tools/objtool/check.c

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