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                 "do_task_dead",
 179                 "__module_put_and_exit",
 180                 "complete_and_exit",
 181                 "kvm_spurious_fault",
 182                 "__reiserfs_panic",
 183                 "lbug_with_loc"
 184         };
 185
 186         if (func->bind == STB_WEAK)
 187                 return 0;
 188
 189         if (func->bind == STB_GLOBAL)
 190                 for (i = 0; i < ARRAY_SIZE(global_noreturns); i++)
 191                         if (!strcmp(func->name, global_noreturns[i]))
 192                                 return 1;
 193
 194         if (!func->sec)
 195                 return 0;
 196
 197         func_for_each_insn(file, func, insn) {
 198                 empty = false;
 199
 200                 if (insn->type == INSN_RETURN)
 201                         return 0;
 202         }
 203
 204         if (empty)
 205                 return 0;
 206
 207         /*
 208          * A function can have a sibling call instead of a return.  In that
 209          * case, the function's dead-end status depends on whether the target
 210          * of the sibling call returns.
 211          */
 212         func_for_each_insn(file, func, insn) {
 213                 if (insn->sec != func->sec ||
 214                     insn->offset >= func->offset + func->len)
 215                         break;
 216
 217                 if (insn->type == INSN_JUMP_UNCONDITIONAL) {
 218                         struct instruction *dest = insn->jump_dest;
 219                         struct symbol *dest_func;
 220
 221                         if (!dest)
 222                                 /* sibling call to another file */
 223                                 return 0;
 224
 225                         if (dest->sec != func->sec ||
 226                             dest->offset < func->offset ||
 227                             dest->offset >= func->offset + func->len) {
 228                                 /* local sibling call */
 229                                 dest_func = find_symbol_by_offset(dest->sec,
 230                                                                   dest->offset);
 231                                 if (!dest_func)
 232                                         continue;
 233
 234                                 if (recursion == 5) {
 235                                         WARN_FUNC("infinite recursion (objtool bug!)",
 236                                                   dest->sec, dest->offset);
 237                                         return -1;
 238                                 }
 239
 240                                 return __dead_end_function(file, dest_func,
 241                                                            recursion + 1);
 242                         }
 243                 }
 244
 245                 if (insn->type == INSN_JUMP_DYNAMIC && list_empty(&insn->alts))
 246                         /* sibling call */
 247                         return 0;
 248         }
 249
 250         return 1;
 251 }
 252
 253 static int dead_end_function(struct objtool_file *file, struct symbol *func)
 254 {
 255         return __dead_end_function(file, func, 0);
 256 }
 257
 258 /*
 259  * Call the arch-specific instruction decoder for all the instructions and add
 260  * them to the global instruction list.
 261  */
 262 static int decode_instructions(struct objtool_file *file)
 263 {
 264         struct section *sec;
 265         struct symbol *func;
 266         unsigned long offset;
 267         struct instruction *insn;
 268         int ret;
 269
 270         list_for_each_entry(sec, &file->elf->sections, list) {
 271
 272                 if (!(sec->sh.sh_flags & SHF_EXECINSTR))
 273                         continue;
 274
 275                 for (offset = 0; offset < sec->len; offset += insn->len) {
 276                         insn = malloc(sizeof(*insn));
 277                         memset(insn, 0, sizeof(*insn));
 278
 279                         INIT_LIST_HEAD(&insn->alts);
 280                         insn->sec = sec;
 281                         insn->offset = offset;
 282
 283                         ret = arch_decode_instruction(file->elf, sec, offset,
 284                                                       sec->len - offset,
 285                                                       &insn->len, &insn->type,
 286                                                       &insn->immediate);
 287                         if (ret)
 288                                 return ret;
 289
 290                         if (!insn->type || insn->type > INSN_LAST) {
 291                                 WARN_FUNC("invalid instruction type %d",
 292                                           insn->sec, insn->offset, insn->type);
 293                                 return -1;
 294                         }
 295
 296                         hash_add(file->insn_hash, &insn->hash, insn->offset);
 297                         list_add_tail(&insn->list, &file->insn_list);
 298                 }
 299
 300                 list_for_each_entry(func, &sec->symbol_list, list) {
 301                         if (func->type != STT_FUNC)
 302                                 continue;
 303
 304                         if (!find_insn(file, sec, func->offset)) {
 305                                 WARN("%s(): can't find starting instruction",
 306                                      func->name);
 307                                 return -1;
 308                         }
 309
 310                         func_for_each_insn(file, func, insn)
 311                                 if (!insn->func)
 312                                         insn->func = func;
 313                 }
 314         }
 315
 316         return 0;
 317 }
 318
 319 /*
 320  * Warnings shouldn't be reported for ignored functions.
 321  */
 322 static void add_ignores(struct objtool_file *file)
 323 {
 324         struct instruction *insn;
 325         struct section *sec;
 326         struct symbol *func;
 327
 328         list_for_each_entry(sec, &file->elf->sections, list) {
 329                 list_for_each_entry(func, &sec->symbol_list, list) {
 330                         if (func->type != STT_FUNC)
 331                                 continue;
 332
 333                         if (!ignore_func(file, func))
 334                                 continue;
 335
 336                         func_for_each_insn(file, func, insn)
 337                                 insn->visited = true;
 338                 }
 339         }
 340 }
 341
 342 /*
 343  * Find the destination instructions for all jumps.
 344  */
 345 static int add_jump_destinations(struct objtool_file *file)
 346 {
 347         struct instruction *insn;
 348         struct rela *rela;
 349         struct section *dest_sec;
 350         unsigned long dest_off;
 351
 352         for_each_insn(file, insn) {
 353                 if (insn->type != INSN_JUMP_CONDITIONAL &&
 354                     insn->type != INSN_JUMP_UNCONDITIONAL)
 355                         continue;
 356
 357                 /* skip ignores */
 358                 if (insn->visited)
 359                         continue;
 360
 361                 rela = find_rela_by_dest_range(insn->sec, insn->offset,
 362                                                insn->len);
 363                 if (!rela) {
 364                         dest_sec = insn->sec;
 365                         dest_off = insn->offset + insn->len + insn->immediate;
 366                 } else if (rela->sym->type == STT_SECTION) {
 367                         dest_sec = rela->sym->sec;
 368                         dest_off = rela->addend + 4;
 369                 } else if (rela->sym->sec->idx) {
 370                         dest_sec = rela->sym->sec;
 371                         dest_off = rela->sym->sym.st_value + rela->addend + 4;
 372                 } else {
 373                         /* sibling call */
 374                         insn->jump_dest = 0;
 375                         continue;
 376                 }
 377
 378                 insn->jump_dest = find_insn(file, dest_sec, dest_off);
 379                 if (!insn->jump_dest) {
 380
 381                         /*
 382                          * This is a special case where an alt instruction
 383                          * jumps past the end of the section.  These are
 384                          * handled later in handle_group_alt().
 385                          */
 386                         if (!strcmp(insn->sec->name, ".altinstr_replacement"))
 387                                 continue;
 388
 389                         WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
 390                                   insn->sec, insn->offset, dest_sec->name,
 391                                   dest_off);
 392                         return -1;
 393                 }
 394         }
 395
 396         return 0;
 397 }
 398
 399 /*
 400  * Find the destination instructions for all calls.
 401  */
 402 static int add_call_destinations(struct objtool_file *file)
 403 {
 404         struct instruction *insn;
 405         unsigned long dest_off;
 406         struct rela *rela;
 407
 408         for_each_insn(file, insn) {
 409                 if (insn->type != INSN_CALL)
 410                         continue;
 411
 412                 rela = find_rela_by_dest_range(insn->sec, insn->offset,
 413                                                insn->len);
 414                 if (!rela) {
 415                         dest_off = insn->offset + insn->len + insn->immediate;
 416                         insn->call_dest = find_symbol_by_offset(insn->sec,
 417                                                                 dest_off);
 418                         if (!insn->call_dest) {
 419                                 WARN_FUNC("can't find call dest symbol at offset 0x%lx",
 420                                           insn->sec, insn->offset, dest_off);
 421                                 return -1;
 422                         }
 423                 } else if (rela->sym->type == STT_SECTION) {
 424                         insn->call_dest = find_symbol_by_offset(rela->sym->sec,
 425                                                                 rela->addend+4);
 426                         if (!insn->call_dest ||
 427                             insn->call_dest->type != STT_FUNC) {
 428                                 WARN_FUNC("can't find call dest symbol at %s+0x%x",
 429                                           insn->sec, insn->offset,
 430                                           rela->sym->sec->name,
 431                                           rela->addend + 4);
 432                                 return -1;
 433                         }
 434                 } else
 435                         insn->call_dest = rela->sym;
 436         }
 437
 438         return 0;
 439 }
 440
 441 /*
 442  * The .alternatives section requires some extra special care, over and above
 443  * what other special sections require:
 444  *
 445  * 1. Because alternatives are patched in-place, we need to insert a fake jump
 446  *    instruction at the end so that validate_branch() skips all the original
 447  *    replaced instructions when validating the new instruction path.
 448  *
 449  * 2. An added wrinkle is that the new instruction length might be zero.  In
 450  *    that case the old instructions are replaced with noops.  We simulate that
 451  *    by creating a fake jump as the only new instruction.
 452  *
 453  * 3. In some cases, the alternative section includes an instruction which
 454  *    conditionally jumps to the _end_ of the entry.  We have to modify these
 455  *    jumps' destinations to point back to .text rather than the end of the
 456  *    entry in .altinstr_replacement.
 457  *
 458  * 4. It has been requested that we don't validate the !POPCNT feature path
 459  *    which is a "very very small percentage of machines".
 460  */
 461 static int handle_group_alt(struct objtool_file *file,
 462                             struct special_alt *special_alt,
 463                             struct instruction *orig_insn,
 464                             struct instruction **new_insn)
 465 {
 466         struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump;
 467         unsigned long dest_off;
 468
 469         last_orig_insn = NULL;
 470         insn = orig_insn;
 471         sec_for_each_insn_from(file, insn) {
 472                 if (insn->offset >= special_alt->orig_off + special_alt->orig_len)
 473                         break;
 474
 475                 if (special_alt->skip_orig)
 476                         insn->type = INSN_NOP;
 477
 478                 insn->alt_group = true;
 479                 last_orig_insn = insn;
 480         }
 481
 482         if (!next_insn_same_sec(file, last_orig_insn)) {
 483                 WARN("%s: don't know how to handle alternatives at end of section",
 484                      special_alt->orig_sec->name);
 485                 return -1;
 486         }
 487
 488         fake_jump = malloc(sizeof(*fake_jump));
 489         if (!fake_jump) {
 490                 WARN("malloc failed");
 491                 return -1;
 492         }
 493         memset(fake_jump, 0, sizeof(*fake_jump));
 494         INIT_LIST_HEAD(&fake_jump->alts);
 495         fake_jump->sec = special_alt->new_sec;
 496         fake_jump->offset = -1;
 497         fake_jump->type = INSN_JUMP_UNCONDITIONAL;
 498         fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
 499
 500         if (!special_alt->new_len) {
 501                 *new_insn = fake_jump;
 502                 return 0;
 503         }
 504
 505         last_new_insn = NULL;
 506         insn = *new_insn;
 507         sec_for_each_insn_from(file, insn) {
 508                 if (insn->offset >= special_alt->new_off + special_alt->new_len)
 509                         break;
 510
 511                 last_new_insn = insn;
 512
 513                 if (insn->type != INSN_JUMP_CONDITIONAL &&
 514                     insn->type != INSN_JUMP_UNCONDITIONAL)
 515                         continue;
 516
 517                 if (!insn->immediate)
 518                         continue;
 519
 520                 dest_off = insn->offset + insn->len + insn->immediate;
 521                 if (dest_off == special_alt->new_off + special_alt->new_len)
 522                         insn->jump_dest = fake_jump;
 523
 524                 if (!insn->jump_dest) {
 525                         WARN_FUNC("can't find alternative jump destination",
 526                                   insn->sec, insn->offset);
 527                         return -1;
 528                 }
 529         }
 530
 531         if (!last_new_insn) {
 532                 WARN_FUNC("can't find last new alternative instruction",
 533                           special_alt->new_sec, special_alt->new_off);
 534                 return -1;
 535         }
 536
 537         list_add(&fake_jump->list, &last_new_insn->list);
 538
 539         return 0;
 540 }
 541
 542 /*
 543  * A jump table entry can either convert a nop to a jump or a jump to a nop.
 544  * If the original instruction is a jump, make the alt entry an effective nop
 545  * by just skipping the original instruction.
 546  */
 547 static int handle_jump_alt(struct objtool_file *file,
 548                            struct special_alt *special_alt,
 549                            struct instruction *orig_insn,
 550                            struct instruction **new_insn)
 551 {
 552         if (orig_insn->type == INSN_NOP)
 553                 return 0;
 554
 555         if (orig_insn->type != INSN_JUMP_UNCONDITIONAL) {
 556                 WARN_FUNC("unsupported instruction at jump label",
 557                           orig_insn->sec, orig_insn->offset);
 558                 return -1;
 559         }
 560
 561         *new_insn = list_next_entry(orig_insn, list);
 562         return 0;
 563 }
 564
 565 /*
 566  * Read all the special sections which have alternate instructions which can be
 567  * patched in or redirected to at runtime.  Each instruction having alternate
 568  * instruction(s) has them added to its insn->alts list, which will be
 569  * traversed in validate_branch().
 570  */
 571 static int add_special_section_alts(struct objtool_file *file)
 572 {
 573         struct list_head special_alts;
 574         struct instruction *orig_insn, *new_insn;
 575         struct special_alt *special_alt, *tmp;
 576         struct alternative *alt;
 577         int ret;
 578
 579         ret = special_get_alts(file->elf, &special_alts);
 580         if (ret)
 581                 return ret;
 582
 583         list_for_each_entry_safe(special_alt, tmp, &special_alts, list) {
 584                 alt = malloc(sizeof(*alt));
 585                 if (!alt) {
 586                         WARN("malloc failed");
 587                         ret = -1;
 588                         goto out;
 589                 }
 590
 591                 orig_insn = find_insn(file, special_alt->orig_sec,
 592                                       special_alt->orig_off);
 593                 if (!orig_insn) {
 594                         WARN_FUNC("special: can't find orig instruction",
 595                                   special_alt->orig_sec, special_alt->orig_off);
 596                         ret = -1;
 597                         goto out;
 598                 }
 599
 600                 new_insn = NULL;
 601                 if (!special_alt->group || special_alt->new_len) {
 602                         new_insn = find_insn(file, special_alt->new_sec,
 603                                              special_alt->new_off);
 604                         if (!new_insn) {
 605                                 WARN_FUNC("special: can't find new instruction",
 606                                           special_alt->new_sec,
 607                                           special_alt->new_off);
 608                                 ret = -1;
 609                                 goto out;
 610                         }
 611                 }
 612
 613                 if (special_alt->group) {
 614                         ret = handle_group_alt(file, special_alt, orig_insn,
 615                                                &new_insn);
 616                         if (ret)
 617                                 goto out;
 618                 } else if (special_alt->jump_or_nop) {
 619                         ret = handle_jump_alt(file, special_alt, orig_insn,
 620                                               &new_insn);
 621                         if (ret)
 622                                 goto out;
 623                 }
 624
 625                 alt->insn = new_insn;
 626                 list_add_tail(&alt->list, &orig_insn->alts);
 627
 628                 list_del(&special_alt->list);
 629                 free(special_alt);
 630         }
 631
 632 out:
 633         return ret;
 634 }
 635
 636 static int add_switch_table(struct objtool_file *file, struct symbol *func,
 637                             struct instruction *insn, struct rela *table,
 638                             struct rela *next_table)
 639 {
 640         struct rela *rela = table;
 641         struct instruction *alt_insn;
 642         struct alternative *alt;
 643
 644         list_for_each_entry_from(rela, &file->rodata->rela->rela_list, list) {
 645                 if (rela == next_table)
 646                         break;
 647
 648                 if (rela->sym->sec != insn->sec ||
 649                     rela->addend <= func->offset ||
 650                     rela->addend >= func->offset + func->len)
 651                         break;
 652
 653                 alt_insn = find_insn(file, insn->sec, rela->addend);
 654                 if (!alt_insn) {
 655                         WARN("%s: can't find instruction at %s+0x%x",
 656                              file->rodata->rela->name, insn->sec->name,
 657                              rela->addend);
 658                         return -1;
 659                 }
 660
 661                 alt = malloc(sizeof(*alt));
 662                 if (!alt) {
 663                         WARN("malloc failed");
 664                         return -1;
 665                 }
 666
 667                 alt->insn = alt_insn;
 668                 list_add_tail(&alt->list, &insn->alts);
 669         }
 670
 671         return 0;
 672 }
 673
 674 /*
 675  * find_switch_table() - Given a dynamic jump, find the switch jump table in
 676  * .rodata associated with it.
 677  *
 678  * There are 3 basic patterns:
 679  *
 680  * 1. jmpq *[rodata addr](,%reg,8)
 681  *
 682  *    This is the most common case by far.  It jumps to an address in a simple
 683  *    jump table which is stored in .rodata.
 684  *
 685  * 2. jmpq *[rodata addr](%rip)
 686  *
 687  *    This is caused by a rare GCC quirk, currently only seen in three driver
 688  *    functions in the kernel, only with certain obscure non-distro configs.
 689  *
 690  *    As part of an optimization, GCC makes a copy of an existing switch jump
 691  *    table, modifies it, and then hard-codes the jump (albeit with an indirect
 692  *    jump) to use a single entry in the table.  The rest of the jump table and
 693  *    some of its jump targets remain as dead code.
 694  *
 695  *    In such a case we can just crudely ignore all unreachable instruction
 696  *    warnings for the entire object file.  Ideally we would just ignore them
 697  *    for the function, but that would require redesigning the code quite a
 698  *    bit.  And honestly that's just not worth doing: unreachable instruction
 699  *    warnings are of questionable value anyway, and this is such a rare issue.
 700  *
 701  * 3. mov [rodata addr],%reg1
 702  *    ... some instructions ...
 703  *    jmpq *(%reg1,%reg2,8)
 704  *
 705  *    This is a fairly uncommon pattern which is new for GCC 6.  As of this
 706  *    writing, there are 11 occurrences of it in the allmodconfig kernel.
 707  *
 708  *    TODO: Once we have DWARF CFI and smarter instruction decoding logic,
 709  *    ensure the same register is used in the mov and jump instructions.
 710  */
 711 static struct rela *find_switch_table(struct objtool_file *file,
 712                                       struct symbol *func,
 713                                       struct instruction *insn)
 714 {
 715         struct rela *text_rela, *rodata_rela;
 716         struct instruction *orig_insn = insn;
 717
 718         text_rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len);
 719         if (text_rela && text_rela->sym == file->rodata->sym) {
 720                 /* case 1 */
 721                 rodata_rela = find_rela_by_dest(file->rodata,
 722                                                 text_rela->addend);
 723                 if (rodata_rela)
 724                         return rodata_rela;
 725
 726                 /* case 2 */
 727                 rodata_rela = find_rela_by_dest(file->rodata,
 728                                                 text_rela->addend + 4);
 729                 if (!rodata_rela)
 730                         return NULL;
 731                 file->ignore_unreachables = true;
 732                 return rodata_rela;
 733         }
 734
 735         /* case 3 */
 736         func_for_each_insn_continue_reverse(file, func, insn) {
 737                 if (insn->type == INSN_JUMP_DYNAMIC)
 738                         break;
 739
 740                 /* allow small jumps within the range */
 741                 if (insn->type == INSN_JUMP_UNCONDITIONAL &&
 742                     insn->jump_dest &&
 743                     (insn->jump_dest->offset <= insn->offset ||
 744                      insn->jump_dest->offset >= orig_insn->offset))
 745                     break;
 746
 747                 text_rela = find_rela_by_dest_range(insn->sec, insn->offset,
 748                                                     insn->len);
 749                 if (text_rela && text_rela->sym == file->rodata->sym)
 750                         return find_rela_by_dest(file->rodata,
 751                                                  text_rela->addend);
 752         }
 753
 754         return NULL;
 755 }
 756
 757 static int add_func_switch_tables(struct objtool_file *file,
 758                                   struct symbol *func)
 759 {
 760         struct instruction *insn, *prev_jump = NULL;
 761         struct rela *rela, *prev_rela = NULL;
 762         int ret;
 763
 764         func_for_each_insn(file, func, insn) {
 765                 if (insn->type != INSN_JUMP_DYNAMIC)
 766                         continue;
 767
 768                 rela = find_switch_table(file, func, insn);
 769                 if (!rela)
 770                         continue;
 771
 772                 /*
 773                  * We found a switch table, but we don't know yet how big it
 774                  * is.  Don't add it until we reach the end of the function or
 775                  * the beginning of another switch table in the same function.
 776                  */
 777                 if (prev_jump) {
 778                         ret = add_switch_table(file, func, prev_jump, prev_rela,
 779                                                rela);
 780                         if (ret)
 781                                 return ret;
 782                 }
 783
 784                 prev_jump = insn;
 785                 prev_rela = rela;
 786         }
 787
 788         if (prev_jump) {
 789                 ret = add_switch_table(file, func, prev_jump, prev_rela, NULL);
 790                 if (ret)
 791                         return ret;
 792         }
 793
 794         return 0;
 795 }
 796
 797 /*
 798  * For some switch statements, gcc generates a jump table in the .rodata
 799  * section which contains a list of addresses within the function to jump to.
 800  * This finds these jump tables and adds them to the insn->alts lists.
 801  */
 802 static int add_switch_table_alts(struct objtool_file *file)
 803 {
 804         struct section *sec;
 805         struct symbol *func;
 806         int ret;
 807
 808         if (!file->rodata || !file->rodata->rela)
 809                 return 0;
 810
 811         list_for_each_entry(sec, &file->elf->sections, list) {
 812                 list_for_each_entry(func, &sec->symbol_list, list) {
 813                         if (func->type != STT_FUNC)
 814                                 continue;
 815
 816                         ret = add_func_switch_tables(file, func);
 817                         if (ret)
 818                                 return ret;
 819                 }
 820         }
 821
 822         return 0;
 823 }
 824
 825 static int decode_sections(struct objtool_file *file)
 826 {
 827         int ret;
 828
 829         ret = decode_instructions(file);
 830         if (ret)
 831                 return ret;
 832
 833         add_ignores(file);
 834
 835         ret = add_jump_destinations(file);
 836         if (ret)
 837                 return ret;
 838
 839         ret = add_call_destinations(file);
 840         if (ret)
 841                 return ret;
 842
 843         ret = add_special_section_alts(file);
 844         if (ret)
 845                 return ret;
 846
 847         ret = add_switch_table_alts(file);
 848         if (ret)
 849                 return ret;
 850
 851         return 0;
 852 }
 853
 854 static bool is_fentry_call(struct instruction *insn)
 855 {
 856         if (insn->type == INSN_CALL &&
 857             insn->call_dest->type == STT_NOTYPE &&
 858             !strcmp(insn->call_dest->name, "__fentry__"))
 859                 return true;
 860
 861         return false;
 862 }
 863
 864 static bool has_modified_stack_frame(struct instruction *insn)
 865 {
 866         return (insn->state & STATE_FP_SAVED) ||
 867                (insn->state & STATE_FP_SETUP);
 868 }
 869
 870 static bool has_valid_stack_frame(struct instruction *insn)
 871 {
 872         return (insn->state & STATE_FP_SAVED) &&
 873                (insn->state & STATE_FP_SETUP);
 874 }
 875
 876 static unsigned int frame_state(unsigned long state)
 877 {
 878         return (state & (STATE_FP_SAVED | STATE_FP_SETUP));
 879 }
 880
 881 /*
 882  * Follow the branch starting at the given instruction, and recursively follow
 883  * any other branches (jumps).  Meanwhile, track the frame pointer state at
 884  * each instruction and validate all the rules described in
 885  * tools/objtool/Documentation/stack-validation.txt.
 886  */
 887 static int validate_branch(struct objtool_file *file,
 888                            struct instruction *first, unsigned char first_state)
 889 {
 890         struct alternative *alt;
 891         struct instruction *insn;
 892         struct section *sec;
 893         struct symbol *func = NULL;
 894         unsigned char state;
 895         int ret;
 896
 897         insn = first;
 898         sec = insn->sec;
 899         state = first_state;
 900
 901         if (insn->alt_group && list_empty(&insn->alts)) {
 902                 WARN_FUNC("don't know how to handle branch to middle of alternative instruction group",
 903                           sec, insn->offset);
 904                 return 1;
 905         }
 906
 907         while (1) {
 908                 if (file->c_file && insn->func) {
 909                         if (func && func != insn->func) {
 910                                 WARN("%s() falls through to next function %s()",
 911                                      func->name, insn->func->name);
 912                                 return 1;
 913                         }
 914
 915                         func = insn->func;
 916                 }
 917
 918                 if (insn->visited) {
 919                         if (frame_state(insn->state) != frame_state(state)) {
 920                                 WARN_FUNC("frame pointer state mismatch",
 921                                           sec, insn->offset);
 922                                 return 1;
 923                         }
 924
 925                         return 0;
 926                 }
 927
 928                 insn->visited = true;
 929                 insn->state = state;
 930
 931                 list_for_each_entry(alt, &insn->alts, list) {
 932                         ret = validate_branch(file, alt->insn, state);
 933                         if (ret)
 934                                 return 1;
 935                 }
 936
 937                 switch (insn->type) {
 938
 939                 case INSN_FP_SAVE:
 940                         if (!nofp) {
 941                                 if (state & STATE_FP_SAVED) {
 942                                         WARN_FUNC("duplicate frame pointer save",
 943                                                   sec, insn->offset);
 944                                         return 1;
 945                                 }
 946                                 state |= STATE_FP_SAVED;
 947                         }
 948                         break;
 949
 950                 case INSN_FP_SETUP:
 951                         if (!nofp) {
 952                                 if (state & STATE_FP_SETUP) {
 953                                         WARN_FUNC("duplicate frame pointer setup",
 954                                                   sec, insn->offset);
 955                                         return 1;
 956                                 }
 957                                 state |= STATE_FP_SETUP;
 958                         }
 959                         break;
 960
 961                 case INSN_FP_RESTORE:
 962                         if (!nofp) {
 963                                 if (has_valid_stack_frame(insn))
 964                                         state &= ~STATE_FP_SETUP;
 965
 966                                 state &= ~STATE_FP_SAVED;
 967                         }
 968                         break;
 969
 970                 case INSN_RETURN:
 971                         if (!nofp && has_modified_stack_frame(insn)) {
 972                                 WARN_FUNC("return without frame pointer restore",
 973                                           sec, insn->offset);
 974                                 return 1;
 975                         }
 976                         return 0;
 977
 978                 case INSN_CALL:
 979                         if (is_fentry_call(insn)) {
 980                                 state |= STATE_FENTRY;
 981                                 break;
 982                         }
 983
 984                         ret = dead_end_function(file, insn->call_dest);
 985                         if (ret == 1)
 986                                 return 0;
 987                         if (ret == -1)
 988                                 return 1;
 989
 990                         /* fallthrough */
 991                 case INSN_CALL_DYNAMIC:
 992                         if (!nofp && !has_valid_stack_frame(insn)) {
 993                                 WARN_FUNC("call without frame pointer save/setup",
 994                                           sec, insn->offset);
 995                                 return 1;
 996                         }
 997                         break;
 998
 999                 case INSN_JUMP_CONDITIONAL:
1000                 case INSN_JUMP_UNCONDITIONAL:
1001                         if (insn->jump_dest) {
1002                                 ret = validate_branch(file, insn->jump_dest,
1003                                                       state);
1004                                 if (ret)
1005                                         return 1;
1006                         } else if (has_modified_stack_frame(insn)) {
1007                                 WARN_FUNC("sibling call from callable instruction with changed frame pointer",
1008                                           sec, insn->offset);
1009                                 return 1;
1010                         } /* else it's a sibling call */
1011
1012                         if (insn->type == INSN_JUMP_UNCONDITIONAL)
1013                                 return 0;
1014
1015                         break;
1016
1017                 case INSN_JUMP_DYNAMIC:
1018                         if (list_empty(&insn->alts) &&
1019                             has_modified_stack_frame(insn)) {
1020                                 WARN_FUNC("sibling call from callable instruction with changed frame pointer",
1021                                           sec, insn->offset);
1022                                 return 1;
1023                         }
1024
1025                         return 0;
1026
1027                 case INSN_BUG:
1028                         return 0;
1029
1030                 default:
1031                         break;
1032                 }
1033
1034                 insn = next_insn_same_sec(file, insn);
1035                 if (!insn) {
1036                         WARN("%s: unexpected end of section", sec->name);
1037                         return 1;
1038                 }
1039         }
1040
1041         return 0;
1042 }
1043
1044 static bool is_gcov_insn(struct instruction *insn)
1045 {
1046         struct rela *rela;
1047         struct section *sec;
1048         struct symbol *sym;
1049         unsigned long offset;
1050
1051         rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len);
1052         if (!rela)
1053                 return false;
1054
1055         if (rela->sym->type != STT_SECTION)
1056                 return false;
1057
1058         sec = rela->sym->sec;
1059         offset = rela->addend + insn->offset + insn->len - rela->offset;
1060
1061         list_for_each_entry(sym, &sec->symbol_list, list) {
1062                 if (sym->type != STT_OBJECT)
1063                         continue;
1064
1065                 if (offset >= sym->offset && offset < sym->offset + sym->len)
1066                         return (!memcmp(sym->name, "__gcov0.", 8));
1067         }
1068
1069         return false;
1070 }
1071
1072 static bool is_kasan_insn(struct instruction *insn)
1073 {
1074         return (insn->type == INSN_CALL &&
1075                 !strcmp(insn->call_dest->name, "__asan_handle_no_return"));
1076 }
1077
1078 static bool is_ubsan_insn(struct instruction *insn)
1079 {
1080         return (insn->type == INSN_CALL &&
1081                 !strcmp(insn->call_dest->name,
1082                         "__ubsan_handle_builtin_unreachable"));
1083 }
1084
1085 static bool ignore_unreachable_insn(struct symbol *func,
1086                                     struct instruction *insn)
1087 {
1088         int i;
1089
1090         if (insn->type == INSN_NOP)
1091                 return true;
1092
1093         if (is_gcov_insn(insn))
1094                 return true;
1095
1096         /*
1097          * Check if this (or a subsequent) instruction is related to
1098          * CONFIG_UBSAN or CONFIG_KASAN.
1099          *
1100          * End the search at 5 instructions to avoid going into the weeds.
1101          */
1102         for (i = 0; i < 5; i++) {
1103
1104                 if (is_kasan_insn(insn) || is_ubsan_insn(insn))
1105                         return true;
1106
1107                 if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest) {
1108                         insn = insn->jump_dest;
1109                         continue;
1110                 }
1111
1112                 if (insn->offset + insn->len >= func->offset + func->len)
1113                         break;
1114                 insn = list_next_entry(insn, list);
1115         }
1116
1117         return false;
1118 }
1119
1120 static int validate_functions(struct objtool_file *file)
1121 {
1122         struct section *sec;
1123         struct symbol *func;
1124         struct instruction *insn;
1125         int ret, warnings = 0;
1126
1127         list_for_each_entry(sec, &file->elf->sections, list) {
1128                 list_for_each_entry(func, &sec->symbol_list, list) {
1129                         if (func->type != STT_FUNC)
1130                                 continue;
1131
1132                         insn = find_insn(file, sec, func->offset);
1133                         if (!insn)
1134                                 continue;
1135
1136                         ret = validate_branch(file, insn, 0);
1137                         warnings += ret;
1138                 }
1139         }
1140
1141         list_for_each_entry(sec, &file->elf->sections, list) {
1142                 list_for_each_entry(func, &sec->symbol_list, list) {
1143                         if (func->type != STT_FUNC)
1144                                 continue;
1145
1146                         func_for_each_insn(file, func, insn) {
1147                                 if (insn->visited)
1148                                         continue;
1149
1150                                 insn->visited = true;
1151
1152                                 if (file->ignore_unreachables || warnings ||
1153                                     ignore_unreachable_insn(func, insn))
1154                                         continue;
1155
1156                                 WARN_FUNC("function has unreachable instruction", insn->sec, insn->offset);
1157                                 warnings++;
1158                         }
1159                 }
1160         }
1161
1162         return warnings;
1163 }
1164
1165 static int validate_uncallable_instructions(struct objtool_file *file)
1166 {
1167         struct instruction *insn;
1168         int warnings = 0;
1169
1170         for_each_insn(file, insn) {
1171                 if (!insn->visited && insn->type == INSN_RETURN) {
1172                         WARN_FUNC("return instruction outside of a callable function",
1173                                   insn->sec, insn->offset);
1174                         warnings++;
1175                 }
1176         }
1177
1178         return warnings;
1179 }
1180
1181 static void cleanup(struct objtool_file *file)
1182 {
1183         struct instruction *insn, *tmpinsn;
1184         struct alternative *alt, *tmpalt;
1185
1186         list_for_each_entry_safe(insn, tmpinsn, &file->insn_list, list) {
1187                 list_for_each_entry_safe(alt, tmpalt, &insn->alts, list) {
1188                         list_del(&alt->list);
1189                         free(alt);
1190                 }
1191                 list_del(&insn->list);
1192                 hash_del(&insn->hash);
1193                 free(insn);
1194         }
1195         elf_close(file->elf);
1196 }
1197
1198 const char * const check_usage[] = {
1199         "objtool check [<options>] file.o",
1200         NULL,
1201 };
1202
1203 int cmd_check(int argc, const char **argv)
1204 {
1205         struct objtool_file file;
1206         int ret, warnings = 0;
1207
1208         const struct option options[] = {
1209                 OPT_BOOLEAN('f', "no-fp", &nofp, "Skip frame pointer validation"),
1210                 OPT_END(),
1211         };
1212
1213         argc = parse_options(argc, argv, options, check_usage, 0);
1214
1215         if (argc != 1)
1216                 usage_with_options(check_usage, options);
1217
1218         objname = argv[0];
1219
1220         file.elf = elf_open(objname);
1221         if (!file.elf) {
1222                 fprintf(stderr, "error reading elf file %s\n", objname);
1223                 return 1;
1224         }
1225
1226         INIT_LIST_HEAD(&file.insn_list);
1227         hash_init(file.insn_hash);
1228         file.whitelist = find_section_by_name(file.elf, "__func_stack_frame_non_standard");
1229         file.rodata = find_section_by_name(file.elf, ".rodata");
1230         file.ignore_unreachables = false;
1231         file.c_file = find_section_by_name(file.elf, ".comment");
1232
1233         ret = decode_sections(&file);
1234         if (ret < 0)
1235                 goto out;
1236         warnings += ret;
1237
1238         ret = validate_functions(&file);
1239         if (ret < 0)
1240                 goto out;
1241         warnings += ret;
1242
1243         ret = validate_uncallable_instructions(&file);
1244         if (ret < 0)
1245                 goto out;
1246         warnings += ret;
1247
1248 out:
1249         cleanup(&file);
1250
1251         /* ignore warnings for now until we get all the code cleaned up */
1252         if (ret || warnings)
1253                 return 0;
1254         return 0;
1255 }