tools/objtool/check.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * Copyright (C) 2015-2017 Josh Poimboeuf <jpoimboe@redhat.com>
   4  */
   5
   6 #include <string.h>
   7 #include <stdlib.h>
   8
   9 #include "builtin.h"
  10 #include "check.h"
  11 #include "elf.h"
  12 #include "special.h"
  13 #include "arch.h"
  14 #include "warn.h"
  15
  16 #include <linux/hashtable.h>
  17 #include <linux/kernel.h>
  18
  19 #define FAKE_JUMP_OFFSET -1
  20
  21 #define C_JUMP_TABLE_SECTION ".rodata..c_jump_table"
  22
  23 struct alternative {
  24         struct list_head list;
  25         struct instruction *insn;
  26         bool skip_orig;
  27 };
  28
  29 const char *objname;
  30 struct cfi_state initial_func_cfi;
  31
  32 struct instruction *find_insn(struct objtool_file *file,
  33                               struct section *sec, unsigned long offset)
  34 {
  35         struct instruction *insn;
  36
  37         hash_for_each_possible(file->insn_hash, insn, hash, offset)
  38                 if (insn->sec == sec && insn->offset == offset)
  39                         return insn;
  40
  41         return NULL;
  42 }
  43
  44 static struct instruction *next_insn_same_sec(struct objtool_file *file,
  45                                               struct instruction *insn)
  46 {
  47         struct instruction *next = list_next_entry(insn, list);
  48
  49         if (!next || &next->list == &file->insn_list || next->sec != insn->sec)
  50                 return NULL;
  51
  52         return next;
  53 }
  54
  55 static struct instruction *next_insn_same_func(struct objtool_file *file,
  56                                                struct instruction *insn)
  57 {
  58         struct instruction *next = list_next_entry(insn, list);
  59         struct symbol *func = insn->func;
  60
  61         if (!func)
  62                 return NULL;
  63
  64         if (&next->list != &file->insn_list && next->func == func)
  65                 return next;
  66
  67         /* Check if we're already in the subfunction: */
  68         if (func == func->cfunc)
  69                 return NULL;
  70
  71         /* Move to the subfunction: */
  72         return find_insn(file, func->cfunc->sec, func->cfunc->offset);
  73 }
  74
  75 #define func_for_each_insn(file, func, insn)                            \
  76         for (insn = find_insn(file, func->sec, func->offset);           \
  77              insn;                                                      \
  78              insn = next_insn_same_func(file, insn))
  79
  80 #define sym_for_each_insn(file, sym, insn)                              \
  81         for (insn = find_insn(file, sym->sec, sym->offset);             \
  82              insn && &insn->list != &file->insn_list &&                 \
  83                 insn->sec == sym->sec &&                                \
  84                 insn->offset < sym->offset + sym->len;                  \
  85              insn = list_next_entry(insn, list))
  86
  87 #define sym_for_each_insn_continue_reverse(file, sym, insn)             \
  88         for (insn = list_prev_entry(insn, list);                        \
  89              &insn->list != &file->insn_list &&                         \
  90                 insn->sec == sym->sec && insn->offset >= sym->offset;   \
  91              insn = list_prev_entry(insn, list))
  92
  93 #define sec_for_each_insn_from(file, insn)                              \
  94         for (; insn; insn = next_insn_same_sec(file, insn))
  95
  96 #define sec_for_each_insn_continue(file, insn)                          \
  97         for (insn = next_insn_same_sec(file, insn); insn;               \
  98              insn = next_insn_same_sec(file, insn))
  99
 100 static bool is_static_jump(struct instruction *insn)
 101 {
 102         return insn->type == INSN_JUMP_CONDITIONAL ||
 103                insn->type == INSN_JUMP_UNCONDITIONAL;
 104 }
 105
 106 static bool is_sibling_call(struct instruction *insn)
 107 {
 108         /* An indirect jump is either a sibling call or a jump to a table. */
 109         if (insn->type == INSN_JUMP_DYNAMIC)
 110                 return list_empty(&insn->alts);
 111
 112         if (!is_static_jump(insn))
 113                 return false;
 114
 115         /* add_jump_destinations() sets insn->call_dest for sibling calls. */
 116         return !!insn->call_dest;
 117 }
 118
 119 /*
 120  * This checks to see if the given function is a "noreturn" function.
 121  *
 122  * For global functions which are outside the scope of this object file, we
 123  * have to keep a manual list of them.
 124  *
 125  * For local functions, we have to detect them manually by simply looking for
 126  * the lack of a return instruction.
 127  */
 128 static bool __dead_end_function(struct objtool_file *file, struct symbol *func,
 129                                 int recursion)
 130 {
 131         int i;
 132         struct instruction *insn;
 133         bool empty = true;
 134
 135         /*
 136          * Unfortunately these have to be hard coded because the noreturn
 137          * attribute isn't provided in ELF data.
 138          */
 139         static const char * const global_noreturns[] = {
 140                 "__stack_chk_fail",
 141                 "panic",
 142                 "do_exit",
 143                 "do_task_dead",
 144                 "__module_put_and_exit",
 145                 "complete_and_exit",
 146                 "__reiserfs_panic",
 147                 "lbug_with_loc",
 148                 "fortify_panic",
 149                 "usercopy_abort",
 150                 "machine_real_restart",
 151                 "rewind_stack_do_exit",
 152                 "kunit_try_catch_throw",
 153         };
 154
 155         if (!func)
 156                 return false;
 157
 158         if (func->bind == STB_WEAK)
 159                 return false;
 160
 161         if (func->bind == STB_GLOBAL)
 162                 for (i = 0; i < ARRAY_SIZE(global_noreturns); i++)
 163                         if (!strcmp(func->name, global_noreturns[i]))
 164                                 return true;
 165
 166         if (!func->len)
 167                 return false;
 168
 169         insn = find_insn(file, func->sec, func->offset);
 170         if (!insn->func)
 171                 return false;
 172
 173         func_for_each_insn(file, func, insn) {
 174                 empty = false;
 175
 176                 if (insn->type == INSN_RETURN)
 177                         return false;
 178         }
 179
 180         if (empty)
 181                 return false;
 182
 183         /*
 184          * A function can have a sibling call instead of a return.  In that
 185          * case, the function's dead-end status depends on whether the target
 186          * of the sibling call returns.
 187          */
 188         func_for_each_insn(file, func, insn) {
 189                 if (is_sibling_call(insn)) {
 190                         struct instruction *dest = insn->jump_dest;
 191
 192                         if (!dest)
 193                                 /* sibling call to another file */
 194                                 return false;
 195
 196                         /* local sibling call */
 197                         if (recursion == 5) {
 198                                 /*
 199                                  * Infinite recursion: two functions have
 200                                  * sibling calls to each other.  This is a very
 201                                  * rare case.  It means they aren't dead ends.
 202                                  */
 203                                 return false;
 204                         }
 205
 206                         return __dead_end_function(file, dest->func, recursion+1);
 207                 }
 208         }
 209
 210         return true;
 211 }
 212
 213 static bool dead_end_function(struct objtool_file *file, struct symbol *func)
 214 {
 215         return __dead_end_function(file, func, 0);
 216 }
 217
 218 static void clear_insn_state(struct insn_state *state)
 219 {
 220         int i;
 221
 222         memset(state, 0, sizeof(*state));
 223         state->cfa.base = CFI_UNDEFINED;
 224         for (i = 0; i < CFI_NUM_REGS; i++) {
 225                 state->regs[i].base = CFI_UNDEFINED;
 226                 state->vals[i].base = CFI_UNDEFINED;
 227         }
 228         state->drap_reg = CFI_UNDEFINED;
 229         state->drap_offset = -1;
 230 }
 231
 232 /*
 233  * Call the arch-specific instruction decoder for all the instructions and add
 234  * them to the global instruction list.
 235  */
 236 static int decode_instructions(struct objtool_file *file)
 237 {
 238         struct section *sec;
 239         struct symbol *func;
 240         unsigned long offset;
 241         struct instruction *insn;
 242         unsigned long nr_insns = 0;
 243         int ret;
 244
 245         for_each_sec(file, sec) {
 246
 247                 if (!(sec->sh.sh_flags & SHF_EXECINSTR))
 248                         continue;
 249
 250                 if (strcmp(sec->name, ".altinstr_replacement") &&
 251                     strcmp(sec->name, ".altinstr_aux") &&
 252                     strncmp(sec->name, ".discard.", 9))
 253                         sec->text = true;
 254
 255                 for (offset = 0; offset < sec->len; offset += insn->len) {
 256                         insn = malloc(sizeof(*insn));
 257                         if (!insn) {
 258                                 WARN("malloc failed");
 259                                 return -1;
 260                         }
 261                         memset(insn, 0, sizeof(*insn));
 262                         INIT_LIST_HEAD(&insn->alts);
 263                         clear_insn_state(&insn->state);
 264
 265                         insn->sec = sec;
 266                         insn->offset = offset;
 267
 268                         ret = arch_decode_instruction(file->elf, sec, offset,
 269                                                       sec->len - offset,
 270                                                       &insn->len, &insn->type,
 271                                                       &insn->immediate,
 272                                                       &insn->stack_op);
 273                         if (ret)
 274                                 goto err;
 275
 276                         hash_add(file->insn_hash, &insn->hash, insn->offset);
 277                         list_add_tail(&insn->list, &file->insn_list);
 278                         nr_insns++;
 279                 }
 280
 281                 list_for_each_entry(func, &sec->symbol_list, list) {
 282                         if (func->type != STT_FUNC || func->alias != func)
 283                                 continue;
 284
 285                         if (!find_insn(file, sec, func->offset)) {
 286                                 WARN("%s(): can't find starting instruction",
 287                                      func->name);
 288                                 return -1;
 289                         }
 290
 291                         sym_for_each_insn(file, func, insn)
 292                                 insn->func = func;
 293                 }
 294         }
 295
 296         if (stats)
 297                 printf("nr_insns: %lu\n", nr_insns);
 298
 299         return 0;
 300
 301 err:
 302         free(insn);
 303         return ret;
 304 }
 305
 306 /*
 307  * Mark "ud2" instructions and manually annotated dead ends.
 308  */
 309 static int add_dead_ends(struct objtool_file *file)
 310 {
 311         struct section *sec;
 312         struct rela *rela;
 313         struct instruction *insn;
 314         bool found;
 315
 316         /*
 317          * By default, "ud2" is a dead end unless otherwise annotated, because
 318          * GCC 7 inserts it for certain divide-by-zero cases.
 319          */
 320         for_each_insn(file, insn)
 321                 if (insn->type == INSN_BUG)
 322                         insn->dead_end = true;
 323
 324         /*
 325          * Check for manually annotated dead ends.
 326          */
 327         sec = find_section_by_name(file->elf, ".rela.discard.unreachable");
 328         if (!sec)
 329                 goto reachable;
 330
 331         list_for_each_entry(rela, &sec->rela_list, list) {
 332                 if (rela->sym->type != STT_SECTION) {
 333                         WARN("unexpected relocation symbol type in %s", sec->name);
 334                         return -1;
 335                 }
 336                 insn = find_insn(file, rela->sym->sec, rela->addend);
 337                 if (insn)
 338                         insn = list_prev_entry(insn, list);
 339                 else if (rela->addend == rela->sym->sec->len) {
 340                         found = false;
 341                         list_for_each_entry_reverse(insn, &file->insn_list, list) {
 342                                 if (insn->sec == rela->sym->sec) {
 343                                         found = true;
 344                                         break;
 345                                 }
 346                         }
 347
 348                         if (!found) {
 349                                 WARN("can't find unreachable insn at %s+0x%x",
 350                                      rela->sym->sec->name, rela->addend);
 351                                 return -1;
 352                         }
 353                 } else {
 354                         WARN("can't find unreachable insn at %s+0x%x",
 355                              rela->sym->sec->name, rela->addend);
 356                         return -1;
 357                 }
 358
 359                 insn->dead_end = true;
 360         }
 361
 362 reachable:
 363         /*
 364          * These manually annotated reachable checks are needed for GCC 4.4,
 365          * where the Linux unreachable() macro isn't supported.  In that case
 366          * GCC doesn't know the "ud2" is fatal, so it generates code as if it's
 367          * not a dead end.
 368          */
 369         sec = find_section_by_name(file->elf, ".rela.discard.reachable");
 370         if (!sec)
 371                 return 0;
 372
 373         list_for_each_entry(rela, &sec->rela_list, list) {
 374                 if (rela->sym->type != STT_SECTION) {
 375                         WARN("unexpected relocation symbol type in %s", sec->name);
 376                         return -1;
 377                 }
 378                 insn = find_insn(file, rela->sym->sec, rela->addend);
 379                 if (insn)
 380                         insn = list_prev_entry(insn, list);
 381                 else if (rela->addend == rela->sym->sec->len) {
 382                         found = false;
 383                         list_for_each_entry_reverse(insn, &file->insn_list, list) {
 384                                 if (insn->sec == rela->sym->sec) {
 385                                         found = true;
 386                                         break;
 387                                 }
 388                         }
 389
 390                         if (!found) {
 391                                 WARN("can't find reachable insn at %s+0x%x",
 392                                      rela->sym->sec->name, rela->addend);
 393                                 return -1;
 394                         }
 395                 } else {
 396                         WARN("can't find reachable insn at %s+0x%x",
 397                              rela->sym->sec->name, rela->addend);
 398                         return -1;
 399                 }
 400
 401                 insn->dead_end = false;
 402         }
 403
 404         return 0;
 405 }
 406
 407 /*
 408  * Warnings shouldn't be reported for ignored functions.
 409  */
 410 static void add_ignores(struct objtool_file *file)
 411 {
 412         struct instruction *insn;
 413         struct section *sec;
 414         struct symbol *func;
 415         struct rela *rela;
 416
 417         sec = find_section_by_name(file->elf, ".rela.discard.func_stack_frame_non_standard");
 418         if (!sec)
 419                 return;
 420
 421         list_for_each_entry(rela, &sec->rela_list, list) {
 422                 switch (rela->sym->type) {
 423                 case STT_FUNC:
 424                         func = rela->sym;
 425                         break;
 426
 427                 case STT_SECTION:
 428                         func = find_func_by_offset(rela->sym->sec, rela->addend);
 429                         if (!func)
 430                                 continue;
 431                         break;
 432
 433                 default:
 434                         WARN("unexpected relocation symbol type in %s: %d", sec->name, rela->sym->type);
 435                         continue;
 436                 }
 437
 438                 func_for_each_insn(file, func, insn)
 439                         insn->ignore = true;
 440         }
 441 }
 442
 443 /*
 444  * This is a whitelist of functions that is allowed to be called with AC set.
 445  * The list is meant to be minimal and only contains compiler instrumentation
 446  * ABI and a few functions used to implement *_{to,from}_user() functions.
 447  *
 448  * These functions must not directly change AC, but may PUSHF/POPF.
 449  */
 450 static const char *uaccess_safe_builtin[] = {
 451         /* KASAN */
 452         "kasan_report",
 453         "check_memory_region",
 454         /* KASAN out-of-line */
 455         "__asan_loadN_noabort",
 456         "__asan_load1_noabort",
 457         "__asan_load2_noabort",
 458         "__asan_load4_noabort",
 459         "__asan_load8_noabort",
 460         "__asan_load16_noabort",
 461         "__asan_storeN_noabort",
 462         "__asan_store1_noabort",
 463         "__asan_store2_noabort",
 464         "__asan_store4_noabort",
 465         "__asan_store8_noabort",
 466         "__asan_store16_noabort",
 467         /* KASAN in-line */
 468         "__asan_report_load_n_noabort",
 469         "__asan_report_load1_noabort",
 470         "__asan_report_load2_noabort",
 471         "__asan_report_load4_noabort",
 472         "__asan_report_load8_noabort",
 473         "__asan_report_load16_noabort",
 474         "__asan_report_store_n_noabort",
 475         "__asan_report_store1_noabort",
 476         "__asan_report_store2_noabort",
 477         "__asan_report_store4_noabort",
 478         "__asan_report_store8_noabort",
 479         "__asan_report_store16_noabort",
 480         /* KCOV */
 481         "write_comp_data",
 482         "__sanitizer_cov_trace_pc",
 483         "__sanitizer_cov_trace_const_cmp1",
 484         "__sanitizer_cov_trace_const_cmp2",
 485         "__sanitizer_cov_trace_const_cmp4",
 486         "__sanitizer_cov_trace_const_cmp8",
 487         "__sanitizer_cov_trace_cmp1",
 488         "__sanitizer_cov_trace_cmp2",
 489         "__sanitizer_cov_trace_cmp4",
 490         "__sanitizer_cov_trace_cmp8",
 491         "__sanitizer_cov_trace_switch",
 492         /* UBSAN */
 493         "ubsan_type_mismatch_common",
 494         "__ubsan_handle_type_mismatch",
 495         "__ubsan_handle_type_mismatch_v1",
 496         "__ubsan_handle_shift_out_of_bounds",
 497         /* misc */
 498         "csum_partial_copy_generic",
 499         "__memcpy_mcsafe",
 500         "mcsafe_handle_tail",
 501         "ftrace_likely_update", /* CONFIG_TRACE_BRANCH_PROFILING */
 502         NULL
 503 };
 504
 505 static void add_uaccess_safe(struct objtool_file *file)
 506 {
 507         struct symbol *func;
 508         const char **name;
 509
 510         if (!uaccess)
 511                 return;
 512
 513         for (name = uaccess_safe_builtin; *name; name++) {
 514                 func = find_symbol_by_name(file->elf, *name);
 515                 if (!func)
 516                         continue;
 517
 518                 func->uaccess_safe = true;
 519         }
 520 }
 521
 522 /*
 523  * FIXME: For now, just ignore any alternatives which add retpolines.  This is
 524  * a temporary hack, as it doesn't allow ORC to unwind from inside a retpoline.
 525  * But it at least allows objtool to understand the control flow *around* the
 526  * retpoline.
 527  */
 528 static int add_ignore_alternatives(struct objtool_file *file)
 529 {
 530         struct section *sec;
 531         struct rela *rela;
 532         struct instruction *insn;
 533
 534         sec = find_section_by_name(file->elf, ".rela.discard.ignore_alts");
 535         if (!sec)
 536                 return 0;
 537
 538         list_for_each_entry(rela, &sec->rela_list, list) {
 539                 if (rela->sym->type != STT_SECTION) {
 540                         WARN("unexpected relocation symbol type in %s", sec->name);
 541                         return -1;
 542                 }
 543
 544                 insn = find_insn(file, rela->sym->sec, rela->addend);
 545                 if (!insn) {
 546                         WARN("bad .discard.ignore_alts entry");
 547                         return -1;
 548                 }
 549
 550                 insn->ignore_alts = true;
 551         }
 552
 553         return 0;
 554 }
 555
 556 /*
 557  * Find the destination instructions for all jumps.
 558  */
 559 static int add_jump_destinations(struct objtool_file *file)
 560 {
 561         struct instruction *insn;
 562         struct rela *rela;
 563         struct section *dest_sec;
 564         unsigned long dest_off;
 565
 566         for_each_insn(file, insn) {
 567                 if (!is_static_jump(insn))
 568                         continue;
 569
 570                 if (insn->ignore || insn->offset == FAKE_JUMP_OFFSET)
 571                         continue;
 572
 573                 rela = find_rela_by_dest_range(file->elf, insn->sec,
 574                                                insn->offset, insn->len);
 575                 if (!rela) {
 576                         dest_sec = insn->sec;
 577                         dest_off = insn->offset + insn->len + insn->immediate;
 578                 } else if (rela->sym->type == STT_SECTION) {
 579                         dest_sec = rela->sym->sec;
 580                         dest_off = rela->addend + 4;
 581                 } else if (rela->sym->sec->idx) {
 582                         dest_sec = rela->sym->sec;
 583                         dest_off = rela->sym->sym.st_value + rela->addend + 4;
 584                 } else if (strstr(rela->sym->name, "_indirect_thunk_")) {
 585                         /*
 586                          * Retpoline jumps are really dynamic jumps in
 587                          * disguise, so convert them accordingly.
 588                          */
 589                         if (insn->type == INSN_JUMP_UNCONDITIONAL)
 590                                 insn->type = INSN_JUMP_DYNAMIC;
 591                         else
 592                                 insn->type = INSN_JUMP_DYNAMIC_CONDITIONAL;
 593
 594                         insn->retpoline_safe = true;
 595                         continue;
 596                 } else {
 597                         /* external sibling call */
 598                         insn->call_dest = rela->sym;
 599                         continue;
 600                 }
 601
 602                 insn->jump_dest = find_insn(file, dest_sec, dest_off);
 603                 if (!insn->jump_dest) {
 604
 605                         /*
 606                          * This is a special case where an alt instruction
 607                          * jumps past the end of the section.  These are
 608                          * handled later in handle_group_alt().
 609                          */
 610                         if (!strcmp(insn->sec->name, ".altinstr_replacement"))
 611                                 continue;
 612
 613                         WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
 614                                   insn->sec, insn->offset, dest_sec->name,
 615                                   dest_off);
 616                         return -1;
 617                 }
 618
 619                 /*
 620                  * Cross-function jump.
 621                  */
 622                 if (insn->func && insn->jump_dest->func &&
 623                     insn->func != insn->jump_dest->func) {
 624
 625                         /*
 626                          * For GCC 8+, create parent/child links for any cold
 627                          * subfunctions.  This is _mostly_ redundant with a
 628                          * similar initialization in read_symbols().
 629                          *
 630                          * If a function has aliases, we want the *first* such
 631                          * function in the symbol table to be the subfunction's
 632                          * parent.  In that case we overwrite the
 633                          * initialization done in read_symbols().
 634                          *
 635                          * However this code can't completely replace the
 636                          * read_symbols() code because this doesn't detect the
 637                          * case where the parent function's only reference to a
 638                          * subfunction is through a jump table.
 639                          */
 640                         if (!strstr(insn->func->name, ".cold.") &&
 641                             strstr(insn->jump_dest->func->name, ".cold.")) {
 642                                 insn->func->cfunc = insn->jump_dest->func;
 643                                 insn->jump_dest->func->pfunc = insn->func;
 644
 645                         } else if (insn->jump_dest->func->pfunc != insn->func->pfunc &&
 646                                    insn->jump_dest->offset == insn->jump_dest->func->offset) {
 647
 648                                 /* internal sibling call */
 649                                 insn->call_dest = insn->jump_dest->func;
 650                         }
 651                 }
 652         }
 653
 654         return 0;
 655 }
 656
 657 /*
 658  * Find the destination instructions for all calls.
 659  */
 660 static int add_call_destinations(struct objtool_file *file)
 661 {
 662         struct instruction *insn;
 663         unsigned long dest_off;
 664         struct rela *rela;
 665
 666         for_each_insn(file, insn) {
 667                 if (insn->type != INSN_CALL)
 668                         continue;
 669
 670                 rela = find_rela_by_dest_range(file->elf, insn->sec,
 671                                                insn->offset, insn->len);
 672                 if (!rela) {
 673                         dest_off = insn->offset + insn->len + insn->immediate;
 674                         insn->call_dest = find_func_by_offset(insn->sec, dest_off);
 675                         if (!insn->call_dest)
 676                                 insn->call_dest = find_symbol_by_offset(insn->sec, dest_off);
 677
 678                         if (insn->ignore)
 679                                 continue;
 680
 681                         if (!insn->call_dest) {
 682                                 WARN_FUNC("unsupported intra-function call",
 683                                           insn->sec, insn->offset);
 684                                 if (retpoline)
 685                                         WARN("If this is a retpoline, please patch it in with alternatives and annotate it with ANNOTATE_NOSPEC_ALTERNATIVE.");
 686                                 return -1;
 687                         }
 688
 689                         if (insn->func && insn->call_dest->type != STT_FUNC) {
 690                                 WARN_FUNC("unsupported call to non-function",
 691                                           insn->sec, insn->offset);
 692                                 return -1;
 693                         }
 694
 695                 } else if (rela->sym->type == STT_SECTION) {
 696                         insn->call_dest = find_func_by_offset(rela->sym->sec,
 697                                                               rela->addend+4);
 698                         if (!insn->call_dest) {
 699                                 WARN_FUNC("can't find call dest symbol at %s+0x%x",
 700                                           insn->sec, insn->offset,
 701                                           rela->sym->sec->name,
 702                                           rela->addend + 4);
 703                                 return -1;
 704                         }
 705                 } else
 706                         insn->call_dest = rela->sym;
 707         }
 708
 709         return 0;
 710 }
 711
 712 /*
 713  * The .alternatives section requires some extra special care, over and above
 714  * what other special sections require:
 715  *
 716  * 1. Because alternatives are patched in-place, we need to insert a fake jump
 717  *    instruction at the end so that validate_branch() skips all the original
 718  *    replaced instructions when validating the new instruction path.
 719  *
 720  * 2. An added wrinkle is that the new instruction length might be zero.  In
 721  *    that case the old instructions are replaced with noops.  We simulate that
 722  *    by creating a fake jump as the only new instruction.
 723  *
 724  * 3. In some cases, the alternative section includes an instruction which
 725  *    conditionally jumps to the _end_ of the entry.  We have to modify these
 726  *    jumps' destinations to point back to .text rather than the end of the
 727  *    entry in .altinstr_replacement.
 728  */
 729 static int handle_group_alt(struct objtool_file *file,
 730                             struct special_alt *special_alt,
 731                             struct instruction *orig_insn,
 732                             struct instruction **new_insn)
 733 {
 734         struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump = NULL;
 735         unsigned long dest_off;
 736
 737         last_orig_insn = NULL;
 738         insn = orig_insn;
 739         sec_for_each_insn_from(file, insn) {
 740                 if (insn->offset >= special_alt->orig_off + special_alt->orig_len)
 741                         break;
 742
 743                 insn->alt_group = true;
 744                 last_orig_insn = insn;
 745         }
 746
 747         if (next_insn_same_sec(file, last_orig_insn)) {
 748                 fake_jump = malloc(sizeof(*fake_jump));
 749                 if (!fake_jump) {
 750                         WARN("malloc failed");
 751                         return -1;
 752                 }
 753                 memset(fake_jump, 0, sizeof(*fake_jump));
 754                 INIT_LIST_HEAD(&fake_jump->alts);
 755                 clear_insn_state(&fake_jump->state);
 756
 757                 fake_jump->sec = special_alt->new_sec;
 758                 fake_jump->offset = FAKE_JUMP_OFFSET;
 759                 fake_jump->type = INSN_JUMP_UNCONDITIONAL;
 760                 fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
 761                 fake_jump->func = orig_insn->func;
 762         }
 763
 764         if (!special_alt->new_len) {
 765                 if (!fake_jump) {
 766                         WARN("%s: empty alternative at end of section",
 767                              special_alt->orig_sec->name);
 768                         return -1;
 769                 }
 770
 771                 *new_insn = fake_jump;
 772                 return 0;
 773         }
 774
 775         last_new_insn = NULL;
 776         insn = *new_insn;
 777         sec_for_each_insn_from(file, insn) {
 778                 if (insn->offset >= special_alt->new_off + special_alt->new_len)
 779                         break;
 780
 781                 last_new_insn = insn;
 782
 783                 insn->ignore = orig_insn->ignore_alts;
 784                 insn->func = orig_insn->func;
 785
 786                 /*
 787                  * Since alternative replacement code is copy/pasted by the
 788                  * kernel after applying relocations, generally such code can't
 789                  * have relative-address relocation references to outside the
 790                  * .altinstr_replacement section, unless the arch's
 791                  * alternatives code can adjust the relative offsets
 792                  * accordingly.
 793                  *
 794                  * The x86 alternatives code adjusts the offsets only when it
 795                  * encounters a branch instruction at the very beginning of the
 796                  * replacement group.
 797                  */
 798                 if ((insn->offset != special_alt->new_off ||
 799                     (insn->type != INSN_CALL && !is_static_jump(insn))) &&
 800                     find_rela_by_dest_range(file->elf, insn->sec, insn->offset, insn->len)) {
 801
 802                         WARN_FUNC("unsupported relocation in alternatives section",
 803                                   insn->sec, insn->offset);
 804                         return -1;
 805                 }
 806
 807                 if (!is_static_jump(insn))
 808                         continue;
 809
 810                 if (!insn->immediate)
 811                         continue;
 812
 813                 dest_off = insn->offset + insn->len + insn->immediate;
 814                 if (dest_off == special_alt->new_off + special_alt->new_len) {
 815                         if (!fake_jump) {
 816                                 WARN("%s: alternative jump to end of section",
 817                                      special_alt->orig_sec->name);
 818                                 return -1;
 819                         }
 820                         insn->jump_dest = fake_jump;
 821                 }
 822
 823                 if (!insn->jump_dest) {
 824                         WARN_FUNC("can't find alternative jump destination",
 825                                   insn->sec, insn->offset);
 826                         return -1;
 827                 }
 828         }
 829
 830         if (!last_new_insn) {
 831                 WARN_FUNC("can't find last new alternative instruction",
 832                           special_alt->new_sec, special_alt->new_off);
 833                 return -1;
 834         }
 835
 836         if (fake_jump)
 837                 list_add(&fake_jump->list, &last_new_insn->list);
 838
 839         return 0;
 840 }
 841
 842 /*
 843  * A jump table entry can either convert a nop to a jump or a jump to a nop.
 844  * If the original instruction is a jump, make the alt entry an effective nop
 845  * by just skipping the original instruction.
 846  */
 847 static int handle_jump_alt(struct objtool_file *file,
 848                            struct special_alt *special_alt,
 849                            struct instruction *orig_insn,
 850                            struct instruction **new_insn)
 851 {
 852         if (orig_insn->type == INSN_NOP)
 853                 return 0;
 854
 855         if (orig_insn->type != INSN_JUMP_UNCONDITIONAL) {
 856                 WARN_FUNC("unsupported instruction at jump label",
 857                           orig_insn->sec, orig_insn->offset);
 858                 return -1;
 859         }
 860
 861         *new_insn = list_next_entry(orig_insn, list);
 862         return 0;
 863 }
 864
 865 /*
 866  * Read all the special sections which have alternate instructions which can be
 867  * patched in or redirected to at runtime.  Each instruction having alternate
 868  * instruction(s) has them added to its insn->alts list, which will be
 869  * traversed in validate_branch().
 870  */
 871 static int add_special_section_alts(struct objtool_file *file)
 872 {
 873         struct list_head special_alts;
 874         struct instruction *orig_insn, *new_insn;
 875         struct special_alt *special_alt, *tmp;
 876         struct alternative *alt;
 877         int ret;
 878
 879         ret = special_get_alts(file->elf, &special_alts);
 880         if (ret)
 881                 return ret;
 882
 883         list_for_each_entry_safe(special_alt, tmp, &special_alts, list) {
 884
 885                 orig_insn = find_insn(file, special_alt->orig_sec,
 886                                       special_alt->orig_off);
 887                 if (!orig_insn) {
 888                         WARN_FUNC("special: can't find orig instruction",
 889                                   special_alt->orig_sec, special_alt->orig_off);
 890                         ret = -1;
 891                         goto out;
 892                 }
 893
 894                 new_insn = NULL;
 895                 if (!special_alt->group || special_alt->new_len) {
 896                         new_insn = find_insn(file, special_alt->new_sec,
 897                                              special_alt->new_off);
 898                         if (!new_insn) {
 899                                 WARN_FUNC("special: can't find new instruction",
 900                                           special_alt->new_sec,
 901                                           special_alt->new_off);
 902                                 ret = -1;
 903                                 goto out;
 904                         }
 905                 }
 906
 907                 if (special_alt->group) {
 908                         ret = handle_group_alt(file, special_alt, orig_insn,
 909                                                &new_insn);
 910                         if (ret)
 911                                 goto out;
 912                 } else if (special_alt->jump_or_nop) {
 913                         ret = handle_jump_alt(file, special_alt, orig_insn,
 914                                               &new_insn);
 915                         if (ret)
 916                                 goto out;
 917                 }
 918
 919                 alt = malloc(sizeof(*alt));
 920                 if (!alt) {
 921                         WARN("malloc failed");
 922                         ret = -1;
 923                         goto out;
 924                 }
 925
 926                 alt->insn = new_insn;
 927                 alt->skip_orig = special_alt->skip_orig;
 928                 orig_insn->ignore_alts |= special_alt->skip_alt;
 929                 list_add_tail(&alt->list, &orig_insn->alts);
 930
 931                 list_del(&special_alt->list);
 932                 free(special_alt);
 933         }
 934
 935 out:
 936         return ret;
 937 }
 938
 939 static int add_jump_table(struct objtool_file *file, struct instruction *insn,
 940                             struct rela *table)
 941 {
 942         struct rela *rela = table;
 943         struct instruction *dest_insn;
 944         struct alternative *alt;
 945         struct symbol *pfunc = insn->func->pfunc;
 946         unsigned int prev_offset = 0;
 947
 948         /*
 949          * Each @rela is a switch table relocation which points to the target
 950          * instruction.
 951          */
 952         list_for_each_entry_from(rela, &table->sec->rela_list, list) {
 953
 954                 /* Check for the end of the table: */
 955                 if (rela != table && rela->jump_table_start)
 956                         break;
 957
 958                 /* Make sure the table entries are consecutive: */
 959                 if (prev_offset && rela->offset != prev_offset + 8)
 960                         break;
 961
 962                 /* Detect function pointers from contiguous objects: */
 963                 if (rela->sym->sec == pfunc->sec &&
 964                     rela->addend == pfunc->offset)
 965                         break;
 966
 967                 dest_insn = find_insn(file, rela->sym->sec, rela->addend);
 968                 if (!dest_insn)
 969                         break;
 970
 971                 /* Make sure the destination is in the same function: */
 972                 if (!dest_insn->func || dest_insn->func->pfunc != pfunc)
 973                         break;
 974
 975                 alt = malloc(sizeof(*alt));
 976                 if (!alt) {
 977                         WARN("malloc failed");
 978                         return -1;
 979                 }
 980
 981                 alt->insn = dest_insn;
 982                 list_add_tail(&alt->list, &insn->alts);
 983                 prev_offset = rela->offset;
 984         }
 985
 986         if (!prev_offset) {
 987                 WARN_FUNC("can't find switch jump table",
 988                           insn->sec, insn->offset);
 989                 return -1;
 990         }
 991
 992         return 0;
 993 }
 994
 995 /*
 996  * find_jump_table() - Given a dynamic jump, find the switch jump table in
 997  * .rodata associated with it.
 998  *
 999  * There are 3 basic patterns:
1000  *
1001  * 1. jmpq *[rodata addr](,%reg,8)
1002  *
1003  *    This is the most common case by far.  It jumps to an address in a simple
1004  *    jump table which is stored in .rodata.
1005  *
1006  * 2. jmpq *[rodata addr](%rip)
1007  *
1008  *    This is caused by a rare GCC quirk, currently only seen in three driver
1009  *    functions in the kernel, only with certain obscure non-distro configs.
1010  *
1011  *    As part of an optimization, GCC makes a copy of an existing switch jump
1012  *    table, modifies it, and then hard-codes the jump (albeit with an indirect
1013  *    jump) to use a single entry in the table.  The rest of the jump table and
1014  *    some of its jump targets remain as dead code.
1015  *
1016  *    In such a case we can just crudely ignore all unreachable instruction
1017  *    warnings for the entire object file.  Ideally we would just ignore them
1018  *    for the function, but that would require redesigning the code quite a
1019  *    bit.  And honestly that's just not worth doing: unreachable instruction
1020  *    warnings are of questionable value anyway, and this is such a rare issue.
1021  *
1022  * 3. mov [rodata addr],%reg1
1023  *    ... some instructions ...
1024  *    jmpq *(%reg1,%reg2,8)
1025  *
1026  *    This is a fairly uncommon pattern which is new for GCC 6.  As of this
1027  *    writing, there are 11 occurrences of it in the allmodconfig kernel.
1028  *
1029  *    As of GCC 7 there are quite a few more of these and the 'in between' code
1030  *    is significant. Esp. with KASAN enabled some of the code between the mov
1031  *    and jmpq uses .rodata itself, which can confuse things.
1032  *
1033  *    TODO: Once we have DWARF CFI and smarter instruction decoding logic,
1034  *    ensure the same register is used in the mov and jump instructions.
1035  *
1036  *    NOTE: RETPOLINE made it harder still to decode dynamic jumps.
1037  */
1038 static struct rela *find_jump_table(struct objtool_file *file,
1039                                       struct symbol *func,
1040                                       struct instruction *insn)
1041 {
1042         struct rela *text_rela, *table_rela;
1043         struct instruction *dest_insn, *orig_insn = insn;
1044         struct section *table_sec;
1045         unsigned long table_offset;
1046
1047         /*
1048          * Backward search using the @first_jump_src links, these help avoid
1049          * much of the 'in between' code. Which avoids us getting confused by
1050          * it.
1051          */
1052         for (;
1053              &insn->list != &file->insn_list && insn->func && insn->func->pfunc == func;
1054              insn = insn->first_jump_src ?: list_prev_entry(insn, list)) {
1055
1056                 if (insn != orig_insn && insn->type == INSN_JUMP_DYNAMIC)
1057                         break;
1058
1059                 /* allow small jumps within the range */
1060                 if (insn->type == INSN_JUMP_UNCONDITIONAL &&
1061                     insn->jump_dest &&
1062                     (insn->jump_dest->offset <= insn->offset ||
1063                      insn->jump_dest->offset > orig_insn->offset))
1064                     break;
1065
1066                 /* look for a relocation which references .rodata */
1067                 text_rela = find_rela_by_dest_range(file->elf, insn->sec,
1068                                                     insn->offset, insn->len);
1069                 if (!text_rela || text_rela->sym->type != STT_SECTION ||
1070                     !text_rela->sym->sec->rodata)
1071                         continue;
1072
1073                 table_offset = text_rela->addend;
1074                 table_sec = text_rela->sym->sec;
1075
1076                 if (text_rela->type == R_X86_64_PC32)
1077                         table_offset += 4;
1078
1079                 /*
1080                  * Make sure the .rodata address isn't associated with a
1081                  * symbol.  GCC jump tables are anonymous data.
1082                  *
1083                  * Also support C jump tables which are in the same format as
1084                  * switch jump tables.  For objtool to recognize them, they
1085                  * need to be placed in the C_JUMP_TABLE_SECTION section.  They
1086                  * have symbols associated with them.
1087                  */
1088                 if (find_symbol_containing(table_sec, table_offset) &&
1089                     strcmp(table_sec->name, C_JUMP_TABLE_SECTION))
1090                         continue;
1091
1092                 /*
1093                  * Each table entry has a rela associated with it.  The rela
1094                  * should reference text in the same function as the original
1095                  * instruction.
1096                  */
1097                 table_rela = find_rela_by_dest(file->elf, table_sec, table_offset);
1098                 if (!table_rela)
1099                         continue;
1100                 dest_insn = find_insn(file, table_rela->sym->sec, table_rela->addend);
1101                 if (!dest_insn || !dest_insn->func || dest_insn->func->pfunc != func)
1102                         continue;
1103
1104                 /*
1105                  * Use of RIP-relative switch jumps is quite rare, and
1106                  * indicates a rare GCC quirk/bug which can leave dead code
1107                  * behind.
1108                  */
1109                 if (text_rela->type == R_X86_64_PC32)
1110                         file->ignore_unreachables = true;
1111
1112                 return table_rela;
1113         }
1114
1115         return NULL;
1116 }
1117
1118 /*
1119  * First pass: Mark the head of each jump table so that in the next pass,
1120  * we know when a given jump table ends and the next one starts.
1121  */
1122 static void mark_func_jump_tables(struct objtool_file *file,
1123                                     struct symbol *func)
1124 {
1125         struct instruction *insn, *last = NULL;
1126         struct rela *rela;
1127
1128         func_for_each_insn(file, func, insn) {
1129                 if (!last)
1130                         last = insn;
1131
1132                 /*
1133                  * Store back-pointers for unconditional forward jumps such
1134                  * that find_jump_table() can back-track using those and
1135                  * avoid some potentially confusing code.
1136                  */
1137                 if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest &&
1138                     insn->offset > last->offset &&
1139                     insn->jump_dest->offset > insn->offset &&
1140                     !insn->jump_dest->first_jump_src) {
1141
1142                         insn->jump_dest->first_jump_src = insn;
1143                         last = insn->jump_dest;
1144                 }
1145
1146                 if (insn->type != INSN_JUMP_DYNAMIC)
1147                         continue;
1148
1149                 rela = find_jump_table(file, func, insn);
1150                 if (rela) {
1151                         rela->jump_table_start = true;
1152                         insn->jump_table = rela;
1153                 }
1154         }
1155 }
1156
1157 static int add_func_jump_tables(struct objtool_file *file,
1158                                   struct symbol *func)
1159 {
1160         struct instruction *insn;
1161         int ret;
1162
1163         func_for_each_insn(file, func, insn) {
1164                 if (!insn->jump_table)
1165                         continue;
1166
1167                 ret = add_jump_table(file, insn, insn->jump_table);
1168                 if (ret)
1169                         return ret;
1170         }
1171
1172         return 0;
1173 }
1174
1175 /*
1176  * For some switch statements, gcc generates a jump table in the .rodata
1177  * section which contains a list of addresses within the function to jump to.
1178  * This finds these jump tables and adds them to the insn->alts lists.
1179  */
1180 static int add_jump_table_alts(struct objtool_file *file)
1181 {
1182         struct section *sec;
1183         struct symbol *func;
1184         int ret;
1185
1186         if (!file->rodata)
1187                 return 0;
1188
1189         for_each_sec(file, sec) {
1190                 list_for_each_entry(func, &sec->symbol_list, list) {
1191                         if (func->type != STT_FUNC)
1192                                 continue;
1193
1194                         mark_func_jump_tables(file, func);
1195                         ret = add_func_jump_tables(file, func);
1196                         if (ret)
1197                                 return ret;
1198                 }
1199         }
1200
1201         return 0;
1202 }
1203
1204 static int read_unwind_hints(struct objtool_file *file)
1205 {
1206         struct section *sec, *relasec;
1207         struct rela *rela;
1208         struct unwind_hint *hint;
1209         struct instruction *insn;
1210         struct cfi_reg *cfa;
1211         int i;
1212
1213         sec = find_section_by_name(file->elf, ".discard.unwind_hints");
1214         if (!sec)
1215                 return 0;
1216
1217         relasec = sec->rela;
1218         if (!relasec) {
1219                 WARN("missing .rela.discard.unwind_hints section");
1220                 return -1;
1221         }
1222
1223         if (sec->len % sizeof(struct unwind_hint)) {
1224                 WARN("struct unwind_hint size mismatch");
1225                 return -1;
1226         }
1227
1228         file->hints = true;
1229
1230         for (i = 0; i < sec->len / sizeof(struct unwind_hint); i++) {
1231                 hint = (struct unwind_hint *)sec->data->d_buf + i;
1232
1233                 rela = find_rela_by_dest(file->elf, sec, i * sizeof(*hint));
1234                 if (!rela) {
1235                         WARN("can't find rela for unwind_hints[%d]", i);
1236                         return -1;
1237                 }
1238
1239                 insn = find_insn(file, rela->sym->sec, rela->addend);
1240                 if (!insn) {
1241                         WARN("can't find insn for unwind_hints[%d]", i);
1242                         return -1;
1243                 }
1244
1245                 cfa = &insn->state.cfa;
1246
1247                 if (hint->type == UNWIND_HINT_TYPE_SAVE) {
1248                         insn->save = true;
1249                         continue;
1250
1251                 } else if (hint->type == UNWIND_HINT_TYPE_RESTORE) {
1252                         insn->restore = true;
1253                         insn->hint = true;
1254                         continue;
1255                 }
1256
1257                 insn->hint = true;
1258
1259                 switch (hint->sp_reg) {
1260                 case ORC_REG_UNDEFINED:
1261                         cfa->base = CFI_UNDEFINED;
1262                         break;
1263                 case ORC_REG_SP:
1264                         cfa->base = CFI_SP;
1265                         break;
1266                 case ORC_REG_BP:
1267                         cfa->base = CFI_BP;
1268                         break;
1269                 case ORC_REG_SP_INDIRECT:
1270                         cfa->base = CFI_SP_INDIRECT;
1271                         break;
1272                 case ORC_REG_R10:
1273                         cfa->base = CFI_R10;
1274                         break;
1275                 case ORC_REG_R13:
1276                         cfa->base = CFI_R13;
1277                         break;
1278                 case ORC_REG_DI:
1279                         cfa->base = CFI_DI;
1280                         break;
1281                 case ORC_REG_DX:
1282                         cfa->base = CFI_DX;
1283                         break;
1284                 default:
1285                         WARN_FUNC("unsupported unwind_hint sp base reg %d",
1286                                   insn->sec, insn->offset, hint->sp_reg);
1287                         return -1;
1288                 }
1289
1290                 cfa->offset = hint->sp_offset;
1291                 insn->state.type = hint->type;
1292                 insn->state.end = hint->end;
1293         }
1294
1295         return 0;
1296 }
1297
1298 static int read_retpoline_hints(struct objtool_file *file)
1299 {
1300         struct section *sec;
1301         struct instruction *insn;
1302         struct rela *rela;
1303
1304         sec = find_section_by_name(file->elf, ".rela.discard.retpoline_safe");
1305         if (!sec)
1306                 return 0;
1307
1308         list_for_each_entry(rela, &sec->rela_list, list) {
1309                 if (rela->sym->type != STT_SECTION) {
1310                         WARN("unexpected relocation symbol type in %s", sec->name);
1311                         return -1;
1312                 }
1313
1314                 insn = find_insn(file, rela->sym->sec, rela->addend);
1315                 if (!insn) {
1316                         WARN("bad .discard.retpoline_safe entry");
1317                         return -1;
1318                 }
1319
1320                 if (insn->type != INSN_JUMP_DYNAMIC &&
1321                     insn->type != INSN_CALL_DYNAMIC) {
1322                         WARN_FUNC("retpoline_safe hint not an indirect jump/call",
1323                                   insn->sec, insn->offset);
1324                         return -1;
1325                 }
1326
1327                 insn->retpoline_safe = true;
1328         }
1329
1330         return 0;
1331 }
1332
1333 static void mark_rodata(struct objtool_file *file)
1334 {
1335         struct section *sec;
1336         bool found = false;
1337
1338         /*
1339          * Search for the following rodata sections, each of which can
1340          * potentially contain jump tables:
1341          *
1342          * - .rodata: can contain GCC switch tables
1343          * - .rodata.<func>: same, if -fdata-sections is being used
1344          * - .rodata..c_jump_table: contains C annotated jump tables
1345          *
1346          * .rodata.str1.* sections are ignored; they don't contain jump tables.
1347          */
1348         for_each_sec(file, sec) {
1349                 if ((!strncmp(sec->name, ".rodata", 7) && !strstr(sec->name, ".str1.")) ||
1350                     !strcmp(sec->name, C_JUMP_TABLE_SECTION)) {
1351                         sec->rodata = true;
1352                         found = true;
1353                 }
1354         }
1355
1356         file->rodata = found;
1357 }
1358
1359 static int decode_sections(struct objtool_file *file)
1360 {
1361         int ret;
1362
1363         mark_rodata(file);
1364
1365         ret = decode_instructions(file);
1366         if (ret)
1367                 return ret;
1368
1369         ret = add_dead_ends(file);
1370         if (ret)
1371                 return ret;
1372
1373         add_ignores(file);
1374         add_uaccess_safe(file);
1375
1376         ret = add_ignore_alternatives(file);
1377         if (ret)
1378                 return ret;
1379
1380         ret = add_jump_destinations(file);
1381         if (ret)
1382                 return ret;
1383
1384         ret = add_special_section_alts(file);
1385         if (ret)
1386                 return ret;
1387
1388         ret = add_call_destinations(file);
1389         if (ret)
1390                 return ret;
1391
1392         ret = add_jump_table_alts(file);
1393         if (ret)
1394                 return ret;
1395
1396         ret = read_unwind_hints(file);
1397         if (ret)
1398                 return ret;
1399
1400         ret = read_retpoline_hints(file);
1401         if (ret)
1402                 return ret;
1403
1404         return 0;
1405 }
1406
1407 static bool is_fentry_call(struct instruction *insn)
1408 {
1409         if (insn->type == INSN_CALL &&
1410             insn->call_dest->type == STT_NOTYPE &&
1411             !strcmp(insn->call_dest->name, "__fentry__"))
1412                 return true;
1413
1414         return false;
1415 }
1416
1417 static bool has_modified_stack_frame(struct insn_state *state)
1418 {
1419         int i;
1420
1421         if (state->cfa.base != initial_func_cfi.cfa.base ||
1422             state->cfa.offset != initial_func_cfi.cfa.offset ||
1423             state->stack_size != initial_func_cfi.cfa.offset ||
1424             state->drap)
1425                 return true;
1426
1427         for (i = 0; i < CFI_NUM_REGS; i++)
1428                 if (state->regs[i].base != initial_func_cfi.regs[i].base ||
1429                     state->regs[i].offset != initial_func_cfi.regs[i].offset)
1430                         return true;
1431
1432         return false;
1433 }
1434
1435 static bool has_valid_stack_frame(struct insn_state *state)
1436 {
1437         if (state->cfa.base == CFI_BP && state->regs[CFI_BP].base == CFI_CFA &&
1438             state->regs[CFI_BP].offset == -16)
1439                 return true;
1440
1441         if (state->drap && state->regs[CFI_BP].base == CFI_BP)
1442                 return true;
1443
1444         return false;
1445 }
1446
1447 static int update_insn_state_regs(struct instruction *insn, struct insn_state *state)
1448 {
1449         struct cfi_reg *cfa = &state->cfa;
1450         struct stack_op *op = &insn->stack_op;
1451
1452         if (cfa->base != CFI_SP)
1453                 return 0;
1454
1455         /* push */
1456         if (op->dest.type == OP_DEST_PUSH || op->dest.type == OP_DEST_PUSHF)
1457                 cfa->offset += 8;
1458
1459         /* pop */
1460         if (op->src.type == OP_SRC_POP || op->src.type == OP_SRC_POPF)
1461                 cfa->offset -= 8;
1462
1463         /* add immediate to sp */
1464         if (op->dest.type == OP_DEST_REG && op->src.type == OP_SRC_ADD &&
1465             op->dest.reg == CFI_SP && op->src.reg == CFI_SP)
1466                 cfa->offset -= op->src.offset;
1467
1468         return 0;
1469 }
1470
1471 static void save_reg(struct insn_state *state, unsigned char reg, int base,
1472                      int offset)
1473 {
1474         if (arch_callee_saved_reg(reg) &&
1475             state->regs[reg].base == CFI_UNDEFINED) {
1476                 state->regs[reg].base = base;
1477                 state->regs[reg].offset = offset;
1478         }
1479 }
1480
1481 static void restore_reg(struct insn_state *state, unsigned char reg)
1482 {
1483         state->regs[reg].base = CFI_UNDEFINED;
1484         state->regs[reg].offset = 0;
1485 }
1486
1487 /*
1488  * A note about DRAP stack alignment:
1489  *
1490  * GCC has the concept of a DRAP register, which is used to help keep track of
1491  * the stack pointer when aligning the stack.  r10 or r13 is used as the DRAP
1492  * register.  The typical DRAP pattern is:
1493  *
1494  *   4c 8d 54 24 08             lea    0x8(%rsp),%r10
1495  *   48 83 e4 c0                and    $0xffffffffffffffc0,%rsp
1496  *   41 ff 72 f8                pushq  -0x8(%r10)
1497  *   55                         push   %rbp
1498  *   48 89 e5                   mov    %rsp,%rbp
1499  *                              (more pushes)
1500  *   41 52                      push   %r10
1501  *                              ...
1502  *   41 5a                      pop    %r10
1503  *                              (more pops)
1504  *   5d                         pop    %rbp
1505  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1506  *   c3                         retq
1507  *
1508  * There are some variations in the epilogues, like:
1509  *
1510  *   5b                         pop    %rbx
1511  *   41 5a                      pop    %r10
1512  *   41 5c                      pop    %r12
1513  *   41 5d                      pop    %r13
1514  *   41 5e                      pop    %r14
1515  *   c9                         leaveq
1516  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1517  *   c3                         retq
1518  *
1519  * and:
1520  *
1521  *   4c 8b 55 e8                mov    -0x18(%rbp),%r10
1522  *   48 8b 5d e0                mov    -0x20(%rbp),%rbx
1523  *   4c 8b 65 f0                mov    -0x10(%rbp),%r12
1524  *   4c 8b 6d f8                mov    -0x8(%rbp),%r13
1525  *   c9                         leaveq
1526  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1527  *   c3                         retq
1528  *
1529  * Sometimes r13 is used as the DRAP register, in which case it's saved and
1530  * restored beforehand:
1531  *
1532  *   41 55                      push   %r13
1533  *   4c 8d 6c 24 10             lea    0x10(%rsp),%r13
1534  *   48 83 e4 f0                and    $0xfffffffffffffff0,%rsp
1535  *                              ...
1536  *   49 8d 65 f0                lea    -0x10(%r13),%rsp
1537  *   41 5d                      pop    %r13
1538  *   c3                         retq
1539  */
1540 static int update_insn_state(struct instruction *insn, struct insn_state *state)
1541 {
1542         struct stack_op *op = &insn->stack_op;
1543         struct cfi_reg *cfa = &state->cfa;
1544         struct cfi_reg *regs = state->regs;
1545
1546         /* stack operations don't make sense with an undefined CFA */
1547         if (cfa->base == CFI_UNDEFINED) {
1548                 if (insn->func) {
1549                         WARN_FUNC("undefined stack state", insn->sec, insn->offset);
1550                         return -1;
1551                 }
1552                 return 0;
1553         }
1554
1555         if (state->type == ORC_TYPE_REGS || state->type == ORC_TYPE_REGS_IRET)
1556                 return update_insn_state_regs(insn, state);
1557
1558         switch (op->dest.type) {
1559
1560         case OP_DEST_REG:
1561                 switch (op->src.type) {
1562
1563                 case OP_SRC_REG:
1564                         if (op->src.reg == CFI_SP && op->dest.reg == CFI_BP &&
1565                             cfa->base == CFI_SP &&
1566                             regs[CFI_BP].base == CFI_CFA &&
1567                             regs[CFI_BP].offset == -cfa->offset) {
1568
1569                                 /* mov %rsp, %rbp */
1570                                 cfa->base = op->dest.reg;
1571                                 state->bp_scratch = false;
1572                         }
1573
1574                         else if (op->src.reg == CFI_SP &&
1575                                  op->dest.reg == CFI_BP && state->drap) {
1576
1577                                 /* drap: mov %rsp, %rbp */
1578                                 regs[CFI_BP].base = CFI_BP;
1579                                 regs[CFI_BP].offset = -state->stack_size;
1580                                 state->bp_scratch = false;
1581                         }
1582
1583                         else if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1584
1585                                 /*
1586                                  * mov %rsp, %reg
1587                                  *
1588                                  * This is needed for the rare case where GCC
1589                                  * does:
1590                                  *
1591                                  *   mov    %rsp, %rax
1592                                  *   ...
1593                                  *   mov    %rax, %rsp
1594                                  */
1595                                 state->vals[op->dest.reg].base = CFI_CFA;
1596                                 state->vals[op->dest.reg].offset = -state->stack_size;
1597                         }
1598
1599                         else if (op->src.reg == CFI_BP && op->dest.reg == CFI_SP &&
1600                                  cfa->base == CFI_BP) {
1601
1602                                 /*
1603                                  * mov %rbp, %rsp
1604                                  *
1605                                  * Restore the original stack pointer (Clang).
1606                                  */
1607                                 state->stack_size = -state->regs[CFI_BP].offset;
1608                         }
1609
1610                         else if (op->dest.reg == cfa->base) {
1611
1612                                 /* mov %reg, %rsp */
1613                                 if (cfa->base == CFI_SP &&
1614                                     state->vals[op->src.reg].base == CFI_CFA) {
1615
1616                                         /*
1617                                          * This is needed for the rare case
1618                                          * where GCC does something dumb like:
1619                                          *
1620                                          *   lea    0x8(%rsp), %rcx
1621                                          *   ...
1622                                          *   mov    %rcx, %rsp
1623                                          */
1624                                         cfa->offset = -state->vals[op->src.reg].offset;
1625                                         state->stack_size = cfa->offset;
1626
1627                                 } else {
1628                                         cfa->base = CFI_UNDEFINED;
1629                                         cfa->offset = 0;
1630                                 }
1631                         }
1632
1633                         break;
1634
1635                 case OP_SRC_ADD:
1636                         if (op->dest.reg == CFI_SP && op->src.reg == CFI_SP) {
1637
1638                                 /* add imm, %rsp */
1639                                 state->stack_size -= op->src.offset;
1640                                 if (cfa->base == CFI_SP)
1641                                         cfa->offset -= op->src.offset;
1642                                 break;
1643                         }
1644
1645                         if (op->dest.reg == CFI_SP && op->src.reg == CFI_BP) {
1646
1647                                 /* lea disp(%rbp), %rsp */
1648                                 state->stack_size = -(op->src.offset + regs[CFI_BP].offset);
1649                                 break;
1650                         }
1651
1652                         if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1653
1654                                 /* drap: lea disp(%rsp), %drap */
1655                                 state->drap_reg = op->dest.reg;
1656
1657                                 /*
1658                                  * lea disp(%rsp), %reg
1659                                  *
1660                                  * This is needed for the rare case where GCC
1661                                  * does something dumb like:
1662                                  *
1663                                  *   lea    0x8(%rsp), %rcx
1664                                  *   ...
1665                                  *   mov    %rcx, %rsp
1666                                  */
1667                                 state->vals[op->dest.reg].base = CFI_CFA;
1668                                 state->vals[op->dest.reg].offset = \
1669                                         -state->stack_size + op->src.offset;
1670
1671                                 break;
1672                         }
1673
1674                         if (state->drap && op->dest.reg == CFI_SP &&
1675                             op->src.reg == state->drap_reg) {
1676
1677                                  /* drap: lea disp(%drap), %rsp */
1678                                 cfa->base = CFI_SP;
1679                                 cfa->offset = state->stack_size = -op->src.offset;
1680                                 state->drap_reg = CFI_UNDEFINED;
1681                                 state->drap = false;
1682                                 break;
1683                         }
1684
1685                         if (op->dest.reg == state->cfa.base) {
1686                                 WARN_FUNC("unsupported stack register modification",
1687                                           insn->sec, insn->offset);
1688                                 return -1;
1689                         }
1690
1691                         break;
1692
1693                 case OP_SRC_AND:
1694                         if (op->dest.reg != CFI_SP ||
1695                             (state->drap_reg != CFI_UNDEFINED && cfa->base != CFI_SP) ||
1696                             (state->drap_reg == CFI_UNDEFINED && cfa->base != CFI_BP)) {
1697                                 WARN_FUNC("unsupported stack pointer realignment",
1698                                           insn->sec, insn->offset);
1699                                 return -1;
1700                         }
1701
1702                         if (state->drap_reg != CFI_UNDEFINED) {
1703                                 /* drap: and imm, %rsp */
1704                                 cfa->base = state->drap_reg;
1705                                 cfa->offset = state->stack_size = 0;
1706                                 state->drap = true;
1707                         }
1708
1709                         /*
1710                          * Older versions of GCC (4.8ish) realign the stack
1711                          * without DRAP, with a frame pointer.
1712                          */
1713
1714                         break;
1715
1716                 case OP_SRC_POP:
1717                 case OP_SRC_POPF:
1718                         if (!state->drap && op->dest.type == OP_DEST_REG &&
1719                             op->dest.reg == cfa->base) {
1720
1721                                 /* pop %rbp */
1722                                 cfa->base = CFI_SP;
1723                         }
1724
1725                         if (state->drap && cfa->base == CFI_BP_INDIRECT &&
1726                             op->dest.type == OP_DEST_REG &&
1727                             op->dest.reg == state->drap_reg &&
1728                             state->drap_offset == -state->stack_size) {
1729
1730                                 /* drap: pop %drap */
1731                                 cfa->base = state->drap_reg;
1732                                 cfa->offset = 0;
1733                                 state->drap_offset = -1;
1734
1735                         } else if (regs[op->dest.reg].offset == -state->stack_size) {
1736
1737                                 /* pop %reg */
1738                                 restore_reg(state, op->dest.reg);
1739                         }
1740
1741                         state->stack_size -= 8;
1742                         if (cfa->base == CFI_SP)
1743                                 cfa->offset -= 8;
1744
1745                         break;
1746
1747                 case OP_SRC_REG_INDIRECT:
1748                         if (state->drap && op->src.reg == CFI_BP &&
1749                             op->src.offset == state->drap_offset) {
1750
1751                                 /* drap: mov disp(%rbp), %drap */
1752                                 cfa->base = state->drap_reg;
1753                                 cfa->offset = 0;
1754                                 state->drap_offset = -1;
1755                         }
1756
1757                         if (state->drap && op->src.reg == CFI_BP &&
1758                             op->src.offset == regs[op->dest.reg].offset) {
1759
1760                                 /* drap: mov disp(%rbp), %reg */
1761                                 restore_reg(state, op->dest.reg);
1762
1763                         } else if (op->src.reg == cfa->base &&
1764                             op->src.offset == regs[op->dest.reg].offset + cfa->offset) {
1765
1766                                 /* mov disp(%rbp), %reg */
1767                                 /* mov disp(%rsp), %reg */
1768                                 restore_reg(state, op->dest.reg);
1769                         }
1770
1771                         break;
1772
1773                 default:
1774                         WARN_FUNC("unknown stack-related instruction",
1775                                   insn->sec, insn->offset);
1776                         return -1;
1777                 }
1778
1779                 break;
1780
1781         case OP_DEST_PUSH:
1782         case OP_DEST_PUSHF:
1783                 state->stack_size += 8;
1784                 if (cfa->base == CFI_SP)
1785                         cfa->offset += 8;
1786
1787                 if (op->src.type != OP_SRC_REG)
1788                         break;
1789
1790                 if (state->drap) {
1791                         if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1792
1793                                 /* drap: push %drap */
1794                                 cfa->base = CFI_BP_INDIRECT;
1795                                 cfa->offset = -state->stack_size;
1796
1797                                 /* save drap so we know when to restore it */
1798                                 state->drap_offset = -state->stack_size;
1799
1800                         } else if (op->src.reg == CFI_BP && cfa->base == state->drap_reg) {
1801
1802                                 /* drap: push %rbp */
1803                                 state->stack_size = 0;
1804
1805                         } else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1806
1807                                 /* drap: push %reg */
1808                                 save_reg(state, op->src.reg, CFI_BP, -state->stack_size);
1809                         }
1810
1811                 } else {
1812
1813                         /* push %reg */
1814                         save_reg(state, op->src.reg, CFI_CFA, -state->stack_size);
1815                 }
1816
1817                 /* detect when asm code uses rbp as a scratch register */
1818                 if (!no_fp && insn->func && op->src.reg == CFI_BP &&
1819                     cfa->base != CFI_BP)
1820                         state->bp_scratch = true;
1821                 break;
1822
1823         case OP_DEST_REG_INDIRECT:
1824
1825                 if (state->drap) {
1826                         if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1827
1828                                 /* drap: mov %drap, disp(%rbp) */
1829                                 cfa->base = CFI_BP_INDIRECT;
1830                                 cfa->offset = op->dest.offset;
1831
1832                                 /* save drap offset so we know when to restore it */
1833                                 state->drap_offset = op->dest.offset;
1834                         }
1835
1836                         else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1837
1838                                 /* drap: mov reg, disp(%rbp) */
1839                                 save_reg(state, op->src.reg, CFI_BP, op->dest.offset);
1840                         }
1841
1842                 } else if (op->dest.reg == cfa->base) {
1843
1844                         /* mov reg, disp(%rbp) */
1845                         /* mov reg, disp(%rsp) */
1846                         save_reg(state, op->src.reg, CFI_CFA,
1847                                  op->dest.offset - state->cfa.offset);
1848                 }
1849
1850                 break;
1851
1852         case OP_DEST_LEAVE:
1853                 if ((!state->drap && cfa->base != CFI_BP) ||
1854                     (state->drap && cfa->base != state->drap_reg)) {
1855                         WARN_FUNC("leave instruction with modified stack frame",
1856                                   insn->sec, insn->offset);
1857                         return -1;
1858                 }
1859
1860                 /* leave (mov %rbp, %rsp; pop %rbp) */
1861
1862                 state->stack_size = -state->regs[CFI_BP].offset - 8;
1863                 restore_reg(state, CFI_BP);
1864
1865                 if (!state->drap) {
1866                         cfa->base = CFI_SP;
1867                         cfa->offset -= 8;
1868                 }
1869
1870                 break;
1871
1872         case OP_DEST_MEM:
1873                 if (op->src.type != OP_SRC_POP && op->src.type != OP_SRC_POPF) {
1874                         WARN_FUNC("unknown stack-related memory operation",
1875                                   insn->sec, insn->offset);
1876                         return -1;
1877                 }
1878
1879                 /* pop mem */
1880                 state->stack_size -= 8;
1881                 if (cfa->base == CFI_SP)
1882                         cfa->offset -= 8;
1883
1884                 break;
1885
1886         default:
1887                 WARN_FUNC("unknown stack-related instruction",
1888                           insn->sec, insn->offset);
1889                 return -1;
1890         }
1891
1892         return 0;
1893 }
1894
1895 static bool insn_state_match(struct instruction *insn, struct insn_state *state)
1896 {
1897         struct insn_state *state1 = &insn->state, *state2 = state;
1898         int i;
1899
1900         if (memcmp(&state1->cfa, &state2->cfa, sizeof(state1->cfa))) {
1901                 WARN_FUNC("stack state mismatch: cfa1=%d%+d cfa2=%d%+d",
1902                           insn->sec, insn->offset,
1903                           state1->cfa.base, state1->cfa.offset,
1904                           state2->cfa.base, state2->cfa.offset);
1905
1906         } else if (memcmp(&state1->regs, &state2->regs, sizeof(state1->regs))) {
1907                 for (i = 0; i < CFI_NUM_REGS; i++) {
1908                         if (!memcmp(&state1->regs[i], &state2->regs[i],
1909                                     sizeof(struct cfi_reg)))
1910                                 continue;
1911
1912                         WARN_FUNC("stack state mismatch: reg1[%d]=%d%+d reg2[%d]=%d%+d",
1913                                   insn->sec, insn->offset,
1914                                   i, state1->regs[i].base, state1->regs[i].offset,
1915                                   i, state2->regs[i].base, state2->regs[i].offset);
1916                         break;
1917                 }
1918
1919         } else if (state1->type != state2->type) {
1920                 WARN_FUNC("stack state mismatch: type1=%d type2=%d",
1921                           insn->sec, insn->offset, state1->type, state2->type);
1922
1923         } else if (state1->drap != state2->drap ||
1924                  (state1->drap && state1->drap_reg != state2->drap_reg) ||
1925                  (state1->drap && state1->drap_offset != state2->drap_offset)) {
1926                 WARN_FUNC("stack state mismatch: drap1=%d(%d,%d) drap2=%d(%d,%d)",
1927                           insn->sec, insn->offset,
1928                           state1->drap, state1->drap_reg, state1->drap_offset,
1929                           state2->drap, state2->drap_reg, state2->drap_offset);
1930
1931         } else
1932                 return true;
1933
1934         return false;
1935 }
1936
1937 static inline bool func_uaccess_safe(struct symbol *func)
1938 {
1939         if (func)
1940                 return func->uaccess_safe;
1941
1942         return false;
1943 }
1944
1945 static inline const char *call_dest_name(struct instruction *insn)
1946 {
1947         if (insn->call_dest)
1948                 return insn->call_dest->name;
1949
1950         return "{dynamic}";
1951 }
1952
1953 static int validate_call(struct instruction *insn, struct insn_state *state)
1954 {
1955         if (state->uaccess && !func_uaccess_safe(insn->call_dest)) {
1956                 WARN_FUNC("call to %s() with UACCESS enabled",
1957                                 insn->sec, insn->offset, call_dest_name(insn));
1958                 return 1;
1959         }
1960
1961         if (state->df) {
1962                 WARN_FUNC("call to %s() with DF set",
1963                                 insn->sec, insn->offset, call_dest_name(insn));
1964                 return 1;
1965         }
1966
1967         return 0;
1968 }
1969
1970 static int validate_sibling_call(struct instruction *insn, struct insn_state *state)
1971 {
1972         if (has_modified_stack_frame(state)) {
1973                 WARN_FUNC("sibling call from callable instruction with modified stack frame",
1974                                 insn->sec, insn->offset);
1975                 return 1;
1976         }
1977
1978         return validate_call(insn, state);
1979 }
1980
1981 static int validate_return(struct symbol *func, struct instruction *insn, struct insn_state *state)
1982 {
1983         if (state->uaccess && !func_uaccess_safe(func)) {
1984                 WARN_FUNC("return with UACCESS enabled",
1985                           insn->sec, insn->offset);
1986                 return 1;
1987         }
1988
1989         if (!state->uaccess && func_uaccess_safe(func)) {
1990                 WARN_FUNC("return with UACCESS disabled from a UACCESS-safe function",
1991                           insn->sec, insn->offset);
1992                 return 1;
1993         }
1994
1995         if (state->df) {
1996                 WARN_FUNC("return with DF set",
1997                           insn->sec, insn->offset);
1998                 return 1;
1999         }
2000
2001         if (func && has_modified_stack_frame(state)) {
2002                 WARN_FUNC("return with modified stack frame",
2003                           insn->sec, insn->offset);
2004                 return 1;
2005         }
2006
2007         if (state->bp_scratch) {
2008                 WARN_FUNC("BP used as a scratch register",
2009                           insn->sec, insn->offset);
2010                 return 1;
2011         }
2012
2013         return 0;
2014 }
2015
2016 /*
2017  * Follow the branch starting at the given instruction, and recursively follow
2018  * any other branches (jumps).  Meanwhile, track the frame pointer state at
2019  * each instruction and validate all the rules described in
2020  * tools/objtool/Documentation/stack-validation.txt.
2021  */
2022 static int validate_branch(struct objtool_file *file, struct symbol *func,
2023                            struct instruction *first, struct insn_state state)
2024 {
2025         struct alternative *alt;
2026         struct instruction *insn, *next_insn;
2027         struct section *sec;
2028         u8 visited;
2029         int ret;
2030
2031         insn = first;
2032         sec = insn->sec;
2033
2034         if (insn->alt_group && list_empty(&insn->alts)) {
2035                 WARN_FUNC("don't know how to handle branch to middle of alternative instruction group",
2036                           sec, insn->offset);
2037                 return 1;
2038         }
2039
2040         while (1) {
2041                 next_insn = next_insn_same_sec(file, insn);
2042
2043                 if (file->c_file && func && insn->func && func != insn->func->pfunc) {
2044                         WARN("%s() falls through to next function %s()",
2045                              func->name, insn->func->name);
2046                         return 1;
2047                 }
2048
2049                 if (func && insn->ignore) {
2050                         WARN_FUNC("BUG: why am I validating an ignored function?",
2051                                   sec, insn->offset);
2052                         return 1;
2053                 }
2054
2055                 visited = 1 << state.uaccess;
2056                 if (insn->visited) {
2057                         if (!insn->hint && !insn_state_match(insn, &state))
2058                                 return 1;
2059
2060                         if (insn->visited & visited)
2061                                 return 0;
2062                 }
2063
2064                 if (insn->hint) {
2065                         if (insn->restore) {
2066                                 struct instruction *save_insn, *i;
2067
2068                                 i = insn;
2069                                 save_insn = NULL;
2070                                 sym_for_each_insn_continue_reverse(file, func, i) {
2071                                         if (i->save) {
2072                                                 save_insn = i;
2073                                                 break;
2074                                         }
2075                                 }
2076
2077                                 if (!save_insn) {
2078                                         WARN_FUNC("no corresponding CFI save for CFI restore",
2079                                                   sec, insn->offset);
2080                                         return 1;
2081                                 }
2082
2083                                 if (!save_insn->visited) {
2084                                         /*
2085                                          * Oops, no state to copy yet.
2086                                          * Hopefully we can reach this
2087                                          * instruction from another branch
2088                                          * after the save insn has been
2089                                          * visited.
2090                                          */
2091                                         if (insn == first)
2092                                                 return 0;
2093
2094                                         WARN_FUNC("objtool isn't smart enough to handle this CFI save/restore combo",
2095                                                   sec, insn->offset);
2096                                         return 1;
2097                                 }
2098
2099                                 insn->state = save_insn->state;
2100                         }
2101
2102                         state = insn->state;
2103
2104                 } else
2105                         insn->state = state;
2106
2107                 insn->visited |= visited;
2108
2109                 if (!insn->ignore_alts) {
2110                         bool skip_orig = false;
2111
2112                         list_for_each_entry(alt, &insn->alts, list) {
2113                                 if (alt->skip_orig)
2114                                         skip_orig = true;
2115
2116                                 ret = validate_branch(file, func, alt->insn, state);
2117                                 if (ret) {
2118                                         if (backtrace)
2119                                                 BT_FUNC("(alt)", insn);
2120                                         return ret;
2121                                 }
2122                         }
2123
2124                         if (skip_orig)
2125                                 return 0;
2126                 }
2127
2128                 switch (insn->type) {
2129
2130                 case INSN_RETURN:
2131                         return validate_return(func, insn, &state);
2132
2133                 case INSN_CALL:
2134                 case INSN_CALL_DYNAMIC:
2135                         ret = validate_call(insn, &state);
2136                         if (ret)
2137                                 return ret;
2138
2139                         if (!no_fp && func && !is_fentry_call(insn) &&
2140                             !has_valid_stack_frame(&state)) {
2141                                 WARN_FUNC("call without frame pointer save/setup",
2142                                           sec, insn->offset);
2143                                 return 1;
2144                         }
2145
2146                         if (dead_end_function(file, insn->call_dest))
2147                                 return 0;
2148
2149                         break;
2150
2151                 case INSN_JUMP_CONDITIONAL:
2152                 case INSN_JUMP_UNCONDITIONAL:
2153                         if (func && is_sibling_call(insn)) {
2154                                 ret = validate_sibling_call(insn, &state);
2155                                 if (ret)
2156                                         return ret;
2157
2158                         } else if (insn->jump_dest) {
2159                                 ret = validate_branch(file, func,
2160                                                       insn->jump_dest, state);
2161                                 if (ret) {
2162                                         if (backtrace)
2163                                                 BT_FUNC("(branch)", insn);
2164                                         return ret;
2165                                 }
2166                         }
2167
2168                         if (insn->type == INSN_JUMP_UNCONDITIONAL)
2169                                 return 0;
2170
2171                         break;
2172
2173                 case INSN_JUMP_DYNAMIC:
2174                 case INSN_JUMP_DYNAMIC_CONDITIONAL:
2175                         if (func && is_sibling_call(insn)) {
2176                                 ret = validate_sibling_call(insn, &state);
2177                                 if (ret)
2178                                         return ret;
2179                         }
2180
2181                         if (insn->type == INSN_JUMP_DYNAMIC)
2182                                 return 0;
2183
2184                         break;
2185
2186                 case INSN_CONTEXT_SWITCH:
2187                         if (func && (!next_insn || !next_insn->hint)) {
2188                                 WARN_FUNC("unsupported instruction in callable function",
2189                                           sec, insn->offset);
2190                                 return 1;
2191                         }
2192                         return 0;
2193
2194                 case INSN_STACK:
2195                         if (update_insn_state(insn, &state))
2196                                 return 1;
2197
2198                         if (insn->stack_op.dest.type == OP_DEST_PUSHF) {
2199                                 if (!state.uaccess_stack) {
2200                                         state.uaccess_stack = 1;
2201                                 } else if (state.uaccess_stack >> 31) {
2202                                         WARN_FUNC("PUSHF stack exhausted", sec, insn->offset);
2203                                         return 1;
2204                                 }
2205                                 state.uaccess_stack <<= 1;
2206                                 state.uaccess_stack  |= state.uaccess;
2207                         }
2208
2209                         if (insn->stack_op.src.type == OP_SRC_POPF) {
2210                                 if (state.uaccess_stack) {
2211                                         state.uaccess = state.uaccess_stack & 1;
2212                                         state.uaccess_stack >>= 1;
2213                                         if (state.uaccess_stack == 1)
2214                                                 state.uaccess_stack = 0;
2215                                 }
2216                         }
2217
2218                         break;
2219
2220                 case INSN_STAC:
2221                         if (state.uaccess) {
2222                                 WARN_FUNC("recursive UACCESS enable", sec, insn->offset);
2223                                 return 1;
2224                         }
2225
2226                         state.uaccess = true;
2227                         break;
2228
2229                 case INSN_CLAC:
2230                         if (!state.uaccess && func) {
2231                                 WARN_FUNC("redundant UACCESS disable", sec, insn->offset);
2232                                 return 1;
2233                         }
2234
2235                         if (func_uaccess_safe(func) && !state.uaccess_stack) {
2236                                 WARN_FUNC("UACCESS-safe disables UACCESS", sec, insn->offset);
2237                                 return 1;
2238                         }
2239
2240                         state.uaccess = false;
2241                         break;
2242
2243                 case INSN_STD:
2244                         if (state.df)
2245                                 WARN_FUNC("recursive STD", sec, insn->offset);
2246
2247                         state.df = true;
2248                         break;
2249
2250                 case INSN_CLD:
2251                         if (!state.df && func)
2252                                 WARN_FUNC("redundant CLD", sec, insn->offset);
2253
2254                         state.df = false;
2255                         break;
2256
2257                 default:
2258                         break;
2259                 }
2260
2261                 if (insn->dead_end)
2262                         return 0;
2263
2264                 if (!next_insn) {
2265                         if (state.cfa.base == CFI_UNDEFINED)
2266                                 return 0;
2267                         WARN("%s: unexpected end of section", sec->name);
2268                         return 1;
2269                 }
2270
2271                 insn = next_insn;
2272         }
2273
2274         return 0;
2275 }
2276
2277 static int validate_unwind_hints(struct objtool_file *file)
2278 {
2279         struct instruction *insn;
2280         int ret, warnings = 0;
2281         struct insn_state state;
2282
2283         if (!file->hints)
2284                 return 0;
2285
2286         clear_insn_state(&state);
2287
2288         for_each_insn(file, insn) {
2289                 if (insn->hint && !insn->visited) {
2290                         ret = validate_branch(file, insn->func, insn, state);
2291                         if (ret && backtrace)
2292                                 BT_FUNC("<=== (hint)", insn);
2293                         warnings += ret;
2294                 }
2295         }
2296
2297         return warnings;
2298 }
2299
2300 static int validate_retpoline(struct objtool_file *file)
2301 {
2302         struct instruction *insn;
2303         int warnings = 0;
2304
2305         for_each_insn(file, insn) {
2306                 if (insn->type != INSN_JUMP_DYNAMIC &&
2307                     insn->type != INSN_CALL_DYNAMIC)
2308                         continue;
2309
2310                 if (insn->retpoline_safe)
2311                         continue;
2312
2313                 /*
2314                  * .init.text code is ran before userspace and thus doesn't
2315                  * strictly need retpolines, except for modules which are
2316                  * loaded late, they very much do need retpoline in their
2317                  * .init.text
2318                  */
2319                 if (!strcmp(insn->sec->name, ".init.text") && !module)
2320                         continue;
2321
2322                 WARN_FUNC("indirect %s found in RETPOLINE build",
2323                           insn->sec, insn->offset,
2324                           insn->type == INSN_JUMP_DYNAMIC ? "jump" : "call");
2325
2326                 warnings++;
2327         }
2328
2329         return warnings;
2330 }
2331
2332 static bool is_kasan_insn(struct instruction *insn)
2333 {
2334         return (insn->type == INSN_CALL &&
2335                 !strcmp(insn->call_dest->name, "__asan_handle_no_return"));
2336 }
2337
2338 static bool is_ubsan_insn(struct instruction *insn)
2339 {
2340         return (insn->type == INSN_CALL &&
2341                 !strcmp(insn->call_dest->name,
2342                         "__ubsan_handle_builtin_unreachable"));
2343 }
2344
2345 static bool ignore_unreachable_insn(struct instruction *insn)
2346 {
2347         int i;
2348
2349         if (insn->ignore || insn->type == INSN_NOP)
2350                 return true;
2351
2352         /*
2353          * Ignore any unused exceptions.  This can happen when a whitelisted
2354          * function has an exception table entry.
2355          *
2356          * Also ignore alternative replacement instructions.  This can happen
2357          * when a whitelisted function uses one of the ALTERNATIVE macros.
2358          */
2359         if (!strcmp(insn->sec->name, ".fixup") ||
2360             !strcmp(insn->sec->name, ".altinstr_replacement") ||
2361             !strcmp(insn->sec->name, ".altinstr_aux"))
2362                 return true;
2363
2364         if (!insn->func)
2365                 return false;
2366
2367         /*
2368          * CONFIG_UBSAN_TRAP inserts a UD2 when it sees
2369          * __builtin_unreachable().  The BUG() macro has an unreachable() after
2370          * the UD2, which causes GCC's undefined trap logic to emit another UD2
2371          * (or occasionally a JMP to UD2).
2372          */
2373         if (list_prev_entry(insn, list)->dead_end &&
2374             (insn->type == INSN_BUG ||
2375              (insn->type == INSN_JUMP_UNCONDITIONAL &&
2376               insn->jump_dest && insn->jump_dest->type == INSN_BUG)))
2377                 return true;
2378
2379         /*
2380          * Check if this (or a subsequent) instruction is related to
2381          * CONFIG_UBSAN or CONFIG_KASAN.
2382          *
2383          * End the search at 5 instructions to avoid going into the weeds.
2384          */
2385         for (i = 0; i < 5; i++) {
2386
2387                 if (is_kasan_insn(insn) || is_ubsan_insn(insn))
2388                         return true;
2389
2390                 if (insn->type == INSN_JUMP_UNCONDITIONAL) {
2391                         if (insn->jump_dest &&
2392                             insn->jump_dest->func == insn->func) {
2393                                 insn = insn->jump_dest;
2394                                 continue;
2395                         }
2396
2397                         break;
2398                 }
2399
2400                 if (insn->offset + insn->len >= insn->func->offset + insn->func->len)
2401                         break;
2402
2403                 insn = list_next_entry(insn, list);
2404         }
2405
2406         return false;
2407 }
2408
2409 static int validate_section(struct objtool_file *file, struct section *sec)
2410 {
2411         struct symbol *func;
2412         struct instruction *insn;
2413         struct insn_state state;
2414         int ret, warnings = 0;
2415
2416         clear_insn_state(&state);
2417
2418         state.cfa = initial_func_cfi.cfa;
2419         memcpy(&state.regs, &initial_func_cfi.regs,
2420                CFI_NUM_REGS * sizeof(struct cfi_reg));
2421         state.stack_size = initial_func_cfi.cfa.offset;
2422
2423         list_for_each_entry(func, &sec->symbol_list, list) {
2424                 if (func->type != STT_FUNC)
2425                         continue;
2426
2427                 if (!func->len) {
2428                         WARN("%s() is missing an ELF size annotation",
2429                              func->name);
2430                         warnings++;
2431                 }
2432
2433                 if (func->pfunc != func || func->alias != func)
2434                         continue;
2435
2436                 insn = find_insn(file, sec, func->offset);
2437                 if (!insn || insn->ignore || insn->visited)
2438                         continue;
2439
2440                 state.uaccess = func->uaccess_safe;
2441
2442                 ret = validate_branch(file, func, insn, state);
2443                 if (ret && backtrace)
2444                         BT_FUNC("<=== (func)", insn);
2445                 warnings += ret;
2446         }
2447
2448         return warnings;
2449 }
2450
2451 static int validate_functions(struct objtool_file *file)
2452 {
2453         struct section *sec;
2454         int warnings = 0;
2455
2456         for_each_sec(file, sec)
2457                 warnings += validate_section(file, sec);
2458
2459         return warnings;
2460 }
2461
2462 static int validate_reachable_instructions(struct objtool_file *file)
2463 {
2464         struct instruction *insn;
2465
2466         if (file->ignore_unreachables)
2467                 return 0;
2468
2469         for_each_insn(file, insn) {
2470                 if (insn->visited || ignore_unreachable_insn(insn))
2471                         continue;
2472
2473                 WARN_FUNC("unreachable instruction", insn->sec, insn->offset);
2474                 return 1;
2475         }
2476
2477         return 0;
2478 }
2479
2480 static struct objtool_file file;
2481
2482 int check(const char *_objname, bool orc)
2483 {
2484         int ret, warnings = 0;
2485
2486         objname = _objname;
2487
2488         file.elf = elf_read(objname, orc ? O_RDWR : O_RDONLY);
2489         if (!file.elf)
2490                 return 1;
2491
2492         INIT_LIST_HEAD(&file.insn_list);
2493         hash_init(file.insn_hash);
2494         file.c_file = find_section_by_name(file.elf, ".comment");
2495         file.ignore_unreachables = no_unreachable;
2496         file.hints = false;
2497
2498         arch_initial_func_cfi_state(&initial_func_cfi);
2499
2500         ret = decode_sections(&file);
2501         if (ret < 0)
2502                 goto out;
2503         warnings += ret;
2504
2505         if (list_empty(&file.insn_list))
2506                 goto out;
2507
2508         if (retpoline) {
2509                 ret = validate_retpoline(&file);
2510                 if (ret < 0)
2511                         return ret;
2512                 warnings += ret;
2513         }
2514
2515         ret = validate_functions(&file);
2516         if (ret < 0)
2517                 goto out;
2518         warnings += ret;
2519
2520         ret = validate_unwind_hints(&file);
2521         if (ret < 0)
2522                 goto out;
2523         warnings += ret;
2524
2525         if (!warnings) {
2526                 ret = validate_reachable_instructions(&file);
2527                 if (ret < 0)
2528                         goto out;
2529                 warnings += ret;
2530         }
2531
2532         if (orc) {
2533                 ret = create_orc(&file);
2534                 if (ret < 0)
2535                         goto out;
2536
2537                 ret = create_orc_sections(&file);
2538                 if (ret < 0)
2539                         goto out;
2540
2541                 ret = elf_write(file.elf);
2542                 if (ret < 0)
2543                         goto out;
2544         }
2545
2546 out:
2547         if (ret < 0) {
2548                 /*
2549                  *  Fatal error.  The binary is corrupt or otherwise broken in
2550                  *  some way, or objtool itself is broken.  Fail the kernel
2551                  *  build.
2552                  */
2553                 return ret;
2554         }
2555
2556         return 0;
2557 }