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                 "kunit_try_catch_throw",
 148         };
 149
 150         if (!func)
 151                 return false;
 152
 153         if (func->bind == STB_WEAK)
 154                 return false;
 155
 156         if (func->bind == STB_GLOBAL)
 157                 for (i = 0; i < ARRAY_SIZE(global_noreturns); i++)
 158                         if (!strcmp(func->name, global_noreturns[i]))
 159                                 return true;
 160
 161         if (!func->len)
 162                 return false;
 163
 164         insn = find_insn(file, func->sec, func->offset);
 165         if (!insn->func)
 166                 return false;
 167
 168         func_for_each_insn_all(file, func, insn) {
 169                 empty = false;
 170
 171                 if (insn->type == INSN_RETURN)
 172                         return false;
 173         }
 174
 175         if (empty)
 176                 return false;
 177
 178         /*
 179          * A function can have a sibling call instead of a return.  In that
 180          * case, the function's dead-end status depends on whether the target
 181          * of the sibling call returns.
 182          */
 183         func_for_each_insn_all(file, func, insn) {
 184                 if (is_sibling_call(insn)) {
 185                         struct instruction *dest = insn->jump_dest;
 186
 187                         if (!dest)
 188                                 /* sibling call to another file */
 189                                 return false;
 190
 191                         /* local sibling call */
 192                         if (recursion == 5) {
 193                                 /*
 194                                  * Infinite recursion: two functions have
 195                                  * sibling calls to each other.  This is a very
 196                                  * rare case.  It means they aren't dead ends.
 197                                  */
 198                                 return false;
 199                         }
 200
 201                         return __dead_end_function(file, dest->func, recursion+1);
 202                 }
 203         }
 204
 205         return true;
 206 }
 207
 208 static bool dead_end_function(struct objtool_file *file, struct symbol *func)
 209 {
 210         return __dead_end_function(file, func, 0);
 211 }
 212
 213 static void clear_insn_state(struct insn_state *state)
 214 {
 215         int i;
 216
 217         memset(state, 0, sizeof(*state));
 218         state->cfa.base = CFI_UNDEFINED;
 219         for (i = 0; i < CFI_NUM_REGS; i++) {
 220                 state->regs[i].base = CFI_UNDEFINED;
 221                 state->vals[i].base = CFI_UNDEFINED;
 222         }
 223         state->drap_reg = CFI_UNDEFINED;
 224         state->drap_offset = -1;
 225 }
 226
 227 /*
 228  * Call the arch-specific instruction decoder for all the instructions and add
 229  * them to the global instruction list.
 230  */
 231 static int decode_instructions(struct objtool_file *file)
 232 {
 233         struct section *sec;
 234         struct symbol *func;
 235         unsigned long offset;
 236         struct instruction *insn;
 237         int ret;
 238
 239         for_each_sec(file, sec) {
 240
 241                 if (!(sec->sh.sh_flags & SHF_EXECINSTR))
 242                         continue;
 243
 244                 if (strcmp(sec->name, ".altinstr_replacement") &&
 245                     strcmp(sec->name, ".altinstr_aux") &&
 246                     strncmp(sec->name, ".discard.", 9))
 247                         sec->text = true;
 248
 249                 for (offset = 0; offset < sec->len; offset += insn->len) {
 250                         insn = malloc(sizeof(*insn));
 251                         if (!insn) {
 252                                 WARN("malloc failed");
 253                                 return -1;
 254                         }
 255                         memset(insn, 0, sizeof(*insn));
 256                         INIT_LIST_HEAD(&insn->alts);
 257                         clear_insn_state(&insn->state);
 258
 259                         insn->sec = sec;
 260                         insn->offset = offset;
 261
 262                         ret = arch_decode_instruction(file->elf, sec, offset,
 263                                                       sec->len - offset,
 264                                                       &insn->len, &insn->type,
 265                                                       &insn->immediate,
 266                                                       &insn->stack_op);
 267                         if (ret)
 268                                 goto err;
 269
 270                         hash_add(file->insn_hash, &insn->hash, insn->offset);
 271                         list_add_tail(&insn->list, &file->insn_list);
 272                 }
 273
 274                 list_for_each_entry(func, &sec->symbol_list, list) {
 275                         if (func->type != STT_FUNC || func->alias != func)
 276                                 continue;
 277
 278                         if (!find_insn(file, sec, func->offset)) {
 279                                 WARN("%s(): can't find starting instruction",
 280                                      func->name);
 281                                 return -1;
 282                         }
 283
 284                         func_for_each_insn(file, func, insn)
 285                                 insn->func = func;
 286                 }
 287         }
 288
 289         return 0;
 290
 291 err:
 292         free(insn);
 293         return ret;
 294 }
 295
 296 /*
 297  * Mark "ud2" instructions and manually annotated dead ends.
 298  */
 299 static int add_dead_ends(struct objtool_file *file)
 300 {
 301         struct section *sec;
 302         struct rela *rela;
 303         struct instruction *insn;
 304         bool found;
 305
 306         /*
 307          * By default, "ud2" is a dead end unless otherwise annotated, because
 308          * GCC 7 inserts it for certain divide-by-zero cases.
 309          */
 310         for_each_insn(file, insn)
 311                 if (insn->type == INSN_BUG)
 312                         insn->dead_end = true;
 313
 314         /*
 315          * Check for manually annotated dead ends.
 316          */
 317         sec = find_section_by_name(file->elf, ".rela.discard.unreachable");
 318         if (!sec)
 319                 goto reachable;
 320
 321         list_for_each_entry(rela, &sec->rela_list, list) {
 322                 if (rela->sym->type != STT_SECTION) {
 323                         WARN("unexpected relocation symbol type in %s", sec->name);
 324                         return -1;
 325                 }
 326                 insn = find_insn(file, rela->sym->sec, rela->addend);
 327                 if (insn)
 328                         insn = list_prev_entry(insn, list);
 329                 else if (rela->addend == rela->sym->sec->len) {
 330                         found = false;
 331                         list_for_each_entry_reverse(insn, &file->insn_list, list) {
 332                                 if (insn->sec == rela->sym->sec) {
 333                                         found = true;
 334                                         break;
 335                                 }
 336                         }
 337
 338                         if (!found) {
 339                                 WARN("can't find unreachable insn at %s+0x%x",
 340                                      rela->sym->sec->name, rela->addend);
 341                                 return -1;
 342                         }
 343                 } else {
 344                         WARN("can't find unreachable insn at %s+0x%x",
 345                              rela->sym->sec->name, rela->addend);
 346                         return -1;
 347                 }
 348
 349                 insn->dead_end = true;
 350         }
 351
 352 reachable:
 353         /*
 354          * These manually annotated reachable checks are needed for GCC 4.4,
 355          * where the Linux unreachable() macro isn't supported.  In that case
 356          * GCC doesn't know the "ud2" is fatal, so it generates code as if it's
 357          * not a dead end.
 358          */
 359         sec = find_section_by_name(file->elf, ".rela.discard.reachable");
 360         if (!sec)
 361                 return 0;
 362
 363         list_for_each_entry(rela, &sec->rela_list, list) {
 364                 if (rela->sym->type != STT_SECTION) {
 365                         WARN("unexpected relocation symbol type in %s", sec->name);
 366                         return -1;
 367                 }
 368                 insn = find_insn(file, rela->sym->sec, rela->addend);
 369                 if (insn)
 370                         insn = list_prev_entry(insn, list);
 371                 else if (rela->addend == rela->sym->sec->len) {
 372                         found = false;
 373                         list_for_each_entry_reverse(insn, &file->insn_list, list) {
 374                                 if (insn->sec == rela->sym->sec) {
 375                                         found = true;
 376                                         break;
 377                                 }
 378                         }
 379
 380                         if (!found) {
 381                                 WARN("can't find reachable insn at %s+0x%x",
 382                                      rela->sym->sec->name, rela->addend);
 383                                 return -1;
 384                         }
 385                 } else {
 386                         WARN("can't find reachable insn at %s+0x%x",
 387                              rela->sym->sec->name, rela->addend);
 388                         return -1;
 389                 }
 390
 391                 insn->dead_end = false;
 392         }
 393
 394         return 0;
 395 }
 396
 397 /*
 398  * Warnings shouldn't be reported for ignored functions.
 399  */
 400 static void add_ignores(struct objtool_file *file)
 401 {
 402         struct instruction *insn;
 403         struct section *sec;
 404         struct symbol *func;
 405         struct rela *rela;
 406
 407         sec = find_section_by_name(file->elf, ".rela.discard.func_stack_frame_non_standard");
 408         if (!sec)
 409                 return;
 410
 411         list_for_each_entry(rela, &sec->rela_list, list) {
 412                 switch (rela->sym->type) {
 413                 case STT_FUNC:
 414                         func = rela->sym;
 415                         break;
 416
 417                 case STT_SECTION:
 418                         func = find_symbol_by_offset(rela->sym->sec, rela->addend);
 419                         if (!func || func->type != STT_FUNC)
 420                                 continue;
 421                         break;
 422
 423                 default:
 424                         WARN("unexpected relocation symbol type in %s: %d", sec->name, rela->sym->type);
 425                         continue;
 426                 }
 427
 428                 func_for_each_insn_all(file, func, insn)
 429                         insn->ignore = true;
 430         }
 431 }
 432
 433 /*
 434  * This is a whitelist of functions that is allowed to be called with AC set.
 435  * The list is meant to be minimal and only contains compiler instrumentation
 436  * ABI and a few functions used to implement *_{to,from}_user() functions.
 437  *
 438  * These functions must not directly change AC, but may PUSHF/POPF.
 439  */
 440 static const char *uaccess_safe_builtin[] = {
 441         /* KASAN */
 442         "kasan_report",
 443         "check_memory_region",
 444         /* KASAN out-of-line */
 445         "__asan_loadN_noabort",
 446         "__asan_load1_noabort",
 447         "__asan_load2_noabort",
 448         "__asan_load4_noabort",
 449         "__asan_load8_noabort",
 450         "__asan_load16_noabort",
 451         "__asan_storeN_noabort",
 452         "__asan_store1_noabort",
 453         "__asan_store2_noabort",
 454         "__asan_store4_noabort",
 455         "__asan_store8_noabort",
 456         "__asan_store16_noabort",
 457         /* KASAN in-line */
 458         "__asan_report_load_n_noabort",
 459         "__asan_report_load1_noabort",
 460         "__asan_report_load2_noabort",
 461         "__asan_report_load4_noabort",
 462         "__asan_report_load8_noabort",
 463         "__asan_report_load16_noabort",
 464         "__asan_report_store_n_noabort",
 465         "__asan_report_store1_noabort",
 466         "__asan_report_store2_noabort",
 467         "__asan_report_store4_noabort",
 468         "__asan_report_store8_noabort",
 469         "__asan_report_store16_noabort",
 470         /* KCSAN */
 471         "kcsan_found_watchpoint",
 472         "kcsan_setup_watchpoint",
 473         /* KCSAN/TSAN */
 474         "__tsan_func_entry",
 475         "__tsan_func_exit",
 476         "__tsan_read_range",
 477         "__tsan_write_range",
 478         "__tsan_read1",
 479         "__tsan_read2",
 480         "__tsan_read4",
 481         "__tsan_read8",
 482         "__tsan_read16",
 483         "__tsan_write1",
 484         "__tsan_write2",
 485         "__tsan_write4",
 486         "__tsan_write8",
 487         "__tsan_write16",
 488         /* KCOV */
 489         "write_comp_data",
 490         "__sanitizer_cov_trace_pc",
 491         "__sanitizer_cov_trace_const_cmp1",
 492         "__sanitizer_cov_trace_const_cmp2",
 493         "__sanitizer_cov_trace_const_cmp4",
 494         "__sanitizer_cov_trace_const_cmp8",
 495         "__sanitizer_cov_trace_cmp1",
 496         "__sanitizer_cov_trace_cmp2",
 497         "__sanitizer_cov_trace_cmp4",
 498         "__sanitizer_cov_trace_cmp8",
 499         /* UBSAN */
 500         "ubsan_type_mismatch_common",
 501         "__ubsan_handle_type_mismatch",
 502         "__ubsan_handle_type_mismatch_v1",
 503         "__ubsan_handle_shift_out_of_bounds",
 504         /* misc */
 505         "csum_partial_copy_generic",
 506         "__memcpy_mcsafe",
 507         "mcsafe_handle_tail",
 508         "ftrace_likely_update", /* CONFIG_TRACE_BRANCH_PROFILING */
 509         NULL
 510 };
 511
 512 static void add_uaccess_safe(struct objtool_file *file)
 513 {
 514         struct symbol *func;
 515         const char **name;
 516
 517         if (!uaccess)
 518                 return;
 519
 520         for (name = uaccess_safe_builtin; *name; name++) {
 521                 func = find_symbol_by_name(file->elf, *name);
 522                 if (!func)
 523                         continue;
 524
 525                 func->uaccess_safe = true;
 526         }
 527 }
 528
 529 /*
 530  * FIXME: For now, just ignore any alternatives which add retpolines.  This is
 531  * a temporary hack, as it doesn't allow ORC to unwind from inside a retpoline.
 532  * But it at least allows objtool to understand the control flow *around* the
 533  * retpoline.
 534  */
 535 static int add_ignore_alternatives(struct objtool_file *file)
 536 {
 537         struct section *sec;
 538         struct rela *rela;
 539         struct instruction *insn;
 540
 541         sec = find_section_by_name(file->elf, ".rela.discard.ignore_alts");
 542         if (!sec)
 543                 return 0;
 544
 545         list_for_each_entry(rela, &sec->rela_list, list) {
 546                 if (rela->sym->type != STT_SECTION) {
 547                         WARN("unexpected relocation symbol type in %s", sec->name);
 548                         return -1;
 549                 }
 550
 551                 insn = find_insn(file, rela->sym->sec, rela->addend);
 552                 if (!insn) {
 553                         WARN("bad .discard.ignore_alts entry");
 554                         return -1;
 555                 }
 556
 557                 insn->ignore_alts = true;
 558         }
 559
 560         return 0;
 561 }
 562
 563 /*
 564  * Find the destination instructions for all jumps.
 565  */
 566 static int add_jump_destinations(struct objtool_file *file)
 567 {
 568         struct instruction *insn;
 569         struct rela *rela;
 570         struct section *dest_sec;
 571         unsigned long dest_off;
 572
 573         for_each_insn(file, insn) {
 574                 if (insn->type != INSN_JUMP_CONDITIONAL &&
 575                     insn->type != INSN_JUMP_UNCONDITIONAL)
 576                         continue;
 577
 578                 if (insn->ignore || insn->offset == FAKE_JUMP_OFFSET)
 579                         continue;
 580
 581                 rela = find_rela_by_dest_range(insn->sec, insn->offset,
 582                                                insn->len);
 583                 if (!rela) {
 584                         dest_sec = insn->sec;
 585                         dest_off = insn->offset + insn->len + insn->immediate;
 586                 } else if (rela->sym->type == STT_SECTION) {
 587                         dest_sec = rela->sym->sec;
 588                         dest_off = rela->addend + 4;
 589                 } else if (rela->sym->sec->idx) {
 590                         dest_sec = rela->sym->sec;
 591                         dest_off = rela->sym->sym.st_value + rela->addend + 4;
 592                 } else if (strstr(rela->sym->name, "_indirect_thunk_")) {
 593                         /*
 594                          * Retpoline jumps are really dynamic jumps in
 595                          * disguise, so convert them accordingly.
 596                          */
 597                         if (insn->type == INSN_JUMP_UNCONDITIONAL)
 598                                 insn->type = INSN_JUMP_DYNAMIC;
 599                         else
 600                                 insn->type = INSN_JUMP_DYNAMIC_CONDITIONAL;
 601
 602                         insn->retpoline_safe = true;
 603                         continue;
 604                 } else {
 605                         /* external sibling call */
 606                         insn->call_dest = rela->sym;
 607                         continue;
 608                 }
 609
 610                 insn->jump_dest = find_insn(file, dest_sec, dest_off);
 611                 if (!insn->jump_dest) {
 612
 613                         /*
 614                          * This is a special case where an alt instruction
 615                          * jumps past the end of the section.  These are
 616                          * handled later in handle_group_alt().
 617                          */
 618                         if (!strcmp(insn->sec->name, ".altinstr_replacement"))
 619                                 continue;
 620
 621                         WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
 622                                   insn->sec, insn->offset, dest_sec->name,
 623                                   dest_off);
 624                         return -1;
 625                 }
 626
 627                 /*
 628                  * Cross-function jump.
 629                  */
 630                 if (insn->func && insn->jump_dest->func &&
 631                     insn->func != insn->jump_dest->func) {
 632
 633                         /*
 634                          * For GCC 8+, create parent/child links for any cold
 635                          * subfunctions.  This is _mostly_ redundant with a
 636                          * similar initialization in read_symbols().
 637                          *
 638                          * If a function has aliases, we want the *first* such
 639                          * function in the symbol table to be the subfunction's
 640                          * parent.  In that case we overwrite the
 641                          * initialization done in read_symbols().
 642                          *
 643                          * However this code can't completely replace the
 644                          * read_symbols() code because this doesn't detect the
 645                          * case where the parent function's only reference to a
 646                          * subfunction is through a jump table.
 647                          */
 648                         if (!strstr(insn->func->name, ".cold.") &&
 649                             strstr(insn->jump_dest->func->name, ".cold.")) {
 650                                 insn->func->cfunc = insn->jump_dest->func;
 651                                 insn->jump_dest->func->pfunc = insn->func;
 652
 653                         } else if (insn->jump_dest->func->pfunc != insn->func->pfunc &&
 654                                    insn->jump_dest->offset == insn->jump_dest->func->offset) {
 655
 656                                 /* internal sibling call */
 657                                 insn->call_dest = insn->jump_dest->func;
 658                         }
 659                 }
 660         }
 661
 662         return 0;
 663 }
 664
 665 /*
 666  * Find the destination instructions for all calls.
 667  */
 668 static int add_call_destinations(struct objtool_file *file)
 669 {
 670         struct instruction *insn;
 671         unsigned long dest_off;
 672         struct rela *rela;
 673
 674         for_each_insn(file, insn) {
 675                 if (insn->type != INSN_CALL)
 676                         continue;
 677
 678                 rela = find_rela_by_dest_range(insn->sec, insn->offset,
 679                                                insn->len);
 680                 if (!rela) {
 681                         dest_off = insn->offset + insn->len + insn->immediate;
 682                         insn->call_dest = find_symbol_by_offset(insn->sec,
 683                                                                 dest_off);
 684
 685                         if (!insn->call_dest && !insn->ignore) {
 686                                 WARN_FUNC("unsupported intra-function call",
 687                                           insn->sec, insn->offset);
 688                                 if (retpoline)
 689                                         WARN("If this is a retpoline, please patch it in with alternatives and annotate it with ANNOTATE_NOSPEC_ALTERNATIVE.");
 690                                 return -1;
 691                         }
 692
 693                 } else if (rela->sym->type == STT_SECTION) {
 694                         insn->call_dest = find_symbol_by_offset(rela->sym->sec,
 695                                                                 rela->addend+4);
 696                         if (!insn->call_dest ||
 697                             insn->call_dest->type != STT_FUNC) {
 698                                 WARN_FUNC("can't find call dest symbol at %s+0x%x",
 699                                           insn->sec, insn->offset,
 700                                           rela->sym->sec->name,
 701                                           rela->addend + 4);
 702                                 return -1;
 703                         }
 704                 } else
 705                         insn->call_dest = rela->sym;
 706         }
 707
 708         return 0;
 709 }
 710
 711 /*
 712  * The .alternatives section requires some extra special care, over and above
 713  * what other special sections require:
 714  *
 715  * 1. Because alternatives are patched in-place, we need to insert a fake jump
 716  *    instruction at the end so that validate_branch() skips all the original
 717  *    replaced instructions when validating the new instruction path.
 718  *
 719  * 2. An added wrinkle is that the new instruction length might be zero.  In
 720  *    that case the old instructions are replaced with noops.  We simulate that
 721  *    by creating a fake jump as the only new instruction.
 722  *
 723  * 3. In some cases, the alternative section includes an instruction which
 724  *    conditionally jumps to the _end_ of the entry.  We have to modify these
 725  *    jumps' destinations to point back to .text rather than the end of the
 726  *    entry in .altinstr_replacement.
 727  */
 728 static int handle_group_alt(struct objtool_file *file,
 729                             struct special_alt *special_alt,
 730                             struct instruction *orig_insn,
 731                             struct instruction **new_insn)
 732 {
 733         struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump = NULL;
 734         unsigned long dest_off;
 735
 736         last_orig_insn = NULL;
 737         insn = orig_insn;
 738         sec_for_each_insn_from(file, insn) {
 739                 if (insn->offset >= special_alt->orig_off + special_alt->orig_len)
 740                         break;
 741
 742                 insn->alt_group = true;
 743                 last_orig_insn = insn;
 744         }
 745
 746         if (next_insn_same_sec(file, last_orig_insn)) {
 747                 fake_jump = malloc(sizeof(*fake_jump));
 748                 if (!fake_jump) {
 749                         WARN("malloc failed");
 750                         return -1;
 751                 }
 752                 memset(fake_jump, 0, sizeof(*fake_jump));
 753                 INIT_LIST_HEAD(&fake_jump->alts);
 754                 clear_insn_state(&fake_jump->state);
 755
 756                 fake_jump->sec = special_alt->new_sec;
 757                 fake_jump->offset = FAKE_JUMP_OFFSET;
 758                 fake_jump->type = INSN_JUMP_UNCONDITIONAL;
 759                 fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
 760                 fake_jump->func = orig_insn->func;
 761         }
 762
 763         if (!special_alt->new_len) {
 764                 if (!fake_jump) {
 765                         WARN("%s: empty alternative at end of section",
 766                              special_alt->orig_sec->name);
 767                         return -1;
 768                 }
 769
 770                 *new_insn = fake_jump;
 771                 return 0;
 772         }
 773
 774         last_new_insn = NULL;
 775         insn = *new_insn;
 776         sec_for_each_insn_from(file, insn) {
 777                 if (insn->offset >= special_alt->new_off + special_alt->new_len)
 778                         break;
 779
 780                 last_new_insn = insn;
 781
 782                 insn->ignore = orig_insn->ignore_alts;
 783                 insn->func = orig_insn->func;
 784
 785                 if (insn->type != INSN_JUMP_CONDITIONAL &&
 786                     insn->type != INSN_JUMP_UNCONDITIONAL)
 787                         continue;
 788
 789                 if (!insn->immediate)
 790                         continue;
 791
 792                 dest_off = insn->offset + insn->len + insn->immediate;
 793                 if (dest_off == special_alt->new_off + special_alt->new_len) {
 794                         if (!fake_jump) {
 795                                 WARN("%s: alternative jump to end of section",
 796                                      special_alt->orig_sec->name);
 797                                 return -1;
 798                         }
 799                         insn->jump_dest = fake_jump;
 800                 }
 801
 802                 if (!insn->jump_dest) {
 803                         WARN_FUNC("can't find alternative jump destination",
 804                                   insn->sec, insn->offset);
 805                         return -1;
 806                 }
 807         }
 808
 809         if (!last_new_insn) {
 810                 WARN_FUNC("can't find last new alternative instruction",
 811                           special_alt->new_sec, special_alt->new_off);
 812                 return -1;
 813         }
 814
 815         if (fake_jump)
 816                 list_add(&fake_jump->list, &last_new_insn->list);
 817
 818         return 0;
 819 }
 820
 821 /*
 822  * A jump table entry can either convert a nop to a jump or a jump to a nop.
 823  * If the original instruction is a jump, make the alt entry an effective nop
 824  * by just skipping the original instruction.
 825  */
 826 static int handle_jump_alt(struct objtool_file *file,
 827                            struct special_alt *special_alt,
 828                            struct instruction *orig_insn,
 829                            struct instruction **new_insn)
 830 {
 831         if (orig_insn->type == INSN_NOP)
 832                 return 0;
 833
 834         if (orig_insn->type != INSN_JUMP_UNCONDITIONAL) {
 835                 WARN_FUNC("unsupported instruction at jump label",
 836                           orig_insn->sec, orig_insn->offset);
 837                 return -1;
 838         }
 839
 840         *new_insn = list_next_entry(orig_insn, list);
 841         return 0;
 842 }
 843
 844 /*
 845  * Read all the special sections which have alternate instructions which can be
 846  * patched in or redirected to at runtime.  Each instruction having alternate
 847  * instruction(s) has them added to its insn->alts list, which will be
 848  * traversed in validate_branch().
 849  */
 850 static int add_special_section_alts(struct objtool_file *file)
 851 {
 852         struct list_head special_alts;
 853         struct instruction *orig_insn, *new_insn;
 854         struct special_alt *special_alt, *tmp;
 855         struct alternative *alt;
 856         int ret;
 857
 858         ret = special_get_alts(file->elf, &special_alts);
 859         if (ret)
 860                 return ret;
 861
 862         list_for_each_entry_safe(special_alt, tmp, &special_alts, list) {
 863
 864                 orig_insn = find_insn(file, special_alt->orig_sec,
 865                                       special_alt->orig_off);
 866                 if (!orig_insn) {
 867                         WARN_FUNC("special: can't find orig instruction",
 868                                   special_alt->orig_sec, special_alt->orig_off);
 869                         ret = -1;
 870                         goto out;
 871                 }
 872
 873                 new_insn = NULL;
 874                 if (!special_alt->group || special_alt->new_len) {
 875                         new_insn = find_insn(file, special_alt->new_sec,
 876                                              special_alt->new_off);
 877                         if (!new_insn) {
 878                                 WARN_FUNC("special: can't find new instruction",
 879                                           special_alt->new_sec,
 880                                           special_alt->new_off);
 881                                 ret = -1;
 882                                 goto out;
 883                         }
 884                 }
 885
 886                 if (special_alt->group) {
 887                         ret = handle_group_alt(file, special_alt, orig_insn,
 888                                                &new_insn);
 889                         if (ret)
 890                                 goto out;
 891                 } else if (special_alt->jump_or_nop) {
 892                         ret = handle_jump_alt(file, special_alt, orig_insn,
 893                                               &new_insn);
 894                         if (ret)
 895                                 goto out;
 896                 }
 897
 898                 alt = malloc(sizeof(*alt));
 899                 if (!alt) {
 900                         WARN("malloc failed");
 901                         ret = -1;
 902                         goto out;
 903                 }
 904
 905                 alt->insn = new_insn;
 906                 alt->skip_orig = special_alt->skip_orig;
 907                 orig_insn->ignore_alts |= special_alt->skip_alt;
 908                 list_add_tail(&alt->list, &orig_insn->alts);
 909
 910                 list_del(&special_alt->list);
 911                 free(special_alt);
 912         }
 913
 914 out:
 915         return ret;
 916 }
 917
 918 static int add_jump_table(struct objtool_file *file, struct instruction *insn,
 919                             struct rela *table)
 920 {
 921         struct rela *rela = table;
 922         struct instruction *dest_insn;
 923         struct alternative *alt;
 924         struct symbol *pfunc = insn->func->pfunc;
 925         unsigned int prev_offset = 0;
 926
 927         /*
 928          * Each @rela is a switch table relocation which points to the target
 929          * instruction.
 930          */
 931         list_for_each_entry_from(rela, &table->sec->rela_list, list) {
 932
 933                 /* Check for the end of the table: */
 934                 if (rela != table && rela->jump_table_start)
 935                         break;
 936
 937                 /* Make sure the table entries are consecutive: */
 938                 if (prev_offset && rela->offset != prev_offset + 8)
 939                         break;
 940
 941                 /* Detect function pointers from contiguous objects: */
 942                 if (rela->sym->sec == pfunc->sec &&
 943                     rela->addend == pfunc->offset)
 944                         break;
 945
 946                 dest_insn = find_insn(file, rela->sym->sec, rela->addend);
 947                 if (!dest_insn)
 948                         break;
 949
 950                 /* Make sure the destination is in the same function: */
 951                 if (!dest_insn->func || dest_insn->func->pfunc != pfunc)
 952                         break;
 953
 954                 alt = malloc(sizeof(*alt));
 955                 if (!alt) {
 956                         WARN("malloc failed");
 957                         return -1;
 958                 }
 959
 960                 alt->insn = dest_insn;
 961                 list_add_tail(&alt->list, &insn->alts);
 962                 prev_offset = rela->offset;
 963         }
 964
 965         if (!prev_offset) {
 966                 WARN_FUNC("can't find switch jump table",
 967                           insn->sec, insn->offset);
 968                 return -1;
 969         }
 970
 971         return 0;
 972 }
 973
 974 /*
 975  * find_jump_table() - Given a dynamic jump, find the switch jump table in
 976  * .rodata associated with it.
 977  *
 978  * There are 3 basic patterns:
 979  *
 980  * 1. jmpq *[rodata addr](,%reg,8)
 981  *
 982  *    This is the most common case by far.  It jumps to an address in a simple
 983  *    jump table which is stored in .rodata.
 984  *
 985  * 2. jmpq *[rodata addr](%rip)
 986  *
 987  *    This is caused by a rare GCC quirk, currently only seen in three driver
 988  *    functions in the kernel, only with certain obscure non-distro configs.
 989  *
 990  *    As part of an optimization, GCC makes a copy of an existing switch jump
 991  *    table, modifies it, and then hard-codes the jump (albeit with an indirect
 992  *    jump) to use a single entry in the table.  The rest of the jump table and
 993  *    some of its jump targets remain as dead code.
 994  *
 995  *    In such a case we can just crudely ignore all unreachable instruction
 996  *    warnings for the entire object file.  Ideally we would just ignore them
 997  *    for the function, but that would require redesigning the code quite a
 998  *    bit.  And honestly that's just not worth doing: unreachable instruction
 999  *    warnings are of questionable value anyway, and this is such a rare issue.
1000  *
1001  * 3. mov [rodata addr],%reg1
1002  *    ... some instructions ...
1003  *    jmpq *(%reg1,%reg2,8)
1004  *
1005  *    This is a fairly uncommon pattern which is new for GCC 6.  As of this
1006  *    writing, there are 11 occurrences of it in the allmodconfig kernel.
1007  *
1008  *    As of GCC 7 there are quite a few more of these and the 'in between' code
1009  *    is significant. Esp. with KASAN enabled some of the code between the mov
1010  *    and jmpq uses .rodata itself, which can confuse things.
1011  *
1012  *    TODO: Once we have DWARF CFI and smarter instruction decoding logic,
1013  *    ensure the same register is used in the mov and jump instructions.
1014  *
1015  *    NOTE: RETPOLINE made it harder still to decode dynamic jumps.
1016  */
1017 static struct rela *find_jump_table(struct objtool_file *file,
1018                                       struct symbol *func,
1019                                       struct instruction *insn)
1020 {
1021         struct rela *text_rela, *table_rela;
1022         struct instruction *orig_insn = insn;
1023         struct section *table_sec;
1024         unsigned long table_offset;
1025
1026         /*
1027          * Backward search using the @first_jump_src links, these help avoid
1028          * much of the 'in between' code. Which avoids us getting confused by
1029          * it.
1030          */
1031         for (;
1032              &insn->list != &file->insn_list &&
1033              insn->sec == func->sec &&
1034              insn->offset >= func->offset;
1035
1036              insn = insn->first_jump_src ?: list_prev_entry(insn, list)) {
1037
1038                 if (insn != orig_insn && insn->type == INSN_JUMP_DYNAMIC)
1039                         break;
1040
1041                 /* allow small jumps within the range */
1042                 if (insn->type == INSN_JUMP_UNCONDITIONAL &&
1043                     insn->jump_dest &&
1044                     (insn->jump_dest->offset <= insn->offset ||
1045                      insn->jump_dest->offset > orig_insn->offset))
1046                     break;
1047
1048                 /* look for a relocation which references .rodata */
1049                 text_rela = find_rela_by_dest_range(insn->sec, insn->offset,
1050                                                     insn->len);
1051                 if (!text_rela || text_rela->sym->type != STT_SECTION ||
1052                     !text_rela->sym->sec->rodata)
1053                         continue;
1054
1055                 table_offset = text_rela->addend;
1056                 table_sec = text_rela->sym->sec;
1057
1058                 if (text_rela->type == R_X86_64_PC32)
1059                         table_offset += 4;
1060
1061                 /*
1062                  * Make sure the .rodata address isn't associated with a
1063                  * symbol.  GCC jump tables are anonymous data.
1064                  *
1065                  * Also support C jump tables which are in the same format as
1066                  * switch jump tables.  For objtool to recognize them, they
1067                  * need to be placed in the C_JUMP_TABLE_SECTION section.  They
1068                  * have symbols associated with them.
1069                  */
1070                 if (find_symbol_containing(table_sec, table_offset) &&
1071                     strcmp(table_sec->name, C_JUMP_TABLE_SECTION))
1072                         continue;
1073
1074                 /* Each table entry has a rela associated with it. */
1075                 table_rela = find_rela_by_dest(table_sec, table_offset);
1076                 if (!table_rela)
1077                         continue;
1078
1079                 /*
1080                  * Use of RIP-relative switch jumps is quite rare, and
1081                  * indicates a rare GCC quirk/bug which can leave dead code
1082                  * behind.
1083                  */
1084                 if (text_rela->type == R_X86_64_PC32)
1085                         file->ignore_unreachables = true;
1086
1087                 return table_rela;
1088         }
1089
1090         return NULL;
1091 }
1092
1093 /*
1094  * First pass: Mark the head of each jump table so that in the next pass,
1095  * we know when a given jump table ends and the next one starts.
1096  */
1097 static void mark_func_jump_tables(struct objtool_file *file,
1098                                     struct symbol *func)
1099 {
1100         struct instruction *insn, *last = NULL;
1101         struct rela *rela;
1102
1103         func_for_each_insn_all(file, func, insn) {
1104                 if (!last)
1105                         last = insn;
1106
1107                 /*
1108                  * Store back-pointers for unconditional forward jumps such
1109                  * that find_jump_table() can back-track using those and
1110                  * avoid some potentially confusing code.
1111                  */
1112                 if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest &&
1113                     insn->offset > last->offset &&
1114                     insn->jump_dest->offset > insn->offset &&
1115                     !insn->jump_dest->first_jump_src) {
1116
1117                         insn->jump_dest->first_jump_src = insn;
1118                         last = insn->jump_dest;
1119                 }
1120
1121                 if (insn->type != INSN_JUMP_DYNAMIC)
1122                         continue;
1123
1124                 rela = find_jump_table(file, func, insn);
1125                 if (rela) {
1126                         rela->jump_table_start = true;
1127                         insn->jump_table = rela;
1128                 }
1129         }
1130 }
1131
1132 static int add_func_jump_tables(struct objtool_file *file,
1133                                   struct symbol *func)
1134 {
1135         struct instruction *insn;
1136         int ret;
1137
1138         func_for_each_insn_all(file, func, insn) {
1139                 if (!insn->jump_table)
1140                         continue;
1141
1142                 ret = add_jump_table(file, insn, insn->jump_table);
1143                 if (ret)
1144                         return ret;
1145         }
1146
1147         return 0;
1148 }
1149
1150 /*
1151  * For some switch statements, gcc generates a jump table in the .rodata
1152  * section which contains a list of addresses within the function to jump to.
1153  * This finds these jump tables and adds them to the insn->alts lists.
1154  */
1155 static int add_jump_table_alts(struct objtool_file *file)
1156 {
1157         struct section *sec;
1158         struct symbol *func;
1159         int ret;
1160
1161         if (!file->rodata)
1162                 return 0;
1163
1164         for_each_sec(file, sec) {
1165                 list_for_each_entry(func, &sec->symbol_list, list) {
1166                         if (func->type != STT_FUNC)
1167                                 continue;
1168
1169                         mark_func_jump_tables(file, func);
1170                         ret = add_func_jump_tables(file, func);
1171                         if (ret)
1172                                 return ret;
1173                 }
1174         }
1175
1176         return 0;
1177 }
1178
1179 static int read_unwind_hints(struct objtool_file *file)
1180 {
1181         struct section *sec, *relasec;
1182         struct rela *rela;
1183         struct unwind_hint *hint;
1184         struct instruction *insn;
1185         struct cfi_reg *cfa;
1186         int i;
1187
1188         sec = find_section_by_name(file->elf, ".discard.unwind_hints");
1189         if (!sec)
1190                 return 0;
1191
1192         relasec = sec->rela;
1193         if (!relasec) {
1194                 WARN("missing .rela.discard.unwind_hints section");
1195                 return -1;
1196         }
1197
1198         if (sec->len % sizeof(struct unwind_hint)) {
1199                 WARN("struct unwind_hint size mismatch");
1200                 return -1;
1201         }
1202
1203         file->hints = true;
1204
1205         for (i = 0; i < sec->len / sizeof(struct unwind_hint); i++) {
1206                 hint = (struct unwind_hint *)sec->data->d_buf + i;
1207
1208                 rela = find_rela_by_dest(sec, i * sizeof(*hint));
1209                 if (!rela) {
1210                         WARN("can't find rela for unwind_hints[%d]", i);
1211                         return -1;
1212                 }
1213
1214                 insn = find_insn(file, rela->sym->sec, rela->addend);
1215                 if (!insn) {
1216                         WARN("can't find insn for unwind_hints[%d]", i);
1217                         return -1;
1218                 }
1219
1220                 cfa = &insn->state.cfa;
1221
1222                 if (hint->type == UNWIND_HINT_TYPE_SAVE) {
1223                         insn->save = true;
1224                         continue;
1225
1226                 } else if (hint->type == UNWIND_HINT_TYPE_RESTORE) {
1227                         insn->restore = true;
1228                         insn->hint = true;
1229                         continue;
1230                 }
1231
1232                 insn->hint = true;
1233
1234                 switch (hint->sp_reg) {
1235                 case ORC_REG_UNDEFINED:
1236                         cfa->base = CFI_UNDEFINED;
1237                         break;
1238                 case ORC_REG_SP:
1239                         cfa->base = CFI_SP;
1240                         break;
1241                 case ORC_REG_BP:
1242                         cfa->base = CFI_BP;
1243                         break;
1244                 case ORC_REG_SP_INDIRECT:
1245                         cfa->base = CFI_SP_INDIRECT;
1246                         break;
1247                 case ORC_REG_R10:
1248                         cfa->base = CFI_R10;
1249                         break;
1250                 case ORC_REG_R13:
1251                         cfa->base = CFI_R13;
1252                         break;
1253                 case ORC_REG_DI:
1254                         cfa->base = CFI_DI;
1255                         break;
1256                 case ORC_REG_DX:
1257                         cfa->base = CFI_DX;
1258                         break;
1259                 default:
1260                         WARN_FUNC("unsupported unwind_hint sp base reg %d",
1261                                   insn->sec, insn->offset, hint->sp_reg);
1262                         return -1;
1263                 }
1264
1265                 cfa->offset = hint->sp_offset;
1266                 insn->state.type = hint->type;
1267                 insn->state.end = hint->end;
1268         }
1269
1270         return 0;
1271 }
1272
1273 static int read_retpoline_hints(struct objtool_file *file)
1274 {
1275         struct section *sec;
1276         struct instruction *insn;
1277         struct rela *rela;
1278
1279         sec = find_section_by_name(file->elf, ".rela.discard.retpoline_safe");
1280         if (!sec)
1281                 return 0;
1282
1283         list_for_each_entry(rela, &sec->rela_list, list) {
1284                 if (rela->sym->type != STT_SECTION) {
1285                         WARN("unexpected relocation symbol type in %s", sec->name);
1286                         return -1;
1287                 }
1288
1289                 insn = find_insn(file, rela->sym->sec, rela->addend);
1290                 if (!insn) {
1291                         WARN("bad .discard.retpoline_safe entry");
1292                         return -1;
1293                 }
1294
1295                 if (insn->type != INSN_JUMP_DYNAMIC &&
1296                     insn->type != INSN_CALL_DYNAMIC) {
1297                         WARN_FUNC("retpoline_safe hint not an indirect jump/call",
1298                                   insn->sec, insn->offset);
1299                         return -1;
1300                 }
1301
1302                 insn->retpoline_safe = true;
1303         }
1304
1305         return 0;
1306 }
1307
1308 static void mark_rodata(struct objtool_file *file)
1309 {
1310         struct section *sec;
1311         bool found = false;
1312
1313         /*
1314          * Search for the following rodata sections, each of which can
1315          * potentially contain jump tables:
1316          *
1317          * - .rodata: can contain GCC switch tables
1318          * - .rodata.<func>: same, if -fdata-sections is being used
1319          * - .rodata..c_jump_table: contains C annotated jump tables
1320          *
1321          * .rodata.str1.* sections are ignored; they don't contain jump tables.
1322          */
1323         for_each_sec(file, sec) {
1324                 if ((!strncmp(sec->name, ".rodata", 7) && !strstr(sec->name, ".str1.")) ||
1325                     !strcmp(sec->name, C_JUMP_TABLE_SECTION)) {
1326                         sec->rodata = true;
1327                         found = true;
1328                 }
1329         }
1330
1331         file->rodata = found;
1332 }
1333
1334 static int decode_sections(struct objtool_file *file)
1335 {
1336         int ret;
1337
1338         mark_rodata(file);
1339
1340         ret = decode_instructions(file);
1341         if (ret)
1342                 return ret;
1343
1344         ret = add_dead_ends(file);
1345         if (ret)
1346                 return ret;
1347
1348         add_ignores(file);
1349         add_uaccess_safe(file);
1350
1351         ret = add_ignore_alternatives(file);
1352         if (ret)
1353                 return ret;
1354
1355         ret = add_jump_destinations(file);
1356         if (ret)
1357                 return ret;
1358
1359         ret = add_special_section_alts(file);
1360         if (ret)
1361                 return ret;
1362
1363         ret = add_call_destinations(file);
1364         if (ret)
1365                 return ret;
1366
1367         ret = add_jump_table_alts(file);
1368         if (ret)
1369                 return ret;
1370
1371         ret = read_unwind_hints(file);
1372         if (ret)
1373                 return ret;
1374
1375         ret = read_retpoline_hints(file);
1376         if (ret)
1377                 return ret;
1378
1379         return 0;
1380 }
1381
1382 static bool is_fentry_call(struct instruction *insn)
1383 {
1384         if (insn->type == INSN_CALL &&
1385             insn->call_dest->type == STT_NOTYPE &&
1386             !strcmp(insn->call_dest->name, "__fentry__"))
1387                 return true;
1388
1389         return false;
1390 }
1391
1392 static bool has_modified_stack_frame(struct insn_state *state)
1393 {
1394         int i;
1395
1396         if (state->cfa.base != initial_func_cfi.cfa.base ||
1397             state->cfa.offset != initial_func_cfi.cfa.offset ||
1398             state->stack_size != initial_func_cfi.cfa.offset ||
1399             state->drap)
1400                 return true;
1401
1402         for (i = 0; i < CFI_NUM_REGS; i++)
1403                 if (state->regs[i].base != initial_func_cfi.regs[i].base ||
1404                     state->regs[i].offset != initial_func_cfi.regs[i].offset)
1405                         return true;
1406
1407         return false;
1408 }
1409
1410 static bool has_valid_stack_frame(struct insn_state *state)
1411 {
1412         if (state->cfa.base == CFI_BP && state->regs[CFI_BP].base == CFI_CFA &&
1413             state->regs[CFI_BP].offset == -16)
1414                 return true;
1415
1416         if (state->drap && state->regs[CFI_BP].base == CFI_BP)
1417                 return true;
1418
1419         return false;
1420 }
1421
1422 static int update_insn_state_regs(struct instruction *insn, struct insn_state *state)
1423 {
1424         struct cfi_reg *cfa = &state->cfa;
1425         struct stack_op *op = &insn->stack_op;
1426
1427         if (cfa->base != CFI_SP)
1428                 return 0;
1429
1430         /* push */
1431         if (op->dest.type == OP_DEST_PUSH || op->dest.type == OP_DEST_PUSHF)
1432                 cfa->offset += 8;
1433
1434         /* pop */
1435         if (op->src.type == OP_SRC_POP || op->src.type == OP_SRC_POPF)
1436                 cfa->offset -= 8;
1437
1438         /* add immediate to sp */
1439         if (op->dest.type == OP_DEST_REG && op->src.type == OP_SRC_ADD &&
1440             op->dest.reg == CFI_SP && op->src.reg == CFI_SP)
1441                 cfa->offset -= op->src.offset;
1442
1443         return 0;
1444 }
1445
1446 static void save_reg(struct insn_state *state, unsigned char reg, int base,
1447                      int offset)
1448 {
1449         if (arch_callee_saved_reg(reg) &&
1450             state->regs[reg].base == CFI_UNDEFINED) {
1451                 state->regs[reg].base = base;
1452                 state->regs[reg].offset = offset;
1453         }
1454 }
1455
1456 static void restore_reg(struct insn_state *state, unsigned char reg)
1457 {
1458         state->regs[reg].base = CFI_UNDEFINED;
1459         state->regs[reg].offset = 0;
1460 }
1461
1462 /*
1463  * A note about DRAP stack alignment:
1464  *
1465  * GCC has the concept of a DRAP register, which is used to help keep track of
1466  * the stack pointer when aligning the stack.  r10 or r13 is used as the DRAP
1467  * register.  The typical DRAP pattern is:
1468  *
1469  *   4c 8d 54 24 08             lea    0x8(%rsp),%r10
1470  *   48 83 e4 c0                and    $0xffffffffffffffc0,%rsp
1471  *   41 ff 72 f8                pushq  -0x8(%r10)
1472  *   55                         push   %rbp
1473  *   48 89 e5                   mov    %rsp,%rbp
1474  *                              (more pushes)
1475  *   41 52                      push   %r10
1476  *                              ...
1477  *   41 5a                      pop    %r10
1478  *                              (more pops)
1479  *   5d                         pop    %rbp
1480  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1481  *   c3                         retq
1482  *
1483  * There are some variations in the epilogues, like:
1484  *
1485  *   5b                         pop    %rbx
1486  *   41 5a                      pop    %r10
1487  *   41 5c                      pop    %r12
1488  *   41 5d                      pop    %r13
1489  *   41 5e                      pop    %r14
1490  *   c9                         leaveq
1491  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1492  *   c3                         retq
1493  *
1494  * and:
1495  *
1496  *   4c 8b 55 e8                mov    -0x18(%rbp),%r10
1497  *   48 8b 5d e0                mov    -0x20(%rbp),%rbx
1498  *   4c 8b 65 f0                mov    -0x10(%rbp),%r12
1499  *   4c 8b 6d f8                mov    -0x8(%rbp),%r13
1500  *   c9                         leaveq
1501  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1502  *   c3                         retq
1503  *
1504  * Sometimes r13 is used as the DRAP register, in which case it's saved and
1505  * restored beforehand:
1506  *
1507  *   41 55                      push   %r13
1508  *   4c 8d 6c 24 10             lea    0x10(%rsp),%r13
1509  *   48 83 e4 f0                and    $0xfffffffffffffff0,%rsp
1510  *                              ...
1511  *   49 8d 65 f0                lea    -0x10(%r13),%rsp
1512  *   41 5d                      pop    %r13
1513  *   c3                         retq
1514  */
1515 static int update_insn_state(struct instruction *insn, struct insn_state *state)
1516 {
1517         struct stack_op *op = &insn->stack_op;
1518         struct cfi_reg *cfa = &state->cfa;
1519         struct cfi_reg *regs = state->regs;
1520
1521         /* stack operations don't make sense with an undefined CFA */
1522         if (cfa->base == CFI_UNDEFINED) {
1523                 if (insn->func) {
1524                         WARN_FUNC("undefined stack state", insn->sec, insn->offset);
1525                         return -1;
1526                 }
1527                 return 0;
1528         }
1529
1530         if (state->type == ORC_TYPE_REGS || state->type == ORC_TYPE_REGS_IRET)
1531                 return update_insn_state_regs(insn, state);
1532
1533         switch (op->dest.type) {
1534
1535         case OP_DEST_REG:
1536                 switch (op->src.type) {
1537
1538                 case OP_SRC_REG:
1539                         if (op->src.reg == CFI_SP && op->dest.reg == CFI_BP &&
1540                             cfa->base == CFI_SP &&
1541                             regs[CFI_BP].base == CFI_CFA &&
1542                             regs[CFI_BP].offset == -cfa->offset) {
1543
1544                                 /* mov %rsp, %rbp */
1545                                 cfa->base = op->dest.reg;
1546                                 state->bp_scratch = false;
1547                         }
1548
1549                         else if (op->src.reg == CFI_SP &&
1550                                  op->dest.reg == CFI_BP && state->drap) {
1551
1552                                 /* drap: mov %rsp, %rbp */
1553                                 regs[CFI_BP].base = CFI_BP;
1554                                 regs[CFI_BP].offset = -state->stack_size;
1555                                 state->bp_scratch = false;
1556                         }
1557
1558                         else if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1559
1560                                 /*
1561                                  * mov %rsp, %reg
1562                                  *
1563                                  * This is needed for the rare case where GCC
1564                                  * does:
1565                                  *
1566                                  *   mov    %rsp, %rax
1567                                  *   ...
1568                                  *   mov    %rax, %rsp
1569                                  */
1570                                 state->vals[op->dest.reg].base = CFI_CFA;
1571                                 state->vals[op->dest.reg].offset = -state->stack_size;
1572                         }
1573
1574                         else if (op->src.reg == CFI_BP && op->dest.reg == CFI_SP &&
1575                                  cfa->base == CFI_BP) {
1576
1577                                 /*
1578                                  * mov %rbp, %rsp
1579                                  *
1580                                  * Restore the original stack pointer (Clang).
1581                                  */
1582                                 state->stack_size = -state->regs[CFI_BP].offset;
1583                         }
1584
1585                         else if (op->dest.reg == cfa->base) {
1586
1587                                 /* mov %reg, %rsp */
1588                                 if (cfa->base == CFI_SP &&
1589                                     state->vals[op->src.reg].base == CFI_CFA) {
1590
1591                                         /*
1592                                          * This is needed for the rare case
1593                                          * where GCC does something dumb like:
1594                                          *
1595                                          *   lea    0x8(%rsp), %rcx
1596                                          *   ...
1597                                          *   mov    %rcx, %rsp
1598                                          */
1599                                         cfa->offset = -state->vals[op->src.reg].offset;
1600                                         state->stack_size = cfa->offset;
1601
1602                                 } else {
1603                                         cfa->base = CFI_UNDEFINED;
1604                                         cfa->offset = 0;
1605                                 }
1606                         }
1607
1608                         break;
1609
1610                 case OP_SRC_ADD:
1611                         if (op->dest.reg == CFI_SP && op->src.reg == CFI_SP) {
1612
1613                                 /* add imm, %rsp */
1614                                 state->stack_size -= op->src.offset;
1615                                 if (cfa->base == CFI_SP)
1616                                         cfa->offset -= op->src.offset;
1617                                 break;
1618                         }
1619
1620                         if (op->dest.reg == CFI_SP && op->src.reg == CFI_BP) {
1621
1622                                 /* lea disp(%rbp), %rsp */
1623                                 state->stack_size = -(op->src.offset + regs[CFI_BP].offset);
1624                                 break;
1625                         }
1626
1627                         if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1628
1629                                 /* drap: lea disp(%rsp), %drap */
1630                                 state->drap_reg = op->dest.reg;
1631
1632                                 /*
1633                                  * lea disp(%rsp), %reg
1634                                  *
1635                                  * This is needed for the rare case where GCC
1636                                  * does something dumb like:
1637                                  *
1638                                  *   lea    0x8(%rsp), %rcx
1639                                  *   ...
1640                                  *   mov    %rcx, %rsp
1641                                  */
1642                                 state->vals[op->dest.reg].base = CFI_CFA;
1643                                 state->vals[op->dest.reg].offset = \
1644                                         -state->stack_size + op->src.offset;
1645
1646                                 break;
1647                         }
1648
1649                         if (state->drap && op->dest.reg == CFI_SP &&
1650                             op->src.reg == state->drap_reg) {
1651
1652                                  /* drap: lea disp(%drap), %rsp */
1653                                 cfa->base = CFI_SP;
1654                                 cfa->offset = state->stack_size = -op->src.offset;
1655                                 state->drap_reg = CFI_UNDEFINED;
1656                                 state->drap = false;
1657                                 break;
1658                         }
1659
1660                         if (op->dest.reg == state->cfa.base) {
1661                                 WARN_FUNC("unsupported stack register modification",
1662                                           insn->sec, insn->offset);
1663                                 return -1;
1664                         }
1665
1666                         break;
1667
1668                 case OP_SRC_AND:
1669                         if (op->dest.reg != CFI_SP ||
1670                             (state->drap_reg != CFI_UNDEFINED && cfa->base != CFI_SP) ||
1671                             (state->drap_reg == CFI_UNDEFINED && cfa->base != CFI_BP)) {
1672                                 WARN_FUNC("unsupported stack pointer realignment",
1673                                           insn->sec, insn->offset);
1674                                 return -1;
1675                         }
1676
1677                         if (state->drap_reg != CFI_UNDEFINED) {
1678                                 /* drap: and imm, %rsp */
1679                                 cfa->base = state->drap_reg;
1680                                 cfa->offset = state->stack_size = 0;
1681                                 state->drap = true;
1682                         }
1683
1684                         /*
1685                          * Older versions of GCC (4.8ish) realign the stack
1686                          * without DRAP, with a frame pointer.
1687                          */
1688
1689                         break;
1690
1691                 case OP_SRC_POP:
1692                 case OP_SRC_POPF:
1693                         if (!state->drap && op->dest.type == OP_DEST_REG &&
1694                             op->dest.reg == cfa->base) {
1695
1696                                 /* pop %rbp */
1697                                 cfa->base = CFI_SP;
1698                         }
1699
1700                         if (state->drap && cfa->base == CFI_BP_INDIRECT &&
1701                             op->dest.type == OP_DEST_REG &&
1702                             op->dest.reg == state->drap_reg &&
1703                             state->drap_offset == -state->stack_size) {
1704
1705                                 /* drap: pop %drap */
1706                                 cfa->base = state->drap_reg;
1707                                 cfa->offset = 0;
1708                                 state->drap_offset = -1;
1709
1710                         } else if (regs[op->dest.reg].offset == -state->stack_size) {
1711
1712                                 /* pop %reg */
1713                                 restore_reg(state, op->dest.reg);
1714                         }
1715
1716                         state->stack_size -= 8;
1717                         if (cfa->base == CFI_SP)
1718                                 cfa->offset -= 8;
1719
1720                         break;
1721
1722                 case OP_SRC_REG_INDIRECT:
1723                         if (state->drap && op->src.reg == CFI_BP &&
1724                             op->src.offset == state->drap_offset) {
1725
1726                                 /* drap: mov disp(%rbp), %drap */
1727                                 cfa->base = state->drap_reg;
1728                                 cfa->offset = 0;
1729                                 state->drap_offset = -1;
1730                         }
1731
1732                         if (state->drap && op->src.reg == CFI_BP &&
1733                             op->src.offset == regs[op->dest.reg].offset) {
1734
1735                                 /* drap: mov disp(%rbp), %reg */
1736                                 restore_reg(state, op->dest.reg);
1737
1738                         } else if (op->src.reg == cfa->base &&
1739                             op->src.offset == regs[op->dest.reg].offset + cfa->offset) {
1740
1741                                 /* mov disp(%rbp), %reg */
1742                                 /* mov disp(%rsp), %reg */
1743                                 restore_reg(state, op->dest.reg);
1744                         }
1745
1746                         break;
1747
1748                 default:
1749                         WARN_FUNC("unknown stack-related instruction",
1750                                   insn->sec, insn->offset);
1751                         return -1;
1752                 }
1753
1754                 break;
1755
1756         case OP_DEST_PUSH:
1757         case OP_DEST_PUSHF:
1758                 state->stack_size += 8;
1759                 if (cfa->base == CFI_SP)
1760                         cfa->offset += 8;
1761
1762                 if (op->src.type != OP_SRC_REG)
1763                         break;
1764
1765                 if (state->drap) {
1766                         if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1767
1768                                 /* drap: push %drap */
1769                                 cfa->base = CFI_BP_INDIRECT;
1770                                 cfa->offset = -state->stack_size;
1771
1772                                 /* save drap so we know when to restore it */
1773                                 state->drap_offset = -state->stack_size;
1774
1775                         } else if (op->src.reg == CFI_BP && cfa->base == state->drap_reg) {
1776
1777                                 /* drap: push %rbp */
1778                                 state->stack_size = 0;
1779
1780                         } else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1781
1782                                 /* drap: push %reg */
1783                                 save_reg(state, op->src.reg, CFI_BP, -state->stack_size);
1784                         }
1785
1786                 } else {
1787
1788                         /* push %reg */
1789                         save_reg(state, op->src.reg, CFI_CFA, -state->stack_size);
1790                 }
1791
1792                 /* detect when asm code uses rbp as a scratch register */
1793                 if (!no_fp && insn->func && op->src.reg == CFI_BP &&
1794                     cfa->base != CFI_BP)
1795                         state->bp_scratch = true;
1796                 break;
1797
1798         case OP_DEST_REG_INDIRECT:
1799
1800                 if (state->drap) {
1801                         if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1802
1803                                 /* drap: mov %drap, disp(%rbp) */
1804                                 cfa->base = CFI_BP_INDIRECT;
1805                                 cfa->offset = op->dest.offset;
1806
1807                                 /* save drap offset so we know when to restore it */
1808                                 state->drap_offset = op->dest.offset;
1809                         }
1810
1811                         else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1812
1813                                 /* drap: mov reg, disp(%rbp) */
1814                                 save_reg(state, op->src.reg, CFI_BP, op->dest.offset);
1815                         }
1816
1817                 } else if (op->dest.reg == cfa->base) {
1818
1819                         /* mov reg, disp(%rbp) */
1820                         /* mov reg, disp(%rsp) */
1821                         save_reg(state, op->src.reg, CFI_CFA,
1822                                  op->dest.offset - state->cfa.offset);
1823                 }
1824
1825                 break;
1826
1827         case OP_DEST_LEAVE:
1828                 if ((!state->drap && cfa->base != CFI_BP) ||
1829                     (state->drap && cfa->base != state->drap_reg)) {
1830                         WARN_FUNC("leave instruction with modified stack frame",
1831                                   insn->sec, insn->offset);
1832                         return -1;
1833                 }
1834
1835                 /* leave (mov %rbp, %rsp; pop %rbp) */
1836
1837                 state->stack_size = -state->regs[CFI_BP].offset - 8;
1838                 restore_reg(state, CFI_BP);
1839
1840                 if (!state->drap) {
1841                         cfa->base = CFI_SP;
1842                         cfa->offset -= 8;
1843                 }
1844
1845                 break;
1846
1847         case OP_DEST_MEM:
1848                 if (op->src.type != OP_SRC_POP && op->src.type != OP_SRC_POPF) {
1849                         WARN_FUNC("unknown stack-related memory operation",
1850                                   insn->sec, insn->offset);
1851                         return -1;
1852                 }
1853
1854                 /* pop mem */
1855                 state->stack_size -= 8;
1856                 if (cfa->base == CFI_SP)
1857                         cfa->offset -= 8;
1858
1859                 break;
1860
1861         default:
1862                 WARN_FUNC("unknown stack-related instruction",
1863                           insn->sec, insn->offset);
1864                 return -1;
1865         }
1866
1867         return 0;
1868 }
1869
1870 static bool insn_state_match(struct instruction *insn, struct insn_state *state)
1871 {
1872         struct insn_state *state1 = &insn->state, *state2 = state;
1873         int i;
1874
1875         if (memcmp(&state1->cfa, &state2->cfa, sizeof(state1->cfa))) {
1876                 WARN_FUNC("stack state mismatch: cfa1=%d%+d cfa2=%d%+d",
1877                           insn->sec, insn->offset,
1878                           state1->cfa.base, state1->cfa.offset,
1879                           state2->cfa.base, state2->cfa.offset);
1880
1881         } else if (memcmp(&state1->regs, &state2->regs, sizeof(state1->regs))) {
1882                 for (i = 0; i < CFI_NUM_REGS; i++) {
1883                         if (!memcmp(&state1->regs[i], &state2->regs[i],
1884                                     sizeof(struct cfi_reg)))
1885                                 continue;
1886
1887                         WARN_FUNC("stack state mismatch: reg1[%d]=%d%+d reg2[%d]=%d%+d",
1888                                   insn->sec, insn->offset,
1889                                   i, state1->regs[i].base, state1->regs[i].offset,
1890                                   i, state2->regs[i].base, state2->regs[i].offset);
1891                         break;
1892                 }
1893
1894         } else if (state1->type != state2->type) {
1895                 WARN_FUNC("stack state mismatch: type1=%d type2=%d",
1896                           insn->sec, insn->offset, state1->type, state2->type);
1897
1898         } else if (state1->drap != state2->drap ||
1899                  (state1->drap && state1->drap_reg != state2->drap_reg) ||
1900                  (state1->drap && state1->drap_offset != state2->drap_offset)) {
1901                 WARN_FUNC("stack state mismatch: drap1=%d(%d,%d) drap2=%d(%d,%d)",
1902                           insn->sec, insn->offset,
1903                           state1->drap, state1->drap_reg, state1->drap_offset,
1904                           state2->drap, state2->drap_reg, state2->drap_offset);
1905
1906         } else
1907                 return true;
1908
1909         return false;
1910 }
1911
1912 static inline bool func_uaccess_safe(struct symbol *func)
1913 {
1914         if (func)
1915                 return func->uaccess_safe;
1916
1917         return false;
1918 }
1919
1920 static inline const char *call_dest_name(struct instruction *insn)
1921 {
1922         if (insn->call_dest)
1923                 return insn->call_dest->name;
1924
1925         return "{dynamic}";
1926 }
1927
1928 static int validate_call(struct instruction *insn, struct insn_state *state)
1929 {
1930         if (state->uaccess && !func_uaccess_safe(insn->call_dest)) {
1931                 WARN_FUNC("call to %s() with UACCESS enabled",
1932                                 insn->sec, insn->offset, call_dest_name(insn));
1933                 return 1;
1934         }
1935
1936         if (state->df) {
1937                 WARN_FUNC("call to %s() with DF set",
1938                                 insn->sec, insn->offset, call_dest_name(insn));
1939                 return 1;
1940         }
1941
1942         return 0;
1943 }
1944
1945 static int validate_sibling_call(struct instruction *insn, struct insn_state *state)
1946 {
1947         if (has_modified_stack_frame(state)) {
1948                 WARN_FUNC("sibling call from callable instruction with modified stack frame",
1949                                 insn->sec, insn->offset);
1950                 return 1;
1951         }
1952
1953         return validate_call(insn, state);
1954 }
1955
1956 /*
1957  * Follow the branch starting at the given instruction, and recursively follow
1958  * any other branches (jumps).  Meanwhile, track the frame pointer state at
1959  * each instruction and validate all the rules described in
1960  * tools/objtool/Documentation/stack-validation.txt.
1961  */
1962 static int validate_branch(struct objtool_file *file, struct symbol *func,
1963                            struct instruction *first, struct insn_state state)
1964 {
1965         struct alternative *alt;
1966         struct instruction *insn, *next_insn;
1967         struct section *sec;
1968         u8 visited;
1969         int ret;
1970
1971         insn = first;
1972         sec = insn->sec;
1973
1974         if (insn->alt_group && list_empty(&insn->alts)) {
1975                 WARN_FUNC("don't know how to handle branch to middle of alternative instruction group",
1976                           sec, insn->offset);
1977                 return 1;
1978         }
1979
1980         while (1) {
1981                 next_insn = next_insn_same_sec(file, insn);
1982
1983                 if (file->c_file && func && insn->func && func != insn->func->pfunc) {
1984                         WARN("%s() falls through to next function %s()",
1985                              func->name, insn->func->name);
1986                         return 1;
1987                 }
1988
1989                 if (func && insn->ignore) {
1990                         WARN_FUNC("BUG: why am I validating an ignored function?",
1991                                   sec, insn->offset);
1992                         return 1;
1993                 }
1994
1995                 visited = 1 << state.uaccess;
1996                 if (insn->visited) {
1997                         if (!insn->hint && !insn_state_match(insn, &state))
1998                                 return 1;
1999
2000                         if (insn->visited & visited)
2001                                 return 0;
2002                 }
2003
2004                 if (insn->hint) {
2005                         if (insn->restore) {
2006                                 struct instruction *save_insn, *i;
2007
2008                                 i = insn;
2009                                 save_insn = NULL;
2010                                 func_for_each_insn_continue_reverse(file, func, i) {
2011                                         if (i->save) {
2012                                                 save_insn = i;
2013                                                 break;
2014                                         }
2015                                 }
2016
2017                                 if (!save_insn) {
2018                                         WARN_FUNC("no corresponding CFI save for CFI restore",
2019                                                   sec, insn->offset);
2020                                         return 1;
2021                                 }
2022
2023                                 if (!save_insn->visited) {
2024                                         /*
2025                                          * Oops, no state to copy yet.
2026                                          * Hopefully we can reach this
2027                                          * instruction from another branch
2028                                          * after the save insn has been
2029                                          * visited.
2030                                          */
2031                                         if (insn == first)
2032                                                 return 0;
2033
2034                                         WARN_FUNC("objtool isn't smart enough to handle this CFI save/restore combo",
2035                                                   sec, insn->offset);
2036                                         return 1;
2037                                 }
2038
2039                                 insn->state = save_insn->state;
2040                         }
2041
2042                         state = insn->state;
2043
2044                 } else
2045                         insn->state = state;
2046
2047                 insn->visited |= visited;
2048
2049                 if (!insn->ignore_alts) {
2050                         bool skip_orig = false;
2051
2052                         list_for_each_entry(alt, &insn->alts, list) {
2053                                 if (alt->skip_orig)
2054                                         skip_orig = true;
2055
2056                                 ret = validate_branch(file, func, alt->insn, state);
2057                                 if (ret) {
2058                                         if (backtrace)
2059                                                 BT_FUNC("(alt)", insn);
2060                                         return ret;
2061                                 }
2062                         }
2063
2064                         if (skip_orig)
2065                                 return 0;
2066                 }
2067
2068                 switch (insn->type) {
2069
2070                 case INSN_RETURN:
2071                         if (state.uaccess && !func_uaccess_safe(func)) {
2072                                 WARN_FUNC("return with UACCESS enabled", sec, insn->offset);
2073                                 return 1;
2074                         }
2075
2076                         if (!state.uaccess && func_uaccess_safe(func)) {
2077                                 WARN_FUNC("return with UACCESS disabled from a UACCESS-safe function", sec, insn->offset);
2078                                 return 1;
2079                         }
2080
2081                         if (state.df) {
2082                                 WARN_FUNC("return with DF set", sec, insn->offset);
2083                                 return 1;
2084                         }
2085
2086                         if (func && has_modified_stack_frame(&state)) {
2087                                 WARN_FUNC("return with modified stack frame",
2088                                           sec, insn->offset);
2089                                 return 1;
2090                         }
2091
2092                         if (state.bp_scratch) {
2093                                 WARN("%s uses BP as a scratch register",
2094                                      func->name);
2095                                 return 1;
2096                         }
2097
2098                         return 0;
2099
2100                 case INSN_CALL:
2101                 case INSN_CALL_DYNAMIC:
2102                         ret = validate_call(insn, &state);
2103                         if (ret)
2104                                 return ret;
2105
2106                         if (!no_fp && func && !is_fentry_call(insn) &&
2107                             !has_valid_stack_frame(&state)) {
2108                                 WARN_FUNC("call without frame pointer save/setup",
2109                                           sec, insn->offset);
2110                                 return 1;
2111                         }
2112
2113                         if (dead_end_function(file, insn->call_dest))
2114                                 return 0;
2115
2116                         break;
2117
2118                 case INSN_JUMP_CONDITIONAL:
2119                 case INSN_JUMP_UNCONDITIONAL:
2120                         if (func && is_sibling_call(insn)) {
2121                                 ret = validate_sibling_call(insn, &state);
2122                                 if (ret)
2123                                         return ret;
2124
2125                         } else if (insn->jump_dest) {
2126                                 ret = validate_branch(file, func,
2127                                                       insn->jump_dest, state);
2128                                 if (ret) {
2129                                         if (backtrace)
2130                                                 BT_FUNC("(branch)", insn);
2131                                         return ret;
2132                                 }
2133                         }
2134
2135                         if (insn->type == INSN_JUMP_UNCONDITIONAL)
2136                                 return 0;
2137
2138                         break;
2139
2140                 case INSN_JUMP_DYNAMIC:
2141                 case INSN_JUMP_DYNAMIC_CONDITIONAL:
2142                         if (func && is_sibling_call(insn)) {
2143                                 ret = validate_sibling_call(insn, &state);
2144                                 if (ret)
2145                                         return ret;
2146                         }
2147
2148                         if (insn->type == INSN_JUMP_DYNAMIC)
2149                                 return 0;
2150
2151                         break;
2152
2153                 case INSN_CONTEXT_SWITCH:
2154                         if (func && (!next_insn || !next_insn->hint)) {
2155                                 WARN_FUNC("unsupported instruction in callable function",
2156                                           sec, insn->offset);
2157                                 return 1;
2158                         }
2159                         return 0;
2160
2161                 case INSN_STACK:
2162                         if (update_insn_state(insn, &state))
2163                                 return 1;
2164
2165                         if (insn->stack_op.dest.type == OP_DEST_PUSHF) {
2166                                 if (!state.uaccess_stack) {
2167                                         state.uaccess_stack = 1;
2168                                 } else if (state.uaccess_stack >> 31) {
2169                                         WARN_FUNC("PUSHF stack exhausted", sec, insn->offset);
2170                                         return 1;
2171                                 }
2172                                 state.uaccess_stack <<= 1;
2173                                 state.uaccess_stack  |= state.uaccess;
2174                         }
2175
2176                         if (insn->stack_op.src.type == OP_SRC_POPF) {
2177                                 if (state.uaccess_stack) {
2178                                         state.uaccess = state.uaccess_stack & 1;
2179                                         state.uaccess_stack >>= 1;
2180                                         if (state.uaccess_stack == 1)
2181                                                 state.uaccess_stack = 0;
2182                                 }
2183                         }
2184
2185                         break;
2186
2187                 case INSN_STAC:
2188                         if (state.uaccess) {
2189                                 WARN_FUNC("recursive UACCESS enable", sec, insn->offset);
2190                                 return 1;
2191                         }
2192
2193                         state.uaccess = true;
2194                         break;
2195
2196                 case INSN_CLAC:
2197                         if (!state.uaccess && func) {
2198                                 WARN_FUNC("redundant UACCESS disable", sec, insn->offset);
2199                                 return 1;
2200                         }
2201
2202                         if (func_uaccess_safe(func) && !state.uaccess_stack) {
2203                                 WARN_FUNC("UACCESS-safe disables UACCESS", sec, insn->offset);
2204                                 return 1;
2205                         }
2206
2207                         state.uaccess = false;
2208                         break;
2209
2210                 case INSN_STD:
2211                         if (state.df)
2212                                 WARN_FUNC("recursive STD", sec, insn->offset);
2213
2214                         state.df = true;
2215                         break;
2216
2217                 case INSN_CLD:
2218                         if (!state.df && func)
2219                                 WARN_FUNC("redundant CLD", sec, insn->offset);
2220
2221                         state.df = false;
2222                         break;
2223
2224                 default:
2225                         break;
2226                 }
2227
2228                 if (insn->dead_end)
2229                         return 0;
2230
2231                 if (!next_insn) {
2232                         if (state.cfa.base == CFI_UNDEFINED)
2233                                 return 0;
2234                         WARN("%s: unexpected end of section", sec->name);
2235                         return 1;
2236                 }
2237
2238                 insn = next_insn;
2239         }
2240
2241         return 0;
2242 }
2243
2244 static int validate_unwind_hints(struct objtool_file *file)
2245 {
2246         struct instruction *insn;
2247         int ret, warnings = 0;
2248         struct insn_state state;
2249
2250         if (!file->hints)
2251                 return 0;
2252
2253         clear_insn_state(&state);
2254
2255         for_each_insn(file, insn) {
2256                 if (insn->hint && !insn->visited) {
2257                         ret = validate_branch(file, insn->func, insn, state);
2258                         if (ret && backtrace)
2259                                 BT_FUNC("<=== (hint)", insn);
2260                         warnings += ret;
2261                 }
2262         }
2263
2264         return warnings;
2265 }
2266
2267 static int validate_retpoline(struct objtool_file *file)
2268 {
2269         struct instruction *insn;
2270         int warnings = 0;
2271
2272         for_each_insn(file, insn) {
2273                 if (insn->type != INSN_JUMP_DYNAMIC &&
2274                     insn->type != INSN_CALL_DYNAMIC)
2275                         continue;
2276
2277                 if (insn->retpoline_safe)
2278                         continue;
2279
2280                 /*
2281                  * .init.text code is ran before userspace and thus doesn't
2282                  * strictly need retpolines, except for modules which are
2283                  * loaded late, they very much do need retpoline in their
2284                  * .init.text
2285                  */
2286                 if (!strcmp(insn->sec->name, ".init.text") && !module)
2287                         continue;
2288
2289                 WARN_FUNC("indirect %s found in RETPOLINE build",
2290                           insn->sec, insn->offset,
2291                           insn->type == INSN_JUMP_DYNAMIC ? "jump" : "call");
2292
2293                 warnings++;
2294         }
2295
2296         return warnings;
2297 }
2298
2299 static bool is_kasan_insn(struct instruction *insn)
2300 {
2301         return (insn->type == INSN_CALL &&
2302                 !strcmp(insn->call_dest->name, "__asan_handle_no_return"));
2303 }
2304
2305 static bool is_ubsan_insn(struct instruction *insn)
2306 {
2307         return (insn->type == INSN_CALL &&
2308                 !strcmp(insn->call_dest->name,
2309                         "__ubsan_handle_builtin_unreachable"));
2310 }
2311
2312 static bool ignore_unreachable_insn(struct instruction *insn)
2313 {
2314         int i;
2315
2316         if (insn->ignore || insn->type == INSN_NOP)
2317                 return true;
2318
2319         /*
2320          * Ignore any unused exceptions.  This can happen when a whitelisted
2321          * function has an exception table entry.
2322          *
2323          * Also ignore alternative replacement instructions.  This can happen
2324          * when a whitelisted function uses one of the ALTERNATIVE macros.
2325          */
2326         if (!strcmp(insn->sec->name, ".fixup") ||
2327             !strcmp(insn->sec->name, ".altinstr_replacement") ||
2328             !strcmp(insn->sec->name, ".altinstr_aux"))
2329                 return true;
2330
2331         /*
2332          * Check if this (or a subsequent) instruction is related to
2333          * CONFIG_UBSAN or CONFIG_KASAN.
2334          *
2335          * End the search at 5 instructions to avoid going into the weeds.
2336          */
2337         if (!insn->func)
2338                 return false;
2339         for (i = 0; i < 5; i++) {
2340
2341                 if (is_kasan_insn(insn) || is_ubsan_insn(insn))
2342                         return true;
2343
2344                 if (insn->type == INSN_JUMP_UNCONDITIONAL) {
2345                         if (insn->jump_dest &&
2346                             insn->jump_dest->func == insn->func) {
2347                                 insn = insn->jump_dest;
2348                                 continue;
2349                         }
2350
2351                         break;
2352                 }
2353
2354                 if (insn->offset + insn->len >= insn->func->offset + insn->func->len)
2355                         break;
2356
2357                 insn = list_next_entry(insn, list);
2358         }
2359
2360         return false;
2361 }
2362
2363 static int validate_functions(struct objtool_file *file)
2364 {
2365         struct section *sec;
2366         struct symbol *func;
2367         struct instruction *insn;
2368         struct insn_state state;
2369         int ret, warnings = 0;
2370
2371         clear_insn_state(&state);
2372
2373         state.cfa = initial_func_cfi.cfa;
2374         memcpy(&state.regs, &initial_func_cfi.regs,
2375                CFI_NUM_REGS * sizeof(struct cfi_reg));
2376         state.stack_size = initial_func_cfi.cfa.offset;
2377
2378         for_each_sec(file, sec) {
2379                 list_for_each_entry(func, &sec->symbol_list, list) {
2380                         if (func->type != STT_FUNC)
2381                                 continue;
2382
2383                         if (!func->len) {
2384                                 WARN("%s() is missing an ELF size annotation",
2385                                      func->name);
2386                                 warnings++;
2387                         }
2388
2389                         if (func->pfunc != func || func->alias != func)
2390                                 continue;
2391
2392                         insn = find_insn(file, sec, func->offset);
2393                         if (!insn || insn->ignore || insn->visited)
2394                                 continue;
2395
2396                         state.uaccess = func->uaccess_safe;
2397
2398                         ret = validate_branch(file, func, insn, state);
2399                         if (ret && backtrace)
2400                                 BT_FUNC("<=== (func)", insn);
2401                         warnings += ret;
2402                 }
2403         }
2404
2405         return warnings;
2406 }
2407
2408 static int validate_reachable_instructions(struct objtool_file *file)
2409 {
2410         struct instruction *insn;
2411
2412         if (file->ignore_unreachables)
2413                 return 0;
2414
2415         for_each_insn(file, insn) {
2416                 if (insn->visited || ignore_unreachable_insn(insn))
2417                         continue;
2418
2419                 WARN_FUNC("unreachable instruction", insn->sec, insn->offset);
2420                 return 1;
2421         }
2422
2423         return 0;
2424 }
2425
2426 static void cleanup(struct objtool_file *file)
2427 {
2428         struct instruction *insn, *tmpinsn;
2429         struct alternative *alt, *tmpalt;
2430
2431         list_for_each_entry_safe(insn, tmpinsn, &file->insn_list, list) {
2432                 list_for_each_entry_safe(alt, tmpalt, &insn->alts, list) {
2433                         list_del(&alt->list);
2434                         free(alt);
2435                 }
2436                 list_del(&insn->list);
2437                 hash_del(&insn->hash);
2438                 free(insn);
2439         }
2440         elf_close(file->elf);
2441 }
2442
2443 static struct objtool_file file;
2444
2445 int check(const char *_objname, bool orc)
2446 {
2447         int ret, warnings = 0;
2448
2449         objname = _objname;
2450
2451         file.elf = elf_read(objname, orc ? O_RDWR : O_RDONLY);
2452         if (!file.elf)
2453                 return 1;
2454
2455         INIT_LIST_HEAD(&file.insn_list);
2456         hash_init(file.insn_hash);
2457         file.c_file = find_section_by_name(file.elf, ".comment");
2458         file.ignore_unreachables = no_unreachable;
2459         file.hints = false;
2460
2461         arch_initial_func_cfi_state(&initial_func_cfi);
2462
2463         ret = decode_sections(&file);
2464         if (ret < 0)
2465                 goto out;
2466         warnings += ret;
2467
2468         if (list_empty(&file.insn_list))
2469                 goto out;
2470
2471         if (retpoline) {
2472                 ret = validate_retpoline(&file);
2473                 if (ret < 0)
2474                         return ret;
2475                 warnings += ret;
2476         }
2477
2478         ret = validate_functions(&file);
2479         if (ret < 0)
2480                 goto out;
2481         warnings += ret;
2482
2483         ret = validate_unwind_hints(&file);
2484         if (ret < 0)
2485                 goto out;
2486         warnings += ret;
2487
2488         if (!warnings) {
2489                 ret = validate_reachable_instructions(&file);
2490                 if (ret < 0)
2491                         goto out;
2492                 warnings += ret;
2493         }
2494
2495         if (orc) {
2496                 ret = create_orc(&file);
2497                 if (ret < 0)
2498                         goto out;
2499
2500                 ret = create_orc_sections(&file);
2501                 if (ret < 0)
2502                         goto out;
2503
2504                 ret = elf_write(file.elf);
2505                 if (ret < 0)
2506                         goto out;
2507         }
2508
2509 out:
2510         cleanup(&file);
2511
2512         /* ignore warnings for now until we get all the code cleaned up */
2513         if (ret || warnings)
2514                 return 0;
2515         return 0;
2516 }