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                 "kvm_spurious_fault",
 142                 "__reiserfs_panic",
 143                 "lbug_with_loc",
 144                 "fortify_panic",
 145                 "usercopy_abort",
 146                 "machine_real_restart",
 147                 "rewind_stack_do_exit",
 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                         insn->type = INSN_JUMP_DYNAMIC;
 579                         insn->retpoline_safe = true;
 580                         continue;
 581                 } else {
 582                         /* external sibling call */
 583                         insn->call_dest = rela->sym;
 584                         continue;
 585                 }
 586
 587                 insn->jump_dest = find_insn(file, dest_sec, dest_off);
 588                 if (!insn->jump_dest) {
 589
 590                         /*
 591                          * This is a special case where an alt instruction
 592                          * jumps past the end of the section.  These are
 593                          * handled later in handle_group_alt().
 594                          */
 595                         if (!strcmp(insn->sec->name, ".altinstr_replacement"))
 596                                 continue;
 597
 598                         WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
 599                                   insn->sec, insn->offset, dest_sec->name,
 600                                   dest_off);
 601                         return -1;
 602                 }
 603
 604                 /*
 605                  * Cross-function jump.
 606                  */
 607                 if (insn->func && insn->jump_dest->func &&
 608                     insn->func != insn->jump_dest->func) {
 609
 610                         /*
 611                          * For GCC 8+, create parent/child links for any cold
 612                          * subfunctions.  This is _mostly_ redundant with a
 613                          * similar initialization in read_symbols().
 614                          *
 615                          * If a function has aliases, we want the *first* such
 616                          * function in the symbol table to be the subfunction's
 617                          * parent.  In that case we overwrite the
 618                          * initialization done in read_symbols().
 619                          *
 620                          * However this code can't completely replace the
 621                          * read_symbols() code because this doesn't detect the
 622                          * case where the parent function's only reference to a
 623                          * subfunction is through a jump table.
 624                          */
 625                         if (!strstr(insn->func->name, ".cold.") &&
 626                             strstr(insn->jump_dest->func->name, ".cold.")) {
 627                                 insn->func->cfunc = insn->jump_dest->func;
 628                                 insn->jump_dest->func->pfunc = insn->func;
 629
 630                         } else if (insn->jump_dest->func->pfunc != insn->func->pfunc &&
 631                                    insn->jump_dest->offset == insn->jump_dest->func->offset) {
 632
 633                                 /* internal sibling call */
 634                                 insn->call_dest = insn->jump_dest->func;
 635                         }
 636                 }
 637         }
 638
 639         return 0;
 640 }
 641
 642 /*
 643  * Find the destination instructions for all calls.
 644  */
 645 static int add_call_destinations(struct objtool_file *file)
 646 {
 647         struct instruction *insn;
 648         unsigned long dest_off;
 649         struct rela *rela;
 650
 651         for_each_insn(file, insn) {
 652                 if (insn->type != INSN_CALL)
 653                         continue;
 654
 655                 rela = find_rela_by_dest_range(insn->sec, insn->offset,
 656                                                insn->len);
 657                 if (!rela) {
 658                         dest_off = insn->offset + insn->len + insn->immediate;
 659                         insn->call_dest = find_symbol_by_offset(insn->sec,
 660                                                                 dest_off);
 661
 662                         if (!insn->call_dest && !insn->ignore) {
 663                                 WARN_FUNC("unsupported intra-function call",
 664                                           insn->sec, insn->offset);
 665                                 if (retpoline)
 666                                         WARN("If this is a retpoline, please patch it in with alternatives and annotate it with ANNOTATE_NOSPEC_ALTERNATIVE.");
 667                                 return -1;
 668                         }
 669
 670                 } else if (rela->sym->type == STT_SECTION) {
 671                         insn->call_dest = find_symbol_by_offset(rela->sym->sec,
 672                                                                 rela->addend+4);
 673                         if (!insn->call_dest ||
 674                             insn->call_dest->type != STT_FUNC) {
 675                                 WARN_FUNC("can't find call dest symbol at %s+0x%x",
 676                                           insn->sec, insn->offset,
 677                                           rela->sym->sec->name,
 678                                           rela->addend + 4);
 679                                 return -1;
 680                         }
 681                 } else
 682                         insn->call_dest = rela->sym;
 683         }
 684
 685         return 0;
 686 }
 687
 688 /*
 689  * The .alternatives section requires some extra special care, over and above
 690  * what other special sections require:
 691  *
 692  * 1. Because alternatives are patched in-place, we need to insert a fake jump
 693  *    instruction at the end so that validate_branch() skips all the original
 694  *    replaced instructions when validating the new instruction path.
 695  *
 696  * 2. An added wrinkle is that the new instruction length might be zero.  In
 697  *    that case the old instructions are replaced with noops.  We simulate that
 698  *    by creating a fake jump as the only new instruction.
 699  *
 700  * 3. In some cases, the alternative section includes an instruction which
 701  *    conditionally jumps to the _end_ of the entry.  We have to modify these
 702  *    jumps' destinations to point back to .text rather than the end of the
 703  *    entry in .altinstr_replacement.
 704  */
 705 static int handle_group_alt(struct objtool_file *file,
 706                             struct special_alt *special_alt,
 707                             struct instruction *orig_insn,
 708                             struct instruction **new_insn)
 709 {
 710         struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump = NULL;
 711         unsigned long dest_off;
 712
 713         last_orig_insn = NULL;
 714         insn = orig_insn;
 715         sec_for_each_insn_from(file, insn) {
 716                 if (insn->offset >= special_alt->orig_off + special_alt->orig_len)
 717                         break;
 718
 719                 insn->alt_group = true;
 720                 last_orig_insn = insn;
 721         }
 722
 723         if (next_insn_same_sec(file, last_orig_insn)) {
 724                 fake_jump = malloc(sizeof(*fake_jump));
 725                 if (!fake_jump) {
 726                         WARN("malloc failed");
 727                         return -1;
 728                 }
 729                 memset(fake_jump, 0, sizeof(*fake_jump));
 730                 INIT_LIST_HEAD(&fake_jump->alts);
 731                 clear_insn_state(&fake_jump->state);
 732
 733                 fake_jump->sec = special_alt->new_sec;
 734                 fake_jump->offset = FAKE_JUMP_OFFSET;
 735                 fake_jump->type = INSN_JUMP_UNCONDITIONAL;
 736                 fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
 737                 fake_jump->func = orig_insn->func;
 738         }
 739
 740         if (!special_alt->new_len) {
 741                 if (!fake_jump) {
 742                         WARN("%s: empty alternative at end of section",
 743                              special_alt->orig_sec->name);
 744                         return -1;
 745                 }
 746
 747                 *new_insn = fake_jump;
 748                 return 0;
 749         }
 750
 751         last_new_insn = NULL;
 752         insn = *new_insn;
 753         sec_for_each_insn_from(file, insn) {
 754                 if (insn->offset >= special_alt->new_off + special_alt->new_len)
 755                         break;
 756
 757                 last_new_insn = insn;
 758
 759                 insn->ignore = orig_insn->ignore_alts;
 760                 insn->func = orig_insn->func;
 761
 762                 if (insn->type != INSN_JUMP_CONDITIONAL &&
 763                     insn->type != INSN_JUMP_UNCONDITIONAL)
 764                         continue;
 765
 766                 if (!insn->immediate)
 767                         continue;
 768
 769                 dest_off = insn->offset + insn->len + insn->immediate;
 770                 if (dest_off == special_alt->new_off + special_alt->new_len) {
 771                         if (!fake_jump) {
 772                                 WARN("%s: alternative jump to end of section",
 773                                      special_alt->orig_sec->name);
 774                                 return -1;
 775                         }
 776                         insn->jump_dest = fake_jump;
 777                 }
 778
 779                 if (!insn->jump_dest) {
 780                         WARN_FUNC("can't find alternative jump destination",
 781                                   insn->sec, insn->offset);
 782                         return -1;
 783                 }
 784         }
 785
 786         if (!last_new_insn) {
 787                 WARN_FUNC("can't find last new alternative instruction",
 788                           special_alt->new_sec, special_alt->new_off);
 789                 return -1;
 790         }
 791
 792         if (fake_jump)
 793                 list_add(&fake_jump->list, &last_new_insn->list);
 794
 795         return 0;
 796 }
 797
 798 /*
 799  * A jump table entry can either convert a nop to a jump or a jump to a nop.
 800  * If the original instruction is a jump, make the alt entry an effective nop
 801  * by just skipping the original instruction.
 802  */
 803 static int handle_jump_alt(struct objtool_file *file,
 804                            struct special_alt *special_alt,
 805                            struct instruction *orig_insn,
 806                            struct instruction **new_insn)
 807 {
 808         if (orig_insn->type == INSN_NOP)
 809                 return 0;
 810
 811         if (orig_insn->type != INSN_JUMP_UNCONDITIONAL) {
 812                 WARN_FUNC("unsupported instruction at jump label",
 813                           orig_insn->sec, orig_insn->offset);
 814                 return -1;
 815         }
 816
 817         *new_insn = list_next_entry(orig_insn, list);
 818         return 0;
 819 }
 820
 821 /*
 822  * Read all the special sections which have alternate instructions which can be
 823  * patched in or redirected to at runtime.  Each instruction having alternate
 824  * instruction(s) has them added to its insn->alts list, which will be
 825  * traversed in validate_branch().
 826  */
 827 static int add_special_section_alts(struct objtool_file *file)
 828 {
 829         struct list_head special_alts;
 830         struct instruction *orig_insn, *new_insn;
 831         struct special_alt *special_alt, *tmp;
 832         struct alternative *alt;
 833         int ret;
 834
 835         ret = special_get_alts(file->elf, &special_alts);
 836         if (ret)
 837                 return ret;
 838
 839         list_for_each_entry_safe(special_alt, tmp, &special_alts, list) {
 840
 841                 orig_insn = find_insn(file, special_alt->orig_sec,
 842                                       special_alt->orig_off);
 843                 if (!orig_insn) {
 844                         WARN_FUNC("special: can't find orig instruction",
 845                                   special_alt->orig_sec, special_alt->orig_off);
 846                         ret = -1;
 847                         goto out;
 848                 }
 849
 850                 new_insn = NULL;
 851                 if (!special_alt->group || special_alt->new_len) {
 852                         new_insn = find_insn(file, special_alt->new_sec,
 853                                              special_alt->new_off);
 854                         if (!new_insn) {
 855                                 WARN_FUNC("special: can't find new instruction",
 856                                           special_alt->new_sec,
 857                                           special_alt->new_off);
 858                                 ret = -1;
 859                                 goto out;
 860                         }
 861                 }
 862
 863                 if (special_alt->group) {
 864                         ret = handle_group_alt(file, special_alt, orig_insn,
 865                                                &new_insn);
 866                         if (ret)
 867                                 goto out;
 868                 } else if (special_alt->jump_or_nop) {
 869                         ret = handle_jump_alt(file, special_alt, orig_insn,
 870                                               &new_insn);
 871                         if (ret)
 872                                 goto out;
 873                 }
 874
 875                 alt = malloc(sizeof(*alt));
 876                 if (!alt) {
 877                         WARN("malloc failed");
 878                         ret = -1;
 879                         goto out;
 880                 }
 881
 882                 alt->insn = new_insn;
 883                 alt->skip_orig = special_alt->skip_orig;
 884                 orig_insn->ignore_alts |= special_alt->skip_alt;
 885                 list_add_tail(&alt->list, &orig_insn->alts);
 886
 887                 list_del(&special_alt->list);
 888                 free(special_alt);
 889         }
 890
 891 out:
 892         return ret;
 893 }
 894
 895 static int add_jump_table(struct objtool_file *file, struct instruction *insn,
 896                             struct rela *table)
 897 {
 898         struct rela *rela = table;
 899         struct instruction *dest_insn;
 900         struct alternative *alt;
 901         struct symbol *pfunc = insn->func->pfunc;
 902         unsigned int prev_offset = 0;
 903
 904         /*
 905          * Each @rela is a switch table relocation which points to the target
 906          * instruction.
 907          */
 908         list_for_each_entry_from(rela, &table->sec->rela_list, list) {
 909
 910                 /* Check for the end of the table: */
 911                 if (rela != table && rela->jump_table_start)
 912                         break;
 913
 914                 /* Make sure the table entries are consecutive: */
 915                 if (prev_offset && rela->offset != prev_offset + 8)
 916                         break;
 917
 918                 /* Detect function pointers from contiguous objects: */
 919                 if (rela->sym->sec == pfunc->sec &&
 920                     rela->addend == pfunc->offset)
 921                         break;
 922
 923                 dest_insn = find_insn(file, rela->sym->sec, rela->addend);
 924                 if (!dest_insn)
 925                         break;
 926
 927                 /* Make sure the destination is in the same function: */
 928                 if (!dest_insn->func || dest_insn->func->pfunc != pfunc)
 929                         break;
 930
 931                 alt = malloc(sizeof(*alt));
 932                 if (!alt) {
 933                         WARN("malloc failed");
 934                         return -1;
 935                 }
 936
 937                 alt->insn = dest_insn;
 938                 list_add_tail(&alt->list, &insn->alts);
 939                 prev_offset = rela->offset;
 940         }
 941
 942         if (!prev_offset) {
 943                 WARN_FUNC("can't find switch jump table",
 944                           insn->sec, insn->offset);
 945                 return -1;
 946         }
 947
 948         return 0;
 949 }
 950
 951 /*
 952  * find_jump_table() - Given a dynamic jump, find the switch jump table in
 953  * .rodata associated with it.
 954  *
 955  * There are 3 basic patterns:
 956  *
 957  * 1. jmpq *[rodata addr](,%reg,8)
 958  *
 959  *    This is the most common case by far.  It jumps to an address in a simple
 960  *    jump table which is stored in .rodata.
 961  *
 962  * 2. jmpq *[rodata addr](%rip)
 963  *
 964  *    This is caused by a rare GCC quirk, currently only seen in three driver
 965  *    functions in the kernel, only with certain obscure non-distro configs.
 966  *
 967  *    As part of an optimization, GCC makes a copy of an existing switch jump
 968  *    table, modifies it, and then hard-codes the jump (albeit with an indirect
 969  *    jump) to use a single entry in the table.  The rest of the jump table and
 970  *    some of its jump targets remain as dead code.
 971  *
 972  *    In such a case we can just crudely ignore all unreachable instruction
 973  *    warnings for the entire object file.  Ideally we would just ignore them
 974  *    for the function, but that would require redesigning the code quite a
 975  *    bit.  And honestly that's just not worth doing: unreachable instruction
 976  *    warnings are of questionable value anyway, and this is such a rare issue.
 977  *
 978  * 3. mov [rodata addr],%reg1
 979  *    ... some instructions ...
 980  *    jmpq *(%reg1,%reg2,8)
 981  *
 982  *    This is a fairly uncommon pattern which is new for GCC 6.  As of this
 983  *    writing, there are 11 occurrences of it in the allmodconfig kernel.
 984  *
 985  *    As of GCC 7 there are quite a few more of these and the 'in between' code
 986  *    is significant. Esp. with KASAN enabled some of the code between the mov
 987  *    and jmpq uses .rodata itself, which can confuse things.
 988  *
 989  *    TODO: Once we have DWARF CFI and smarter instruction decoding logic,
 990  *    ensure the same register is used in the mov and jump instructions.
 991  *
 992  *    NOTE: RETPOLINE made it harder still to decode dynamic jumps.
 993  */
 994 static struct rela *find_jump_table(struct objtool_file *file,
 995                                       struct symbol *func,
 996                                       struct instruction *insn)
 997 {
 998         struct rela *text_rela, *table_rela;
 999         struct instruction *orig_insn = insn;
1000         struct section *table_sec;
1001         unsigned long table_offset;
1002
1003         /*
1004          * Backward search using the @first_jump_src links, these help avoid
1005          * much of the 'in between' code. Which avoids us getting confused by
1006          * it.
1007          */
1008         for (;
1009              &insn->list != &file->insn_list &&
1010              insn->sec == func->sec &&
1011              insn->offset >= func->offset;
1012
1013              insn = insn->first_jump_src ?: list_prev_entry(insn, list)) {
1014
1015                 if (insn != orig_insn && insn->type == INSN_JUMP_DYNAMIC)
1016                         break;
1017
1018                 /* allow small jumps within the range */
1019                 if (insn->type == INSN_JUMP_UNCONDITIONAL &&
1020                     insn->jump_dest &&
1021                     (insn->jump_dest->offset <= insn->offset ||
1022                      insn->jump_dest->offset > orig_insn->offset))
1023                     break;
1024
1025                 /* look for a relocation which references .rodata */
1026                 text_rela = find_rela_by_dest_range(insn->sec, insn->offset,
1027                                                     insn->len);
1028                 if (!text_rela || text_rela->sym->type != STT_SECTION ||
1029                     !text_rela->sym->sec->rodata)
1030                         continue;
1031
1032                 table_offset = text_rela->addend;
1033                 table_sec = text_rela->sym->sec;
1034
1035                 if (text_rela->type == R_X86_64_PC32)
1036                         table_offset += 4;
1037
1038                 /*
1039                  * Make sure the .rodata address isn't associated with a
1040                  * symbol.  GCC jump tables are anonymous data.
1041                  *
1042                  * Also support C jump tables which are in the same format as
1043                  * switch jump tables.  For objtool to recognize them, they
1044                  * need to be placed in the C_JUMP_TABLE_SECTION section.  They
1045                  * have symbols associated with them.
1046                  */
1047                 if (find_symbol_containing(table_sec, table_offset) &&
1048                     strcmp(table_sec->name, C_JUMP_TABLE_SECTION))
1049                         continue;
1050
1051                 /* Each table entry has a rela associated with it. */
1052                 table_rela = find_rela_by_dest(table_sec, table_offset);
1053                 if (!table_rela)
1054                         continue;
1055
1056                 /*
1057                  * Use of RIP-relative switch jumps is quite rare, and
1058                  * indicates a rare GCC quirk/bug which can leave dead code
1059                  * behind.
1060                  */
1061                 if (text_rela->type == R_X86_64_PC32)
1062                         file->ignore_unreachables = true;
1063
1064                 return table_rela;
1065         }
1066
1067         return NULL;
1068 }
1069
1070 /*
1071  * First pass: Mark the head of each jump table so that in the next pass,
1072  * we know when a given jump table ends and the next one starts.
1073  */
1074 static void mark_func_jump_tables(struct objtool_file *file,
1075                                     struct symbol *func)
1076 {
1077         struct instruction *insn, *last = NULL;
1078         struct rela *rela;
1079
1080         func_for_each_insn_all(file, func, insn) {
1081                 if (!last)
1082                         last = insn;
1083
1084                 /*
1085                  * Store back-pointers for unconditional forward jumps such
1086                  * that find_jump_table() can back-track using those and
1087                  * avoid some potentially confusing code.
1088                  */
1089                 if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest &&
1090                     insn->offset > last->offset &&
1091                     insn->jump_dest->offset > insn->offset &&
1092                     !insn->jump_dest->first_jump_src) {
1093
1094                         insn->jump_dest->first_jump_src = insn;
1095                         last = insn->jump_dest;
1096                 }
1097
1098                 if (insn->type != INSN_JUMP_DYNAMIC)
1099                         continue;
1100
1101                 rela = find_jump_table(file, func, insn);
1102                 if (rela) {
1103                         rela->jump_table_start = true;
1104                         insn->jump_table = rela;
1105                 }
1106         }
1107 }
1108
1109 static int add_func_jump_tables(struct objtool_file *file,
1110                                   struct symbol *func)
1111 {
1112         struct instruction *insn;
1113         int ret;
1114
1115         func_for_each_insn_all(file, func, insn) {
1116                 if (!insn->jump_table)
1117                         continue;
1118
1119                 ret = add_jump_table(file, insn, insn->jump_table);
1120                 if (ret)
1121                         return ret;
1122         }
1123
1124         return 0;
1125 }
1126
1127 /*
1128  * For some switch statements, gcc generates a jump table in the .rodata
1129  * section which contains a list of addresses within the function to jump to.
1130  * This finds these jump tables and adds them to the insn->alts lists.
1131  */
1132 static int add_jump_table_alts(struct objtool_file *file)
1133 {
1134         struct section *sec;
1135         struct symbol *func;
1136         int ret;
1137
1138         if (!file->rodata)
1139                 return 0;
1140
1141         for_each_sec(file, sec) {
1142                 list_for_each_entry(func, &sec->symbol_list, list) {
1143                         if (func->type != STT_FUNC)
1144                                 continue;
1145
1146                         mark_func_jump_tables(file, func);
1147                         ret = add_func_jump_tables(file, func);
1148                         if (ret)
1149                                 return ret;
1150                 }
1151         }
1152
1153         return 0;
1154 }
1155
1156 static int read_unwind_hints(struct objtool_file *file)
1157 {
1158         struct section *sec, *relasec;
1159         struct rela *rela;
1160         struct unwind_hint *hint;
1161         struct instruction *insn;
1162         struct cfi_reg *cfa;
1163         int i;
1164
1165         sec = find_section_by_name(file->elf, ".discard.unwind_hints");
1166         if (!sec)
1167                 return 0;
1168
1169         relasec = sec->rela;
1170         if (!relasec) {
1171                 WARN("missing .rela.discard.unwind_hints section");
1172                 return -1;
1173         }
1174
1175         if (sec->len % sizeof(struct unwind_hint)) {
1176                 WARN("struct unwind_hint size mismatch");
1177                 return -1;
1178         }
1179
1180         file->hints = true;
1181
1182         for (i = 0; i < sec->len / sizeof(struct unwind_hint); i++) {
1183                 hint = (struct unwind_hint *)sec->data->d_buf + i;
1184
1185                 rela = find_rela_by_dest(sec, i * sizeof(*hint));
1186                 if (!rela) {
1187                         WARN("can't find rela for unwind_hints[%d]", i);
1188                         return -1;
1189                 }
1190
1191                 insn = find_insn(file, rela->sym->sec, rela->addend);
1192                 if (!insn) {
1193                         WARN("can't find insn for unwind_hints[%d]", i);
1194                         return -1;
1195                 }
1196
1197                 cfa = &insn->state.cfa;
1198
1199                 if (hint->type == UNWIND_HINT_TYPE_SAVE) {
1200                         insn->save = true;
1201                         continue;
1202
1203                 } else if (hint->type == UNWIND_HINT_TYPE_RESTORE) {
1204                         insn->restore = true;
1205                         insn->hint = true;
1206                         continue;
1207                 }
1208
1209                 insn->hint = true;
1210
1211                 switch (hint->sp_reg) {
1212                 case ORC_REG_UNDEFINED:
1213                         cfa->base = CFI_UNDEFINED;
1214                         break;
1215                 case ORC_REG_SP:
1216                         cfa->base = CFI_SP;
1217                         break;
1218                 case ORC_REG_BP:
1219                         cfa->base = CFI_BP;
1220                         break;
1221                 case ORC_REG_SP_INDIRECT:
1222                         cfa->base = CFI_SP_INDIRECT;
1223                         break;
1224                 case ORC_REG_R10:
1225                         cfa->base = CFI_R10;
1226                         break;
1227                 case ORC_REG_R13:
1228                         cfa->base = CFI_R13;
1229                         break;
1230                 case ORC_REG_DI:
1231                         cfa->base = CFI_DI;
1232                         break;
1233                 case ORC_REG_DX:
1234                         cfa->base = CFI_DX;
1235                         break;
1236                 default:
1237                         WARN_FUNC("unsupported unwind_hint sp base reg %d",
1238                                   insn->sec, insn->offset, hint->sp_reg);
1239                         return -1;
1240                 }
1241
1242                 cfa->offset = hint->sp_offset;
1243                 insn->state.type = hint->type;
1244                 insn->state.end = hint->end;
1245         }
1246
1247         return 0;
1248 }
1249
1250 static int read_retpoline_hints(struct objtool_file *file)
1251 {
1252         struct section *sec;
1253         struct instruction *insn;
1254         struct rela *rela;
1255
1256         sec = find_section_by_name(file->elf, ".rela.discard.retpoline_safe");
1257         if (!sec)
1258                 return 0;
1259
1260         list_for_each_entry(rela, &sec->rela_list, list) {
1261                 if (rela->sym->type != STT_SECTION) {
1262                         WARN("unexpected relocation symbol type in %s", sec->name);
1263                         return -1;
1264                 }
1265
1266                 insn = find_insn(file, rela->sym->sec, rela->addend);
1267                 if (!insn) {
1268                         WARN("bad .discard.retpoline_safe entry");
1269                         return -1;
1270                 }
1271
1272                 if (insn->type != INSN_JUMP_DYNAMIC &&
1273                     insn->type != INSN_CALL_DYNAMIC) {
1274                         WARN_FUNC("retpoline_safe hint not an indirect jump/call",
1275                                   insn->sec, insn->offset);
1276                         return -1;
1277                 }
1278
1279                 insn->retpoline_safe = true;
1280         }
1281
1282         return 0;
1283 }
1284
1285 static void mark_rodata(struct objtool_file *file)
1286 {
1287         struct section *sec;
1288         bool found = false;
1289
1290         /*
1291          * Search for the following rodata sections, each of which can
1292          * potentially contain jump tables:
1293          *
1294          * - .rodata: can contain GCC switch tables
1295          * - .rodata.<func>: same, if -fdata-sections is being used
1296          * - .rodata..c_jump_table: contains C annotated jump tables
1297          *
1298          * .rodata.str1.* sections are ignored; they don't contain jump tables.
1299          */
1300         for_each_sec(file, sec) {
1301                 if ((!strncmp(sec->name, ".rodata", 7) && !strstr(sec->name, ".str1.")) ||
1302                     !strcmp(sec->name, C_JUMP_TABLE_SECTION)) {
1303                         sec->rodata = true;
1304                         found = true;
1305                 }
1306         }
1307
1308         file->rodata = found;
1309 }
1310
1311 static int decode_sections(struct objtool_file *file)
1312 {
1313         int ret;
1314
1315         mark_rodata(file);
1316
1317         ret = decode_instructions(file);
1318         if (ret)
1319                 return ret;
1320
1321         ret = add_dead_ends(file);
1322         if (ret)
1323                 return ret;
1324
1325         add_ignores(file);
1326         add_uaccess_safe(file);
1327
1328         ret = add_ignore_alternatives(file);
1329         if (ret)
1330                 return ret;
1331
1332         ret = add_jump_destinations(file);
1333         if (ret)
1334                 return ret;
1335
1336         ret = add_special_section_alts(file);
1337         if (ret)
1338                 return ret;
1339
1340         ret = add_call_destinations(file);
1341         if (ret)
1342                 return ret;
1343
1344         ret = add_jump_table_alts(file);
1345         if (ret)
1346                 return ret;
1347
1348         ret = read_unwind_hints(file);
1349         if (ret)
1350                 return ret;
1351
1352         ret = read_retpoline_hints(file);
1353         if (ret)
1354                 return ret;
1355
1356         return 0;
1357 }
1358
1359 static bool is_fentry_call(struct instruction *insn)
1360 {
1361         if (insn->type == INSN_CALL &&
1362             insn->call_dest->type == STT_NOTYPE &&
1363             !strcmp(insn->call_dest->name, "__fentry__"))
1364                 return true;
1365
1366         return false;
1367 }
1368
1369 static bool has_modified_stack_frame(struct insn_state *state)
1370 {
1371         int i;
1372
1373         if (state->cfa.base != initial_func_cfi.cfa.base ||
1374             state->cfa.offset != initial_func_cfi.cfa.offset ||
1375             state->stack_size != initial_func_cfi.cfa.offset ||
1376             state->drap)
1377                 return true;
1378
1379         for (i = 0; i < CFI_NUM_REGS; i++)
1380                 if (state->regs[i].base != initial_func_cfi.regs[i].base ||
1381                     state->regs[i].offset != initial_func_cfi.regs[i].offset)
1382                         return true;
1383
1384         return false;
1385 }
1386
1387 static bool has_valid_stack_frame(struct insn_state *state)
1388 {
1389         if (state->cfa.base == CFI_BP && state->regs[CFI_BP].base == CFI_CFA &&
1390             state->regs[CFI_BP].offset == -16)
1391                 return true;
1392
1393         if (state->drap && state->regs[CFI_BP].base == CFI_BP)
1394                 return true;
1395
1396         return false;
1397 }
1398
1399 static int update_insn_state_regs(struct instruction *insn, struct insn_state *state)
1400 {
1401         struct cfi_reg *cfa = &state->cfa;
1402         struct stack_op *op = &insn->stack_op;
1403
1404         if (cfa->base != CFI_SP)
1405                 return 0;
1406
1407         /* push */
1408         if (op->dest.type == OP_DEST_PUSH || op->dest.type == OP_DEST_PUSHF)
1409                 cfa->offset += 8;
1410
1411         /* pop */
1412         if (op->src.type == OP_SRC_POP || op->src.type == OP_SRC_POPF)
1413                 cfa->offset -= 8;
1414
1415         /* add immediate to sp */
1416         if (op->dest.type == OP_DEST_REG && op->src.type == OP_SRC_ADD &&
1417             op->dest.reg == CFI_SP && op->src.reg == CFI_SP)
1418                 cfa->offset -= op->src.offset;
1419
1420         return 0;
1421 }
1422
1423 static void save_reg(struct insn_state *state, unsigned char reg, int base,
1424                      int offset)
1425 {
1426         if (arch_callee_saved_reg(reg) &&
1427             state->regs[reg].base == CFI_UNDEFINED) {
1428                 state->regs[reg].base = base;
1429                 state->regs[reg].offset = offset;
1430         }
1431 }
1432
1433 static void restore_reg(struct insn_state *state, unsigned char reg)
1434 {
1435         state->regs[reg].base = CFI_UNDEFINED;
1436         state->regs[reg].offset = 0;
1437 }
1438
1439 /*
1440  * A note about DRAP stack alignment:
1441  *
1442  * GCC has the concept of a DRAP register, which is used to help keep track of
1443  * the stack pointer when aligning the stack.  r10 or r13 is used as the DRAP
1444  * register.  The typical DRAP pattern is:
1445  *
1446  *   4c 8d 54 24 08             lea    0x8(%rsp),%r10
1447  *   48 83 e4 c0                and    $0xffffffffffffffc0,%rsp
1448  *   41 ff 72 f8                pushq  -0x8(%r10)
1449  *   55                         push   %rbp
1450  *   48 89 e5                   mov    %rsp,%rbp
1451  *                              (more pushes)
1452  *   41 52                      push   %r10
1453  *                              ...
1454  *   41 5a                      pop    %r10
1455  *                              (more pops)
1456  *   5d                         pop    %rbp
1457  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1458  *   c3                         retq
1459  *
1460  * There are some variations in the epilogues, like:
1461  *
1462  *   5b                         pop    %rbx
1463  *   41 5a                      pop    %r10
1464  *   41 5c                      pop    %r12
1465  *   41 5d                      pop    %r13
1466  *   41 5e                      pop    %r14
1467  *   c9                         leaveq
1468  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1469  *   c3                         retq
1470  *
1471  * and:
1472  *
1473  *   4c 8b 55 e8                mov    -0x18(%rbp),%r10
1474  *   48 8b 5d e0                mov    -0x20(%rbp),%rbx
1475  *   4c 8b 65 f0                mov    -0x10(%rbp),%r12
1476  *   4c 8b 6d f8                mov    -0x8(%rbp),%r13
1477  *   c9                         leaveq
1478  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1479  *   c3                         retq
1480  *
1481  * Sometimes r13 is used as the DRAP register, in which case it's saved and
1482  * restored beforehand:
1483  *
1484  *   41 55                      push   %r13
1485  *   4c 8d 6c 24 10             lea    0x10(%rsp),%r13
1486  *   48 83 e4 f0                and    $0xfffffffffffffff0,%rsp
1487  *                              ...
1488  *   49 8d 65 f0                lea    -0x10(%r13),%rsp
1489  *   41 5d                      pop    %r13
1490  *   c3                         retq
1491  */
1492 static int update_insn_state(struct instruction *insn, struct insn_state *state)
1493 {
1494         struct stack_op *op = &insn->stack_op;
1495         struct cfi_reg *cfa = &state->cfa;
1496         struct cfi_reg *regs = state->regs;
1497
1498         /* stack operations don't make sense with an undefined CFA */
1499         if (cfa->base == CFI_UNDEFINED) {
1500                 if (insn->func) {
1501                         WARN_FUNC("undefined stack state", insn->sec, insn->offset);
1502                         return -1;
1503                 }
1504                 return 0;
1505         }
1506
1507         if (state->type == ORC_TYPE_REGS || state->type == ORC_TYPE_REGS_IRET)
1508                 return update_insn_state_regs(insn, state);
1509
1510         switch (op->dest.type) {
1511
1512         case OP_DEST_REG:
1513                 switch (op->src.type) {
1514
1515                 case OP_SRC_REG:
1516                         if (op->src.reg == CFI_SP && op->dest.reg == CFI_BP &&
1517                             cfa->base == CFI_SP &&
1518                             regs[CFI_BP].base == CFI_CFA &&
1519                             regs[CFI_BP].offset == -cfa->offset) {
1520
1521                                 /* mov %rsp, %rbp */
1522                                 cfa->base = op->dest.reg;
1523                                 state->bp_scratch = false;
1524                         }
1525
1526                         else if (op->src.reg == CFI_SP &&
1527                                  op->dest.reg == CFI_BP && state->drap) {
1528
1529                                 /* drap: mov %rsp, %rbp */
1530                                 regs[CFI_BP].base = CFI_BP;
1531                                 regs[CFI_BP].offset = -state->stack_size;
1532                                 state->bp_scratch = false;
1533                         }
1534
1535                         else if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1536
1537                                 /*
1538                                  * mov %rsp, %reg
1539                                  *
1540                                  * This is needed for the rare case where GCC
1541                                  * does:
1542                                  *
1543                                  *   mov    %rsp, %rax
1544                                  *   ...
1545                                  *   mov    %rax, %rsp
1546                                  */
1547                                 state->vals[op->dest.reg].base = CFI_CFA;
1548                                 state->vals[op->dest.reg].offset = -state->stack_size;
1549                         }
1550
1551                         else if (op->src.reg == CFI_BP && op->dest.reg == CFI_SP &&
1552                                  cfa->base == CFI_BP) {
1553
1554                                 /*
1555                                  * mov %rbp, %rsp
1556                                  *
1557                                  * Restore the original stack pointer (Clang).
1558                                  */
1559                                 state->stack_size = -state->regs[CFI_BP].offset;
1560                         }
1561
1562                         else if (op->dest.reg == cfa->base) {
1563
1564                                 /* mov %reg, %rsp */
1565                                 if (cfa->base == CFI_SP &&
1566                                     state->vals[op->src.reg].base == CFI_CFA) {
1567
1568                                         /*
1569                                          * This is needed for the rare case
1570                                          * where GCC does something dumb like:
1571                                          *
1572                                          *   lea    0x8(%rsp), %rcx
1573                                          *   ...
1574                                          *   mov    %rcx, %rsp
1575                                          */
1576                                         cfa->offset = -state->vals[op->src.reg].offset;
1577                                         state->stack_size = cfa->offset;
1578
1579                                 } else {
1580                                         cfa->base = CFI_UNDEFINED;
1581                                         cfa->offset = 0;
1582                                 }
1583                         }
1584
1585                         break;
1586
1587                 case OP_SRC_ADD:
1588                         if (op->dest.reg == CFI_SP && op->src.reg == CFI_SP) {
1589
1590                                 /* add imm, %rsp */
1591                                 state->stack_size -= op->src.offset;
1592                                 if (cfa->base == CFI_SP)
1593                                         cfa->offset -= op->src.offset;
1594                                 break;
1595                         }
1596
1597                         if (op->dest.reg == CFI_SP && op->src.reg == CFI_BP) {
1598
1599                                 /* lea disp(%rbp), %rsp */
1600                                 state->stack_size = -(op->src.offset + regs[CFI_BP].offset);
1601                                 break;
1602                         }
1603
1604                         if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1605
1606                                 /* drap: lea disp(%rsp), %drap */
1607                                 state->drap_reg = op->dest.reg;
1608
1609                                 /*
1610                                  * lea disp(%rsp), %reg
1611                                  *
1612                                  * This is needed for the rare case where GCC
1613                                  * does something dumb like:
1614                                  *
1615                                  *   lea    0x8(%rsp), %rcx
1616                                  *   ...
1617                                  *   mov    %rcx, %rsp
1618                                  */
1619                                 state->vals[op->dest.reg].base = CFI_CFA;
1620                                 state->vals[op->dest.reg].offset = \
1621                                         -state->stack_size + op->src.offset;
1622
1623                                 break;
1624                         }
1625
1626                         if (state->drap && op->dest.reg == CFI_SP &&
1627                             op->src.reg == state->drap_reg) {
1628
1629                                  /* drap: lea disp(%drap), %rsp */
1630                                 cfa->base = CFI_SP;
1631                                 cfa->offset = state->stack_size = -op->src.offset;
1632                                 state->drap_reg = CFI_UNDEFINED;
1633                                 state->drap = false;
1634                                 break;
1635                         }
1636
1637                         if (op->dest.reg == state->cfa.base) {
1638                                 WARN_FUNC("unsupported stack register modification",
1639                                           insn->sec, insn->offset);
1640                                 return -1;
1641                         }
1642
1643                         break;
1644
1645                 case OP_SRC_AND:
1646                         if (op->dest.reg != CFI_SP ||
1647                             (state->drap_reg != CFI_UNDEFINED && cfa->base != CFI_SP) ||
1648                             (state->drap_reg == CFI_UNDEFINED && cfa->base != CFI_BP)) {
1649                                 WARN_FUNC("unsupported stack pointer realignment",
1650                                           insn->sec, insn->offset);
1651                                 return -1;
1652                         }
1653
1654                         if (state->drap_reg != CFI_UNDEFINED) {
1655                                 /* drap: and imm, %rsp */
1656                                 cfa->base = state->drap_reg;
1657                                 cfa->offset = state->stack_size = 0;
1658                                 state->drap = true;
1659                         }
1660
1661                         /*
1662                          * Older versions of GCC (4.8ish) realign the stack
1663                          * without DRAP, with a frame pointer.
1664                          */
1665
1666                         break;
1667
1668                 case OP_SRC_POP:
1669                 case OP_SRC_POPF:
1670                         if (!state->drap && op->dest.type == OP_DEST_REG &&
1671                             op->dest.reg == cfa->base) {
1672
1673                                 /* pop %rbp */
1674                                 cfa->base = CFI_SP;
1675                         }
1676
1677                         if (state->drap && cfa->base == CFI_BP_INDIRECT &&
1678                             op->dest.type == OP_DEST_REG &&
1679                             op->dest.reg == state->drap_reg &&
1680                             state->drap_offset == -state->stack_size) {
1681
1682                                 /* drap: pop %drap */
1683                                 cfa->base = state->drap_reg;
1684                                 cfa->offset = 0;
1685                                 state->drap_offset = -1;
1686
1687                         } else if (regs[op->dest.reg].offset == -state->stack_size) {
1688
1689                                 /* pop %reg */
1690                                 restore_reg(state, op->dest.reg);
1691                         }
1692
1693                         state->stack_size -= 8;
1694                         if (cfa->base == CFI_SP)
1695                                 cfa->offset -= 8;
1696
1697                         break;
1698
1699                 case OP_SRC_REG_INDIRECT:
1700                         if (state->drap && op->src.reg == CFI_BP &&
1701                             op->src.offset == state->drap_offset) {
1702
1703                                 /* drap: mov disp(%rbp), %drap */
1704                                 cfa->base = state->drap_reg;
1705                                 cfa->offset = 0;
1706                                 state->drap_offset = -1;
1707                         }
1708
1709                         if (state->drap && op->src.reg == CFI_BP &&
1710                             op->src.offset == regs[op->dest.reg].offset) {
1711
1712                                 /* drap: mov disp(%rbp), %reg */
1713                                 restore_reg(state, op->dest.reg);
1714
1715                         } else if (op->src.reg == cfa->base &&
1716                             op->src.offset == regs[op->dest.reg].offset + cfa->offset) {
1717
1718                                 /* mov disp(%rbp), %reg */
1719                                 /* mov disp(%rsp), %reg */
1720                                 restore_reg(state, op->dest.reg);
1721                         }
1722
1723                         break;
1724
1725                 default:
1726                         WARN_FUNC("unknown stack-related instruction",
1727                                   insn->sec, insn->offset);
1728                         return -1;
1729                 }
1730
1731                 break;
1732
1733         case OP_DEST_PUSH:
1734         case OP_DEST_PUSHF:
1735                 state->stack_size += 8;
1736                 if (cfa->base == CFI_SP)
1737                         cfa->offset += 8;
1738
1739                 if (op->src.type != OP_SRC_REG)
1740                         break;
1741
1742                 if (state->drap) {
1743                         if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1744
1745                                 /* drap: push %drap */
1746                                 cfa->base = CFI_BP_INDIRECT;
1747                                 cfa->offset = -state->stack_size;
1748
1749                                 /* save drap so we know when to restore it */
1750                                 state->drap_offset = -state->stack_size;
1751
1752                         } else if (op->src.reg == CFI_BP && cfa->base == state->drap_reg) {
1753
1754                                 /* drap: push %rbp */
1755                                 state->stack_size = 0;
1756
1757                         } else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1758
1759                                 /* drap: push %reg */
1760                                 save_reg(state, op->src.reg, CFI_BP, -state->stack_size);
1761                         }
1762
1763                 } else {
1764
1765                         /* push %reg */
1766                         save_reg(state, op->src.reg, CFI_CFA, -state->stack_size);
1767                 }
1768
1769                 /* detect when asm code uses rbp as a scratch register */
1770                 if (!no_fp && insn->func && op->src.reg == CFI_BP &&
1771                     cfa->base != CFI_BP)
1772                         state->bp_scratch = true;
1773                 break;
1774
1775         case OP_DEST_REG_INDIRECT:
1776
1777                 if (state->drap) {
1778                         if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1779
1780                                 /* drap: mov %drap, disp(%rbp) */
1781                                 cfa->base = CFI_BP_INDIRECT;
1782                                 cfa->offset = op->dest.offset;
1783
1784                                 /* save drap offset so we know when to restore it */
1785                                 state->drap_offset = op->dest.offset;
1786                         }
1787
1788                         else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1789
1790                                 /* drap: mov reg, disp(%rbp) */
1791                                 save_reg(state, op->src.reg, CFI_BP, op->dest.offset);
1792                         }
1793
1794                 } else if (op->dest.reg == cfa->base) {
1795
1796                         /* mov reg, disp(%rbp) */
1797                         /* mov reg, disp(%rsp) */
1798                         save_reg(state, op->src.reg, CFI_CFA,
1799                                  op->dest.offset - state->cfa.offset);
1800                 }
1801
1802                 break;
1803
1804         case OP_DEST_LEAVE:
1805                 if ((!state->drap && cfa->base != CFI_BP) ||
1806                     (state->drap && cfa->base != state->drap_reg)) {
1807                         WARN_FUNC("leave instruction with modified stack frame",
1808                                   insn->sec, insn->offset);
1809                         return -1;
1810                 }
1811
1812                 /* leave (mov %rbp, %rsp; pop %rbp) */
1813
1814                 state->stack_size = -state->regs[CFI_BP].offset - 8;
1815                 restore_reg(state, CFI_BP);
1816
1817                 if (!state->drap) {
1818                         cfa->base = CFI_SP;
1819                         cfa->offset -= 8;
1820                 }
1821
1822                 break;
1823
1824         case OP_DEST_MEM:
1825                 if (op->src.type != OP_SRC_POP && op->src.type != OP_SRC_POPF) {
1826                         WARN_FUNC("unknown stack-related memory operation",
1827                                   insn->sec, insn->offset);
1828                         return -1;
1829                 }
1830
1831                 /* pop mem */
1832                 state->stack_size -= 8;
1833                 if (cfa->base == CFI_SP)
1834                         cfa->offset -= 8;
1835
1836                 break;
1837
1838         default:
1839                 WARN_FUNC("unknown stack-related instruction",
1840                           insn->sec, insn->offset);
1841                 return -1;
1842         }
1843
1844         return 0;
1845 }
1846
1847 static bool insn_state_match(struct instruction *insn, struct insn_state *state)
1848 {
1849         struct insn_state *state1 = &insn->state, *state2 = state;
1850         int i;
1851
1852         if (memcmp(&state1->cfa, &state2->cfa, sizeof(state1->cfa))) {
1853                 WARN_FUNC("stack state mismatch: cfa1=%d%+d cfa2=%d%+d",
1854                           insn->sec, insn->offset,
1855                           state1->cfa.base, state1->cfa.offset,
1856                           state2->cfa.base, state2->cfa.offset);
1857
1858         } else if (memcmp(&state1->regs, &state2->regs, sizeof(state1->regs))) {
1859                 for (i = 0; i < CFI_NUM_REGS; i++) {
1860                         if (!memcmp(&state1->regs[i], &state2->regs[i],
1861                                     sizeof(struct cfi_reg)))
1862                                 continue;
1863
1864                         WARN_FUNC("stack state mismatch: reg1[%d]=%d%+d reg2[%d]=%d%+d",
1865                                   insn->sec, insn->offset,
1866                                   i, state1->regs[i].base, state1->regs[i].offset,
1867                                   i, state2->regs[i].base, state2->regs[i].offset);
1868                         break;
1869                 }
1870
1871         } else if (state1->type != state2->type) {
1872                 WARN_FUNC("stack state mismatch: type1=%d type2=%d",
1873                           insn->sec, insn->offset, state1->type, state2->type);
1874
1875         } else if (state1->drap != state2->drap ||
1876                  (state1->drap && state1->drap_reg != state2->drap_reg) ||
1877                  (state1->drap && state1->drap_offset != state2->drap_offset)) {
1878                 WARN_FUNC("stack state mismatch: drap1=%d(%d,%d) drap2=%d(%d,%d)",
1879                           insn->sec, insn->offset,
1880                           state1->drap, state1->drap_reg, state1->drap_offset,
1881                           state2->drap, state2->drap_reg, state2->drap_offset);
1882
1883         } else
1884                 return true;
1885
1886         return false;
1887 }
1888
1889 static inline bool func_uaccess_safe(struct symbol *func)
1890 {
1891         if (func)
1892                 return func->uaccess_safe;
1893
1894         return false;
1895 }
1896
1897 static inline const char *call_dest_name(struct instruction *insn)
1898 {
1899         if (insn->call_dest)
1900                 return insn->call_dest->name;
1901
1902         return "{dynamic}";
1903 }
1904
1905 static int validate_call(struct instruction *insn, struct insn_state *state)
1906 {
1907         if (state->uaccess && !func_uaccess_safe(insn->call_dest)) {
1908                 WARN_FUNC("call to %s() with UACCESS enabled",
1909                                 insn->sec, insn->offset, call_dest_name(insn));
1910                 return 1;
1911         }
1912
1913         if (state->df) {
1914                 WARN_FUNC("call to %s() with DF set",
1915                                 insn->sec, insn->offset, call_dest_name(insn));
1916                 return 1;
1917         }
1918
1919         return 0;
1920 }
1921
1922 static int validate_sibling_call(struct instruction *insn, struct insn_state *state)
1923 {
1924         if (has_modified_stack_frame(state)) {
1925                 WARN_FUNC("sibling call from callable instruction with modified stack frame",
1926                                 insn->sec, insn->offset);
1927                 return 1;
1928         }
1929
1930         return validate_call(insn, state);
1931 }
1932
1933 /*
1934  * Follow the branch starting at the given instruction, and recursively follow
1935  * any other branches (jumps).  Meanwhile, track the frame pointer state at
1936  * each instruction and validate all the rules described in
1937  * tools/objtool/Documentation/stack-validation.txt.
1938  */
1939 static int validate_branch(struct objtool_file *file, struct symbol *func,
1940                            struct instruction *first, struct insn_state state)
1941 {
1942         struct alternative *alt;
1943         struct instruction *insn, *next_insn;
1944         struct section *sec;
1945         int ret;
1946
1947         insn = first;
1948         sec = insn->sec;
1949
1950         if (insn->alt_group && list_empty(&insn->alts)) {
1951                 WARN_FUNC("don't know how to handle branch to middle of alternative instruction group",
1952                           sec, insn->offset);
1953                 return 1;
1954         }
1955
1956         while (1) {
1957                 next_insn = next_insn_same_sec(file, insn);
1958
1959                 if (file->c_file && func && insn->func && func != insn->func->pfunc) {
1960                         WARN("%s() falls through to next function %s()",
1961                              func->name, insn->func->name);
1962                         return 1;
1963                 }
1964
1965                 if (func && insn->ignore) {
1966                         WARN_FUNC("BUG: why am I validating an ignored function?",
1967                                   sec, insn->offset);
1968                         return 1;
1969                 }
1970
1971                 if (insn->visited) {
1972                         if (!insn->hint && !insn_state_match(insn, &state))
1973                                 return 1;
1974
1975                         /* If we were here with AC=0, but now have AC=1, go again */
1976                         if (insn->state.uaccess || !state.uaccess)
1977                                 return 0;
1978                 }
1979
1980                 if (insn->hint) {
1981                         if (insn->restore) {
1982                                 struct instruction *save_insn, *i;
1983
1984                                 i = insn;
1985                                 save_insn = NULL;
1986                                 func_for_each_insn_continue_reverse(file, func, i) {
1987                                         if (i->save) {
1988                                                 save_insn = i;
1989                                                 break;
1990                                         }
1991                                 }
1992
1993                                 if (!save_insn) {
1994                                         WARN_FUNC("no corresponding CFI save for CFI restore",
1995                                                   sec, insn->offset);
1996                                         return 1;
1997                                 }
1998
1999                                 if (!save_insn->visited) {
2000                                         /*
2001                                          * Oops, no state to copy yet.
2002                                          * Hopefully we can reach this
2003                                          * instruction from another branch
2004                                          * after the save insn has been
2005                                          * visited.
2006                                          */
2007                                         if (insn == first)
2008                                                 return 0;
2009
2010                                         WARN_FUNC("objtool isn't smart enough to handle this CFI save/restore combo",
2011                                                   sec, insn->offset);
2012                                         return 1;
2013                                 }
2014
2015                                 insn->state = save_insn->state;
2016                         }
2017
2018                         state = insn->state;
2019
2020                 } else
2021                         insn->state = state;
2022
2023                 insn->visited = true;
2024
2025                 if (!insn->ignore_alts) {
2026                         bool skip_orig = false;
2027
2028                         list_for_each_entry(alt, &insn->alts, list) {
2029                                 if (alt->skip_orig)
2030                                         skip_orig = true;
2031
2032                                 ret = validate_branch(file, func, alt->insn, state);
2033                                 if (ret) {
2034                                         if (backtrace)
2035                                                 BT_FUNC("(alt)", insn);
2036                                         return ret;
2037                                 }
2038                         }
2039
2040                         if (skip_orig)
2041                                 return 0;
2042                 }
2043
2044                 switch (insn->type) {
2045
2046                 case INSN_RETURN:
2047                         if (state.uaccess && !func_uaccess_safe(func)) {
2048                                 WARN_FUNC("return with UACCESS enabled", sec, insn->offset);
2049                                 return 1;
2050                         }
2051
2052                         if (!state.uaccess && func_uaccess_safe(func)) {
2053                                 WARN_FUNC("return with UACCESS disabled from a UACCESS-safe function", sec, insn->offset);
2054                                 return 1;
2055                         }
2056
2057                         if (state.df) {
2058                                 WARN_FUNC("return with DF set", sec, insn->offset);
2059                                 return 1;
2060                         }
2061
2062                         if (func && has_modified_stack_frame(&state)) {
2063                                 WARN_FUNC("return with modified stack frame",
2064                                           sec, insn->offset);
2065                                 return 1;
2066                         }
2067
2068                         if (state.bp_scratch) {
2069                                 WARN("%s uses BP as a scratch register",
2070                                      func->name);
2071                                 return 1;
2072                         }
2073
2074                         return 0;
2075
2076                 case INSN_CALL:
2077                 case INSN_CALL_DYNAMIC:
2078                         ret = validate_call(insn, &state);
2079                         if (ret)
2080                                 return ret;
2081
2082                         if (!no_fp && func && !is_fentry_call(insn) &&
2083                             !has_valid_stack_frame(&state)) {
2084                                 WARN_FUNC("call without frame pointer save/setup",
2085                                           sec, insn->offset);
2086                                 return 1;
2087                         }
2088
2089                         if (dead_end_function(file, insn->call_dest))
2090                                 return 0;
2091
2092                         break;
2093
2094                 case INSN_JUMP_CONDITIONAL:
2095                 case INSN_JUMP_UNCONDITIONAL:
2096                         if (func && is_sibling_call(insn)) {
2097                                 ret = validate_sibling_call(insn, &state);
2098                                 if (ret)
2099                                         return ret;
2100
2101                         } else if (insn->jump_dest) {
2102                                 ret = validate_branch(file, func,
2103                                                       insn->jump_dest, state);
2104                                 if (ret) {
2105                                         if (backtrace)
2106                                                 BT_FUNC("(branch)", insn);
2107                                         return ret;
2108                                 }
2109                         }
2110
2111                         if (insn->type == INSN_JUMP_UNCONDITIONAL)
2112                                 return 0;
2113
2114                         break;
2115
2116                 case INSN_JUMP_DYNAMIC:
2117                         if (func && is_sibling_call(insn)) {
2118                                 ret = validate_sibling_call(insn, &state);
2119                                 if (ret)
2120                                         return ret;
2121                         }
2122
2123                         return 0;
2124
2125                 case INSN_CONTEXT_SWITCH:
2126                         if (func && (!next_insn || !next_insn->hint)) {
2127                                 WARN_FUNC("unsupported instruction in callable function",
2128                                           sec, insn->offset);
2129                                 return 1;
2130                         }
2131                         return 0;
2132
2133                 case INSN_STACK:
2134                         if (update_insn_state(insn, &state))
2135                                 return 1;
2136
2137                         if (insn->stack_op.dest.type == OP_DEST_PUSHF) {
2138                                 if (!state.uaccess_stack) {
2139                                         state.uaccess_stack = 1;
2140                                 } else if (state.uaccess_stack >> 31) {
2141                                         WARN_FUNC("PUSHF stack exhausted", sec, insn->offset);
2142                                         return 1;
2143                                 }
2144                                 state.uaccess_stack <<= 1;
2145                                 state.uaccess_stack  |= state.uaccess;
2146                         }
2147
2148                         if (insn->stack_op.src.type == OP_SRC_POPF) {
2149                                 if (state.uaccess_stack) {
2150                                         state.uaccess = state.uaccess_stack & 1;
2151                                         state.uaccess_stack >>= 1;
2152                                         if (state.uaccess_stack == 1)
2153                                                 state.uaccess_stack = 0;
2154                                 }
2155                         }
2156
2157                         break;
2158
2159                 case INSN_STAC:
2160                         if (state.uaccess) {
2161                                 WARN_FUNC("recursive UACCESS enable", sec, insn->offset);
2162                                 return 1;
2163                         }
2164
2165                         state.uaccess = true;
2166                         break;
2167
2168                 case INSN_CLAC:
2169                         if (!state.uaccess && func) {
2170                                 WARN_FUNC("redundant UACCESS disable", sec, insn->offset);
2171                                 return 1;
2172                         }
2173
2174                         if (func_uaccess_safe(func) && !state.uaccess_stack) {
2175                                 WARN_FUNC("UACCESS-safe disables UACCESS", sec, insn->offset);
2176                                 return 1;
2177                         }
2178
2179                         state.uaccess = false;
2180                         break;
2181
2182                 case INSN_STD:
2183                         if (state.df)
2184                                 WARN_FUNC("recursive STD", sec, insn->offset);
2185
2186                         state.df = true;
2187                         break;
2188
2189                 case INSN_CLD:
2190                         if (!state.df && func)
2191                                 WARN_FUNC("redundant CLD", sec, insn->offset);
2192
2193                         state.df = false;
2194                         break;
2195
2196                 default:
2197                         break;
2198                 }
2199
2200                 if (insn->dead_end)
2201                         return 0;
2202
2203                 if (!next_insn) {
2204                         if (state.cfa.base == CFI_UNDEFINED)
2205                                 return 0;
2206                         WARN("%s: unexpected end of section", sec->name);
2207                         return 1;
2208                 }
2209
2210                 insn = next_insn;
2211         }
2212
2213         return 0;
2214 }
2215
2216 static int validate_unwind_hints(struct objtool_file *file)
2217 {
2218         struct instruction *insn;
2219         int ret, warnings = 0;
2220         struct insn_state state;
2221
2222         if (!file->hints)
2223                 return 0;
2224
2225         clear_insn_state(&state);
2226
2227         for_each_insn(file, insn) {
2228                 if (insn->hint && !insn->visited) {
2229                         ret = validate_branch(file, insn->func, insn, state);
2230                         if (ret && backtrace)
2231                                 BT_FUNC("<=== (hint)", insn);
2232                         warnings += ret;
2233                 }
2234         }
2235
2236         return warnings;
2237 }
2238
2239 static int validate_retpoline(struct objtool_file *file)
2240 {
2241         struct instruction *insn;
2242         int warnings = 0;
2243
2244         for_each_insn(file, insn) {
2245                 if (insn->type != INSN_JUMP_DYNAMIC &&
2246                     insn->type != INSN_CALL_DYNAMIC)
2247                         continue;
2248
2249                 if (insn->retpoline_safe)
2250                         continue;
2251
2252                 /*
2253                  * .init.text code is ran before userspace and thus doesn't
2254                  * strictly need retpolines, except for modules which are
2255                  * loaded late, they very much do need retpoline in their
2256                  * .init.text
2257                  */
2258                 if (!strcmp(insn->sec->name, ".init.text") && !module)
2259                         continue;
2260
2261                 WARN_FUNC("indirect %s found in RETPOLINE build",
2262                           insn->sec, insn->offset,
2263                           insn->type == INSN_JUMP_DYNAMIC ? "jump" : "call");
2264
2265                 warnings++;
2266         }
2267
2268         return warnings;
2269 }
2270
2271 static bool is_kasan_insn(struct instruction *insn)
2272 {
2273         return (insn->type == INSN_CALL &&
2274                 !strcmp(insn->call_dest->name, "__asan_handle_no_return"));
2275 }
2276
2277 static bool is_ubsan_insn(struct instruction *insn)
2278 {
2279         return (insn->type == INSN_CALL &&
2280                 !strcmp(insn->call_dest->name,
2281                         "__ubsan_handle_builtin_unreachable"));
2282 }
2283
2284 static bool ignore_unreachable_insn(struct instruction *insn)
2285 {
2286         int i;
2287
2288         if (insn->ignore || insn->type == INSN_NOP)
2289                 return true;
2290
2291         /*
2292          * Ignore any unused exceptions.  This can happen when a whitelisted
2293          * function has an exception table entry.
2294          *
2295          * Also ignore alternative replacement instructions.  This can happen
2296          * when a whitelisted function uses one of the ALTERNATIVE macros.
2297          */
2298         if (!strcmp(insn->sec->name, ".fixup") ||
2299             !strcmp(insn->sec->name, ".altinstr_replacement") ||
2300             !strcmp(insn->sec->name, ".altinstr_aux"))
2301                 return true;
2302
2303         /*
2304          * Check if this (or a subsequent) instruction is related to
2305          * CONFIG_UBSAN or CONFIG_KASAN.
2306          *
2307          * End the search at 5 instructions to avoid going into the weeds.
2308          */
2309         if (!insn->func)
2310                 return false;
2311         for (i = 0; i < 5; i++) {
2312
2313                 if (is_kasan_insn(insn) || is_ubsan_insn(insn))
2314                         return true;
2315
2316                 if (insn->type == INSN_JUMP_UNCONDITIONAL) {
2317                         if (insn->jump_dest &&
2318                             insn->jump_dest->func == insn->func) {
2319                                 insn = insn->jump_dest;
2320                                 continue;
2321                         }
2322
2323                         break;
2324                 }
2325
2326                 if (insn->offset + insn->len >= insn->func->offset + insn->func->len)
2327                         break;
2328
2329                 insn = list_next_entry(insn, list);
2330         }
2331
2332         return false;
2333 }
2334
2335 static int validate_functions(struct objtool_file *file)
2336 {
2337         struct section *sec;
2338         struct symbol *func;
2339         struct instruction *insn;
2340         struct insn_state state;
2341         int ret, warnings = 0;
2342
2343         clear_insn_state(&state);
2344
2345         state.cfa = initial_func_cfi.cfa;
2346         memcpy(&state.regs, &initial_func_cfi.regs,
2347                CFI_NUM_REGS * sizeof(struct cfi_reg));
2348         state.stack_size = initial_func_cfi.cfa.offset;
2349
2350         for_each_sec(file, sec) {
2351                 list_for_each_entry(func, &sec->symbol_list, list) {
2352                         if (func->type != STT_FUNC)
2353                                 continue;
2354
2355                         if (!func->len) {
2356                                 WARN("%s() is missing an ELF size annotation",
2357                                      func->name);
2358                                 warnings++;
2359                         }
2360
2361                         if (func->pfunc != func || func->alias != func)
2362                                 continue;
2363
2364                         insn = find_insn(file, sec, func->offset);
2365                         if (!insn || insn->ignore || insn->visited)
2366                                 continue;
2367
2368                         state.uaccess = func->uaccess_safe;
2369
2370                         ret = validate_branch(file, func, insn, state);
2371                         if (ret && backtrace)
2372                                 BT_FUNC("<=== (func)", insn);
2373                         warnings += ret;
2374                 }
2375         }
2376
2377         return warnings;
2378 }
2379
2380 static int validate_reachable_instructions(struct objtool_file *file)
2381 {
2382         struct instruction *insn;
2383
2384         if (file->ignore_unreachables)
2385                 return 0;
2386
2387         for_each_insn(file, insn) {
2388                 if (insn->visited || ignore_unreachable_insn(insn))
2389                         continue;
2390
2391                 WARN_FUNC("unreachable instruction", insn->sec, insn->offset);
2392                 return 1;
2393         }
2394
2395         return 0;
2396 }
2397
2398 static void cleanup(struct objtool_file *file)
2399 {
2400         struct instruction *insn, *tmpinsn;
2401         struct alternative *alt, *tmpalt;
2402
2403         list_for_each_entry_safe(insn, tmpinsn, &file->insn_list, list) {
2404                 list_for_each_entry_safe(alt, tmpalt, &insn->alts, list) {
2405                         list_del(&alt->list);
2406                         free(alt);
2407                 }
2408                 list_del(&insn->list);
2409                 hash_del(&insn->hash);
2410                 free(insn);
2411         }
2412         elf_close(file->elf);
2413 }
2414
2415 static struct objtool_file file;
2416
2417 int check(const char *_objname, bool orc)
2418 {
2419         int ret, warnings = 0;
2420
2421         objname = _objname;
2422
2423         file.elf = elf_read(objname, orc ? O_RDWR : O_RDONLY);
2424         if (!file.elf)
2425                 return 1;
2426
2427         INIT_LIST_HEAD(&file.insn_list);
2428         hash_init(file.insn_hash);
2429         file.c_file = find_section_by_name(file.elf, ".comment");
2430         file.ignore_unreachables = no_unreachable;
2431         file.hints = false;
2432
2433         arch_initial_func_cfi_state(&initial_func_cfi);
2434
2435         ret = decode_sections(&file);
2436         if (ret < 0)
2437                 goto out;
2438         warnings += ret;
2439
2440         if (list_empty(&file.insn_list))
2441                 goto out;
2442
2443         if (retpoline) {
2444                 ret = validate_retpoline(&file);
2445                 if (ret < 0)
2446                         return ret;
2447                 warnings += ret;
2448         }
2449
2450         ret = validate_functions(&file);
2451         if (ret < 0)
2452                 goto out;
2453         warnings += ret;
2454
2455         ret = validate_unwind_hints(&file);
2456         if (ret < 0)
2457                 goto out;
2458         warnings += ret;
2459
2460         if (!warnings) {
2461                 ret = validate_reachable_instructions(&file);
2462                 if (ret < 0)
2463                         goto out;
2464                 warnings += ret;
2465         }
2466
2467         if (orc) {
2468                 ret = create_orc(&file);
2469                 if (ret < 0)
2470                         goto out;
2471
2472                 ret = create_orc_sections(&file);
2473                 if (ret < 0)
2474                         goto out;
2475
2476                 ret = elf_write(file.elf);
2477                 if (ret < 0)
2478                         goto out;
2479         }
2480
2481 out:
2482         cleanup(&file);
2483
2484         /* ignore warnings for now until we get all the code cleaned up */
2485         if (ret || warnings)
2486                 return 0;
2487         return 0;
2488 }