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 struct alternative {
  22         struct list_head list;
  23         struct instruction *insn;
  24         bool skip_orig;
  25 };
  26
  27 const char *objname;
  28 struct cfi_state initial_func_cfi;
  29
  30 struct instruction *find_insn(struct objtool_file *file,
  31                               struct section *sec, unsigned long offset)
  32 {
  33         struct instruction *insn;
  34
  35         hash_for_each_possible(file->insn_hash, insn, hash, offset)
  36                 if (insn->sec == sec && insn->offset == offset)
  37                         return insn;
  38
  39         return NULL;
  40 }
  41
  42 static struct instruction *next_insn_same_sec(struct objtool_file *file,
  43                                               struct instruction *insn)
  44 {
  45         struct instruction *next = list_next_entry(insn, list);
  46
  47         if (!next || &next->list == &file->insn_list || next->sec != insn->sec)
  48                 return NULL;
  49
  50         return next;
  51 }
  52
  53 static struct instruction *next_insn_same_func(struct objtool_file *file,
  54                                                struct instruction *insn)
  55 {
  56         struct instruction *next = list_next_entry(insn, list);
  57         struct symbol *func = insn->func;
  58
  59         if (!func)
  60                 return NULL;
  61
  62         if (&next->list != &file->insn_list && next->func == func)
  63                 return next;
  64
  65         /* Check if we're already in the subfunction: */
  66         if (func == func->cfunc)
  67                 return NULL;
  68
  69         /* Move to the subfunction: */
  70         return find_insn(file, func->cfunc->sec, func->cfunc->offset);
  71 }
  72
  73 #define func_for_each_insn_all(file, func, insn)                        \
  74         for (insn = find_insn(file, func->sec, func->offset);           \
  75              insn;                                                      \
  76              insn = next_insn_same_func(file, insn))
  77
  78 #define func_for_each_insn(file, func, insn)                            \
  79         for (insn = find_insn(file, func->sec, func->offset);           \
  80              insn && &insn->list != &file->insn_list &&                 \
  81                 insn->sec == func->sec &&                               \
  82                 insn->offset < func->offset + func->len;                \
  83              insn = list_next_entry(insn, list))
  84
  85 #define func_for_each_insn_continue_reverse(file, func, insn)           \
  86         for (insn = list_prev_entry(insn, list);                        \
  87              &insn->list != &file->insn_list &&                         \
  88                 insn->sec == func->sec && insn->offset >= func->offset; \
  89              insn = list_prev_entry(insn, list))
  90
  91 #define sec_for_each_insn_from(file, insn)                              \
  92         for (; insn; insn = next_insn_same_sec(file, insn))
  93
  94 #define sec_for_each_insn_continue(file, insn)                          \
  95         for (insn = next_insn_same_sec(file, insn); insn;               \
  96              insn = next_insn_same_sec(file, insn))
  97
  98 /*
  99  * This checks to see if the given function is a "noreturn" function.
 100  *
 101  * For global functions which are outside the scope of this object file, we
 102  * have to keep a manual list of them.
 103  *
 104  * For local functions, we have to detect them manually by simply looking for
 105  * the lack of a return instruction.
 106  *
 107  * Returns:
 108  *  -1: error
 109  *   0: no dead end
 110  *   1: dead end
 111  */
 112 static int __dead_end_function(struct objtool_file *file, struct symbol *func,
 113                                int recursion)
 114 {
 115         int i;
 116         struct instruction *insn;
 117         bool empty = true;
 118
 119         /*
 120          * Unfortunately these have to be hard coded because the noreturn
 121          * attribute isn't provided in ELF data.
 122          */
 123         static const char * const global_noreturns[] = {
 124                 "__stack_chk_fail",
 125                 "panic",
 126                 "do_exit",
 127                 "do_task_dead",
 128                 "__module_put_and_exit",
 129                 "complete_and_exit",
 130                 "kvm_spurious_fault",
 131                 "__reiserfs_panic",
 132                 "lbug_with_loc",
 133                 "fortify_panic",
 134                 "usercopy_abort",
 135                 "machine_real_restart",
 136                 "rewind_stack_do_exit",
 137         };
 138
 139         if (func->bind == STB_WEAK)
 140                 return 0;
 141
 142         if (func->bind == STB_GLOBAL)
 143                 for (i = 0; i < ARRAY_SIZE(global_noreturns); i++)
 144                         if (!strcmp(func->name, global_noreturns[i]))
 145                                 return 1;
 146
 147         if (!func->len)
 148                 return 0;
 149
 150         insn = find_insn(file, func->sec, func->offset);
 151         if (!insn->func)
 152                 return 0;
 153
 154         func_for_each_insn_all(file, func, insn) {
 155                 empty = false;
 156
 157                 if (insn->type == INSN_RETURN)
 158                         return 0;
 159         }
 160
 161         if (empty)
 162                 return 0;
 163
 164         /*
 165          * A function can have a sibling call instead of a return.  In that
 166          * case, the function's dead-end status depends on whether the target
 167          * of the sibling call returns.
 168          */
 169         func_for_each_insn_all(file, func, insn) {
 170                 if (insn->type == INSN_JUMP_UNCONDITIONAL) {
 171                         struct instruction *dest = insn->jump_dest;
 172
 173                         if (!dest)
 174                                 /* sibling call to another file */
 175                                 return 0;
 176
 177                         if (dest->func && dest->func->pfunc != insn->func->pfunc) {
 178
 179                                 /* local sibling call */
 180                                 if (recursion == 5) {
 181                                         /*
 182                                          * Infinite recursion: two functions
 183                                          * have sibling calls to each other.
 184                                          * This is a very rare case.  It means
 185                                          * they aren't dead ends.
 186                                          */
 187                                         return 0;
 188                                 }
 189
 190                                 return __dead_end_function(file, dest->func,
 191                                                            recursion + 1);
 192                         }
 193                 }
 194
 195                 if (insn->type == INSN_JUMP_DYNAMIC && list_empty(&insn->alts))
 196                         /* sibling call */
 197                         return 0;
 198         }
 199
 200         return 1;
 201 }
 202
 203 static int dead_end_function(struct objtool_file *file, struct symbol *func)
 204 {
 205         return __dead_end_function(file, func, 0);
 206 }
 207
 208 static void clear_insn_state(struct insn_state *state)
 209 {
 210         int i;
 211
 212         memset(state, 0, sizeof(*state));
 213         state->cfa.base = CFI_UNDEFINED;
 214         for (i = 0; i < CFI_NUM_REGS; i++) {
 215                 state->regs[i].base = CFI_UNDEFINED;
 216                 state->vals[i].base = CFI_UNDEFINED;
 217         }
 218         state->drap_reg = CFI_UNDEFINED;
 219         state->drap_offset = -1;
 220 }
 221
 222 /*
 223  * Call the arch-specific instruction decoder for all the instructions and add
 224  * them to the global instruction list.
 225  */
 226 static int decode_instructions(struct objtool_file *file)
 227 {
 228         struct section *sec;
 229         struct symbol *func;
 230         unsigned long offset;
 231         struct instruction *insn;
 232         int ret;
 233
 234         for_each_sec(file, sec) {
 235
 236                 if (!(sec->sh.sh_flags & SHF_EXECINSTR))
 237                         continue;
 238
 239                 if (strcmp(sec->name, ".altinstr_replacement") &&
 240                     strcmp(sec->name, ".altinstr_aux") &&
 241                     strncmp(sec->name, ".discard.", 9))
 242                         sec->text = true;
 243
 244                 for (offset = 0; offset < sec->len; offset += insn->len) {
 245                         insn = malloc(sizeof(*insn));
 246                         if (!insn) {
 247                                 WARN("malloc failed");
 248                                 return -1;
 249                         }
 250                         memset(insn, 0, sizeof(*insn));
 251                         INIT_LIST_HEAD(&insn->alts);
 252                         clear_insn_state(&insn->state);
 253
 254                         insn->sec = sec;
 255                         insn->offset = offset;
 256
 257                         ret = arch_decode_instruction(file->elf, sec, offset,
 258                                                       sec->len - offset,
 259                                                       &insn->len, &insn->type,
 260                                                       &insn->immediate,
 261                                                       &insn->stack_op);
 262                         if (ret)
 263                                 goto err;
 264
 265                         if (!insn->type || insn->type > INSN_LAST) {
 266                                 WARN_FUNC("invalid instruction type %d",
 267                                           insn->sec, insn->offset, insn->type);
 268                                 ret = -1;
 269                                 goto err;
 270                         }
 271
 272                         hash_add(file->insn_hash, &insn->hash, insn->offset);
 273                         list_add_tail(&insn->list, &file->insn_list);
 274                 }
 275
 276                 list_for_each_entry(func, &sec->symbol_list, list) {
 277                         if (func->type != STT_FUNC)
 278                                 continue;
 279
 280                         if (!find_insn(file, sec, func->offset)) {
 281                                 WARN("%s(): can't find starting instruction",
 282                                      func->name);
 283                                 return -1;
 284                         }
 285
 286                         func_for_each_insn(file, func, insn)
 287                                 if (!insn->func)
 288                                         insn->func = func;
 289                 }
 290         }
 291
 292         return 0;
 293
 294 err:
 295         free(insn);
 296         return ret;
 297 }
 298
 299 /*
 300  * Mark "ud2" instructions and manually annotated dead ends.
 301  */
 302 static int add_dead_ends(struct objtool_file *file)
 303 {
 304         struct section *sec;
 305         struct rela *rela;
 306         struct instruction *insn;
 307         bool found;
 308
 309         /*
 310          * By default, "ud2" is a dead end unless otherwise annotated, because
 311          * GCC 7 inserts it for certain divide-by-zero cases.
 312          */
 313         for_each_insn(file, insn)
 314                 if (insn->type == INSN_BUG)
 315                         insn->dead_end = true;
 316
 317         /*
 318          * Check for manually annotated dead ends.
 319          */
 320         sec = find_section_by_name(file->elf, ".rela.discard.unreachable");
 321         if (!sec)
 322                 goto reachable;
 323
 324         list_for_each_entry(rela, &sec->rela_list, list) {
 325                 if (rela->sym->type != STT_SECTION) {
 326                         WARN("unexpected relocation symbol type in %s", sec->name);
 327                         return -1;
 328                 }
 329                 insn = find_insn(file, rela->sym->sec, rela->addend);
 330                 if (insn)
 331                         insn = list_prev_entry(insn, list);
 332                 else if (rela->addend == rela->sym->sec->len) {
 333                         found = false;
 334                         list_for_each_entry_reverse(insn, &file->insn_list, list) {
 335                                 if (insn->sec == rela->sym->sec) {
 336                                         found = true;
 337                                         break;
 338                                 }
 339                         }
 340
 341                         if (!found) {
 342                                 WARN("can't find unreachable insn at %s+0x%x",
 343                                      rela->sym->sec->name, rela->addend);
 344                                 return -1;
 345                         }
 346                 } else {
 347                         WARN("can't find unreachable insn at %s+0x%x",
 348                              rela->sym->sec->name, rela->addend);
 349                         return -1;
 350                 }
 351
 352                 insn->dead_end = true;
 353         }
 354
 355 reachable:
 356         /*
 357          * These manually annotated reachable checks are needed for GCC 4.4,
 358          * where the Linux unreachable() macro isn't supported.  In that case
 359          * GCC doesn't know the "ud2" is fatal, so it generates code as if it's
 360          * not a dead end.
 361          */
 362         sec = find_section_by_name(file->elf, ".rela.discard.reachable");
 363         if (!sec)
 364                 return 0;
 365
 366         list_for_each_entry(rela, &sec->rela_list, list) {
 367                 if (rela->sym->type != STT_SECTION) {
 368                         WARN("unexpected relocation symbol type in %s", sec->name);
 369                         return -1;
 370                 }
 371                 insn = find_insn(file, rela->sym->sec, rela->addend);
 372                 if (insn)
 373                         insn = list_prev_entry(insn, list);
 374                 else if (rela->addend == rela->sym->sec->len) {
 375                         found = false;
 376                         list_for_each_entry_reverse(insn, &file->insn_list, list) {
 377                                 if (insn->sec == rela->sym->sec) {
 378                                         found = true;
 379                                         break;
 380                                 }
 381                         }
 382
 383                         if (!found) {
 384                                 WARN("can't find reachable insn at %s+0x%x",
 385                                      rela->sym->sec->name, rela->addend);
 386                                 return -1;
 387                         }
 388                 } else {
 389                         WARN("can't find reachable insn at %s+0x%x",
 390                              rela->sym->sec->name, rela->addend);
 391                         return -1;
 392                 }
 393
 394                 insn->dead_end = false;
 395         }
 396
 397         return 0;
 398 }
 399
 400 /*
 401  * Warnings shouldn't be reported for ignored functions.
 402  */
 403 static void add_ignores(struct objtool_file *file)
 404 {
 405         struct instruction *insn;
 406         struct section *sec;
 407         struct symbol *func;
 408         struct rela *rela;
 409
 410         sec = find_section_by_name(file->elf, ".rela.discard.func_stack_frame_non_standard");
 411         if (!sec)
 412                 return;
 413
 414         list_for_each_entry(rela, &sec->rela_list, list) {
 415                 switch (rela->sym->type) {
 416                 case STT_FUNC:
 417                         func = rela->sym;
 418                         break;
 419
 420                 case STT_SECTION:
 421                         func = find_symbol_by_offset(rela->sym->sec, rela->addend);
 422                         if (!func || func->type != STT_FUNC)
 423                                 continue;
 424                         break;
 425
 426                 default:
 427                         WARN("unexpected relocation symbol type in %s: %d", sec->name, rela->sym->type);
 428                         continue;
 429                 }
 430
 431                 func_for_each_insn_all(file, func, insn)
 432                         insn->ignore = true;
 433         }
 434 }
 435
 436 /*
 437  * This is a whitelist of functions that is allowed to be called with AC set.
 438  * The list is meant to be minimal and only contains compiler instrumentation
 439  * ABI and a few functions used to implement *_{to,from}_user() functions.
 440  *
 441  * These functions must not directly change AC, but may PUSHF/POPF.
 442  */
 443 static const char *uaccess_safe_builtin[] = {
 444         /* KASAN */
 445         "kasan_report",
 446         "check_memory_region",
 447         /* KASAN out-of-line */
 448         "__asan_loadN_noabort",
 449         "__asan_load1_noabort",
 450         "__asan_load2_noabort",
 451         "__asan_load4_noabort",
 452         "__asan_load8_noabort",
 453         "__asan_load16_noabort",
 454         "__asan_storeN_noabort",
 455         "__asan_store1_noabort",
 456         "__asan_store2_noabort",
 457         "__asan_store4_noabort",
 458         "__asan_store8_noabort",
 459         "__asan_store16_noabort",
 460         /* KASAN in-line */
 461         "__asan_report_load_n_noabort",
 462         "__asan_report_load1_noabort",
 463         "__asan_report_load2_noabort",
 464         "__asan_report_load4_noabort",
 465         "__asan_report_load8_noabort",
 466         "__asan_report_load16_noabort",
 467         "__asan_report_store_n_noabort",
 468         "__asan_report_store1_noabort",
 469         "__asan_report_store2_noabort",
 470         "__asan_report_store4_noabort",
 471         "__asan_report_store8_noabort",
 472         "__asan_report_store16_noabort",
 473         /* KCOV */
 474         "write_comp_data",
 475         "__sanitizer_cov_trace_pc",
 476         "__sanitizer_cov_trace_const_cmp1",
 477         "__sanitizer_cov_trace_const_cmp2",
 478         "__sanitizer_cov_trace_const_cmp4",
 479         "__sanitizer_cov_trace_const_cmp8",
 480         "__sanitizer_cov_trace_cmp1",
 481         "__sanitizer_cov_trace_cmp2",
 482         "__sanitizer_cov_trace_cmp4",
 483         "__sanitizer_cov_trace_cmp8",
 484         /* UBSAN */
 485         "ubsan_type_mismatch_common",
 486         "__ubsan_handle_type_mismatch",
 487         "__ubsan_handle_type_mismatch_v1",
 488         /* misc */
 489         "csum_partial_copy_generic",
 490         "__memcpy_mcsafe",
 491         "ftrace_likely_update", /* CONFIG_TRACE_BRANCH_PROFILING */
 492         NULL
 493 };
 494
 495 static void add_uaccess_safe(struct objtool_file *file)
 496 {
 497         struct symbol *func;
 498         const char **name;
 499
 500         if (!uaccess)
 501                 return;
 502
 503         for (name = uaccess_safe_builtin; *name; name++) {
 504                 func = find_symbol_by_name(file->elf, *name);
 505                 if (!func)
 506                         continue;
 507
 508                 func->alias->uaccess_safe = true;
 509         }
 510 }
 511
 512 /*
 513  * FIXME: For now, just ignore any alternatives which add retpolines.  This is
 514  * a temporary hack, as it doesn't allow ORC to unwind from inside a retpoline.
 515  * But it at least allows objtool to understand the control flow *around* the
 516  * retpoline.
 517  */
 518 static int add_ignore_alternatives(struct objtool_file *file)
 519 {
 520         struct section *sec;
 521         struct rela *rela;
 522         struct instruction *insn;
 523
 524         sec = find_section_by_name(file->elf, ".rela.discard.ignore_alts");
 525         if (!sec)
 526                 return 0;
 527
 528         list_for_each_entry(rela, &sec->rela_list, list) {
 529                 if (rela->sym->type != STT_SECTION) {
 530                         WARN("unexpected relocation symbol type in %s", sec->name);
 531                         return -1;
 532                 }
 533
 534                 insn = find_insn(file, rela->sym->sec, rela->addend);
 535                 if (!insn) {
 536                         WARN("bad .discard.ignore_alts entry");
 537                         return -1;
 538                 }
 539
 540                 insn->ignore_alts = true;
 541         }
 542
 543         return 0;
 544 }
 545
 546 /*
 547  * Find the destination instructions for all jumps.
 548  */
 549 static int add_jump_destinations(struct objtool_file *file)
 550 {
 551         struct instruction *insn;
 552         struct rela *rela;
 553         struct section *dest_sec;
 554         unsigned long dest_off;
 555
 556         for_each_insn(file, insn) {
 557                 if (insn->type != INSN_JUMP_CONDITIONAL &&
 558                     insn->type != INSN_JUMP_UNCONDITIONAL)
 559                         continue;
 560
 561                 if (insn->ignore || insn->offset == FAKE_JUMP_OFFSET)
 562                         continue;
 563
 564                 rela = find_rela_by_dest_range(insn->sec, insn->offset,
 565                                                insn->len);
 566                 if (!rela) {
 567                         dest_sec = insn->sec;
 568                         dest_off = insn->offset + insn->len + insn->immediate;
 569                 } else if (rela->sym->type == STT_SECTION) {
 570                         dest_sec = rela->sym->sec;
 571                         dest_off = rela->addend + 4;
 572                 } else if (rela->sym->sec->idx) {
 573                         dest_sec = rela->sym->sec;
 574                         dest_off = rela->sym->sym.st_value + rela->addend + 4;
 575                 } else if (strstr(rela->sym->name, "_indirect_thunk_")) {
 576                         /*
 577                          * Retpoline jumps are really dynamic jumps in
 578                          * disguise, so convert them accordingly.
 579                          */
 580                         insn->type = INSN_JUMP_DYNAMIC;
 581                         insn->retpoline_safe = true;
 582                         continue;
 583                 } else {
 584                         /* sibling call */
 585                         insn->call_dest = rela->sym;
 586                         insn->jump_dest = NULL;
 587                         continue;
 588                 }
 589
 590                 insn->jump_dest = find_insn(file, dest_sec, dest_off);
 591                 if (!insn->jump_dest) {
 592
 593                         /*
 594                          * This is a special case where an alt instruction
 595                          * jumps past the end of the section.  These are
 596                          * handled later in handle_group_alt().
 597                          */
 598                         if (!strcmp(insn->sec->name, ".altinstr_replacement"))
 599                                 continue;
 600
 601                         WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
 602                                   insn->sec, insn->offset, dest_sec->name,
 603                                   dest_off);
 604                         return -1;
 605                 }
 606
 607                 /*
 608                  * Cross-function jump.
 609                  */
 610                 if (insn->func && insn->jump_dest->func &&
 611                     insn->func != insn->jump_dest->func) {
 612
 613                         /*
 614                          * For GCC 8+, create parent/child links for any cold
 615                          * subfunctions.  This is _mostly_ redundant with a
 616                          * similar initialization in read_symbols().
 617                          *
 618                          * If a function has aliases, we want the *first* such
 619                          * function in the symbol table to be the subfunction's
 620                          * parent.  In that case we overwrite the
 621                          * initialization done in read_symbols().
 622                          *
 623                          * However this code can't completely replace the
 624                          * read_symbols() code because this doesn't detect the
 625                          * case where the parent function's only reference to a
 626                          * subfunction is through a switch table.
 627                          */
 628                         if (!strstr(insn->func->name, ".cold.") &&
 629                             strstr(insn->jump_dest->func->name, ".cold.")) {
 630                                 insn->func->cfunc = insn->jump_dest->func;
 631                                 insn->jump_dest->func->pfunc = insn->func;
 632
 633                         } else if (insn->jump_dest->func->pfunc != insn->func->pfunc &&
 634                                    insn->jump_dest->offset == insn->jump_dest->func->offset) {
 635
 636                                 /* sibling class */
 637                                 insn->call_dest = insn->jump_dest->func;
 638                                 insn->jump_dest = NULL;
 639                         }
 640                 }
 641         }
 642
 643         return 0;
 644 }
 645
 646 /*
 647  * Find the destination instructions for all calls.
 648  */
 649 static int add_call_destinations(struct objtool_file *file)
 650 {
 651         struct instruction *insn;
 652         unsigned long dest_off;
 653         struct rela *rela;
 654
 655         for_each_insn(file, insn) {
 656                 if (insn->type != INSN_CALL)
 657                         continue;
 658
 659                 rela = find_rela_by_dest_range(insn->sec, insn->offset,
 660                                                insn->len);
 661                 if (!rela) {
 662                         dest_off = insn->offset + insn->len + insn->immediate;
 663                         insn->call_dest = find_symbol_by_offset(insn->sec,
 664                                                                 dest_off);
 665
 666                         if (!insn->call_dest && !insn->ignore) {
 667                                 WARN_FUNC("unsupported intra-function call",
 668                                           insn->sec, insn->offset);
 669                                 if (retpoline)
 670                                         WARN("If this is a retpoline, please patch it in with alternatives and annotate it with ANNOTATE_NOSPEC_ALTERNATIVE.");
 671                                 return -1;
 672                         }
 673
 674                 } else if (rela->sym->type == STT_SECTION) {
 675                         insn->call_dest = find_symbol_by_offset(rela->sym->sec,
 676                                                                 rela->addend+4);
 677                         if (!insn->call_dest ||
 678                             insn->call_dest->type != STT_FUNC) {
 679                                 WARN_FUNC("can't find call dest symbol at %s+0x%x",
 680                                           insn->sec, insn->offset,
 681                                           rela->sym->sec->name,
 682                                           rela->addend + 4);
 683                                 return -1;
 684                         }
 685                 } else
 686                         insn->call_dest = rela->sym;
 687         }
 688
 689         return 0;
 690 }
 691
 692 /*
 693  * The .alternatives section requires some extra special care, over and above
 694  * what other special sections require:
 695  *
 696  * 1. Because alternatives are patched in-place, we need to insert a fake jump
 697  *    instruction at the end so that validate_branch() skips all the original
 698  *    replaced instructions when validating the new instruction path.
 699  *
 700  * 2. An added wrinkle is that the new instruction length might be zero.  In
 701  *    that case the old instructions are replaced with noops.  We simulate that
 702  *    by creating a fake jump as the only new instruction.
 703  *
 704  * 3. In some cases, the alternative section includes an instruction which
 705  *    conditionally jumps to the _end_ of the entry.  We have to modify these
 706  *    jumps' destinations to point back to .text rather than the end of the
 707  *    entry in .altinstr_replacement.
 708  */
 709 static int handle_group_alt(struct objtool_file *file,
 710                             struct special_alt *special_alt,
 711                             struct instruction *orig_insn,
 712                             struct instruction **new_insn)
 713 {
 714         struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump = NULL;
 715         unsigned long dest_off;
 716
 717         last_orig_insn = NULL;
 718         insn = orig_insn;
 719         sec_for_each_insn_from(file, insn) {
 720                 if (insn->offset >= special_alt->orig_off + special_alt->orig_len)
 721                         break;
 722
 723                 insn->alt_group = true;
 724                 last_orig_insn = insn;
 725         }
 726
 727         if (next_insn_same_sec(file, last_orig_insn)) {
 728                 fake_jump = malloc(sizeof(*fake_jump));
 729                 if (!fake_jump) {
 730                         WARN("malloc failed");
 731                         return -1;
 732                 }
 733                 memset(fake_jump, 0, sizeof(*fake_jump));
 734                 INIT_LIST_HEAD(&fake_jump->alts);
 735                 clear_insn_state(&fake_jump->state);
 736
 737                 fake_jump->sec = special_alt->new_sec;
 738                 fake_jump->offset = FAKE_JUMP_OFFSET;
 739                 fake_jump->type = INSN_JUMP_UNCONDITIONAL;
 740                 fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
 741                 fake_jump->func = orig_insn->func;
 742         }
 743
 744         if (!special_alt->new_len) {
 745                 if (!fake_jump) {
 746                         WARN("%s: empty alternative at end of section",
 747                              special_alt->orig_sec->name);
 748                         return -1;
 749                 }
 750
 751                 *new_insn = fake_jump;
 752                 return 0;
 753         }
 754
 755         last_new_insn = NULL;
 756         insn = *new_insn;
 757         sec_for_each_insn_from(file, insn) {
 758                 if (insn->offset >= special_alt->new_off + special_alt->new_len)
 759                         break;
 760
 761                 last_new_insn = insn;
 762
 763                 insn->ignore = orig_insn->ignore_alts;
 764                 insn->func = orig_insn->func;
 765
 766                 if (insn->type != INSN_JUMP_CONDITIONAL &&
 767                     insn->type != INSN_JUMP_UNCONDITIONAL)
 768                         continue;
 769
 770                 if (!insn->immediate)
 771                         continue;
 772
 773                 dest_off = insn->offset + insn->len + insn->immediate;
 774                 if (dest_off == special_alt->new_off + special_alt->new_len) {
 775                         if (!fake_jump) {
 776                                 WARN("%s: alternative jump to end of section",
 777                                      special_alt->orig_sec->name);
 778                                 return -1;
 779                         }
 780                         insn->jump_dest = fake_jump;
 781                 }
 782
 783                 if (!insn->jump_dest) {
 784                         WARN_FUNC("can't find alternative jump destination",
 785                                   insn->sec, insn->offset);
 786                         return -1;
 787                 }
 788         }
 789
 790         if (!last_new_insn) {
 791                 WARN_FUNC("can't find last new alternative instruction",
 792                           special_alt->new_sec, special_alt->new_off);
 793                 return -1;
 794         }
 795
 796         if (fake_jump)
 797                 list_add(&fake_jump->list, &last_new_insn->list);
 798
 799         return 0;
 800 }
 801
 802 /*
 803  * A jump table entry can either convert a nop to a jump or a jump to a nop.
 804  * If the original instruction is a jump, make the alt entry an effective nop
 805  * by just skipping the original instruction.
 806  */
 807 static int handle_jump_alt(struct objtool_file *file,
 808                            struct special_alt *special_alt,
 809                            struct instruction *orig_insn,
 810                            struct instruction **new_insn)
 811 {
 812         if (orig_insn->type == INSN_NOP)
 813                 return 0;
 814
 815         if (orig_insn->type != INSN_JUMP_UNCONDITIONAL) {
 816                 WARN_FUNC("unsupported instruction at jump label",
 817                           orig_insn->sec, orig_insn->offset);
 818                 return -1;
 819         }
 820
 821         *new_insn = list_next_entry(orig_insn, list);
 822         return 0;
 823 }
 824
 825 /*
 826  * Read all the special sections which have alternate instructions which can be
 827  * patched in or redirected to at runtime.  Each instruction having alternate
 828  * instruction(s) has them added to its insn->alts list, which will be
 829  * traversed in validate_branch().
 830  */
 831 static int add_special_section_alts(struct objtool_file *file)
 832 {
 833         struct list_head special_alts;
 834         struct instruction *orig_insn, *new_insn;
 835         struct special_alt *special_alt, *tmp;
 836         struct alternative *alt;
 837         int ret;
 838
 839         ret = special_get_alts(file->elf, &special_alts);
 840         if (ret)
 841                 return ret;
 842
 843         list_for_each_entry_safe(special_alt, tmp, &special_alts, list) {
 844
 845                 orig_insn = find_insn(file, special_alt->orig_sec,
 846                                       special_alt->orig_off);
 847                 if (!orig_insn) {
 848                         WARN_FUNC("special: can't find orig instruction",
 849                                   special_alt->orig_sec, special_alt->orig_off);
 850                         ret = -1;
 851                         goto out;
 852                 }
 853
 854                 new_insn = NULL;
 855                 if (!special_alt->group || special_alt->new_len) {
 856                         new_insn = find_insn(file, special_alt->new_sec,
 857                                              special_alt->new_off);
 858                         if (!new_insn) {
 859                                 WARN_FUNC("special: can't find new instruction",
 860                                           special_alt->new_sec,
 861                                           special_alt->new_off);
 862                                 ret = -1;
 863                                 goto out;
 864                         }
 865                 }
 866
 867                 if (special_alt->group) {
 868                         ret = handle_group_alt(file, special_alt, orig_insn,
 869                                                &new_insn);
 870                         if (ret)
 871                                 goto out;
 872                 } else if (special_alt->jump_or_nop) {
 873                         ret = handle_jump_alt(file, special_alt, orig_insn,
 874                                               &new_insn);
 875                         if (ret)
 876                                 goto out;
 877                 }
 878
 879                 alt = malloc(sizeof(*alt));
 880                 if (!alt) {
 881                         WARN("malloc failed");
 882                         ret = -1;
 883                         goto out;
 884                 }
 885
 886                 alt->insn = new_insn;
 887                 alt->skip_orig = special_alt->skip_orig;
 888                 orig_insn->ignore_alts |= special_alt->skip_alt;
 889                 list_add_tail(&alt->list, &orig_insn->alts);
 890
 891                 list_del(&special_alt->list);
 892                 free(special_alt);
 893         }
 894
 895 out:
 896         return ret;
 897 }
 898
 899 static int add_switch_table(struct objtool_file *file, struct instruction *insn,
 900                             struct rela *table, struct rela *next_table)
 901 {
 902         struct rela *rela = table;
 903         struct instruction *alt_insn;
 904         struct alternative *alt;
 905         struct symbol *pfunc = insn->func->pfunc;
 906         unsigned int prev_offset = 0;
 907
 908         list_for_each_entry_from(rela, &table->rela_sec->rela_list, list) {
 909                 if (rela == next_table)
 910                         break;
 911
 912                 /* Make sure the switch table entries are consecutive: */
 913                 if (prev_offset && rela->offset != prev_offset + 8)
 914                         break;
 915
 916                 /* Detect function pointers from contiguous objects: */
 917                 if (rela->sym->sec == pfunc->sec &&
 918                     rela->addend == pfunc->offset)
 919                         break;
 920
 921                 alt_insn = find_insn(file, rela->sym->sec, rela->addend);
 922                 if (!alt_insn)
 923                         break;
 924
 925                 /* Make sure the jmp dest is in the function or subfunction: */
 926                 if (alt_insn->func->pfunc != pfunc)
 927                         break;
 928
 929                 alt = malloc(sizeof(*alt));
 930                 if (!alt) {
 931                         WARN("malloc failed");
 932                         return -1;
 933                 }
 934
 935                 alt->insn = alt_insn;
 936                 list_add_tail(&alt->list, &insn->alts);
 937                 prev_offset = rela->offset;
 938         }
 939
 940         if (!prev_offset) {
 941                 WARN_FUNC("can't find switch jump table",
 942                           insn->sec, insn->offset);
 943                 return -1;
 944         }
 945
 946         return 0;
 947 }
 948
 949 /*
 950  * find_switch_table() - Given a dynamic jump, find the switch jump table in
 951  * .rodata associated with it.
 952  *
 953  * There are 3 basic patterns:
 954  *
 955  * 1. jmpq *[rodata addr](,%reg,8)
 956  *
 957  *    This is the most common case by far.  It jumps to an address in a simple
 958  *    jump table which is stored in .rodata.
 959  *
 960  * 2. jmpq *[rodata addr](%rip)
 961  *
 962  *    This is caused by a rare GCC quirk, currently only seen in three driver
 963  *    functions in the kernel, only with certain obscure non-distro configs.
 964  *
 965  *    As part of an optimization, GCC makes a copy of an existing switch jump
 966  *    table, modifies it, and then hard-codes the jump (albeit with an indirect
 967  *    jump) to use a single entry in the table.  The rest of the jump table and
 968  *    some of its jump targets remain as dead code.
 969  *
 970  *    In such a case we can just crudely ignore all unreachable instruction
 971  *    warnings for the entire object file.  Ideally we would just ignore them
 972  *    for the function, but that would require redesigning the code quite a
 973  *    bit.  And honestly that's just not worth doing: unreachable instruction
 974  *    warnings are of questionable value anyway, and this is such a rare issue.
 975  *
 976  * 3. mov [rodata addr],%reg1
 977  *    ... some instructions ...
 978  *    jmpq *(%reg1,%reg2,8)
 979  *
 980  *    This is a fairly uncommon pattern which is new for GCC 6.  As of this
 981  *    writing, there are 11 occurrences of it in the allmodconfig kernel.
 982  *
 983  *    As of GCC 7 there are quite a few more of these and the 'in between' code
 984  *    is significant. Esp. with KASAN enabled some of the code between the mov
 985  *    and jmpq uses .rodata itself, which can confuse things.
 986  *
 987  *    TODO: Once we have DWARF CFI and smarter instruction decoding logic,
 988  *    ensure the same register is used in the mov and jump instructions.
 989  *
 990  *    NOTE: RETPOLINE made it harder still to decode dynamic jumps.
 991  */
 992 static struct rela *find_switch_table(struct objtool_file *file,
 993                                       struct symbol *func,
 994                                       struct instruction *insn)
 995 {
 996         struct rela *text_rela, *rodata_rela;
 997         struct instruction *orig_insn = insn;
 998         struct section *rodata_sec;
 999         unsigned long table_offset;
1000
1001         /*
1002          * Backward search using the @first_jump_src links, these help avoid
1003          * much of the 'in between' code. Which avoids us getting confused by
1004          * it.
1005          */
1006         for (;
1007              &insn->list != &file->insn_list &&
1008              insn->sec == func->sec &&
1009              insn->offset >= func->offset;
1010
1011              insn = insn->first_jump_src ?: list_prev_entry(insn, list)) {
1012
1013                 if (insn != orig_insn && insn->type == INSN_JUMP_DYNAMIC)
1014                         break;
1015
1016                 /* allow small jumps within the range */
1017                 if (insn->type == INSN_JUMP_UNCONDITIONAL &&
1018                     insn->jump_dest &&
1019                     (insn->jump_dest->offset <= insn->offset ||
1020                      insn->jump_dest->offset > orig_insn->offset))
1021                     break;
1022
1023                 /* look for a relocation which references .rodata */
1024                 text_rela = find_rela_by_dest_range(insn->sec, insn->offset,
1025                                                     insn->len);
1026                 if (!text_rela || text_rela->sym->type != STT_SECTION ||
1027                     !text_rela->sym->sec->rodata)
1028                         continue;
1029
1030                 table_offset = text_rela->addend;
1031                 rodata_sec = text_rela->sym->sec;
1032
1033                 if (text_rela->type == R_X86_64_PC32)
1034                         table_offset += 4;
1035
1036                 /*
1037                  * Make sure the .rodata address isn't associated with a
1038                  * symbol.  gcc jump tables are anonymous data.
1039                  */
1040                 if (find_symbol_containing(rodata_sec, table_offset))
1041                         continue;
1042
1043                 rodata_rela = find_rela_by_dest(rodata_sec, table_offset);
1044                 if (rodata_rela) {
1045                         /*
1046                          * Use of RIP-relative switch jumps is quite rare, and
1047                          * indicates a rare GCC quirk/bug which can leave dead
1048                          * code behind.
1049                          */
1050                         if (text_rela->type == R_X86_64_PC32)
1051                                 file->ignore_unreachables = true;
1052
1053                         return rodata_rela;
1054                 }
1055         }
1056
1057         return NULL;
1058 }
1059
1060
1061 static int add_func_switch_tables(struct objtool_file *file,
1062                                   struct symbol *func)
1063 {
1064         struct instruction *insn, *last = NULL, *prev_jump = NULL;
1065         struct rela *rela, *prev_rela = NULL;
1066         int ret;
1067
1068         func_for_each_insn_all(file, func, insn) {
1069                 if (!last)
1070                         last = insn;
1071
1072                 /*
1073                  * Store back-pointers for unconditional forward jumps such
1074                  * that find_switch_table() can back-track using those and
1075                  * avoid some potentially confusing code.
1076                  */
1077                 if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest &&
1078                     insn->offset > last->offset &&
1079                     insn->jump_dest->offset > insn->offset &&
1080                     !insn->jump_dest->first_jump_src) {
1081
1082                         insn->jump_dest->first_jump_src = insn;
1083                         last = insn->jump_dest;
1084                 }
1085
1086                 if (insn->type != INSN_JUMP_DYNAMIC)
1087                         continue;
1088
1089                 rela = find_switch_table(file, func, insn);
1090                 if (!rela)
1091                         continue;
1092
1093                 /*
1094                  * We found a switch table, but we don't know yet how big it
1095                  * is.  Don't add it until we reach the end of the function or
1096                  * the beginning of another switch table in the same function.
1097                  */
1098                 if (prev_jump) {
1099                         ret = add_switch_table(file, prev_jump, prev_rela, rela);
1100                         if (ret)
1101                                 return ret;
1102                 }
1103
1104                 prev_jump = insn;
1105                 prev_rela = rela;
1106         }
1107
1108         if (prev_jump) {
1109                 ret = add_switch_table(file, prev_jump, prev_rela, NULL);
1110                 if (ret)
1111                         return ret;
1112         }
1113
1114         return 0;
1115 }
1116
1117 /*
1118  * For some switch statements, gcc generates a jump table in the .rodata
1119  * section which contains a list of addresses within the function to jump to.
1120  * This finds these jump tables and adds them to the insn->alts lists.
1121  */
1122 static int add_switch_table_alts(struct objtool_file *file)
1123 {
1124         struct section *sec;
1125         struct symbol *func;
1126         int ret;
1127
1128         if (!file->rodata)
1129                 return 0;
1130
1131         for_each_sec(file, sec) {
1132                 list_for_each_entry(func, &sec->symbol_list, list) {
1133                         if (func->type != STT_FUNC)
1134                                 continue;
1135
1136                         ret = add_func_switch_tables(file, func);
1137                         if (ret)
1138                                 return ret;
1139                 }
1140         }
1141
1142         return 0;
1143 }
1144
1145 static int read_unwind_hints(struct objtool_file *file)
1146 {
1147         struct section *sec, *relasec;
1148         struct rela *rela;
1149         struct unwind_hint *hint;
1150         struct instruction *insn;
1151         struct cfi_reg *cfa;
1152         int i;
1153
1154         sec = find_section_by_name(file->elf, ".discard.unwind_hints");
1155         if (!sec)
1156                 return 0;
1157
1158         relasec = sec->rela;
1159         if (!relasec) {
1160                 WARN("missing .rela.discard.unwind_hints section");
1161                 return -1;
1162         }
1163
1164         if (sec->len % sizeof(struct unwind_hint)) {
1165                 WARN("struct unwind_hint size mismatch");
1166                 return -1;
1167         }
1168
1169         file->hints = true;
1170
1171         for (i = 0; i < sec->len / sizeof(struct unwind_hint); i++) {
1172                 hint = (struct unwind_hint *)sec->data->d_buf + i;
1173
1174                 rela = find_rela_by_dest(sec, i * sizeof(*hint));
1175                 if (!rela) {
1176                         WARN("can't find rela for unwind_hints[%d]", i);
1177                         return -1;
1178                 }
1179
1180                 insn = find_insn(file, rela->sym->sec, rela->addend);
1181                 if (!insn) {
1182                         WARN("can't find insn for unwind_hints[%d]", i);
1183                         return -1;
1184                 }
1185
1186                 cfa = &insn->state.cfa;
1187
1188                 if (hint->type == UNWIND_HINT_TYPE_SAVE) {
1189                         insn->save = true;
1190                         continue;
1191
1192                 } else if (hint->type == UNWIND_HINT_TYPE_RESTORE) {
1193                         insn->restore = true;
1194                         insn->hint = true;
1195                         continue;
1196                 }
1197
1198                 insn->hint = true;
1199
1200                 switch (hint->sp_reg) {
1201                 case ORC_REG_UNDEFINED:
1202                         cfa->base = CFI_UNDEFINED;
1203                         break;
1204                 case ORC_REG_SP:
1205                         cfa->base = CFI_SP;
1206                         break;
1207                 case ORC_REG_BP:
1208                         cfa->base = CFI_BP;
1209                         break;
1210                 case ORC_REG_SP_INDIRECT:
1211                         cfa->base = CFI_SP_INDIRECT;
1212                         break;
1213                 case ORC_REG_R10:
1214                         cfa->base = CFI_R10;
1215                         break;
1216                 case ORC_REG_R13:
1217                         cfa->base = CFI_R13;
1218                         break;
1219                 case ORC_REG_DI:
1220                         cfa->base = CFI_DI;
1221                         break;
1222                 case ORC_REG_DX:
1223                         cfa->base = CFI_DX;
1224                         break;
1225                 default:
1226                         WARN_FUNC("unsupported unwind_hint sp base reg %d",
1227                                   insn->sec, insn->offset, hint->sp_reg);
1228                         return -1;
1229                 }
1230
1231                 cfa->offset = hint->sp_offset;
1232                 insn->state.type = hint->type;
1233                 insn->state.end = hint->end;
1234         }
1235
1236         return 0;
1237 }
1238
1239 static int read_retpoline_hints(struct objtool_file *file)
1240 {
1241         struct section *sec;
1242         struct instruction *insn;
1243         struct rela *rela;
1244
1245         sec = find_section_by_name(file->elf, ".rela.discard.retpoline_safe");
1246         if (!sec)
1247                 return 0;
1248
1249         list_for_each_entry(rela, &sec->rela_list, list) {
1250                 if (rela->sym->type != STT_SECTION) {
1251                         WARN("unexpected relocation symbol type in %s", sec->name);
1252                         return -1;
1253                 }
1254
1255                 insn = find_insn(file, rela->sym->sec, rela->addend);
1256                 if (!insn) {
1257                         WARN("bad .discard.retpoline_safe entry");
1258                         return -1;
1259                 }
1260
1261                 if (insn->type != INSN_JUMP_DYNAMIC &&
1262                     insn->type != INSN_CALL_DYNAMIC) {
1263                         WARN_FUNC("retpoline_safe hint not an indirect jump/call",
1264                                   insn->sec, insn->offset);
1265                         return -1;
1266                 }
1267
1268                 insn->retpoline_safe = true;
1269         }
1270
1271         return 0;
1272 }
1273
1274 static void mark_rodata(struct objtool_file *file)
1275 {
1276         struct section *sec;
1277         bool found = false;
1278
1279         /*
1280          * This searches for the .rodata section or multiple .rodata.func_name
1281          * sections if -fdata-sections is being used. The .str.1.1 and .str.1.8
1282          * rodata sections are ignored as they don't contain jump tables.
1283          */
1284         for_each_sec(file, sec) {
1285                 if (!strncmp(sec->name, ".rodata", 7) &&
1286                     !strstr(sec->name, ".str1.")) {
1287                         sec->rodata = true;
1288                         found = true;
1289                 }
1290         }
1291
1292         file->rodata = found;
1293 }
1294
1295 static int decode_sections(struct objtool_file *file)
1296 {
1297         int ret;
1298
1299         mark_rodata(file);
1300
1301         ret = decode_instructions(file);
1302         if (ret)
1303                 return ret;
1304
1305         ret = add_dead_ends(file);
1306         if (ret)
1307                 return ret;
1308
1309         add_ignores(file);
1310         add_uaccess_safe(file);
1311
1312         ret = add_ignore_alternatives(file);
1313         if (ret)
1314                 return ret;
1315
1316         ret = add_jump_destinations(file);
1317         if (ret)
1318                 return ret;
1319
1320         ret = add_special_section_alts(file);
1321         if (ret)
1322                 return ret;
1323
1324         ret = add_call_destinations(file);
1325         if (ret)
1326                 return ret;
1327
1328         ret = add_switch_table_alts(file);
1329         if (ret)
1330                 return ret;
1331
1332         ret = read_unwind_hints(file);
1333         if (ret)
1334                 return ret;
1335
1336         ret = read_retpoline_hints(file);
1337         if (ret)
1338                 return ret;
1339
1340         return 0;
1341 }
1342
1343 static bool is_fentry_call(struct instruction *insn)
1344 {
1345         if (insn->type == INSN_CALL &&
1346             insn->call_dest->type == STT_NOTYPE &&
1347             !strcmp(insn->call_dest->name, "__fentry__"))
1348                 return true;
1349
1350         return false;
1351 }
1352
1353 static bool has_modified_stack_frame(struct insn_state *state)
1354 {
1355         int i;
1356
1357         if (state->cfa.base != initial_func_cfi.cfa.base ||
1358             state->cfa.offset != initial_func_cfi.cfa.offset ||
1359             state->stack_size != initial_func_cfi.cfa.offset ||
1360             state->drap)
1361                 return true;
1362
1363         for (i = 0; i < CFI_NUM_REGS; i++)
1364                 if (state->regs[i].base != initial_func_cfi.regs[i].base ||
1365                     state->regs[i].offset != initial_func_cfi.regs[i].offset)
1366                         return true;
1367
1368         return false;
1369 }
1370
1371 static bool has_valid_stack_frame(struct insn_state *state)
1372 {
1373         if (state->cfa.base == CFI_BP && state->regs[CFI_BP].base == CFI_CFA &&
1374             state->regs[CFI_BP].offset == -16)
1375                 return true;
1376
1377         if (state->drap && state->regs[CFI_BP].base == CFI_BP)
1378                 return true;
1379
1380         return false;
1381 }
1382
1383 static int update_insn_state_regs(struct instruction *insn, struct insn_state *state)
1384 {
1385         struct cfi_reg *cfa = &state->cfa;
1386         struct stack_op *op = &insn->stack_op;
1387
1388         if (cfa->base != CFI_SP)
1389                 return 0;
1390
1391         /* push */
1392         if (op->dest.type == OP_DEST_PUSH || op->dest.type == OP_DEST_PUSHF)
1393                 cfa->offset += 8;
1394
1395         /* pop */
1396         if (op->src.type == OP_SRC_POP || op->src.type == OP_SRC_POPF)
1397                 cfa->offset -= 8;
1398
1399         /* add immediate to sp */
1400         if (op->dest.type == OP_DEST_REG && op->src.type == OP_SRC_ADD &&
1401             op->dest.reg == CFI_SP && op->src.reg == CFI_SP)
1402                 cfa->offset -= op->src.offset;
1403
1404         return 0;
1405 }
1406
1407 static void save_reg(struct insn_state *state, unsigned char reg, int base,
1408                      int offset)
1409 {
1410         if (arch_callee_saved_reg(reg) &&
1411             state->regs[reg].base == CFI_UNDEFINED) {
1412                 state->regs[reg].base = base;
1413                 state->regs[reg].offset = offset;
1414         }
1415 }
1416
1417 static void restore_reg(struct insn_state *state, unsigned char reg)
1418 {
1419         state->regs[reg].base = CFI_UNDEFINED;
1420         state->regs[reg].offset = 0;
1421 }
1422
1423 /*
1424  * A note about DRAP stack alignment:
1425  *
1426  * GCC has the concept of a DRAP register, which is used to help keep track of
1427  * the stack pointer when aligning the stack.  r10 or r13 is used as the DRAP
1428  * register.  The typical DRAP pattern is:
1429  *
1430  *   4c 8d 54 24 08             lea    0x8(%rsp),%r10
1431  *   48 83 e4 c0                and    $0xffffffffffffffc0,%rsp
1432  *   41 ff 72 f8                pushq  -0x8(%r10)
1433  *   55                         push   %rbp
1434  *   48 89 e5                   mov    %rsp,%rbp
1435  *                              (more pushes)
1436  *   41 52                      push   %r10
1437  *                              ...
1438  *   41 5a                      pop    %r10
1439  *                              (more pops)
1440  *   5d                         pop    %rbp
1441  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1442  *   c3                         retq
1443  *
1444  * There are some variations in the epilogues, like:
1445  *
1446  *   5b                         pop    %rbx
1447  *   41 5a                      pop    %r10
1448  *   41 5c                      pop    %r12
1449  *   41 5d                      pop    %r13
1450  *   41 5e                      pop    %r14
1451  *   c9                         leaveq
1452  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1453  *   c3                         retq
1454  *
1455  * and:
1456  *
1457  *   4c 8b 55 e8                mov    -0x18(%rbp),%r10
1458  *   48 8b 5d e0                mov    -0x20(%rbp),%rbx
1459  *   4c 8b 65 f0                mov    -0x10(%rbp),%r12
1460  *   4c 8b 6d f8                mov    -0x8(%rbp),%r13
1461  *   c9                         leaveq
1462  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1463  *   c3                         retq
1464  *
1465  * Sometimes r13 is used as the DRAP register, in which case it's saved and
1466  * restored beforehand:
1467  *
1468  *   41 55                      push   %r13
1469  *   4c 8d 6c 24 10             lea    0x10(%rsp),%r13
1470  *   48 83 e4 f0                and    $0xfffffffffffffff0,%rsp
1471  *                              ...
1472  *   49 8d 65 f0                lea    -0x10(%r13),%rsp
1473  *   41 5d                      pop    %r13
1474  *   c3                         retq
1475  */
1476 static int update_insn_state(struct instruction *insn, struct insn_state *state)
1477 {
1478         struct stack_op *op = &insn->stack_op;
1479         struct cfi_reg *cfa = &state->cfa;
1480         struct cfi_reg *regs = state->regs;
1481
1482         /* stack operations don't make sense with an undefined CFA */
1483         if (cfa->base == CFI_UNDEFINED) {
1484                 if (insn->func) {
1485                         WARN_FUNC("undefined stack state", insn->sec, insn->offset);
1486                         return -1;
1487                 }
1488                 return 0;
1489         }
1490
1491         if (state->type == ORC_TYPE_REGS || state->type == ORC_TYPE_REGS_IRET)
1492                 return update_insn_state_regs(insn, state);
1493
1494         switch (op->dest.type) {
1495
1496         case OP_DEST_REG:
1497                 switch (op->src.type) {
1498
1499                 case OP_SRC_REG:
1500                         if (op->src.reg == CFI_SP && op->dest.reg == CFI_BP &&
1501                             cfa->base == CFI_SP &&
1502                             regs[CFI_BP].base == CFI_CFA &&
1503                             regs[CFI_BP].offset == -cfa->offset) {
1504
1505                                 /* mov %rsp, %rbp */
1506                                 cfa->base = op->dest.reg;
1507                                 state->bp_scratch = false;
1508                         }
1509
1510                         else if (op->src.reg == CFI_SP &&
1511                                  op->dest.reg == CFI_BP && state->drap) {
1512
1513                                 /* drap: mov %rsp, %rbp */
1514                                 regs[CFI_BP].base = CFI_BP;
1515                                 regs[CFI_BP].offset = -state->stack_size;
1516                                 state->bp_scratch = false;
1517                         }
1518
1519                         else if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1520
1521                                 /*
1522                                  * mov %rsp, %reg
1523                                  *
1524                                  * This is needed for the rare case where GCC
1525                                  * does:
1526                                  *
1527                                  *   mov    %rsp, %rax
1528                                  *   ...
1529                                  *   mov    %rax, %rsp
1530                                  */
1531                                 state->vals[op->dest.reg].base = CFI_CFA;
1532                                 state->vals[op->dest.reg].offset = -state->stack_size;
1533                         }
1534
1535                         else if (op->src.reg == CFI_BP && op->dest.reg == CFI_SP &&
1536                                  cfa->base == CFI_BP) {
1537
1538                                 /*
1539                                  * mov %rbp, %rsp
1540                                  *
1541                                  * Restore the original stack pointer (Clang).
1542                                  */
1543                                 state->stack_size = -state->regs[CFI_BP].offset;
1544                         }
1545
1546                         else if (op->dest.reg == cfa->base) {
1547
1548                                 /* mov %reg, %rsp */
1549                                 if (cfa->base == CFI_SP &&
1550                                     state->vals[op->src.reg].base == CFI_CFA) {
1551
1552                                         /*
1553                                          * This is needed for the rare case
1554                                          * where GCC does something dumb like:
1555                                          *
1556                                          *   lea    0x8(%rsp), %rcx
1557                                          *   ...
1558                                          *   mov    %rcx, %rsp
1559                                          */
1560                                         cfa->offset = -state->vals[op->src.reg].offset;
1561                                         state->stack_size = cfa->offset;
1562
1563                                 } else {
1564                                         cfa->base = CFI_UNDEFINED;
1565                                         cfa->offset = 0;
1566                                 }
1567                         }
1568
1569                         break;
1570
1571                 case OP_SRC_ADD:
1572                         if (op->dest.reg == CFI_SP && op->src.reg == CFI_SP) {
1573
1574                                 /* add imm, %rsp */
1575                                 state->stack_size -= op->src.offset;
1576                                 if (cfa->base == CFI_SP)
1577                                         cfa->offset -= op->src.offset;
1578                                 break;
1579                         }
1580
1581                         if (op->dest.reg == CFI_SP && op->src.reg == CFI_BP) {
1582
1583                                 /* lea disp(%rbp), %rsp */
1584                                 state->stack_size = -(op->src.offset + regs[CFI_BP].offset);
1585                                 break;
1586                         }
1587
1588                         if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1589
1590                                 /* drap: lea disp(%rsp), %drap */
1591                                 state->drap_reg = op->dest.reg;
1592
1593                                 /*
1594                                  * lea disp(%rsp), %reg
1595                                  *
1596                                  * This is needed for the rare case where GCC
1597                                  * does something dumb like:
1598                                  *
1599                                  *   lea    0x8(%rsp), %rcx
1600                                  *   ...
1601                                  *   mov    %rcx, %rsp
1602                                  */
1603                                 state->vals[op->dest.reg].base = CFI_CFA;
1604                                 state->vals[op->dest.reg].offset = \
1605                                         -state->stack_size + op->src.offset;
1606
1607                                 break;
1608                         }
1609
1610                         if (state->drap && op->dest.reg == CFI_SP &&
1611                             op->src.reg == state->drap_reg) {
1612
1613                                  /* drap: lea disp(%drap), %rsp */
1614                                 cfa->base = CFI_SP;
1615                                 cfa->offset = state->stack_size = -op->src.offset;
1616                                 state->drap_reg = CFI_UNDEFINED;
1617                                 state->drap = false;
1618                                 break;
1619                         }
1620
1621                         if (op->dest.reg == state->cfa.base) {
1622                                 WARN_FUNC("unsupported stack register modification",
1623                                           insn->sec, insn->offset);
1624                                 return -1;
1625                         }
1626
1627                         break;
1628
1629                 case OP_SRC_AND:
1630                         if (op->dest.reg != CFI_SP ||
1631                             (state->drap_reg != CFI_UNDEFINED && cfa->base != CFI_SP) ||
1632                             (state->drap_reg == CFI_UNDEFINED && cfa->base != CFI_BP)) {
1633                                 WARN_FUNC("unsupported stack pointer realignment",
1634                                           insn->sec, insn->offset);
1635                                 return -1;
1636                         }
1637
1638                         if (state->drap_reg != CFI_UNDEFINED) {
1639                                 /* drap: and imm, %rsp */
1640                                 cfa->base = state->drap_reg;
1641                                 cfa->offset = state->stack_size = 0;
1642                                 state->drap = true;
1643                         }
1644
1645                         /*
1646                          * Older versions of GCC (4.8ish) realign the stack
1647                          * without DRAP, with a frame pointer.
1648                          */
1649
1650                         break;
1651
1652                 case OP_SRC_POP:
1653                 case OP_SRC_POPF:
1654                         if (!state->drap && op->dest.type == OP_DEST_REG &&
1655                             op->dest.reg == cfa->base) {
1656
1657                                 /* pop %rbp */
1658                                 cfa->base = CFI_SP;
1659                         }
1660
1661                         if (state->drap && cfa->base == CFI_BP_INDIRECT &&
1662                             op->dest.type == OP_DEST_REG &&
1663                             op->dest.reg == state->drap_reg &&
1664                             state->drap_offset == -state->stack_size) {
1665
1666                                 /* drap: pop %drap */
1667                                 cfa->base = state->drap_reg;
1668                                 cfa->offset = 0;
1669                                 state->drap_offset = -1;
1670
1671                         } else if (regs[op->dest.reg].offset == -state->stack_size) {
1672
1673                                 /* pop %reg */
1674                                 restore_reg(state, op->dest.reg);
1675                         }
1676
1677                         state->stack_size -= 8;
1678                         if (cfa->base == CFI_SP)
1679                                 cfa->offset -= 8;
1680
1681                         break;
1682
1683                 case OP_SRC_REG_INDIRECT:
1684                         if (state->drap && op->src.reg == CFI_BP &&
1685                             op->src.offset == state->drap_offset) {
1686
1687                                 /* drap: mov disp(%rbp), %drap */
1688                                 cfa->base = state->drap_reg;
1689                                 cfa->offset = 0;
1690                                 state->drap_offset = -1;
1691                         }
1692
1693                         if (state->drap && op->src.reg == CFI_BP &&
1694                             op->src.offset == regs[op->dest.reg].offset) {
1695
1696                                 /* drap: mov disp(%rbp), %reg */
1697                                 restore_reg(state, op->dest.reg);
1698
1699                         } else if (op->src.reg == cfa->base &&
1700                             op->src.offset == regs[op->dest.reg].offset + cfa->offset) {
1701
1702                                 /* mov disp(%rbp), %reg */
1703                                 /* mov disp(%rsp), %reg */
1704                                 restore_reg(state, op->dest.reg);
1705                         }
1706
1707                         break;
1708
1709                 default:
1710                         WARN_FUNC("unknown stack-related instruction",
1711                                   insn->sec, insn->offset);
1712                         return -1;
1713                 }
1714
1715                 break;
1716
1717         case OP_DEST_PUSH:
1718         case OP_DEST_PUSHF:
1719                 state->stack_size += 8;
1720                 if (cfa->base == CFI_SP)
1721                         cfa->offset += 8;
1722
1723                 if (op->src.type != OP_SRC_REG)
1724                         break;
1725
1726                 if (state->drap) {
1727                         if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1728
1729                                 /* drap: push %drap */
1730                                 cfa->base = CFI_BP_INDIRECT;
1731                                 cfa->offset = -state->stack_size;
1732
1733                                 /* save drap so we know when to restore it */
1734                                 state->drap_offset = -state->stack_size;
1735
1736                         } else if (op->src.reg == CFI_BP && cfa->base == state->drap_reg) {
1737
1738                                 /* drap: push %rbp */
1739                                 state->stack_size = 0;
1740
1741                         } else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1742
1743                                 /* drap: push %reg */
1744                                 save_reg(state, op->src.reg, CFI_BP, -state->stack_size);
1745                         }
1746
1747                 } else {
1748
1749                         /* push %reg */
1750                         save_reg(state, op->src.reg, CFI_CFA, -state->stack_size);
1751                 }
1752
1753                 /* detect when asm code uses rbp as a scratch register */
1754                 if (!no_fp && insn->func && op->src.reg == CFI_BP &&
1755                     cfa->base != CFI_BP)
1756                         state->bp_scratch = true;
1757                 break;
1758
1759         case OP_DEST_REG_INDIRECT:
1760
1761                 if (state->drap) {
1762                         if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1763
1764                                 /* drap: mov %drap, disp(%rbp) */
1765                                 cfa->base = CFI_BP_INDIRECT;
1766                                 cfa->offset = op->dest.offset;
1767
1768                                 /* save drap offset so we know when to restore it */
1769                                 state->drap_offset = op->dest.offset;
1770                         }
1771
1772                         else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1773
1774                                 /* drap: mov reg, disp(%rbp) */
1775                                 save_reg(state, op->src.reg, CFI_BP, op->dest.offset);
1776                         }
1777
1778                 } else if (op->dest.reg == cfa->base) {
1779
1780                         /* mov reg, disp(%rbp) */
1781                         /* mov reg, disp(%rsp) */
1782                         save_reg(state, op->src.reg, CFI_CFA,
1783                                  op->dest.offset - state->cfa.offset);
1784                 }
1785
1786                 break;
1787
1788         case OP_DEST_LEAVE:
1789                 if ((!state->drap && cfa->base != CFI_BP) ||
1790                     (state->drap && cfa->base != state->drap_reg)) {
1791                         WARN_FUNC("leave instruction with modified stack frame",
1792                                   insn->sec, insn->offset);
1793                         return -1;
1794                 }
1795
1796                 /* leave (mov %rbp, %rsp; pop %rbp) */
1797
1798                 state->stack_size = -state->regs[CFI_BP].offset - 8;
1799                 restore_reg(state, CFI_BP);
1800
1801                 if (!state->drap) {
1802                         cfa->base = CFI_SP;
1803                         cfa->offset -= 8;
1804                 }
1805
1806                 break;
1807
1808         case OP_DEST_MEM:
1809                 if (op->src.type != OP_SRC_POP && op->src.type != OP_SRC_POPF) {
1810                         WARN_FUNC("unknown stack-related memory operation",
1811                                   insn->sec, insn->offset);
1812                         return -1;
1813                 }
1814
1815                 /* pop mem */
1816                 state->stack_size -= 8;
1817                 if (cfa->base == CFI_SP)
1818                         cfa->offset -= 8;
1819
1820                 break;
1821
1822         default:
1823                 WARN_FUNC("unknown stack-related instruction",
1824                           insn->sec, insn->offset);
1825                 return -1;
1826         }
1827
1828         return 0;
1829 }
1830
1831 static bool insn_state_match(struct instruction *insn, struct insn_state *state)
1832 {
1833         struct insn_state *state1 = &insn->state, *state2 = state;
1834         int i;
1835
1836         if (memcmp(&state1->cfa, &state2->cfa, sizeof(state1->cfa))) {
1837                 WARN_FUNC("stack state mismatch: cfa1=%d%+d cfa2=%d%+d",
1838                           insn->sec, insn->offset,
1839                           state1->cfa.base, state1->cfa.offset,
1840                           state2->cfa.base, state2->cfa.offset);
1841
1842         } else if (memcmp(&state1->regs, &state2->regs, sizeof(state1->regs))) {
1843                 for (i = 0; i < CFI_NUM_REGS; i++) {
1844                         if (!memcmp(&state1->regs[i], &state2->regs[i],
1845                                     sizeof(struct cfi_reg)))
1846                                 continue;
1847
1848                         WARN_FUNC("stack state mismatch: reg1[%d]=%d%+d reg2[%d]=%d%+d",
1849                                   insn->sec, insn->offset,
1850                                   i, state1->regs[i].base, state1->regs[i].offset,
1851                                   i, state2->regs[i].base, state2->regs[i].offset);
1852                         break;
1853                 }
1854
1855         } else if (state1->type != state2->type) {
1856                 WARN_FUNC("stack state mismatch: type1=%d type2=%d",
1857                           insn->sec, insn->offset, state1->type, state2->type);
1858
1859         } else if (state1->drap != state2->drap ||
1860                  (state1->drap && state1->drap_reg != state2->drap_reg) ||
1861                  (state1->drap && state1->drap_offset != state2->drap_offset)) {
1862                 WARN_FUNC("stack state mismatch: drap1=%d(%d,%d) drap2=%d(%d,%d)",
1863                           insn->sec, insn->offset,
1864                           state1->drap, state1->drap_reg, state1->drap_offset,
1865                           state2->drap, state2->drap_reg, state2->drap_offset);
1866
1867         } else
1868                 return true;
1869
1870         return false;
1871 }
1872
1873 static inline bool func_uaccess_safe(struct symbol *func)
1874 {
1875         if (func)
1876                 return func->alias->uaccess_safe;
1877
1878         return false;
1879 }
1880
1881 static inline const char *insn_dest_name(struct instruction *insn)
1882 {
1883         if (insn->call_dest)
1884                 return insn->call_dest->name;
1885
1886         return "{dynamic}";
1887 }
1888
1889 static int validate_call(struct instruction *insn, struct insn_state *state)
1890 {
1891         if (state->uaccess && !func_uaccess_safe(insn->call_dest)) {
1892                 WARN_FUNC("call to %s() with UACCESS enabled",
1893                                 insn->sec, insn->offset, insn_dest_name(insn));
1894                 return 1;
1895         }
1896
1897         if (state->df) {
1898                 WARN_FUNC("call to %s() with DF set",
1899                                 insn->sec, insn->offset, insn_dest_name(insn));
1900                 return 1;
1901         }
1902
1903         return 0;
1904 }
1905
1906 static int validate_sibling_call(struct instruction *insn, struct insn_state *state)
1907 {
1908         if (has_modified_stack_frame(state)) {
1909                 WARN_FUNC("sibling call from callable instruction with modified stack frame",
1910                                 insn->sec, insn->offset);
1911                 return 1;
1912         }
1913
1914         return validate_call(insn, state);
1915 }
1916
1917 /*
1918  * Follow the branch starting at the given instruction, and recursively follow
1919  * any other branches (jumps).  Meanwhile, track the frame pointer state at
1920  * each instruction and validate all the rules described in
1921  * tools/objtool/Documentation/stack-validation.txt.
1922  */
1923 static int validate_branch(struct objtool_file *file, struct instruction *first,
1924                            struct insn_state state)
1925 {
1926         struct alternative *alt;
1927         struct instruction *insn, *next_insn;
1928         struct section *sec;
1929         struct symbol *func = NULL;
1930         int ret;
1931
1932         insn = first;
1933         sec = insn->sec;
1934
1935         if (insn->alt_group && list_empty(&insn->alts)) {
1936                 WARN_FUNC("don't know how to handle branch to middle of alternative instruction group",
1937                           sec, insn->offset);
1938                 return 1;
1939         }
1940
1941         while (1) {
1942                 next_insn = next_insn_same_sec(file, insn);
1943
1944                 if (file->c_file && func && insn->func && func != insn->func->pfunc) {
1945                         WARN("%s() falls through to next function %s()",
1946                              func->name, insn->func->name);
1947                         return 1;
1948                 }
1949
1950                 if (insn->func)
1951                         func = insn->func->pfunc;
1952
1953                 if (func && insn->ignore) {
1954                         WARN_FUNC("BUG: why am I validating an ignored function?",
1955                                   sec, insn->offset);
1956                         return 1;
1957                 }
1958
1959                 if (insn->visited) {
1960                         if (!insn->hint && !insn_state_match(insn, &state))
1961                                 return 1;
1962
1963                         /* If we were here with AC=0, but now have AC=1, go again */
1964                         if (insn->state.uaccess || !state.uaccess)
1965                                 return 0;
1966                 }
1967
1968                 if (insn->hint) {
1969                         if (insn->restore) {
1970                                 struct instruction *save_insn, *i;
1971
1972                                 i = insn;
1973                                 save_insn = NULL;
1974                                 func_for_each_insn_continue_reverse(file, insn->func, i) {
1975                                         if (i->save) {
1976                                                 save_insn = i;
1977                                                 break;
1978                                         }
1979                                 }
1980
1981                                 if (!save_insn) {
1982                                         WARN_FUNC("no corresponding CFI save for CFI restore",
1983                                                   sec, insn->offset);
1984                                         return 1;
1985                                 }
1986
1987                                 if (!save_insn->visited) {
1988                                         /*
1989                                          * Oops, no state to copy yet.
1990                                          * Hopefully we can reach this
1991                                          * instruction from another branch
1992                                          * after the save insn has been
1993                                          * visited.
1994                                          */
1995                                         if (insn == first)
1996                                                 return 0;
1997
1998                                         WARN_FUNC("objtool isn't smart enough to handle this CFI save/restore combo",
1999                                                   sec, insn->offset);
2000                                         return 1;
2001                                 }
2002
2003                                 insn->state = save_insn->state;
2004                         }
2005
2006                         state = insn->state;
2007
2008                 } else
2009                         insn->state = state;
2010
2011                 insn->visited = true;
2012
2013                 if (!insn->ignore_alts) {
2014                         bool skip_orig = false;
2015
2016                         list_for_each_entry(alt, &insn->alts, list) {
2017                                 if (alt->skip_orig)
2018                                         skip_orig = true;
2019
2020                                 ret = validate_branch(file, alt->insn, state);
2021                                 if (ret) {
2022                                         if (backtrace)
2023                                                 BT_FUNC("(alt)", insn);
2024                                         return ret;
2025                                 }
2026                         }
2027
2028                         if (skip_orig)
2029                                 return 0;
2030                 }
2031
2032                 switch (insn->type) {
2033
2034                 case INSN_RETURN:
2035                         if (state.uaccess && !func_uaccess_safe(func)) {
2036                                 WARN_FUNC("return with UACCESS enabled", sec, insn->offset);
2037                                 return 1;
2038                         }
2039
2040                         if (!state.uaccess && func_uaccess_safe(func)) {
2041                                 WARN_FUNC("return with UACCESS disabled from a UACCESS-safe function", sec, insn->offset);
2042                                 return 1;
2043                         }
2044
2045                         if (state.df) {
2046                                 WARN_FUNC("return with DF set", sec, insn->offset);
2047                                 return 1;
2048                         }
2049
2050                         if (func && has_modified_stack_frame(&state)) {
2051                                 WARN_FUNC("return with modified stack frame",
2052                                           sec, insn->offset);
2053                                 return 1;
2054                         }
2055
2056                         if (state.bp_scratch) {
2057                                 WARN("%s uses BP as a scratch register",
2058                                      insn->func->name);
2059                                 return 1;
2060                         }
2061
2062                         return 0;
2063
2064                 case INSN_CALL:
2065                 case INSN_CALL_DYNAMIC:
2066                         ret = validate_call(insn, &state);
2067                         if (ret)
2068                                 return ret;
2069
2070                         if (insn->type == INSN_CALL) {
2071                                 if (is_fentry_call(insn))
2072                                         break;
2073
2074                                 ret = dead_end_function(file, insn->call_dest);
2075                                 if (ret == 1)
2076                                         return 0;
2077                                 if (ret == -1)
2078                                         return 1;
2079                         }
2080
2081                         if (!no_fp && func && !has_valid_stack_frame(&state)) {
2082                                 WARN_FUNC("call without frame pointer save/setup",
2083                                           sec, insn->offset);
2084                                 return 1;
2085                         }
2086                         break;
2087
2088                 case INSN_JUMP_CONDITIONAL:
2089                 case INSN_JUMP_UNCONDITIONAL:
2090                         if (func && !insn->jump_dest) {
2091                                 ret = validate_sibling_call(insn, &state);
2092                                 if (ret)
2093                                         return ret;
2094
2095                         } else if (insn->jump_dest &&
2096                                    (!func || !insn->jump_dest->func ||
2097                                     insn->jump_dest->func->pfunc == func)) {
2098                                 ret = validate_branch(file, insn->jump_dest,
2099                                                       state);
2100                                 if (ret) {
2101                                         if (backtrace)
2102                                                 BT_FUNC("(branch)", insn);
2103                                         return ret;
2104                                 }
2105                         }
2106
2107                         if (insn->type == INSN_JUMP_UNCONDITIONAL)
2108                                 return 0;
2109
2110                         break;
2111
2112                 case INSN_JUMP_DYNAMIC:
2113                         if (func && list_empty(&insn->alts)) {
2114                                 ret = validate_sibling_call(insn, &state);
2115                                 if (ret)
2116                                         return ret;
2117                         }
2118
2119                         return 0;
2120
2121                 case INSN_CONTEXT_SWITCH:
2122                         if (func && (!next_insn || !next_insn->hint)) {
2123                                 WARN_FUNC("unsupported instruction in callable function",
2124                                           sec, insn->offset);
2125                                 return 1;
2126                         }
2127                         return 0;
2128
2129                 case INSN_STACK:
2130                         if (update_insn_state(insn, &state))
2131                                 return 1;
2132
2133                         if (insn->stack_op.dest.type == OP_DEST_PUSHF) {
2134                                 if (!state.uaccess_stack) {
2135                                         state.uaccess_stack = 1;
2136                                 } else if (state.uaccess_stack >> 31) {
2137                                         WARN_FUNC("PUSHF stack exhausted", sec, insn->offset);
2138                                         return 1;
2139                                 }
2140                                 state.uaccess_stack <<= 1;
2141                                 state.uaccess_stack  |= state.uaccess;
2142                         }
2143
2144                         if (insn->stack_op.src.type == OP_SRC_POPF) {
2145                                 if (state.uaccess_stack) {
2146                                         state.uaccess = state.uaccess_stack & 1;
2147                                         state.uaccess_stack >>= 1;
2148                                         if (state.uaccess_stack == 1)
2149                                                 state.uaccess_stack = 0;
2150                                 }
2151                         }
2152
2153                         break;
2154
2155                 case INSN_STAC:
2156                         if (state.uaccess) {
2157                                 WARN_FUNC("recursive UACCESS enable", sec, insn->offset);
2158                                 return 1;
2159                         }
2160
2161                         state.uaccess = true;
2162                         break;
2163
2164                 case INSN_CLAC:
2165                         if (!state.uaccess && insn->func) {
2166                                 WARN_FUNC("redundant UACCESS disable", sec, insn->offset);
2167                                 return 1;
2168                         }
2169
2170                         if (func_uaccess_safe(func) && !state.uaccess_stack) {
2171                                 WARN_FUNC("UACCESS-safe disables UACCESS", sec, insn->offset);
2172                                 return 1;
2173                         }
2174
2175                         state.uaccess = false;
2176                         break;
2177
2178                 case INSN_STD:
2179                         if (state.df)
2180                                 WARN_FUNC("recursive STD", sec, insn->offset);
2181
2182                         state.df = true;
2183                         break;
2184
2185                 case INSN_CLD:
2186                         if (!state.df && insn->func)
2187                                 WARN_FUNC("redundant CLD", sec, insn->offset);
2188
2189                         state.df = false;
2190                         break;
2191
2192                 default:
2193                         break;
2194                 }
2195
2196                 if (insn->dead_end)
2197                         return 0;
2198
2199                 if (!next_insn) {
2200                         if (state.cfa.base == CFI_UNDEFINED)
2201                                 return 0;
2202                         WARN("%s: unexpected end of section", sec->name);
2203                         return 1;
2204                 }
2205
2206                 insn = next_insn;
2207         }
2208
2209         return 0;
2210 }
2211
2212 static int validate_unwind_hints(struct objtool_file *file)
2213 {
2214         struct instruction *insn;
2215         int ret, warnings = 0;
2216         struct insn_state state;
2217
2218         if (!file->hints)
2219                 return 0;
2220
2221         clear_insn_state(&state);
2222
2223         for_each_insn(file, insn) {
2224                 if (insn->hint && !insn->visited) {
2225                         ret = validate_branch(file, insn, state);
2226                         if (ret && backtrace)
2227                                 BT_FUNC("<=== (hint)", insn);
2228                         warnings += ret;
2229                 }
2230         }
2231
2232         return warnings;
2233 }
2234
2235 static int validate_retpoline(struct objtool_file *file)
2236 {
2237         struct instruction *insn;
2238         int warnings = 0;
2239
2240         for_each_insn(file, insn) {
2241                 if (insn->type != INSN_JUMP_DYNAMIC &&
2242                     insn->type != INSN_CALL_DYNAMIC)
2243                         continue;
2244
2245                 if (insn->retpoline_safe)
2246                         continue;
2247
2248                 /*
2249                  * .init.text code is ran before userspace and thus doesn't
2250                  * strictly need retpolines, except for modules which are
2251                  * loaded late, they very much do need retpoline in their
2252                  * .init.text
2253                  */
2254                 if (!strcmp(insn->sec->name, ".init.text") && !module)
2255                         continue;
2256
2257                 WARN_FUNC("indirect %s found in RETPOLINE build",
2258                           insn->sec, insn->offset,
2259                           insn->type == INSN_JUMP_DYNAMIC ? "jump" : "call");
2260
2261                 warnings++;
2262         }
2263
2264         return warnings;
2265 }
2266
2267 static bool is_kasan_insn(struct instruction *insn)
2268 {
2269         return (insn->type == INSN_CALL &&
2270                 !strcmp(insn->call_dest->name, "__asan_handle_no_return"));
2271 }
2272
2273 static bool is_ubsan_insn(struct instruction *insn)
2274 {
2275         return (insn->type == INSN_CALL &&
2276                 !strcmp(insn->call_dest->name,
2277                         "__ubsan_handle_builtin_unreachable"));
2278 }
2279
2280 static bool ignore_unreachable_insn(struct instruction *insn)
2281 {
2282         int i;
2283
2284         if (insn->ignore || insn->type == INSN_NOP)
2285                 return true;
2286
2287         /*
2288          * Ignore any unused exceptions.  This can happen when a whitelisted
2289          * function has an exception table entry.
2290          *
2291          * Also ignore alternative replacement instructions.  This can happen
2292          * when a whitelisted function uses one of the ALTERNATIVE macros.
2293          */
2294         if (!strcmp(insn->sec->name, ".fixup") ||
2295             !strcmp(insn->sec->name, ".altinstr_replacement") ||
2296             !strcmp(insn->sec->name, ".altinstr_aux"))
2297                 return true;
2298
2299         /*
2300          * Check if this (or a subsequent) instruction is related to
2301          * CONFIG_UBSAN or CONFIG_KASAN.
2302          *
2303          * End the search at 5 instructions to avoid going into the weeds.
2304          */
2305         if (!insn->func)
2306                 return false;
2307         for (i = 0; i < 5; i++) {
2308
2309                 if (is_kasan_insn(insn) || is_ubsan_insn(insn))
2310                         return true;
2311
2312                 if (insn->type == INSN_JUMP_UNCONDITIONAL) {
2313                         if (insn->jump_dest &&
2314                             insn->jump_dest->func == insn->func) {
2315                                 insn = insn->jump_dest;
2316                                 continue;
2317                         }
2318
2319                         break;
2320                 }
2321
2322                 if (insn->offset + insn->len >= insn->func->offset + insn->func->len)
2323                         break;
2324
2325                 insn = list_next_entry(insn, list);
2326         }
2327
2328         return false;
2329 }
2330
2331 static int validate_functions(struct objtool_file *file)
2332 {
2333         struct section *sec;
2334         struct symbol *func;
2335         struct instruction *insn;
2336         struct insn_state state;
2337         int ret, warnings = 0;
2338
2339         clear_insn_state(&state);
2340
2341         state.cfa = initial_func_cfi.cfa;
2342         memcpy(&state.regs, &initial_func_cfi.regs,
2343                CFI_NUM_REGS * sizeof(struct cfi_reg));
2344         state.stack_size = initial_func_cfi.cfa.offset;
2345
2346         for_each_sec(file, sec) {
2347                 list_for_each_entry(func, &sec->symbol_list, list) {
2348                         if (func->type != STT_FUNC || func->pfunc != func)
2349                                 continue;
2350
2351                         insn = find_insn(file, sec, func->offset);
2352                         if (!insn || insn->ignore)
2353                                 continue;
2354
2355                         state.uaccess = func->alias->uaccess_safe;
2356
2357                         ret = validate_branch(file, insn, state);
2358                         if (ret && backtrace)
2359                                 BT_FUNC("<=== (func)", insn);
2360                         warnings += ret;
2361                 }
2362         }
2363
2364         return warnings;
2365 }
2366
2367 static int validate_reachable_instructions(struct objtool_file *file)
2368 {
2369         struct instruction *insn;
2370
2371         if (file->ignore_unreachables)
2372                 return 0;
2373
2374         for_each_insn(file, insn) {
2375                 if (insn->visited || ignore_unreachable_insn(insn))
2376                         continue;
2377
2378                 WARN_FUNC("unreachable instruction", insn->sec, insn->offset);
2379                 return 1;
2380         }
2381
2382         return 0;
2383 }
2384
2385 static void cleanup(struct objtool_file *file)
2386 {
2387         struct instruction *insn, *tmpinsn;
2388         struct alternative *alt, *tmpalt;
2389
2390         list_for_each_entry_safe(insn, tmpinsn, &file->insn_list, list) {
2391                 list_for_each_entry_safe(alt, tmpalt, &insn->alts, list) {
2392                         list_del(&alt->list);
2393                         free(alt);
2394                 }
2395                 list_del(&insn->list);
2396                 hash_del(&insn->hash);
2397                 free(insn);
2398         }
2399         elf_close(file->elf);
2400 }
2401
2402 static struct objtool_file file;
2403
2404 int check(const char *_objname, bool orc)
2405 {
2406         int ret, warnings = 0;
2407
2408         objname = _objname;
2409
2410         file.elf = elf_open(objname, orc ? O_RDWR : O_RDONLY);
2411         if (!file.elf)
2412                 return 1;
2413
2414         INIT_LIST_HEAD(&file.insn_list);
2415         hash_init(file.insn_hash);
2416         file.c_file = find_section_by_name(file.elf, ".comment");
2417         file.ignore_unreachables = no_unreachable;
2418         file.hints = false;
2419
2420         arch_initial_func_cfi_state(&initial_func_cfi);
2421
2422         ret = decode_sections(&file);
2423         if (ret < 0)
2424                 goto out;
2425         warnings += ret;
2426
2427         if (list_empty(&file.insn_list))
2428                 goto out;
2429
2430         if (retpoline) {
2431                 ret = validate_retpoline(&file);
2432                 if (ret < 0)
2433                         return ret;
2434                 warnings += ret;
2435         }
2436
2437         ret = validate_functions(&file);
2438         if (ret < 0)
2439                 goto out;
2440         warnings += ret;
2441
2442         ret = validate_unwind_hints(&file);
2443         if (ret < 0)
2444                 goto out;
2445         warnings += ret;
2446
2447         if (!warnings) {
2448                 ret = validate_reachable_instructions(&file);
2449                 if (ret < 0)
2450                         goto out;
2451                 warnings += ret;
2452         }
2453
2454         if (orc) {
2455                 ret = create_orc(&file);
2456                 if (ret < 0)
2457                         goto out;
2458
2459                 ret = create_orc_sections(&file);
2460                 if (ret < 0)
2461                         goto out;
2462
2463                 ret = elf_write(file.elf);
2464                 if (ret < 0)
2465                         goto out;
2466         }
2467
2468 out:
2469         cleanup(&file);
2470
2471         /* ignore warnings for now until we get all the code cleaned up */
2472         if (ret || warnings)
2473                 return 0;
2474         return 0;
2475 }