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 func_for_each_insn_continue_reverse(file, func, insn)           \
 111         for (insn = list_prev_entry(insn, list);                        \
 112              &insn->list != &file->insn_list &&                         \
 113                 insn->sec == func->sec && insn->offset >= func->offset; \
 114              insn = list_prev_entry(insn, list))
 115
 116 #define sec_for_each_insn_from(file, insn)                              \
 117         for (; insn; insn = next_insn_same_sec(file, insn))
 118
 119
 120 /*
 121  * Check if the function has been manually whitelisted with the
 122  * STACK_FRAME_NON_STANDARD macro, or if it should be automatically whitelisted
 123  * due to its use of a context switching instruction.
 124  */
 125 static bool ignore_func(struct objtool_file *file, struct symbol *func)
 126 {
 127         struct rela *rela;
 128         struct instruction *insn;
 129
 130         /* check for STACK_FRAME_NON_STANDARD */
 131         if (file->whitelist && file->whitelist->rela)
 132                 list_for_each_entry(rela, &file->whitelist->rela->rela_list, list) {
 133                         if (rela->sym->type == STT_SECTION &&
 134                             rela->sym->sec == func->sec &&
 135                             rela->addend == func->offset)
 136                                 return true;
 137                         if (rela->sym->type == STT_FUNC && rela->sym == func)
 138                                 return true;
 139                 }
 140
 141         /* check if it has a context switching instruction */
 142         func_for_each_insn(file, func, insn)
 143                 if (insn->type == INSN_CONTEXT_SWITCH)
 144                         return true;
 145
 146         return false;
 147 }
 148
 149 /*
 150  * This checks to see if the given function is a "noreturn" function.
 151  *
 152  * For global functions which are outside the scope of this object file, we
 153  * have to keep a manual list of them.
 154  *
 155  * For local functions, we have to detect them manually by simply looking for
 156  * the lack of a return instruction.
 157  *
 158  * Returns:
 159  *  -1: error
 160  *   0: no dead end
 161  *   1: dead end
 162  */
 163 static int __dead_end_function(struct objtool_file *file, struct symbol *func,
 164                                int recursion)
 165 {
 166         int i;
 167         struct instruction *insn;
 168         bool empty = true;
 169
 170         /*
 171          * Unfortunately these have to be hard coded because the noreturn
 172          * attribute isn't provided in ELF data.
 173          */
 174         static const char * const global_noreturns[] = {
 175                 "__stack_chk_fail",
 176                 "panic",
 177                 "do_exit",
 178                 "__module_put_and_exit",
 179                 "complete_and_exit",
 180                 "kvm_spurious_fault",
 181                 "__reiserfs_panic",
 182                 "lbug_with_loc"
 183         };
 184
 185         if (func->bind == STB_WEAK)
 186                 return 0;
 187
 188         if (func->bind == STB_GLOBAL)
 189                 for (i = 0; i < ARRAY_SIZE(global_noreturns); i++)
 190                         if (!strcmp(func->name, global_noreturns[i]))
 191                                 return 1;
 192
 193         if (!func->sec)
 194                 return 0;
 195
 196         func_for_each_insn(file, func, insn) {
 197                 empty = false;
 198
 199                 if (insn->type == INSN_RETURN)
 200                         return 0;
 201         }
 202
 203         if (empty)
 204                 return 0;
 205
 206         /*
 207          * A function can have a sibling call instead of a return.  In that
 208          * case, the function's dead-end status depends on whether the target
 209          * of the sibling call returns.
 210          */
 211         func_for_each_insn(file, func, insn) {
 212                 if (insn->sec != func->sec ||
 213                     insn->offset >= func->offset + func->len)
 214                         break;
 215
 216                 if (insn->type == INSN_JUMP_UNCONDITIONAL) {
 217                         struct instruction *dest = insn->jump_dest;
 218                         struct symbol *dest_func;
 219
 220                         if (!dest)
 221                                 /* sibling call to another file */
 222                                 return 0;
 223
 224                         if (dest->sec != func->sec ||
 225                             dest->offset < func->offset ||
 226                             dest->offset >= func->offset + func->len) {
 227                                 /* local sibling call */
 228                                 dest_func = find_symbol_by_offset(dest->sec,
 229                                                                   dest->offset);
 230                                 if (!dest_func)
 231                                         continue;
 232
 233                                 if (recursion == 5) {
 234                                         WARN_FUNC("infinite recursion (objtool bug!)",
 235                                                   dest->sec, dest->offset);
 236                                         return -1;
 237                                 }
 238
 239                                 return __dead_end_function(file, dest_func,
 240                                                            recursion + 1);
 241                         }
 242                 }
 243
 244                 if (insn->type == INSN_JUMP_DYNAMIC && list_empty(&insn->alts))
 245                         /* sibling call */
 246                         return 0;
 247         }
 248
 249         return 1;
 250 }
 251
 252 static int dead_end_function(struct objtool_file *file, struct symbol *func)
 253 {
 254         return __dead_end_function(file, func, 0);
 255 }
 256
 257 /*
 258  * Call the arch-specific instruction decoder for all the instructions and add
 259  * them to the global instruction list.
 260  */
 261 static int decode_instructions(struct objtool_file *file)
 262 {
 263         struct section *sec;
 264         struct symbol *func;
 265         unsigned long offset;
 266         struct instruction *insn;
 267         int ret;
 268
 269         list_for_each_entry(sec, &file->elf->sections, list) {
 270
 271                 if (!(sec->sh.sh_flags & SHF_EXECINSTR))
 272                         continue;
 273
 274                 for (offset = 0; offset < sec->len; offset += insn->len) {
 275                         insn = malloc(sizeof(*insn));
 276                         memset(insn, 0, sizeof(*insn));
 277
 278                         INIT_LIST_HEAD(&insn->alts);
 279                         insn->sec = sec;
 280                         insn->offset = offset;
 281
 282                         ret = arch_decode_instruction(file->elf, sec, offset,
 283                                                       sec->len - offset,
 284                                                       &insn->len, &insn->type,
 285                                                       &insn->immediate);
 286                         if (ret)
 287                                 return ret;
 288
 289                         if (!insn->type || insn->type > INSN_LAST) {
 290                                 WARN_FUNC("invalid instruction type %d",
 291                                           insn->sec, insn->offset, insn->type);
 292                                 return -1;
 293                         }
 294
 295                         hash_add(file->insn_hash, &insn->hash, insn->offset);
 296                         list_add_tail(&insn->list, &file->insn_list);
 297                 }
 298
 299                 list_for_each_entry(func, &sec->symbol_list, list) {
 300                         if (func->type != STT_FUNC)
 301                                 continue;
 302
 303                         if (!find_insn(file, sec, func->offset)) {
 304                                 WARN("%s(): can't find starting instruction",
 305                                      func->name);
 306                                 return -1;
 307                         }
 308
 309                         func_for_each_insn(file, func, insn)
 310                                 if (!insn->func)
 311                                         insn->func = func;
 312                 }
 313         }
 314
 315         return 0;
 316 }
 317
 318 /*
 319  * Warnings shouldn't be reported for ignored functions.
 320  */
 321 static void add_ignores(struct objtool_file *file)
 322 {
 323         struct instruction *insn;
 324         struct section *sec;
 325         struct symbol *func;
 326
 327         list_for_each_entry(sec, &file->elf->sections, list) {
 328                 list_for_each_entry(func, &sec->symbol_list, list) {
 329                         if (func->type != STT_FUNC)
 330                                 continue;
 331
 332                         if (!ignore_func(file, func))
 333                                 continue;
 334
 335                         func_for_each_insn(file, func, insn)
 336                                 insn->visited = true;
 337                 }
 338         }
 339 }
 340
 341 /*
 342  * Find the destination instructions for all jumps.
 343  */
 344 static int add_jump_destinations(struct objtool_file *file)
 345 {
 346         struct instruction *insn;
 347         struct rela *rela;
 348         struct section *dest_sec;
 349         unsigned long dest_off;
 350
 351         for_each_insn(file, insn) {
 352                 if (insn->type != INSN_JUMP_CONDITIONAL &&
 353                     insn->type != INSN_JUMP_UNCONDITIONAL)
 354                         continue;
 355
 356                 /* skip ignores */
 357                 if (insn->visited)
 358                         continue;
 359
 360                 rela = find_rela_by_dest_range(insn->sec, insn->offset,
 361                                                insn->len);
 362                 if (!rela) {
 363                         dest_sec = insn->sec;
 364                         dest_off = insn->offset + insn->len + insn->immediate;
 365                 } else if (rela->sym->type == STT_SECTION) {
 366                         dest_sec = rela->sym->sec;
 367                         dest_off = rela->addend + 4;
 368                 } else if (rela->sym->sec->idx) {
 369                         dest_sec = rela->sym->sec;
 370                         dest_off = rela->sym->sym.st_value + rela->addend + 4;
 371                 } else {
 372                         /* sibling call */
 373                         insn->jump_dest = 0;
 374                         continue;
 375                 }
 376
 377                 insn->jump_dest = find_insn(file, dest_sec, dest_off);
 378                 if (!insn->jump_dest) {
 379
 380                         /*
 381                          * This is a special case where an alt instruction
 382                          * jumps past the end of the section.  These are
 383                          * handled later in handle_group_alt().
 384                          */
 385                         if (!strcmp(insn->sec->name, ".altinstr_replacement"))
 386                                 continue;
 387
 388                         WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
 389                                   insn->sec, insn->offset, dest_sec->name,
 390                                   dest_off);
 391                         return -1;
 392                 }
 393         }
 394
 395         return 0;
 396 }
 397
 398 /*
 399  * Find the destination instructions for all calls.
 400  */
 401 static int add_call_destinations(struct objtool_file *file)
 402 {
 403         struct instruction *insn;
 404         unsigned long dest_off;
 405         struct rela *rela;
 406
 407         for_each_insn(file, insn) {
 408                 if (insn->type != INSN_CALL)
 409                         continue;
 410
 411                 rela = find_rela_by_dest_range(insn->sec, insn->offset,
 412                                                insn->len);
 413                 if (!rela) {
 414                         dest_off = insn->offset + insn->len + insn->immediate;
 415                         insn->call_dest = find_symbol_by_offset(insn->sec,
 416                                                                 dest_off);
 417                         if (!insn->call_dest) {
 418                                 WARN_FUNC("can't find call dest symbol at offset 0x%lx",
 419                                           insn->sec, insn->offset, dest_off);
 420                                 return -1;
 421                         }
 422                 } else if (rela->sym->type == STT_SECTION) {
 423                         insn->call_dest = find_symbol_by_offset(rela->sym->sec,
 424                                                                 rela->addend+4);
 425                         if (!insn->call_dest ||
 426                             insn->call_dest->type != STT_FUNC) {
 427                                 WARN_FUNC("can't find call dest symbol at %s+0x%x",
 428                                           insn->sec, insn->offset,
 429                                           rela->sym->sec->name,
 430                                           rela->addend + 4);
 431                                 return -1;
 432                         }
 433                 } else
 434                         insn->call_dest = rela->sym;
 435         }
 436
 437         return 0;
 438 }
 439
 440 /*
 441  * The .alternatives section requires some extra special care, over and above
 442  * what other special sections require:
 443  *
 444  * 1. Because alternatives are patched in-place, we need to insert a fake jump
 445  *    instruction at the end so that validate_branch() skips all the original
 446  *    replaced instructions when validating the new instruction path.
 447  *
 448  * 2. An added wrinkle is that the new instruction length might be zero.  In
 449  *    that case the old instructions are replaced with noops.  We simulate that
 450  *    by creating a fake jump as the only new instruction.
 451  *
 452  * 3. In some cases, the alternative section includes an instruction which
 453  *    conditionally jumps to the _end_ of the entry.  We have to modify these
 454  *    jumps' destinations to point back to .text rather than the end of the
 455  *    entry in .altinstr_replacement.
 456  *
 457  * 4. It has been requested that we don't validate the !POPCNT feature path
 458  *    which is a "very very small percentage of machines".
 459  */
 460 static int handle_group_alt(struct objtool_file *file,
 461                             struct special_alt *special_alt,
 462                             struct instruction *orig_insn,
 463                             struct instruction **new_insn)
 464 {
 465         struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump;
 466         unsigned long dest_off;
 467
 468         last_orig_insn = NULL;
 469         insn = orig_insn;
 470         sec_for_each_insn_from(file, insn) {
 471                 if (insn->offset >= special_alt->orig_off + special_alt->orig_len)
 472                         break;
 473
 474                 if (special_alt->skip_orig)
 475                         insn->type = INSN_NOP;
 476
 477                 insn->alt_group = true;
 478                 last_orig_insn = insn;
 479         }
 480
 481         if (!next_insn_same_sec(file, last_orig_insn)) {
 482                 WARN("%s: don't know how to handle alternatives at end of section",
 483                      special_alt->orig_sec->name);
 484                 return -1;
 485         }
 486
 487         fake_jump = malloc(sizeof(*fake_jump));
 488         if (!fake_jump) {
 489                 WARN("malloc failed");
 490                 return -1;
 491         }
 492         memset(fake_jump, 0, sizeof(*fake_jump));
 493         INIT_LIST_HEAD(&fake_jump->alts);
 494         fake_jump->sec = special_alt->new_sec;
 495         fake_jump->offset = -1;
 496         fake_jump->type = INSN_JUMP_UNCONDITIONAL;
 497         fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
 498
 499         if (!special_alt->new_len) {
 500                 *new_insn = fake_jump;
 501                 return 0;
 502         }
 503
 504         last_new_insn = NULL;
 505         insn = *new_insn;
 506         sec_for_each_insn_from(file, insn) {
 507                 if (insn->offset >= special_alt->new_off + special_alt->new_len)
 508                         break;
 509
 510                 last_new_insn = insn;
 511
 512                 if (insn->type != INSN_JUMP_CONDITIONAL &&
 513                     insn->type != INSN_JUMP_UNCONDITIONAL)
 514                         continue;
 515
 516                 if (!insn->immediate)
 517                         continue;
 518
 519                 dest_off = insn->offset + insn->len + insn->immediate;
 520                 if (dest_off == special_alt->new_off + special_alt->new_len)
 521                         insn->jump_dest = fake_jump;
 522
 523                 if (!insn->jump_dest) {
 524                         WARN_FUNC("can't find alternative jump destination",
 525                                   insn->sec, insn->offset);
 526                         return -1;
 527                 }
 528         }
 529
 530         if (!last_new_insn) {
 531                 WARN_FUNC("can't find last new alternative instruction",
 532                           special_alt->new_sec, special_alt->new_off);
 533                 return -1;
 534         }
 535
 536         list_add(&fake_jump->list, &last_new_insn->list);
 537
 538         return 0;
 539 }
 540
 541 /*
 542  * A jump table entry can either convert a nop to a jump or a jump to a nop.
 543  * If the original instruction is a jump, make the alt entry an effective nop
 544  * by just skipping the original instruction.
 545  */
 546 static int handle_jump_alt(struct objtool_file *file,
 547                            struct special_alt *special_alt,
 548                            struct instruction *orig_insn,
 549                            struct instruction **new_insn)
 550 {
 551         if (orig_insn->type == INSN_NOP)
 552                 return 0;
 553
 554         if (orig_insn->type != INSN_JUMP_UNCONDITIONAL) {
 555                 WARN_FUNC("unsupported instruction at jump label",
 556                           orig_insn->sec, orig_insn->offset);
 557                 return -1;
 558         }
 559
 560         *new_insn = list_next_entry(orig_insn, list);
 561         return 0;
 562 }
 563
 564 /*
 565  * Read all the special sections which have alternate instructions which can be
 566  * patched in or redirected to at runtime.  Each instruction having alternate
 567  * instruction(s) has them added to its insn->alts list, which will be
 568  * traversed in validate_branch().
 569  */
 570 static int add_special_section_alts(struct objtool_file *file)
 571 {
 572         struct list_head special_alts;
 573         struct instruction *orig_insn, *new_insn;
 574         struct special_alt *special_alt, *tmp;
 575         struct alternative *alt;
 576         int ret;
 577
 578         ret = special_get_alts(file->elf, &special_alts);
 579         if (ret)
 580                 return ret;
 581
 582         list_for_each_entry_safe(special_alt, tmp, &special_alts, list) {
 583                 alt = malloc(sizeof(*alt));
 584                 if (!alt) {
 585                         WARN("malloc failed");
 586                         ret = -1;
 587                         goto out;
 588                 }
 589
 590                 orig_insn = find_insn(file, special_alt->orig_sec,
 591                                       special_alt->orig_off);
 592                 if (!orig_insn) {
 593                         WARN_FUNC("special: can't find orig instruction",
 594                                   special_alt->orig_sec, special_alt->orig_off);
 595                         ret = -1;
 596                         goto out;
 597                 }
 598
 599                 new_insn = NULL;
 600                 if (!special_alt->group || special_alt->new_len) {
 601                         new_insn = find_insn(file, special_alt->new_sec,
 602                                              special_alt->new_off);
 603                         if (!new_insn) {
 604                                 WARN_FUNC("special: can't find new instruction",
 605                                           special_alt->new_sec,
 606                                           special_alt->new_off);
 607                                 ret = -1;
 608                                 goto out;
 609                         }
 610                 }
 611
 612                 if (special_alt->group) {
 613                         ret = handle_group_alt(file, special_alt, orig_insn,
 614                                                &new_insn);
 615                         if (ret)
 616                                 goto out;
 617                 } else if (special_alt->jump_or_nop) {
 618                         ret = handle_jump_alt(file, special_alt, orig_insn,
 619                                               &new_insn);
 620                         if (ret)
 621                                 goto out;
 622                 }
 623
 624                 alt->insn = new_insn;
 625                 list_add_tail(&alt->list, &orig_insn->alts);
 626
 627                 list_del(&special_alt->list);
 628                 free(special_alt);
 629         }
 630
 631 out:
 632         return ret;
 633 }
 634
 635 static int add_switch_table(struct objtool_file *file, struct symbol *func,
 636                             struct instruction *insn, struct rela *table,
 637                             struct rela *next_table)
 638 {
 639         struct rela *rela = table;
 640         struct instruction *alt_insn;
 641         struct alternative *alt;
 642
 643         list_for_each_entry_from(rela, &file->rodata->rela->rela_list, list) {
 644                 if (rela == next_table)
 645                         break;
 646
 647                 if (rela->sym->sec != insn->sec ||
 648                     rela->addend <= func->offset ||
 649                     rela->addend >= func->offset + func->len)
 650                         break;
 651
 652                 alt_insn = find_insn(file, insn->sec, rela->addend);
 653                 if (!alt_insn) {
 654                         WARN("%s: can't find instruction at %s+0x%x",
 655                              file->rodata->rela->name, insn->sec->name,
 656                              rela->addend);
 657                         return -1;
 658                 }
 659
 660                 alt = malloc(sizeof(*alt));
 661                 if (!alt) {
 662                         WARN("malloc failed");
 663                         return -1;
 664                 }
 665
 666                 alt->insn = alt_insn;
 667                 list_add_tail(&alt->list, &insn->alts);
 668         }
 669
 670         return 0;
 671 }
 672
 673 /*
 674  * find_switch_table() - Given a dynamic jump, find the switch jump table in
 675  * .rodata associated with it.
 676  *
 677  * There are 3 basic patterns:
 678  *
 679  * 1. jmpq *[rodata addr](,%reg,8)
 680  *
 681  *    This is the most common case by far.  It jumps to an address in a simple
 682  *    jump table which is stored in .rodata.
 683  *
 684  * 2. jmpq *[rodata addr](%rip)
 685  *
 686  *    This is caused by a rare GCC quirk, currently only seen in three driver
 687  *    functions in the kernel, only with certain obscure non-distro configs.
 688  *
 689  *    As part of an optimization, GCC makes a copy of an existing switch jump
 690  *    table, modifies it, and then hard-codes the jump (albeit with an indirect
 691  *    jump) to use a single entry in the table.  The rest of the jump table and
 692  *    some of its jump targets remain as dead code.
 693  *
 694  *    In such a case we can just crudely ignore all unreachable instruction
 695  *    warnings for the entire object file.  Ideally we would just ignore them
 696  *    for the function, but that would require redesigning the code quite a
 697  *    bit.  And honestly that's just not worth doing: unreachable instruction
 698  *    warnings are of questionable value anyway, and this is such a rare issue.
 699  *
 700  * 3. mov [rodata addr],%reg1
 701  *    ... some instructions ...
 702  *    jmpq *(%reg1,%reg2,8)
 703  *
 704  *    This is a fairly uncommon pattern which is new for GCC 6.  As of this
 705  *    writing, there are 11 occurrences of it in the allmodconfig kernel.
 706  *
 707  *    TODO: Once we have DWARF CFI and smarter instruction decoding logic,
 708  *    ensure the same register is used in the mov and jump instructions.
 709  */
 710 static struct rela *find_switch_table(struct objtool_file *file,
 711                                       struct symbol *func,
 712                                       struct instruction *insn)
 713 {
 714         struct rela *text_rela, *rodata_rela;
 715
 716         text_rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len);
 717         if (text_rela && text_rela->sym == file->rodata->sym) {
 718                 /* case 1 */
 719                 rodata_rela = find_rela_by_dest(file->rodata,
 720                                                 text_rela->addend);
 721                 if (rodata_rela)
 722                         return rodata_rela;
 723
 724                 /* case 2 */
 725                 rodata_rela = find_rela_by_dest(file->rodata,
 726                                                 text_rela->addend + 4);
 727                 if (!rodata_rela)
 728                         return NULL;
 729                 file->ignore_unreachables = true;
 730                 return rodata_rela;
 731         }
 732
 733         /* case 3 */
 734         func_for_each_insn_continue_reverse(file, func, insn) {
 735                 if (insn->type == INSN_JUMP_UNCONDITIONAL ||
 736                     insn->type == INSN_JUMP_DYNAMIC)
 737                         break;
 738
 739                 text_rela = find_rela_by_dest_range(insn->sec, insn->offset,
 740                                                     insn->len);
 741                 if (text_rela && text_rela->sym == file->rodata->sym)
 742                         return find_rela_by_dest(file->rodata,
 743                                                  text_rela->addend);
 744         }
 745
 746         return NULL;
 747 }
 748
 749 static int add_func_switch_tables(struct objtool_file *file,
 750                                   struct symbol *func)
 751 {
 752         struct instruction *insn, *prev_jump = NULL;
 753         struct rela *rela, *prev_rela = NULL;
 754         int ret;
 755
 756         func_for_each_insn(file, func, insn) {
 757                 if (insn->type != INSN_JUMP_DYNAMIC)
 758                         continue;
 759
 760                 rela = find_switch_table(file, func, insn);
 761                 if (!rela)
 762                         continue;
 763
 764                 /*
 765                  * We found a switch table, but we don't know yet how big it
 766                  * is.  Don't add it until we reach the end of the function or
 767                  * the beginning of another switch table in the same function.
 768                  */
 769                 if (prev_jump) {
 770                         ret = add_switch_table(file, func, prev_jump, prev_rela,
 771                                                rela);
 772                         if (ret)
 773                                 return ret;
 774                 }
 775
 776                 prev_jump = insn;
 777                 prev_rela = rela;
 778         }
 779
 780         if (prev_jump) {
 781                 ret = add_switch_table(file, func, prev_jump, prev_rela, NULL);
 782                 if (ret)
 783                         return ret;
 784         }
 785
 786         return 0;
 787 }
 788
 789 /*
 790  * For some switch statements, gcc generates a jump table in the .rodata
 791  * section which contains a list of addresses within the function to jump to.
 792  * This finds these jump tables and adds them to the insn->alts lists.
 793  */
 794 static int add_switch_table_alts(struct objtool_file *file)
 795 {
 796         struct section *sec;
 797         struct symbol *func;
 798         int ret;
 799
 800         if (!file->rodata || !file->rodata->rela)
 801                 return 0;
 802
 803         list_for_each_entry(sec, &file->elf->sections, list) {
 804                 list_for_each_entry(func, &sec->symbol_list, list) {
 805                         if (func->type != STT_FUNC)
 806                                 continue;
 807
 808                         ret = add_func_switch_tables(file, func);
 809                         if (ret)
 810                                 return ret;
 811                 }
 812         }
 813
 814         return 0;
 815 }
 816
 817 static int decode_sections(struct objtool_file *file)
 818 {
 819         int ret;
 820
 821         ret = decode_instructions(file);
 822         if (ret)
 823                 return ret;
 824
 825         add_ignores(file);
 826
 827         ret = add_jump_destinations(file);
 828         if (ret)
 829                 return ret;
 830
 831         ret = add_call_destinations(file);
 832         if (ret)
 833                 return ret;
 834
 835         ret = add_special_section_alts(file);
 836         if (ret)
 837                 return ret;
 838
 839         ret = add_switch_table_alts(file);
 840         if (ret)
 841                 return ret;
 842
 843         return 0;
 844 }
 845
 846 static bool is_fentry_call(struct instruction *insn)
 847 {
 848         if (insn->type == INSN_CALL &&
 849             insn->call_dest->type == STT_NOTYPE &&
 850             !strcmp(insn->call_dest->name, "__fentry__"))
 851                 return true;
 852
 853         return false;
 854 }
 855
 856 static bool has_modified_stack_frame(struct instruction *insn)
 857 {
 858         return (insn->state & STATE_FP_SAVED) ||
 859                (insn->state & STATE_FP_SETUP);
 860 }
 861
 862 static bool has_valid_stack_frame(struct instruction *insn)
 863 {
 864         return (insn->state & STATE_FP_SAVED) &&
 865                (insn->state & STATE_FP_SETUP);
 866 }
 867
 868 static unsigned int frame_state(unsigned long state)
 869 {
 870         return (state & (STATE_FP_SAVED | STATE_FP_SETUP));
 871 }
 872
 873 /*
 874  * Follow the branch starting at the given instruction, and recursively follow
 875  * any other branches (jumps).  Meanwhile, track the frame pointer state at
 876  * each instruction and validate all the rules described in
 877  * tools/objtool/Documentation/stack-validation.txt.
 878  */
 879 static int validate_branch(struct objtool_file *file,
 880                            struct instruction *first, unsigned char first_state)
 881 {
 882         struct alternative *alt;
 883         struct instruction *insn;
 884         struct section *sec;
 885         struct symbol *func = NULL;
 886         unsigned char state;
 887         int ret;
 888
 889         insn = first;
 890         sec = insn->sec;
 891         state = first_state;
 892
 893         if (insn->alt_group && list_empty(&insn->alts)) {
 894                 WARN_FUNC("don't know how to handle branch to middle of alternative instruction group",
 895                           sec, insn->offset);
 896                 return 1;
 897         }
 898
 899         while (1) {
 900                 if (file->c_file && insn->func) {
 901                         if (func && func != insn->func) {
 902                                 WARN("%s() falls through to next function %s()",
 903                                      func->name, insn->func->name);
 904                                 return 1;
 905                         }
 906
 907                         func = insn->func;
 908                 }
 909
 910                 if (insn->visited) {
 911                         if (frame_state(insn->state) != frame_state(state)) {
 912                                 WARN_FUNC("frame pointer state mismatch",
 913                                           sec, insn->offset);
 914                                 return 1;
 915                         }
 916
 917                         return 0;
 918                 }
 919
 920                 insn->visited = true;
 921                 insn->state = state;
 922
 923                 list_for_each_entry(alt, &insn->alts, list) {
 924                         ret = validate_branch(file, alt->insn, state);
 925                         if (ret)
 926                                 return 1;
 927                 }
 928
 929                 switch (insn->type) {
 930
 931                 case INSN_FP_SAVE:
 932                         if (!nofp) {
 933                                 if (state & STATE_FP_SAVED) {
 934                                         WARN_FUNC("duplicate frame pointer save",
 935                                                   sec, insn->offset);
 936                                         return 1;
 937                                 }
 938                                 state |= STATE_FP_SAVED;
 939                         }
 940                         break;
 941
 942                 case INSN_FP_SETUP:
 943                         if (!nofp) {
 944                                 if (state & STATE_FP_SETUP) {
 945                                         WARN_FUNC("duplicate frame pointer setup",
 946                                                   sec, insn->offset);
 947                                         return 1;
 948                                 }
 949                                 state |= STATE_FP_SETUP;
 950                         }
 951                         break;
 952
 953                 case INSN_FP_RESTORE:
 954                         if (!nofp) {
 955                                 if (has_valid_stack_frame(insn))
 956                                         state &= ~STATE_FP_SETUP;
 957
 958                                 state &= ~STATE_FP_SAVED;
 959                         }
 960                         break;
 961
 962                 case INSN_RETURN:
 963                         if (!nofp && has_modified_stack_frame(insn)) {
 964                                 WARN_FUNC("return without frame pointer restore",
 965                                           sec, insn->offset);
 966                                 return 1;
 967                         }
 968                         return 0;
 969
 970                 case INSN_CALL:
 971                         if (is_fentry_call(insn)) {
 972                                 state |= STATE_FENTRY;
 973                                 break;
 974                         }
 975
 976                         ret = dead_end_function(file, insn->call_dest);
 977                         if (ret == 1)
 978                                 return 0;
 979                         if (ret == -1)
 980                                 return 1;
 981
 982                         /* fallthrough */
 983                 case INSN_CALL_DYNAMIC:
 984                         if (!nofp && !has_valid_stack_frame(insn)) {
 985                                 WARN_FUNC("call without frame pointer save/setup",
 986                                           sec, insn->offset);
 987                                 return 1;
 988                         }
 989                         break;
 990
 991                 case INSN_JUMP_CONDITIONAL:
 992                 case INSN_JUMP_UNCONDITIONAL:
 993                         if (insn->jump_dest) {
 994                                 ret = validate_branch(file, insn->jump_dest,
 995                                                       state);
 996                                 if (ret)
 997                                         return 1;
 998                         } else if (has_modified_stack_frame(insn)) {
 999                                 WARN_FUNC("sibling call from callable instruction with changed frame pointer",
1000                                           sec, insn->offset);
1001                                 return 1;
1002                         } /* else it's a sibling call */
1003
1004                         if (insn->type == INSN_JUMP_UNCONDITIONAL)
1005                                 return 0;
1006
1007                         break;
1008
1009                 case INSN_JUMP_DYNAMIC:
1010                         if (list_empty(&insn->alts) &&
1011                             has_modified_stack_frame(insn)) {
1012                                 WARN_FUNC("sibling call from callable instruction with changed frame pointer",
1013                                           sec, insn->offset);
1014                                 return 1;
1015                         }
1016
1017                         return 0;
1018
1019                 case INSN_BUG:
1020                         return 0;
1021
1022                 default:
1023                         break;
1024                 }
1025
1026                 insn = next_insn_same_sec(file, insn);
1027                 if (!insn) {
1028                         WARN("%s: unexpected end of section", sec->name);
1029                         return 1;
1030                 }
1031         }
1032
1033         return 0;
1034 }
1035
1036 static bool is_gcov_insn(struct instruction *insn)
1037 {
1038         struct rela *rela;
1039         struct section *sec;
1040         struct symbol *sym;
1041         unsigned long offset;
1042
1043         rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len);
1044         if (!rela)
1045                 return false;
1046
1047         if (rela->sym->type != STT_SECTION)
1048                 return false;
1049
1050         sec = rela->sym->sec;
1051         offset = rela->addend + insn->offset + insn->len - rela->offset;
1052
1053         list_for_each_entry(sym, &sec->symbol_list, list) {
1054                 if (sym->type != STT_OBJECT)
1055                         continue;
1056
1057                 if (offset >= sym->offset && offset < sym->offset + sym->len)
1058                         return (!memcmp(sym->name, "__gcov0.", 8));
1059         }
1060
1061         return false;
1062 }
1063
1064 static bool is_kasan_insn(struct instruction *insn)
1065 {
1066         return (insn->type == INSN_CALL &&
1067                 !strcmp(insn->call_dest->name, "__asan_handle_no_return"));
1068 }
1069
1070 static bool is_ubsan_insn(struct instruction *insn)
1071 {
1072         return (insn->type == INSN_CALL &&
1073                 !strcmp(insn->call_dest->name,
1074                         "__ubsan_handle_builtin_unreachable"));
1075 }
1076
1077 static bool ignore_unreachable_insn(struct symbol *func,
1078                                     struct instruction *insn)
1079 {
1080         int i;
1081
1082         if (insn->type == INSN_NOP)
1083                 return true;
1084
1085         if (is_gcov_insn(insn))
1086                 return true;
1087
1088         /*
1089          * Check if this (or a subsequent) instruction is related to
1090          * CONFIG_UBSAN or CONFIG_KASAN.
1091          *
1092          * End the search at 5 instructions to avoid going into the weeds.
1093          */
1094         for (i = 0; i < 5; i++) {
1095
1096                 if (is_kasan_insn(insn) || is_ubsan_insn(insn))
1097                         return true;
1098
1099                 if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest) {
1100                         insn = insn->jump_dest;
1101                         continue;
1102                 }
1103
1104                 if (insn->offset + insn->len >= func->offset + func->len)
1105                         break;
1106                 insn = list_next_entry(insn, list);
1107         }
1108
1109         return false;
1110 }
1111
1112 static int validate_functions(struct objtool_file *file)
1113 {
1114         struct section *sec;
1115         struct symbol *func;
1116         struct instruction *insn;
1117         int ret, warnings = 0;
1118
1119         list_for_each_entry(sec, &file->elf->sections, list) {
1120                 list_for_each_entry(func, &sec->symbol_list, list) {
1121                         if (func->type != STT_FUNC)
1122                                 continue;
1123
1124                         insn = find_insn(file, sec, func->offset);
1125                         if (!insn)
1126                                 continue;
1127
1128                         ret = validate_branch(file, insn, 0);
1129                         warnings += ret;
1130                 }
1131         }
1132
1133         list_for_each_entry(sec, &file->elf->sections, list) {
1134                 list_for_each_entry(func, &sec->symbol_list, list) {
1135                         if (func->type != STT_FUNC)
1136                                 continue;
1137
1138                         func_for_each_insn(file, func, insn) {
1139                                 if (insn->visited)
1140                                         continue;
1141
1142                                 insn->visited = true;
1143
1144                                 if (file->ignore_unreachables || warnings ||
1145                                     ignore_unreachable_insn(func, insn))
1146                                         continue;
1147
1148                                 WARN_FUNC("function has unreachable instruction", insn->sec, insn->offset);
1149                                 warnings++;
1150                         }
1151                 }
1152         }
1153
1154         return warnings;
1155 }
1156
1157 static int validate_uncallable_instructions(struct objtool_file *file)
1158 {
1159         struct instruction *insn;
1160         int warnings = 0;
1161
1162         for_each_insn(file, insn) {
1163                 if (!insn->visited && insn->type == INSN_RETURN) {
1164                         WARN_FUNC("return instruction outside of a callable function",
1165                                   insn->sec, insn->offset);
1166                         warnings++;
1167                 }
1168         }
1169
1170         return warnings;
1171 }
1172
1173 static void cleanup(struct objtool_file *file)
1174 {
1175         struct instruction *insn, *tmpinsn;
1176         struct alternative *alt, *tmpalt;
1177
1178         list_for_each_entry_safe(insn, tmpinsn, &file->insn_list, list) {
1179                 list_for_each_entry_safe(alt, tmpalt, &insn->alts, list) {
1180                         list_del(&alt->list);
1181                         free(alt);
1182                 }
1183                 list_del(&insn->list);
1184                 hash_del(&insn->hash);
1185                 free(insn);
1186         }
1187         elf_close(file->elf);
1188 }
1189
1190 const char * const check_usage[] = {
1191         "objtool check [<options>] file.o",
1192         NULL,
1193 };
1194
1195 int cmd_check(int argc, const char **argv)
1196 {
1197         struct objtool_file file;
1198         int ret, warnings = 0;
1199
1200         const struct option options[] = {
1201                 OPT_BOOLEAN('f', "no-fp", &nofp, "Skip frame pointer validation"),
1202                 OPT_END(),
1203         };
1204
1205         argc = parse_options(argc, argv, options, check_usage, 0);
1206
1207         if (argc != 1)
1208                 usage_with_options(check_usage, options);
1209
1210         objname = argv[0];
1211
1212         file.elf = elf_open(objname);
1213         if (!file.elf) {
1214                 fprintf(stderr, "error reading elf file %s\n", objname);
1215                 return 1;
1216         }
1217
1218         INIT_LIST_HEAD(&file.insn_list);
1219         hash_init(file.insn_hash);
1220         file.whitelist = find_section_by_name(file.elf, "__func_stack_frame_non_standard");
1221         file.rodata = find_section_by_name(file.elf, ".rodata");
1222         file.ignore_unreachables = false;
1223         file.c_file = find_section_by_name(file.elf, ".comment");
1224
1225         ret = decode_sections(&file);
1226         if (ret < 0)
1227                 goto out;
1228         warnings += ret;
1229
1230         ret = validate_functions(&file);
1231         if (ret < 0)
1232                 goto out;
1233         warnings += ret;
1234
1235         ret = validate_uncallable_instructions(&file);
1236         if (ret < 0)
1237                 goto out;
1238         warnings += ret;
1239
1240 out:
1241         cleanup(&file);
1242
1243         /* ignore warnings for now until we get all the code cleaned up */
1244         if (ret || warnings)
1245                 return 0;
1246         return 0;
1247 }