tools/objtool/check.c

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