tools/objtool/check.c

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