tools/objtool/check.c

   1 /*
   2  * Copyright (C) 2015-2017 Josh Poimboeuf <jpoimboe@redhat.com>
   3  *
   4  * This program is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU General Public License
   6  * as published by the Free Software Foundation; either version 2
   7  * of the License, or (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, see <http://www.gnu.org/licenses/>.
  16  */
  17
  18 #include <string.h>
  19 #include <stdlib.h>
  20
  21 #include "builtin.h"
  22 #include "check.h"
  23 #include "elf.h"
  24 #include "special.h"
  25 #include "arch.h"
  26 #include "warn.h"
  27
  28 #include <linux/hashtable.h>
  29 #include <linux/kernel.h>
  30
  31 struct alternative {
  32         struct list_head list;
  33         struct instruction *insn;
  34         bool skip_orig;
  35 };
  36
  37 const char *objname;
  38 struct cfi_state initial_func_cfi;
  39
  40 struct instruction *find_insn(struct objtool_file *file,
  41                               struct section *sec, unsigned long offset)
  42 {
  43         struct instruction *insn;
  44
  45         hash_for_each_possible(file->insn_hash, insn, hash, offset)
  46                 if (insn->sec == sec && insn->offset == offset)
  47                         return insn;
  48
  49         return NULL;
  50 }
  51
  52 static struct instruction *next_insn_same_sec(struct objtool_file *file,
  53                                               struct instruction *insn)
  54 {
  55         struct instruction *next = list_next_entry(insn, list);
  56
  57         if (!next || &next->list == &file->insn_list || next->sec != insn->sec)
  58                 return NULL;
  59
  60         return next;
  61 }
  62
  63 static struct instruction *next_insn_same_func(struct objtool_file *file,
  64                                                struct instruction *insn)
  65 {
  66         struct instruction *next = list_next_entry(insn, list);
  67         struct symbol *func = insn->func;
  68
  69         if (!func)
  70                 return NULL;
  71
  72         if (&next->list != &file->insn_list && next->func == func)
  73                 return next;
  74
  75         /* Check if we're already in the subfunction: */
  76         if (func == func->cfunc)
  77                 return NULL;
  78
  79         /* Move to the subfunction: */
  80         return find_insn(file, func->cfunc->sec, func->cfunc->offset);
  81 }
  82
  83 #define func_for_each_insn_all(file, func, insn)                        \
  84         for (insn = find_insn(file, func->sec, func->offset);           \
  85              insn;                                                      \
  86              insn = next_insn_same_func(file, insn))
  87
  88 #define func_for_each_insn(file, func, insn)                            \
  89         for (insn = find_insn(file, func->sec, func->offset);           \
  90              insn && &insn->list != &file->insn_list &&                 \
  91                 insn->sec == func->sec &&                               \
  92                 insn->offset < func->offset + func->len;                \
  93              insn = list_next_entry(insn, list))
  94
  95 #define func_for_each_insn_continue_reverse(file, func, insn)           \
  96         for (insn = list_prev_entry(insn, list);                        \
  97              &insn->list != &file->insn_list &&                         \
  98                 insn->sec == func->sec && insn->offset >= func->offset; \
  99              insn = list_prev_entry(insn, list))
 100
 101 #define sec_for_each_insn_from(file, insn)                              \
 102         for (; insn; insn = next_insn_same_sec(file, insn))
 103
 104 #define sec_for_each_insn_continue(file, insn)                          \
 105         for (insn = next_insn_same_sec(file, insn); insn;               \
 106              insn = next_insn_same_sec(file, insn))
 107
 108 /*
 109  * This checks to see if the given function is a "noreturn" function.
 110  *
 111  * For global functions which are outside the scope of this object file, we
 112  * have to keep a manual list of them.
 113  *
 114  * For local functions, we have to detect them manually by simply looking for
 115  * the lack of a return instruction.
 116  *
 117  * Returns:
 118  *  -1: error
 119  *   0: no dead end
 120  *   1: dead end
 121  */
 122 static int __dead_end_function(struct objtool_file *file, struct symbol *func,
 123                                int recursion)
 124 {
 125         int i;
 126         struct instruction *insn;
 127         bool empty = true;
 128
 129         /*
 130          * Unfortunately these have to be hard coded because the noreturn
 131          * attribute isn't provided in ELF data.
 132          */
 133         static const char * const global_noreturns[] = {
 134                 "__stack_chk_fail",
 135                 "panic",
 136                 "do_exit",
 137                 "do_task_dead",
 138                 "__module_put_and_exit",
 139                 "complete_and_exit",
 140                 "kvm_spurious_fault",
 141                 "__reiserfs_panic",
 142                 "lbug_with_loc",
 143                 "fortify_panic",
 144                 "usercopy_abort",
 145                 "machine_real_restart",
 146                 "rewind_stack_do_exit",
 147         };
 148
 149         if (func->bind == STB_WEAK)
 150                 return 0;
 151
 152         if (func->bind == STB_GLOBAL)
 153                 for (i = 0; i < ARRAY_SIZE(global_noreturns); i++)
 154                         if (!strcmp(func->name, global_noreturns[i]))
 155                                 return 1;
 156
 157         if (!func->len)
 158                 return 0;
 159
 160         insn = find_insn(file, func->sec, func->offset);
 161         if (!insn->func)
 162                 return 0;
 163
 164         func_for_each_insn_all(file, func, insn) {
 165                 empty = false;
 166
 167                 if (insn->type == INSN_RETURN)
 168                         return 0;
 169         }
 170
 171         if (empty)
 172                 return 0;
 173
 174         /*
 175          * A function can have a sibling call instead of a return.  In that
 176          * case, the function's dead-end status depends on whether the target
 177          * of the sibling call returns.
 178          */
 179         func_for_each_insn_all(file, func, insn) {
 180                 if (insn->type == INSN_JUMP_UNCONDITIONAL) {
 181                         struct instruction *dest = insn->jump_dest;
 182
 183                         if (!dest)
 184                                 /* sibling call to another file */
 185                                 return 0;
 186
 187                         if (dest->func && dest->func->pfunc != insn->func->pfunc) {
 188
 189                                 /* local sibling call */
 190                                 if (recursion == 5) {
 191                                         /*
 192                                          * Infinite recursion: two functions
 193                                          * have sibling calls to each other.
 194                                          * This is a very rare case.  It means
 195                                          * they aren't dead ends.
 196                                          */
 197                                         return 0;
 198                                 }
 199
 200                                 return __dead_end_function(file, dest->func,
 201                                                            recursion + 1);
 202                         }
 203                 }
 204
 205                 if (insn->type == INSN_JUMP_DYNAMIC && list_empty(&insn->alts))
 206                         /* sibling call */
 207                         return 0;
 208         }
 209
 210         return 1;
 211 }
 212
 213 static int dead_end_function(struct objtool_file *file, struct symbol *func)
 214 {
 215         return __dead_end_function(file, func, 0);
 216 }
 217
 218 static void clear_insn_state(struct insn_state *state)
 219 {
 220         int i;
 221
 222         memset(state, 0, sizeof(*state));
 223         state->cfa.base = CFI_UNDEFINED;
 224         for (i = 0; i < CFI_NUM_REGS; i++) {
 225                 state->regs[i].base = CFI_UNDEFINED;
 226                 state->vals[i].base = CFI_UNDEFINED;
 227         }
 228         state->drap_reg = CFI_UNDEFINED;
 229         state->drap_offset = -1;
 230 }
 231
 232 /*
 233  * Call the arch-specific instruction decoder for all the instructions and add
 234  * them to the global instruction list.
 235  */
 236 static int decode_instructions(struct objtool_file *file)
 237 {
 238         struct section *sec;
 239         struct symbol *func;
 240         unsigned long offset;
 241         struct instruction *insn;
 242         int ret;
 243
 244         for_each_sec(file, sec) {
 245
 246                 if (!(sec->sh.sh_flags & SHF_EXECINSTR))
 247                         continue;
 248
 249                 if (strcmp(sec->name, ".altinstr_replacement") &&
 250                     strcmp(sec->name, ".altinstr_aux") &&
 251                     strncmp(sec->name, ".discard.", 9))
 252                         sec->text = true;
 253
 254                 for (offset = 0; offset < sec->len; offset += insn->len) {
 255                         insn = malloc(sizeof(*insn));
 256                         if (!insn) {
 257                                 WARN("malloc failed");
 258                                 return -1;
 259                         }
 260                         memset(insn, 0, sizeof(*insn));
 261                         INIT_LIST_HEAD(&insn->alts);
 262                         clear_insn_state(&insn->state);
 263
 264                         insn->sec = sec;
 265                         insn->offset = offset;
 266
 267                         ret = arch_decode_instruction(file->elf, sec, offset,
 268                                                       sec->len - offset,
 269                                                       &insn->len, &insn->type,
 270                                                       &insn->immediate,
 271                                                       &insn->stack_op);
 272                         if (ret)
 273                                 goto err;
 274
 275                         if (!insn->type || insn->type > INSN_LAST) {
 276                                 WARN_FUNC("invalid instruction type %d",
 277                                           insn->sec, insn->offset, insn->type);
 278                                 ret = -1;
 279                                 goto err;
 280                         }
 281
 282                         hash_add(file->insn_hash, &insn->hash, insn->offset);
 283                         list_add_tail(&insn->list, &file->insn_list);
 284                 }
 285
 286                 list_for_each_entry(func, &sec->symbol_list, list) {
 287                         if (func->type != STT_FUNC)
 288                                 continue;
 289
 290                         if (!find_insn(file, sec, func->offset)) {
 291                                 WARN("%s(): can't find starting instruction",
 292                                      func->name);
 293                                 return -1;
 294                         }
 295
 296                         func_for_each_insn(file, func, insn)
 297                                 if (!insn->func)
 298                                         insn->func = func;
 299                 }
 300         }
 301
 302         return 0;
 303
 304 err:
 305         free(insn);
 306         return ret;
 307 }
 308
 309 /*
 310  * Mark "ud2" instructions and manually annotated dead ends.
 311  */
 312 static int add_dead_ends(struct objtool_file *file)
 313 {
 314         struct section *sec;
 315         struct rela *rela;
 316         struct instruction *insn;
 317         bool found;
 318
 319         /*
 320          * By default, "ud2" is a dead end unless otherwise annotated, because
 321          * GCC 7 inserts it for certain divide-by-zero cases.
 322          */
 323         for_each_insn(file, insn)
 324                 if (insn->type == INSN_BUG)
 325                         insn->dead_end = true;
 326
 327         /*
 328          * Check for manually annotated dead ends.
 329          */
 330         sec = find_section_by_name(file->elf, ".rela.discard.unreachable");
 331         if (!sec)
 332                 goto reachable;
 333
 334         list_for_each_entry(rela, &sec->rela_list, list) {
 335                 if (rela->sym->type != STT_SECTION) {
 336                         WARN("unexpected relocation symbol type in %s", sec->name);
 337                         return -1;
 338                 }
 339                 insn = find_insn(file, rela->sym->sec, rela->addend);
 340                 if (insn)
 341                         insn = list_prev_entry(insn, list);
 342                 else if (rela->addend == rela->sym->sec->len) {
 343                         found = false;
 344                         list_for_each_entry_reverse(insn, &file->insn_list, list) {
 345                                 if (insn->sec == rela->sym->sec) {
 346                                         found = true;
 347                                         break;
 348                                 }
 349                         }
 350
 351                         if (!found) {
 352                                 WARN("can't find unreachable insn at %s+0x%x",
 353                                      rela->sym->sec->name, rela->addend);
 354                                 return -1;
 355                         }
 356                 } else {
 357                         WARN("can't find unreachable insn at %s+0x%x",
 358                              rela->sym->sec->name, rela->addend);
 359                         return -1;
 360                 }
 361
 362                 insn->dead_end = true;
 363         }
 364
 365 reachable:
 366         /*
 367          * These manually annotated reachable checks are needed for GCC 4.4,
 368          * where the Linux unreachable() macro isn't supported.  In that case
 369          * GCC doesn't know the "ud2" is fatal, so it generates code as if it's
 370          * not a dead end.
 371          */
 372         sec = find_section_by_name(file->elf, ".rela.discard.reachable");
 373         if (!sec)
 374                 return 0;
 375
 376         list_for_each_entry(rela, &sec->rela_list, list) {
 377                 if (rela->sym->type != STT_SECTION) {
 378                         WARN("unexpected relocation symbol type in %s", sec->name);
 379                         return -1;
 380                 }
 381                 insn = find_insn(file, rela->sym->sec, rela->addend);
 382                 if (insn)
 383                         insn = list_prev_entry(insn, list);
 384                 else if (rela->addend == rela->sym->sec->len) {
 385                         found = false;
 386                         list_for_each_entry_reverse(insn, &file->insn_list, list) {
 387                                 if (insn->sec == rela->sym->sec) {
 388                                         found = true;
 389                                         break;
 390                                 }
 391                         }
 392
 393                         if (!found) {
 394                                 WARN("can't find reachable insn at %s+0x%x",
 395                                      rela->sym->sec->name, rela->addend);
 396                                 return -1;
 397                         }
 398                 } else {
 399                         WARN("can't find reachable insn at %s+0x%x",
 400                              rela->sym->sec->name, rela->addend);
 401                         return -1;
 402                 }
 403
 404                 insn->dead_end = false;
 405         }
 406
 407         return 0;
 408 }
 409
 410 /*
 411  * Warnings shouldn't be reported for ignored functions.
 412  */
 413 static void add_ignores(struct objtool_file *file)
 414 {
 415         struct instruction *insn;
 416         struct section *sec;
 417         struct symbol *func;
 418         struct rela *rela;
 419
 420         sec = find_section_by_name(file->elf, ".rela.discard.func_stack_frame_non_standard");
 421         if (!sec)
 422                 return;
 423
 424         list_for_each_entry(rela, &sec->rela_list, list) {
 425                 switch (rela->sym->type) {
 426                 case STT_FUNC:
 427                         func = rela->sym;
 428                         break;
 429
 430                 case STT_SECTION:
 431                         func = find_symbol_by_offset(rela->sym->sec, rela->addend);
 432                         if (!func || func->type != STT_FUNC)
 433                                 continue;
 434                         break;
 435
 436                 default:
 437                         WARN("unexpected relocation symbol type in %s: %d", sec->name, rela->sym->type);
 438                         continue;
 439                 }
 440
 441                 func_for_each_insn_all(file, func, insn)
 442                         insn->ignore = true;
 443         }
 444 }
 445
 446 /*
 447  * This is a whitelist of functions that is allowed to be called with AC set.
 448  * The list is meant to be minimal and only contains compiler instrumentation
 449  * ABI and a few functions used to implement *_{to,from}_user() functions.
 450  *
 451  * These functions must not directly change AC, but may PUSHF/POPF.
 452  */
 453 static const char *uaccess_safe_builtin[] = {
 454         /* KASAN */
 455         "kasan_report",
 456         "check_memory_region",
 457         /* KASAN out-of-line */
 458         "__asan_loadN_noabort",
 459         "__asan_load1_noabort",
 460         "__asan_load2_noabort",
 461         "__asan_load4_noabort",
 462         "__asan_load8_noabort",
 463         "__asan_load16_noabort",
 464         "__asan_storeN_noabort",
 465         "__asan_store1_noabort",
 466         "__asan_store2_noabort",
 467         "__asan_store4_noabort",
 468         "__asan_store8_noabort",
 469         "__asan_store16_noabort",
 470         /* KASAN in-line */
 471         "__asan_report_load_n_noabort",
 472         "__asan_report_load1_noabort",
 473         "__asan_report_load2_noabort",
 474         "__asan_report_load4_noabort",
 475         "__asan_report_load8_noabort",
 476         "__asan_report_load16_noabort",
 477         "__asan_report_store_n_noabort",
 478         "__asan_report_store1_noabort",
 479         "__asan_report_store2_noabort",
 480         "__asan_report_store4_noabort",
 481         "__asan_report_store8_noabort",
 482         "__asan_report_store16_noabort",
 483         /* KCOV */
 484         "write_comp_data",
 485         "__sanitizer_cov_trace_pc",
 486         "__sanitizer_cov_trace_const_cmp1",
 487         "__sanitizer_cov_trace_const_cmp2",
 488         "__sanitizer_cov_trace_const_cmp4",
 489         "__sanitizer_cov_trace_const_cmp8",
 490         "__sanitizer_cov_trace_cmp1",
 491         "__sanitizer_cov_trace_cmp2",
 492         "__sanitizer_cov_trace_cmp4",
 493         "__sanitizer_cov_trace_cmp8",
 494         /* UBSAN */
 495         "ubsan_type_mismatch_common",
 496         "__ubsan_handle_type_mismatch",
 497         "__ubsan_handle_type_mismatch_v1",
 498         /* misc */
 499         "csum_partial_copy_generic",
 500         "__memcpy_mcsafe",
 501         "ftrace_likely_update", /* CONFIG_TRACE_BRANCH_PROFILING */
 502         NULL
 503 };
 504
 505 static void add_uaccess_safe(struct objtool_file *file)
 506 {
 507         struct symbol *func;
 508         const char **name;
 509
 510         if (!uaccess)
 511                 return;
 512
 513         for (name = uaccess_safe_builtin; *name; name++) {
 514                 func = find_symbol_by_name(file->elf, *name);
 515                 if (!func)
 516                         continue;
 517
 518                 func->alias->uaccess_safe = true;
 519         }
 520 }
 521
 522 /*
 523  * FIXME: For now, just ignore any alternatives which add retpolines.  This is
 524  * a temporary hack, as it doesn't allow ORC to unwind from inside a retpoline.
 525  * But it at least allows objtool to understand the control flow *around* the
 526  * retpoline.
 527  */
 528 static int add_ignore_alternatives(struct objtool_file *file)
 529 {
 530         struct section *sec;
 531         struct rela *rela;
 532         struct instruction *insn;
 533
 534         sec = find_section_by_name(file->elf, ".rela.discard.ignore_alts");
 535         if (!sec)
 536                 return 0;
 537
 538         list_for_each_entry(rela, &sec->rela_list, list) {
 539                 if (rela->sym->type != STT_SECTION) {
 540                         WARN("unexpected relocation symbol type in %s", sec->name);
 541                         return -1;
 542                 }
 543
 544                 insn = find_insn(file, rela->sym->sec, rela->addend);
 545                 if (!insn) {
 546                         WARN("bad .discard.ignore_alts entry");
 547                         return -1;
 548                 }
 549
 550                 insn->ignore_alts = true;
 551         }
 552
 553         return 0;
 554 }
 555
 556 /*
 557  * Find the destination instructions for all jumps.
 558  */
 559 static int add_jump_destinations(struct objtool_file *file)
 560 {
 561         struct instruction *insn;
 562         struct rela *rela;
 563         struct section *dest_sec;
 564         unsigned long dest_off;
 565
 566         for_each_insn(file, insn) {
 567                 if (insn->type != INSN_JUMP_CONDITIONAL &&
 568                     insn->type != INSN_JUMP_UNCONDITIONAL)
 569                         continue;
 570
 571                 if (insn->ignore)
 572                         continue;
 573
 574                 rela = find_rela_by_dest_range(insn->sec, insn->offset,
 575                                                insn->len);
 576                 if (!rela) {
 577                         dest_sec = insn->sec;
 578                         dest_off = insn->offset + insn->len + insn->immediate;
 579                 } else if (rela->sym->type == STT_SECTION) {
 580                         dest_sec = rela->sym->sec;
 581                         dest_off = rela->addend + 4;
 582                 } else if (rela->sym->sec->idx) {
 583                         dest_sec = rela->sym->sec;
 584                         dest_off = rela->sym->sym.st_value + rela->addend + 4;
 585                 } else if (strstr(rela->sym->name, "_indirect_thunk_")) {
 586                         /*
 587                          * Retpoline jumps are really dynamic jumps in
 588                          * disguise, so convert them accordingly.
 589                          */
 590                         insn->type = INSN_JUMP_DYNAMIC;
 591                         insn->retpoline_safe = true;
 592                         continue;
 593                 } else {
 594                         /* sibling call */
 595                         insn->call_dest = rela->sym;
 596                         insn->jump_dest = NULL;
 597                         continue;
 598                 }
 599
 600                 insn->jump_dest = find_insn(file, dest_sec, dest_off);
 601                 if (!insn->jump_dest) {
 602
 603                         /*
 604                          * This is a special case where an alt instruction
 605                          * jumps past the end of the section.  These are
 606                          * handled later in handle_group_alt().
 607                          */
 608                         if (!strcmp(insn->sec->name, ".altinstr_replacement"))
 609                                 continue;
 610
 611                         WARN_FUNC("can't find jump dest instruction at %s+0x%lx",
 612                                   insn->sec, insn->offset, dest_sec->name,
 613                                   dest_off);
 614                         return -1;
 615                 }
 616
 617                 /*
 618                  * Cross-function jump.
 619                  */
 620                 if (insn->func && insn->jump_dest->func &&
 621                     insn->func != insn->jump_dest->func) {
 622
 623                         /*
 624                          * For GCC 8+, create parent/child links for any cold
 625                          * subfunctions.  This is _mostly_ redundant with a
 626                          * similar initialization in read_symbols().
 627                          *
 628                          * If a function has aliases, we want the *first* such
 629                          * function in the symbol table to be the subfunction's
 630                          * parent.  In that case we overwrite the
 631                          * initialization done in read_symbols().
 632                          *
 633                          * However this code can't completely replace the
 634                          * read_symbols() code because this doesn't detect the
 635                          * case where the parent function's only reference to a
 636                          * subfunction is through a switch table.
 637                          */
 638                         if (!strstr(insn->func->name, ".cold.") &&
 639                             strstr(insn->jump_dest->func->name, ".cold.")) {
 640                                 insn->func->cfunc = insn->jump_dest->func;
 641                                 insn->jump_dest->func->pfunc = insn->func;
 642
 643                         } else if (insn->jump_dest->func->pfunc != insn->func->pfunc &&
 644                                    insn->jump_dest->offset == insn->jump_dest->func->offset) {
 645
 646                                 /* sibling class */
 647                                 insn->call_dest = insn->jump_dest->func;
 648                                 insn->jump_dest = NULL;
 649                         }
 650                 }
 651         }
 652
 653         return 0;
 654 }
 655
 656 /*
 657  * Find the destination instructions for all calls.
 658  */
 659 static int add_call_destinations(struct objtool_file *file)
 660 {
 661         struct instruction *insn;
 662         unsigned long dest_off;
 663         struct rela *rela;
 664
 665         for_each_insn(file, insn) {
 666                 if (insn->type != INSN_CALL)
 667                         continue;
 668
 669                 rela = find_rela_by_dest_range(insn->sec, insn->offset,
 670                                                insn->len);
 671                 if (!rela) {
 672                         dest_off = insn->offset + insn->len + insn->immediate;
 673                         insn->call_dest = find_symbol_by_offset(insn->sec,
 674                                                                 dest_off);
 675
 676                         if (!insn->call_dest && !insn->ignore) {
 677                                 WARN_FUNC("unsupported intra-function call",
 678                                           insn->sec, insn->offset);
 679                                 if (retpoline)
 680                                         WARN("If this is a retpoline, please patch it in with alternatives and annotate it with ANNOTATE_NOSPEC_ALTERNATIVE.");
 681                                 return -1;
 682                         }
 683
 684                 } else if (rela->sym->type == STT_SECTION) {
 685                         insn->call_dest = find_symbol_by_offset(rela->sym->sec,
 686                                                                 rela->addend+4);
 687                         if (!insn->call_dest ||
 688                             insn->call_dest->type != STT_FUNC) {
 689                                 WARN_FUNC("can't find call dest symbol at %s+0x%x",
 690                                           insn->sec, insn->offset,
 691                                           rela->sym->sec->name,
 692                                           rela->addend + 4);
 693                                 return -1;
 694                         }
 695                 } else
 696                         insn->call_dest = rela->sym;
 697         }
 698
 699         return 0;
 700 }
 701
 702 /*
 703  * The .alternatives section requires some extra special care, over and above
 704  * what other special sections require:
 705  *
 706  * 1. Because alternatives are patched in-place, we need to insert a fake jump
 707  *    instruction at the end so that validate_branch() skips all the original
 708  *    replaced instructions when validating the new instruction path.
 709  *
 710  * 2. An added wrinkle is that the new instruction length might be zero.  In
 711  *    that case the old instructions are replaced with noops.  We simulate that
 712  *    by creating a fake jump as the only new instruction.
 713  *
 714  * 3. In some cases, the alternative section includes an instruction which
 715  *    conditionally jumps to the _end_ of the entry.  We have to modify these
 716  *    jumps' destinations to point back to .text rather than the end of the
 717  *    entry in .altinstr_replacement.
 718  */
 719 static int handle_group_alt(struct objtool_file *file,
 720                             struct special_alt *special_alt,
 721                             struct instruction *orig_insn,
 722                             struct instruction **new_insn)
 723 {
 724         struct instruction *last_orig_insn, *last_new_insn, *insn, *fake_jump = NULL;
 725         unsigned long dest_off;
 726
 727         last_orig_insn = NULL;
 728         insn = orig_insn;
 729         sec_for_each_insn_from(file, insn) {
 730                 if (insn->offset >= special_alt->orig_off + special_alt->orig_len)
 731                         break;
 732
 733                 insn->alt_group = true;
 734                 last_orig_insn = insn;
 735         }
 736
 737         if (next_insn_same_sec(file, last_orig_insn)) {
 738                 fake_jump = malloc(sizeof(*fake_jump));
 739                 if (!fake_jump) {
 740                         WARN("malloc failed");
 741                         return -1;
 742                 }
 743                 memset(fake_jump, 0, sizeof(*fake_jump));
 744                 INIT_LIST_HEAD(&fake_jump->alts);
 745                 clear_insn_state(&fake_jump->state);
 746
 747                 fake_jump->sec = special_alt->new_sec;
 748                 fake_jump->offset = -1;
 749                 fake_jump->type = INSN_JUMP_UNCONDITIONAL;
 750                 fake_jump->jump_dest = list_next_entry(last_orig_insn, list);
 751                 fake_jump->ignore = true;
 752         }
 753
 754         if (!special_alt->new_len) {
 755                 if (!fake_jump) {
 756                         WARN("%s: empty alternative at end of section",
 757                              special_alt->orig_sec->name);
 758                         return -1;
 759                 }
 760
 761                 *new_insn = fake_jump;
 762                 return 0;
 763         }
 764
 765         last_new_insn = NULL;
 766         insn = *new_insn;
 767         sec_for_each_insn_from(file, insn) {
 768                 if (insn->offset >= special_alt->new_off + special_alt->new_len)
 769                         break;
 770
 771                 last_new_insn = insn;
 772
 773                 insn->ignore = orig_insn->ignore_alts;
 774                 insn->func = orig_insn->func;
 775
 776                 if (insn->type != INSN_JUMP_CONDITIONAL &&
 777                     insn->type != INSN_JUMP_UNCONDITIONAL)
 778                         continue;
 779
 780                 if (!insn->immediate)
 781                         continue;
 782
 783                 dest_off = insn->offset + insn->len + insn->immediate;
 784                 if (dest_off == special_alt->new_off + special_alt->new_len) {
 785                         if (!fake_jump) {
 786                                 WARN("%s: alternative jump to end of section",
 787                                      special_alt->orig_sec->name);
 788                                 return -1;
 789                         }
 790                         insn->jump_dest = fake_jump;
 791                 }
 792
 793                 if (!insn->jump_dest) {
 794                         WARN_FUNC("can't find alternative jump destination",
 795                                   insn->sec, insn->offset);
 796                         return -1;
 797                 }
 798         }
 799
 800         if (!last_new_insn) {
 801                 WARN_FUNC("can't find last new alternative instruction",
 802                           special_alt->new_sec, special_alt->new_off);
 803                 return -1;
 804         }
 805
 806         if (fake_jump)
 807                 list_add(&fake_jump->list, &last_new_insn->list);
 808
 809         return 0;
 810 }
 811
 812 /*
 813  * A jump table entry can either convert a nop to a jump or a jump to a nop.
 814  * If the original instruction is a jump, make the alt entry an effective nop
 815  * by just skipping the original instruction.
 816  */
 817 static int handle_jump_alt(struct objtool_file *file,
 818                            struct special_alt *special_alt,
 819                            struct instruction *orig_insn,
 820                            struct instruction **new_insn)
 821 {
 822         if (orig_insn->type == INSN_NOP)
 823                 return 0;
 824
 825         if (orig_insn->type != INSN_JUMP_UNCONDITIONAL) {
 826                 WARN_FUNC("unsupported instruction at jump label",
 827                           orig_insn->sec, orig_insn->offset);
 828                 return -1;
 829         }
 830
 831         *new_insn = list_next_entry(orig_insn, list);
 832         return 0;
 833 }
 834
 835 /*
 836  * Read all the special sections which have alternate instructions which can be
 837  * patched in or redirected to at runtime.  Each instruction having alternate
 838  * instruction(s) has them added to its insn->alts list, which will be
 839  * traversed in validate_branch().
 840  */
 841 static int add_special_section_alts(struct objtool_file *file)
 842 {
 843         struct list_head special_alts;
 844         struct instruction *orig_insn, *new_insn;
 845         struct special_alt *special_alt, *tmp;
 846         struct alternative *alt;
 847         int ret;
 848
 849         ret = special_get_alts(file->elf, &special_alts);
 850         if (ret)
 851                 return ret;
 852
 853         list_for_each_entry_safe(special_alt, tmp, &special_alts, list) {
 854
 855                 orig_insn = find_insn(file, special_alt->orig_sec,
 856                                       special_alt->orig_off);
 857                 if (!orig_insn) {
 858                         WARN_FUNC("special: can't find orig instruction",
 859                                   special_alt->orig_sec, special_alt->orig_off);
 860                         ret = -1;
 861                         goto out;
 862                 }
 863
 864                 new_insn = NULL;
 865                 if (!special_alt->group || special_alt->new_len) {
 866                         new_insn = find_insn(file, special_alt->new_sec,
 867                                              special_alt->new_off);
 868                         if (!new_insn) {
 869                                 WARN_FUNC("special: can't find new instruction",
 870                                           special_alt->new_sec,
 871                                           special_alt->new_off);
 872                                 ret = -1;
 873                                 goto out;
 874                         }
 875                 }
 876
 877                 if (special_alt->group) {
 878                         ret = handle_group_alt(file, special_alt, orig_insn,
 879                                                &new_insn);
 880                         if (ret)
 881                                 goto out;
 882                 } else if (special_alt->jump_or_nop) {
 883                         ret = handle_jump_alt(file, special_alt, orig_insn,
 884                                               &new_insn);
 885                         if (ret)
 886                                 goto out;
 887                 }
 888
 889                 alt = malloc(sizeof(*alt));
 890                 if (!alt) {
 891                         WARN("malloc failed");
 892                         ret = -1;
 893                         goto out;
 894                 }
 895
 896                 alt->insn = new_insn;
 897                 alt->skip_orig = special_alt->skip_orig;
 898                 orig_insn->ignore_alts |= special_alt->skip_alt;
 899                 list_add_tail(&alt->list, &orig_insn->alts);
 900
 901                 list_del(&special_alt->list);
 902                 free(special_alt);
 903         }
 904
 905 out:
 906         return ret;
 907 }
 908
 909 static int add_switch_table(struct objtool_file *file, struct instruction *insn,
 910                             struct rela *table, struct rela *next_table)
 911 {
 912         struct rela *rela = table;
 913         struct instruction *alt_insn;
 914         struct alternative *alt;
 915         struct symbol *pfunc = insn->func->pfunc;
 916         unsigned int prev_offset = 0;
 917
 918         list_for_each_entry_from(rela, &table->rela_sec->rela_list, list) {
 919                 if (rela == next_table)
 920                         break;
 921
 922                 /* Make sure the switch table entries are consecutive: */
 923                 if (prev_offset && rela->offset != prev_offset + 8)
 924                         break;
 925
 926                 /* Detect function pointers from contiguous objects: */
 927                 if (rela->sym->sec == pfunc->sec &&
 928                     rela->addend == pfunc->offset)
 929                         break;
 930
 931                 alt_insn = find_insn(file, rela->sym->sec, rela->addend);
 932                 if (!alt_insn)
 933                         break;
 934
 935                 /* Make sure the jmp dest is in the function or subfunction: */
 936                 if (alt_insn->func->pfunc != pfunc)
 937                         break;
 938
 939                 alt = malloc(sizeof(*alt));
 940                 if (!alt) {
 941                         WARN("malloc failed");
 942                         return -1;
 943                 }
 944
 945                 alt->insn = alt_insn;
 946                 list_add_tail(&alt->list, &insn->alts);
 947                 prev_offset = rela->offset;
 948         }
 949
 950         if (!prev_offset) {
 951                 WARN_FUNC("can't find switch jump table",
 952                           insn->sec, insn->offset);
 953                 return -1;
 954         }
 955
 956         return 0;
 957 }
 958
 959 /*
 960  * find_switch_table() - Given a dynamic jump, find the switch jump table in
 961  * .rodata associated with it.
 962  *
 963  * There are 3 basic patterns:
 964  *
 965  * 1. jmpq *[rodata addr](,%reg,8)
 966  *
 967  *    This is the most common case by far.  It jumps to an address in a simple
 968  *    jump table which is stored in .rodata.
 969  *
 970  * 2. jmpq *[rodata addr](%rip)
 971  *
 972  *    This is caused by a rare GCC quirk, currently only seen in three driver
 973  *    functions in the kernel, only with certain obscure non-distro configs.
 974  *
 975  *    As part of an optimization, GCC makes a copy of an existing switch jump
 976  *    table, modifies it, and then hard-codes the jump (albeit with an indirect
 977  *    jump) to use a single entry in the table.  The rest of the jump table and
 978  *    some of its jump targets remain as dead code.
 979  *
 980  *    In such a case we can just crudely ignore all unreachable instruction
 981  *    warnings for the entire object file.  Ideally we would just ignore them
 982  *    for the function, but that would require redesigning the code quite a
 983  *    bit.  And honestly that's just not worth doing: unreachable instruction
 984  *    warnings are of questionable value anyway, and this is such a rare issue.
 985  *
 986  * 3. mov [rodata addr],%reg1
 987  *    ... some instructions ...
 988  *    jmpq *(%reg1,%reg2,8)
 989  *
 990  *    This is a fairly uncommon pattern which is new for GCC 6.  As of this
 991  *    writing, there are 11 occurrences of it in the allmodconfig kernel.
 992  *
 993  *    As of GCC 7 there are quite a few more of these and the 'in between' code
 994  *    is significant. Esp. with KASAN enabled some of the code between the mov
 995  *    and jmpq uses .rodata itself, which can confuse things.
 996  *
 997  *    TODO: Once we have DWARF CFI and smarter instruction decoding logic,
 998  *    ensure the same register is used in the mov and jump instructions.
 999  *
1000  *    NOTE: RETPOLINE made it harder still to decode dynamic jumps.
1001  */
1002 static struct rela *find_switch_table(struct objtool_file *file,
1003                                       struct symbol *func,
1004                                       struct instruction *insn)
1005 {
1006         struct rela *text_rela, *rodata_rela;
1007         struct instruction *orig_insn = insn;
1008         struct section *rodata_sec;
1009         unsigned long table_offset;
1010
1011         /*
1012          * Backward search using the @first_jump_src links, these help avoid
1013          * much of the 'in between' code. Which avoids us getting confused by
1014          * it.
1015          */
1016         for (;
1017              &insn->list != &file->insn_list &&
1018              insn->sec == func->sec &&
1019              insn->offset >= func->offset;
1020
1021              insn = insn->first_jump_src ?: list_prev_entry(insn, list)) {
1022
1023                 if (insn != orig_insn && insn->type == INSN_JUMP_DYNAMIC)
1024                         break;
1025
1026                 /* allow small jumps within the range */
1027                 if (insn->type == INSN_JUMP_UNCONDITIONAL &&
1028                     insn->jump_dest &&
1029                     (insn->jump_dest->offset <= insn->offset ||
1030                      insn->jump_dest->offset > orig_insn->offset))
1031                     break;
1032
1033                 /* look for a relocation which references .rodata */
1034                 text_rela = find_rela_by_dest_range(insn->sec, insn->offset,
1035                                                     insn->len);
1036                 if (!text_rela || text_rela->sym->type != STT_SECTION ||
1037                     !text_rela->sym->sec->rodata)
1038                         continue;
1039
1040                 table_offset = text_rela->addend;
1041                 rodata_sec = text_rela->sym->sec;
1042
1043                 if (text_rela->type == R_X86_64_PC32)
1044                         table_offset += 4;
1045
1046                 /*
1047                  * Make sure the .rodata address isn't associated with a
1048                  * symbol.  gcc jump tables are anonymous data.
1049                  */
1050                 if (find_symbol_containing(rodata_sec, table_offset))
1051                         continue;
1052
1053                 rodata_rela = find_rela_by_dest(rodata_sec, table_offset);
1054                 if (rodata_rela) {
1055                         /*
1056                          * Use of RIP-relative switch jumps is quite rare, and
1057                          * indicates a rare GCC quirk/bug which can leave dead
1058                          * code behind.
1059                          */
1060                         if (text_rela->type == R_X86_64_PC32)
1061                                 file->ignore_unreachables = true;
1062
1063                         return rodata_rela;
1064                 }
1065         }
1066
1067         return NULL;
1068 }
1069
1070
1071 static int add_func_switch_tables(struct objtool_file *file,
1072                                   struct symbol *func)
1073 {
1074         struct instruction *insn, *last = NULL, *prev_jump = NULL;
1075         struct rela *rela, *prev_rela = NULL;
1076         int ret;
1077
1078         func_for_each_insn_all(file, func, insn) {
1079                 if (!last)
1080                         last = insn;
1081
1082                 /*
1083                  * Store back-pointers for unconditional forward jumps such
1084                  * that find_switch_table() can back-track using those and
1085                  * avoid some potentially confusing code.
1086                  */
1087                 if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest &&
1088                     insn->offset > last->offset &&
1089                     insn->jump_dest->offset > insn->offset &&
1090                     !insn->jump_dest->first_jump_src) {
1091
1092                         insn->jump_dest->first_jump_src = insn;
1093                         last = insn->jump_dest;
1094                 }
1095
1096                 if (insn->type != INSN_JUMP_DYNAMIC)
1097                         continue;
1098
1099                 rela = find_switch_table(file, func, insn);
1100                 if (!rela)
1101                         continue;
1102
1103                 /*
1104                  * We found a switch table, but we don't know yet how big it
1105                  * is.  Don't add it until we reach the end of the function or
1106                  * the beginning of another switch table in the same function.
1107                  */
1108                 if (prev_jump) {
1109                         ret = add_switch_table(file, prev_jump, prev_rela, rela);
1110                         if (ret)
1111                                 return ret;
1112                 }
1113
1114                 prev_jump = insn;
1115                 prev_rela = rela;
1116         }
1117
1118         if (prev_jump) {
1119                 ret = add_switch_table(file, prev_jump, prev_rela, NULL);
1120                 if (ret)
1121                         return ret;
1122         }
1123
1124         return 0;
1125 }
1126
1127 /*
1128  * For some switch statements, gcc generates a jump table in the .rodata
1129  * section which contains a list of addresses within the function to jump to.
1130  * This finds these jump tables and adds them to the insn->alts lists.
1131  */
1132 static int add_switch_table_alts(struct objtool_file *file)
1133 {
1134         struct section *sec;
1135         struct symbol *func;
1136         int ret;
1137
1138         if (!file->rodata)
1139                 return 0;
1140
1141         for_each_sec(file, sec) {
1142                 list_for_each_entry(func, &sec->symbol_list, list) {
1143                         if (func->type != STT_FUNC)
1144                                 continue;
1145
1146                         ret = add_func_switch_tables(file, func);
1147                         if (ret)
1148                                 return ret;
1149                 }
1150         }
1151
1152         return 0;
1153 }
1154
1155 static int read_unwind_hints(struct objtool_file *file)
1156 {
1157         struct section *sec, *relasec;
1158         struct rela *rela;
1159         struct unwind_hint *hint;
1160         struct instruction *insn;
1161         struct cfi_reg *cfa;
1162         int i;
1163
1164         sec = find_section_by_name(file->elf, ".discard.unwind_hints");
1165         if (!sec)
1166                 return 0;
1167
1168         relasec = sec->rela;
1169         if (!relasec) {
1170                 WARN("missing .rela.discard.unwind_hints section");
1171                 return -1;
1172         }
1173
1174         if (sec->len % sizeof(struct unwind_hint)) {
1175                 WARN("struct unwind_hint size mismatch");
1176                 return -1;
1177         }
1178
1179         file->hints = true;
1180
1181         for (i = 0; i < sec->len / sizeof(struct unwind_hint); i++) {
1182                 hint = (struct unwind_hint *)sec->data->d_buf + i;
1183
1184                 rela = find_rela_by_dest(sec, i * sizeof(*hint));
1185                 if (!rela) {
1186                         WARN("can't find rela for unwind_hints[%d]", i);
1187                         return -1;
1188                 }
1189
1190                 insn = find_insn(file, rela->sym->sec, rela->addend);
1191                 if (!insn) {
1192                         WARN("can't find insn for unwind_hints[%d]", i);
1193                         return -1;
1194                 }
1195
1196                 cfa = &insn->state.cfa;
1197
1198                 if (hint->type == UNWIND_HINT_TYPE_SAVE) {
1199                         insn->save = true;
1200                         continue;
1201
1202                 } else if (hint->type == UNWIND_HINT_TYPE_RESTORE) {
1203                         insn->restore = true;
1204                         insn->hint = true;
1205                         continue;
1206                 }
1207
1208                 insn->hint = true;
1209
1210                 switch (hint->sp_reg) {
1211                 case ORC_REG_UNDEFINED:
1212                         cfa->base = CFI_UNDEFINED;
1213                         break;
1214                 case ORC_REG_SP:
1215                         cfa->base = CFI_SP;
1216                         break;
1217                 case ORC_REG_BP:
1218                         cfa->base = CFI_BP;
1219                         break;
1220                 case ORC_REG_SP_INDIRECT:
1221                         cfa->base = CFI_SP_INDIRECT;
1222                         break;
1223                 case ORC_REG_R10:
1224                         cfa->base = CFI_R10;
1225                         break;
1226                 case ORC_REG_R13:
1227                         cfa->base = CFI_R13;
1228                         break;
1229                 case ORC_REG_DI:
1230                         cfa->base = CFI_DI;
1231                         break;
1232                 case ORC_REG_DX:
1233                         cfa->base = CFI_DX;
1234                         break;
1235                 default:
1236                         WARN_FUNC("unsupported unwind_hint sp base reg %d",
1237                                   insn->sec, insn->offset, hint->sp_reg);
1238                         return -1;
1239                 }
1240
1241                 cfa->offset = hint->sp_offset;
1242                 insn->state.type = hint->type;
1243                 insn->state.end = hint->end;
1244         }
1245
1246         return 0;
1247 }
1248
1249 static int read_retpoline_hints(struct objtool_file *file)
1250 {
1251         struct section *sec;
1252         struct instruction *insn;
1253         struct rela *rela;
1254
1255         sec = find_section_by_name(file->elf, ".rela.discard.retpoline_safe");
1256         if (!sec)
1257                 return 0;
1258
1259         list_for_each_entry(rela, &sec->rela_list, list) {
1260                 if (rela->sym->type != STT_SECTION) {
1261                         WARN("unexpected relocation symbol type in %s", sec->name);
1262                         return -1;
1263                 }
1264
1265                 insn = find_insn(file, rela->sym->sec, rela->addend);
1266                 if (!insn) {
1267                         WARN("bad .discard.retpoline_safe entry");
1268                         return -1;
1269                 }
1270
1271                 if (insn->type != INSN_JUMP_DYNAMIC &&
1272                     insn->type != INSN_CALL_DYNAMIC) {
1273                         WARN_FUNC("retpoline_safe hint not an indirect jump/call",
1274                                   insn->sec, insn->offset);
1275                         return -1;
1276                 }
1277
1278                 insn->retpoline_safe = true;
1279         }
1280
1281         return 0;
1282 }
1283
1284 static void mark_rodata(struct objtool_file *file)
1285 {
1286         struct section *sec;
1287         bool found = false;
1288
1289         /*
1290          * This searches for the .rodata section or multiple .rodata.func_name
1291          * sections if -fdata-sections is being used. The .str.1.1 and .str.1.8
1292          * rodata sections are ignored as they don't contain jump tables.
1293          */
1294         for_each_sec(file, sec) {
1295                 if (!strncmp(sec->name, ".rodata", 7) &&
1296                     !strstr(sec->name, ".str1.")) {
1297                         sec->rodata = true;
1298                         found = true;
1299                 }
1300         }
1301
1302         file->rodata = found;
1303 }
1304
1305 static int decode_sections(struct objtool_file *file)
1306 {
1307         int ret;
1308
1309         mark_rodata(file);
1310
1311         ret = decode_instructions(file);
1312         if (ret)
1313                 return ret;
1314
1315         ret = add_dead_ends(file);
1316         if (ret)
1317                 return ret;
1318
1319         add_ignores(file);
1320         add_uaccess_safe(file);
1321
1322         ret = add_ignore_alternatives(file);
1323         if (ret)
1324                 return ret;
1325
1326         ret = add_jump_destinations(file);
1327         if (ret)
1328                 return ret;
1329
1330         ret = add_special_section_alts(file);
1331         if (ret)
1332                 return ret;
1333
1334         ret = add_call_destinations(file);
1335         if (ret)
1336                 return ret;
1337
1338         ret = add_switch_table_alts(file);
1339         if (ret)
1340                 return ret;
1341
1342         ret = read_unwind_hints(file);
1343         if (ret)
1344                 return ret;
1345
1346         ret = read_retpoline_hints(file);
1347         if (ret)
1348                 return ret;
1349
1350         return 0;
1351 }
1352
1353 static bool is_fentry_call(struct instruction *insn)
1354 {
1355         if (insn->type == INSN_CALL &&
1356             insn->call_dest->type == STT_NOTYPE &&
1357             !strcmp(insn->call_dest->name, "__fentry__"))
1358                 return true;
1359
1360         return false;
1361 }
1362
1363 static bool has_modified_stack_frame(struct insn_state *state)
1364 {
1365         int i;
1366
1367         if (state->cfa.base != initial_func_cfi.cfa.base ||
1368             state->cfa.offset != initial_func_cfi.cfa.offset ||
1369             state->stack_size != initial_func_cfi.cfa.offset ||
1370             state->drap)
1371                 return true;
1372
1373         for (i = 0; i < CFI_NUM_REGS; i++)
1374                 if (state->regs[i].base != initial_func_cfi.regs[i].base ||
1375                     state->regs[i].offset != initial_func_cfi.regs[i].offset)
1376                         return true;
1377
1378         return false;
1379 }
1380
1381 static bool has_valid_stack_frame(struct insn_state *state)
1382 {
1383         if (state->cfa.base == CFI_BP && state->regs[CFI_BP].base == CFI_CFA &&
1384             state->regs[CFI_BP].offset == -16)
1385                 return true;
1386
1387         if (state->drap && state->regs[CFI_BP].base == CFI_BP)
1388                 return true;
1389
1390         return false;
1391 }
1392
1393 static int update_insn_state_regs(struct instruction *insn, struct insn_state *state)
1394 {
1395         struct cfi_reg *cfa = &state->cfa;
1396         struct stack_op *op = &insn->stack_op;
1397
1398         if (cfa->base != CFI_SP)
1399                 return 0;
1400
1401         /* push */
1402         if (op->dest.type == OP_DEST_PUSH || op->dest.type == OP_DEST_PUSHF)
1403                 cfa->offset += 8;
1404
1405         /* pop */
1406         if (op->src.type == OP_SRC_POP || op->src.type == OP_SRC_POPF)
1407                 cfa->offset -= 8;
1408
1409         /* add immediate to sp */
1410         if (op->dest.type == OP_DEST_REG && op->src.type == OP_SRC_ADD &&
1411             op->dest.reg == CFI_SP && op->src.reg == CFI_SP)
1412                 cfa->offset -= op->src.offset;
1413
1414         return 0;
1415 }
1416
1417 static void save_reg(struct insn_state *state, unsigned char reg, int base,
1418                      int offset)
1419 {
1420         if (arch_callee_saved_reg(reg) &&
1421             state->regs[reg].base == CFI_UNDEFINED) {
1422                 state->regs[reg].base = base;
1423                 state->regs[reg].offset = offset;
1424         }
1425 }
1426
1427 static void restore_reg(struct insn_state *state, unsigned char reg)
1428 {
1429         state->regs[reg].base = CFI_UNDEFINED;
1430         state->regs[reg].offset = 0;
1431 }
1432
1433 /*
1434  * A note about DRAP stack alignment:
1435  *
1436  * GCC has the concept of a DRAP register, which is used to help keep track of
1437  * the stack pointer when aligning the stack.  r10 or r13 is used as the DRAP
1438  * register.  The typical DRAP pattern is:
1439  *
1440  *   4c 8d 54 24 08             lea    0x8(%rsp),%r10
1441  *   48 83 e4 c0                and    $0xffffffffffffffc0,%rsp
1442  *   41 ff 72 f8                pushq  -0x8(%r10)
1443  *   55                         push   %rbp
1444  *   48 89 e5                   mov    %rsp,%rbp
1445  *                              (more pushes)
1446  *   41 52                      push   %r10
1447  *                              ...
1448  *   41 5a                      pop    %r10
1449  *                              (more pops)
1450  *   5d                         pop    %rbp
1451  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1452  *   c3                         retq
1453  *
1454  * There are some variations in the epilogues, like:
1455  *
1456  *   5b                         pop    %rbx
1457  *   41 5a                      pop    %r10
1458  *   41 5c                      pop    %r12
1459  *   41 5d                      pop    %r13
1460  *   41 5e                      pop    %r14
1461  *   c9                         leaveq
1462  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1463  *   c3                         retq
1464  *
1465  * and:
1466  *
1467  *   4c 8b 55 e8                mov    -0x18(%rbp),%r10
1468  *   48 8b 5d e0                mov    -0x20(%rbp),%rbx
1469  *   4c 8b 65 f0                mov    -0x10(%rbp),%r12
1470  *   4c 8b 6d f8                mov    -0x8(%rbp),%r13
1471  *   c9                         leaveq
1472  *   49 8d 62 f8                lea    -0x8(%r10),%rsp
1473  *   c3                         retq
1474  *
1475  * Sometimes r13 is used as the DRAP register, in which case it's saved and
1476  * restored beforehand:
1477  *
1478  *   41 55                      push   %r13
1479  *   4c 8d 6c 24 10             lea    0x10(%rsp),%r13
1480  *   48 83 e4 f0                and    $0xfffffffffffffff0,%rsp
1481  *                              ...
1482  *   49 8d 65 f0                lea    -0x10(%r13),%rsp
1483  *   41 5d                      pop    %r13
1484  *   c3                         retq
1485  */
1486 static int update_insn_state(struct instruction *insn, struct insn_state *state)
1487 {
1488         struct stack_op *op = &insn->stack_op;
1489         struct cfi_reg *cfa = &state->cfa;
1490         struct cfi_reg *regs = state->regs;
1491
1492         /* stack operations don't make sense with an undefined CFA */
1493         if (cfa->base == CFI_UNDEFINED) {
1494                 if (insn->func) {
1495                         WARN_FUNC("undefined stack state", insn->sec, insn->offset);
1496                         return -1;
1497                 }
1498                 return 0;
1499         }
1500
1501         if (state->type == ORC_TYPE_REGS || state->type == ORC_TYPE_REGS_IRET)
1502                 return update_insn_state_regs(insn, state);
1503
1504         switch (op->dest.type) {
1505
1506         case OP_DEST_REG:
1507                 switch (op->src.type) {
1508
1509                 case OP_SRC_REG:
1510                         if (op->src.reg == CFI_SP && op->dest.reg == CFI_BP &&
1511                             cfa->base == CFI_SP &&
1512                             regs[CFI_BP].base == CFI_CFA &&
1513                             regs[CFI_BP].offset == -cfa->offset) {
1514
1515                                 /* mov %rsp, %rbp */
1516                                 cfa->base = op->dest.reg;
1517                                 state->bp_scratch = false;
1518                         }
1519
1520                         else if (op->src.reg == CFI_SP &&
1521                                  op->dest.reg == CFI_BP && state->drap) {
1522
1523                                 /* drap: mov %rsp, %rbp */
1524                                 regs[CFI_BP].base = CFI_BP;
1525                                 regs[CFI_BP].offset = -state->stack_size;
1526                                 state->bp_scratch = false;
1527                         }
1528
1529                         else if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1530
1531                                 /*
1532                                  * mov %rsp, %reg
1533                                  *
1534                                  * This is needed for the rare case where GCC
1535                                  * does:
1536                                  *
1537                                  *   mov    %rsp, %rax
1538                                  *   ...
1539                                  *   mov    %rax, %rsp
1540                                  */
1541                                 state->vals[op->dest.reg].base = CFI_CFA;
1542                                 state->vals[op->dest.reg].offset = -state->stack_size;
1543                         }
1544
1545                         else if (op->src.reg == CFI_BP && op->dest.reg == CFI_SP &&
1546                                  cfa->base == CFI_BP) {
1547
1548                                 /*
1549                                  * mov %rbp, %rsp
1550                                  *
1551                                  * Restore the original stack pointer (Clang).
1552                                  */
1553                                 state->stack_size = -state->regs[CFI_BP].offset;
1554                         }
1555
1556                         else if (op->dest.reg == cfa->base) {
1557
1558                                 /* mov %reg, %rsp */
1559                                 if (cfa->base == CFI_SP &&
1560                                     state->vals[op->src.reg].base == CFI_CFA) {
1561
1562                                         /*
1563                                          * This is needed for the rare case
1564                                          * where GCC does something dumb like:
1565                                          *
1566                                          *   lea    0x8(%rsp), %rcx
1567                                          *   ...
1568                                          *   mov    %rcx, %rsp
1569                                          */
1570                                         cfa->offset = -state->vals[op->src.reg].offset;
1571                                         state->stack_size = cfa->offset;
1572
1573                                 } else {
1574                                         cfa->base = CFI_UNDEFINED;
1575                                         cfa->offset = 0;
1576                                 }
1577                         }
1578
1579                         break;
1580
1581                 case OP_SRC_ADD:
1582                         if (op->dest.reg == CFI_SP && op->src.reg == CFI_SP) {
1583
1584                                 /* add imm, %rsp */
1585                                 state->stack_size -= op->src.offset;
1586                                 if (cfa->base == CFI_SP)
1587                                         cfa->offset -= op->src.offset;
1588                                 break;
1589                         }
1590
1591                         if (op->dest.reg == CFI_SP && op->src.reg == CFI_BP) {
1592
1593                                 /* lea disp(%rbp), %rsp */
1594                                 state->stack_size = -(op->src.offset + regs[CFI_BP].offset);
1595                                 break;
1596                         }
1597
1598                         if (op->src.reg == CFI_SP && cfa->base == CFI_SP) {
1599
1600                                 /* drap: lea disp(%rsp), %drap */
1601                                 state->drap_reg = op->dest.reg;
1602
1603                                 /*
1604                                  * lea disp(%rsp), %reg
1605                                  *
1606                                  * This is needed for the rare case where GCC
1607                                  * does something dumb like:
1608                                  *
1609                                  *   lea    0x8(%rsp), %rcx
1610                                  *   ...
1611                                  *   mov    %rcx, %rsp
1612                                  */
1613                                 state->vals[op->dest.reg].base = CFI_CFA;
1614                                 state->vals[op->dest.reg].offset = \
1615                                         -state->stack_size + op->src.offset;
1616
1617                                 break;
1618                         }
1619
1620                         if (state->drap && op->dest.reg == CFI_SP &&
1621                             op->src.reg == state->drap_reg) {
1622
1623                                  /* drap: lea disp(%drap), %rsp */
1624                                 cfa->base = CFI_SP;
1625                                 cfa->offset = state->stack_size = -op->src.offset;
1626                                 state->drap_reg = CFI_UNDEFINED;
1627                                 state->drap = false;
1628                                 break;
1629                         }
1630
1631                         if (op->dest.reg == state->cfa.base) {
1632                                 WARN_FUNC("unsupported stack register modification",
1633                                           insn->sec, insn->offset);
1634                                 return -1;
1635                         }
1636
1637                         break;
1638
1639                 case OP_SRC_AND:
1640                         if (op->dest.reg != CFI_SP ||
1641                             (state->drap_reg != CFI_UNDEFINED && cfa->base != CFI_SP) ||
1642                             (state->drap_reg == CFI_UNDEFINED && cfa->base != CFI_BP)) {
1643                                 WARN_FUNC("unsupported stack pointer realignment",
1644                                           insn->sec, insn->offset);
1645                                 return -1;
1646                         }
1647
1648                         if (state->drap_reg != CFI_UNDEFINED) {
1649                                 /* drap: and imm, %rsp */
1650                                 cfa->base = state->drap_reg;
1651                                 cfa->offset = state->stack_size = 0;
1652                                 state->drap = true;
1653                         }
1654
1655                         /*
1656                          * Older versions of GCC (4.8ish) realign the stack
1657                          * without DRAP, with a frame pointer.
1658                          */
1659
1660                         break;
1661
1662                 case OP_SRC_POP:
1663                 case OP_SRC_POPF:
1664                         if (!state->drap && op->dest.type == OP_DEST_REG &&
1665                             op->dest.reg == cfa->base) {
1666
1667                                 /* pop %rbp */
1668                                 cfa->base = CFI_SP;
1669                         }
1670
1671                         if (state->drap && cfa->base == CFI_BP_INDIRECT &&
1672                             op->dest.type == OP_DEST_REG &&
1673                             op->dest.reg == state->drap_reg &&
1674                             state->drap_offset == -state->stack_size) {
1675
1676                                 /* drap: pop %drap */
1677                                 cfa->base = state->drap_reg;
1678                                 cfa->offset = 0;
1679                                 state->drap_offset = -1;
1680
1681                         } else if (regs[op->dest.reg].offset == -state->stack_size) {
1682
1683                                 /* pop %reg */
1684                                 restore_reg(state, op->dest.reg);
1685                         }
1686
1687                         state->stack_size -= 8;
1688                         if (cfa->base == CFI_SP)
1689                                 cfa->offset -= 8;
1690
1691                         break;
1692
1693                 case OP_SRC_REG_INDIRECT:
1694                         if (state->drap && op->src.reg == CFI_BP &&
1695                             op->src.offset == state->drap_offset) {
1696
1697                                 /* drap: mov disp(%rbp), %drap */
1698                                 cfa->base = state->drap_reg;
1699                                 cfa->offset = 0;
1700                                 state->drap_offset = -1;
1701                         }
1702
1703                         if (state->drap && op->src.reg == CFI_BP &&
1704                             op->src.offset == regs[op->dest.reg].offset) {
1705
1706                                 /* drap: mov disp(%rbp), %reg */
1707                                 restore_reg(state, op->dest.reg);
1708
1709                         } else if (op->src.reg == cfa->base &&
1710                             op->src.offset == regs[op->dest.reg].offset + cfa->offset) {
1711
1712                                 /* mov disp(%rbp), %reg */
1713                                 /* mov disp(%rsp), %reg */
1714                                 restore_reg(state, op->dest.reg);
1715                         }
1716
1717                         break;
1718
1719                 default:
1720                         WARN_FUNC("unknown stack-related instruction",
1721                                   insn->sec, insn->offset);
1722                         return -1;
1723                 }
1724
1725                 break;
1726
1727         case OP_DEST_PUSH:
1728         case OP_DEST_PUSHF:
1729                 state->stack_size += 8;
1730                 if (cfa->base == CFI_SP)
1731                         cfa->offset += 8;
1732
1733                 if (op->src.type != OP_SRC_REG)
1734                         break;
1735
1736                 if (state->drap) {
1737                         if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1738
1739                                 /* drap: push %drap */
1740                                 cfa->base = CFI_BP_INDIRECT;
1741                                 cfa->offset = -state->stack_size;
1742
1743                                 /* save drap so we know when to restore it */
1744                                 state->drap_offset = -state->stack_size;
1745
1746                         } else if (op->src.reg == CFI_BP && cfa->base == state->drap_reg) {
1747
1748                                 /* drap: push %rbp */
1749                                 state->stack_size = 0;
1750
1751                         } else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1752
1753                                 /* drap: push %reg */
1754                                 save_reg(state, op->src.reg, CFI_BP, -state->stack_size);
1755                         }
1756
1757                 } else {
1758
1759                         /* push %reg */
1760                         save_reg(state, op->src.reg, CFI_CFA, -state->stack_size);
1761                 }
1762
1763                 /* detect when asm code uses rbp as a scratch register */
1764                 if (!no_fp && insn->func && op->src.reg == CFI_BP &&
1765                     cfa->base != CFI_BP)
1766                         state->bp_scratch = true;
1767                 break;
1768
1769         case OP_DEST_REG_INDIRECT:
1770
1771                 if (state->drap) {
1772                         if (op->src.reg == cfa->base && op->src.reg == state->drap_reg) {
1773
1774                                 /* drap: mov %drap, disp(%rbp) */
1775                                 cfa->base = CFI_BP_INDIRECT;
1776                                 cfa->offset = op->dest.offset;
1777
1778                                 /* save drap offset so we know when to restore it */
1779                                 state->drap_offset = op->dest.offset;
1780                         }
1781
1782                         else if (regs[op->src.reg].base == CFI_UNDEFINED) {
1783
1784                                 /* drap: mov reg, disp(%rbp) */
1785                                 save_reg(state, op->src.reg, CFI_BP, op->dest.offset);
1786                         }
1787
1788                 } else if (op->dest.reg == cfa->base) {
1789
1790                         /* mov reg, disp(%rbp) */
1791                         /* mov reg, disp(%rsp) */
1792                         save_reg(state, op->src.reg, CFI_CFA,
1793                                  op->dest.offset - state->cfa.offset);
1794                 }
1795
1796                 break;
1797
1798         case OP_DEST_LEAVE:
1799                 if ((!state->drap && cfa->base != CFI_BP) ||
1800                     (state->drap && cfa->base != state->drap_reg)) {
1801                         WARN_FUNC("leave instruction with modified stack frame",
1802                                   insn->sec, insn->offset);
1803                         return -1;
1804                 }
1805
1806                 /* leave (mov %rbp, %rsp; pop %rbp) */
1807
1808                 state->stack_size = -state->regs[CFI_BP].offset - 8;
1809                 restore_reg(state, CFI_BP);
1810
1811                 if (!state->drap) {
1812                         cfa->base = CFI_SP;
1813                         cfa->offset -= 8;
1814                 }
1815
1816                 break;
1817
1818         case OP_DEST_MEM:
1819                 if (op->src.type != OP_SRC_POP && op->src.type != OP_SRC_POPF) {
1820                         WARN_FUNC("unknown stack-related memory operation",
1821                                   insn->sec, insn->offset);
1822                         return -1;
1823                 }
1824
1825                 /* pop mem */
1826                 state->stack_size -= 8;
1827                 if (cfa->base == CFI_SP)
1828                         cfa->offset -= 8;
1829
1830                 break;
1831
1832         default:
1833                 WARN_FUNC("unknown stack-related instruction",
1834                           insn->sec, insn->offset);
1835                 return -1;
1836         }
1837
1838         return 0;
1839 }
1840
1841 static bool insn_state_match(struct instruction *insn, struct insn_state *state)
1842 {
1843         struct insn_state *state1 = &insn->state, *state2 = state;
1844         int i;
1845
1846         if (memcmp(&state1->cfa, &state2->cfa, sizeof(state1->cfa))) {
1847                 WARN_FUNC("stack state mismatch: cfa1=%d%+d cfa2=%d%+d",
1848                           insn->sec, insn->offset,
1849                           state1->cfa.base, state1->cfa.offset,
1850                           state2->cfa.base, state2->cfa.offset);
1851
1852         } else if (memcmp(&state1->regs, &state2->regs, sizeof(state1->regs))) {
1853                 for (i = 0; i < CFI_NUM_REGS; i++) {
1854                         if (!memcmp(&state1->regs[i], &state2->regs[i],
1855                                     sizeof(struct cfi_reg)))
1856                                 continue;
1857
1858                         WARN_FUNC("stack state mismatch: reg1[%d]=%d%+d reg2[%d]=%d%+d",
1859                                   insn->sec, insn->offset,
1860                                   i, state1->regs[i].base, state1->regs[i].offset,
1861                                   i, state2->regs[i].base, state2->regs[i].offset);
1862                         break;
1863                 }
1864
1865         } else if (state1->type != state2->type) {
1866                 WARN_FUNC("stack state mismatch: type1=%d type2=%d",
1867                           insn->sec, insn->offset, state1->type, state2->type);
1868
1869         } else if (state1->drap != state2->drap ||
1870                  (state1->drap && state1->drap_reg != state2->drap_reg) ||
1871                  (state1->drap && state1->drap_offset != state2->drap_offset)) {
1872                 WARN_FUNC("stack state mismatch: drap1=%d(%d,%d) drap2=%d(%d,%d)",
1873                           insn->sec, insn->offset,
1874                           state1->drap, state1->drap_reg, state1->drap_offset,
1875                           state2->drap, state2->drap_reg, state2->drap_offset);
1876
1877         } else
1878                 return true;
1879
1880         return false;
1881 }
1882
1883 static inline bool func_uaccess_safe(struct symbol *func)
1884 {
1885         if (func)
1886                 return func->alias->uaccess_safe;
1887
1888         return false;
1889 }
1890
1891 static inline const char *insn_dest_name(struct instruction *insn)
1892 {
1893         if (insn->call_dest)
1894                 return insn->call_dest->name;
1895
1896         return "{dynamic}";
1897 }
1898
1899 static int validate_call(struct instruction *insn, struct insn_state *state)
1900 {
1901         if (state->uaccess && !func_uaccess_safe(insn->call_dest)) {
1902                 WARN_FUNC("call to %s() with UACCESS enabled",
1903                                 insn->sec, insn->offset, insn_dest_name(insn));
1904                 return 1;
1905         }
1906
1907         if (state->df) {
1908                 WARN_FUNC("call to %s() with DF set",
1909                                 insn->sec, insn->offset, insn_dest_name(insn));
1910                 return 1;
1911         }
1912
1913         return 0;
1914 }
1915
1916 static int validate_sibling_call(struct instruction *insn, struct insn_state *state)
1917 {
1918         if (has_modified_stack_frame(state)) {
1919                 WARN_FUNC("sibling call from callable instruction with modified stack frame",
1920                                 insn->sec, insn->offset);
1921                 return 1;
1922         }
1923
1924         return validate_call(insn, state);
1925 }
1926
1927 /*
1928  * Follow the branch starting at the given instruction, and recursively follow
1929  * any other branches (jumps).  Meanwhile, track the frame pointer state at
1930  * each instruction and validate all the rules described in
1931  * tools/objtool/Documentation/stack-validation.txt.
1932  */
1933 static int validate_branch(struct objtool_file *file, struct instruction *first,
1934                            struct insn_state state)
1935 {
1936         struct alternative *alt;
1937         struct instruction *insn, *next_insn;
1938         struct section *sec;
1939         struct symbol *func = NULL;
1940         int ret;
1941
1942         insn = first;
1943         sec = insn->sec;
1944
1945         if (insn->alt_group && list_empty(&insn->alts)) {
1946                 WARN_FUNC("don't know how to handle branch to middle of alternative instruction group",
1947                           sec, insn->offset);
1948                 return 1;
1949         }
1950
1951         while (1) {
1952                 next_insn = next_insn_same_sec(file, insn);
1953
1954                 if (file->c_file && func && insn->func && func != insn->func->pfunc) {
1955                         WARN("%s() falls through to next function %s()",
1956                              func->name, insn->func->name);
1957                         return 1;
1958                 }
1959
1960                 func = insn->func ? insn->func->pfunc : NULL;
1961
1962                 if (func && insn->ignore) {
1963                         WARN_FUNC("BUG: why am I validating an ignored function?",
1964                                   sec, insn->offset);
1965                         return 1;
1966                 }
1967
1968                 if (insn->visited) {
1969                         if (!insn->hint && !insn_state_match(insn, &state))
1970                                 return 1;
1971
1972                         /* If we were here with AC=0, but now have AC=1, go again */
1973                         if (insn->state.uaccess || !state.uaccess)
1974                                 return 0;
1975                 }
1976
1977                 if (insn->hint) {
1978                         if (insn->restore) {
1979                                 struct instruction *save_insn, *i;
1980
1981                                 i = insn;
1982                                 save_insn = NULL;
1983                                 func_for_each_insn_continue_reverse(file, insn->func, i) {
1984                                         if (i->save) {
1985                                                 save_insn = i;
1986                                                 break;
1987                                         }
1988                                 }
1989
1990                                 if (!save_insn) {
1991                                         WARN_FUNC("no corresponding CFI save for CFI restore",
1992                                                   sec, insn->offset);
1993                                         return 1;
1994                                 }
1995
1996                                 if (!save_insn->visited) {
1997                                         /*
1998                                          * Oops, no state to copy yet.
1999                                          * Hopefully we can reach this
2000                                          * instruction from another branch
2001                                          * after the save insn has been
2002                                          * visited.
2003                                          */
2004                                         if (insn == first)
2005                                                 return 0;
2006
2007                                         WARN_FUNC("objtool isn't smart enough to handle this CFI save/restore combo",
2008                                                   sec, insn->offset);
2009                                         return 1;
2010                                 }
2011
2012                                 insn->state = save_insn->state;
2013                         }
2014
2015                         state = insn->state;
2016
2017                 } else
2018                         insn->state = state;
2019
2020                 insn->visited = true;
2021
2022                 if (!insn->ignore_alts) {
2023                         bool skip_orig = false;
2024
2025                         list_for_each_entry(alt, &insn->alts, list) {
2026                                 if (alt->skip_orig)
2027                                         skip_orig = true;
2028
2029                                 ret = validate_branch(file, alt->insn, state);
2030                                 if (ret) {
2031                                         if (backtrace)
2032                                                 BT_FUNC("(alt)", insn);
2033                                         return ret;
2034                                 }
2035                         }
2036
2037                         if (skip_orig)
2038                                 return 0;
2039                 }
2040
2041                 switch (insn->type) {
2042
2043                 case INSN_RETURN:
2044                         if (state.uaccess && !func_uaccess_safe(func)) {
2045                                 WARN_FUNC("return with UACCESS enabled", sec, insn->offset);
2046                                 return 1;
2047                         }
2048
2049                         if (!state.uaccess && func_uaccess_safe(func)) {
2050                                 WARN_FUNC("return with UACCESS disabled from a UACCESS-safe function", sec, insn->offset);
2051                                 return 1;
2052                         }
2053
2054                         if (state.df) {
2055                                 WARN_FUNC("return with DF set", sec, insn->offset);
2056                                 return 1;
2057                         }
2058
2059                         if (func && has_modified_stack_frame(&state)) {
2060                                 WARN_FUNC("return with modified stack frame",
2061                                           sec, insn->offset);
2062                                 return 1;
2063                         }
2064
2065                         if (state.bp_scratch) {
2066                                 WARN("%s uses BP as a scratch register",
2067                                      insn->func->name);
2068                                 return 1;
2069                         }
2070
2071                         return 0;
2072
2073                 case INSN_CALL:
2074                 case INSN_CALL_DYNAMIC:
2075                         ret = validate_call(insn, &state);
2076                         if (ret)
2077                                 return ret;
2078
2079                         if (insn->type == INSN_CALL) {
2080                                 if (is_fentry_call(insn))
2081                                         break;
2082
2083                                 ret = dead_end_function(file, insn->call_dest);
2084                                 if (ret == 1)
2085                                         return 0;
2086                                 if (ret == -1)
2087                                         return 1;
2088                         }
2089
2090                         if (!no_fp && func && !has_valid_stack_frame(&state)) {
2091                                 WARN_FUNC("call without frame pointer save/setup",
2092                                           sec, insn->offset);
2093                                 return 1;
2094                         }
2095                         break;
2096
2097                 case INSN_JUMP_CONDITIONAL:
2098                 case INSN_JUMP_UNCONDITIONAL:
2099                         if (func && !insn->jump_dest) {
2100                                 ret = validate_sibling_call(insn, &state);
2101                                 if (ret)
2102                                         return ret;
2103
2104                         } else if (insn->jump_dest &&
2105                                    (!func || !insn->jump_dest->func ||
2106                                     insn->jump_dest->func->pfunc == func)) {
2107                                 ret = validate_branch(file, insn->jump_dest,
2108                                                       state);
2109                                 if (ret) {
2110                                         if (backtrace)
2111                                                 BT_FUNC("(branch)", insn);
2112                                         return ret;
2113                                 }
2114                         }
2115
2116                         if (insn->type == INSN_JUMP_UNCONDITIONAL)
2117                                 return 0;
2118
2119                         break;
2120
2121                 case INSN_JUMP_DYNAMIC:
2122                         if (func && list_empty(&insn->alts)) {
2123                                 ret = validate_sibling_call(insn, &state);
2124                                 if (ret)
2125                                         return ret;
2126                         }
2127
2128                         return 0;
2129
2130                 case INSN_CONTEXT_SWITCH:
2131                         if (func && (!next_insn || !next_insn->hint)) {
2132                                 WARN_FUNC("unsupported instruction in callable function",
2133                                           sec, insn->offset);
2134                                 return 1;
2135                         }
2136                         return 0;
2137
2138                 case INSN_STACK:
2139                         if (update_insn_state(insn, &state))
2140                                 return 1;
2141
2142                         if (insn->stack_op.dest.type == OP_DEST_PUSHF) {
2143                                 if (!state.uaccess_stack) {
2144                                         state.uaccess_stack = 1;
2145                                 } else if (state.uaccess_stack >> 31) {
2146                                         WARN_FUNC("PUSHF stack exhausted", sec, insn->offset);
2147                                         return 1;
2148                                 }
2149                                 state.uaccess_stack <<= 1;
2150                                 state.uaccess_stack  |= state.uaccess;
2151                         }
2152
2153                         if (insn->stack_op.src.type == OP_SRC_POPF) {
2154                                 if (state.uaccess_stack) {
2155                                         state.uaccess = state.uaccess_stack & 1;
2156                                         state.uaccess_stack >>= 1;
2157                                         if (state.uaccess_stack == 1)
2158                                                 state.uaccess_stack = 0;
2159                                 }
2160                         }
2161
2162                         break;
2163
2164                 case INSN_STAC:
2165                         if (state.uaccess) {
2166                                 WARN_FUNC("recursive UACCESS enable", sec, insn->offset);
2167                                 return 1;
2168                         }
2169
2170                         state.uaccess = true;
2171                         break;
2172
2173                 case INSN_CLAC:
2174                         if (!state.uaccess && insn->func) {
2175                                 WARN_FUNC("redundant UACCESS disable", sec, insn->offset);
2176                                 return 1;
2177                         }
2178
2179                         if (func_uaccess_safe(func) && !state.uaccess_stack) {
2180                                 WARN_FUNC("UACCESS-safe disables UACCESS", sec, insn->offset);
2181                                 return 1;
2182                         }
2183
2184                         state.uaccess = false;
2185                         break;
2186
2187                 case INSN_STD:
2188                         if (state.df)
2189                                 WARN_FUNC("recursive STD", sec, insn->offset);
2190
2191                         state.df = true;
2192                         break;
2193
2194                 case INSN_CLD:
2195                         if (!state.df && insn->func)
2196                                 WARN_FUNC("redundant CLD", sec, insn->offset);
2197
2198                         state.df = false;
2199                         break;
2200
2201                 default:
2202                         break;
2203                 }
2204
2205                 if (insn->dead_end)
2206                         return 0;
2207
2208                 if (!next_insn) {
2209                         if (state.cfa.base == CFI_UNDEFINED)
2210                                 return 0;
2211                         WARN("%s: unexpected end of section", sec->name);
2212                         return 1;
2213                 }
2214
2215                 insn = next_insn;
2216         }
2217
2218         return 0;
2219 }
2220
2221 static int validate_unwind_hints(struct objtool_file *file)
2222 {
2223         struct instruction *insn;
2224         int ret, warnings = 0;
2225         struct insn_state state;
2226
2227         if (!file->hints)
2228                 return 0;
2229
2230         clear_insn_state(&state);
2231
2232         for_each_insn(file, insn) {
2233                 if (insn->hint && !insn->visited) {
2234                         ret = validate_branch(file, insn, state);
2235                         if (ret && backtrace)
2236                                 BT_FUNC("<=== (hint)", insn);
2237                         warnings += ret;
2238                 }
2239         }
2240
2241         return warnings;
2242 }
2243
2244 static int validate_retpoline(struct objtool_file *file)
2245 {
2246         struct instruction *insn;
2247         int warnings = 0;
2248
2249         for_each_insn(file, insn) {
2250                 if (insn->type != INSN_JUMP_DYNAMIC &&
2251                     insn->type != INSN_CALL_DYNAMIC)
2252                         continue;
2253
2254                 if (insn->retpoline_safe)
2255                         continue;
2256
2257                 /*
2258                  * .init.text code is ran before userspace and thus doesn't
2259                  * strictly need retpolines, except for modules which are
2260                  * loaded late, they very much do need retpoline in their
2261                  * .init.text
2262                  */
2263                 if (!strcmp(insn->sec->name, ".init.text") && !module)
2264                         continue;
2265
2266                 WARN_FUNC("indirect %s found in RETPOLINE build",
2267                           insn->sec, insn->offset,
2268                           insn->type == INSN_JUMP_DYNAMIC ? "jump" : "call");
2269
2270                 warnings++;
2271         }
2272
2273         return warnings;
2274 }
2275
2276 static bool is_kasan_insn(struct instruction *insn)
2277 {
2278         return (insn->type == INSN_CALL &&
2279                 !strcmp(insn->call_dest->name, "__asan_handle_no_return"));
2280 }
2281
2282 static bool is_ubsan_insn(struct instruction *insn)
2283 {
2284         return (insn->type == INSN_CALL &&
2285                 !strcmp(insn->call_dest->name,
2286                         "__ubsan_handle_builtin_unreachable"));
2287 }
2288
2289 static bool ignore_unreachable_insn(struct instruction *insn)
2290 {
2291         int i;
2292
2293         if (insn->ignore || insn->type == INSN_NOP)
2294                 return true;
2295
2296         /*
2297          * Ignore any unused exceptions.  This can happen when a whitelisted
2298          * function has an exception table entry.
2299          *
2300          * Also ignore alternative replacement instructions.  This can happen
2301          * when a whitelisted function uses one of the ALTERNATIVE macros.
2302          */
2303         if (!strcmp(insn->sec->name, ".fixup") ||
2304             !strcmp(insn->sec->name, ".altinstr_replacement") ||
2305             !strcmp(insn->sec->name, ".altinstr_aux"))
2306                 return true;
2307
2308         /*
2309          * Check if this (or a subsequent) instruction is related to
2310          * CONFIG_UBSAN or CONFIG_KASAN.
2311          *
2312          * End the search at 5 instructions to avoid going into the weeds.
2313          */
2314         if (!insn->func)
2315                 return false;
2316         for (i = 0; i < 5; i++) {
2317
2318                 if (is_kasan_insn(insn) || is_ubsan_insn(insn))
2319                         return true;
2320
2321                 if (insn->type == INSN_JUMP_UNCONDITIONAL) {
2322                         if (insn->jump_dest &&
2323                             insn->jump_dest->func == insn->func) {
2324                                 insn = insn->jump_dest;
2325                                 continue;
2326                         }
2327
2328                         break;
2329                 }
2330
2331                 if (insn->offset + insn->len >= insn->func->offset + insn->func->len)
2332                         break;
2333
2334                 insn = list_next_entry(insn, list);
2335         }
2336
2337         return false;
2338 }
2339
2340 static int validate_functions(struct objtool_file *file)
2341 {
2342         struct section *sec;
2343         struct symbol *func;
2344         struct instruction *insn;
2345         struct insn_state state;
2346         int ret, warnings = 0;
2347
2348         clear_insn_state(&state);
2349
2350         state.cfa = initial_func_cfi.cfa;
2351         memcpy(&state.regs, &initial_func_cfi.regs,
2352                CFI_NUM_REGS * sizeof(struct cfi_reg));
2353         state.stack_size = initial_func_cfi.cfa.offset;
2354
2355         for_each_sec(file, sec) {
2356                 list_for_each_entry(func, &sec->symbol_list, list) {
2357                         if (func->type != STT_FUNC || func->pfunc != func)
2358                                 continue;
2359
2360                         insn = find_insn(file, sec, func->offset);
2361                         if (!insn || insn->ignore)
2362                                 continue;
2363
2364                         state.uaccess = func->alias->uaccess_safe;
2365
2366                         ret = validate_branch(file, insn, state);
2367                         if (ret && backtrace)
2368                                 BT_FUNC("<=== (func)", insn);
2369                         warnings += ret;
2370                 }
2371         }
2372
2373         return warnings;
2374 }
2375
2376 static int validate_reachable_instructions(struct objtool_file *file)
2377 {
2378         struct instruction *insn;
2379
2380         if (file->ignore_unreachables)
2381                 return 0;
2382
2383         for_each_insn(file, insn) {
2384                 if (insn->visited || ignore_unreachable_insn(insn))
2385                         continue;
2386
2387                 WARN_FUNC("unreachable instruction", insn->sec, insn->offset);
2388                 return 1;
2389         }
2390
2391         return 0;
2392 }
2393
2394 static void cleanup(struct objtool_file *file)
2395 {
2396         struct instruction *insn, *tmpinsn;
2397         struct alternative *alt, *tmpalt;
2398
2399         list_for_each_entry_safe(insn, tmpinsn, &file->insn_list, list) {
2400                 list_for_each_entry_safe(alt, tmpalt, &insn->alts, list) {
2401                         list_del(&alt->list);
2402                         free(alt);
2403                 }
2404                 list_del(&insn->list);
2405                 hash_del(&insn->hash);
2406                 free(insn);
2407         }
2408         elf_close(file->elf);
2409 }
2410
2411 static struct objtool_file file;
2412
2413 int check(const char *_objname, bool orc)
2414 {
2415         int ret, warnings = 0;
2416
2417         objname = _objname;
2418
2419         file.elf = elf_open(objname, orc ? O_RDWR : O_RDONLY);
2420         if (!file.elf)
2421                 return 1;
2422
2423         INIT_LIST_HEAD(&file.insn_list);
2424         hash_init(file.insn_hash);
2425         file.c_file = find_section_by_name(file.elf, ".comment");
2426         file.ignore_unreachables = no_unreachable;
2427         file.hints = false;
2428
2429         arch_initial_func_cfi_state(&initial_func_cfi);
2430
2431         ret = decode_sections(&file);
2432         if (ret < 0)
2433                 goto out;
2434         warnings += ret;
2435
2436         if (list_empty(&file.insn_list))
2437                 goto out;
2438
2439         if (retpoline) {
2440                 ret = validate_retpoline(&file);
2441                 if (ret < 0)
2442                         return ret;
2443                 warnings += ret;
2444         }
2445
2446         ret = validate_functions(&file);
2447         if (ret < 0)
2448                 goto out;
2449         warnings += ret;
2450
2451         ret = validate_unwind_hints(&file);
2452         if (ret < 0)
2453                 goto out;
2454         warnings += ret;
2455
2456         if (!warnings) {
2457                 ret = validate_reachable_instructions(&file);
2458                 if (ret < 0)
2459                         goto out;
2460                 warnings += ret;
2461         }
2462
2463         if (orc) {
2464                 ret = create_orc(&file);
2465                 if (ret < 0)
2466                         goto out;
2467
2468                 ret = create_orc_sections(&file);
2469                 if (ret < 0)
2470                         goto out;
2471
2472                 ret = elf_write(file.elf);
2473                 if (ret < 0)
2474                         goto out;
2475         }
2476
2477 out:
2478         cleanup(&file);
2479
2480         /* ignore warnings for now until we get all the code cleaned up */
2481         if (ret || warnings)
2482                 return 0;
2483         return 0;
2484 }