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