tools/objtool/check.c

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