tools/objtool/check.c

   1 /*
   2  * Copyright (C) 2015-2017 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 #include <string.h>
  19 #include <stdlib.h>
  20
  21 #include "builtin.h"
  22 #include "check.h"
  23 #include "elf.h"
  24 #include "special.h"
  25 #include "arch.h"
  26 #include "warn.h"
  27
  28 #include <linux/hashtable.h>
  29 #include <linux/kernel.h>
  30
  31 struct alternative {
  32         struct list_head list;
  33         struct instruction *insn;
  34 };
  35
  36 const char *objname;
  37 struct cfi_state initial_func_cfi;
  38
  39 struct instruction *find_insn(struct objtool_file *file,
  40                               struct section *sec, unsigned long offset)
  41 {
  42         struct instruction *insn;
  43
  44         hash_for_each_possible(file->insn_hash, insn, hash, offset)
  45                 if (insn->sec == sec && insn->offset == offset)
  46                         return insn;
  47
  48         return NULL;
  49 }
  50
  51 static struct instruction *next_insn_same_sec(struct objtool_file *file,
  52                                               struct instruction *insn)
  53 {
  54         struct instruction *next = list_next_entry(insn, list);
  55
  56         if (!next || &next->list == &file->insn_list || next->sec != insn->sec)
  57                 return NULL;
  58
  59         return next;
  60 }
  61
  62 #define func_for_each_insn(file, func, insn)                            \
  63         for (insn = find_insn(file, func->sec, func->offset);           \
  64              insn && &insn->list != &file->insn_list &&                 \
  65                 insn->sec == func->sec &&                               \
  66                 insn->offset < func->offset + func->len;                \
  67              insn = list_next_entry(insn, list))
  68
  69 #define func_for_each_insn_continue_reverse(file, func, insn)           \
  70         for (insn = list_prev_entry(insn, list);                        \
  71              &insn->list != &file->insn_list &&                         \
  72                 insn->sec == func->sec && insn->offset >= func->offset; \
  73              insn = list_prev_entry(insn, list))
  74
  75 #define sec_for_each_insn_from(file, insn)                              \
  76         for (; insn; insn = next_insn_same_sec(file, insn))
  77
  78 #define sec_for_each_insn_continue(file, insn)                          \
  79         for (insn = next_insn_same_sec(file, insn); insn;               \
  80              insn = next_insn_same_sec(file, insn))
  81
  82 /*
  83  * Check if the function has been manually whitelisted with the
  84  * STACK_FRAME_NON_STANDARD macro, or if it should be automatically whitelisted
  85  * due to its use of a context switching instruction.
  86  */
  87 static bool ignore_func(struct objtool_file *file, struct symbol *func)
  88 {
  89         struct rela *rela;
  90
  91         /* check for STACK_FRAME_NON_STANDARD */
  92         if (file->whitelist && file->whitelist->rela)
  93                 list_for_each_entry(rela, &file->whitelist->rela->rela_list, list) {
  94                         if (rela->sym->type == STT_SECTION &&
  95                             rela->sym->sec == func->sec &&
  96                             rela->addend == func->offset)
  97                                 return true;
  98                         if (rela->sym->type == STT_FUNC && rela->sym == func)
  99                                 return true;
 100                 }
 101
 102         return false;
 103 }
 104
 105 /*
 106  * This checks to see if the given function is a "noreturn" function.
 107  *
 108  * For global functions which are outside the scope of this object file, we
 109  * have to keep a manual list of them.
 110  *
 111  * For local functions, we have to detect them manually by simply looking for
 112  * the lack of a return instruction.
 113  *
 114  * Returns:
 115  *  -1: error
 116  *   0: no dead end
 117  *   1: dead end
 118  */
 119 static int __dead_end_function(struct objtool_file *file, struct symbol *func,
 120                                int recursion)
 121 {
 122         int i;
 123         struct instruction *insn;
 124         bool empty = true;
 125
 126         /*
 127          * Unfortunately these have to be hard coded because the noreturn
 128          * attribute isn't provided in ELF data.
 129          */
 130         static const char * const global_noreturns[] = {
 131                 "__stack_chk_fail",
 132                 "panic",
 133                 "do_exit",
 134                 "do_task_dead",
 135                 "__module_put_and_exit",
 136                 "complete_and_exit",
 137                 "kvm_spurious_fault",
 138                 "__reiserfs_panic",
 139                 "lbug_with_loc",
 140                 "fortify_panic",
 141                 "usercopy_abort",
 142         };
 143
 144         if (func->bind == STB_WEAK)
 145                 return 0;
 146
 147         if (func->bind == STB_GLOBAL)
 148                 for (i = 0; i < ARRAY_SIZE(global_noreturns); i++)
 149                         if (!strcmp(func->name, global_noreturns[i]))
 150                                 return 1;
 151
 152         if (!func->sec)
 153                 return 0;
 154
 155         func_for_each_insn(file, func, insn) {
 156                 empty = false;
 157
 158                 if (insn->type == INSN_RETURN)
 159                         return 0;
 160         }
 161
 162         if (empty)
 163                 return 0;
 164
 165         /*
 166          * A function can have a sibling call instead of a return.  In that
 167          * case, the function's dead-end status depends on whether the target
 168          * of the sibling call returns.
 169          */
 170         func_for_each_insn(file, func, insn) {
 171                 if (insn->sec != func->sec ||
 172                     insn->offset >= func->offset + func->len)
 173                         break;
 174
 175                 if (insn->type == INSN_JUMP_UNCONDITIONAL) {
 176                         struct instruction *dest = insn->jump_dest;
 177                         struct symbol *dest_func;
 178
 179                         if (!dest)
 180                                 /* sibling call to another file */
 181                                 return 0;
 182
 183                         if (dest->sec != func->sec ||
 184                             dest->offset < func->offset ||
 185                             dest->offset >= func->offset + func->len) {
 186                                 /* local sibling call */
 187                                 dest_func = find_symbol_by_offset(dest->sec,
 188                                                                   dest->offset);
 189                                 if (!dest_func)
 190                                         continue;
 191
 192                                 if (recursion == 5) {
 193                                         WARN_FUNC("infinite recursion (objtool bug!)",
 194                                                   dest->sec, dest->offset);
 195                                         return -1;
 196                                 }
 197
 198                                 return __dead_end_function(file, dest_func,
 199                                                            recursion + 1);
 200                         }
 201                 }
 202
 203                 if (insn->type == INSN_JUMP_DYNAMIC && list_empty(&insn->alts))
 204                         /* sibling call */
 205                         return 0;
 206         }
 207
 208         return 1;
 209 }
 210
 211 static int dead_end_function(struct objtool_file *file, struct symbol *func)
 212 {
 213         return __dead_end_function(file, func, 0);
 214 }
 215
 216 static void clear_insn_state(struct insn_state *state)
 217 {
 218         int i;
 219
 220         memset(state, 0, sizeof(*state));
 221         state->cfa.base = CFI_UNDEFINED;
 222         for (i = 0; i < CFI_NUM_REGS; i++) {
 223                 state->regs[i].base = CFI_UNDEFINED;
 224                 state->vals[i].base = CFI_UNDEFINED;
 225         }
 226         state->drap_reg = CFI_UNDEFINED;
 227         state->drap_offset = -1;
 228 }
 229
 230 /*
 231  * Call the arch-specific instruction decoder for all the instructions and add
 232  * them to the global instruction list.
 233  */
 234 static int decode_instructions(struct objtool_file *file)
 235 {
 236         struct section *sec;
 237         struct symbol *func;
 238         unsigned long offset;
 239         struct instruction *insn;
 240         int ret;
 241
 242         for_each_sec(file, sec) {
 243
 244                 if (!(sec->sh.sh_flags & SHF_EXECINSTR))
 245                         continue;
 246
 247                 if (strcmp(sec->name, ".altinstr_replacement") &&
 248                     strcmp(sec->name, ".altinstr_aux") &&
 249                     strncmp(sec->name, ".discard.", 9))
 250                         sec->text = true;
 251
 252                 for (offset = 0; offset < sec->len; offset += insn->len) {
 253                         insn = malloc(sizeof(*insn));
 254                         if (!insn) {
 255                                 WARN("malloc failed");
 256                                 return -1;
 257                         }
 258                         memset(insn, 0, sizeof(*insn));
 259                         INIT_LIST_HEAD(&insn->alts);
 260                         clear_insn_state(&insn->state);
 261
 262                         insn->sec = sec;
 263                         insn->offset = offset;
 264
 265                         ret = arch_decode_instruction(file->elf, sec, offset,
 266                                                       sec->len - offset,
 267                                                       &insn->len, &insn->type,
 268                                                       &insn->immediate,
 269                                                       &insn->stack_op);
 270                         if (ret)
 271                                 goto err;
 272
 273                         if (!insn->type || insn->type > INSN_LAST) {
 274                                 WARN_FUNC("invalid instruction type %d",
 275                                           insn->sec, insn->offset, insn->type);
 276                                 ret = -1;
 277                                 goto err;
 278                         }
 279
 280                         hash_add(file->insn_hash, &insn->hash, insn->offset);
 281                         list_add_tail(&insn->list, &file->insn_list);
 282                 }
 283
 284                 list_for_each_entry(func, &sec->symbol_list, list) {
 285                         if (func->type != STT_FUNC)
 286                                 continue;
 287
 288                         if (!find_insn(file, sec, func->offset)) {
 289                                 WARN("%s(): can't find starting instruction",
 290                                      func->name);
 291                                 return -1;
 292                         }
 293
 294                         func_for_each_insn(file, func, insn)
 295                                 if (!insn->func)
 296                                         insn->func = func;
 297                 }
 298         }
 299
 300         return 0;
 301
 302 err:
 303         free(insn);
 304         return ret;
 305 }
 306
 307 /*
 308  * Mark "ud2" instructions and manually annotated dead ends.
 309  */
 310 static int add_dead_ends(struct objtool_file *file)
 311 {
 312         struct section *sec;
 313         struct rela *rela;
 314         struct instruction *insn;
 315         bool found;
 316
 317         /*
 318          * By default, "ud2" is a dead end unless otherwise annotated, because
 319          * GCC 7 inserts it for certain divide-by-zero cases.
 320          */
 321         for_each_insn(file, insn)
 322                 if (insn->type == INSN_BUG)
 323                         insn->dead_end = true;
 324
 325         /*
 326          * Check for manually annotated dead ends.
 327          */
 328         sec = find_section_by_name(file->elf, ".rela.discard.unreachable");
 329         if (!sec)
 330                 goto reachable;
 331
 332         list_for_each_entry(rela, &sec->rela_list, list) {
 333                 if (rela->sym->type != STT_SECTION) {
 334                         WARN("unexpected relocation symbol type in %s", sec->name);
 335                         return -1;
 336                 }
 337                 insn = find_insn(file, rela->sym->sec, rela->addend);
 338                 if (insn)
 339                         insn = list_prev_entry(insn, list);
 340                 else if (rela->addend == rela->sym->sec->len) {
 341                         found = false;
 342                         list_for_each_entry_reverse(insn, &file->insn_list, list) {
 343                                 if (insn->sec == rela->sym->sec) {
 344                                         found = true;
 345                                         break;
 346                                 }
 347                         }
 348
 349                         if (!found) {
 350                                 WARN("can't find unreachable insn at %s+0x%x",
 351                                      rela->sym->sec->name, rela->addend);
 352                                 return -1;
 353                         }
 354                 } else {
 355                         WARN("can't find unreachable insn at %s+0x%x",
 356                              rela->sym->sec->name, rela->addend);
 357                         return -1;
 358                 }
 359
 360                 insn->dead_end = true;
 361         }
 362
 363 reachable:
 364         /*
 365          * These manually annotated reachable checks are needed for GCC 4.4,
 366          * where the Linux unreachable() macro isn't supported.  In that case
 367          * GCC doesn't know the "ud2" is fatal, so it generates code as if it's
 368          * not a dead end.
 369          */
 370         sec = find_section_by_name(file->elf, ".rela.discard.reachable");
 371         if (!sec)
 372                 return 0;
 373
 374         list_for_each_entry(rela, &sec->rela_list, list) {
 375                 if (rela->sym->type != STT_SECTION) {
 376                         WARN("unexpected relocation symbol type in %s", sec->name);
 377                         return -1;
 378                 }
 379                 insn = find_insn(file, rela->sym->sec, rela->addend);
 380                 if (insn)
 381                         insn = list_prev_entry(insn, list);
 382                 else if (rela->addend == rela->sym->sec->len) {
 383                         found = false;
 384                         list_for_each_entry_reverse(insn, &file->insn_list, list) {
 385                                 if (insn->sec == rela->sym->sec) {
 386                                         found = true;
 387                                         break;
 388                                 }
 389                         }
 390
 391                         if (!found) {
 392                                 WARN("can't find reachable insn at %s+0x%x",
 393                                      rela->sym->sec->name, rela->addend);
 394                                 return -1;
 395                         }
 396                 } else {
 397                         WARN("can't find reachable insn at %s+0x%x",
 398                              rela->sym->sec->name, rela->addend);
 399                         return -1;
 400                 }
 401
 402                 insn->dead_end = false;
 403         }
 404
 405         return 0;
 406 }
 407
 408 /*
 409  * Warnings shouldn't be reported for ignored functions.
 410  */
 411 static void add_ignores(struct objtool_file *file)
 412 {
 413         struct instruction *insn;
 414         struct section *sec;
 415         struct symbol *func;
 416
 417         for_each_sec(file, sec) {
 418                 list_for_each_entry(func, &sec->symbol_list, list) {
 419                         if (func->type != STT_FUNC)
 420                                 continue;
 421
 422                         if (!ignore_func(file, func))
 423                                 continue;
 424
 425                         func_for_each_insn(file, func, insn)
 426                                 insn->ignore = true;
 427                 }
 428         }
 429 }
 430
 431 /*
 432  * FIXME: For now, just ignore any alternatives which add retpolines.  This is
 433  * a temporary hack, as it doesn't allow ORC to unwind from inside a retpoline.
 434  * But it at least allows objtool to understand the control flow *around* the
 435  * retpoline.
 436  */
 437 static int add_nospec_ignores(struct objtool_file *file)
 438 {
 439         struct section *sec;
 440         struct rela *rela;
 441         struct instruction *insn;
 442
 443         sec = find_section_by_name(file->elf, ".rela.discard.nospec");
 444         if (!sec)
 445                 return 0;
 446
 447         list_for_each_entry(rela, &sec->rela_list, list) {
 448                 if (rela->sym->type != STT_SECTION) {
 449                         WARN("unexpected relocation symbol type in %s", sec->name);
 450                         return -1;
 451                 }
 452
 453                 insn = find_insn(file, rela->sym->sec, rela->addend);
 454                 if (!insn) {
 455                         WARN("bad .discard.nospec entry");
 456                         return -1;
 457                 }
 458
 459                 insn->ignore_alts = true;
 460         }
 461
 462         return 0;
 463 }
 464
 465 /*
 466  * Find the destination instructions for all jumps.
 467  */
 468 static int add_jump_destinations(struct objtool_file *file)
 469 {
 470         struct instruction *insn;
 471         struct rela *rela;
 472         struct section *dest_sec;
 473         unsigned long dest_off;
 474
 475         for_each_insn(file, insn) {
 476                 if (insn->type != INSN_JUMP_CONDITIONAL &&
 477                     insn->type != INSN_JUMP_UNCONDITIONAL)
 478                         continue;
 479
 480                 if (insn->ignore)
 481                         continue;
 482
 483                 rela = find_rela_by_dest_range(insn->sec, insn->offset,
 484                                                insn->len);
 485                 if (!rela) {
 486                         dest_sec = insn->sec;
 487                         dest_off = insn->offset + insn->len + insn->immediate;
 488                 } else if (rela->sym->type == STT_SECTION) {
 489                         dest_sec = rela->sym->sec;
 490                         dest_off = rela->addend + 4;
 491                 } else if (rela->sym->sec->idx) {
 492                         dest_sec = rela->sym->sec;
 493                         dest_off = rela->sym->sym.st_value + rela->addend + 4;
 494                 } else if (strstr(rela->sym->name, "_indirect_thunk_")) {
 495                         /*
 496                          * Retpoline jumps are really dynamic jumps in
 497                          * disguise, so convert them accordingly.
 498                          */
 499                         insn->type = INSN_JUMP_DYNAMIC;
 500                         insn->retpoline_safe = true;
 501                         continue;
 502                 } else {
 503                         /* sibling call */
 504                         insn->jump_dest = 0;
 505                         continue;
 506                 }
 507
 508                 insn->jump_dest = find_insn(file, dest_sec, dest_off);
 509                 if (!insn->jump_dest) {
 510
 511                         /*
 512                          * This is a special case where an alt instruction
 513                          * jumps past the end of the section.  These are
 514                          * handled later in handle_group_alt().
 515                          */
 516                         if (!strcmp(insn->sec->name, ".altinstr_replacement"))
 517                                 continue;
 518
 519                         WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
 520                                   insn->sec, insn->offset, dest_sec->name,
 521                                   dest_off);
 522                         return -1;
 523                 }
 524         }
 525
 526         return 0;
 527 }
 528
 529 /*
 530  * Find the destination instructions for all calls.
 531  */
 532 static int add_call_destinations(struct objtool_file *file)
 533 {
 534         struct instruction *insn;
 535         unsigned long dest_off;
 536         struct rela *rela;
 537
 538         for_each_insn(file, insn) {
 539                 if (insn->type != INSN_CALL)
 540                         continue;
 541
 542                 rela = find_rela_by_dest_range(insn->sec, insn->offset,
 543                                                insn->len);
 544                 if (!rela) {
 545                         dest_off = insn->offset + insn->len + insn->immediate;
 546                         insn->call_dest = find_symbol_by_offset(insn->sec,
 547                                                                 dest_off);
 548
 549                         if (!insn->call_dest && !insn->ignore) {
 550                                 WARN_FUNC("unsupported intra-function call",
 551                                           insn->sec, insn->offset);
 552                                 if (retpoline)
 553                                         WARN("If this is a retpoline, please patch it in with alternatives and annotate it with ANNOTATE_NOSPEC_ALTERNATIVE.");
 554                                 return -1;
 555                         }
 556
 557                 } else if (rela->sym->type == STT_SECTION) {
 558                         insn->call_dest = find_symbol_by_offset(rela->sym->sec,
 559                                                                 rela->addend+4);
 560                         if (!insn->call_dest ||
 561                             insn->call_dest->type != STT_FUNC) {
 562                                 WARN_FUNC("can't find call dest symbol at %s+0x%x",
 563                                           insn->sec, insn->offset,
 564                                           rela->sym->sec->name,
 565                                           rela->addend + 4);
 566                                 return -1;
 567                         }
 568                 } else
 569                         insn->call_dest = rela->sym;
 570         }
 571
 572         return 0;
 573 }
 574
 575 /*
 576  * The .alternatives section requires some extra special care, over and above
 577  * what other special sections require:
 578  *
 579  * 1. Because alternatives are patched in-place, we need to insert a fake jump
 580  *    instruction at the end so that validate_branch() skips all the original
 581  *    replaced instructions when validating the new instruction path.
 582  *
 583  * 2. An added wrinkle is that the new instruction length might be zero.  In
 584  *    that case the old instructions are replaced with noops.  We simulate that
 585  *    by creating a fake jump as the only new instruction.
 586  *
 587  * 3. In some cases, the alternative section includes an instruction which
 588  *    conditionally jumps to the _end_ of the entry.  We have to modify these
 589  *    jumps' destinations to point back to .text rather than the end of the
 590  *    entry in .altinstr_replacement.
 591  *
 592  * 4. It has been requested that we don't validate the !POPCNT feature path
 593  *    which is a "very very small percentage of machines".
 594  */
 595 static int handle_group_alt(struct objtool_file *file,
 596                             struct special_alt *special_alt,
 597                             struct instruction *orig_insn,
 598                             struct instruction **new_insn)
 599 {
 600         struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump = NULL;
 601         unsigned long dest_off;
 602
 603         last_orig_insn = NULL;
 604         insn = orig_insn;
 605         sec_for_each_insn_from(file, insn) {
 606                 if (insn->offset >= special_alt->orig_off + special_alt->orig_len)
 607                         break;
 608
 609                 if (special_alt->skip_orig)
 610                         insn->type = INSN_NOP;
 611
 612                 insn->alt_group = true;
 613                 last_orig_insn = insn;
 614         }
 615
 616         if (next_insn_same_sec(file, last_orig_insn)) {
 617                 fake_jump = malloc(sizeof(*fake_jump));
 618                 if (!fake_jump) {
 619                         WARN("malloc failed");
 620                         return -1;
 621                 }
 622                 memset(fake_jump, 0, sizeof(*fake_jump));
 623                 INIT_LIST_HEAD(&fake_jump->alts);
 624                 clear_insn_state(&fake_jump->state);
 625
 626                 fake_jump->sec = special_alt->new_sec;
 627                 fake_jump->offset = -1;
 628                 fake_jump->type = INSN_JUMP_UNCONDITIONAL;
 629                 fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
 630                 fake_jump->ignore = true;
 631         }
 632
 633         if (!special_alt->new_len) {
 634                 if (!fake_jump) {
 635                         WARN("%s: empty alternative at end of section",
 636                              special_alt->orig_sec->name);
 637                         return -1;
 638                 }
 639
 640                 *new_insn = fake_jump;
 641                 return 0;
 642         }
 643
 644         last_new_insn = NULL;
 645         insn = *new_insn;
 646         sec_for_each_insn_from(file, insn) {
 647                 if (insn->offset >= special_alt->new_off + special_alt->new_len)
 648                         break;
 649
 650                 last_new_insn = insn;
 651
 652                 insn->ignore = orig_insn->ignore_alts;
 653
 654                 if (insn->type != INSN_JUMP_CONDITIONAL &&
 655                     insn->type != INSN_JUMP_UNCONDITIONAL)
 656                         continue;
 657
 658                 if (!insn->immediate)
 659                         continue;
 660
 661                 dest_off = insn->offset + insn->len + insn->immediate;
 662                 if (dest_off == special_alt->new_off + special_alt->new_len) {
 663                         if (!fake_jump) {
 664                                 WARN("%s: alternative jump to end of section",
 665                                      special_alt->orig_sec->name);
 666                                 return -1;
 667                         }
 668                         insn->jump_dest = fake_jump;
 669                 }
 670
 671                 if (!insn->jump_dest) {
 672                         WARN_FUNC("can't find alternative jump destination",
 673                                   insn->sec, insn->offset);
 674                         return -1;
 675                 }
 676         }
 677
 678         if (!last_new_insn) {
 679                 WARN_FUNC("can't find last new alternative instruction",
 680                           special_alt->new_sec, special_alt->new_off);
 681                 return -1;
 682         }
 683
 684         if (fake_jump)
 685                 list_add(&fake_jump->list, &last_new_insn->list);
 686
 687         return 0;
 688 }
 689
 690 /*
 691  * A jump table entry can either convert a nop to a jump or a jump to a nop.
 692  * If the original instruction is a jump, make the alt entry an effective nop
 693  * by just skipping the original instruction.
 694  */
 695 static int handle_jump_alt(struct objtool_file *file,
 696                            struct special_alt *special_alt,
 697                            struct instruction *orig_insn,
 698                            struct instruction **new_insn)
 699 {
 700         if (orig_insn->type == INSN_NOP)
 701                 return 0;
 702
 703         if (orig_insn->type != INSN_JUMP_UNCONDITIONAL) {
 704                 WARN_FUNC("unsupported instruction at jump label",
 705                           orig_insn->sec, orig_insn->offset);
 706                 return -1;
 707         }
 708
 709         *new_insn = list_next_entry(orig_insn, list);
 710         return 0;
 711 }
 712
 713 /*
 714  * Read all the special sections which have alternate instructions which can be
 715  * patched in or redirected to at runtime.  Each instruction having alternate
 716  * instruction(s) has them added to its insn->alts list, which will be
 717  * traversed in validate_branch().
 718  */
 719 static int add_special_section_alts(struct objtool_file *file)
 720 {
 721         struct list_head special_alts;
 722         struct instruction *orig_insn, *new_insn;
 723         struct special_alt *special_alt, *tmp;
 724         struct alternative *alt;
 725         int ret;
 726
 727         ret = special_get_alts(file->elf, &special_alts);
 728         if (ret)
 729                 return ret;
 730
 731         list_for_each_entry_safe(special_alt, tmp, &special_alts, list) {
 732
 733                 orig_insn = find_insn(file, special_alt->orig_sec,
 734                                       special_alt->orig_off);
 735                 if (!orig_insn) {
 736                         WARN_FUNC("special: can't find orig instruction",
 737                                   special_alt->orig_sec, special_alt->orig_off);
 738                         ret = -1;
 739                         goto out;
 740                 }
 741
 742                 new_insn = NULL;
 743                 if (!special_alt->group || special_alt->new_len) {
 744                         new_insn = find_insn(file, special_alt->new_sec,
 745                                              special_alt->new_off);
 746                         if (!new_insn) {
 747                                 WARN_FUNC("special: can't find new instruction",
 748                                           special_alt->new_sec,
 749                                           special_alt->new_off);
 750                                 ret = -1;
 751                                 goto out;
 752                         }
 753                 }
 754
 755                 if (special_alt->group) {
 756                         ret = handle_group_alt(file, special_alt, orig_insn,
 757                                                &new_insn);
 758                         if (ret)
 759                                 goto out;
 760                 } else if (special_alt->jump_or_nop) {
 761                         ret = handle_jump_alt(file, special_alt, orig_insn,
 762                                               &new_insn);
 763                         if (ret)
 764                                 goto out;
 765                 }
 766
 767                 alt = malloc(sizeof(*alt));
 768                 if (!alt) {
 769                         WARN("malloc failed");
 770                         ret = -1;
 771                         goto out;
 772                 }
 773
 774                 alt->insn = new_insn;
 775                 list_add_tail(&alt->list, &orig_insn->alts);
 776
 777                 list_del(&special_alt->list);
 778                 free(special_alt);
 779         }
 780
 781 out:
 782         return ret;
 783 }
 784
 785 static int add_switch_table(struct objtool_file *file, struct symbol *func,
 786                             struct instruction *insn, struct rela *table,
 787                             struct rela *next_table)
 788 {
 789         struct rela *rela = table;
 790         struct instruction *alt_insn;
 791         struct alternative *alt;
 792
 793         list_for_each_entry_from(rela, &file->rodata->rela->rela_list, list) {
 794                 if (rela == next_table)
 795                         break;
 796
 797                 if (rela->sym->sec != insn->sec ||
 798                     rela->addend <= func->offset ||
 799                     rela->addend >= func->offset + func->len)
 800                         break;
 801
 802                 alt_insn = find_insn(file, insn->sec, rela->addend);
 803                 if (!alt_insn) {
 804                         WARN("%s: can't find instruction at %s+0x%x",
 805                              file->rodata->rela->name, insn->sec->name,
 806                              rela->addend);
 807                         return -1;
 808                 }
 809
 810                 alt = malloc(sizeof(*alt));
 811                 if (!alt) {
 812                         WARN("malloc failed");
 813                         return -1;
 814                 }
 815
 816                 alt->insn = alt_insn;
 817                 list_add_tail(&alt->list, &insn->alts);
 818         }
 819
 820         return 0;
 821 }
 822
 823 /*
 824  * find_switch_table() - Given a dynamic jump, find the switch jump table in
 825  * .rodata associated with it.
 826  *
 827  * There are 3 basic patterns:
 828  *
 829  * 1. jmpq *[rodata addr](,%reg,8)
 830  *
 831  *    This is the most common case by far.  It jumps to an address in a simple
 832  *    jump table which is stored in .rodata.
 833  *
 834  * 2. jmpq *[rodata addr](%rip)
 835  *
 836  *    This is caused by a rare GCC quirk, currently only seen in three driver
 837  *    functions in the kernel, only with certain obscure non-distro configs.
 838  *
 839  *    As part of an optimization, GCC makes a copy of an existing switch jump
 840  *    table, modifies it, and then hard-codes the jump (albeit with an indirect
 841  *    jump) to use a single entry in the table.  The rest of the jump table and
 842  *    some of its jump targets remain as dead code.
 843  *
 844  *    In such a case we can just crudely ignore all unreachable instruction
 845  *    warnings for the entire object file.  Ideally we would just ignore them
 846  *    for the function, but that would require redesigning the code quite a
 847  *    bit.  And honestly that's just not worth doing: unreachable instruction
 848  *    warnings are of questionable value anyway, and this is such a rare issue.
 849  *
 850  * 3. mov [rodata addr],%reg1
 851  *    ... some instructions ...
 852  *    jmpq *(%reg1,%reg2,8)
 853  *
 854  *    This is a fairly uncommon pattern which is new for GCC 6.  As of this
 855  *    writing, there are 11 occurrences of it in the allmodconfig kernel.
 856  *
 857  *    As of GCC 7 there are quite a few more of these and the 'in between' code
 858  *    is significant. Esp. with KASAN enabled some of the code between the mov
 859  *    and jmpq uses .rodata itself, which can confuse things.
 860  *
 861  *    TODO: Once we have DWARF CFI and smarter instruction decoding logic,
 862  *    ensure the same register is used in the mov and jump instructions.
 863  *
 864  *    NOTE: RETPOLINE made it harder still to decode dynamic jumps.
 865  */
 866 static struct rela *find_switch_table(struct objtool_file *file,
 867                                       struct symbol *func,
 868                                       struct instruction *insn)
 869 {
 870         struct rela *text_rela, *rodata_rela;
 871         struct instruction *orig_insn = insn;
 872
 873         text_rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len);
 874         if (text_rela && text_rela->sym == file->rodata->sym) {
 875                 /* case 1 */
 876                 rodata_rela = find_rela_by_dest(file->rodata,
 877                                                 text_rela->addend);
 878                 if (rodata_rela)
 879                         return rodata_rela;
 880
 881                 /* case 2 */
 882                 rodata_rela = find_rela_by_dest(file->rodata,
 883                                                 text_rela->addend + 4);
 884                 if (!rodata_rela)
 885                         return NULL;
 886
 887                 file->ignore_unreachables = true;
 888                 return rodata_rela;
 889         }
 890
 891         /* case 3 */
 892         /*
 893          * Backward search using the @first_jump_src links, these help avoid
 894          * much of the 'in between' code. Which avoids us getting confused by
 895          * it.
 896          */
 897         for (insn = list_prev_entry(insn, list);
 898
 899              &insn->list != &file->insn_list &&
 900              insn->sec == func->sec &&
 901              insn->offset >= func->offset;
 902
 903              insn = insn->first_jump_src ?: list_prev_entry(insn, list)) {
 904
 905                 if (insn->type == INSN_JUMP_DYNAMIC)
 906                         break;
 907
 908                 /* allow small jumps within the range */
 909                 if (insn->type == INSN_JUMP_UNCONDITIONAL &&
 910                     insn->jump_dest &&
 911                     (insn->jump_dest->offset <= insn->offset ||
 912                      insn->jump_dest->offset > orig_insn->offset))
 913                     break;
 914
 915                 /* look for a relocation which references .rodata */
 916                 text_rela = find_rela_by_dest_range(insn->sec, insn->offset,
 917                                                     insn->len);
 918                 if (!text_rela || text_rela->sym != file->rodata->sym)
 919                         continue;
 920
 921                 /*
 922                  * Make sure the .rodata address isn't associated with a
 923                  * symbol.  gcc jump tables are anonymous data.
 924                  */
 925                 if (find_symbol_containing(file->rodata, text_rela->addend))
 926                         continue;
 927
 928                 rodata_rela = find_rela_by_dest(file->rodata, text_rela->addend);
 929                 if (!rodata_rela)
 930                         continue;
 931
 932                 return rodata_rela;
 933         }
 934
 935         return NULL;
 936 }
 937
 938
 939 static int add_func_switch_tables(struct objtool_file *file,
 940                                   struct symbol *func)
 941 {
 942         struct instruction *insn, *last = NULL, *prev_jump = NULL;
 943         struct rela *rela, *prev_rela = NULL;
 944         int ret;
 945
 946         func_for_each_insn(file, func, insn) {
 947                 if (!last)
 948                         last = insn;
 949
 950                 /*
 951                  * Store back-pointers for unconditional forward jumps such
 952                  * that find_switch_table() can back-track using those and
 953                  * avoid some potentially confusing code.
 954                  */
 955                 if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest &&
 956                     insn->offset > last->offset &&
 957                     insn->jump_dest->offset > insn->offset &&
 958                     !insn->jump_dest->first_jump_src) {
 959
 960                         insn->jump_dest->first_jump_src = insn;
 961                         last = insn->jump_dest;
 962                 }
 963
 964                 if (insn->type != INSN_JUMP_DYNAMIC)
 965                         continue;
 966
 967                 rela = find_switch_table(file, func, insn);
 968                 if (!rela)
 969                         continue;
 970
 971                 /*
 972                  * We found a switch table, but we don't know yet how big it
 973                  * is.  Don't add it until we reach the end of the function or
 974                  * the beginning of another switch table in the same function.
 975                  */
 976                 if (prev_jump) {
 977                         ret = add_switch_table(file, func, prev_jump, prev_rela,
 978                                                rela);
 979                         if (ret)
 980                                 return ret;
 981                 }
 982
 983                 prev_jump = insn;
 984                 prev_rela = rela;
 985         }
 986
 987         if (prev_jump) {
 988                 ret = add_switch_table(file, func, prev_jump, prev_rela, NULL);
 989                 if (ret)
 990                         return ret;
 991         }
 992
 993         return 0;
 994 }
 995
 996 /*
 997  * For some switch statements, gcc generates a jump table in the .rodata
 998  * section which contains a list of addresses within the function to jump to.
 999  * This finds these jump tables and adds them to the insn->alts lists.
1000  */
1001 static int add_switch_table_alts(struct objtool_file *file)
1002 {
1003         struct section *sec;
1004         struct symbol *func;
1005         int ret;
1006
1007         if (!file->rodata || !file->rodata->rela)
1008                 return 0;
1009
1010         for_each_sec(file, sec) {
1011                 list_for_each_entry(func, &sec->symbol_list, list) {
1012                         if (func->type != STT_FUNC)
1013                                 continue;
1014
1015                         ret = add_func_switch_tables(file, func);
1016                         if (ret)
1017                                 return ret;
1018                 }
1019         }
1020
1021         return 0;
1022 }
1023
1024 static int read_unwind_hints(struct objtool_file *file)
1025 {
1026         struct section *sec, *relasec;
1027         struct rela *rela;
1028         struct unwind_hint *hint;
1029         struct instruction *insn;
1030         struct cfi_reg *cfa;
1031         int i;
1032
1033         sec = find_section_by_name(file->elf, ".discard.unwind_hints");
1034         if (!sec)
1035                 return 0;
1036
1037         relasec = sec->rela;
1038         if (!relasec) {
1039                 WARN("missing .rela.discard.unwind_hints section");
1040                 return -1;
1041         }
1042
1043         if (sec->len % sizeof(struct unwind_hint)) {
1044                 WARN("struct unwind_hint size mismatch");
1045                 return -1;
1046         }
1047
1048         file->hints = true;
1049
1050         for (i = 0; i < sec->len / sizeof(struct unwind_hint); i++) {
1051                 hint = (struct unwind_hint *)sec->data->d_buf + i;
1052
1053                 rela = find_rela_by_dest(sec, i * sizeof(*hint));
1054                 if (!rela) {
1055                         WARN("can't find rela for unwind_hints[%d]", i);
1056                         return -1;
1057                 }
1058
1059                 insn = find_insn(file, rela->sym->sec, rela->addend);
1060                 if (!insn) {
1061                         WARN("can't find insn for unwind_hints[%d]", i);
1062                         return -1;
1063                 }
1064
1065                 cfa = &insn->state.cfa;
1066
1067                 if (hint->type == UNWIND_HINT_TYPE_SAVE) {
1068                         insn->save = true;
1069                         continue;
1070
1071                 } else if (hint->type == UNWIND_HINT_TYPE_RESTORE) {
1072                         insn->restore = true;
1073                         insn->hint = true;
1074                         continue;
1075                 }
1076
1077                 insn->hint = true;
1078
1079                 switch (hint->sp_reg) {
1080                 case ORC_REG_UNDEFINED:
1081                         cfa->base = CFI_UNDEFINED;
1082                         break;
1083                 case ORC_REG_SP:
1084                         cfa->base = CFI_SP;
1085                         break;
1086                 case ORC_REG_BP:
1087                         cfa->base = CFI_BP;
1088                         break;
1089                 case ORC_REG_SP_INDIRECT:
1090                         cfa->base = CFI_SP_INDIRECT;
1091                         break;
1092                 case ORC_REG_R10:
1093                         cfa->base = CFI_R10;
1094                         break;
1095                 case ORC_REG_R13:
1096                         cfa->base = CFI_R13;
1097                         break;
1098                 case ORC_REG_DI:
1099                         cfa->base = CFI_DI;
1100                         break;
1101                 case ORC_REG_DX:
1102                         cfa->base = CFI_DX;
1103                         break;
1104                 default:
1105                         WARN_FUNC("unsupported unwind_hint sp base reg %d",
1106                                   insn->sec, insn->offset, hint->sp_reg);
1107                         return -1;
1108                 }
1109
1110                 cfa->offset = hint->sp_offset;
1111                 insn->state.type = hint->type;
1112         }
1113
1114         return 0;
1115 }
1116
1117 static int read_retpoline_hints(struct objtool_file *file)
1118 {
1119         struct section *sec;
1120         struct instruction *insn;
1121         struct rela *rela;
1122
1123         sec = find_section_by_name(file->elf, ".rela.discard.retpoline_safe");
1124         if (!sec)
1125                 return 0;
1126
1127         list_for_each_entry(rela, &sec->rela_list, list) {
1128                 if (rela->sym->type != STT_SECTION) {
1129                         WARN("unexpected relocation symbol type in %s", sec->name);
1130                         return -1;
1131                 }
1132
1133                 insn = find_insn(file, rela->sym->sec, rela->addend);
1134                 if (!insn) {
1135                         WARN("bad .discard.retpoline_safe entry");
1136                         return -1;
1137                 }
1138
1139                 if (insn->type != INSN_JUMP_DYNAMIC &&
1140                     insn->type != INSN_CALL_DYNAMIC) {
1141                         WARN_FUNC("retpoline_safe hint not an indirect jump/call",
1142                                   insn->sec, insn->offset);
1143                         return -1;
1144                 }
1145
1146                 insn->retpoline_safe = true;
1147         }
1148
1149         return 0;
1150 }
1151
1152 static int decode_sections(struct objtool_file *file)
1153 {
1154         int ret;
1155
1156         ret = decode_instructions(file);
1157         if (ret)
1158                 return ret;
1159
1160         ret = add_dead_ends(file);
1161         if (ret)
1162                 return ret;
1163
1164         add_ignores(file);
1165
1166         ret = add_nospec_ignores(file);
1167         if (ret)
1168                 return ret;
1169
1170         ret = add_jump_destinations(file);
1171         if (ret)
1172                 return ret;
1173
1174         ret = add_special_section_alts(file);
1175         if (ret)
1176                 return ret;
1177
1178         ret = add_call_destinations(file);
1179         if (ret)
1180                 return ret;
1181
1182         ret = add_switch_table_alts(file);
1183         if (ret)
1184                 return ret;
1185
1186         ret = read_unwind_hints(file);
1187         if (ret)
1188                 return ret;
1189
1190         ret = read_retpoline_hints(file);
1191         if (ret)
1192                 return ret;
1193
1194         return 0;
1195 }
1196
1197 static bool is_fentry_call(struct instruction *insn)
1198 {
1199         if (insn->type == INSN_CALL &&
1200             insn->call_dest->type == STT_NOTYPE &&
1201             !strcmp(insn->call_dest->name, "__fentry__"))
1202                 return true;
1203
1204         return false;
1205 }
1206
1207 static bool has_modified_stack_frame(struct insn_state *state)
1208 {
1209         int i;
1210
1211         if (state->cfa.base != initial_func_cfi.cfa.base ||
1212             state->cfa.offset != initial_func_cfi.cfa.offset ||
1213             state->stack_size != initial_func_cfi.cfa.offset ||
1214             state->drap)
1215                 return true;
1216
1217         for (i = 0; i < CFI_NUM_REGS; i++)
1218                 if (state->regs[i].base != initial_func_cfi.regs[i].base ||
1219                     state->regs[i].offset != initial_func_cfi.regs[i].offset)
1220                         return true;
1221
1222         return false;
1223 }
1224
1225 static bool has_valid_stack_frame(struct insn_state *state)
1226 {
1227         if (state->cfa.base == CFI_BP && state->regs[CFI_BP].base == CFI_CFA &&
1228             state->regs[CFI_BP].offset == -16)
1229                 return true;
1230
1231         if (state->drap && state->regs[CFI_BP].base == CFI_BP)
1232                 return true;
1233
1234         return false;
1235 }
1236
1237 static int update_insn_state_regs(struct instruction *insn, struct insn_state *state)
1238 {
1239         struct cfi_reg *cfa = &state->cfa;
1240         struct stack_op *op = &insn->stack_op;
1241
1242         if (cfa->base != CFI_SP)
1243                 return 0;
1244
1245         /* push */
1246         if (op->dest.type == OP_DEST_PUSH)
1247                 cfa->offset += 8;
1248
1249         /* pop */
1250         if (op->src.type == OP_SRC_POP)
1251                 cfa->offset -= 8;
1252
1253         /* add immediate to sp */
1254         if (op->dest.type == OP_DEST_REG && op->src.type == OP_SRC_ADD &&
1255             op->dest.reg == CFI_SP && op->src.reg == CFI_SP)
1256                 cfa->offset -= op->src.offset;
1257
1258         return 0;
1259 }
1260
1261 static void save_reg(struct insn_state *state, unsigned char reg, int base,
1262                      int offset)
1263 {
1264         if (arch_callee_saved_reg(reg) &&
1265             state->regs[reg].base == CFI_UNDEFINED) {
1266                 state->regs[reg].base = base;
1267                 state->regs[reg].offset = offset;
1268         }
1269 }
1270
1271 static void restore_reg(struct insn_state *state, unsigned char reg)
1272 {
1273         state->regs[reg].base = CFI_UNDEFINED;
1274         state->regs[reg].offset = 0;
1275 }
1276
1277 /*
1278  * A note about DRAP stack alignment:
1279  *
1280  * GCC has the concept of a DRAP register, which is used to help keep track of
1281  * the stack pointer when aligning the stack.  r10 or r13 is used as the DRAP
1282  * register.  The typical DRAP pattern is:
1283  *
1284  *   4c 8d 54 24 08             lea    0x8(%rsp),%r10
1285  *   48 83 e4 c0                and    $0xffffffffffffffc0,%rsp
1286  *   41 ff 72 f8                pushq  -0x8(%r10)
1287  *   55                         push   %rbp
1288  *   48 89 e5                   mov    %rsp,%rbp
1289  *                              (more pushes)
1290  *   41 52                      push   %r10
1291  *                              ...
1292  *   41 5a                      pop    %r10
1293  *                              (more pops)
1294  *   5d                         pop    %rbp
1295  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1296  *   c3                         retq
1297  *
1298  * There are some variations in the epilogues, like:
1299  *
1300  *   5b                         pop    %rbx
1301  *   41 5a                      pop    %r10
1302  *   41 5c                      pop    %r12
1303  *   41 5d                      pop    %r13
1304  *   41 5e                      pop    %r14
1305  *   c9                         leaveq
1306  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1307  *   c3                         retq
1308  *
1309  * and:
1310  *
1311  *   4c 8b 55 e8                mov    -0x18(%rbp),%r10
1312  *   48 8b 5d e0                mov    -0x20(%rbp),%rbx
1313  *   4c 8b 65 f0                mov    -0x10(%rbp),%r12
1314  *   4c 8b 6d f8                mov    -0x8(%rbp),%r13
1315  *   c9                         leaveq
1316  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1317  *   c3                         retq
1318  *
1319  * Sometimes r13 is used as the DRAP register, in which case it's saved and
1320  * restored beforehand:
1321  *
1322  *   41 55                      push   %r13
1323  *   4c 8d 6c 24 10             lea    0x10(%rsp),%r13
1324  *   48 83 e4 f0                and    $0xfffffffffffffff0,%rsp
1325  *                              ...
1326  *   49 8d 65 f0                lea    -0x10(%r13),%rsp
1327  *   41 5d                      pop    %r13
1328  *   c3                         retq
1329  */
1330 static int update_insn_state(struct instruction *insn, struct insn_state *state)
1331 {
1332         struct stack_op *op = &insn->stack_op;
1333         struct cfi_reg *cfa = &state->cfa;
1334         struct cfi_reg *regs = state->regs;
1335
1336         /* stack operations don't make sense with an undefined CFA */
1337         if (cfa->base == CFI_UNDEFINED) {
1338                 if (insn->func) {
1339                         WARN_FUNC("undefined stack state", insn->sec, insn->offset);
1340                         return -1;
1341                 }
1342                 return 0;
1343         }
1344
1345         if (state->type == ORC_TYPE_REGS || state->type == ORC_TYPE_REGS_IRET)
1346                 return update_insn_state_regs(insn, state);
1347
1348         switch (op->dest.type) {
1349
1350         case OP_DEST_REG:
1351                 switch (op->src.type) {
1352
1353                 case OP_SRC_REG:
1354                         if (op->src.reg == CFI_SP && op->dest.reg == CFI_BP &&
1355                             cfa->base == CFI_SP &&
1356                             regs[CFI_BP].base == CFI_CFA &&
1357                             regs[CFI_BP].offset == -cfa->offset) {
1358
1359                                 /* mov %rsp, %rbp */
1360                                 cfa->base = op->dest.reg;
1361                                 state->bp_scratch = false;
1362                         }
1363
1364                         else if (op->src.reg == CFI_SP &&
1365                                  op->dest.reg == CFI_BP && state->drap) {
1366
1367                                 /* drap: mov %rsp, %rbp */
1368                                 regs[CFI_BP].base = CFI_BP;
1369                                 regs[CFI_BP].offset = -state->stack_size;
1370                                 state->bp_scratch = false;
1371                         }
1372
1373                         else if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1374
1375                                 /*
1376                                  * mov %rsp, %reg
1377                                  *
1378                                  * This is needed for the rare case where GCC
1379                                  * does:
1380                                  *
1381                                  *   mov    %rsp, %rax
1382                                  *   ...
1383                                  *   mov    %rax, %rsp
1384                                  */
1385                                 state->vals[op->dest.reg].base = CFI_CFA;
1386                                 state->vals[op->dest.reg].offset = -state->stack_size;
1387                         }
1388
1389                         else if (op->dest.reg == cfa->base) {
1390
1391                                 /* mov %reg, %rsp */
1392                                 if (cfa->base == CFI_SP &&
1393                                     state->vals[op->src.reg].base == CFI_CFA) {
1394
1395                                         /*
1396                                          * This is needed for the rare case
1397                                          * where GCC does something dumb like:
1398                                          *
1399                                          *   lea    0x8(%rsp), %rcx
1400                                          *   ...
1401                                          *   mov    %rcx, %rsp
1402                                          */
1403                                         cfa->offset = -state->vals[op->src.reg].offset;
1404                                         state->stack_size = cfa->offset;
1405
1406                                 } else {
1407                                         cfa->base = CFI_UNDEFINED;
1408                                         cfa->offset = 0;
1409                                 }
1410                         }
1411
1412                         break;
1413
1414                 case OP_SRC_ADD:
1415                         if (op->dest.reg == CFI_SP && op->src.reg == CFI_SP) {
1416
1417                                 /* add imm, %rsp */
1418                                 state->stack_size -= op->src.offset;
1419                                 if (cfa->base == CFI_SP)
1420                                         cfa->offset -= op->src.offset;
1421                                 break;
1422                         }
1423
1424                         if (op->dest.reg == CFI_SP && op->src.reg == CFI_BP) {
1425
1426                                 /* lea disp(%rbp), %rsp */
1427                                 state->stack_size = -(op->src.offset + regs[CFI_BP].offset);
1428                                 break;
1429                         }
1430
1431                         if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1432
1433                                 /* drap: lea disp(%rsp), %drap */
1434                                 state->drap_reg = op->dest.reg;
1435
1436                                 /*
1437                                  * lea disp(%rsp), %reg
1438                                  *
1439                                  * This is needed for the rare case where GCC
1440                                  * does something dumb like:
1441                                  *
1442                                  *   lea    0x8(%rsp), %rcx
1443                                  *   ...
1444                                  *   mov    %rcx, %rsp
1445                                  */
1446                                 state->vals[op->dest.reg].base = CFI_CFA;
1447                                 state->vals[op->dest.reg].offset = \
1448                                         -state->stack_size + op->src.offset;
1449
1450                                 break;
1451                         }
1452
1453                         if (state->drap && op->dest.reg == CFI_SP &&
1454                             op->src.reg == state->drap_reg) {
1455
1456                                  /* drap: lea disp(%drap), %rsp */
1457                                 cfa->base = CFI_SP;
1458                                 cfa->offset = state->stack_size = -op->src.offset;
1459                                 state->drap_reg = CFI_UNDEFINED;
1460                                 state->drap = false;
1461                                 break;
1462                         }
1463
1464                         if (op->dest.reg == state->cfa.base) {
1465                                 WARN_FUNC("unsupported stack register modification",
1466                                           insn->sec, insn->offset);
1467                                 return -1;
1468                         }
1469
1470                         break;
1471
1472                 case OP_SRC_AND:
1473                         if (op->dest.reg != CFI_SP ||
1474                             (state->drap_reg != CFI_UNDEFINED && cfa->base != CFI_SP) ||
1475                             (state->drap_reg == CFI_UNDEFINED && cfa->base != CFI_BP)) {
1476                                 WARN_FUNC("unsupported stack pointer realignment",
1477                                           insn->sec, insn->offset);
1478                                 return -1;
1479                         }
1480
1481                         if (state->drap_reg != CFI_UNDEFINED) {
1482                                 /* drap: and imm, %rsp */
1483                                 cfa->base = state->drap_reg;
1484                                 cfa->offset = state->stack_size = 0;
1485                                 state->drap = true;
1486                         }
1487
1488                         /*
1489                          * Older versions of GCC (4.8ish) realign the stack
1490                          * without DRAP, with a frame pointer.
1491                          */
1492
1493                         break;
1494
1495                 case OP_SRC_POP:
1496                         if (!state->drap && op->dest.type == OP_DEST_REG &&
1497                             op->dest.reg == cfa->base) {
1498
1499                                 /* pop %rbp */
1500                                 cfa->base = CFI_SP;
1501                         }
1502
1503                         if (state->drap && cfa->base == CFI_BP_INDIRECT &&
1504                             op->dest.type == OP_DEST_REG &&
1505                             op->dest.reg == state->drap_reg &&
1506                             state->drap_offset == -state->stack_size) {
1507
1508                                 /* drap: pop %drap */
1509                                 cfa->base = state->drap_reg;
1510                                 cfa->offset = 0;
1511                                 state->drap_offset = -1;
1512
1513                         } else if (regs[op->dest.reg].offset == -state->stack_size) {
1514
1515                                 /* pop %reg */
1516                                 restore_reg(state, op->dest.reg);
1517                         }
1518
1519                         state->stack_size -= 8;
1520                         if (cfa->base == CFI_SP)
1521                                 cfa->offset -= 8;
1522
1523                         break;
1524
1525                 case OP_SRC_REG_INDIRECT:
1526                         if (state->drap && op->src.reg == CFI_BP &&
1527                             op->src.offset == state->drap_offset) {
1528
1529                                 /* drap: mov disp(%rbp), %drap */
1530                                 cfa->base = state->drap_reg;
1531                                 cfa->offset = 0;
1532                                 state->drap_offset = -1;
1533                         }
1534
1535                         if (state->drap && op->src.reg == CFI_BP &&
1536                             op->src.offset == regs[op->dest.reg].offset) {
1537
1538                                 /* drap: mov disp(%rbp), %reg */
1539                                 restore_reg(state, op->dest.reg);
1540
1541                         } else if (op->src.reg == cfa->base &&
1542                             op->src.offset == regs[op->dest.reg].offset + cfa->offset) {
1543
1544                                 /* mov disp(%rbp), %reg */
1545                                 /* mov disp(%rsp), %reg */
1546                                 restore_reg(state, op->dest.reg);
1547                         }
1548
1549                         break;
1550
1551                 default:
1552                         WARN_FUNC("unknown stack-related instruction",
1553                                   insn->sec, insn->offset);
1554                         return -1;
1555                 }
1556
1557                 break;
1558
1559         case OP_DEST_PUSH:
1560                 state->stack_size += 8;
1561                 if (cfa->base == CFI_SP)
1562                         cfa->offset += 8;
1563
1564                 if (op->src.type != OP_SRC_REG)
1565                         break;
1566
1567                 if (state->drap) {
1568                         if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1569
1570                                 /* drap: push %drap */
1571                                 cfa->base = CFI_BP_INDIRECT;
1572                                 cfa->offset = -state->stack_size;
1573
1574                                 /* save drap so we know when to restore it */
1575                                 state->drap_offset = -state->stack_size;
1576
1577                         } else if (op->src.reg == CFI_BP && cfa->base == state->drap_reg) {
1578
1579                                 /* drap: push %rbp */
1580                                 state->stack_size = 0;
1581
1582                         } else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1583
1584                                 /* drap: push %reg */
1585                                 save_reg(state, op->src.reg, CFI_BP, -state->stack_size);
1586                         }
1587
1588                 } else {
1589
1590                         /* push %reg */
1591                         save_reg(state, op->src.reg, CFI_CFA, -state->stack_size);
1592                 }
1593
1594                 /* detect when asm code uses rbp as a scratch register */
1595                 if (!no_fp && insn->func && op->src.reg == CFI_BP &&
1596                     cfa->base != CFI_BP)
1597                         state->bp_scratch = true;
1598                 break;
1599
1600         case OP_DEST_REG_INDIRECT:
1601
1602                 if (state->drap) {
1603                         if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1604
1605                                 /* drap: mov %drap, disp(%rbp) */
1606                                 cfa->base = CFI_BP_INDIRECT;
1607                                 cfa->offset = op->dest.offset;
1608
1609                                 /* save drap offset so we know when to restore it */
1610                                 state->drap_offset = op->dest.offset;
1611                         }
1612
1613                         else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1614
1615                                 /* drap: mov reg, disp(%rbp) */
1616                                 save_reg(state, op->src.reg, CFI_BP, op->dest.offset);
1617                         }
1618
1619                 } else if (op->dest.reg == cfa->base) {
1620
1621                         /* mov reg, disp(%rbp) */
1622                         /* mov reg, disp(%rsp) */
1623                         save_reg(state, op->src.reg, CFI_CFA,
1624                                  op->dest.offset - state->cfa.offset);
1625                 }
1626
1627                 break;
1628
1629         case OP_DEST_LEAVE:
1630                 if ((!state->drap && cfa->base != CFI_BP) ||
1631                     (state->drap && cfa->base != state->drap_reg)) {
1632                         WARN_FUNC("leave instruction with modified stack frame",
1633                                   insn->sec, insn->offset);
1634                         return -1;
1635                 }
1636
1637                 /* leave (mov %rbp, %rsp; pop %rbp) */
1638
1639                 state->stack_size = -state->regs[CFI_BP].offset - 8;
1640                 restore_reg(state, CFI_BP);
1641
1642                 if (!state->drap) {
1643                         cfa->base = CFI_SP;
1644                         cfa->offset -= 8;
1645                 }
1646
1647                 break;
1648
1649         case OP_DEST_MEM:
1650                 if (op->src.type != OP_SRC_POP) {
1651                         WARN_FUNC("unknown stack-related memory operation",
1652                                   insn->sec, insn->offset);
1653                         return -1;
1654                 }
1655
1656                 /* pop mem */
1657                 state->stack_size -= 8;
1658                 if (cfa->base == CFI_SP)
1659                         cfa->offset -= 8;
1660
1661                 break;
1662
1663         default:
1664                 WARN_FUNC("unknown stack-related instruction",
1665                           insn->sec, insn->offset);
1666                 return -1;
1667         }
1668
1669         return 0;
1670 }
1671
1672 static bool insn_state_match(struct instruction *insn, struct insn_state *state)
1673 {
1674         struct insn_state *state1 = &insn->state, *state2 = state;
1675         int i;
1676
1677         if (memcmp(&state1->cfa, &state2->cfa, sizeof(state1->cfa))) {
1678                 WARN_FUNC("stack state mismatch: cfa1=%d%+d cfa2=%d%+d",
1679                           insn->sec, insn->offset,
1680                           state1->cfa.base, state1->cfa.offset,
1681                           state2->cfa.base, state2->cfa.offset);
1682
1683         } else if (memcmp(&state1->regs, &state2->regs, sizeof(state1->regs))) {
1684                 for (i = 0; i < CFI_NUM_REGS; i++) {
1685                         if (!memcmp(&state1->regs[i], &state2->regs[i],
1686                                     sizeof(struct cfi_reg)))
1687                                 continue;
1688
1689                         WARN_FUNC("stack state mismatch: reg1[%d]=%d%+d reg2[%d]=%d%+d",
1690                                   insn->sec, insn->offset,
1691                                   i, state1->regs[i].base, state1->regs[i].offset,
1692                                   i, state2->regs[i].base, state2->regs[i].offset);
1693                         break;
1694                 }
1695
1696         } else if (state1->type != state2->type) {
1697                 WARN_FUNC("stack state mismatch: type1=%d type2=%d",
1698                           insn->sec, insn->offset, state1->type, state2->type);
1699
1700         } else if (state1->drap != state2->drap ||
1701                  (state1->drap && state1->drap_reg != state2->drap_reg) ||
1702                  (state1->drap && state1->drap_offset != state2->drap_offset)) {
1703                 WARN_FUNC("stack state mismatch: drap1=%d(%d,%d) drap2=%d(%d,%d)",
1704                           insn->sec, insn->offset,
1705                           state1->drap, state1->drap_reg, state1->drap_offset,
1706                           state2->drap, state2->drap_reg, state2->drap_offset);
1707
1708         } else
1709                 return true;
1710
1711         return false;
1712 }
1713
1714 /*
1715  * Follow the branch starting at the given instruction, and recursively follow
1716  * any other branches (jumps).  Meanwhile, track the frame pointer state at
1717  * each instruction and validate all the rules described in
1718  * tools/objtool/Documentation/stack-validation.txt.
1719  */
1720 static int validate_branch(struct objtool_file *file, struct instruction *first,
1721                            struct insn_state state)
1722 {
1723         struct alternative *alt;
1724         struct instruction *insn, *next_insn;
1725         struct section *sec;
1726         struct symbol *func = NULL;
1727         int ret;
1728
1729         insn = first;
1730         sec = insn->sec;
1731
1732         if (insn->alt_group && list_empty(&insn->alts)) {
1733                 WARN_FUNC("don't know how to handle branch to middle of alternative instruction group",
1734                           sec, insn->offset);
1735                 return 1;
1736         }
1737
1738         while (1) {
1739                 next_insn = next_insn_same_sec(file, insn);
1740
1741
1742                 if (file->c_file && func && insn->func && func != insn->func) {
1743                         WARN("%s() falls through to next function %s()",
1744                              func->name, insn->func->name);
1745                         return 1;
1746                 }
1747
1748                 if (insn->func)
1749                         func = insn->func;
1750
1751                 if (func && insn->ignore) {
1752                         WARN_FUNC("BUG: why am I validating an ignored function?",
1753                                   sec, insn->offset);
1754                         return 1;
1755                 }
1756
1757                 if (insn->visited) {
1758                         if (!insn->hint && !insn_state_match(insn, &state))
1759                                 return 1;
1760
1761                         return 0;
1762                 }
1763
1764                 if (insn->hint) {
1765                         if (insn->restore) {
1766                                 struct instruction *save_insn, *i;
1767
1768                                 i = insn;
1769                                 save_insn = NULL;
1770                                 func_for_each_insn_continue_reverse(file, func, i) {
1771                                         if (i->save) {
1772                                                 save_insn = i;
1773                                                 break;
1774                                         }
1775                                 }
1776
1777                                 if (!save_insn) {
1778                                         WARN_FUNC("no corresponding CFI save for CFI restore",
1779                                                   sec, insn->offset);
1780                                         return 1;
1781                                 }
1782
1783                                 if (!save_insn->visited) {
1784                                         /*
1785                                          * Oops, no state to copy yet.
1786                                          * Hopefully we can reach this
1787                                          * instruction from another branch
1788                                          * after the save insn has been
1789                                          * visited.
1790                                          */
1791                                         if (insn == first)
1792                                                 return 0;
1793
1794                                         WARN_FUNC("objtool isn't smart enough to handle this CFI save/restore combo",
1795                                                   sec, insn->offset);
1796                                         return 1;
1797                                 }
1798
1799                                 insn->state = save_insn->state;
1800                         }
1801
1802                         state = insn->state;
1803
1804                 } else
1805                         insn->state = state;
1806
1807                 insn->visited = true;
1808
1809                 if (!insn->ignore_alts) {
1810                         list_for_each_entry(alt, &insn->alts, list) {
1811                                 ret = validate_branch(file, alt->insn, state);
1812                                 if (ret)
1813                                         return 1;
1814                         }
1815                 }
1816
1817                 switch (insn->type) {
1818
1819                 case INSN_RETURN:
1820                         if (func && has_modified_stack_frame(&state)) {
1821                                 WARN_FUNC("return with modified stack frame",
1822                                           sec, insn->offset);
1823                                 return 1;
1824                         }
1825
1826                         if (state.bp_scratch) {
1827                                 WARN("%s uses BP as a scratch register",
1828                                      insn->func->name);
1829                                 return 1;
1830                         }
1831
1832                         return 0;
1833
1834                 case INSN_CALL:
1835                         if (is_fentry_call(insn))
1836                                 break;
1837
1838                         ret = dead_end_function(file, insn->call_dest);
1839                         if (ret == 1)
1840                                 return 0;
1841                         if (ret == -1)
1842                                 return 1;
1843
1844                         /* fallthrough */
1845                 case INSN_CALL_DYNAMIC:
1846                         if (!no_fp && func && !has_valid_stack_frame(&state)) {
1847                                 WARN_FUNC("call without frame pointer save/setup",
1848                                           sec, insn->offset);
1849                                 return 1;
1850                         }
1851                         break;
1852
1853                 case INSN_JUMP_CONDITIONAL:
1854                 case INSN_JUMP_UNCONDITIONAL:
1855                         if (insn->jump_dest &&
1856                             (!func || !insn->jump_dest->func ||
1857                              func == insn->jump_dest->func)) {
1858                                 ret = validate_branch(file, insn->jump_dest,
1859                                                       state);
1860                                 if (ret)
1861                                         return 1;
1862
1863                         } else if (func && has_modified_stack_frame(&state)) {
1864                                 WARN_FUNC("sibling call from callable instruction with modified stack frame",
1865                                           sec, insn->offset);
1866                                 return 1;
1867                         }
1868
1869                         if (insn->type == INSN_JUMP_UNCONDITIONAL)
1870                                 return 0;
1871
1872                         break;
1873
1874                 case INSN_JUMP_DYNAMIC:
1875                         if (func && list_empty(&insn->alts) &&
1876                             has_modified_stack_frame(&state)) {
1877                                 WARN_FUNC("sibling call from callable instruction with modified stack frame",
1878                                           sec, insn->offset);
1879                                 return 1;
1880                         }
1881
1882                         return 0;
1883
1884                 case INSN_CONTEXT_SWITCH:
1885                         if (func && (!next_insn || !next_insn->hint)) {
1886                                 WARN_FUNC("unsupported instruction in callable function",
1887                                           sec, insn->offset);
1888                                 return 1;
1889                         }
1890                         return 0;
1891
1892                 case INSN_STACK:
1893                         if (update_insn_state(insn, &state))
1894                                 return 1;
1895
1896                         break;
1897
1898                 default:
1899                         break;
1900                 }
1901
1902                 if (insn->dead_end)
1903                         return 0;
1904
1905                 if (!next_insn) {
1906                         if (state.cfa.base == CFI_UNDEFINED)
1907                                 return 0;
1908                         WARN("%s: unexpected end of section", sec->name);
1909                         return 1;
1910                 }
1911
1912                 insn = next_insn;
1913         }
1914
1915         return 0;
1916 }
1917
1918 static int validate_unwind_hints(struct objtool_file *file)
1919 {
1920         struct instruction *insn;
1921         int ret, warnings = 0;
1922         struct insn_state state;
1923
1924         if (!file->hints)
1925                 return 0;
1926
1927         clear_insn_state(&state);
1928
1929         for_each_insn(file, insn) {
1930                 if (insn->hint && !insn->visited) {
1931                         ret = validate_branch(file, insn, state);
1932                         warnings += ret;
1933                 }
1934         }
1935
1936         return warnings;
1937 }
1938
1939 static int validate_retpoline(struct objtool_file *file)
1940 {
1941         struct instruction *insn;
1942         int warnings = 0;
1943
1944         for_each_insn(file, insn) {
1945                 if (insn->type != INSN_JUMP_DYNAMIC &&
1946                     insn->type != INSN_CALL_DYNAMIC)
1947                         continue;
1948
1949                 if (insn->retpoline_safe)
1950                         continue;
1951
1952                 /*
1953                  * .init.text code is ran before userspace and thus doesn't
1954                  * strictly need retpolines, except for modules which are
1955                  * loaded late, they very much do need retpoline in their
1956                  * .init.text
1957                  */
1958                 if (!strcmp(insn->sec->name, ".init.text") && !module)
1959                         continue;
1960
1961                 WARN_FUNC("indirect %s found in RETPOLINE build",
1962                           insn->sec, insn->offset,
1963                           insn->type == INSN_JUMP_DYNAMIC ? "jump" : "call");
1964
1965                 warnings++;
1966         }
1967
1968         return warnings;
1969 }
1970
1971 static bool is_kasan_insn(struct instruction *insn)
1972 {
1973         return (insn->type == INSN_CALL &&
1974                 !strcmp(insn->call_dest->name, "__asan_handle_no_return"));
1975 }
1976
1977 static bool is_ubsan_insn(struct instruction *insn)
1978 {
1979         return (insn->type == INSN_CALL &&
1980                 !strcmp(insn->call_dest->name,
1981                         "__ubsan_handle_builtin_unreachable"));
1982 }
1983
1984 static bool ignore_unreachable_insn(struct instruction *insn)
1985 {
1986         int i;
1987
1988         if (insn->ignore || insn->type == INSN_NOP)
1989                 return true;
1990
1991         /*
1992          * Ignore any unused exceptions.  This can happen when a whitelisted
1993          * function has an exception table entry.
1994          *
1995          * Also ignore alternative replacement instructions.  This can happen
1996          * when a whitelisted function uses one of the ALTERNATIVE macros.
1997          */
1998         if (!strcmp(insn->sec->name, ".fixup") ||
1999             !strcmp(insn->sec->name, ".altinstr_replacement") ||
2000             !strcmp(insn->sec->name, ".altinstr_aux"))
2001                 return true;
2002
2003         /*
2004          * Check if this (or a subsequent) instruction is related to
2005          * CONFIG_UBSAN or CONFIG_KASAN.
2006          *
2007          * End the search at 5 instructions to avoid going into the weeds.
2008          */
2009         if (!insn->func)
2010                 return false;
2011         for (i = 0; i < 5; i++) {
2012
2013                 if (is_kasan_insn(insn) || is_ubsan_insn(insn))
2014                         return true;
2015
2016                 if (insn->type == INSN_JUMP_UNCONDITIONAL) {
2017                         if (insn->jump_dest &&
2018                             insn->jump_dest->func == insn->func) {
2019                                 insn = insn->jump_dest;
2020                                 continue;
2021                         }
2022
2023                         break;
2024                 }
2025
2026                 if (insn->offset + insn->len >= insn->func->offset + insn->func->len)
2027                         break;
2028
2029                 insn = list_next_entry(insn, list);
2030         }
2031
2032         return false;
2033 }
2034
2035 static int validate_functions(struct objtool_file *file)
2036 {
2037         struct section *sec;
2038         struct symbol *func;
2039         struct instruction *insn;
2040         struct insn_state state;
2041         int ret, warnings = 0;
2042
2043         clear_insn_state(&state);
2044
2045         state.cfa = initial_func_cfi.cfa;
2046         memcpy(&state.regs, &initial_func_cfi.regs,
2047                CFI_NUM_REGS * sizeof(struct cfi_reg));
2048         state.stack_size = initial_func_cfi.cfa.offset;
2049
2050         for_each_sec(file, sec) {
2051                 list_for_each_entry(func, &sec->symbol_list, list) {
2052                         if (func->type != STT_FUNC)
2053                                 continue;
2054
2055                         insn = find_insn(file, sec, func->offset);
2056                         if (!insn || insn->ignore)
2057                                 continue;
2058
2059                         ret = validate_branch(file, insn, state);
2060                         warnings += ret;
2061                 }
2062         }
2063
2064         return warnings;
2065 }
2066
2067 static int validate_reachable_instructions(struct objtool_file *file)
2068 {
2069         struct instruction *insn;
2070
2071         if (file->ignore_unreachables)
2072                 return 0;
2073
2074         for_each_insn(file, insn) {
2075                 if (insn->visited || ignore_unreachable_insn(insn))
2076                         continue;
2077
2078                 WARN_FUNC("unreachable instruction", insn->sec, insn->offset);
2079                 return 1;
2080         }
2081
2082         return 0;
2083 }
2084
2085 static void cleanup(struct objtool_file *file)
2086 {
2087         struct instruction *insn, *tmpinsn;
2088         struct alternative *alt, *tmpalt;
2089
2090         list_for_each_entry_safe(insn, tmpinsn, &file->insn_list, list) {
2091                 list_for_each_entry_safe(alt, tmpalt, &insn->alts, list) {
2092                         list_del(&alt->list);
2093                         free(alt);
2094                 }
2095                 list_del(&insn->list);
2096                 hash_del(&insn->hash);
2097                 free(insn);
2098         }
2099         elf_close(file->elf);
2100 }
2101
2102 int check(const char *_objname, bool orc)
2103 {
2104         struct objtool_file file;
2105         int ret, warnings = 0;
2106
2107         objname = _objname;
2108
2109         file.elf = elf_open(objname, orc ? O_RDWR : O_RDONLY);
2110         if (!file.elf)
2111                 return 1;
2112
2113         INIT_LIST_HEAD(&file.insn_list);
2114         hash_init(file.insn_hash);
2115         file.whitelist = find_section_by_name(file.elf, ".discard.func_stack_frame_non_standard");
2116         file.rodata = find_section_by_name(file.elf, ".rodata");
2117         file.c_file = find_section_by_name(file.elf, ".comment");
2118         file.ignore_unreachables = no_unreachable;
2119         file.hints = false;
2120
2121         arch_initial_func_cfi_state(&initial_func_cfi);
2122
2123         ret = decode_sections(&file);
2124         if (ret < 0)
2125                 goto out;
2126         warnings += ret;
2127
2128         if (list_empty(&file.insn_list))
2129                 goto out;
2130
2131         if (retpoline) {
2132                 ret = validate_retpoline(&file);
2133                 if (ret < 0)
2134                         return ret;
2135                 warnings += ret;
2136         }
2137
2138         ret = validate_functions(&file);
2139         if (ret < 0)
2140                 goto out;
2141         warnings += ret;
2142
2143         ret = validate_unwind_hints(&file);
2144         if (ret < 0)
2145                 goto out;
2146         warnings += ret;
2147
2148         if (!warnings) {
2149                 ret = validate_reachable_instructions(&file);
2150                 if (ret < 0)
2151                         goto out;
2152                 warnings += ret;
2153         }
2154
2155         if (orc) {
2156                 ret = create_orc(&file);
2157                 if (ret < 0)
2158                         goto out;
2159
2160                 ret = create_orc_sections(&file);
2161                 if (ret < 0)
2162                         goto out;
2163
2164                 ret = elf_write(file.elf);
2165                 if (ret < 0)
2166                         goto out;
2167         }
2168
2169 out:
2170         cleanup(&file);
2171
2172         /* ignore warnings for now until we get all the code cleaned up */
2173         if (ret || warnings)
2174                 return 0;
2175         return 0;
2176 }