tools/objtool/check.c

   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                 "kunit_try_catch_throw",
 148         };
 149
 150         if (!func)
 151                 return false;
 152
 153         if (func->bind == STB_WEAK)
 154                 return false;
 155
 156         if (func->bind == STB_GLOBAL)
 157                 for (i = 0; i < ARRAY_SIZE(global_noreturns); i++)
 158                         if (!strcmp(func->name, global_noreturns[i]))
 159                                 return true;
 160
 161         if (!func->len)
 162                 return false;
 163
 164         insn = find_insn(file, func->sec, func->offset);
 165         if (!insn->func)
 166                 return false;
 167
 168         func_for_each_insn_all(file, func, insn) {
 169                 empty = false;
 170
 171                 if (insn->type == INSN_RETURN)
 172                         return false;
 173         }
 174
 175         if (empty)
 176                 return false;
 177
 178         /*
 179          * A function can have a sibling call instead of a return.  In that
 180          * case, the function's dead-end status depends on whether the target
 181          * of the sibling call returns.
 182          */
 183         func_for_each_insn_all(file, func, insn) {
 184                 if (is_sibling_call(insn)) {
 185                         struct instruction *dest = insn->jump_dest;
 186
 187                         if (!dest)
 188                                 /* sibling call to another file */
 189                                 return false;
 190
 191                         /* local sibling call */
 192                         if (recursion == 5) {
 193                                 /*
 194                                  * Infinite recursion: two functions have
 195                                  * sibling calls to each other.  This is a very
 196                                  * rare case.  It means they aren't dead ends.
 197                                  */
 198                                 return false;
 199                         }
 200
 201                         return __dead_end_function(file, dest->func, recursion+1);
 202                 }
 203         }
 204
 205         return true;
 206 }
 207
 208 static bool dead_end_function(struct objtool_file *file, struct symbol *func)
 209 {
 210         return __dead_end_function(file, func, 0);
 211 }
 212
 213 static void clear_insn_state(struct insn_state *state)
 214 {
 215         int i;
 216
 217         memset(state, 0, sizeof(*state));
 218         state->cfa.base = CFI_UNDEFINED;
 219         for (i = 0; i < CFI_NUM_REGS; i++) {
 220                 state->regs[i].base = CFI_UNDEFINED;
 221                 state->vals[i].base = CFI_UNDEFINED;
 222         }
 223         state->drap_reg = CFI_UNDEFINED;
 224         state->drap_offset = -1;
 225 }
 226
 227 /*
 228  * Call the arch-specific instruction decoder for all the instructions and add
 229  * them to the global instruction list.
 230  */
 231 static int decode_instructions(struct objtool_file *file)
 232 {
 233         struct section *sec;
 234         struct symbol *func;
 235         unsigned long offset;
 236         struct instruction *insn;
 237         int ret;
 238
 239         for_each_sec(file, sec) {
 240
 241                 if (!(sec->sh.sh_flags & SHF_EXECINSTR))
 242                         continue;
 243
 244                 if (strcmp(sec->name, ".altinstr_replacement") &&
 245                     strcmp(sec->name, ".altinstr_aux") &&
 246                     strncmp(sec->name, ".discard.", 9))
 247                         sec->text = true;
 248
 249                 for (offset = 0; offset < sec->len; offset += insn->len) {
 250                         insn = malloc(sizeof(*insn));
 251                         if (!insn) {
 252                                 WARN("malloc failed");
 253                                 return -1;
 254                         }
 255                         memset(insn, 0, sizeof(*insn));
 256                         INIT_LIST_HEAD(&insn->alts);
 257                         clear_insn_state(&insn->state);
 258
 259                         insn->sec = sec;
 260                         insn->offset = offset;
 261
 262                         ret = arch_decode_instruction(file->elf, sec, offset,
 263                                                       sec->len - offset,
 264                                                       &insn->len, &insn->type,
 265                                                       &insn->immediate,
 266                                                       &insn->stack_op);
 267                         if (ret)
 268                                 goto err;
 269
 270                         hash_add(file->insn_hash, &insn->hash, insn->offset);
 271                         list_add_tail(&insn->list, &file->insn_list);
 272                 }
 273
 274                 list_for_each_entry(func, &sec->symbol_list, list) {
 275                         if (func->type != STT_FUNC || func->alias != func)
 276                                 continue;
 277
 278                         if (!find_insn(file, sec, func->offset)) {
 279                                 WARN("%s(): can't find starting instruction",
 280                                      func->name);
 281                                 return -1;
 282                         }
 283
 284                         func_for_each_insn(file, func, insn)
 285                                 insn->func = func;
 286                 }
 287         }
 288
 289         return 0;
 290
 291 err:
 292         free(insn);
 293         return ret;
 294 }
 295
 296 /*
 297  * Mark "ud2" instructions and manually annotated dead ends.
 298  */
 299 static int add_dead_ends(struct objtool_file *file)
 300 {
 301         struct section *sec;
 302         struct rela *rela;
 303         struct instruction *insn;
 304         bool found;
 305
 306         /*
 307          * By default, "ud2" is a dead end unless otherwise annotated, because
 308          * GCC 7 inserts it for certain divide-by-zero cases.
 309          */
 310         for_each_insn(file, insn)
 311                 if (insn->type == INSN_BUG)
 312                         insn->dead_end = true;
 313
 314         /*
 315          * Check for manually annotated dead ends.
 316          */
 317         sec = find_section_by_name(file->elf, ".rela.discard.unreachable");
 318         if (!sec)
 319                 goto reachable;
 320
 321         list_for_each_entry(rela, &sec->rela_list, list) {
 322                 if (rela->sym->type != STT_SECTION) {
 323                         WARN("unexpected relocation symbol type in %s", sec->name);
 324                         return -1;
 325                 }
 326                 insn = find_insn(file, rela->sym->sec, rela->addend);
 327                 if (insn)
 328                         insn = list_prev_entry(insn, list);
 329                 else if (rela->addend == rela->sym->sec->len) {
 330                         found = false;
 331                         list_for_each_entry_reverse(insn, &file->insn_list, list) {
 332                                 if (insn->sec == rela->sym->sec) {
 333                                         found = true;
 334                                         break;
 335                                 }
 336                         }
 337
 338                         if (!found) {
 339                                 WARN("can't find unreachable insn at %s+0x%x",
 340                                      rela->sym->sec->name, rela->addend);
 341                                 return -1;
 342                         }
 343                 } else {
 344                         WARN("can't find unreachable insn at %s+0x%x",
 345                              rela->sym->sec->name, rela->addend);
 346                         return -1;
 347                 }
 348
 349                 insn->dead_end = true;
 350         }
 351
 352 reachable:
 353         /*
 354          * These manually annotated reachable checks are needed for GCC 4.4,
 355          * where the Linux unreachable() macro isn't supported.  In that case
 356          * GCC doesn't know the "ud2" is fatal, so it generates code as if it's
 357          * not a dead end.
 358          */
 359         sec = find_section_by_name(file->elf, ".rela.discard.reachable");
 360         if (!sec)
 361                 return 0;
 362
 363         list_for_each_entry(rela, &sec->rela_list, list) {
 364                 if (rela->sym->type != STT_SECTION) {
 365                         WARN("unexpected relocation symbol type in %s", sec->name);
 366                         return -1;
 367                 }
 368                 insn = find_insn(file, rela->sym->sec, rela->addend);
 369                 if (insn)
 370                         insn = list_prev_entry(insn, list);
 371                 else if (rela->addend == rela->sym->sec->len) {
 372                         found = false;
 373                         list_for_each_entry_reverse(insn, &file->insn_list, list) {
 374                                 if (insn->sec == rela->sym->sec) {
 375                                         found = true;
 376                                         break;
 377                                 }
 378                         }
 379
 380                         if (!found) {
 381                                 WARN("can't find reachable insn at %s+0x%x",
 382                                      rela->sym->sec->name, rela->addend);
 383                                 return -1;
 384                         }
 385                 } else {
 386                         WARN("can't find reachable insn at %s+0x%x",
 387                              rela->sym->sec->name, rela->addend);
 388                         return -1;
 389                 }
 390
 391                 insn->dead_end = false;
 392         }
 393
 394         return 0;
 395 }
 396
 397 /*
 398  * Warnings shouldn't be reported for ignored functions.
 399  */
 400 static void add_ignores(struct objtool_file *file)
 401 {
 402         struct instruction *insn;
 403         struct section *sec;
 404         struct symbol *func;
 405         struct rela *rela;
 406
 407         sec = find_section_by_name(file->elf, ".rela.discard.func_stack_frame_non_standard");
 408         if (!sec)
 409                 return;
 410
 411         list_for_each_entry(rela, &sec->rela_list, list) {
 412                 switch (rela->sym->type) {
 413                 case STT_FUNC:
 414                         func = rela->sym;
 415                         break;
 416
 417                 case STT_SECTION:
 418                         func = find_symbol_by_offset(rela->sym->sec, rela->addend);
 419                         if (!func || func->type != STT_FUNC)
 420                                 continue;
 421                         break;
 422
 423                 default:
 424                         WARN("unexpected relocation symbol type in %s: %d", sec->name, rela->sym->type);
 425                         continue;
 426                 }
 427
 428                 func_for_each_insn_all(file, func, insn)
 429                         insn->ignore = true;
 430         }
 431 }
 432
 433 /*
 434  * This is a whitelist of functions that is allowed to be called with AC set.
 435  * The list is meant to be minimal and only contains compiler instrumentation
 436  * ABI and a few functions used to implement *_{to,from}_user() functions.
 437  *
 438  * These functions must not directly change AC, but may PUSHF/POPF.
 439  */
 440 static const char *uaccess_safe_builtin[] = {
 441         /* KASAN */
 442         "kasan_report",
 443         "check_memory_region",
 444         /* KASAN out-of-line */
 445         "__asan_loadN_noabort",
 446         "__asan_load1_noabort",
 447         "__asan_load2_noabort",
 448         "__asan_load4_noabort",
 449         "__asan_load8_noabort",
 450         "__asan_load16_noabort",
 451         "__asan_storeN_noabort",
 452         "__asan_store1_noabort",
 453         "__asan_store2_noabort",
 454         "__asan_store4_noabort",
 455         "__asan_store8_noabort",
 456         "__asan_store16_noabort",
 457         /* KASAN in-line */
 458         "__asan_report_load_n_noabort",
 459         "__asan_report_load1_noabort",
 460         "__asan_report_load2_noabort",
 461         "__asan_report_load4_noabort",
 462         "__asan_report_load8_noabort",
 463         "__asan_report_load16_noabort",
 464         "__asan_report_store_n_noabort",
 465         "__asan_report_store1_noabort",
 466         "__asan_report_store2_noabort",
 467         "__asan_report_store4_noabort",
 468         "__asan_report_store8_noabort",
 469         "__asan_report_store16_noabort",
 470         /* KCOV */
 471         "write_comp_data",
 472         "__sanitizer_cov_trace_pc",
 473         "__sanitizer_cov_trace_const_cmp1",
 474         "__sanitizer_cov_trace_const_cmp2",
 475         "__sanitizer_cov_trace_const_cmp4",
 476         "__sanitizer_cov_trace_const_cmp8",
 477         "__sanitizer_cov_trace_cmp1",
 478         "__sanitizer_cov_trace_cmp2",
 479         "__sanitizer_cov_trace_cmp4",
 480         "__sanitizer_cov_trace_cmp8",
 481         /* UBSAN */
 482         "ubsan_type_mismatch_common",
 483         "__ubsan_handle_type_mismatch",
 484         "__ubsan_handle_type_mismatch_v1",
 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 &&
1014              insn->sec == func->sec &&
1015              insn->offset >= func->offset;
1016
1017              insn = insn->first_jump_src ?: list_prev_entry(insn, list)) {
1018
1019                 if (insn != orig_insn && insn->type == INSN_JUMP_DYNAMIC)
1020                         break;
1021
1022                 /* allow small jumps within the range */
1023                 if (insn->type == INSN_JUMP_UNCONDITIONAL &&
1024                     insn->jump_dest &&
1025                     (insn->jump_dest->offset <= insn->offset ||
1026                      insn->jump_dest->offset > orig_insn->offset))
1027                     break;
1028
1029                 /* look for a relocation which references .rodata */
1030                 text_rela = find_rela_by_dest_range(insn->sec, insn->offset,
1031                                                     insn->len);
1032                 if (!text_rela || text_rela->sym->type != STT_SECTION ||
1033                     !text_rela->sym->sec->rodata)
1034                         continue;
1035
1036                 table_offset = text_rela->addend;
1037                 table_sec = text_rela->sym->sec;
1038
1039                 if (text_rela->type == R_X86_64_PC32)
1040                         table_offset += 4;
1041
1042                 /*
1043                  * Make sure the .rodata address isn't associated with a
1044                  * symbol.  GCC jump tables are anonymous data.
1045                  *
1046                  * Also support C jump tables which are in the same format as
1047                  * switch jump tables.  For objtool to recognize them, they
1048                  * need to be placed in the C_JUMP_TABLE_SECTION section.  They
1049                  * have symbols associated with them.
1050                  */
1051                 if (find_symbol_containing(table_sec, table_offset) &&
1052                     strcmp(table_sec->name, C_JUMP_TABLE_SECTION))
1053                         continue;
1054
1055                 /* Each table entry has a rela associated with it. */
1056                 table_rela = find_rela_by_dest(table_sec, table_offset);
1057                 if (!table_rela)
1058                         continue;
1059
1060                 /*
1061                  * Use of RIP-relative switch jumps is quite rare, and
1062                  * indicates a rare GCC quirk/bug which can leave dead code
1063                  * behind.
1064                  */
1065                 if (text_rela->type == R_X86_64_PC32)
1066                         file->ignore_unreachables = true;
1067
1068                 return table_rela;
1069         }
1070
1071         return NULL;
1072 }
1073
1074 /*
1075  * First pass: Mark the head of each jump table so that in the next pass,
1076  * we know when a given jump table ends and the next one starts.
1077  */
1078 static void mark_func_jump_tables(struct objtool_file *file,
1079                                     struct symbol *func)
1080 {
1081         struct instruction *insn, *last = NULL;
1082         struct rela *rela;
1083
1084         func_for_each_insn_all(file, func, insn) {
1085                 if (!last)
1086                         last = insn;
1087
1088                 /*
1089                  * Store back-pointers for unconditional forward jumps such
1090                  * that find_jump_table() can back-track using those and
1091                  * avoid some potentially confusing code.
1092                  */
1093                 if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest &&
1094                     insn->offset > last->offset &&
1095                     insn->jump_dest->offset > insn->offset &&
1096                     !insn->jump_dest->first_jump_src) {
1097
1098                         insn->jump_dest->first_jump_src = insn;
1099                         last = insn->jump_dest;
1100                 }
1101
1102                 if (insn->type != INSN_JUMP_DYNAMIC)
1103                         continue;
1104
1105                 rela = find_jump_table(file, func, insn);
1106                 if (rela) {
1107                         rela->jump_table_start = true;
1108                         insn->jump_table = rela;
1109                 }
1110         }
1111 }
1112
1113 static int add_func_jump_tables(struct objtool_file *file,
1114                                   struct symbol *func)
1115 {
1116         struct instruction *insn;
1117         int ret;
1118
1119         func_for_each_insn_all(file, func, insn) {
1120                 if (!insn->jump_table)
1121                         continue;
1122
1123                 ret = add_jump_table(file, insn, insn->jump_table);
1124                 if (ret)
1125                         return ret;
1126         }
1127
1128         return 0;
1129 }
1130
1131 /*
1132  * For some switch statements, gcc generates a jump table in the .rodata
1133  * section which contains a list of addresses within the function to jump to.
1134  * This finds these jump tables and adds them to the insn->alts lists.
1135  */
1136 static int add_jump_table_alts(struct objtool_file *file)
1137 {
1138         struct section *sec;
1139         struct symbol *func;
1140         int ret;
1141
1142         if (!file->rodata)
1143                 return 0;
1144
1145         for_each_sec(file, sec) {
1146                 list_for_each_entry(func, &sec->symbol_list, list) {
1147                         if (func->type != STT_FUNC)
1148                                 continue;
1149
1150                         mark_func_jump_tables(file, func);
1151                         ret = add_func_jump_tables(file, func);
1152                         if (ret)
1153                                 return ret;
1154                 }
1155         }
1156
1157         return 0;
1158 }
1159
1160 static int read_unwind_hints(struct objtool_file *file)
1161 {
1162         struct section *sec, *relasec;
1163         struct rela *rela;
1164         struct unwind_hint *hint;
1165         struct instruction *insn;
1166         struct cfi_reg *cfa;
1167         int i;
1168
1169         sec = find_section_by_name(file->elf, ".discard.unwind_hints");
1170         if (!sec)
1171                 return 0;
1172
1173         relasec = sec->rela;
1174         if (!relasec) {
1175                 WARN("missing .rela.discard.unwind_hints section");
1176                 return -1;
1177         }
1178
1179         if (sec->len % sizeof(struct unwind_hint)) {
1180                 WARN("struct unwind_hint size mismatch");
1181                 return -1;
1182         }
1183
1184         file->hints = true;
1185
1186         for (i = 0; i < sec->len / sizeof(struct unwind_hint); i++) {
1187                 hint = (struct unwind_hint *)sec->data->d_buf + i;
1188
1189                 rela = find_rela_by_dest(sec, i * sizeof(*hint));
1190                 if (!rela) {
1191                         WARN("can't find rela for unwind_hints[%d]", i);
1192                         return -1;
1193                 }
1194
1195                 insn = find_insn(file, rela->sym->sec, rela->addend);
1196                 if (!insn) {
1197                         WARN("can't find insn for unwind_hints[%d]", i);
1198                         return -1;
1199                 }
1200
1201                 cfa = &insn->state.cfa;
1202
1203                 if (hint->type == UNWIND_HINT_TYPE_SAVE) {
1204                         insn->save = true;
1205                         continue;
1206
1207                 } else if (hint->type == UNWIND_HINT_TYPE_RESTORE) {
1208                         insn->restore = true;
1209                         insn->hint = true;
1210                         continue;
1211                 }
1212
1213                 insn->hint = true;
1214
1215                 switch (hint->sp_reg) {
1216                 case ORC_REG_UNDEFINED:
1217                         cfa->base = CFI_UNDEFINED;
1218                         break;
1219                 case ORC_REG_SP:
1220                         cfa->base = CFI_SP;
1221                         break;
1222                 case ORC_REG_BP:
1223                         cfa->base = CFI_BP;
1224                         break;
1225                 case ORC_REG_SP_INDIRECT:
1226                         cfa->base = CFI_SP_INDIRECT;
1227                         break;
1228                 case ORC_REG_R10:
1229                         cfa->base = CFI_R10;
1230                         break;
1231                 case ORC_REG_R13:
1232                         cfa->base = CFI_R13;
1233                         break;
1234                 case ORC_REG_DI:
1235                         cfa->base = CFI_DI;
1236                         break;
1237                 case ORC_REG_DX:
1238                         cfa->base = CFI_DX;
1239                         break;
1240                 default:
1241                         WARN_FUNC("unsupported unwind_hint sp base reg %d",
1242                                   insn->sec, insn->offset, hint->sp_reg);
1243                         return -1;
1244                 }
1245
1246                 cfa->offset = hint->sp_offset;
1247                 insn->state.type = hint->type;
1248                 insn->state.end = hint->end;
1249         }
1250
1251         return 0;
1252 }
1253
1254 static int read_retpoline_hints(struct objtool_file *file)
1255 {
1256         struct section *sec;
1257         struct instruction *insn;
1258         struct rela *rela;
1259
1260         sec = find_section_by_name(file->elf, ".rela.discard.retpoline_safe");
1261         if (!sec)
1262                 return 0;
1263
1264         list_for_each_entry(rela, &sec->rela_list, list) {
1265                 if (rela->sym->type != STT_SECTION) {
1266                         WARN("unexpected relocation symbol type in %s", sec->name);
1267                         return -1;
1268                 }
1269
1270                 insn = find_insn(file, rela->sym->sec, rela->addend);
1271                 if (!insn) {
1272                         WARN("bad .discard.retpoline_safe entry");
1273                         return -1;
1274                 }
1275
1276                 if (insn->type != INSN_JUMP_DYNAMIC &&
1277                     insn->type != INSN_CALL_DYNAMIC) {
1278                         WARN_FUNC("retpoline_safe hint not an indirect jump/call",
1279                                   insn->sec, insn->offset);
1280                         return -1;
1281                 }
1282
1283                 insn->retpoline_safe = true;
1284         }
1285
1286         return 0;
1287 }
1288
1289 static void mark_rodata(struct objtool_file *file)
1290 {
1291         struct section *sec;
1292         bool found = false;
1293
1294         /*
1295          * Search for the following rodata sections, each of which can
1296          * potentially contain jump tables:
1297          *
1298          * - .rodata: can contain GCC switch tables
1299          * - .rodata.<func>: same, if -fdata-sections is being used
1300          * - .rodata..c_jump_table: contains C annotated jump tables
1301          *
1302          * .rodata.str1.* sections are ignored; they don't contain jump tables.
1303          */
1304         for_each_sec(file, sec) {
1305                 if ((!strncmp(sec->name, ".rodata", 7) && !strstr(sec->name, ".str1.")) ||
1306                     !strcmp(sec->name, C_JUMP_TABLE_SECTION)) {
1307                         sec->rodata = true;
1308                         found = true;
1309                 }
1310         }
1311
1312         file->rodata = found;
1313 }
1314
1315 static int decode_sections(struct objtool_file *file)
1316 {
1317         int ret;
1318
1319         mark_rodata(file);
1320
1321         ret = decode_instructions(file);
1322         if (ret)
1323                 return ret;
1324
1325         ret = add_dead_ends(file);
1326         if (ret)
1327                 return ret;
1328
1329         add_ignores(file);
1330         add_uaccess_safe(file);
1331
1332         ret = add_ignore_alternatives(file);
1333         if (ret)
1334                 return ret;
1335
1336         ret = add_jump_destinations(file);
1337         if (ret)
1338                 return ret;
1339
1340         ret = add_special_section_alts(file);
1341         if (ret)
1342                 return ret;
1343
1344         ret = add_call_destinations(file);
1345         if (ret)
1346                 return ret;
1347
1348         ret = add_jump_table_alts(file);
1349         if (ret)
1350                 return ret;
1351
1352         ret = read_unwind_hints(file);
1353         if (ret)
1354                 return ret;
1355
1356         ret = read_retpoline_hints(file);
1357         if (ret)
1358                 return ret;
1359
1360         return 0;
1361 }
1362
1363 static bool is_fentry_call(struct instruction *insn)
1364 {
1365         if (insn->type == INSN_CALL &&
1366             insn->call_dest->type == STT_NOTYPE &&
1367             !strcmp(insn->call_dest->name, "__fentry__"))
1368                 return true;
1369
1370         return false;
1371 }
1372
1373 static bool has_modified_stack_frame(struct insn_state *state)
1374 {
1375         int i;
1376
1377         if (state->cfa.base != initial_func_cfi.cfa.base ||
1378             state->cfa.offset != initial_func_cfi.cfa.offset ||
1379             state->stack_size != initial_func_cfi.cfa.offset ||
1380             state->drap)
1381                 return true;
1382
1383         for (i = 0; i < CFI_NUM_REGS; i++)
1384                 if (state->regs[i].base != initial_func_cfi.regs[i].base ||
1385                     state->regs[i].offset != initial_func_cfi.regs[i].offset)
1386                         return true;
1387
1388         return false;
1389 }
1390
1391 static bool has_valid_stack_frame(struct insn_state *state)
1392 {
1393         if (state->cfa.base == CFI_BP && state->regs[CFI_BP].base == CFI_CFA &&
1394             state->regs[CFI_BP].offset == -16)
1395                 return true;
1396
1397         if (state->drap && state->regs[CFI_BP].base == CFI_BP)
1398                 return true;
1399
1400         return false;
1401 }
1402
1403 static int update_insn_state_regs(struct instruction *insn, struct insn_state *state)
1404 {
1405         struct cfi_reg *cfa = &state->cfa;
1406         struct stack_op *op = &insn->stack_op;
1407
1408         if (cfa->base != CFI_SP)
1409                 return 0;
1410
1411         /* push */
1412         if (op->dest.type == OP_DEST_PUSH || op->dest.type == OP_DEST_PUSHF)
1413                 cfa->offset += 8;
1414
1415         /* pop */
1416         if (op->src.type == OP_SRC_POP || op->src.type == OP_SRC_POPF)
1417                 cfa->offset -= 8;
1418
1419         /* add immediate to sp */
1420         if (op->dest.type == OP_DEST_REG && op->src.type == OP_SRC_ADD &&
1421             op->dest.reg == CFI_SP && op->src.reg == CFI_SP)
1422                 cfa->offset -= op->src.offset;
1423
1424         return 0;
1425 }
1426
1427 static void save_reg(struct insn_state *state, unsigned char reg, int base,
1428                      int offset)
1429 {
1430         if (arch_callee_saved_reg(reg) &&
1431             state->regs[reg].base == CFI_UNDEFINED) {
1432                 state->regs[reg].base = base;
1433                 state->regs[reg].offset = offset;
1434         }
1435 }
1436
1437 static void restore_reg(struct insn_state *state, unsigned char reg)
1438 {
1439         state->regs[reg].base = CFI_UNDEFINED;
1440         state->regs[reg].offset = 0;
1441 }
1442
1443 /*
1444  * A note about DRAP stack alignment:
1445  *
1446  * GCC has the concept of a DRAP register, which is used to help keep track of
1447  * the stack pointer when aligning the stack.  r10 or r13 is used as the DRAP
1448  * register.  The typical DRAP pattern is:
1449  *
1450  *   4c 8d 54 24 08             lea    0x8(%rsp),%r10
1451  *   48 83 e4 c0                and    $0xffffffffffffffc0,%rsp
1452  *   41 ff 72 f8                pushq  -0x8(%r10)
1453  *   55                         push   %rbp
1454  *   48 89 e5                   mov    %rsp,%rbp
1455  *                              (more pushes)
1456  *   41 52                      push   %r10
1457  *                              ...
1458  *   41 5a                      pop    %r10
1459  *                              (more pops)
1460  *   5d                         pop    %rbp
1461  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1462  *   c3                         retq
1463  *
1464  * There are some variations in the epilogues, like:
1465  *
1466  *   5b                         pop    %rbx
1467  *   41 5a                      pop    %r10
1468  *   41 5c                      pop    %r12
1469  *   41 5d                      pop    %r13
1470  *   41 5e                      pop    %r14
1471  *   c9                         leaveq
1472  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1473  *   c3                         retq
1474  *
1475  * and:
1476  *
1477  *   4c 8b 55 e8                mov    -0x18(%rbp),%r10
1478  *   48 8b 5d e0                mov    -0x20(%rbp),%rbx
1479  *   4c 8b 65 f0                mov    -0x10(%rbp),%r12
1480  *   4c 8b 6d f8                mov    -0x8(%rbp),%r13
1481  *   c9                         leaveq
1482  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1483  *   c3                         retq
1484  *
1485  * Sometimes r13 is used as the DRAP register, in which case it's saved and
1486  * restored beforehand:
1487  *
1488  *   41 55                      push   %r13
1489  *   4c 8d 6c 24 10             lea    0x10(%rsp),%r13
1490  *   48 83 e4 f0                and    $0xfffffffffffffff0,%rsp
1491  *                              ...
1492  *   49 8d 65 f0                lea    -0x10(%r13),%rsp
1493  *   41 5d                      pop    %r13
1494  *   c3                         retq
1495  */
1496 static int update_insn_state(struct instruction *insn, struct insn_state *state)
1497 {
1498         struct stack_op *op = &insn->stack_op;
1499         struct cfi_reg *cfa = &state->cfa;
1500         struct cfi_reg *regs = state->regs;
1501
1502         /* stack operations don't make sense with an undefined CFA */
1503         if (cfa->base == CFI_UNDEFINED) {
1504                 if (insn->func) {
1505                         WARN_FUNC("undefined stack state", insn->sec, insn->offset);
1506                         return -1;
1507                 }
1508                 return 0;
1509         }
1510
1511         if (state->type == ORC_TYPE_REGS || state->type == ORC_TYPE_REGS_IRET)
1512                 return update_insn_state_regs(insn, state);
1513
1514         switch (op->dest.type) {
1515
1516         case OP_DEST_REG:
1517                 switch (op->src.type) {
1518
1519                 case OP_SRC_REG:
1520                         if (op->src.reg == CFI_SP && op->dest.reg == CFI_BP &&
1521                             cfa->base == CFI_SP &&
1522                             regs[CFI_BP].base == CFI_CFA &&
1523                             regs[CFI_BP].offset == -cfa->offset) {
1524
1525                                 /* mov %rsp, %rbp */
1526                                 cfa->base = op->dest.reg;
1527                                 state->bp_scratch = false;
1528                         }
1529
1530                         else if (op->src.reg == CFI_SP &&
1531                                  op->dest.reg == CFI_BP && state->drap) {
1532
1533                                 /* drap: mov %rsp, %rbp */
1534                                 regs[CFI_BP].base = CFI_BP;
1535                                 regs[CFI_BP].offset = -state->stack_size;
1536                                 state->bp_scratch = false;
1537                         }
1538
1539                         else if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1540
1541                                 /*
1542                                  * mov %rsp, %reg
1543                                  *
1544                                  * This is needed for the rare case where GCC
1545                                  * does:
1546                                  *
1547                                  *   mov    %rsp, %rax
1548                                  *   ...
1549                                  *   mov    %rax, %rsp
1550                                  */
1551                                 state->vals[op->dest.reg].base = CFI_CFA;
1552                                 state->vals[op->dest.reg].offset = -state->stack_size;
1553                         }
1554
1555                         else if (op->src.reg == CFI_BP && op->dest.reg == CFI_SP &&
1556                                  cfa->base == CFI_BP) {
1557
1558                                 /*
1559                                  * mov %rbp, %rsp
1560                                  *
1561                                  * Restore the original stack pointer (Clang).
1562                                  */
1563                                 state->stack_size = -state->regs[CFI_BP].offset;
1564                         }
1565
1566                         else if (op->dest.reg == cfa->base) {
1567
1568                                 /* mov %reg, %rsp */
1569                                 if (cfa->base == CFI_SP &&
1570                                     state->vals[op->src.reg].base == CFI_CFA) {
1571
1572                                         /*
1573                                          * This is needed for the rare case
1574                                          * where GCC does something dumb like:
1575                                          *
1576                                          *   lea    0x8(%rsp), %rcx
1577                                          *   ...
1578                                          *   mov    %rcx, %rsp
1579                                          */
1580                                         cfa->offset = -state->vals[op->src.reg].offset;
1581                                         state->stack_size = cfa->offset;
1582
1583                                 } else {
1584                                         cfa->base = CFI_UNDEFINED;
1585                                         cfa->offset = 0;
1586                                 }
1587                         }
1588
1589                         break;
1590
1591                 case OP_SRC_ADD:
1592                         if (op->dest.reg == CFI_SP && op->src.reg == CFI_SP) {
1593
1594                                 /* add imm, %rsp */
1595                                 state->stack_size -= op->src.offset;
1596                                 if (cfa->base == CFI_SP)
1597                                         cfa->offset -= op->src.offset;
1598                                 break;
1599                         }
1600
1601                         if (op->dest.reg == CFI_SP && op->src.reg == CFI_BP) {
1602
1603                                 /* lea disp(%rbp), %rsp */
1604                                 state->stack_size = -(op->src.offset + regs[CFI_BP].offset);
1605                                 break;
1606                         }
1607
1608                         if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1609
1610                                 /* drap: lea disp(%rsp), %drap */
1611                                 state->drap_reg = op->dest.reg;
1612
1613                                 /*
1614                                  * lea disp(%rsp), %reg
1615                                  *
1616                                  * This is needed for the rare case where GCC
1617                                  * does something dumb like:
1618                                  *
1619                                  *   lea    0x8(%rsp), %rcx
1620                                  *   ...
1621                                  *   mov    %rcx, %rsp
1622                                  */
1623                                 state->vals[op->dest.reg].base = CFI_CFA;
1624                                 state->vals[op->dest.reg].offset = \
1625                                         -state->stack_size + op->src.offset;
1626
1627                                 break;
1628                         }
1629
1630                         if (state->drap && op->dest.reg == CFI_SP &&
1631                             op->src.reg == state->drap_reg) {
1632
1633                                  /* drap: lea disp(%drap), %rsp */
1634                                 cfa->base = CFI_SP;
1635                                 cfa->offset = state->stack_size = -op->src.offset;
1636                                 state->drap_reg = CFI_UNDEFINED;
1637                                 state->drap = false;
1638                                 break;
1639                         }
1640
1641                         if (op->dest.reg == state->cfa.base) {
1642                                 WARN_FUNC("unsupported stack register modification",
1643                                           insn->sec, insn->offset);
1644                                 return -1;
1645                         }
1646
1647                         break;
1648
1649                 case OP_SRC_AND:
1650                         if (op->dest.reg != CFI_SP ||
1651                             (state->drap_reg != CFI_UNDEFINED && cfa->base != CFI_SP) ||
1652                             (state->drap_reg == CFI_UNDEFINED && cfa->base != CFI_BP)) {
1653                                 WARN_FUNC("unsupported stack pointer realignment",
1654                                           insn->sec, insn->offset);
1655                                 return -1;
1656                         }
1657
1658                         if (state->drap_reg != CFI_UNDEFINED) {
1659                                 /* drap: and imm, %rsp */
1660                                 cfa->base = state->drap_reg;
1661                                 cfa->offset = state->stack_size = 0;
1662                                 state->drap = true;
1663                         }
1664
1665                         /*
1666                          * Older versions of GCC (4.8ish) realign the stack
1667                          * without DRAP, with a frame pointer.
1668                          */
1669
1670                         break;
1671
1672                 case OP_SRC_POP:
1673                 case OP_SRC_POPF:
1674                         if (!state->drap && op->dest.type == OP_DEST_REG &&
1675                             op->dest.reg == cfa->base) {
1676
1677                                 /* pop %rbp */
1678                                 cfa->base = CFI_SP;
1679                         }
1680
1681                         if (state->drap && cfa->base == CFI_BP_INDIRECT &&
1682                             op->dest.type == OP_DEST_REG &&
1683                             op->dest.reg == state->drap_reg &&
1684                             state->drap_offset == -state->stack_size) {
1685
1686                                 /* drap: pop %drap */
1687                                 cfa->base = state->drap_reg;
1688                                 cfa->offset = 0;
1689                                 state->drap_offset = -1;
1690
1691                         } else if (regs[op->dest.reg].offset == -state->stack_size) {
1692
1693                                 /* pop %reg */
1694                                 restore_reg(state, op->dest.reg);
1695                         }
1696
1697                         state->stack_size -= 8;
1698                         if (cfa->base == CFI_SP)
1699                                 cfa->offset -= 8;
1700
1701                         break;
1702
1703                 case OP_SRC_REG_INDIRECT:
1704                         if (state->drap && op->src.reg == CFI_BP &&
1705                             op->src.offset == state->drap_offset) {
1706
1707                                 /* drap: mov disp(%rbp), %drap */
1708                                 cfa->base = state->drap_reg;
1709                                 cfa->offset = 0;
1710                                 state->drap_offset = -1;
1711                         }
1712
1713                         if (state->drap && op->src.reg == CFI_BP &&
1714                             op->src.offset == regs[op->dest.reg].offset) {
1715
1716                                 /* drap: mov disp(%rbp), %reg */
1717                                 restore_reg(state, op->dest.reg);
1718
1719                         } else if (op->src.reg == cfa->base &&
1720                             op->src.offset == regs[op->dest.reg].offset + cfa->offset) {
1721
1722                                 /* mov disp(%rbp), %reg */
1723                                 /* mov disp(%rsp), %reg */
1724                                 restore_reg(state, op->dest.reg);
1725                         }
1726
1727                         break;
1728
1729                 default:
1730                         WARN_FUNC("unknown stack-related instruction",
1731                                   insn->sec, insn->offset);
1732                         return -1;
1733                 }
1734
1735                 break;
1736
1737         case OP_DEST_PUSH:
1738         case OP_DEST_PUSHF:
1739                 state->stack_size += 8;
1740                 if (cfa->base == CFI_SP)
1741                         cfa->offset += 8;
1742
1743                 if (op->src.type != OP_SRC_REG)
1744                         break;
1745
1746                 if (state->drap) {
1747                         if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1748
1749                                 /* drap: push %drap */
1750                                 cfa->base = CFI_BP_INDIRECT;
1751                                 cfa->offset = -state->stack_size;
1752
1753                                 /* save drap so we know when to restore it */
1754                                 state->drap_offset = -state->stack_size;
1755
1756                         } else if (op->src.reg == CFI_BP && cfa->base == state->drap_reg) {
1757
1758                                 /* drap: push %rbp */
1759                                 state->stack_size = 0;
1760
1761                         } else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1762
1763                                 /* drap: push %reg */
1764                                 save_reg(state, op->src.reg, CFI_BP, -state->stack_size);
1765                         }
1766
1767                 } else {
1768
1769                         /* push %reg */
1770                         save_reg(state, op->src.reg, CFI_CFA, -state->stack_size);
1771                 }
1772
1773                 /* detect when asm code uses rbp as a scratch register */
1774                 if (!no_fp && insn->func && op->src.reg == CFI_BP &&
1775                     cfa->base != CFI_BP)
1776                         state->bp_scratch = true;
1777                 break;
1778
1779         case OP_DEST_REG_INDIRECT:
1780
1781                 if (state->drap) {
1782                         if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1783
1784                                 /* drap: mov %drap, disp(%rbp) */
1785                                 cfa->base = CFI_BP_INDIRECT;
1786                                 cfa->offset = op->dest.offset;
1787
1788                                 /* save drap offset so we know when to restore it */
1789                                 state->drap_offset = op->dest.offset;
1790                         }
1791
1792                         else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1793
1794                                 /* drap: mov reg, disp(%rbp) */
1795                                 save_reg(state, op->src.reg, CFI_BP, op->dest.offset);
1796                         }
1797
1798                 } else if (op->dest.reg == cfa->base) {
1799
1800                         /* mov reg, disp(%rbp) */
1801                         /* mov reg, disp(%rsp) */
1802                         save_reg(state, op->src.reg, CFI_CFA,
1803                                  op->dest.offset - state->cfa.offset);
1804                 }
1805
1806                 break;
1807
1808         case OP_DEST_LEAVE:
1809                 if ((!state->drap && cfa->base != CFI_BP) ||
1810                     (state->drap && cfa->base != state->drap_reg)) {
1811                         WARN_FUNC("leave instruction with modified stack frame",
1812                                   insn->sec, insn->offset);
1813                         return -1;
1814                 }
1815
1816                 /* leave (mov %rbp, %rsp; pop %rbp) */
1817
1818                 state->stack_size = -state->regs[CFI_BP].offset - 8;
1819                 restore_reg(state, CFI_BP);
1820
1821                 if (!state->drap) {
1822                         cfa->base = CFI_SP;
1823                         cfa->offset -= 8;
1824                 }
1825
1826                 break;
1827
1828         case OP_DEST_MEM:
1829                 if (op->src.type != OP_SRC_POP && op->src.type != OP_SRC_POPF) {
1830                         WARN_FUNC("unknown stack-related memory operation",
1831                                   insn->sec, insn->offset);
1832                         return -1;
1833                 }
1834
1835                 /* pop mem */
1836                 state->stack_size -= 8;
1837                 if (cfa->base == CFI_SP)
1838                         cfa->offset -= 8;
1839
1840                 break;
1841
1842         default:
1843                 WARN_FUNC("unknown stack-related instruction",
1844                           insn->sec, insn->offset);
1845                 return -1;
1846         }
1847
1848         return 0;
1849 }
1850
1851 static bool insn_state_match(struct instruction *insn, struct insn_state *state)
1852 {
1853         struct insn_state *state1 = &insn->state, *state2 = state;
1854         int i;
1855
1856         if (memcmp(&state1->cfa, &state2->cfa, sizeof(state1->cfa))) {
1857                 WARN_FUNC("stack state mismatch: cfa1=%d%+d cfa2=%d%+d",
1858                           insn->sec, insn->offset,
1859                           state1->cfa.base, state1->cfa.offset,
1860                           state2->cfa.base, state2->cfa.offset);
1861
1862         } else if (memcmp(&state1->regs, &state2->regs, sizeof(state1->regs))) {
1863                 for (i = 0; i < CFI_NUM_REGS; i++) {
1864                         if (!memcmp(&state1->regs[i], &state2->regs[i],
1865                                     sizeof(struct cfi_reg)))
1866                                 continue;
1867
1868                         WARN_FUNC("stack state mismatch: reg1[%d]=%d%+d reg2[%d]=%d%+d",
1869                                   insn->sec, insn->offset,
1870                                   i, state1->regs[i].base, state1->regs[i].offset,
1871                                   i, state2->regs[i].base, state2->regs[i].offset);
1872                         break;
1873                 }
1874
1875         } else if (state1->type != state2->type) {
1876                 WARN_FUNC("stack state mismatch: type1=%d type2=%d",
1877                           insn->sec, insn->offset, state1->type, state2->type);
1878
1879         } else if (state1->drap != state2->drap ||
1880                  (state1->drap && state1->drap_reg != state2->drap_reg) ||
1881                  (state1->drap && state1->drap_offset != state2->drap_offset)) {
1882                 WARN_FUNC("stack state mismatch: drap1=%d(%d,%d) drap2=%d(%d,%d)",
1883                           insn->sec, insn->offset,
1884                           state1->drap, state1->drap_reg, state1->drap_offset,
1885                           state2->drap, state2->drap_reg, state2->drap_offset);
1886
1887         } else
1888                 return true;
1889
1890         return false;
1891 }
1892
1893 static inline bool func_uaccess_safe(struct symbol *func)
1894 {
1895         if (func)
1896                 return func->uaccess_safe;
1897
1898         return false;
1899 }
1900
1901 static inline const char *call_dest_name(struct instruction *insn)
1902 {
1903         if (insn->call_dest)
1904                 return insn->call_dest->name;
1905
1906         return "{dynamic}";
1907 }
1908
1909 static int validate_call(struct instruction *insn, struct insn_state *state)
1910 {
1911         if (state->uaccess && !func_uaccess_safe(insn->call_dest)) {
1912                 WARN_FUNC("call to %s() with UACCESS enabled",
1913                                 insn->sec, insn->offset, call_dest_name(insn));
1914                 return 1;
1915         }
1916
1917         if (state->df) {
1918                 WARN_FUNC("call to %s() with DF set",
1919                                 insn->sec, insn->offset, call_dest_name(insn));
1920                 return 1;
1921         }
1922
1923         return 0;
1924 }
1925
1926 static int validate_sibling_call(struct instruction *insn, struct insn_state *state)
1927 {
1928         if (has_modified_stack_frame(state)) {
1929                 WARN_FUNC("sibling call from callable instruction with modified stack frame",
1930                                 insn->sec, insn->offset);
1931                 return 1;
1932         }
1933
1934         return validate_call(insn, state);
1935 }
1936
1937 /*
1938  * Follow the branch starting at the given instruction, and recursively follow
1939  * any other branches (jumps).  Meanwhile, track the frame pointer state at
1940  * each instruction and validate all the rules described in
1941  * tools/objtool/Documentation/stack-validation.txt.
1942  */
1943 static int validate_branch(struct objtool_file *file, struct symbol *func,
1944                            struct instruction *first, struct insn_state state)
1945 {
1946         struct alternative *alt;
1947         struct instruction *insn, *next_insn;
1948         struct section *sec;
1949         u8 visited;
1950         int ret;
1951
1952         insn = first;
1953         sec = insn->sec;
1954
1955         if (insn->alt_group && list_empty(&insn->alts)) {
1956                 WARN_FUNC("don't know how to handle branch to middle of alternative instruction group",
1957                           sec, insn->offset);
1958                 return 1;
1959         }
1960
1961         while (1) {
1962                 next_insn = next_insn_same_sec(file, insn);
1963
1964                 if (file->c_file && func && insn->func && func != insn->func->pfunc) {
1965                         WARN("%s() falls through to next function %s()",
1966                              func->name, insn->func->name);
1967                         return 1;
1968                 }
1969
1970                 if (func && insn->ignore) {
1971                         WARN_FUNC("BUG: why am I validating an ignored function?",
1972                                   sec, insn->offset);
1973                         return 1;
1974                 }
1975
1976                 visited = 1 << state.uaccess;
1977                 if (insn->visited) {
1978                         if (!insn->hint && !insn_state_match(insn, &state))
1979                                 return 1;
1980
1981                         if (insn->visited & visited)
1982                                 return 0;
1983                 }
1984
1985                 if (insn->hint) {
1986                         if (insn->restore) {
1987                                 struct instruction *save_insn, *i;
1988
1989                                 i = insn;
1990                                 save_insn = NULL;
1991                                 func_for_each_insn_continue_reverse(file, func, i) {
1992                                         if (i->save) {
1993                                                 save_insn = i;
1994                                                 break;
1995                                         }
1996                                 }
1997
1998                                 if (!save_insn) {
1999                                         WARN_FUNC("no corresponding CFI save for CFI restore",
2000                                                   sec, insn->offset);
2001                                         return 1;
2002                                 }
2003
2004                                 if (!save_insn->visited) {
2005                                         /*
2006                                          * Oops, no state to copy yet.
2007                                          * Hopefully we can reach this
2008                                          * instruction from another branch
2009                                          * after the save insn has been
2010                                          * visited.
2011                                          */
2012                                         if (insn == first)
2013                                                 return 0;
2014
2015                                         WARN_FUNC("objtool isn't smart enough to handle this CFI save/restore combo",
2016                                                   sec, insn->offset);
2017                                         return 1;
2018                                 }
2019
2020                                 insn->state = save_insn->state;
2021                         }
2022
2023                         state = insn->state;
2024
2025                 } else
2026                         insn->state = state;
2027
2028                 insn->visited |= visited;
2029
2030                 if (!insn->ignore_alts) {
2031                         bool skip_orig = false;
2032
2033                         list_for_each_entry(alt, &insn->alts, list) {
2034                                 if (alt->skip_orig)
2035                                         skip_orig = true;
2036
2037                                 ret = validate_branch(file, func, alt->insn, state);
2038                                 if (ret) {
2039                                         if (backtrace)
2040                                                 BT_FUNC("(alt)", insn);
2041                                         return ret;
2042                                 }
2043                         }
2044
2045                         if (skip_orig)
2046                                 return 0;
2047                 }
2048
2049                 switch (insn->type) {
2050
2051                 case INSN_RETURN:
2052                         if (state.uaccess && !func_uaccess_safe(func)) {
2053                                 WARN_FUNC("return with UACCESS enabled", sec, insn->offset);
2054                                 return 1;
2055                         }
2056
2057                         if (!state.uaccess && func_uaccess_safe(func)) {
2058                                 WARN_FUNC("return with UACCESS disabled from a UACCESS-safe function", sec, insn->offset);
2059                                 return 1;
2060                         }
2061
2062                         if (state.df) {
2063                                 WARN_FUNC("return with DF set", sec, insn->offset);
2064                                 return 1;
2065                         }
2066
2067                         if (func && has_modified_stack_frame(&state)) {
2068                                 WARN_FUNC("return with modified stack frame",
2069                                           sec, insn->offset);
2070                                 return 1;
2071                         }
2072
2073                         if (state.bp_scratch) {
2074                                 WARN("%s uses BP as a scratch register",
2075                                      func->name);
2076                                 return 1;
2077                         }
2078
2079                         return 0;
2080
2081                 case INSN_CALL:
2082                 case INSN_CALL_DYNAMIC:
2083                         ret = validate_call(insn, &state);
2084                         if (ret)
2085                                 return ret;
2086
2087                         if (!no_fp && func && !is_fentry_call(insn) &&
2088                             !has_valid_stack_frame(&state)) {
2089                                 WARN_FUNC("call without frame pointer save/setup",
2090                                           sec, insn->offset);
2091                                 return 1;
2092                         }
2093
2094                         if (dead_end_function(file, insn->call_dest))
2095                                 return 0;
2096
2097                         break;
2098
2099                 case INSN_JUMP_CONDITIONAL:
2100                 case INSN_JUMP_UNCONDITIONAL:
2101                         if (func && is_sibling_call(insn)) {
2102                                 ret = validate_sibling_call(insn, &state);
2103                                 if (ret)
2104                                         return ret;
2105
2106                         } else if (insn->jump_dest) {
2107                                 ret = validate_branch(file, func,
2108                                                       insn->jump_dest, state);
2109                                 if (ret) {
2110                                         if (backtrace)
2111                                                 BT_FUNC("(branch)", insn);
2112                                         return ret;
2113                                 }
2114                         }
2115
2116                         if (insn->type == INSN_JUMP_UNCONDITIONAL)
2117                                 return 0;
2118
2119                         break;
2120
2121                 case INSN_JUMP_DYNAMIC:
2122                 case INSN_JUMP_DYNAMIC_CONDITIONAL:
2123                         if (func && is_sibling_call(insn)) {
2124                                 ret = validate_sibling_call(insn, &state);
2125                                 if (ret)
2126                                         return ret;
2127                         }
2128
2129                         if (insn->type == INSN_JUMP_DYNAMIC)
2130                                 return 0;
2131
2132                         break;
2133
2134                 case INSN_CONTEXT_SWITCH:
2135                         if (func && (!next_insn || !next_insn->hint)) {
2136                                 WARN_FUNC("unsupported instruction in callable function",
2137                                           sec, insn->offset);
2138                                 return 1;
2139                         }
2140                         return 0;
2141
2142                 case INSN_STACK:
2143                         if (update_insn_state(insn, &state))
2144                                 return 1;
2145
2146                         if (insn->stack_op.dest.type == OP_DEST_PUSHF) {
2147                                 if (!state.uaccess_stack) {
2148                                         state.uaccess_stack = 1;
2149                                 } else if (state.uaccess_stack >> 31) {
2150                                         WARN_FUNC("PUSHF stack exhausted", sec, insn->offset);
2151                                         return 1;
2152                                 }
2153                                 state.uaccess_stack <<= 1;
2154                                 state.uaccess_stack  |= state.uaccess;
2155                         }
2156
2157                         if (insn->stack_op.src.type == OP_SRC_POPF) {
2158                                 if (state.uaccess_stack) {
2159                                         state.uaccess = state.uaccess_stack & 1;
2160                                         state.uaccess_stack >>= 1;
2161                                         if (state.uaccess_stack == 1)
2162                                                 state.uaccess_stack = 0;
2163                                 }
2164                         }
2165
2166                         break;
2167
2168                 case INSN_STAC:
2169                         if (state.uaccess) {
2170                                 WARN_FUNC("recursive UACCESS enable", sec, insn->offset);
2171                                 return 1;
2172                         }
2173
2174                         state.uaccess = true;
2175                         break;
2176
2177                 case INSN_CLAC:
2178                         if (!state.uaccess && func) {
2179                                 WARN_FUNC("redundant UACCESS disable", sec, insn->offset);
2180                                 return 1;
2181                         }
2182
2183                         if (func_uaccess_safe(func) && !state.uaccess_stack) {
2184                                 WARN_FUNC("UACCESS-safe disables UACCESS", sec, insn->offset);
2185                                 return 1;
2186                         }
2187
2188                         state.uaccess = false;
2189                         break;
2190
2191                 case INSN_STD:
2192                         if (state.df)
2193                                 WARN_FUNC("recursive STD", sec, insn->offset);
2194
2195                         state.df = true;
2196                         break;
2197
2198                 case INSN_CLD:
2199                         if (!state.df && func)
2200                                 WARN_FUNC("redundant CLD", sec, insn->offset);
2201
2202                         state.df = false;
2203                         break;
2204
2205                 default:
2206                         break;
2207                 }
2208
2209                 if (insn->dead_end)
2210                         return 0;
2211
2212                 if (!next_insn) {
2213                         if (state.cfa.base == CFI_UNDEFINED)
2214                                 return 0;
2215                         WARN("%s: unexpected end of section", sec->name);
2216                         return 1;
2217                 }
2218
2219                 insn = next_insn;
2220         }
2221
2222         return 0;
2223 }
2224
2225 static int validate_unwind_hints(struct objtool_file *file)
2226 {
2227         struct instruction *insn;
2228         int ret, warnings = 0;
2229         struct insn_state state;
2230
2231         if (!file->hints)
2232                 return 0;
2233
2234         clear_insn_state(&state);
2235
2236         for_each_insn(file, insn) {
2237                 if (insn->hint && !insn->visited) {
2238                         ret = validate_branch(file, insn->func, insn, state);
2239                         if (ret && backtrace)
2240                                 BT_FUNC("<=== (hint)", insn);
2241                         warnings += ret;
2242                 }
2243         }
2244
2245         return warnings;
2246 }
2247
2248 static int validate_retpoline(struct objtool_file *file)
2249 {
2250         struct instruction *insn;
2251         int warnings = 0;
2252
2253         for_each_insn(file, insn) {
2254                 if (insn->type != INSN_JUMP_DYNAMIC &&
2255                     insn->type != INSN_CALL_DYNAMIC)
2256                         continue;
2257
2258                 if (insn->retpoline_safe)
2259                         continue;
2260
2261                 /*
2262                  * .init.text code is ran before userspace and thus doesn't
2263                  * strictly need retpolines, except for modules which are
2264                  * loaded late, they very much do need retpoline in their
2265                  * .init.text
2266                  */
2267                 if (!strcmp(insn->sec->name, ".init.text") && !module)
2268                         continue;
2269
2270                 WARN_FUNC("indirect %s found in RETPOLINE build",
2271                           insn->sec, insn->offset,
2272                           insn->type == INSN_JUMP_DYNAMIC ? "jump" : "call");
2273
2274                 warnings++;
2275         }
2276
2277         return warnings;
2278 }
2279
2280 static bool is_kasan_insn(struct instruction *insn)
2281 {
2282         return (insn->type == INSN_CALL &&
2283                 !strcmp(insn->call_dest->name, "__asan_handle_no_return"));
2284 }
2285
2286 static bool is_ubsan_insn(struct instruction *insn)
2287 {
2288         return (insn->type == INSN_CALL &&
2289                 !strcmp(insn->call_dest->name,
2290                         "__ubsan_handle_builtin_unreachable"));
2291 }
2292
2293 static bool ignore_unreachable_insn(struct instruction *insn)
2294 {
2295         int i;
2296
2297         if (insn->ignore || insn->type == INSN_NOP)
2298                 return true;
2299
2300         /*
2301          * Ignore any unused exceptions.  This can happen when a whitelisted
2302          * function has an exception table entry.
2303          *
2304          * Also ignore alternative replacement instructions.  This can happen
2305          * when a whitelisted function uses one of the ALTERNATIVE macros.
2306          */
2307         if (!strcmp(insn->sec->name, ".fixup") ||
2308             !strcmp(insn->sec->name, ".altinstr_replacement") ||
2309             !strcmp(insn->sec->name, ".altinstr_aux"))
2310                 return true;
2311
2312         /*
2313          * Check if this (or a subsequent) instruction is related to
2314          * CONFIG_UBSAN or CONFIG_KASAN.
2315          *
2316          * End the search at 5 instructions to avoid going into the weeds.
2317          */
2318         if (!insn->func)
2319                 return false;
2320         for (i = 0; i < 5; i++) {
2321
2322                 if (is_kasan_insn(insn) || is_ubsan_insn(insn))
2323                         return true;
2324
2325                 if (insn->type == INSN_JUMP_UNCONDITIONAL) {
2326                         if (insn->jump_dest &&
2327                             insn->jump_dest->func == insn->func) {
2328                                 insn = insn->jump_dest;
2329                                 continue;
2330                         }
2331
2332                         break;
2333                 }
2334
2335                 if (insn->offset + insn->len >= insn->func->offset + insn->func->len)
2336                         break;
2337
2338                 insn = list_next_entry(insn, list);
2339         }
2340
2341         return false;
2342 }
2343
2344 static int validate_functions(struct objtool_file *file)
2345 {
2346         struct section *sec;
2347         struct symbol *func;
2348         struct instruction *insn;
2349         struct insn_state state;
2350         int ret, warnings = 0;
2351
2352         clear_insn_state(&state);
2353
2354         state.cfa = initial_func_cfi.cfa;
2355         memcpy(&state.regs, &initial_func_cfi.regs,
2356                CFI_NUM_REGS * sizeof(struct cfi_reg));
2357         state.stack_size = initial_func_cfi.cfa.offset;
2358
2359         for_each_sec(file, sec) {
2360                 list_for_each_entry(func, &sec->symbol_list, list) {
2361                         if (func->type != STT_FUNC)
2362                                 continue;
2363
2364                         if (!func->len) {
2365                                 WARN("%s() is missing an ELF size annotation",
2366                                      func->name);
2367                                 warnings++;
2368                         }
2369
2370                         if (func->pfunc != func || func->alias != func)
2371                                 continue;
2372
2373                         insn = find_insn(file, sec, func->offset);
2374                         if (!insn || insn->ignore || insn->visited)
2375                                 continue;
2376
2377                         state.uaccess = func->uaccess_safe;
2378
2379                         ret = validate_branch(file, func, insn, state);
2380                         if (ret && backtrace)
2381                                 BT_FUNC("<=== (func)", insn);
2382                         warnings += ret;
2383                 }
2384         }
2385
2386         return warnings;
2387 }
2388
2389 static int validate_reachable_instructions(struct objtool_file *file)
2390 {
2391         struct instruction *insn;
2392
2393         if (file->ignore_unreachables)
2394                 return 0;
2395
2396         for_each_insn(file, insn) {
2397                 if (insn->visited || ignore_unreachable_insn(insn))
2398                         continue;
2399
2400                 WARN_FUNC("unreachable instruction", insn->sec, insn->offset);
2401                 return 1;
2402         }
2403
2404         return 0;
2405 }
2406
2407 static void cleanup(struct objtool_file *file)
2408 {
2409         struct instruction *insn, *tmpinsn;
2410         struct alternative *alt, *tmpalt;
2411
2412         list_for_each_entry_safe(insn, tmpinsn, &file->insn_list, list) {
2413                 list_for_each_entry_safe(alt, tmpalt, &insn->alts, list) {
2414                         list_del(&alt->list);
2415                         free(alt);
2416                 }
2417                 list_del(&insn->list);
2418                 hash_del(&insn->hash);
2419                 free(insn);
2420         }
2421         elf_close(file->elf);
2422 }
2423
2424 static struct objtool_file file;
2425
2426 int check(const char *_objname, bool orc)
2427 {
2428         int ret, warnings = 0;
2429
2430         objname = _objname;
2431
2432         file.elf = elf_read(objname, orc ? O_RDWR : O_RDONLY);
2433         if (!file.elf)
2434                 return 1;
2435
2436         INIT_LIST_HEAD(&file.insn_list);
2437         hash_init(file.insn_hash);
2438         file.c_file = find_section_by_name(file.elf, ".comment");
2439         file.ignore_unreachables = no_unreachable;
2440         file.hints = false;
2441
2442         arch_initial_func_cfi_state(&initial_func_cfi);
2443
2444         ret = decode_sections(&file);
2445         if (ret < 0)
2446                 goto out;
2447         warnings += ret;
2448
2449         if (list_empty(&file.insn_list))
2450                 goto out;
2451
2452         if (retpoline) {
2453                 ret = validate_retpoline(&file);
2454                 if (ret < 0)
2455                         return ret;
2456                 warnings += ret;
2457         }
2458
2459         ret = validate_functions(&file);
2460         if (ret < 0)
2461                 goto out;
2462         warnings += ret;
2463
2464         ret = validate_unwind_hints(&file);
2465         if (ret < 0)
2466                 goto out;
2467         warnings += ret;
2468
2469         if (!warnings) {
2470                 ret = validate_reachable_instructions(&file);
2471                 if (ret < 0)
2472                         goto out;
2473                 warnings += ret;
2474         }
2475
2476         if (orc) {
2477                 ret = create_orc(&file);
2478                 if (ret < 0)
2479                         goto out;
2480
2481                 ret = create_orc_sections(&file);
2482                 if (ret < 0)
2483                         goto out;
2484
2485                 ret = elf_write(file.elf);
2486                 if (ret < 0)
2487                         goto out;
2488         }
2489
2490 out:
2491         cleanup(&file);
2492
2493         /* ignore warnings for now until we get all the code cleaned up */
2494         if (ret || warnings)
2495                 return 0;
2496         return 0;
2497 }