 618                 free(special_alt);
 619         }
 620
 621 out:
 622         return ret;
 623 }
 624
 625 static int add_switch_table(struct objtool_file *file, struct symbol *func,
 626                             struct instruction *insn, struct rela *table,
 627                             struct rela *next_table)
 628 {
 629         struct rela *rela = table;
 630         struct instruction *alt_insn;
 631         struct alternative *alt;
 632
 633         list_for_each_entry_from(rela, &file->rodata->rela->rela_list, list) {
 634                 if (rela == next_table)
 635                         break;
 636
 637                 if (rela->sym->sec != insn->sec ||
 638                     rela->addend <= func->offset ||
 639                     rela->addend >= func->offset + func->len)
 640                         break;
 641
 642                 alt_insn = find_insn(file, insn->sec, rela->addend);
 643                 if (!alt_insn) {
 644                         WARN("%s: can't find instruction at %s+0x%x",
 645                              file->rodata->rela->name, insn->sec->name,
 646                              rela->addend);
 647                         return -1;
 648                 }
 649
 650                 alt = malloc(sizeof(*alt));
 651                 if (!alt) {
 652                         WARN("malloc failed");
 653                         return -1;
 654                 }
 655
 656                 alt->insn = alt_insn;
 657                 list_add_tail(&alt->list, &insn->alts);
 658         }
 659
 660         return 0;
 661 }
 662
 663 static int add_func_switch_tables(struct objtool_file *file,
 664                                   struct symbol *func)
 665 {
 666         struct instruction *insn, *prev_jump;
 667         struct rela *text_rela, *rodata_rela, *prev_rela = NULL;
 668         int ret;
 669
 670         prev_jump = NULL;
 671
 672         func_for_each_insn(file, func, insn) {
 673                 if (insn->type != INSN_JUMP_DYNAMIC)
 674                         continue;
 675
 676                 text_rela = find_rela_by_dest_range(insn->sec, insn->offset,
 677                                                     insn->len);
 678                 if (!text_rela || text_rela->sym != file->rodata->sym)
 679                         continue;
 680
 681                 /* common case: jmpq *[addr](,%rax,8) */
 682                 rodata_rela = find_rela_by_dest(file->rodata,
 683                                                 text_rela->addend);
 684
 685                 /*
 686                  * rare case:   jmpq *[addr](%rip)
 687                  *
 688                  * This check is for a rare gcc quirk, currently only seen in
 689                  * three driver functions in the kernel, only with certain
 690                  * obscure non-distro configs.
 691                  *
 692                  * As part of an optimization, gcc makes a copy of an existing
 693                  * switch jump table, modifies it, and then hard-codes the jump
 694                  * (albeit with an indirect jump) to use a single entry in the
 695                  * table.  The rest of the jump table and some of its jump
 696                  * targets remain as dead code.
 697                  *
 698                  * In such a case we can just crudely ignore all unreachable
 699                  * instruction warnings for the entire object file.  Ideally we
 700                  * would just ignore them for the function, but that would
 701                  * require redesigning the code quite a bit.  And honestly
 702                  * that's just not worth doing: unreachable instruction
 703                  * warnings are of questionable value anyway, and this is such
 704                  * a rare issue.
 705                  *
 706                  * kbuild reports:
 707                  * - https://lkml.kernel.org/r/201603231906.LWcVUpxm%25fengguang.wu@intel.com
 708                  * - https://lkml.kernel.org/r/201603271114.K9i45biy%25fengguang.wu@intel.com
 709                  * - https://lkml.kernel.org/r/201603291058.zuJ6ben1%25fengguang.wu@intel.com
 710                  *
 711                  * gcc bug:
 712                  * - https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70604
 713                  */
 714                 if (!rodata_rela) {
 715                         rodata_rela = find_rela_by_dest(file->rodata,
 716                                                         text_rela->addend + 4);
 717                         if (rodata_rela)
 718                                 file->ignore_unreachables = true;
 719                 }
 720
 721                 if (!rodata_rela)
 722                         continue;
 723
 724                 /*
 725                  * We found a switch table, but we don't know yet how big it
 726                  * is.  Don't add it until we reach the end of the function or
 727                  * the beginning of another switch table in the same function.
 728                  */
 729                 if (prev_jump) {
 730                         ret = add_switch_table(file, func, prev_jump, prev_rela,
 731                                                rodata_rela);
 732                         if (ret)
 733                                 return ret;
 734                 }
 735
 736                 prev_jump = insn;
 737                 prev_rela = rodata_rela;
 738         }
 739
 740         if (prev_jump) {
 741                 ret = add_switch_table(file, func, prev_jump, prev_rela, NULL);
 742                 if (ret)
 743                         return ret;
 744         }
 745
 746         return 0;
 747 }
 748
 749 /*
 750  * For some switch statements, gcc generates a jump table in the .rodata
 751  * section which contains a list of addresses within the function to jump to.
 752  * This finds these jump tables and adds them to the insn->alts lists.
 753  */
 754 static int add_switch_table_alts(struct objtool_file *file)
 755 {
 756         struct section *sec;
 757         struct symbol *func;
 758         int ret;
 759
 760         if (!file->rodata || !file->rodata->rela)
 761                 return 0;
 762
 763         list_for_each_entry(sec, &file->elf->sections, list) {
 764                 list_for_each_entry(func, &sec->symbol_list, list) {
 765                         if (func->type != STT_FUNC)
 766                                 continue;
 767
 768                         ret = add_func_switch_tables(file, func);
 769                         if (ret)
 770                                 return ret;
 771                 }
 772         }
 773
 774         return 0;
 775 }
 776
 777 static int decode_sections(struct objtool_file *file)
 778 {
 779         int ret;
 780
 781         ret = decode_instructions(file);
 782         if (ret)
 783                 return ret;
 784
 785         add_ignores(file);
 786
 787         ret = add_jump_destinations(file);
 788         if (ret)
 789                 return ret;
 790
 791         ret = add_call_destinations(file);
 792         if (ret)
 793                 return ret;
 794
 795         ret = add_special_section_alts(file);
 796         if (ret)
 797                 return ret;
 798
 799         ret = add_switch_table_alts(file);
 800         if (ret)
 801                 return ret;
 802
 803         return 0;
 804 }
 805
 806 static bool is_fentry_call(struct instruction *insn)
 807 {
 808         if (insn->type == INSN_CALL &&
 809             insn->call_dest->type == STT_NOTYPE &&
 810             !strcmp(insn->call_dest->name, "__fentry__"))
 811                 return true;
 812
 813         return false;
 814 }
 815
 816 static bool has_modified_stack_frame(struct instruction *insn)
 817 {
 818         return (insn->state & STATE_FP_SAVED) ||
 819                (insn->state & STATE_FP_SETUP);
 820 }
 821
 822 static bool has_valid_stack_frame(struct instruction *insn)
 823 {
 824         return (insn->state & STATE_FP_SAVED) &&
 825                (insn->state & STATE_FP_SETUP);
 826 }
 827
 828 static unsigned int frame_state(unsigned long state)
 829 {
 830         return (state & (STATE_FP_SAVED | STATE_FP_SETUP));
 831 }
 832
 833 /*
 834  * Follow the branch starting at the given instruction, and recursively follow
 835  * any other branches (jumps).  Meanwhile, track the frame pointer state at
 836  * each instruction and validate all the rules described in
 837  * tools/objtool/Documentation/stack-validation.txt.
 838  */
 839 static int validate_branch(struct objtool_file *file,
 840                            struct instruction *first, unsigned char first_state)
 841 {
 842         struct alternative *alt;
 843         struct instruction *insn;
 844         struct section *sec;
 845         struct symbol *func = NULL;
 846         unsigned char state;
 847         int ret;
 848
 849         insn = first;
 850         sec = insn->sec;
 851         state = first_state;
 852
 853         if (insn->alt_group && list_empty(&insn->alts)) {
 854                 WARN_FUNC("don't know how to handle branch to middle of alternative instruction group",
 855                           sec, insn->offset);
 856                 return 1;
 857         }
 858
 859         while (1) {
 860                 if (file->c_file && insn->func) {
 861                         if (func && func != insn->func) {
 862                                 WARN("%s() falls through to next function %s()",
 863                                      func->name, insn->func->name);
 864                                 return 1;
 865                         }
 866
 867                         func = insn->func;
 868                 }
 869
 870                 if (insn->visited) {
 871                         if (frame_state(insn->state) != frame_state(state)) {
 872                                 WARN_FUNC("frame pointer state mismatch",
 873                                           sec, insn->offset);
 874                                 return 1;
 875                         }
 876
 877                         return 0;
 878                 }
 879
 880                 insn->visited = true;
 881                 insn->state = state;
 882
 883                 list_for_each_entry(alt, &insn->alts, list) {
 884                         ret = validate_branch(file, alt->insn, state);
 885                         if (ret)
 886                                 return 1;
 887                 }
 888
 889                 switch (insn->type) {
 890
 891                 case INSN_FP_SAVE:
 892                         if (!nofp) {
 893                                 if (state & STATE_FP_SAVED) {
 894                                         WARN_FUNC("duplicate frame pointer save",
 895                                                   sec, insn->offset);
 896                                         return 1;
 897                                 }
 898                                 state |= STATE_FP_SAVED;
 899                         }
 900                         break;
 901
 902                 case INSN_FP_SETUP:
 903                         if (!nofp) {
 904                                 if (state & STATE_FP_SETUP) {
 905                                         WARN_FUNC("duplicate frame pointer setup",
 906                                                   sec, insn->offset);
 907                                         return 1;
 908                                 }
 909                                 state |= STATE_FP_SETUP;
 910                         }
 911                         break;
 912
 913                 case INSN_FP_RESTORE:
 914                         if (!nofp) {
 915                                 if (has_valid_stack_frame(insn))
 916                                         state &= ~STATE_FP_SETUP;
 917
 918                                 state &= ~STATE_FP_SAVED;
 919                         }
 920                         break;
 921
 922                 case INSN_RETURN:
 923                         if (!nofp && has_modified_stack_frame(insn)) {
 924                                 WARN_FUNC("return without frame pointer restore",
 925                                           sec, insn->offset);
 926                                 return 1;
 927                         }
 928                         return 0;
 929
 930                 case INSN_CALL:
 931                         if (is_fentry_call(insn)) {
 932                                 state |= STATE_FENTRY;
 933                                 break;
 934                         }
 935
 936                         ret = dead_end_function(file, insn->call_dest);
 937                         if (ret == 1)
 938                                 return 0;
 939                         if (ret == -1)
 940                                 return 1;
 941
 942                         /* fallthrough */
 943                 case INSN_CALL_DYNAMIC:
 944                         if (!nofp && !has_valid_stack_frame(insn)) {
 945                                 WARN_FUNC("call without frame pointer save/setup",
 946                                           sec, insn->offset);
 947                                 return 1;
 948                         }
 949                         break;
 950
 951                 case INSN_JUMP_CONDITIONAL:
 952                 case INSN_JUMP_UNCONDITIONAL:
 953                         if (insn->jump_dest) {
 954                                 ret = validate_branch(file, insn->jump_dest,
 955                                                       state);
 956                                 if (ret)
 957                                         return 1;
 958                         } else if (has_modified_stack_frame(insn)) {
 959                                 WARN_FUNC("sibling call from callable instruction with changed frame pointer",
 960                                           sec, insn->offset);
 961                                 return 1;
 962                         } /* else it's a sibling call */
 963
 964                         if (insn->type == INSN_JUMP_UNCONDITIONAL)
 965                                 return 0;
 966
 967                         break;
 968
 969                 case INSN_JUMP_DYNAMIC:
 970                         if (list_empty(&insn->alts) &&
 971                             has_modified_stack_frame(insn)) {
 972                                 WARN_FUNC("sibling call from callable instruction with changed frame pointer",
 973                                           sec, insn->offset);
 974                                 return 1;
 975                         }
 976
 977                         return 0;
 978
 979                 case INSN_BUG:
 980                         return 0;
 981
 982                 default:
 983                         break;
 984                 }
 985
 986                 insn = next_insn_same_sec(file, insn);
 987                 if (!insn) {
 988                         WARN("%s: unexpected end of section", sec->name);
 989                         return 1;
 990                 }
 991         }
 992
 993         return 0;
 994 }
 995
 996 static bool is_gcov_insn(struct instruction *insn)
 997 {
 998         struct rela *rela;
 999         struct section *sec;
1000         struct symbol *sym;
1001         unsigned long offset;
1002
1003         rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len);
1004         if (!rela)
1005                 return false;
1006
1007         if (rela->sym->type != STT_SECTION)
1008                 return false;
1009
1010         sec = rela->sym->sec;
1011         offset = rela->addend + insn->offset + insn->len - rela->offset;
1012
1013         list_for_each_entry(sym, &sec->symbol_list, list) {
1014                 if (sym->type != STT_OBJECT)
1015                         continue;
1016
1017                 if (offset >= sym->offset && offset < sym->offset + sym->len)
1018                         return (!memcmp(sym->name, "__gcov0.", 8));
1019         }
1020
1021         return false;
1022 }
1023
1024 static bool is_kasan_insn(struct instruction *insn)
1025 {
1026         return (insn->type == INSN_CALL &&
1027                 !strcmp(insn->call_dest->name, "__asan_handle_no_return"));
1028 }
1029
1030 static bool is_ubsan_insn(struct instruction *insn)
1031 {
1032         return (insn->type == INSN_CALL &&
1033                 !strcmp(insn->call_dest->name,
1034                         "__ubsan_handle_builtin_unreachable"));
1035 }
1036
1037 static bool ignore_unreachable_insn(struct symbol *func,
1038                                     struct instruction *insn)
1039 {
1040         int i;
1041
1042         if (insn->type == INSN_NOP)
1043                 return true;
1044
1045         if (is_gcov_insn(insn))
1046                 return true;
1047
1048         /*
1049          * Check if this (or a subsequent) instruction is related to
1050          * CONFIG_UBSAN or CONFIG_KASAN.
1051          *
1052          * End the search at 5 instructions to avoid going into the weeds.
1053          */
1054         for (i = 0; i < 5; i++) {
1055
1056                 if (is_kasan_insn(insn) || is_ubsan_insn(insn))
1057                         return true;
1058
1059                 if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest) {
1060                         insn = insn->jump_dest;
1061                         continue;
1062                 }
1063
1064                 if (insn->offset + insn->len >= func->offset + func->len)
1065                         break;
1066                 insn = list_next_entry(insn, list);
1067         }
1068
1069         return false;
1070 }
1071
1072 static int validate_functions(struct objtool_file *file)
1073 {
1074         struct section *sec;
1075         struct symbol *func;
1076         struct instruction *insn;
1077         int ret, warnings = 0;
1078
1079         list_for_each_entry(sec, &file->elf->sections, list) {
1080                 list_for_each_entry(func, &sec->symbol_list, list) {
1081                         if (func->type != STT_FUNC)
1082                                 continue;
1083
1084                         insn = find_insn(file, sec, func->offset);
1085                         if (!insn)
1086                                 continue;
1087
1088                         ret = validate_branch(file, insn, 0);
1089                         warnings += ret;
1090                 }
1091         }
1092
1093         list_for_each_entry(sec, &file->elf->sections, list) {
1094                 list_for_each_entry(func, &sec->symbol_list, list) {
1095                         if (func->type != STT_FUNC)
1096                                 continue;
1097
1098                         func_for_each_insn(file, func, insn) {
1099                                 if (insn->visited)
1100                                         continue;
1101
1102                                 insn->visited = true;
1103
1104                                 if (file->ignore_unreachables || warnings ||
1105                                     ignore_unreachable_insn(func, insn))
1106                                         continue;
1107
1108                                 WARN_FUNC("function has unreachable instruction", insn->sec, insn->offset);
1109                                 warnings++;
1110                         }
1111                 }
1112         }
1113
1114         return warnings;
1115 }
1116
1117 static int validate_uncallable_instructions(struct objtool_file *file)
1118 {
1119         struct instruction *insn;
1120         int warnings = 0;
1121
1122         for_each_insn(file, insn) {
1123                 if (!insn->visited && insn->type == INSN_RETURN) {
1124                         WARN_FUNC("return instruction outside of a callable function",
1125                                   insn->sec, insn->offset);
1126                         warnings++;
1127                 }
1128         }
1129
1130         return warnings;
1131 }
1132
1133 static void cleanup(struct objtool_file *file)
1134 {
1135         struct instruction *insn, *tmpinsn;
1136         struct alternative *alt, *tmpalt;
1137
1138         list_for_each_entry_safe(insn, tmpinsn, &file->insn_list, list) {
1139                 list_for_each_entry_safe(alt, tmpalt, &insn->alts, list) {
1140                         list_del(&alt->list);
1141                         free(alt);
1142                 }
1143                 list_del(&insn->list);
1144                 hash_del(&insn->hash);
1145                 free(insn);
1146         }
1147         elf_close(file->elf);
1148 }
1149
1150 const char * const check_usage[] = {
1151         "objtool check [<options>] file.o",
1152         NULL,
1153 };
1154
1155 int cmd_check(int argc, const char **argv)
1156 {
1157         struct objtool_file file;
1158         int ret, warnings = 0;
1159
1160         const struct option options[] = {
1161                 OPT_BOOLEAN('f', "no-fp", &nofp, "Skip frame pointer validation"),
1162                 OPT_END(),
1163         };
1164
1165         argc = parse_options(argc, argv, options, check_usage, 0);
1166
1167         if (argc != 1)
1168                 usage_with_options(check_usage, options);
1169
1170         objname = argv[0];
1171
1172         file.elf = elf_open(objname);
1173         if (!file.elf) {
1174                 fprintf(stderr, "error reading elf file %s\n", objname);
1175                 return 1;
1176         }
1177
1178         INIT_LIST_HEAD(&file.insn_list);
1179         hash_init(file.insn_hash);
1180         file.whitelist = find_section_by_name(file.elf, "__func_stack_frame_non_standard");
1181         file.rodata = find_section_by_name(file.elf, ".rodata");
1182         file.ignore_unreachables = false;
1183         file.c_file = find_section_by_name(file.elf, ".comment");
1184
1185         ret = decode_sections(&file);
1186         if (ret < 0)
1187                 goto out;
1188         warnings += ret;
1189
1190         ret = validate_functions(&file);
1191         if (ret < 0)
1192                 goto out;
1193         warnings += ret;
1194
1195         ret = validate_uncallable_instructions(&file);
1196         if (ret < 0)
1197                 goto out;
1198         warnings += ret;
1199
1200 out:
1201         cleanup(&file);
1202
1203         /* ignore warnings for now until we get all the code cleaned up */
1204         if (ret || warnings)
1205                 return 0;
1206         return 0;
1207 }