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