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 "check.h"
  22 #include "elf.h"
  23 #include "special.h"
  24 #include "arch.h"
  25 #include "warn.h"
  26
  27 #include <linux/hashtable.h>
  28 #include <linux/kernel.h>
  29
  30 struct alternative {
  31         struct list_head list;
  32         struct instruction *insn;
  33 };
  34
  35 const char *objname;
  36 static bool no_fp;
  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                         continue;
 501                 } else {
 502                         /* sibling call */
 503                         insn->jump_dest = 0;
 504                         continue;
 505                 }
 506
 507                 insn->jump_dest = find_insn(file, dest_sec, dest_off);
 508                 if (!insn->jump_dest) {
 509
 510                         /*
 511                          * This is a special case where an alt instruction
 512                          * jumps past the end of the section.  These are
 513                          * handled later in handle_group_alt().
 514                          */
 515                         if (!strcmp(insn->sec->name, ".altinstr_replacement"))
 516                                 continue;
 517
 518                         WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
 519                                   insn->sec, insn->offset, dest_sec->name,
 520                                   dest_off);
 521                         return -1;
 522                 }
 523         }
 524
 525         return 0;
 526 }
 527
 528 /*
 529  * Find the destination instructions for all calls.
 530  */
 531 static int add_call_destinations(struct objtool_file *file)
 532 {
 533         struct instruction *insn;
 534         unsigned long dest_off;
 535         struct rela *rela;
 536
 537         for_each_insn(file, insn) {
 538                 if (insn->type != INSN_CALL)
 539                         continue;
 540
 541                 rela = find_rela_by_dest_range(insn->sec, insn->offset,
 542                                                insn->len);
 543                 if (!rela) {
 544                         dest_off = insn->offset + insn->len + insn->immediate;
 545                         insn->call_dest = find_symbol_by_offset(insn->sec,
 546                                                                 dest_off);
 547
 548                         if (!insn->call_dest && !insn->ignore) {
 549                                 WARN_FUNC("unsupported intra-function call",
 550                                           insn->sec, insn->offset);
 551                                 WARN("If this is a retpoline, please patch it in with alternatives and annotate it with ANNOTATE_NOSPEC_ALTERNATIVE.");
 552                                 return -1;
 553                         }
 554
 555                 } else if (rela->sym->type == STT_SECTION) {
 556                         insn->call_dest = find_symbol_by_offset(rela->sym->sec,
 557                                                                 rela->addend+4);
 558                         if (!insn->call_dest ||
 559                             insn->call_dest->type != STT_FUNC) {
 560                                 WARN_FUNC("can't find call dest symbol at %s+0x%x",
 561                                           insn->sec, insn->offset,
 562                                           rela->sym->sec->name,
 563                                           rela->addend + 4);
 564                                 return -1;
 565                         }
 566                 } else
 567                         insn->call_dest = rela->sym;
 568         }
 569
 570         return 0;
 571 }
 572
 573 /*
 574  * The .alternatives section requires some extra special care, over and above
 575  * what other special sections require:
 576  *
 577  * 1. Because alternatives are patched in-place, we need to insert a fake jump
 578  *    instruction at the end so that validate_branch() skips all the original
 579  *    replaced instructions when validating the new instruction path.
 580  *
 581  * 2. An added wrinkle is that the new instruction length might be zero.  In
 582  *    that case the old instructions are replaced with noops.  We simulate that
 583  *    by creating a fake jump as the only new instruction.
 584  *
 585  * 3. In some cases, the alternative section includes an instruction which
 586  *    conditionally jumps to the _end_ of the entry.  We have to modify these
 587  *    jumps' destinations to point back to .text rather than the end of the
 588  *    entry in .altinstr_replacement.
 589  *
 590  * 4. It has been requested that we don't validate the !POPCNT feature path
 591  *    which is a "very very small percentage of machines".
 592  */
 593 static int handle_group_alt(struct objtool_file *file,
 594                             struct special_alt *special_alt,
 595                             struct instruction *orig_insn,
 596                             struct instruction **new_insn)
 597 {
 598         struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump = NULL;
 599         unsigned long dest_off;
 600
 601         last_orig_insn = NULL;
 602         insn = orig_insn;
 603         sec_for_each_insn_from(file, insn) {
 604                 if (insn->offset >= special_alt->orig_off + special_alt->orig_len)
 605                         break;
 606
 607                 if (special_alt->skip_orig)
 608                         insn->type = INSN_NOP;
 609
 610                 insn->alt_group = true;
 611                 last_orig_insn = insn;
 612         }
 613
 614         if (next_insn_same_sec(file, last_orig_insn)) {
 615                 fake_jump = malloc(sizeof(*fake_jump));
 616                 if (!fake_jump) {
 617                         WARN("malloc failed");
 618                         return -1;
 619                 }
 620                 memset(fake_jump, 0, sizeof(*fake_jump));
 621                 INIT_LIST_HEAD(&fake_jump->alts);
 622                 clear_insn_state(&fake_jump->state);
 623
 624                 fake_jump->sec = special_alt->new_sec;
 625                 fake_jump->offset = -1;
 626                 fake_jump->type = INSN_JUMP_UNCONDITIONAL;
 627                 fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
 628                 fake_jump->ignore = true;
 629         }
 630
 631         if (!special_alt->new_len) {
 632                 if (!fake_jump) {
 633                         WARN("%s: empty alternative at end of section",
 634                              special_alt->orig_sec->name);
 635                         return -1;
 636                 }
 637
 638                 *new_insn = fake_jump;
 639                 return 0;
 640         }
 641
 642         last_new_insn = NULL;
 643         insn = *new_insn;
 644         sec_for_each_insn_from(file, insn) {
 645                 if (insn->offset >= special_alt->new_off + special_alt->new_len)
 646                         break;
 647
 648                 last_new_insn = insn;
 649
 650                 insn->ignore = orig_insn->ignore_alts;
 651
 652                 if (insn->type != INSN_JUMP_CONDITIONAL &&
 653                     insn->type != INSN_JUMP_UNCONDITIONAL)
 654                         continue;
 655
 656                 if (!insn->immediate)
 657                         continue;
 658
 659                 dest_off = insn->offset + insn->len + insn->immediate;
 660                 if (dest_off == special_alt->new_off + special_alt->new_len) {
 661                         if (!fake_jump) {
 662                                 WARN("%s: alternative jump to end of section",
 663                                      special_alt->orig_sec->name);
 664                                 return -1;
 665                         }
 666                         insn->jump_dest = fake_jump;
 667                 }
 668
 669                 if (!insn->jump_dest) {
 670                         WARN_FUNC("can't find alternative jump destination",
 671                                   insn->sec, insn->offset);
 672                         return -1;
 673                 }
 674         }
 675
 676         if (!last_new_insn) {
 677                 WARN_FUNC("can't find last new alternative instruction",
 678                           special_alt->new_sec, special_alt->new_off);
 679                 return -1;
 680         }
 681
 682         if (fake_jump)
 683                 list_add(&fake_jump->list, &last_new_insn->list);
 684
 685         return 0;
 686 }
 687
 688 /*
 689  * A jump table entry can either convert a nop to a jump or a jump to a nop.
 690  * If the original instruction is a jump, make the alt entry an effective nop
 691  * by just skipping the original instruction.
 692  */
 693 static int handle_jump_alt(struct objtool_file *file,
 694                            struct special_alt *special_alt,
 695                            struct instruction *orig_insn,
 696                            struct instruction **new_insn)
 697 {
 698         if (orig_insn->type == INSN_NOP)
 699                 return 0;
 700
 701         if (orig_insn->type != INSN_JUMP_UNCONDITIONAL) {
 702                 WARN_FUNC("unsupported instruction at jump label",
 703                           orig_insn->sec, orig_insn->offset);
 704                 return -1;
 705         }
 706
 707         *new_insn = list_next_entry(orig_insn, list);
 708         return 0;
 709 }
 710
 711 /*
 712  * Read all the special sections which have alternate instructions which can be
 713  * patched in or redirected to at runtime.  Each instruction having alternate
 714  * instruction(s) has them added to its insn->alts list, which will be
 715  * traversed in validate_branch().
 716  */
 717 static int add_special_section_alts(struct objtool_file *file)
 718 {
 719         struct list_head special_alts;
 720         struct instruction *orig_insn, *new_insn;
 721         struct special_alt *special_alt, *tmp;
 722         struct alternative *alt;
 723         int ret;
 724
 725         ret = special_get_alts(file->elf, &special_alts);
 726         if (ret)
 727                 return ret;
 728
 729         list_for_each_entry_safe(special_alt, tmp, &special_alts, list) {
 730
 731                 orig_insn = find_insn(file, special_alt->orig_sec,
 732                                       special_alt->orig_off);
 733                 if (!orig_insn) {
 734                         WARN_FUNC("special: can't find orig instruction",
 735                                   special_alt->orig_sec, special_alt->orig_off);
 736                         ret = -1;
 737                         goto out;
 738                 }
 739
 740                 new_insn = NULL;
 741                 if (!special_alt->group || special_alt->new_len) {
 742                         new_insn = find_insn(file, special_alt->new_sec,
 743                                              special_alt->new_off);
 744                         if (!new_insn) {
 745                                 WARN_FUNC("special: can't find new instruction",
 746                                           special_alt->new_sec,
 747                                           special_alt->new_off);
 748                                 ret = -1;
 749                                 goto out;
 750                         }
 751                 }
 752
 753                 if (special_alt->group) {
 754                         ret = handle_group_alt(file, special_alt, orig_insn,
 755                                                &new_insn);
 756                         if (ret)
 757                                 goto out;
 758                 } else if (special_alt->jump_or_nop) {
 759                         ret = handle_jump_alt(file, special_alt, orig_insn,
 760                                               &new_insn);
 761                         if (ret)
 762                                 goto out;
 763                 }
 764
 765                 alt = malloc(sizeof(*alt));
 766                 if (!alt) {
 767                         WARN("malloc failed");
 768                         ret = -1;
 769                         goto out;
 770                 }
 771
 772                 alt->insn = new_insn;
 773                 list_add_tail(&alt->list, &orig_insn->alts);
 774
 775                 list_del(&special_alt->list);
 776                 free(special_alt);
 777         }
 778
 779 out:
 780         return ret;
 781 }
 782
 783 static int add_switch_table(struct objtool_file *file, struct symbol *func,
 784                             struct instruction *insn, struct rela *table,
 785                             struct rela *next_table)
 786 {
 787         struct rela *rela = table;
 788         struct instruction *alt_insn;
 789         struct alternative *alt;
 790
 791         list_for_each_entry_from(rela, &file->rodata->rela->rela_list, list) {
 792                 if (rela == next_table)
 793                         break;
 794
 795                 if (rela->sym->sec != insn->sec ||
 796                     rela->addend <= func->offset ||
 797                     rela->addend >= func->offset + func->len)
 798                         break;
 799
 800                 alt_insn = find_insn(file, insn->sec, rela->addend);
 801                 if (!alt_insn) {
 802                         WARN("%s: can't find instruction at %s+0x%x",
 803                              file->rodata->rela->name, insn->sec->name,
 804                              rela->addend);
 805                         return -1;
 806                 }
 807
 808                 alt = malloc(sizeof(*alt));
 809                 if (!alt) {
 810                         WARN("malloc failed");
 811                         return -1;
 812                 }
 813
 814                 alt->insn = alt_insn;
 815                 list_add_tail(&alt->list, &insn->alts);
 816         }
 817
 818         return 0;
 819 }
 820
 821 /*
 822  * find_switch_table() - Given a dynamic jump, find the switch jump table in
 823  * .rodata associated with it.
 824  *
 825  * There are 3 basic patterns:
 826  *
 827  * 1. jmpq *[rodata addr](,%reg,8)
 828  *
 829  *    This is the most common case by far.  It jumps to an address in a simple
 830  *    jump table which is stored in .rodata.
 831  *
 832  * 2. jmpq *[rodata addr](%rip)
 833  *
 834  *    This is caused by a rare GCC quirk, currently only seen in three driver
 835  *    functions in the kernel, only with certain obscure non-distro configs.
 836  *
 837  *    As part of an optimization, GCC makes a copy of an existing switch jump
 838  *    table, modifies it, and then hard-codes the jump (albeit with an indirect
 839  *    jump) to use a single entry in the table.  The rest of the jump table and
 840  *    some of its jump targets remain as dead code.
 841  *
 842  *    In such a case we can just crudely ignore all unreachable instruction
 843  *    warnings for the entire object file.  Ideally we would just ignore them
 844  *    for the function, but that would require redesigning the code quite a
 845  *    bit.  And honestly that's just not worth doing: unreachable instruction
 846  *    warnings are of questionable value anyway, and this is such a rare issue.
 847  *
 848  * 3. mov [rodata addr],%reg1
 849  *    ... some instructions ...
 850  *    jmpq *(%reg1,%reg2,8)
 851  *
 852  *    This is a fairly uncommon pattern which is new for GCC 6.  As of this
 853  *    writing, there are 11 occurrences of it in the allmodconfig kernel.
 854  *
 855  *    As of GCC 7 there are quite a few more of these and the 'in between' code
 856  *    is significant. Esp. with KASAN enabled some of the code between the mov
 857  *    and jmpq uses .rodata itself, which can confuse things.
 858  *
 859  *    TODO: Once we have DWARF CFI and smarter instruction decoding logic,
 860  *    ensure the same register is used in the mov and jump instructions.
 861  *
 862  *    NOTE: RETPOLINE made it harder still to decode dynamic jumps.
 863  */
 864 static struct rela *find_switch_table(struct objtool_file *file,
 865                                       struct symbol *func,
 866                                       struct instruction *insn)
 867 {
 868         struct rela *text_rela, *rodata_rela;
 869         struct instruction *orig_insn = insn;
 870
 871         text_rela = find_rela_by_dest_range(insn->sec, insn->offset, insn->len);
 872         if (text_rela && text_rela->sym == file->rodata->sym) {
 873                 /* case 1 */
 874                 rodata_rela = find_rela_by_dest(file->rodata,
 875                                                 text_rela->addend);
 876                 if (rodata_rela)
 877                         return rodata_rela;
 878
 879                 /* case 2 */
 880                 rodata_rela = find_rela_by_dest(file->rodata,
 881                                                 text_rela->addend + 4);
 882                 if (!rodata_rela)
 883                         return NULL;
 884
 885                 file->ignore_unreachables = true;
 886                 return rodata_rela;
 887         }
 888
 889         /* case 3 */
 890         /*
 891          * Backward search using the @first_jump_src links, these help avoid
 892          * much of the 'in between' code. Which avoids us getting confused by
 893          * it.
 894          */
 895         for (insn = list_prev_entry(insn, list);
 896
 897              &insn->list != &file->insn_list &&
 898              insn->sec == func->sec &&
 899              insn->offset >= func->offset;
 900
 901              insn = insn->first_jump_src ?: list_prev_entry(insn, list)) {
 902
 903                 if (insn->type == INSN_JUMP_DYNAMIC)
 904                         break;
 905
 906                 /* allow small jumps within the range */
 907                 if (insn->type == INSN_JUMP_UNCONDITIONAL &&
 908                     insn->jump_dest &&
 909                     (insn->jump_dest->offset <= insn->offset ||
 910                      insn->jump_dest->offset > orig_insn->offset))
 911                     break;
 912
 913                 /* look for a relocation which references .rodata */
 914                 text_rela = find_rela_by_dest_range(insn->sec, insn->offset,
 915                                                     insn->len);
 916                 if (!text_rela || text_rela->sym != file->rodata->sym)
 917                         continue;
 918
 919                 /*
 920                  * Make sure the .rodata address isn't associated with a
 921                  * symbol.  gcc jump tables are anonymous data.
 922                  */
 923                 if (find_symbol_containing(file->rodata, text_rela->addend))
 924                         continue;
 925
 926                 return find_rela_by_dest(file->rodata, text_rela->addend);
 927         }
 928
 929         return NULL;
 930 }
 931
 932
 933 static int add_func_switch_tables(struct objtool_file *file,
 934                                   struct symbol *func)
 935 {
 936         struct instruction *insn, *last = NULL, *prev_jump = NULL;
 937         struct rela *rela, *prev_rela = NULL;
 938         int ret;
 939
 940         func_for_each_insn(file, func, insn) {
 941                 if (!last)
 942                         last = insn;
 943
 944                 /*
 945                  * Store back-pointers for unconditional forward jumps such
 946                  * that find_switch_table() can back-track using those and
 947                  * avoid some potentially confusing code.
 948                  */
 949                 if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest &&
 950                     insn->offset > last->offset &&
 951                     insn->jump_dest->offset > insn->offset &&
 952                     !insn->jump_dest->first_jump_src) {
 953
 954                         insn->jump_dest->first_jump_src = insn;
 955                         last = insn->jump_dest;
 956                 }
 957
 958                 if (insn->type != INSN_JUMP_DYNAMIC)
 959                         continue;
 960
 961                 rela = find_switch_table(file, func, insn);
 962                 if (!rela)
 963                         continue;
 964
 965                 /*
 966                  * We found a switch table, but we don't know yet how big it
 967                  * is.  Don't add it until we reach the end of the function or
 968                  * the beginning of another switch table in the same function.
 969                  */
 970                 if (prev_jump) {
 971                         ret = add_switch_table(file, func, prev_jump, prev_rela,
 972                                                rela);
 973                         if (ret)
 974                                 return ret;
 975                 }
 976
 977                 prev_jump = insn;
 978                 prev_rela = rela;
 979         }
 980
 981         if (prev_jump) {
 982                 ret = add_switch_table(file, func, prev_jump, prev_rela, NULL);
 983                 if (ret)
 984                         return ret;
 985         }
 986
 987         return 0;
 988 }
 989
 990 /*
 991  * For some switch statements, gcc generates a jump table in the .rodata
 992  * section which contains a list of addresses within the function to jump to.
 993  * This finds these jump tables and adds them to the insn->alts lists.
 994  */
 995 static int add_switch_table_alts(struct objtool_file *file)
 996 {
 997         struct section *sec;
 998         struct symbol *func;
 999         int ret;
1000
1001         if (!file->rodata || !file->rodata->rela)
1002                 return 0;
1003
1004         for_each_sec(file, sec) {
1005                 list_for_each_entry(func, &sec->symbol_list, list) {
1006                         if (func->type != STT_FUNC)
1007                                 continue;
1008
1009                         ret = add_func_switch_tables(file, func);
1010                         if (ret)
1011                                 return ret;
1012                 }
1013         }
1014
1015         return 0;
1016 }
1017
1018 static int read_unwind_hints(struct objtool_file *file)
1019 {
1020         struct section *sec, *relasec;
1021         struct rela *rela;
1022         struct unwind_hint *hint;
1023         struct instruction *insn;
1024         struct cfi_reg *cfa;
1025         int i;
1026
1027         sec = find_section_by_name(file->elf, ".discard.unwind_hints");
1028         if (!sec)
1029                 return 0;
1030
1031         relasec = sec->rela;
1032         if (!relasec) {
1033                 WARN("missing .rela.discard.unwind_hints section");
1034                 return -1;
1035         }
1036
1037         if (sec->len % sizeof(struct unwind_hint)) {
1038                 WARN("struct unwind_hint size mismatch");
1039                 return -1;
1040         }
1041
1042         file->hints = true;
1043
1044         for (i = 0; i < sec->len / sizeof(struct unwind_hint); i++) {
1045                 hint = (struct unwind_hint *)sec->data->d_buf + i;
1046
1047                 rela = find_rela_by_dest(sec, i * sizeof(*hint));
1048                 if (!rela) {
1049                         WARN("can't find rela for unwind_hints[%d]", i);
1050                         return -1;
1051                 }
1052
1053                 insn = find_insn(file, rela->sym->sec, rela->addend);
1054                 if (!insn) {
1055                         WARN("can't find insn for unwind_hints[%d]", i);
1056                         return -1;
1057                 }
1058
1059                 cfa = &insn->state.cfa;
1060
1061                 if (hint->type == UNWIND_HINT_TYPE_SAVE) {
1062                         insn->save = true;
1063                         continue;
1064
1065                 } else if (hint->type == UNWIND_HINT_TYPE_RESTORE) {
1066                         insn->restore = true;
1067                         insn->hint = true;
1068                         continue;
1069                 }
1070
1071                 insn->hint = true;
1072
1073                 switch (hint->sp_reg) {
1074                 case ORC_REG_UNDEFINED:
1075                         cfa->base = CFI_UNDEFINED;
1076                         break;
1077                 case ORC_REG_SP:
1078                         cfa->base = CFI_SP;
1079                         break;
1080                 case ORC_REG_BP:
1081                         cfa->base = CFI_BP;
1082                         break;
1083                 case ORC_REG_SP_INDIRECT:
1084                         cfa->base = CFI_SP_INDIRECT;
1085                         break;
1086                 case ORC_REG_R10:
1087                         cfa->base = CFI_R10;
1088                         break;
1089                 case ORC_REG_R13:
1090                         cfa->base = CFI_R13;
1091                         break;
1092                 case ORC_REG_DI:
1093                         cfa->base = CFI_DI;
1094                         break;
1095                 case ORC_REG_DX:
1096                         cfa->base = CFI_DX;
1097                         break;
1098                 default:
1099                         WARN_FUNC("unsupported unwind_hint sp base reg %d",
1100                                   insn->sec, insn->offset, hint->sp_reg);
1101                         return -1;
1102                 }
1103
1104                 cfa->offset = hint->sp_offset;
1105                 insn->state.type = hint->type;
1106         }
1107
1108         return 0;
1109 }
1110
1111 static int decode_sections(struct objtool_file *file)
1112 {
1113         int ret;
1114
1115         ret = decode_instructions(file);
1116         if (ret)
1117                 return ret;
1118
1119         ret = add_dead_ends(file);
1120         if (ret)
1121                 return ret;
1122
1123         add_ignores(file);
1124
1125         ret = add_nospec_ignores(file);
1126         if (ret)
1127                 return ret;
1128
1129         ret = add_jump_destinations(file);
1130         if (ret)
1131                 return ret;
1132
1133         ret = add_special_section_alts(file);
1134         if (ret)
1135                 return ret;
1136
1137         ret = add_call_destinations(file);
1138         if (ret)
1139                 return ret;
1140
1141         ret = add_switch_table_alts(file);
1142         if (ret)
1143                 return ret;
1144
1145         ret = read_unwind_hints(file);
1146         if (ret)
1147                 return ret;
1148
1149         return 0;
1150 }
1151
1152 static bool is_fentry_call(struct instruction *insn)
1153 {
1154         if (insn->type == INSN_CALL &&
1155             insn->call_dest->type == STT_NOTYPE &&
1156             !strcmp(insn->call_dest->name, "__fentry__"))
1157                 return true;
1158
1159         return false;
1160 }
1161
1162 static bool has_modified_stack_frame(struct insn_state *state)
1163 {
1164         int i;
1165
1166         if (state->cfa.base != initial_func_cfi.cfa.base ||
1167             state->cfa.offset != initial_func_cfi.cfa.offset ||
1168             state->stack_size != initial_func_cfi.cfa.offset ||
1169             state->drap)
1170                 return true;
1171
1172         for (i = 0; i < CFI_NUM_REGS; i++)
1173                 if (state->regs[i].base != initial_func_cfi.regs[i].base ||
1174                     state->regs[i].offset != initial_func_cfi.regs[i].offset)
1175                         return true;
1176
1177         return false;
1178 }
1179
1180 static bool has_valid_stack_frame(struct insn_state *state)
1181 {
1182         if (state->cfa.base == CFI_BP && state->regs[CFI_BP].base == CFI_CFA &&
1183             state->regs[CFI_BP].offset == -16)
1184                 return true;
1185
1186         if (state->drap && state->regs[CFI_BP].base == CFI_BP)
1187                 return true;
1188
1189         return false;
1190 }
1191
1192 static int update_insn_state_regs(struct instruction *insn, struct insn_state *state)
1193 {
1194         struct cfi_reg *cfa = &state->cfa;
1195         struct stack_op *op = &insn->stack_op;
1196
1197         if (cfa->base != CFI_SP)
1198                 return 0;
1199
1200         /* push */
1201         if (op->dest.type == OP_DEST_PUSH)
1202                 cfa->offset += 8;
1203
1204         /* pop */
1205         if (op->src.type == OP_SRC_POP)
1206                 cfa->offset -= 8;
1207
1208         /* add immediate to sp */
1209         if (op->dest.type == OP_DEST_REG && op->src.type == OP_SRC_ADD &&
1210             op->dest.reg == CFI_SP && op->src.reg == CFI_SP)
1211                 cfa->offset -= op->src.offset;
1212
1213         return 0;
1214 }
1215
1216 static void save_reg(struct insn_state *state, unsigned char reg, int base,
1217                      int offset)
1218 {
1219         if (arch_callee_saved_reg(reg) &&
1220             state->regs[reg].base == CFI_UNDEFINED) {
1221                 state->regs[reg].base = base;
1222                 state->regs[reg].offset = offset;
1223         }
1224 }
1225
1226 static void restore_reg(struct insn_state *state, unsigned char reg)
1227 {
1228         state->regs[reg].base = CFI_UNDEFINED;
1229         state->regs[reg].offset = 0;
1230 }
1231
1232 /*
1233  * A note about DRAP stack alignment:
1234  *
1235  * GCC has the concept of a DRAP register, which is used to help keep track of
1236  * the stack pointer when aligning the stack.  r10 or r13 is used as the DRAP
1237  * register.  The typical DRAP pattern is:
1238  *
1239  *   4c 8d 54 24 08             lea    0x8(%rsp),%r10
1240  *   48 83 e4 c0                and    $0xffffffffffffffc0,%rsp
1241  *   41 ff 72 f8                pushq  -0x8(%r10)
1242  *   55                         push   %rbp
1243  *   48 89 e5                   mov    %rsp,%rbp
1244  *                              (more pushes)
1245  *   41 52                      push   %r10
1246  *                              ...
1247  *   41 5a                      pop    %r10
1248  *                              (more pops)
1249  *   5d                         pop    %rbp
1250  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1251  *   c3                         retq
1252  *
1253  * There are some variations in the epilogues, like:
1254  *
1255  *   5b                         pop    %rbx
1256  *   41 5a                      pop    %r10
1257  *   41 5c                      pop    %r12
1258  *   41 5d                      pop    %r13
1259  *   41 5e                      pop    %r14
1260  *   c9                         leaveq
1261  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1262  *   c3                         retq
1263  *
1264  * and:
1265  *
1266  *   4c 8b 55 e8                mov    -0x18(%rbp),%r10
1267  *   48 8b 5d e0                mov    -0x20(%rbp),%rbx
1268  *   4c 8b 65 f0                mov    -0x10(%rbp),%r12
1269  *   4c 8b 6d f8                mov    -0x8(%rbp),%r13
1270  *   c9                         leaveq
1271  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1272  *   c3                         retq
1273  *
1274  * Sometimes r13 is used as the DRAP register, in which case it's saved and
1275  * restored beforehand:
1276  *
1277  *   41 55                      push   %r13
1278  *   4c 8d 6c 24 10             lea    0x10(%rsp),%r13
1279  *   48 83 e4 f0                and    $0xfffffffffffffff0,%rsp
1280  *                              ...
1281  *   49 8d 65 f0                lea    -0x10(%r13),%rsp
1282  *   41 5d                      pop    %r13
1283  *   c3                         retq
1284  */
1285 static int update_insn_state(struct instruction *insn, struct insn_state *state)
1286 {
1287         struct stack_op *op = &insn->stack_op;
1288         struct cfi_reg *cfa = &state->cfa;
1289         struct cfi_reg *regs = state->regs;
1290
1291         /* stack operations don't make sense with an undefined CFA */
1292         if (cfa->base == CFI_UNDEFINED) {
1293                 if (insn->func) {
1294                         WARN_FUNC("undefined stack state", insn->sec, insn->offset);
1295                         return -1;
1296                 }
1297                 return 0;
1298         }
1299
1300         if (state->type == ORC_TYPE_REGS || state->type == ORC_TYPE_REGS_IRET)
1301                 return update_insn_state_regs(insn, state);
1302
1303         switch (op->dest.type) {
1304
1305         case OP_DEST_REG:
1306                 switch (op->src.type) {
1307
1308                 case OP_SRC_REG:
1309                         if (op->src.reg == CFI_SP && op->dest.reg == CFI_BP &&
1310                             cfa->base == CFI_SP &&
1311                             regs[CFI_BP].base == CFI_CFA &&
1312                             regs[CFI_BP].offset == -cfa->offset) {
1313
1314                                 /* mov %rsp, %rbp */
1315                                 cfa->base = op->dest.reg;
1316                                 state->bp_scratch = false;
1317                         }
1318
1319                         else if (op->src.reg == CFI_SP &&
1320                                  op->dest.reg == CFI_BP && state->drap) {
1321
1322                                 /* drap: mov %rsp, %rbp */
1323                                 regs[CFI_BP].base = CFI_BP;
1324                                 regs[CFI_BP].offset = -state->stack_size;
1325                                 state->bp_scratch = false;
1326                         }
1327
1328                         else if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1329
1330                                 /*
1331                                  * mov %rsp, %reg
1332                                  *
1333                                  * This is needed for the rare case where GCC
1334                                  * does:
1335                                  *
1336                                  *   mov    %rsp, %rax
1337                                  *   ...
1338                                  *   mov    %rax, %rsp
1339                                  */
1340                                 state->vals[op->dest.reg].base = CFI_CFA;
1341                                 state->vals[op->dest.reg].offset = -state->stack_size;
1342                         }
1343
1344                         else if (op->dest.reg == cfa->base) {
1345
1346                                 /* mov %reg, %rsp */
1347                                 if (cfa->base == CFI_SP &&
1348                                     state->vals[op->src.reg].base == CFI_CFA) {
1349
1350                                         /*
1351                                          * This is needed for the rare case
1352                                          * where GCC does something dumb like:
1353                                          *
1354                                          *   lea    0x8(%rsp), %rcx
1355                                          *   ...
1356                                          *   mov    %rcx, %rsp
1357                                          */
1358                                         cfa->offset = -state->vals[op->src.reg].offset;
1359                                         state->stack_size = cfa->offset;
1360
1361                                 } else {
1362                                         cfa->base = CFI_UNDEFINED;
1363                                         cfa->offset = 0;
1364                                 }
1365                         }
1366
1367                         break;
1368
1369                 case OP_SRC_ADD:
1370                         if (op->dest.reg == CFI_SP && op->src.reg == CFI_SP) {
1371
1372                                 /* add imm, %rsp */
1373                                 state->stack_size -= op->src.offset;
1374                                 if (cfa->base == CFI_SP)
1375                                         cfa->offset -= op->src.offset;
1376                                 break;
1377                         }
1378
1379                         if (op->dest.reg == CFI_SP && op->src.reg == CFI_BP) {
1380
1381                                 /* lea disp(%rbp), %rsp */
1382                                 state->stack_size = -(op->src.offset + regs[CFI_BP].offset);
1383                                 break;
1384                         }
1385
1386                         if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1387
1388                                 /* drap: lea disp(%rsp), %drap */
1389                                 state->drap_reg = op->dest.reg;
1390
1391                                 /*
1392                                  * lea disp(%rsp), %reg
1393                                  *
1394                                  * This is needed for the rare case where GCC
1395                                  * does something dumb like:
1396                                  *
1397                                  *   lea    0x8(%rsp), %rcx
1398                                  *   ...
1399                                  *   mov    %rcx, %rsp
1400                                  */
1401                                 state->vals[op->dest.reg].base = CFI_CFA;
1402                                 state->vals[op->dest.reg].offset = \
1403                                         -state->stack_size + op->src.offset;
1404
1405                                 break;
1406                         }
1407
1408                         if (state->drap && op->dest.reg == CFI_SP &&
1409                             op->src.reg == state->drap_reg) {
1410
1411                                  /* drap: lea disp(%drap), %rsp */
1412                                 cfa->base = CFI_SP;
1413                                 cfa->offset = state->stack_size = -op->src.offset;
1414                                 state->drap_reg = CFI_UNDEFINED;
1415                                 state->drap = false;
1416                                 break;
1417                         }
1418
1419                         if (op->dest.reg == state->cfa.base) {
1420                                 WARN_FUNC("unsupported stack register modification",
1421                                           insn->sec, insn->offset);
1422                                 return -1;
1423                         }
1424
1425                         break;
1426
1427                 case OP_SRC_AND:
1428                         if (op->dest.reg != CFI_SP ||
1429                             (state->drap_reg != CFI_UNDEFINED && cfa->base != CFI_SP) ||
1430                             (state->drap_reg == CFI_UNDEFINED && cfa->base != CFI_BP)) {
1431                                 WARN_FUNC("unsupported stack pointer realignment",
1432                                           insn->sec, insn->offset);
1433                                 return -1;
1434                         }
1435
1436                         if (state->drap_reg != CFI_UNDEFINED) {
1437                                 /* drap: and imm, %rsp */
1438                                 cfa->base = state->drap_reg;
1439                                 cfa->offset = state->stack_size = 0;
1440                                 state->drap = true;
1441                         }
1442
1443                         /*
1444                          * Older versions of GCC (4.8ish) realign the stack
1445                          * without DRAP, with a frame pointer.
1446                          */
1447
1448                         break;
1449
1450                 case OP_SRC_POP:
1451                         if (!state->drap && op->dest.type == OP_DEST_REG &&
1452                             op->dest.reg == cfa->base) {
1453
1454                                 /* pop %rbp */
1455                                 cfa->base = CFI_SP;
1456                         }
1457
1458                         if (state->drap && cfa->base == CFI_BP_INDIRECT &&
1459                             op->dest.type == OP_DEST_REG &&
1460                             op->dest.reg == state->drap_reg &&
1461                             state->drap_offset == -state->stack_size) {
1462
1463                                 /* drap: pop %drap */
1464                                 cfa->base = state->drap_reg;
1465                                 cfa->offset = 0;
1466                                 state->drap_offset = -1;
1467
1468                         } else if (regs[op->dest.reg].offset == -state->stack_size) {
1469
1470                                 /* pop %reg */
1471                                 restore_reg(state, op->dest.reg);
1472                         }
1473
1474                         state->stack_size -= 8;
1475                         if (cfa->base == CFI_SP)
1476                                 cfa->offset -= 8;
1477
1478                         break;
1479
1480                 case OP_SRC_REG_INDIRECT:
1481                         if (state->drap && op->src.reg == CFI_BP &&
1482                             op->src.offset == state->drap_offset) {
1483
1484                                 /* drap: mov disp(%rbp), %drap */
1485                                 cfa->base = state->drap_reg;
1486                                 cfa->offset = 0;
1487                                 state->drap_offset = -1;
1488                         }
1489
1490                         if (state->drap && op->src.reg == CFI_BP &&
1491                             op->src.offset == regs[op->dest.reg].offset) {
1492
1493                                 /* drap: mov disp(%rbp), %reg */
1494                                 restore_reg(state, op->dest.reg);
1495
1496                         } else if (op->src.reg == cfa->base &&
1497                             op->src.offset == regs[op->dest.reg].offset + cfa->offset) {
1498
1499                                 /* mov disp(%rbp), %reg */
1500                                 /* mov disp(%rsp), %reg */
1501                                 restore_reg(state, op->dest.reg);
1502                         }
1503
1504                         break;
1505
1506                 default:
1507                         WARN_FUNC("unknown stack-related instruction",
1508                                   insn->sec, insn->offset);
1509                         return -1;
1510                 }
1511
1512                 break;
1513
1514         case OP_DEST_PUSH:
1515                 state->stack_size += 8;
1516                 if (cfa->base == CFI_SP)
1517                         cfa->offset += 8;
1518
1519                 if (op->src.type != OP_SRC_REG)
1520                         break;
1521
1522                 if (state->drap) {
1523                         if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1524
1525                                 /* drap: push %drap */
1526                                 cfa->base = CFI_BP_INDIRECT;
1527                                 cfa->offset = -state->stack_size;
1528
1529                                 /* save drap so we know when to restore it */
1530                                 state->drap_offset = -state->stack_size;
1531
1532                         } else if (op->src.reg == CFI_BP && cfa->base == state->drap_reg) {
1533
1534                                 /* drap: push %rbp */
1535                                 state->stack_size = 0;
1536
1537                         } else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1538
1539                                 /* drap: push %reg */
1540                                 save_reg(state, op->src.reg, CFI_BP, -state->stack_size);
1541                         }
1542
1543                 } else {
1544
1545                         /* push %reg */
1546                         save_reg(state, op->src.reg, CFI_CFA, -state->stack_size);
1547                 }
1548
1549                 /* detect when asm code uses rbp as a scratch register */
1550                 if (!no_fp && insn->func && op->src.reg == CFI_BP &&
1551                     cfa->base != CFI_BP)
1552                         state->bp_scratch = true;
1553                 break;
1554
1555         case OP_DEST_REG_INDIRECT:
1556
1557                 if (state->drap) {
1558                         if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1559
1560                                 /* drap: mov %drap, disp(%rbp) */
1561                                 cfa->base = CFI_BP_INDIRECT;
1562                                 cfa->offset = op->dest.offset;
1563
1564                                 /* save drap offset so we know when to restore it */
1565                                 state->drap_offset = op->dest.offset;
1566                         }
1567
1568                         else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1569
1570                                 /* drap: mov reg, disp(%rbp) */
1571                                 save_reg(state, op->src.reg, CFI_BP, op->dest.offset);
1572                         }
1573
1574                 } else if (op->dest.reg == cfa->base) {
1575
1576                         /* mov reg, disp(%rbp) */
1577                         /* mov reg, disp(%rsp) */
1578                         save_reg(state, op->src.reg, CFI_CFA,
1579                                  op->dest.offset - state->cfa.offset);
1580                 }
1581
1582                 break;
1583
1584         case OP_DEST_LEAVE:
1585                 if ((!state->drap && cfa->base != CFI_BP) ||
1586                     (state->drap && cfa->base != state->drap_reg)) {
1587                         WARN_FUNC("leave instruction with modified stack frame",
1588                                   insn->sec, insn->offset);
1589                         return -1;
1590                 }
1591
1592                 /* leave (mov %rbp, %rsp; pop %rbp) */
1593
1594                 state->stack_size = -state->regs[CFI_BP].offset - 8;
1595                 restore_reg(state, CFI_BP);
1596
1597                 if (!state->drap) {
1598                         cfa->base = CFI_SP;
1599                         cfa->offset -= 8;
1600                 }
1601
1602                 break;
1603
1604         case OP_DEST_MEM:
1605                 if (op->src.type != OP_SRC_POP) {
1606                         WARN_FUNC("unknown stack-related memory operation",
1607                                   insn->sec, insn->offset);
1608                         return -1;
1609                 }
1610
1611                 /* pop mem */
1612                 state->stack_size -= 8;
1613                 if (cfa->base == CFI_SP)
1614                         cfa->offset -= 8;
1615
1616                 break;
1617
1618         default:
1619                 WARN_FUNC("unknown stack-related instruction",
1620                           insn->sec, insn->offset);
1621                 return -1;
1622         }
1623
1624         return 0;
1625 }
1626
1627 static bool insn_state_match(struct instruction *insn, struct insn_state *state)
1628 {
1629         struct insn_state *state1 = &insn->state, *state2 = state;
1630         int i;
1631
1632         if (memcmp(&state1->cfa, &state2->cfa, sizeof(state1->cfa))) {
1633                 WARN_FUNC("stack state mismatch: cfa1=%d%+d cfa2=%d%+d",
1634                           insn->sec, insn->offset,
1635                           state1->cfa.base, state1->cfa.offset,
1636                           state2->cfa.base, state2->cfa.offset);
1637
1638         } else if (memcmp(&state1->regs, &state2->regs, sizeof(state1->regs))) {
1639                 for (i = 0; i < CFI_NUM_REGS; i++) {
1640                         if (!memcmp(&state1->regs[i], &state2->regs[i],
1641                                     sizeof(struct cfi_reg)))
1642                                 continue;
1643
1644                         WARN_FUNC("stack state mismatch: reg1[%d]=%d%+d reg2[%d]=%d%+d",
1645                                   insn->sec, insn->offset,
1646                                   i, state1->regs[i].base, state1->regs[i].offset,
1647                                   i, state2->regs[i].base, state2->regs[i].offset);
1648                         break;
1649                 }
1650
1651         } else if (state1->type != state2->type) {
1652                 WARN_FUNC("stack state mismatch: type1=%d type2=%d",
1653                           insn->sec, insn->offset, state1->type, state2->type);
1654
1655         } else if (state1->drap != state2->drap ||
1656                  (state1->drap && state1->drap_reg != state2->drap_reg) ||
1657                  (state1->drap && state1->drap_offset != state2->drap_offset)) {
1658                 WARN_FUNC("stack state mismatch: drap1=%d(%d,%d) drap2=%d(%d,%d)",
1659                           insn->sec, insn->offset,
1660                           state1->drap, state1->drap_reg, state1->drap_offset,
1661                           state2->drap, state2->drap_reg, state2->drap_offset);
1662
1663         } else
1664                 return true;
1665
1666         return false;
1667 }
1668
1669 /*
1670  * Follow the branch starting at the given instruction, and recursively follow
1671  * any other branches (jumps).  Meanwhile, track the frame pointer state at
1672  * each instruction and validate all the rules described in
1673  * tools/objtool/Documentation/stack-validation.txt.
1674  */
1675 static int validate_branch(struct objtool_file *file, struct instruction *first,
1676                            struct insn_state state)
1677 {
1678         struct alternative *alt;
1679         struct instruction *insn, *next_insn;
1680         struct section *sec;
1681         struct symbol *func = NULL;
1682         int ret;
1683
1684         insn = first;
1685         sec = insn->sec;
1686
1687         if (insn->alt_group && list_empty(&insn->alts)) {
1688                 WARN_FUNC("don't know how to handle branch to middle of alternative instruction group",
1689                           sec, insn->offset);
1690                 return 1;
1691         }
1692
1693         while (1) {
1694                 next_insn = next_insn_same_sec(file, insn);
1695
1696
1697                 if (file->c_file && func && insn->func && func != insn->func) {
1698                         WARN("%s() falls through to next function %s()",
1699                              func->name, insn->func->name);
1700                         return 1;
1701                 }
1702
1703                 if (insn->func)
1704                         func = insn->func;
1705
1706                 if (func && insn->ignore) {
1707                         WARN_FUNC("BUG: why am I validating an ignored function?",
1708                                   sec, insn->offset);
1709                         return 1;
1710                 }
1711
1712                 if (insn->visited) {
1713                         if (!insn->hint && !insn_state_match(insn, &state))
1714                                 return 1;
1715
1716                         return 0;
1717                 }
1718
1719                 if (insn->hint) {
1720                         if (insn->restore) {
1721                                 struct instruction *save_insn, *i;
1722
1723                                 i = insn;
1724                                 save_insn = NULL;
1725                                 func_for_each_insn_continue_reverse(file, func, i) {
1726                                         if (i->save) {
1727                                                 save_insn = i;
1728                                                 break;
1729                                         }
1730                                 }
1731
1732                                 if (!save_insn) {
1733                                         WARN_FUNC("no corresponding CFI save for CFI restore",
1734                                                   sec, insn->offset);
1735                                         return 1;
1736                                 }
1737
1738                                 if (!save_insn->visited) {
1739                                         /*
1740                                          * Oops, no state to copy yet.
1741                                          * Hopefully we can reach this
1742                                          * instruction from another branch
1743                                          * after the save insn has been
1744                                          * visited.
1745                                          */
1746                                         if (insn == first)
1747                                                 return 0;
1748
1749                                         WARN_FUNC("objtool isn't smart enough to handle this CFI save/restore combo",
1750                                                   sec, insn->offset);
1751                                         return 1;
1752                                 }
1753
1754                                 insn->state = save_insn->state;
1755                         }
1756
1757                         state = insn->state;
1758
1759                 } else
1760                         insn->state = state;
1761
1762                 insn->visited = true;
1763
1764                 if (!insn->ignore_alts) {
1765                         list_for_each_entry(alt, &insn->alts, list) {
1766                                 ret = validate_branch(file, alt->insn, state);
1767                                 if (ret)
1768                                         return 1;
1769                         }
1770                 }
1771
1772                 switch (insn->type) {
1773
1774                 case INSN_RETURN:
1775                         if (func && has_modified_stack_frame(&state)) {
1776                                 WARN_FUNC("return with modified stack frame",
1777                                           sec, insn->offset);
1778                                 return 1;
1779                         }
1780
1781                         if (state.bp_scratch) {
1782                                 WARN("%s uses BP as a scratch register",
1783                                      insn->func->name);
1784                                 return 1;
1785                         }
1786
1787                         return 0;
1788
1789                 case INSN_CALL:
1790                         if (is_fentry_call(insn))
1791                                 break;
1792
1793                         ret = dead_end_function(file, insn->call_dest);
1794                         if (ret == 1)
1795                                 return 0;
1796                         if (ret == -1)
1797                                 return 1;
1798
1799                         /* fallthrough */
1800                 case INSN_CALL_DYNAMIC:
1801                         if (!no_fp && func && !has_valid_stack_frame(&state)) {
1802                                 WARN_FUNC("call without frame pointer save/setup",
1803                                           sec, insn->offset);
1804                                 return 1;
1805                         }
1806                         break;
1807
1808                 case INSN_JUMP_CONDITIONAL:
1809                 case INSN_JUMP_UNCONDITIONAL:
1810                         if (insn->jump_dest &&
1811                             (!func || !insn->jump_dest->func ||
1812                              func == insn->jump_dest->func)) {
1813                                 ret = validate_branch(file, insn->jump_dest,
1814                                                       state);
1815                                 if (ret)
1816                                         return 1;
1817
1818                         } else if (func && has_modified_stack_frame(&state)) {
1819                                 WARN_FUNC("sibling call from callable instruction with modified stack frame",
1820                                           sec, insn->offset);
1821                                 return 1;
1822                         }
1823
1824                         if (insn->type == INSN_JUMP_UNCONDITIONAL)
1825                                 return 0;
1826
1827                         break;
1828
1829                 case INSN_JUMP_DYNAMIC:
1830                         if (func && list_empty(&insn->alts) &&
1831                             has_modified_stack_frame(&state)) {
1832                                 WARN_FUNC("sibling call from callable instruction with modified stack frame",
1833                                           sec, insn->offset);
1834                                 return 1;
1835                         }
1836
1837                         return 0;
1838
1839                 case INSN_CONTEXT_SWITCH:
1840                         if (func && (!next_insn || !next_insn->hint)) {
1841                                 WARN_FUNC("unsupported instruction in callable function",
1842                                           sec, insn->offset);
1843                                 return 1;
1844                         }
1845                         return 0;
1846
1847                 case INSN_STACK:
1848                         if (update_insn_state(insn, &state))
1849                                 return 1;
1850
1851                         break;
1852
1853                 default:
1854                         break;
1855                 }
1856
1857                 if (insn->dead_end)
1858                         return 0;
1859
1860                 if (!next_insn) {
1861                         if (state.cfa.base == CFI_UNDEFINED)
1862                                 return 0;
1863                         WARN("%s: unexpected end of section", sec->name);
1864                         return 1;
1865                 }
1866
1867                 insn = next_insn;
1868         }
1869
1870         return 0;
1871 }
1872
1873 static int validate_unwind_hints(struct objtool_file *file)
1874 {
1875         struct instruction *insn;
1876         int ret, warnings = 0;
1877         struct insn_state state;
1878
1879         if (!file->hints)
1880                 return 0;
1881
1882         clear_insn_state(&state);
1883
1884         for_each_insn(file, insn) {
1885                 if (insn->hint && !insn->visited) {
1886                         ret = validate_branch(file, insn, state);
1887                         warnings += ret;
1888                 }
1889         }
1890
1891         return warnings;
1892 }
1893
1894 static bool is_kasan_insn(struct instruction *insn)
1895 {
1896         return (insn->type == INSN_CALL &&
1897                 !strcmp(insn->call_dest->name, "__asan_handle_no_return"));
1898 }
1899
1900 static bool is_ubsan_insn(struct instruction *insn)
1901 {
1902         return (insn->type == INSN_CALL &&
1903                 !strcmp(insn->call_dest->name,
1904                         "__ubsan_handle_builtin_unreachable"));
1905 }
1906
1907 static bool ignore_unreachable_insn(struct instruction *insn)
1908 {
1909         int i;
1910
1911         if (insn->ignore || insn->type == INSN_NOP)
1912                 return true;
1913
1914         /*
1915          * Ignore any unused exceptions.  This can happen when a whitelisted
1916          * function has an exception table entry.
1917          *
1918          * Also ignore alternative replacement instructions.  This can happen
1919          * when a whitelisted function uses one of the ALTERNATIVE macros.
1920          */
1921         if (!strcmp(insn->sec->name, ".fixup") ||
1922             !strcmp(insn->sec->name, ".altinstr_replacement") ||
1923             !strcmp(insn->sec->name, ".altinstr_aux"))
1924                 return true;
1925
1926         /*
1927          * Check if this (or a subsequent) instruction is related to
1928          * CONFIG_UBSAN or CONFIG_KASAN.
1929          *
1930          * End the search at 5 instructions to avoid going into the weeds.
1931          */
1932         if (!insn->func)
1933                 return false;
1934         for (i = 0; i < 5; i++) {
1935
1936                 if (is_kasan_insn(insn) || is_ubsan_insn(insn))
1937                         return true;
1938
1939                 if (insn->type == INSN_JUMP_UNCONDITIONAL) {
1940                         if (insn->jump_dest &&
1941                             insn->jump_dest->func == insn->func) {
1942                                 insn = insn->jump_dest;
1943                                 continue;
1944                         }
1945
1946                         break;
1947                 }
1948
1949                 if (insn->offset + insn->len >= insn->func->offset + insn->func->len)
1950                         break;
1951
1952                 insn = list_next_entry(insn, list);
1953         }
1954
1955         return false;
1956 }
1957
1958 static int validate_functions(struct objtool_file *file)
1959 {
1960         struct section *sec;
1961         struct symbol *func;
1962         struct instruction *insn;
1963         struct insn_state state;
1964         int ret, warnings = 0;
1965
1966         clear_insn_state(&state);
1967
1968         state.cfa = initial_func_cfi.cfa;
1969         memcpy(&state.regs, &initial_func_cfi.regs,
1970                CFI_NUM_REGS * sizeof(struct cfi_reg));
1971         state.stack_size = initial_func_cfi.cfa.offset;
1972
1973         for_each_sec(file, sec) {
1974                 list_for_each_entry(func, &sec->symbol_list, list) {
1975                         if (func->type != STT_FUNC)
1976                                 continue;
1977
1978                         insn = find_insn(file, sec, func->offset);
1979                         if (!insn || insn->ignore)
1980                                 continue;
1981
1982                         ret = validate_branch(file, insn, state);
1983                         warnings += ret;
1984                 }
1985         }
1986
1987         return warnings;
1988 }
1989
1990 static int validate_reachable_instructions(struct objtool_file *file)
1991 {
1992         struct instruction *insn;
1993
1994         if (file->ignore_unreachables)
1995                 return 0;
1996
1997         for_each_insn(file, insn) {
1998                 if (insn->visited || ignore_unreachable_insn(insn))
1999                         continue;
2000
2001                 WARN_FUNC("unreachable instruction", insn->sec, insn->offset);
2002                 return 1;
2003         }
2004
2005         return 0;
2006 }
2007
2008 static void cleanup(struct objtool_file *file)
2009 {
2010         struct instruction *insn, *tmpinsn;
2011         struct alternative *alt, *tmpalt;
2012
2013         list_for_each_entry_safe(insn, tmpinsn, &file->insn_list, list) {
2014                 list_for_each_entry_safe(alt, tmpalt, &insn->alts, list) {
2015                         list_del(&alt->list);
2016                         free(alt);
2017                 }
2018                 list_del(&insn->list);
2019                 hash_del(&insn->hash);
2020                 free(insn);
2021         }
2022         elf_close(file->elf);
2023 }
2024
2025 int check(const char *_objname, bool _no_fp, bool no_unreachable, bool orc)
2026 {
2027         struct objtool_file file;
2028         int ret, warnings = 0;
2029
2030         objname = _objname;
2031         no_fp = _no_fp;
2032
2033         file.elf = elf_open(objname, orc ? O_RDWR : O_RDONLY);
2034         if (!file.elf)
2035                 return 1;
2036
2037         INIT_LIST_HEAD(&file.insn_list);
2038         hash_init(file.insn_hash);
2039         file.whitelist = find_section_by_name(file.elf, ".discard.func_stack_frame_non_standard");
2040         file.rodata = find_section_by_name(file.elf, ".rodata");
2041         file.c_file = find_section_by_name(file.elf, ".comment");
2042         file.ignore_unreachables = no_unreachable;
2043         file.hints = false;
2044
2045         arch_initial_func_cfi_state(&initial_func_cfi);
2046
2047         ret = decode_sections(&file);
2048         if (ret < 0)
2049                 goto out;
2050         warnings += ret;
2051
2052         if (list_empty(&file.insn_list))
2053                 goto out;
2054
2055         ret = validate_functions(&file);
2056         if (ret < 0)
2057                 goto out;
2058         warnings += ret;
2059
2060         ret = validate_unwind_hints(&file);
2061         if (ret < 0)
2062                 goto out;
2063         warnings += ret;
2064
2065         if (!warnings) {
2066                 ret = validate_reachable_instructions(&file);
2067                 if (ret < 0)
2068                         goto out;
2069                 warnings += ret;
2070         }
2071
2072         if (orc) {
2073                 ret = create_orc(&file);
2074                 if (ret < 0)
2075                         goto out;
2076
2077                 ret = create_orc_sections(&file);
2078                 if (ret < 0)
2079                         goto out;
2080
2081                 ret = elf_write(file.elf);
2082                 if (ret < 0)
2083                         goto out;
2084         }
2085
2086 out:
2087         cleanup(&file);
2088
2089         /* ignore warnings for now until we get all the code cleaned up */
2090         if (ret || warnings)
2091                 return 0;
2092         return 0;
2093 }