root/tools/objtool/check.c

DEFINITIONS

1. find_insn
2. next_insn_same_sec
3. next_insn_same_func
4. is_sibling_call
5. __dead_end_function
6. dead_end_function
7. clear_insn_state
8. decode_instructions
9. add_dead_ends
10. add_ignores
11. add_uaccess_safe
12. add_ignore_alternatives
13. add_jump_destinations
14. add_call_destinations
15. handle_group_alt
16. handle_jump_alt
17. add_special_section_alts
18. add_jump_table
19. find_jump_table
20. mark_func_jump_tables
21. add_func_jump_tables
22. add_jump_table_alts
23. read_unwind_hints
24. read_retpoline_hints
25. mark_rodata
26. decode_sections
27. is_fentry_call
28. has_modified_stack_frame
29. has_valid_stack_frame
30. update_insn_state_regs
31. save_reg
32. restore_reg
33. update_insn_state
34. insn_state_match
35. func_uaccess_safe
36. call_dest_name
37. validate_call
38. validate_sibling_call
39. validate_branch
40. validate_unwind_hints
41. validate_retpoline
42. is_kasan_insn
43. is_ubsan_insn
44. ignore_unreachable_insn
45. validate_functions
46. validate_reachable_instructions
47. cleanup
48. check

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * Copyright (C) 2015-2017 Josh Poimboeuf <jpoimboe@redhat.com>
   4  */
   5 
   6 #include <string.h>
   7 #include <stdlib.h>
   8 
   9 #include "builtin.h"
  10 #include "check.h"
  11 #include "elf.h"
  12 #include "special.h"
  13 #include "arch.h"
  14 #include "warn.h"
  15 
  16 #include <linux/hashtable.h>
  17 #include <linux/kernel.h>
  18 
  19 #define FAKE_JUMP_OFFSET -1
  20 
  21 #define C_JUMP_TABLE_SECTION ".rodata..c_jump_table"
  22 
  23 struct alternative {
  24         struct list_head list;
  25         struct instruction *insn;
  26         bool skip_orig;
  27 };
  28 
  29 const char *objname;
  30 struct cfi_state initial_func_cfi;
  31 
  32 struct instruction *find_insn(struct objtool_file *file,
  33                               struct section *sec, unsigned long offset)
  34 {
  35         struct instruction *insn;
  36 
  37         hash_for_each_possible(file->insn_hash, insn, hash, offset)
  38                 if (insn->sec == sec && insn->offset == offset)
  39                         return insn;
  40 
  41         return NULL;
  42 }
  43 
  44 static struct instruction *next_insn_same_sec(struct objtool_file *file,
  45                                               struct instruction *insn)
  46 {
  47         struct instruction *next = list_next_entry(insn, list);
  48 
  49         if (!next || &next->list == &file->insn_list || next->sec != insn->sec)
  50                 return NULL;
  51 
  52         return next;
  53 }
  54 
  55 static struct instruction *next_insn_same_func(struct objtool_file *file,
  56                                                struct instruction *insn)
  57 {
  58         struct instruction *next = list_next_entry(insn, list);
  59         struct symbol *func = insn->func;
  60 
  61         if (!func)
  62                 return NULL;
  63 
  64         if (&next->list != &file->insn_list && next->func == func)
  65                 return next;
  66 
  67         /* Check if we're already in the subfunction: */
  68         if (func == func->cfunc)
  69                 return NULL;
  70 
  71         /* Move to the subfunction: */
  72         return find_insn(file, func->cfunc->sec, func->cfunc->offset);
  73 }
  74 
  75 #define func_for_each_insn_all(file, func, insn)                        \
  76         for (insn = find_insn(file, func->sec, func->offset);           \
  77              insn;                                                      \
  78              insn = next_insn_same_func(file, insn))
  79 
  80 #define func_for_each_insn(file, func, insn)                            \
  81         for (insn = find_insn(file, func->sec, func->offset);           \
  82              insn && &insn->list != &file->insn_list &&                 \
  83                 insn->sec == func->sec &&                               \
  84                 insn->offset < func->offset + func->len;                \
  85              insn = list_next_entry(insn, list))
  86 
  87 #define func_for_each_insn_continue_reverse(file, func, insn)           \
  88         for (insn = list_prev_entry(insn, list);                        \
  89              &insn->list != &file->insn_list &&                         \
  90                 insn->sec == func->sec && insn->offset >= func->offset; \
  91              insn = list_prev_entry(insn, list))
  92 
  93 #define sec_for_each_insn_from(file, insn)                              \
  94         for (; insn; insn = next_insn_same_sec(file, insn))
  95 
  96 #define sec_for_each_insn_continue(file, insn)                          \
  97         for (insn = next_insn_same_sec(file, insn); insn;               \
  98              insn = next_insn_same_sec(file, insn))
  99 
 100 static bool is_sibling_call(struct instruction *insn)
 101 {
 102         /* An indirect jump is either a sibling call or a jump to a table. */
 103         if (insn->type == INSN_JUMP_DYNAMIC)
 104                 return list_empty(&insn->alts);
 105 
 106         if (insn->type != INSN_JUMP_CONDITIONAL &&
 107             insn->type != INSN_JUMP_UNCONDITIONAL)
 108                 return false;
 109 
 110         /* add_jump_destinations() sets insn->call_dest for sibling calls. */
 111         return !!insn->call_dest;
 112 }
 113 
 114 /*
 115  * This checks to see if the given function is a "noreturn" function.
 116  *
 117  * For global functions which are outside the scope of this object file, we
 118  * have to keep a manual list of them.
 119  *
 120  * For local functions, we have to detect them manually by simply looking for
 121  * the lack of a return instruction.
 122  */
 123 static bool __dead_end_function(struct objtool_file *file, struct symbol *func,
 124                                 int recursion)
 125 {
 126         int i;
 127         struct instruction *insn;
 128         bool empty = true;
 129 
 130         /*
 131          * Unfortunately these have to be hard coded because the noreturn
 132          * attribute isn't provided in ELF data.
 133          */
 134         static const char * const global_noreturns[] = {
 135                 "__stack_chk_fail",
 136                 "panic",
 137                 "do_exit",
 138                 "do_task_dead",
 139                 "__module_put_and_exit",
 140                 "complete_and_exit",
 141                 "__reiserfs_panic",
 142                 "lbug_with_loc",
 143                 "fortify_panic",
 144                 "usercopy_abort",
 145                 "machine_real_restart",
 146                 "rewind_stack_do_exit",
 147         };
 148 
 149         if (!func)
 150                 return false;
 151 
 152         if (func->bind == STB_WEAK)
 153                 return false;
 154 
 155         if (func->bind == STB_GLOBAL)
 156                 for (i = 0; i < ARRAY_SIZE(global_noreturns); i++)
 157                         if (!strcmp(func->name, global_noreturns[i]))
 158                                 return true;
 159 
 160         if (!func->len)
 161                 return false;
 162 
 163         insn = find_insn(file, func->sec, func->offset);
 164         if (!insn->func)
 165                 return false;
 166 
 167         func_for_each_insn_all(file, func, insn) {
 168                 empty = false;
 169 
 170                 if (insn->type == INSN_RETURN)
 171                         return false;
 172         }
 173 
 174         if (empty)
 175                 return false;
 176 
 177         /*
 178          * A function can have a sibling call instead of a return.  In that
 179          * case, the function's dead-end status depends on whether the target
 180          * of the sibling call returns.
 181          */
 182         func_for_each_insn_all(file, func, insn) {
 183                 if (is_sibling_call(insn)) {
 184                         struct instruction *dest = insn->jump_dest;
 185 
 186                         if (!dest)
 187                                 /* sibling call to another file */
 188                                 return false;
 189 
 190                         /* local sibling call */
 191                         if (recursion == 5) {
 192                                 /*
 193                                  * Infinite recursion: two functions have
 194                                  * sibling calls to each other.  This is a very
 195                                  * rare case.  It means they aren't dead ends.
 196                                  */
 197                                 return false;
 198                         }
 199 
 200                         return __dead_end_function(file, dest->func, recursion+1);
 201                 }
 202         }
 203 
 204         return true;
 205 }
 206 
 207 static bool dead_end_function(struct objtool_file *file, struct symbol *func)
 208 {
 209         return __dead_end_function(file, func, 0);
 210 }
 211 
 212 static void clear_insn_state(struct insn_state *state)
 213 {
 214         int i;
 215 
 216         memset(state, 0, sizeof(*state));
 217         state->cfa.base = CFI_UNDEFINED;
 218         for (i = 0; i < CFI_NUM_REGS; i++) {
 219                 state->regs[i].base = CFI_UNDEFINED;
 220                 state->vals[i].base = CFI_UNDEFINED;
 221         }
 222         state->drap_reg = CFI_UNDEFINED;
 223         state->drap_offset = -1;
 224 }
 225 
 226 /*
 227  * Call the arch-specific instruction decoder for all the instructions and add
 228  * them to the global instruction list.
 229  */
 230 static int decode_instructions(struct objtool_file *file)
 231 {
 232         struct section *sec;
 233         struct symbol *func;
 234         unsigned long offset;
 235         struct instruction *insn;
 236         int ret;
 237 
 238         for_each_sec(file, sec) {
 239 
 240                 if (!(sec->sh.sh_flags & SHF_EXECINSTR))
 241                         continue;
 242 
 243                 if (strcmp(sec->name, ".altinstr_replacement") &&
 244                     strcmp(sec->name, ".altinstr_aux") &&
 245                     strncmp(sec->name, ".discard.", 9))
 246                         sec->text = true;
 247 
 248                 for (offset = 0; offset < sec->len; offset += insn->len) {
 249                         insn = malloc(sizeof(*insn));
 250                         if (!insn) {
 251                                 WARN("malloc failed");
 252                                 return -1;
 253                         }
 254                         memset(insn, 0, sizeof(*insn));
 255                         INIT_LIST_HEAD(&insn->alts);
 256                         clear_insn_state(&insn->state);
 257 
 258                         insn->sec = sec;
 259                         insn->offset = offset;
 260 
 261                         ret = arch_decode_instruction(file->elf, sec, offset,
 262                                                       sec->len - offset,
 263                                                       &insn->len, &insn->type,
 264                                                       &insn->immediate,
 265                                                       &insn->stack_op);
 266                         if (ret)
 267                                 goto err;
 268 
 269                         hash_add(file->insn_hash, &insn->hash, insn->offset);
 270                         list_add_tail(&insn->list, &file->insn_list);
 271                 }
 272 
 273                 list_for_each_entry(func, &sec->symbol_list, list) {
 274                         if (func->type != STT_FUNC || func->alias != func)
 275                                 continue;
 276 
 277                         if (!find_insn(file, sec, func->offset)) {
 278                                 WARN("%s(): can't find starting instruction",
 279                                      func->name);
 280                                 return -1;
 281                         }
 282 
 283                         func_for_each_insn(file, func, insn)
 284                                 insn->func = func;
 285                 }
 286         }
 287 
 288         return 0;
 289 
 290 err:
 291         free(insn);
 292         return ret;
 293 }
 294 
 295 /*
 296  * Mark "ud2" instructions and manually annotated dead ends.
 297  */
 298 static int add_dead_ends(struct objtool_file *file)
 299 {
 300         struct section *sec;
 301         struct rela *rela;
 302         struct instruction *insn;
 303         bool found;
 304 
 305         /*
 306          * By default, "ud2" is a dead end unless otherwise annotated, because
 307          * GCC 7 inserts it for certain divide-by-zero cases.
 308          */
 309         for_each_insn(file, insn)
 310                 if (insn->type == INSN_BUG)
 311                         insn->dead_end = true;
 312 
 313         /*
 314          * Check for manually annotated dead ends.
 315          */
 316         sec = find_section_by_name(file->elf, ".rela.discard.unreachable");
 317         if (!sec)
 318                 goto reachable;
 319 
 320         list_for_each_entry(rela, &sec->rela_list, list) {
 321                 if (rela->sym->type != STT_SECTION) {
 322                         WARN("unexpected relocation symbol type in %s", sec->name);
 323                         return -1;
 324                 }
 325                 insn = find_insn(file, rela->sym->sec, rela->addend);
 326                 if (insn)
 327                         insn = list_prev_entry(insn, list);
 328                 else if (rela->addend == rela->sym->sec->len) {
 329                         found = false;
 330                         list_for_each_entry_reverse(insn, &file->insn_list, list) {
 331                                 if (insn->sec == rela->sym->sec) {
 332                                         found = true;
 333                                         break;
 334                                 }
 335                         }
 336 
 337                         if (!found) {
 338                                 WARN("can't find unreachable insn at %s+0x%x",
 339                                      rela->sym->sec->name, rela->addend);
 340                                 return -1;
 341                         }
 342                 } else {
 343                         WARN("can't find unreachable insn at %s+0x%x",
 344                              rela->sym->sec->name, rela->addend);
 345                         return -1;
 346                 }
 347 
 348                 insn->dead_end = true;
 349         }
 350 
 351 reachable:
 352         /*
 353          * These manually annotated reachable checks are needed for GCC 4.4,
 354          * where the Linux unreachable() macro isn't supported.  In that case
 355          * GCC doesn't know the "ud2" is fatal, so it generates code as if it's
 356          * not a dead end.
 357          */
 358         sec = find_section_by_name(file->elf, ".rela.discard.reachable");
 359         if (!sec)
 360                 return 0;
 361 
 362         list_for_each_entry(rela, &sec->rela_list, list) {
 363                 if (rela->sym->type != STT_SECTION) {
 364                         WARN("unexpected relocation symbol type in %s", sec->name);
 365                         return -1;
 366                 }
 367                 insn = find_insn(file, rela->sym->sec, rela->addend);
 368                 if (insn)
 369                         insn = list_prev_entry(insn, list);
 370                 else if (rela->addend == rela->sym->sec->len) {
 371                         found = false;
 372                         list_for_each_entry_reverse(insn, &file->insn_list, list) {
 373                                 if (insn->sec == rela->sym->sec) {
 374                                         found = true;
 375                                         break;
 376                                 }
 377                         }
 378 
 379                         if (!found) {
 380                                 WARN("can't find reachable insn at %s+0x%x",
 381                                      rela->sym->sec->name, rela->addend);
 382                                 return -1;
 383                         }
 384                 } else {
 385                         WARN("can't find reachable insn at %s+0x%x",
 386                              rela->sym->sec->name, rela->addend);
 387                         return -1;
 388                 }
 389 
 390                 insn->dead_end = false;
 391         }
 392 
 393         return 0;
 394 }
 395 
 396 /*
 397  * Warnings shouldn't be reported for ignored functions.
 398  */
 399 static void add_ignores(struct objtool_file *file)
 400 {
 401         struct instruction *insn;
 402         struct section *sec;
 403         struct symbol *func;
 404         struct rela *rela;
 405 
 406         sec = find_section_by_name(file->elf, ".rela.discard.func_stack_frame_non_standard");
 407         if (!sec)
 408                 return;
 409 
 410         list_for_each_entry(rela, &sec->rela_list, list) {
 411                 switch (rela->sym->type) {
 412                 case STT_FUNC:
 413                         func = rela->sym;
 414                         break;
 415 
 416                 case STT_SECTION:
 417                         func = find_symbol_by_offset(rela->sym->sec, rela->addend);
 418                         if (!func || func->type != STT_FUNC)
 419                                 continue;
 420                         break;
 421 
 422                 default:
 423                         WARN("unexpected relocation symbol type in %s: %d", sec->name, rela->sym->type);
 424                         continue;
 425                 }
 426 
 427                 func_for_each_insn_all(file, func, insn)
 428                         insn->ignore = true;
 429         }
 430 }
 431 
 432 /*
 433  * This is a whitelist of functions that is allowed to be called with AC set.
 434  * The list is meant to be minimal and only contains compiler instrumentation
 435  * ABI and a few functions used to implement *_{to,from}_user() functions.
 436  *
 437  * These functions must not directly change AC, but may PUSHF/POPF.
 438  */
 439 static const char *uaccess_safe_builtin[] = {
 440         /* KASAN */
 441         "kasan_report",
 442         "check_memory_region",
 443         /* KASAN out-of-line */
 444         "__asan_loadN_noabort",
 445         "__asan_load1_noabort",
 446         "__asan_load2_noabort",
 447         "__asan_load4_noabort",
 448         "__asan_load8_noabort",
 449         "__asan_load16_noabort",
 450         "__asan_storeN_noabort",
 451         "__asan_store1_noabort",
 452         "__asan_store2_noabort",
 453         "__asan_store4_noabort",
 454         "__asan_store8_noabort",
 455         "__asan_store16_noabort",
 456         /* KASAN in-line */
 457         "__asan_report_load_n_noabort",
 458         "__asan_report_load1_noabort",
 459         "__asan_report_load2_noabort",
 460         "__asan_report_load4_noabort",
 461         "__asan_report_load8_noabort",
 462         "__asan_report_load16_noabort",
 463         "__asan_report_store_n_noabort",
 464         "__asan_report_store1_noabort",
 465         "__asan_report_store2_noabort",
 466         "__asan_report_store4_noabort",
 467         "__asan_report_store8_noabort",
 468         "__asan_report_store16_noabort",
 469         /* KCOV */
 470         "write_comp_data",
 471         "__sanitizer_cov_trace_pc",
 472         "__sanitizer_cov_trace_const_cmp1",
 473         "__sanitizer_cov_trace_const_cmp2",
 474         "__sanitizer_cov_trace_const_cmp4",
 475         "__sanitizer_cov_trace_const_cmp8",
 476         "__sanitizer_cov_trace_cmp1",
 477         "__sanitizer_cov_trace_cmp2",
 478         "__sanitizer_cov_trace_cmp4",
 479         "__sanitizer_cov_trace_cmp8",
 480         /* UBSAN */
 481         "ubsan_type_mismatch_common",
 482         "__ubsan_handle_type_mismatch",
 483         "__ubsan_handle_type_mismatch_v1",
 484         "__ubsan_handle_shift_out_of_bounds",
 485         /* misc */
 486         "csum_partial_copy_generic",
 487         "__memcpy_mcsafe",
 488         "mcsafe_handle_tail",
 489         "ftrace_likely_update", /* CONFIG_TRACE_BRANCH_PROFILING */
 490         NULL
 491 };
 492 
 493 static void add_uaccess_safe(struct objtool_file *file)
 494 {
 495         struct symbol *func;
 496         const char **name;
 497 
 498         if (!uaccess)
 499                 return;
 500 
 501         for (name = uaccess_safe_builtin; *name; name++) {
 502                 func = find_symbol_by_name(file->elf, *name);
 503                 if (!func)
 504                         continue;
 505 
 506                 func->uaccess_safe = true;
 507         }
 508 }
 509 
 510 /*
 511  * FIXME: For now, just ignore any alternatives which add retpolines.  This is
 512  * a temporary hack, as it doesn't allow ORC to unwind from inside a retpoline.
 513  * But it at least allows objtool to understand the control flow *around* the
 514  * retpoline.
 515  */
 516 static int add_ignore_alternatives(struct objtool_file *file)
 517 {
 518         struct section *sec;
 519         struct rela *rela;
 520         struct instruction *insn;
 521 
 522         sec = find_section_by_name(file->elf, ".rela.discard.ignore_alts");
 523         if (!sec)
 524                 return 0;
 525 
 526         list_for_each_entry(rela, &sec->rela_list, list) {
 527                 if (rela->sym->type != STT_SECTION) {
 528                         WARN("unexpected relocation symbol type in %s", sec->name);
 529                         return -1;
 530                 }
 531 
 532                 insn = find_insn(file, rela->sym->sec, rela->addend);
 533                 if (!insn) {
 534                         WARN("bad .discard.ignore_alts entry");
 535                         return -1;
 536                 }
 537 
 538                 insn->ignore_alts = true;
 539         }
 540 
 541         return 0;
 542 }
 543 
 544 /*
 545  * Find the destination instructions for all jumps.
 546  */
 547 static int add_jump_destinations(struct objtool_file *file)
 548 {
 549         struct instruction *insn;
 550         struct rela *rela;
 551         struct section *dest_sec;
 552         unsigned long dest_off;
 553 
 554         for_each_insn(file, insn) {
 555                 if (insn->type != INSN_JUMP_CONDITIONAL &&
 556                     insn->type != INSN_JUMP_UNCONDITIONAL)
 557                         continue;
 558 
 559                 if (insn->ignore || insn->offset == FAKE_JUMP_OFFSET)
 560                         continue;
 561 
 562                 rela = find_rela_by_dest_range(insn->sec, insn->offset,
 563                                                insn->len);
 564                 if (!rela) {
 565                         dest_sec = insn->sec;
 566                         dest_off = insn->offset + insn->len + insn->immediate;
 567                 } else if (rela->sym->type == STT_SECTION) {
 568                         dest_sec = rela->sym->sec;
 569                         dest_off = rela->addend + 4;
 570                 } else if (rela->sym->sec->idx) {
 571                         dest_sec = rela->sym->sec;
 572                         dest_off = rela->sym->sym.st_value + rela->addend + 4;
 573                 } else if (strstr(rela->sym->name, "_indirect_thunk_")) {
 574                         /*
 575                          * Retpoline jumps are really dynamic jumps in
 576                          * disguise, so convert them accordingly.
 577                          */
 578                         if (insn->type == INSN_JUMP_UNCONDITIONAL)
 579                                 insn->type = INSN_JUMP_DYNAMIC;
 580                         else
 581                                 insn->type = INSN_JUMP_DYNAMIC_CONDITIONAL;
 582 
 583                         insn->retpoline_safe = true;
 584                         continue;
 585                 } else {
 586                         /* external sibling call */
 587                         insn->call_dest = rela->sym;
 588                         continue;
 589                 }
 590 
 591                 insn->jump_dest = find_insn(file, dest_sec, dest_off);
 592                 if (!insn->jump_dest) {
 593 
 594                         /*
 595                          * This is a special case where an alt instruction
 596                          * jumps past the end of the section.  These are
 597                          * handled later in handle_group_alt().
 598                          */
 599                         if (!strcmp(insn->sec->name, ".altinstr_replacement"))
 600                                 continue;
 601 
 602                         WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
 603                                   insn->sec, insn->offset, dest_sec->name,
 604                                   dest_off);
 605                         return -1;
 606                 }
 607 
 608                 /*
 609                  * Cross-function jump.
 610                  */
 611                 if (insn->func && insn->jump_dest->func &&
 612                     insn->func != insn->jump_dest->func) {
 613 
 614                         /*
 615                          * For GCC 8+, create parent/child links for any cold
 616                          * subfunctions.  This is _mostly_ redundant with a
 617                          * similar initialization in read_symbols().
 618                          *
 619                          * If a function has aliases, we want the *first* such
 620                          * function in the symbol table to be the subfunction's
 621                          * parent.  In that case we overwrite the
 622                          * initialization done in read_symbols().
 623                          *
 624                          * However this code can't completely replace the
 625                          * read_symbols() code because this doesn't detect the
 626                          * case where the parent function's only reference to a
 627                          * subfunction is through a jump table.
 628                          */
 629                         if (!strstr(insn->func->name, ".cold.") &&
 630                             strstr(insn->jump_dest->func->name, ".cold.")) {
 631                                 insn->func->cfunc = insn->jump_dest->func;
 632                                 insn->jump_dest->func->pfunc = insn->func;
 633 
 634                         } else if (insn->jump_dest->func->pfunc != insn->func->pfunc &&
 635                                    insn->jump_dest->offset == insn->jump_dest->func->offset) {
 636 
 637                                 /* internal sibling call */
 638                                 insn->call_dest = insn->jump_dest->func;
 639                         }
 640                 }
 641         }
 642 
 643         return 0;
 644 }
 645 
 646 /*
 647  * Find the destination instructions for all calls.
 648  */
 649 static int add_call_destinations(struct objtool_file *file)
 650 {
 651         struct instruction *insn;
 652         unsigned long dest_off;
 653         struct rela *rela;
 654 
 655         for_each_insn(file, insn) {
 656                 if (insn->type != INSN_CALL)
 657                         continue;
 658 
 659                 rela = find_rela_by_dest_range(insn->sec, insn->offset,
 660                                                insn->len);
 661                 if (!rela) {
 662                         dest_off = insn->offset + insn->len + insn->immediate;
 663                         insn->call_dest = find_symbol_by_offset(insn->sec,
 664                                                                 dest_off);
 665 
 666                         if (!insn->call_dest && !insn->ignore) {
 667                                 WARN_FUNC("unsupported intra-function call",
 668                                           insn->sec, insn->offset);
 669                                 if (retpoline)
 670                                         WARN("If this is a retpoline, please patch it in with alternatives and annotate it with ANNOTATE_NOSPEC_ALTERNATIVE.");
 671                                 return -1;
 672                         }
 673 
 674                 } else if (rela->sym->type == STT_SECTION) {
 675                         insn->call_dest = find_symbol_by_offset(rela->sym->sec,
 676                                                                 rela->addend+4);
 677                         if (!insn->call_dest ||
 678                             insn->call_dest->type != STT_FUNC) {
 679                                 WARN_FUNC("can't find call dest symbol at %s+0x%x",
 680                                           insn->sec, insn->offset,
 681                                           rela->sym->sec->name,
 682                                           rela->addend + 4);
 683                                 return -1;
 684                         }
 685                 } else
 686                         insn->call_dest = rela->sym;
 687         }
 688 
 689         return 0;
 690 }
 691 
 692 /*
 693  * The .alternatives section requires some extra special care, over and above
 694  * what other special sections require:
 695  *
 696  * 1. Because alternatives are patched in-place, we need to insert a fake jump
 697  *    instruction at the end so that validate_branch() skips all the original
 698  *    replaced instructions when validating the new instruction path.
 699  *
 700  * 2. An added wrinkle is that the new instruction length might be zero.  In
 701  *    that case the old instructions are replaced with noops.  We simulate that
 702  *    by creating a fake jump as the only new instruction.
 703  *
 704  * 3. In some cases, the alternative section includes an instruction which
 705  *    conditionally jumps to the _end_ of the entry.  We have to modify these
 706  *    jumps' destinations to point back to .text rather than the end of the
 707  *    entry in .altinstr_replacement.
 708  */
 709 static int handle_group_alt(struct objtool_file *file,
 710                             struct special_alt *special_alt,
 711                             struct instruction *orig_insn,
 712                             struct instruction **new_insn)
 713 {
 714         struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump = NULL;
 715         unsigned long dest_off;
 716 
 717         last_orig_insn = NULL;
 718         insn = orig_insn;
 719         sec_for_each_insn_from(file, insn) {
 720                 if (insn->offset >= special_alt->orig_off + special_alt->orig_len)
 721                         break;
 722 
 723                 insn->alt_group = true;
 724                 last_orig_insn = insn;
 725         }
 726 
 727         if (next_insn_same_sec(file, last_orig_insn)) {
 728                 fake_jump = malloc(sizeof(*fake_jump));
 729                 if (!fake_jump) {
 730                         WARN("malloc failed");
 731                         return -1;
 732                 }
 733                 memset(fake_jump, 0, sizeof(*fake_jump));
 734                 INIT_LIST_HEAD(&fake_jump->alts);
 735                 clear_insn_state(&fake_jump->state);
 736 
 737                 fake_jump->sec = special_alt->new_sec;
 738                 fake_jump->offset = FAKE_JUMP_OFFSET;
 739                 fake_jump->type = INSN_JUMP_UNCONDITIONAL;
 740                 fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
 741                 fake_jump->func = orig_insn->func;
 742         }
 743 
 744         if (!special_alt->new_len) {
 745                 if (!fake_jump) {
 746                         WARN("%s: empty alternative at end of section",
 747                              special_alt->orig_sec->name);
 748                         return -1;
 749                 }
 750 
 751                 *new_insn = fake_jump;
 752                 return 0;
 753         }
 754 
 755         last_new_insn = NULL;
 756         insn = *new_insn;
 757         sec_for_each_insn_from(file, insn) {
 758                 if (insn->offset >= special_alt->new_off + special_alt->new_len)
 759                         break;
 760 
 761                 last_new_insn = insn;
 762 
 763                 insn->ignore = orig_insn->ignore_alts;
 764                 insn->func = orig_insn->func;
 765 
 766                 if (insn->type != INSN_JUMP_CONDITIONAL &&
 767                     insn->type != INSN_JUMP_UNCONDITIONAL)
 768                         continue;
 769 
 770                 if (!insn->immediate)
 771                         continue;
 772 
 773                 dest_off = insn->offset + insn->len + insn->immediate;
 774                 if (dest_off == special_alt->new_off + special_alt->new_len) {
 775                         if (!fake_jump) {
 776                                 WARN("%s: alternative jump to end of section",
 777                                      special_alt->orig_sec->name);
 778                                 return -1;
 779                         }
 780                         insn->jump_dest = fake_jump;
 781                 }
 782 
 783                 if (!insn->jump_dest) {
 784                         WARN_FUNC("can't find alternative jump destination",
 785                                   insn->sec, insn->offset);
 786                         return -1;
 787                 }
 788         }
 789 
 790         if (!last_new_insn) {
 791                 WARN_FUNC("can't find last new alternative instruction",
 792                           special_alt->new_sec, special_alt->new_off);
 793                 return -1;
 794         }
 795 
 796         if (fake_jump)
 797                 list_add(&fake_jump->list, &last_new_insn->list);
 798 
 799         return 0;
 800 }
 801 
 802 /*
 803  * A jump table entry can either convert a nop to a jump or a jump to a nop.
 804  * If the original instruction is a jump, make the alt entry an effective nop
 805  * by just skipping the original instruction.
 806  */
 807 static int handle_jump_alt(struct objtool_file *file,
 808                            struct special_alt *special_alt,
 809                            struct instruction *orig_insn,
 810                            struct instruction **new_insn)
 811 {
 812         if (orig_insn->type == INSN_NOP)
 813                 return 0;
 814 
 815         if (orig_insn->type != INSN_JUMP_UNCONDITIONAL) {
 816                 WARN_FUNC("unsupported instruction at jump label",
 817                           orig_insn->sec, orig_insn->offset);
 818                 return -1;
 819         }
 820 
 821         *new_insn = list_next_entry(orig_insn, list);
 822         return 0;
 823 }
 824 
 825 /*
 826  * Read all the special sections which have alternate instructions which can be
 827  * patched in or redirected to at runtime.  Each instruction having alternate
 828  * instruction(s) has them added to its insn->alts list, which will be
 829  * traversed in validate_branch().
 830  */
 831 static int add_special_section_alts(struct objtool_file *file)
 832 {
 833         struct list_head special_alts;
 834         struct instruction *orig_insn, *new_insn;
 835         struct special_alt *special_alt, *tmp;
 836         struct alternative *alt;
 837         int ret;
 838 
 839         ret = special_get_alts(file->elf, &special_alts);
 840         if (ret)
 841                 return ret;
 842 
 843         list_for_each_entry_safe(special_alt, tmp, &special_alts, list) {
 844 
 845                 orig_insn = find_insn(file, special_alt->orig_sec,
 846                                       special_alt->orig_off);
 847                 if (!orig_insn) {
 848                         WARN_FUNC("special: can't find orig instruction",
 849                                   special_alt->orig_sec, special_alt->orig_off);
 850                         ret = -1;
 851                         goto out;
 852                 }
 853 
 854                 new_insn = NULL;
 855                 if (!special_alt->group || special_alt->new_len) {
 856                         new_insn = find_insn(file, special_alt->new_sec,
 857                                              special_alt->new_off);
 858                         if (!new_insn) {
 859                                 WARN_FUNC("special: can't find new instruction",
 860                                           special_alt->new_sec,
 861                                           special_alt->new_off);
 862                                 ret = -1;
 863                                 goto out;
 864                         }
 865                 }
 866 
 867                 if (special_alt->group) {
 868                         ret = handle_group_alt(file, special_alt, orig_insn,
 869                                                &new_insn);
 870                         if (ret)
 871                                 goto out;
 872                 } else if (special_alt->jump_or_nop) {
 873                         ret = handle_jump_alt(file, special_alt, orig_insn,
 874                                               &new_insn);
 875                         if (ret)
 876                                 goto out;
 877                 }
 878 
 879                 alt = malloc(sizeof(*alt));
 880                 if (!alt) {
 881                         WARN("malloc failed");
 882                         ret = -1;
 883                         goto out;
 884                 }
 885 
 886                 alt->insn = new_insn;
 887                 alt->skip_orig = special_alt->skip_orig;
 888                 orig_insn->ignore_alts |= special_alt->skip_alt;
 889                 list_add_tail(&alt->list, &orig_insn->alts);
 890 
 891                 list_del(&special_alt->list);
 892                 free(special_alt);
 893         }
 894 
 895 out:
 896         return ret;
 897 }
 898 
 899 static int add_jump_table(struct objtool_file *file, struct instruction *insn,
 900                             struct rela *table)
 901 {
 902         struct rela *rela = table;
 903         struct instruction *dest_insn;
 904         struct alternative *alt;
 905         struct symbol *pfunc = insn->func->pfunc;
 906         unsigned int prev_offset = 0;
 907 
 908         /*
 909          * Each @rela is a switch table relocation which points to the target
 910          * instruction.
 911          */
 912         list_for_each_entry_from(rela, &table->sec->rela_list, list) {
 913 
 914                 /* Check for the end of the table: */
 915                 if (rela != table && rela->jump_table_start)
 916                         break;
 917 
 918                 /* Make sure the table entries are consecutive: */
 919                 if (prev_offset && rela->offset != prev_offset + 8)
 920                         break;
 921 
 922                 /* Detect function pointers from contiguous objects: */
 923                 if (rela->sym->sec == pfunc->sec &&
 924                     rela->addend == pfunc->offset)
 925                         break;
 926 
 927                 dest_insn = find_insn(file, rela->sym->sec, rela->addend);
 928                 if (!dest_insn)
 929                         break;
 930 
 931                 /* Make sure the destination is in the same function: */
 932                 if (!dest_insn->func || dest_insn->func->pfunc != pfunc)
 933                         break;
 934 
 935                 alt = malloc(sizeof(*alt));
 936                 if (!alt) {
 937                         WARN("malloc failed");
 938                         return -1;
 939                 }
 940 
 941                 alt->insn = dest_insn;
 942                 list_add_tail(&alt->list, &insn->alts);
 943                 prev_offset = rela->offset;
 944         }
 945 
 946         if (!prev_offset) {
 947                 WARN_FUNC("can't find switch jump table",
 948                           insn->sec, insn->offset);
 949                 return -1;
 950         }
 951 
 952         return 0;
 953 }
 954 
 955 /*
 956  * find_jump_table() - Given a dynamic jump, find the switch jump table in
 957  * .rodata associated with it.
 958  *
 959  * There are 3 basic patterns:
 960  *
 961  * 1. jmpq *[rodata addr](,%reg,8)
 962  *
 963  *    This is the most common case by far.  It jumps to an address in a simple
 964  *    jump table which is stored in .rodata.
 965  *
 966  * 2. jmpq *[rodata addr](%rip)
 967  *
 968  *    This is caused by a rare GCC quirk, currently only seen in three driver
 969  *    functions in the kernel, only with certain obscure non-distro configs.
 970  *
 971  *    As part of an optimization, GCC makes a copy of an existing switch jump
 972  *    table, modifies it, and then hard-codes the jump (albeit with an indirect
 973  *    jump) to use a single entry in the table.  The rest of the jump table and
 974  *    some of its jump targets remain as dead code.
 975  *
 976  *    In such a case we can just crudely ignore all unreachable instruction
 977  *    warnings for the entire object file.  Ideally we would just ignore them
 978  *    for the function, but that would require redesigning the code quite a
 979  *    bit.  And honestly that's just not worth doing: unreachable instruction
 980  *    warnings are of questionable value anyway, and this is such a rare issue.
 981  *
 982  * 3. mov [rodata addr],%reg1
 983  *    ... some instructions ...
 984  *    jmpq *(%reg1,%reg2,8)
 985  *
 986  *    This is a fairly uncommon pattern which is new for GCC 6.  As of this
 987  *    writing, there are 11 occurrences of it in the allmodconfig kernel.
 988  *
 989  *    As of GCC 7 there are quite a few more of these and the 'in between' code
 990  *    is significant. Esp. with KASAN enabled some of the code between the mov
 991  *    and jmpq uses .rodata itself, which can confuse things.
 992  *
 993  *    TODO: Once we have DWARF CFI and smarter instruction decoding logic,
 994  *    ensure the same register is used in the mov and jump instructions.
 995  *
 996  *    NOTE: RETPOLINE made it harder still to decode dynamic jumps.
 997  */
 998 static struct rela *find_jump_table(struct objtool_file *file,
 999                                       struct symbol *func,
1000                                       struct instruction *insn)
1001 {
1002         struct rela *text_rela, *table_rela;
1003         struct instruction *orig_insn = insn;
1004         struct section *table_sec;
1005         unsigned long table_offset;
1006 
1007         /*
1008          * Backward search using the @first_jump_src links, these help avoid
1009          * much of the 'in between' code. Which avoids us getting confused by
1010          * it.
1011          */
1012         for (;
1013              &insn->list != &file->insn_list && insn->func && insn->func->pfunc == func;
1014              insn = insn->first_jump_src ?: list_prev_entry(insn, list)) {
1015 
1016                 if (insn != orig_insn && insn->type == INSN_JUMP_DYNAMIC)
1017                         break;
1018 
1019                 /* allow small jumps within the range */
1020                 if (insn->type == INSN_JUMP_UNCONDITIONAL &&
1021                     insn->jump_dest &&
1022                     (insn->jump_dest->offset <= insn->offset ||
1023                      insn->jump_dest->offset > orig_insn->offset))
1024                     break;
1025 
1026                 /* look for a relocation which references .rodata */
1027                 text_rela = find_rela_by_dest_range(insn->sec, insn->offset,
1028                                                     insn->len);
1029                 if (!text_rela || text_rela->sym->type != STT_SECTION ||
1030                     !text_rela->sym->sec->rodata)
1031                         continue;
1032 
1033                 table_offset = text_rela->addend;
1034                 table_sec = text_rela->sym->sec;
1035 
1036                 if (text_rela->type == R_X86_64_PC32)
1037                         table_offset += 4;
1038 
1039                 /*
1040                  * Make sure the .rodata address isn't associated with a
1041                  * symbol.  GCC jump tables are anonymous data.
1042                  *
1043                  * Also support C jump tables which are in the same format as
1044                  * switch jump tables.  For objtool to recognize them, they
1045                  * need to be placed in the C_JUMP_TABLE_SECTION section.  They
1046                  * have symbols associated with them.
1047                  */
1048                 if (find_symbol_containing(table_sec, table_offset) &&
1049                     strcmp(table_sec->name, C_JUMP_TABLE_SECTION))
1050                         continue;
1051 
1052                 /* Each table entry has a rela associated with it. */
1053                 table_rela = find_rela_by_dest(table_sec, table_offset);
1054                 if (!table_rela)
1055                         continue;
1056 
1057                 /*
1058                  * Use of RIP-relative switch jumps is quite rare, and
1059                  * indicates a rare GCC quirk/bug which can leave dead code
1060                  * behind.
1061                  */
1062                 if (text_rela->type == R_X86_64_PC32)
1063                         file->ignore_unreachables = true;
1064 
1065                 return table_rela;
1066         }
1067 
1068         return NULL;
1069 }
1070 
1071 /*
1072  * First pass: Mark the head of each jump table so that in the next pass,
1073  * we know when a given jump table ends and the next one starts.
1074  */
1075 static void mark_func_jump_tables(struct objtool_file *file,
1076                                     struct symbol *func)
1077 {
1078         struct instruction *insn, *last = NULL;
1079         struct rela *rela;
1080 
1081         func_for_each_insn_all(file, func, insn) {
1082                 if (!last)
1083                         last = insn;
1084 
1085                 /*
1086                  * Store back-pointers for unconditional forward jumps such
1087                  * that find_jump_table() can back-track using those and
1088                  * avoid some potentially confusing code.
1089                  */
1090                 if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest &&
1091                     insn->offset > last->offset &&
1092                     insn->jump_dest->offset > insn->offset &&
1093                     !insn->jump_dest->first_jump_src) {
1094 
1095                         insn->jump_dest->first_jump_src = insn;
1096                         last = insn->jump_dest;
1097                 }
1098 
1099                 if (insn->type != INSN_JUMP_DYNAMIC)
1100                         continue;
1101 
1102                 rela = find_jump_table(file, func, insn);
1103                 if (rela) {
1104                         rela->jump_table_start = true;
1105                         insn->jump_table = rela;
1106                 }
1107         }
1108 }
1109 
1110 static int add_func_jump_tables(struct objtool_file *file,
1111                                   struct symbol *func)
1112 {
1113         struct instruction *insn;
1114         int ret;
1115 
1116         func_for_each_insn_all(file, func, insn) {
1117                 if (!insn->jump_table)
1118                         continue;
1119 
1120                 ret = add_jump_table(file, insn, insn->jump_table);
1121                 if (ret)
1122                         return ret;
1123         }
1124 
1125         return 0;
1126 }
1127 
1128 /*
1129  * For some switch statements, gcc generates a jump table in the .rodata
1130  * section which contains a list of addresses within the function to jump to.
1131  * This finds these jump tables and adds them to the insn->alts lists.
1132  */
1133 static int add_jump_table_alts(struct objtool_file *file)
1134 {
1135         struct section *sec;
1136         struct symbol *func;
1137         int ret;
1138 
1139         if (!file->rodata)
1140                 return 0;
1141 
1142         for_each_sec(file, sec) {
1143                 list_for_each_entry(func, &sec->symbol_list, list) {
1144                         if (func->type != STT_FUNC)
1145                                 continue;
1146 
1147                         mark_func_jump_tables(file, func);
1148                         ret = add_func_jump_tables(file, func);
1149                         if (ret)
1150                                 return ret;
1151                 }
1152         }
1153 
1154         return 0;
1155 }
1156 
1157 static int read_unwind_hints(struct objtool_file *file)
1158 {
1159         struct section *sec, *relasec;
1160         struct rela *rela;
1161         struct unwind_hint *hint;
1162         struct instruction *insn;
1163         struct cfi_reg *cfa;
1164         int i;
1165 
1166         sec = find_section_by_name(file->elf, ".discard.unwind_hints");
1167         if (!sec)
1168                 return 0;
1169 
1170         relasec = sec->rela;
1171         if (!relasec) {
1172                 WARN("missing .rela.discard.unwind_hints section");
1173                 return -1;
1174         }
1175 
1176         if (sec->len % sizeof(struct unwind_hint)) {
1177                 WARN("struct unwind_hint size mismatch");
1178                 return -1;
1179         }
1180 
1181         file->hints = true;
1182 
1183         for (i = 0; i < sec->len / sizeof(struct unwind_hint); i++) {
1184                 hint = (struct unwind_hint *)sec->data->d_buf + i;
1185 
1186                 rela = find_rela_by_dest(sec, i * sizeof(*hint));
1187                 if (!rela) {
1188                         WARN("can't find rela for unwind_hints[%d]", i);
1189                         return -1;
1190                 }
1191 
1192                 insn = find_insn(file, rela->sym->sec, rela->addend);
1193                 if (!insn) {
1194                         WARN("can't find insn for unwind_hints[%d]", i);
1195                         return -1;
1196                 }
1197 
1198                 cfa = &insn->state.cfa;
1199 
1200                 if (hint->type == UNWIND_HINT_TYPE_SAVE) {
1201                         insn->save = true;
1202                         continue;
1203 
1204                 } else if (hint->type == UNWIND_HINT_TYPE_RESTORE) {
1205                         insn->restore = true;
1206                         insn->hint = true;
1207                         continue;
1208                 }
1209 
1210                 insn->hint = true;
1211 
1212                 switch (hint->sp_reg) {
1213                 case ORC_REG_UNDEFINED:
1214                         cfa->base = CFI_UNDEFINED;
1215                         break;
1216                 case ORC_REG_SP:
1217                         cfa->base = CFI_SP;
1218                         break;
1219                 case ORC_REG_BP:
1220                         cfa->base = CFI_BP;
1221                         break;
1222                 case ORC_REG_SP_INDIRECT:
1223                         cfa->base = CFI_SP_INDIRECT;
1224                         break;
1225                 case ORC_REG_R10:
1226                         cfa->base = CFI_R10;
1227                         break;
1228                 case ORC_REG_R13:
1229                         cfa->base = CFI_R13;
1230                         break;
1231                 case ORC_REG_DI:
1232                         cfa->base = CFI_DI;
1233                         break;
1234                 case ORC_REG_DX:
1235                         cfa->base = CFI_DX;
1236                         break;
1237                 default:
1238                         WARN_FUNC("unsupported unwind_hint sp base reg %d",
1239                                   insn->sec, insn->offset, hint->sp_reg);
1240                         return -1;
1241                 }
1242 
1243                 cfa->offset = hint->sp_offset;
1244                 insn->state.type = hint->type;
1245                 insn->state.end = hint->end;
1246         }
1247 
1248         return 0;
1249 }
1250 
1251 static int read_retpoline_hints(struct objtool_file *file)
1252 {
1253         struct section *sec;
1254         struct instruction *insn;
1255         struct rela *rela;
1256 
1257         sec = find_section_by_name(file->elf, ".rela.discard.retpoline_safe");
1258         if (!sec)
1259                 return 0;
1260 
1261         list_for_each_entry(rela, &sec->rela_list, list) {
1262                 if (rela->sym->type != STT_SECTION) {
1263                         WARN("unexpected relocation symbol type in %s", sec->name);
1264                         return -1;
1265                 }
1266 
1267                 insn = find_insn(file, rela->sym->sec, rela->addend);
1268                 if (!insn) {
1269                         WARN("bad .discard.retpoline_safe entry");
1270                         return -1;
1271                 }
1272 
1273                 if (insn->type != INSN_JUMP_DYNAMIC &&
1274                     insn->type != INSN_CALL_DYNAMIC) {
1275                         WARN_FUNC("retpoline_safe hint not an indirect jump/call",
1276                                   insn->sec, insn->offset);
1277                         return -1;
1278                 }
1279 
1280                 insn->retpoline_safe = true;
1281         }
1282 
1283         return 0;
1284 }
1285 
1286 static void mark_rodata(struct objtool_file *file)
1287 {
1288         struct section *sec;
1289         bool found = false;
1290 
1291         /*
1292          * Search for the following rodata sections, each of which can
1293          * potentially contain jump tables:
1294          *
1295          * - .rodata: can contain GCC switch tables
1296          * - .rodata.<func>: same, if -fdata-sections is being used
1297          * - .rodata..c_jump_table: contains C annotated jump tables
1298          *
1299          * .rodata.str1.* sections are ignored; they don't contain jump tables.
1300          */
1301         for_each_sec(file, sec) {
1302                 if ((!strncmp(sec->name, ".rodata", 7) && !strstr(sec->name, ".str1.")) ||
1303                     !strcmp(sec->name, C_JUMP_TABLE_SECTION)) {
1304                         sec->rodata = true;
1305                         found = true;
1306                 }
1307         }
1308 
1309         file->rodata = found;
1310 }
1311 
1312 static int decode_sections(struct objtool_file *file)
1313 {
1314         int ret;
1315 
1316         mark_rodata(file);
1317 
1318         ret = decode_instructions(file);
1319         if (ret)
1320                 return ret;
1321 
1322         ret = add_dead_ends(file);
1323         if (ret)
1324                 return ret;
1325 
1326         add_ignores(file);
1327         add_uaccess_safe(file);
1328 
1329         ret = add_ignore_alternatives(file);
1330         if (ret)
1331                 return ret;
1332 
1333         ret = add_jump_destinations(file);
1334         if (ret)
1335                 return ret;
1336 
1337         ret = add_special_section_alts(file);
1338         if (ret)
1339                 return ret;
1340 
1341         ret = add_call_destinations(file);
1342         if (ret)
1343                 return ret;
1344 
1345         ret = add_jump_table_alts(file);
1346         if (ret)
1347                 return ret;
1348 
1349         ret = read_unwind_hints(file);
1350         if (ret)
1351                 return ret;
1352 
1353         ret = read_retpoline_hints(file);
1354         if (ret)
1355                 return ret;
1356 
1357         return 0;
1358 }
1359 
1360 static bool is_fentry_call(struct instruction *insn)
1361 {
1362         if (insn->type == INSN_CALL &&
1363             insn->call_dest->type == STT_NOTYPE &&
1364             !strcmp(insn->call_dest->name, "__fentry__"))
1365                 return true;
1366 
1367         return false;
1368 }
1369 
1370 static bool has_modified_stack_frame(struct insn_state *state)
1371 {
1372         int i;
1373 
1374         if (state->cfa.base != initial_func_cfi.cfa.base ||
1375             state->cfa.offset != initial_func_cfi.cfa.offset ||
1376             state->stack_size != initial_func_cfi.cfa.offset ||
1377             state->drap)
1378                 return true;
1379 
1380         for (i = 0; i < CFI_NUM_REGS; i++)
1381                 if (state->regs[i].base != initial_func_cfi.regs[i].base ||
1382                     state->regs[i].offset != initial_func_cfi.regs[i].offset)
1383                         return true;
1384 
1385         return false;
1386 }
1387 
1388 static bool has_valid_stack_frame(struct insn_state *state)
1389 {
1390         if (state->cfa.base == CFI_BP && state->regs[CFI_BP].base == CFI_CFA &&
1391             state->regs[CFI_BP].offset == -16)
1392                 return true;
1393 
1394         if (state->drap && state->regs[CFI_BP].base == CFI_BP)
1395                 return true;
1396 
1397         return false;
1398 }
1399 
1400 static int update_insn_state_regs(struct instruction *insn, struct insn_state *state)
1401 {
1402         struct cfi_reg *cfa = &state->cfa;
1403         struct stack_op *op = &insn->stack_op;
1404 
1405         if (cfa->base != CFI_SP && cfa->base != CFI_SP_INDIRECT)
1406                 return 0;
1407 
1408         /* push */
1409         if (op->dest.type == OP_DEST_PUSH || op->dest.type == OP_DEST_PUSHF)
1410                 cfa->offset += 8;
1411 
1412         /* pop */
1413         if (op->src.type == OP_SRC_POP || op->src.type == OP_SRC_POPF)
1414                 cfa->offset -= 8;
1415 
1416         /* add immediate to sp */
1417         if (op->dest.type == OP_DEST_REG && op->src.type == OP_SRC_ADD &&
1418             op->dest.reg == CFI_SP && op->src.reg == CFI_SP)
1419                 cfa->offset -= op->src.offset;
1420 
1421         return 0;
1422 }
1423 
1424 static void save_reg(struct insn_state *state, unsigned char reg, int base,
1425                      int offset)
1426 {
1427         if (arch_callee_saved_reg(reg) &&
1428             state->regs[reg].base == CFI_UNDEFINED) {
1429                 state->regs[reg].base = base;
1430                 state->regs[reg].offset = offset;
1431         }
1432 }
1433 
1434 static void restore_reg(struct insn_state *state, unsigned char reg)
1435 {
1436         state->regs[reg].base = CFI_UNDEFINED;
1437         state->regs[reg].offset = 0;
1438 }
1439 
1440 /*
1441  * A note about DRAP stack alignment:
1442  *
1443  * GCC has the concept of a DRAP register, which is used to help keep track of
1444  * the stack pointer when aligning the stack.  r10 or r13 is used as the DRAP
1445  * register.  The typical DRAP pattern is:
1446  *
1447  *   4c 8d 54 24 08             lea    0x8(%rsp),%r10
1448  *   48 83 e4 c0                and    $0xffffffffffffffc0,%rsp
1449  *   41 ff 72 f8                pushq  -0x8(%r10)
1450  *   55                         push   %rbp
1451  *   48 89 e5                   mov    %rsp,%rbp
1452  *                              (more pushes)
1453  *   41 52                      push   %r10
1454  *                              ...
1455  *   41 5a                      pop    %r10
1456  *                              (more pops)
1457  *   5d                         pop    %rbp
1458  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1459  *   c3                         retq
1460  *
1461  * There are some variations in the epilogues, like:
1462  *
1463  *   5b                         pop    %rbx
1464  *   41 5a                      pop    %r10
1465  *   41 5c                      pop    %r12
1466  *   41 5d                      pop    %r13
1467  *   41 5e                      pop    %r14
1468  *   c9                         leaveq
1469  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1470  *   c3                         retq
1471  *
1472  * and:
1473  *
1474  *   4c 8b 55 e8                mov    -0x18(%rbp),%r10
1475  *   48 8b 5d e0                mov    -0x20(%rbp),%rbx
1476  *   4c 8b 65 f0                mov    -0x10(%rbp),%r12
1477  *   4c 8b 6d f8                mov    -0x8(%rbp),%r13
1478  *   c9                         leaveq
1479  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1480  *   c3                         retq
1481  *
1482  * Sometimes r13 is used as the DRAP register, in which case it's saved and
1483  * restored beforehand:
1484  *
1485  *   41 55                      push   %r13
1486  *   4c 8d 6c 24 10             lea    0x10(%rsp),%r13
1487  *   48 83 e4 f0                and    $0xfffffffffffffff0,%rsp
1488  *                              ...
1489  *   49 8d 65 f0                lea    -0x10(%r13),%rsp
1490  *   41 5d                      pop    %r13
1491  *   c3                         retq
1492  */
1493 static int update_insn_state(struct instruction *insn, struct insn_state *state)
1494 {
1495         struct stack_op *op = &insn->stack_op;
1496         struct cfi_reg *cfa = &state->cfa;
1497         struct cfi_reg *regs = state->regs;
1498 
1499         /* stack operations don't make sense with an undefined CFA */
1500         if (cfa->base == CFI_UNDEFINED) {
1501                 if (insn->func) {
1502                         WARN_FUNC("undefined stack state", insn->sec, insn->offset);
1503                         return -1;
1504                 }
1505                 return 0;
1506         }
1507 
1508         if (state->type == ORC_TYPE_REGS || state->type == ORC_TYPE_REGS_IRET)
1509                 return update_insn_state_regs(insn, state);
1510 
1511         switch (op->dest.type) {
1512 
1513         case OP_DEST_REG:
1514                 switch (op->src.type) {
1515 
1516                 case OP_SRC_REG:
1517                         if (op->src.reg == CFI_SP && op->dest.reg == CFI_BP &&
1518                             cfa->base == CFI_SP &&
1519                             regs[CFI_BP].base == CFI_CFA &&
1520                             regs[CFI_BP].offset == -cfa->offset) {
1521 
1522                                 /* mov %rsp, %rbp */
1523                                 cfa->base = op->dest.reg;
1524                                 state->bp_scratch = false;
1525                         }
1526 
1527                         else if (op->src.reg == CFI_SP &&
1528                                  op->dest.reg == CFI_BP && state->drap) {
1529 
1530                                 /* drap: mov %rsp, %rbp */
1531                                 regs[CFI_BP].base = CFI_BP;
1532                                 regs[CFI_BP].offset = -state->stack_size;
1533                                 state->bp_scratch = false;
1534                         }
1535 
1536                         else if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1537 
1538                                 /*
1539                                  * mov %rsp, %reg
1540                                  *
1541                                  * This is needed for the rare case where GCC
1542                                  * does:
1543                                  *
1544                                  *   mov    %rsp, %rax
1545                                  *   ...
1546                                  *   mov    %rax, %rsp
1547                                  */
1548                                 state->vals[op->dest.reg].base = CFI_CFA;
1549                                 state->vals[op->dest.reg].offset = -state->stack_size;
1550                         }
1551 
1552                         else if (op->src.reg == CFI_BP && op->dest.reg == CFI_SP &&
1553                                  cfa->base == CFI_BP) {
1554 
1555                                 /*
1556                                  * mov %rbp, %rsp
1557                                  *
1558                                  * Restore the original stack pointer (Clang).
1559                                  */
1560                                 state->stack_size = -state->regs[CFI_BP].offset;
1561                         }
1562 
1563                         else if (op->dest.reg == cfa->base) {
1564 
1565                                 /* mov %reg, %rsp */
1566                                 if (cfa->base == CFI_SP &&
1567                                     state->vals[op->src.reg].base == CFI_CFA) {
1568 
1569                                         /*
1570                                          * This is needed for the rare case
1571                                          * where GCC does something dumb like:
1572                                          *
1573                                          *   lea    0x8(%rsp), %rcx
1574                                          *   ...
1575                                          *   mov    %rcx, %rsp
1576                                          */
1577                                         cfa->offset = -state->vals[op->src.reg].offset;
1578                                         state->stack_size = cfa->offset;
1579 
1580                                 } else {
1581                                         cfa->base = CFI_UNDEFINED;
1582                                         cfa->offset = 0;
1583                                 }
1584                         }
1585 
1586                         break;
1587 
1588                 case OP_SRC_ADD:
1589                         if (op->dest.reg == CFI_SP && op->src.reg == CFI_SP) {
1590 
1591                                 /* add imm, %rsp */
1592                                 state->stack_size -= op->src.offset;
1593                                 if (cfa->base == CFI_SP)
1594                                         cfa->offset -= op->src.offset;
1595                                 break;
1596                         }
1597 
1598                         if (op->dest.reg == CFI_SP && op->src.reg == CFI_BP) {
1599 
1600                                 /* lea disp(%rbp), %rsp */
1601                                 state->stack_size = -(op->src.offset + regs[CFI_BP].offset);
1602                                 break;
1603                         }
1604 
1605                         if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1606 
1607                                 /* drap: lea disp(%rsp), %drap */
1608                                 state->drap_reg = op->dest.reg;
1609 
1610                                 /*
1611                                  * lea disp(%rsp), %reg
1612                                  *
1613                                  * This is needed for the rare case where GCC
1614                                  * does something dumb like:
1615                                  *
1616                                  *   lea    0x8(%rsp), %rcx
1617                                  *   ...
1618                                  *   mov    %rcx, %rsp
1619                                  */
1620                                 state->vals[op->dest.reg].base = CFI_CFA;
1621                                 state->vals[op->dest.reg].offset = \
1622                                         -state->stack_size + op->src.offset;
1623 
1624                                 break;
1625                         }
1626 
1627                         if (state->drap && op->dest.reg == CFI_SP &&
1628                             op->src.reg == state->drap_reg) {
1629 
1630                                  /* drap: lea disp(%drap), %rsp */
1631                                 cfa->base = CFI_SP;
1632                                 cfa->offset = state->stack_size = -op->src.offset;
1633                                 state->drap_reg = CFI_UNDEFINED;
1634                                 state->drap = false;
1635                                 break;
1636                         }
1637 
1638                         if (op->dest.reg == state->cfa.base) {
1639                                 WARN_FUNC("unsupported stack register modification",
1640                                           insn->sec, insn->offset);
1641                                 return -1;
1642                         }
1643 
1644                         break;
1645 
1646                 case OP_SRC_AND:
1647                         if (op->dest.reg != CFI_SP ||
1648                             (state->drap_reg != CFI_UNDEFINED && cfa->base != CFI_SP) ||
1649                             (state->drap_reg == CFI_UNDEFINED && cfa->base != CFI_BP)) {
1650                                 WARN_FUNC("unsupported stack pointer realignment",
1651                                           insn->sec, insn->offset);
1652                                 return -1;
1653                         }
1654 
1655                         if (state->drap_reg != CFI_UNDEFINED) {
1656                                 /* drap: and imm, %rsp */
1657                                 cfa->base = state->drap_reg;
1658                                 cfa->offset = state->stack_size = 0;
1659                                 state->drap = true;
1660                         }
1661 
1662                         /*
1663                          * Older versions of GCC (4.8ish) realign the stack
1664                          * without DRAP, with a frame pointer.
1665                          */
1666 
1667                         break;
1668 
1669                 case OP_SRC_POP:
1670                 case OP_SRC_POPF:
1671                         if (!state->drap && op->dest.type == OP_DEST_REG &&
1672                             op->dest.reg == cfa->base) {
1673 
1674                                 /* pop %rbp */
1675                                 cfa->base = CFI_SP;
1676                         }
1677 
1678                         if (state->drap && cfa->base == CFI_BP_INDIRECT &&
1679                             op->dest.type == OP_DEST_REG &&
1680                             op->dest.reg == state->drap_reg &&
1681                             state->drap_offset == -state->stack_size) {
1682 
1683                                 /* drap: pop %drap */
1684                                 cfa->base = state->drap_reg;
1685                                 cfa->offset = 0;
1686                                 state->drap_offset = -1;
1687 
1688                         } else if (regs[op->dest.reg].offset == -state->stack_size) {
1689 
1690                                 /* pop %reg */
1691                                 restore_reg(state, op->dest.reg);
1692                         }
1693 
1694                         state->stack_size -= 8;
1695                         if (cfa->base == CFI_SP)
1696                                 cfa->offset -= 8;
1697 
1698                         break;
1699 
1700                 case OP_SRC_REG_INDIRECT:
1701                         if (state->drap && op->src.reg == CFI_BP &&
1702                             op->src.offset == state->drap_offset) {
1703 
1704                                 /* drap: mov disp(%rbp), %drap */
1705                                 cfa->base = state->drap_reg;
1706                                 cfa->offset = 0;
1707                                 state->drap_offset = -1;
1708                         }
1709 
1710                         if (state->drap && op->src.reg == CFI_BP &&
1711                             op->src.offset == regs[op->dest.reg].offset) {
1712 
1713                                 /* drap: mov disp(%rbp), %reg */
1714                                 restore_reg(state, op->dest.reg);
1715 
1716                         } else if (op->src.reg == cfa->base &&
1717                             op->src.offset == regs[op->dest.reg].offset + cfa->offset) {
1718 
1719                                 /* mov disp(%rbp), %reg */
1720                                 /* mov disp(%rsp), %reg */
1721                                 restore_reg(state, op->dest.reg);
1722                         }
1723 
1724                         break;
1725 
1726                 default:
1727                         WARN_FUNC("unknown stack-related instruction",
1728                                   insn->sec, insn->offset);
1729                         return -1;
1730                 }
1731 
1732                 break;
1733 
1734         case OP_DEST_PUSH:
1735         case OP_DEST_PUSHF:
1736                 state->stack_size += 8;
1737                 if (cfa->base == CFI_SP)
1738                         cfa->offset += 8;
1739 
1740                 if (op->src.type != OP_SRC_REG)
1741                         break;
1742 
1743                 if (state->drap) {
1744                         if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1745 
1746                                 /* drap: push %drap */
1747                                 cfa->base = CFI_BP_INDIRECT;
1748                                 cfa->offset = -state->stack_size;
1749 
1750                                 /* save drap so we know when to restore it */
1751                                 state->drap_offset = -state->stack_size;
1752 
1753                         } else if (op->src.reg == CFI_BP && cfa->base == state->drap_reg) {
1754 
1755                                 /* drap: push %rbp */
1756                                 state->stack_size = 0;
1757 
1758                         } else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1759 
1760                                 /* drap: push %reg */
1761                                 save_reg(state, op->src.reg, CFI_BP, -state->stack_size);
1762                         }
1763 
1764                 } else {
1765 
1766                         /* push %reg */
1767                         save_reg(state, op->src.reg, CFI_CFA, -state->stack_size);
1768                 }
1769 
1770                 /* detect when asm code uses rbp as a scratch register */
1771                 if (!no_fp && insn->func && op->src.reg == CFI_BP &&
1772                     cfa->base != CFI_BP)
1773                         state->bp_scratch = true;
1774                 break;
1775 
1776         case OP_DEST_REG_INDIRECT:
1777 
1778                 if (state->drap) {
1779                         if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1780 
1781                                 /* drap: mov %drap, disp(%rbp) */
1782                                 cfa->base = CFI_BP_INDIRECT;
1783                                 cfa->offset = op->dest.offset;
1784 
1785                                 /* save drap offset so we know when to restore it */
1786                                 state->drap_offset = op->dest.offset;
1787                         }
1788 
1789                         else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1790 
1791                                 /* drap: mov reg, disp(%rbp) */
1792                                 save_reg(state, op->src.reg, CFI_BP, op->dest.offset);
1793                         }
1794 
1795                 } else if (op->dest.reg == cfa->base) {
1796 
1797                         /* mov reg, disp(%rbp) */
1798                         /* mov reg, disp(%rsp) */
1799                         save_reg(state, op->src.reg, CFI_CFA,
1800                                  op->dest.offset - state->cfa.offset);
1801                 }
1802 
1803                 break;
1804 
1805         case OP_DEST_LEAVE:
1806                 if ((!state->drap && cfa->base != CFI_BP) ||
1807                     (state->drap && cfa->base != state->drap_reg)) {
1808                         WARN_FUNC("leave instruction with modified stack frame",
1809                                   insn->sec, insn->offset);
1810                         return -1;
1811                 }
1812 
1813                 /* leave (mov %rbp, %rsp; pop %rbp) */
1814 
1815                 state->stack_size = -state->regs[CFI_BP].offset - 8;
1816                 restore_reg(state, CFI_BP);
1817 
1818                 if (!state->drap) {
1819                         cfa->base = CFI_SP;
1820                         cfa->offset -= 8;
1821                 }
1822 
1823                 break;
1824 
1825         case OP_DEST_MEM:
1826                 if (op->src.type != OP_SRC_POP && op->src.type != OP_SRC_POPF) {
1827                         WARN_FUNC("unknown stack-related memory operation",
1828                                   insn->sec, insn->offset);
1829                         return -1;
1830                 }
1831 
1832                 /* pop mem */
1833                 state->stack_size -= 8;
1834                 if (cfa->base == CFI_SP)
1835                         cfa->offset -= 8;
1836 
1837                 break;
1838 
1839         default:
1840                 WARN_FUNC("unknown stack-related instruction",
1841                           insn->sec, insn->offset);
1842                 return -1;
1843         }
1844 
1845         return 0;
1846 }
1847 
1848 static bool insn_state_match(struct instruction *insn, struct insn_state *state)
1849 {
1850         struct insn_state *state1 = &insn->state, *state2 = state;
1851         int i;
1852 
1853         if (memcmp(&state1->cfa, &state2->cfa, sizeof(state1->cfa))) {
1854                 WARN_FUNC("stack state mismatch: cfa1=%d%+d cfa2=%d%+d",
1855                           insn->sec, insn->offset,
1856                           state1->cfa.base, state1->cfa.offset,
1857                           state2->cfa.base, state2->cfa.offset);
1858 
1859         } else if (memcmp(&state1->regs, &state2->regs, sizeof(state1->regs))) {
1860                 for (i = 0; i < CFI_NUM_REGS; i++) {
1861                         if (!memcmp(&state1->regs[i], &state2->regs[i],
1862                                     sizeof(struct cfi_reg)))
1863                                 continue;
1864 
1865                         WARN_FUNC("stack state mismatch: reg1[%d]=%d%+d reg2[%d]=%d%+d",
1866                                   insn->sec, insn->offset,
1867                                   i, state1->regs[i].base, state1->regs[i].offset,
1868                                   i, state2->regs[i].base, state2->regs[i].offset);
1869                         break;
1870                 }
1871 
1872         } else if (state1->type != state2->type) {
1873                 WARN_FUNC("stack state mismatch: type1=%d type2=%d",
1874                           insn->sec, insn->offset, state1->type, state2->type);
1875 
1876         } else if (state1->drap != state2->drap ||
1877                  (state1->drap && state1->drap_reg != state2->drap_reg) ||
1878                  (state1->drap && state1->drap_offset != state2->drap_offset)) {
1879                 WARN_FUNC("stack state mismatch: drap1=%d(%d,%d) drap2=%d(%d,%d)",
1880                           insn->sec, insn->offset,
1881                           state1->drap, state1->drap_reg, state1->drap_offset,
1882                           state2->drap, state2->drap_reg, state2->drap_offset);
1883 
1884         } else
1885                 return true;
1886 
1887         return false;
1888 }
1889 
1890 static inline bool func_uaccess_safe(struct symbol *func)
1891 {
1892         if (func)
1893                 return func->uaccess_safe;
1894 
1895         return false;
1896 }
1897 
1898 static inline const char *call_dest_name(struct instruction *insn)
1899 {
1900         if (insn->call_dest)
1901                 return insn->call_dest->name;
1902 
1903         return "{dynamic}";
1904 }
1905 
1906 static int validate_call(struct instruction *insn, struct insn_state *state)
1907 {
1908         if (state->uaccess && !func_uaccess_safe(insn->call_dest)) {
1909                 WARN_FUNC("call to %s() with UACCESS enabled",
1910                                 insn->sec, insn->offset, call_dest_name(insn));
1911                 return 1;
1912         }
1913 
1914         if (state->df) {
1915                 WARN_FUNC("call to %s() with DF set",
1916                                 insn->sec, insn->offset, call_dest_name(insn));
1917                 return 1;
1918         }
1919 
1920         return 0;
1921 }
1922 
1923 static int validate_sibling_call(struct instruction *insn, struct insn_state *state)
1924 {
1925         if (has_modified_stack_frame(state)) {
1926                 WARN_FUNC("sibling call from callable instruction with modified stack frame",
1927                                 insn->sec, insn->offset);
1928                 return 1;
1929         }
1930 
1931         return validate_call(insn, state);
1932 }
1933 
1934 /*
1935  * Follow the branch starting at the given instruction, and recursively follow
1936  * any other branches (jumps).  Meanwhile, track the frame pointer state at
1937  * each instruction and validate all the rules described in
1938  * tools/objtool/Documentation/stack-validation.txt.
1939  */
1940 static int validate_branch(struct objtool_file *file, struct symbol *func,
1941                            struct instruction *first, struct insn_state state)
1942 {
1943         struct alternative *alt;
1944         struct instruction *insn, *next_insn;
1945         struct section *sec;
1946         u8 visited;
1947         int ret;
1948 
1949         insn = first;
1950         sec = insn->sec;
1951 
1952         if (insn->alt_group && list_empty(&insn->alts)) {
1953                 WARN_FUNC("don't know how to handle branch to middle of alternative instruction group",
1954                           sec, insn->offset);
1955                 return 1;
1956         }
1957 
1958         while (1) {
1959                 next_insn = next_insn_same_sec(file, insn);
1960 
1961                 if (file->c_file && func && insn->func && func != insn->func->pfunc) {
1962                         WARN("%s() falls through to next function %s()",
1963                              func->name, insn->func->name);
1964                         return 1;
1965                 }
1966 
1967                 if (func && insn->ignore) {
1968                         WARN_FUNC("BUG: why am I validating an ignored function?",
1969                                   sec, insn->offset);
1970                         return 1;
1971                 }
1972 
1973                 visited = 1 << state.uaccess;
1974                 if (insn->visited) {
1975                         if (!insn->hint && !insn_state_match(insn, &state))
1976                                 return 1;
1977 
1978                         if (insn->visited & visited)
1979                                 return 0;
1980                 }
1981 
1982                 if (insn->hint) {
1983                         if (insn->restore) {
1984                                 struct instruction *save_insn, *i;
1985 
1986                                 i = insn;
1987                                 save_insn = NULL;
1988                                 func_for_each_insn_continue_reverse(file, func, i) {
1989                                         if (i->save) {
1990                                                 save_insn = i;
1991                                                 break;
1992                                         }
1993                                 }
1994 
1995                                 if (!save_insn) {
1996                                         WARN_FUNC("no corresponding CFI save for CFI restore",
1997                                                   sec, insn->offset);
1998                                         return 1;
1999                                 }
2000 
2001                                 if (!save_insn->visited) {
2002                                         /*
2003                                          * Oops, no state to copy yet.
2004                                          * Hopefully we can reach this
2005                                          * instruction from another branch
2006                                          * after the save insn has been
2007                                          * visited.
2008                                          */
2009                                         if (insn == first)
2010                                                 return 0;
2011 
2012                                         WARN_FUNC("objtool isn't smart enough to handle this CFI save/restore combo",
2013                                                   sec, insn->offset);
2014                                         return 1;
2015                                 }
2016 
2017                                 insn->state = save_insn->state;
2018                         }
2019 
2020                         state = insn->state;
2021 
2022                 } else
2023                         insn->state = state;
2024 
2025                 insn->visited |= visited;
2026 
2027                 if (!insn->ignore_alts) {
2028                         bool skip_orig = false;
2029 
2030                         list_for_each_entry(alt, &insn->alts, list) {
2031                                 if (alt->skip_orig)
2032                                         skip_orig = true;
2033 
2034                                 ret = validate_branch(file, func, alt->insn, state);
2035                                 if (ret) {
2036                                         if (backtrace)
2037                                                 BT_FUNC("(alt)", insn);
2038                                         return ret;
2039                                 }
2040                         }
2041 
2042                         if (skip_orig)
2043                                 return 0;
2044                 }
2045 
2046                 switch (insn->type) {
2047 
2048                 case INSN_RETURN:
2049                         if (state.uaccess && !func_uaccess_safe(func)) {
2050                                 WARN_FUNC("return with UACCESS enabled", sec, insn->offset);
2051                                 return 1;
2052                         }
2053 
2054                         if (!state.uaccess && func_uaccess_safe(func)) {
2055                                 WARN_FUNC("return with UACCESS disabled from a UACCESS-safe function", sec, insn->offset);
2056                                 return 1;
2057                         }
2058 
2059                         if (state.df) {
2060                                 WARN_FUNC("return with DF set", sec, insn->offset);
2061                                 return 1;
2062                         }
2063 
2064                         if (func && has_modified_stack_frame(&state)) {
2065                                 WARN_FUNC("return with modified stack frame",
2066                                           sec, insn->offset);
2067                                 return 1;
2068                         }
2069 
2070                         if (state.bp_scratch) {
2071                                 WARN("%s uses BP as a scratch register",
2072                                      func->name);
2073                                 return 1;
2074                         }
2075 
2076                         return 0;
2077 
2078                 case INSN_CALL:
2079                 case INSN_CALL_DYNAMIC:
2080                         ret = validate_call(insn, &state);
2081                         if (ret)
2082                                 return ret;
2083 
2084                         if (!no_fp && func && !is_fentry_call(insn) &&
2085                             !has_valid_stack_frame(&state)) {
2086                                 WARN_FUNC("call without frame pointer save/setup",
2087                                           sec, insn->offset);
2088                                 return 1;
2089                         }
2090 
2091                         if (dead_end_function(file, insn->call_dest))
2092                                 return 0;
2093 
2094                         break;
2095 
2096                 case INSN_JUMP_CONDITIONAL:
2097                 case INSN_JUMP_UNCONDITIONAL:
2098                         if (func && is_sibling_call(insn)) {
2099                                 ret = validate_sibling_call(insn, &state);
2100                                 if (ret)
2101                                         return ret;
2102 
2103                         } else if (insn->jump_dest) {
2104                                 ret = validate_branch(file, func,
2105                                                       insn->jump_dest, state);
2106                                 if (ret) {
2107                                         if (backtrace)
2108                                                 BT_FUNC("(branch)", insn);
2109                                         return ret;
2110                                 }
2111                         }
2112 
2113                         if (insn->type == INSN_JUMP_UNCONDITIONAL)
2114                                 return 0;
2115 
2116                         break;
2117 
2118                 case INSN_JUMP_DYNAMIC:
2119                 case INSN_JUMP_DYNAMIC_CONDITIONAL:
2120                         if (func && is_sibling_call(insn)) {
2121                                 ret = validate_sibling_call(insn, &state);
2122                                 if (ret)
2123                                         return ret;
2124                         }
2125 
2126                         if (insn->type == INSN_JUMP_DYNAMIC)
2127                                 return 0;
2128 
2129                         break;
2130 
2131                 case INSN_CONTEXT_SWITCH:
2132                         if (func && (!next_insn || !next_insn->hint)) {
2133                                 WARN_FUNC("unsupported instruction in callable function",
2134                                           sec, insn->offset);
2135                                 return 1;
2136                         }
2137                         return 0;
2138 
2139                 case INSN_STACK:
2140                         if (update_insn_state(insn, &state))
2141                                 return 1;
2142 
2143                         if (insn->stack_op.dest.type == OP_DEST_PUSHF) {
2144                                 if (!state.uaccess_stack) {
2145                                         state.uaccess_stack = 1;
2146                                 } else if (state.uaccess_stack >> 31) {
2147                                         WARN_FUNC("PUSHF stack exhausted", sec, insn->offset);
2148                                         return 1;
2149                                 }
2150                                 state.uaccess_stack <<= 1;
2151                                 state.uaccess_stack  |= state.uaccess;
2152                         }
2153 
2154                         if (insn->stack_op.src.type == OP_SRC_POPF) {
2155                                 if (state.uaccess_stack) {
2156                                         state.uaccess = state.uaccess_stack & 1;
2157                                         state.uaccess_stack >>= 1;
2158                                         if (state.uaccess_stack == 1)
2159                                                 state.uaccess_stack = 0;
2160                                 }
2161                         }
2162 
2163                         break;
2164 
2165                 case INSN_STAC:
2166                         if (state.uaccess) {
2167                                 WARN_FUNC("recursive UACCESS enable", sec, insn->offset);
2168                                 return 1;
2169                         }
2170 
2171                         state.uaccess = true;
2172                         break;
2173 
2174                 case INSN_CLAC:
2175                         if (!state.uaccess && func) {
2176                                 WARN_FUNC("redundant UACCESS disable", sec, insn->offset);
2177                                 return 1;
2178                         }
2179 
2180                         if (func_uaccess_safe(func) && !state.uaccess_stack) {
2181                                 WARN_FUNC("UACCESS-safe disables UACCESS", sec, insn->offset);
2182                                 return 1;
2183                         }
2184 
2185                         state.uaccess = false;
2186                         break;
2187 
2188                 case INSN_STD:
2189                         if (state.df)
2190                                 WARN_FUNC("recursive STD", sec, insn->offset);
2191 
2192                         state.df = true;
2193                         break;
2194 
2195                 case INSN_CLD:
2196                         if (!state.df && func)
2197                                 WARN_FUNC("redundant CLD", sec, insn->offset);
2198 
2199                         state.df = false;
2200                         break;
2201 
2202                 default:
2203                         break;
2204                 }
2205 
2206                 if (insn->dead_end)
2207                         return 0;
2208 
2209                 if (!next_insn) {
2210                         if (state.cfa.base == CFI_UNDEFINED)
2211                                 return 0;
2212                         WARN("%s: unexpected end of section", sec->name);
2213                         return 1;
2214                 }
2215 
2216                 insn = next_insn;
2217         }
2218 
2219         return 0;
2220 }
2221 
2222 static int validate_unwind_hints(struct objtool_file *file)
2223 {
2224         struct instruction *insn;
2225         int ret, warnings = 0;
2226         struct insn_state state;
2227 
2228         if (!file->hints)
2229                 return 0;
2230 
2231         clear_insn_state(&state);
2232 
2233         for_each_insn(file, insn) {
2234                 if (insn->hint && !insn->visited) {
2235                         ret = validate_branch(file, insn->func, insn, state);
2236                         if (ret && backtrace)
2237                                 BT_FUNC("<=== (hint)", insn);
2238                         warnings += ret;
2239                 }
2240         }
2241 
2242         return warnings;
2243 }
2244 
2245 static int validate_retpoline(struct objtool_file *file)
2246 {
2247         struct instruction *insn;
2248         int warnings = 0;
2249 
2250         for_each_insn(file, insn) {
2251                 if (insn->type != INSN_JUMP_DYNAMIC &&
2252                     insn->type != INSN_CALL_DYNAMIC)
2253                         continue;
2254 
2255                 if (insn->retpoline_safe)
2256                         continue;
2257 
2258                 /*
2259                  * .init.text code is ran before userspace and thus doesn't
2260                  * strictly need retpolines, except for modules which are
2261                  * loaded late, they very much do need retpoline in their
2262                  * .init.text
2263                  */
2264                 if (!strcmp(insn->sec->name, ".init.text") && !module)
2265                         continue;
2266 
2267                 WARN_FUNC("indirect %s found in RETPOLINE build",
2268                           insn->sec, insn->offset,
2269                           insn->type == INSN_JUMP_DYNAMIC ? "jump" : "call");
2270 
2271                 warnings++;
2272         }
2273 
2274         return warnings;
2275 }
2276 
2277 static bool is_kasan_insn(struct instruction *insn)
2278 {
2279         return (insn->type == INSN_CALL &&
2280                 !strcmp(insn->call_dest->name, "__asan_handle_no_return"));
2281 }
2282 
2283 static bool is_ubsan_insn(struct instruction *insn)
2284 {
2285         return (insn->type == INSN_CALL &&
2286                 !strcmp(insn->call_dest->name,
2287                         "__ubsan_handle_builtin_unreachable"));
2288 }
2289 
2290 static bool ignore_unreachable_insn(struct instruction *insn)
2291 {
2292         int i;
2293 
2294         if (insn->ignore || insn->type == INSN_NOP)
2295                 return true;
2296 
2297         /*
2298          * Ignore any unused exceptions.  This can happen when a whitelisted
2299          * function has an exception table entry.
2300          *
2301          * Also ignore alternative replacement instructions.  This can happen
2302          * when a whitelisted function uses one of the ALTERNATIVE macros.
2303          */
2304         if (!strcmp(insn->sec->name, ".fixup") ||
2305             !strcmp(insn->sec->name, ".altinstr_replacement") ||
2306             !strcmp(insn->sec->name, ".altinstr_aux"))
2307                 return true;
2308 
2309         if (!insn->func)
2310                 return false;
2311 
2312         /*
2313          * CONFIG_UBSAN_TRAP inserts a UD2 when it sees
2314          * __builtin_unreachable().  The BUG() macro has an unreachable() after
2315          * the UD2, which causes GCC's undefined trap logic to emit another UD2
2316          * (or occasionally a JMP to UD2).
2317          */
2318         if (list_prev_entry(insn, list)->dead_end &&
2319             (insn->type == INSN_BUG ||
2320              (insn->type == INSN_JUMP_UNCONDITIONAL &&
2321               insn->jump_dest && insn->jump_dest->type == INSN_BUG)))
2322                 return true;
2323 
2324         /*
2325          * Check if this (or a subsequent) instruction is related to
2326          * CONFIG_UBSAN or CONFIG_KASAN.
2327          *
2328          * End the search at 5 instructions to avoid going into the weeds.
2329          */
2330         for (i = 0; i < 5; i++) {
2331 
2332                 if (is_kasan_insn(insn) || is_ubsan_insn(insn))
2333                         return true;
2334 
2335                 if (insn->type == INSN_JUMP_UNCONDITIONAL) {
2336                         if (insn->jump_dest &&
2337                             insn->jump_dest->func == insn->func) {
2338                                 insn = insn->jump_dest;
2339                                 continue;
2340                         }
2341 
2342                         break;
2343                 }
2344 
2345                 if (insn->offset + insn->len >= insn->func->offset + insn->func->len)
2346                         break;
2347 
2348                 insn = list_next_entry(insn, list);
2349         }
2350 
2351         return false;
2352 }
2353 
2354 static int validate_functions(struct objtool_file *file)
2355 {
2356         struct section *sec;
2357         struct symbol *func;
2358         struct instruction *insn;
2359         struct insn_state state;
2360         int ret, warnings = 0;
2361 
2362         clear_insn_state(&state);
2363 
2364         state.cfa = initial_func_cfi.cfa;
2365         memcpy(&state.regs, &initial_func_cfi.regs,
2366                CFI_NUM_REGS * sizeof(struct cfi_reg));
2367         state.stack_size = initial_func_cfi.cfa.offset;
2368 
2369         for_each_sec(file, sec) {
2370                 list_for_each_entry(func, &sec->symbol_list, list) {
2371                         if (func->type != STT_FUNC)
2372                                 continue;
2373 
2374                         if (!func->len) {
2375                                 WARN("%s() is missing an ELF size annotation",
2376                                      func->name);
2377                                 warnings++;
2378                         }
2379 
2380                         if (func->pfunc != func || func->alias != func)
2381                                 continue;
2382 
2383                         insn = find_insn(file, sec, func->offset);
2384                         if (!insn || insn->ignore || insn->visited)
2385                                 continue;
2386 
2387                         state.uaccess = func->uaccess_safe;
2388 
2389                         ret = validate_branch(file, func, insn, state);
2390                         if (ret && backtrace)
2391                                 BT_FUNC("<=== (func)", insn);
2392                         warnings += ret;
2393                 }
2394         }
2395 
2396         return warnings;
2397 }
2398 
2399 static int validate_reachable_instructions(struct objtool_file *file)
2400 {
2401         struct instruction *insn;
2402 
2403         if (file->ignore_unreachables)
2404                 return 0;
2405 
2406         for_each_insn(file, insn) {
2407                 if (insn->visited || ignore_unreachable_insn(insn))
2408                         continue;
2409 
2410                 WARN_FUNC("unreachable instruction", insn->sec, insn->offset);
2411                 return 1;
2412         }
2413 
2414         return 0;
2415 }
2416 
2417 static void cleanup(struct objtool_file *file)
2418 {
2419         struct instruction *insn, *tmpinsn;
2420         struct alternative *alt, *tmpalt;
2421 
2422         list_for_each_entry_safe(insn, tmpinsn, &file->insn_list, list) {
2423                 list_for_each_entry_safe(alt, tmpalt, &insn->alts, list) {
2424                         list_del(&alt->list);
2425                         free(alt);
2426                 }
2427                 list_del(&insn->list);
2428                 hash_del(&insn->hash);
2429                 free(insn);
2430         }
2431         elf_close(file->elf);
2432 }
2433 
2434 static struct objtool_file file;
2435 
2436 int check(const char *_objname, bool orc)
2437 {
2438         int ret, warnings = 0;
2439 
2440         objname = _objname;
2441 
2442         file.elf = elf_read(objname, orc ? O_RDWR : O_RDONLY);
2443         if (!file.elf)
2444                 return 1;
2445 
2446         INIT_LIST_HEAD(&file.insn_list);
2447         hash_init(file.insn_hash);
2448         file.c_file = find_section_by_name(file.elf, ".comment");
2449         file.ignore_unreachables = no_unreachable;
2450         file.hints = false;
2451 
2452         arch_initial_func_cfi_state(&initial_func_cfi);
2453 
2454         ret = decode_sections(&file);
2455         if (ret < 0)
2456                 goto out;
2457         warnings += ret;
2458 
2459         if (list_empty(&file.insn_list))
2460                 goto out;
2461 
2462         if (retpoline) {
2463                 ret = validate_retpoline(&file);
2464                 if (ret < 0)
2465                         return ret;
2466                 warnings += ret;
2467         }
2468 
2469         ret = validate_functions(&file);
2470         if (ret < 0)
2471                 goto out;
2472         warnings += ret;
2473 
2474         ret = validate_unwind_hints(&file);
2475         if (ret < 0)
2476                 goto out;
2477         warnings += ret;
2478 
2479         if (!warnings) {
2480                 ret = validate_reachable_instructions(&file);
2481                 if (ret < 0)
2482                         goto out;
2483                 warnings += ret;
2484         }
2485 
2486         if (orc) {
2487                 ret = create_orc(&file);
2488                 if (ret < 0)
2489                         goto out;
2490 
2491                 ret = create_orc_sections(&file);
2492                 if (ret < 0)
2493                         goto out;
2494 
2495                 ret = elf_write(file.elf);
2496                 if (ret < 0)
2497                         goto out;
2498         }
2499 
2500 out:
2501         cleanup(&file);
2502 
2503         /* ignore warnings for now until we get all the code cleaned up */
2504         if (ret || warnings)
2505                 return 0;
2506         return 0;
2507 }