tools/objtool/elf.c

   1 /*
   2  * elf.c - ELF access library
   3  *
   4  * Adapted from kpatch (https://github.com/dynup/kpatch):
   5  * Copyright (C) 2013-2015 Josh Poimboeuf <jpoimboe@redhat.com>
   6  * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
   7  *
   8  * This program is free software; you can redistribute it and/or
   9  * modify it under the terms of the GNU General Public License
  10  * as published by the Free Software Foundation; either version 2
  11  * of the License, or (at your option) any later version.
  12  *
  13  * This program is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16  * GNU General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU General Public License
  19  * along with this program; if not, see <http://www.gnu.org/licenses/>.
  20  */
  21
  22 #include <sys/types.h>
  23 #include <sys/stat.h>
  24 #include <fcntl.h>
  25 #include <stdio.h>
  26 #include <stdlib.h>
  27 #include <string.h>
  28 #include <unistd.h>
  29
  30 #include "elf.h"
  31 #include "warn.h"
  32
  33 struct section *find_section_by_name(struct elf *elf, const char *name)
  34 {
  35         struct section *sec;
  36
  37         list_for_each_entry(sec, &elf->sections, list)
  38                 if (!strcmp(sec->name, name))
  39                         return sec;
  40
  41         return NULL;
  42 }
  43
  44 static struct section *find_section_by_index(struct elf *elf,
  45                                              unsigned int idx)
  46 {
  47         struct section *sec;
  48
  49         list_for_each_entry(sec, &elf->sections, list)
  50                 if (sec->idx == idx)
  51                         return sec;
  52
  53         return NULL;
  54 }
  55
  56 static struct symbol *find_symbol_by_index(struct elf *elf, unsigned int idx)
  57 {
  58         struct section *sec;
  59         struct symbol *sym;
  60
  61         list_for_each_entry(sec, &elf->sections, list)
  62                 hash_for_each_possible(sec->symbol_hash, sym, hash, idx)
  63                         if (sym->idx == idx)
  64                                 return sym;
  65
  66         return NULL;
  67 }
  68
  69 struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset)
  70 {
  71         struct symbol *sym;
  72
  73         list_for_each_entry(sym, &sec->symbol_list, list)
  74                 if (sym->type != STT_SECTION &&
  75                     sym->offset == offset)
  76                         return sym;
  77
  78         return NULL;
  79 }
  80
  81 struct symbol *find_symbol_containing(struct section *sec, unsigned long offset)
  82 {
  83         struct symbol *sym;
  84
  85         list_for_each_entry(sym, &sec->symbol_list, list)
  86                 if (sym->type != STT_SECTION &&
  87                     offset >= sym->offset && offset < sym->offset + sym->len)
  88                         return sym;
  89
  90         return NULL;
  91 }
  92
  93 struct rela *find_rela_by_dest_range(struct section *sec, unsigned long offset,
  94                                      unsigned int len)
  95 {
  96         struct rela *rela;
  97         unsigned long o;
  98
  99         if (!sec->rela)
 100                 return NULL;
 101
 102         for (o = offset; o < offset + len; o++)
 103                 hash_for_each_possible(sec->rela->rela_hash, rela, hash, o)
 104                         if (rela->offset == o)
 105                                 return rela;
 106
 107         return NULL;
 108 }
 109
 110 struct rela *find_rela_by_dest(struct section *sec, unsigned long offset)
 111 {
 112         return find_rela_by_dest_range(sec, offset, 1);
 113 }
 114
 115 struct symbol *find_containing_func(struct section *sec, unsigned long offset)
 116 {
 117         struct symbol *func;
 118
 119         list_for_each_entry(func, &sec->symbol_list, list)
 120                 if (func->type == STT_FUNC && offset >= func->offset &&
 121                     offset < func->offset + func->len)
 122                         return func;
 123
 124         return NULL;
 125 }
 126
 127 static int read_sections(struct elf *elf)
 128 {
 129         Elf_Scn *s = NULL;
 130         struct section *sec;
 131         size_t shstrndx, sections_nr;
 132         int i;
 133
 134         if (elf_getshdrnum(elf->elf, &sections_nr)) {
 135                 WARN_ELF("elf_getshdrnum");
 136                 return -1;
 137         }
 138
 139         if (elf_getshdrstrndx(elf->elf, &shstrndx)) {
 140                 WARN_ELF("elf_getshdrstrndx");
 141                 return -1;
 142         }
 143
 144         for (i = 0; i < sections_nr; i++) {
 145                 sec = malloc(sizeof(*sec));
 146                 if (!sec) {
 147                         perror("malloc");
 148                         return -1;
 149                 }
 150                 memset(sec, 0, sizeof(*sec));
 151
 152                 INIT_LIST_HEAD(&sec->symbol_list);
 153                 INIT_LIST_HEAD(&sec->rela_list);
 154                 hash_init(sec->rela_hash);
 155                 hash_init(sec->symbol_hash);
 156
 157                 list_add_tail(&sec->list, &elf->sections);
 158
 159                 s = elf_getscn(elf->elf, i);
 160                 if (!s) {
 161                         WARN_ELF("elf_getscn");
 162                         return -1;
 163                 }
 164
 165                 sec->idx = elf_ndxscn(s);
 166
 167                 if (!gelf_getshdr(s, &sec->sh)) {
 168                         WARN_ELF("gelf_getshdr");
 169                         return -1;
 170                 }
 171
 172                 sec->name = elf_strptr(elf->elf, shstrndx, sec->sh.sh_name);
 173                 if (!sec->name) {
 174                         WARN_ELF("elf_strptr");
 175                         return -1;
 176                 }
 177
 178                 sec->data = elf_getdata(s, NULL);
 179                 if (!sec->data) {
 180                         WARN_ELF("elf_getdata");
 181                         return -1;
 182                 }
 183
 184                 if (sec->data->d_off != 0 ||
 185                     sec->data->d_size != sec->sh.sh_size) {
 186                         WARN("unexpected data attributes for %s", sec->name);
 187                         return -1;
 188                 }
 189
 190                 sec->len = sec->data->d_size;
 191         }
 192
 193         /* sanity check, one more call to elf_nextscn() should return NULL */
 194         if (elf_nextscn(elf->elf, s)) {
 195                 WARN("section entry mismatch");
 196                 return -1;
 197         }
 198
 199         return 0;
 200 }
 201
 202 static int read_symbols(struct elf *elf)
 203 {
 204         struct section *symtab;
 205         struct symbol *sym;
 206         struct list_head *entry, *tmp;
 207         int symbols_nr, i;
 208
 209         symtab = find_section_by_name(elf, ".symtab");
 210         if (!symtab) {
 211                 WARN("missing symbol table");
 212                 return -1;
 213         }
 214
 215         symbols_nr = symtab->sh.sh_size / symtab->sh.sh_entsize;
 216
 217         for (i = 0; i < symbols_nr; i++) {
 218                 sym = malloc(sizeof(*sym));
 219                 if (!sym) {
 220                         perror("malloc");
 221                         return -1;
 222                 }
 223                 memset(sym, 0, sizeof(*sym));
 224
 225                 sym->idx = i;
 226
 227                 if (!gelf_getsym(symtab->data, i, &sym->sym)) {
 228                         WARN_ELF("gelf_getsym");
 229                         goto err;
 230                 }
 231
 232                 sym->name = elf_strptr(elf->elf, symtab->sh.sh_link,
 233                                        sym->sym.st_name);
 234                 if (!sym->name) {
 235                         WARN_ELF("elf_strptr");
 236                         goto err;
 237                 }
 238
 239                 sym->type = GELF_ST_TYPE(sym->sym.st_info);
 240                 sym->bind = GELF_ST_BIND(sym->sym.st_info);
 241
 242                 if (sym->sym.st_shndx > SHN_UNDEF &&
 243                     sym->sym.st_shndx < SHN_LORESERVE) {
 244                         sym->sec = find_section_by_index(elf,
 245                                                          sym->sym.st_shndx);
 246                         if (!sym->sec) {
 247                                 WARN("couldn't find section for symbol %s",
 248                                      sym->name);
 249                                 goto err;
 250                         }
 251                         if (sym->type == STT_SECTION) {
 252                                 sym->name = sym->sec->name;
 253                                 sym->sec->sym = sym;
 254                         }
 255                 } else
 256                         sym->sec = find_section_by_index(elf, 0);
 257
 258                 sym->offset = sym->sym.st_value;
 259                 sym->len = sym->sym.st_size;
 260
 261                 /* sorted insert into a per-section list */
 262                 entry = &sym->sec->symbol_list;
 263                 list_for_each_prev(tmp, &sym->sec->symbol_list) {
 264                         struct symbol *s;
 265
 266                         s = list_entry(tmp, struct symbol, list);
 267
 268                         if (sym->offset > s->offset) {
 269                                 entry = tmp;
 270                                 break;
 271                         }
 272
 273                         if (sym->offset == s->offset && sym->len >= s->len) {
 274                                 entry = tmp;
 275                                 break;
 276                         }
 277                 }
 278                 list_add(&sym->list, entry);
 279                 hash_add(sym->sec->symbol_hash, &sym->hash, sym->idx);
 280         }
 281
 282         return 0;
 283
 284 err:
 285         free(sym);
 286         return -1;
 287 }
 288
 289 static int read_relas(struct elf *elf)
 290 {
 291         struct section *sec;
 292         struct rela *rela;
 293         int i;
 294         unsigned int symndx;
 295
 296         list_for_each_entry(sec, &elf->sections, list) {
 297                 if (sec->sh.sh_type != SHT_RELA)
 298                         continue;
 299
 300                 sec->base = find_section_by_name(elf, sec->name + 5);
 301                 if (!sec->base) {
 302                         WARN("can't find base section for rela section %s",
 303                              sec->name);
 304                         return -1;
 305                 }
 306
 307                 sec->base->rela = sec;
 308
 309                 for (i = 0; i < sec->sh.sh_size / sec->sh.sh_entsize; i++) {
 310                         rela = malloc(sizeof(*rela));
 311                         if (!rela) {
 312                                 perror("malloc");
 313                                 return -1;
 314                         }
 315                         memset(rela, 0, sizeof(*rela));
 316
 317                         if (!gelf_getrela(sec->data, i, &rela->rela)) {
 318                                 WARN_ELF("gelf_getrela");
 319                                 return -1;
 320                         }
 321
 322                         rela->type = GELF_R_TYPE(rela->rela.r_info);
 323                         rela->addend = rela->rela.r_addend;
 324                         rela->offset = rela->rela.r_offset;
 325                         symndx = GELF_R_SYM(rela->rela.r_info);
 326                         rela->sym = find_symbol_by_index(elf, symndx);
 327                         if (!rela->sym) {
 328                                 WARN("can't find rela entry symbol %d for %s",
 329                                      symndx, sec->name);
 330                                 return -1;
 331                         }
 332
 333                         list_add_tail(&rela->list, &sec->rela_list);
 334                         hash_add(sec->rela_hash, &rela->hash, rela->offset);
 335
 336                 }
 337         }
 338
 339         return 0;
 340 }
 341
 342 struct elf *elf_open(const char *name, int flags)
 343 {
 344         struct elf *elf;
 345         Elf_Cmd cmd;
 346
 347         elf_version(EV_CURRENT);
 348
 349         elf = malloc(sizeof(*elf));
 350         if (!elf) {
 351                 perror("malloc");
 352                 return NULL;
 353         }
 354         memset(elf, 0, sizeof(*elf));
 355
 356         INIT_LIST_HEAD(&elf->sections);
 357
 358         elf->fd = open(name, flags);
 359         if (elf->fd == -1) {
 360                 perror("open");
 361                 goto err;
 362         }
 363
 364         if ((flags & O_ACCMODE) == O_RDONLY)
 365                 cmd = ELF_C_READ_MMAP;
 366         else if ((flags & O_ACCMODE) == O_RDWR)
 367                 cmd = ELF_C_RDWR;
 368         else /* O_WRONLY */
 369                 cmd = ELF_C_WRITE;
 370
 371         elf->elf = elf_begin(elf->fd, cmd, NULL);
 372         if (!elf->elf) {
 373                 WARN_ELF("elf_begin");
 374                 goto err;
 375         }
 376
 377         if (!gelf_getehdr(elf->elf, &elf->ehdr)) {
 378                 WARN_ELF("gelf_getehdr");
 379                 goto err;
 380         }
 381
 382         if (read_sections(elf))
 383                 goto err;
 384
 385         if (read_symbols(elf))
 386                 goto err;
 387
 388         if (read_relas(elf))
 389                 goto err;
 390
 391         return elf;
 392
 393 err:
 394         elf_close(elf);
 395         return NULL;
 396 }
 397
 398 struct section *elf_create_section(struct elf *elf, const char *name,
 399                                    size_t entsize, int nr)
 400 {
 401         struct section *sec, *shstrtab;
 402         size_t size = entsize * nr;
 403         struct Elf_Scn *s;
 404         Elf_Data *data;
 405
 406         sec = malloc(sizeof(*sec));
 407         if (!sec) {
 408                 perror("malloc");
 409                 return NULL;
 410         }
 411         memset(sec, 0, sizeof(*sec));
 412
 413         INIT_LIST_HEAD(&sec->symbol_list);
 414         INIT_LIST_HEAD(&sec->rela_list);
 415         hash_init(sec->rela_hash);
 416         hash_init(sec->symbol_hash);
 417
 418         list_add_tail(&sec->list, &elf->sections);
 419
 420         s = elf_newscn(elf->elf);
 421         if (!s) {
 422                 WARN_ELF("elf_newscn");
 423                 return NULL;
 424         }
 425
 426         sec->name = strdup(name);
 427         if (!sec->name) {
 428                 perror("strdup");
 429                 return NULL;
 430         }
 431
 432         sec->idx = elf_ndxscn(s);
 433         sec->len = size;
 434         sec->changed = true;
 435
 436         sec->data = elf_newdata(s);
 437         if (!sec->data) {
 438                 WARN_ELF("elf_newdata");
 439                 return NULL;
 440         }
 441
 442         sec->data->d_size = size;
 443         sec->data->d_align = 1;
 444
 445         if (size) {
 446                 sec->data->d_buf = malloc(size);
 447                 if (!sec->data->d_buf) {
 448                         perror("malloc");
 449                         return NULL;
 450                 }
 451                 memset(sec->data->d_buf, 0, size);
 452         }
 453
 454         if (!gelf_getshdr(s, &sec->sh)) {
 455                 WARN_ELF("gelf_getshdr");
 456                 return NULL;
 457         }
 458
 459         sec->sh.sh_size = size;
 460         sec->sh.sh_entsize = entsize;
 461         sec->sh.sh_type = SHT_PROGBITS;
 462         sec->sh.sh_addralign = 1;
 463         sec->sh.sh_flags = SHF_ALLOC;
 464
 465
 466         /* Add section name to .shstrtab */
 467         shstrtab = find_section_by_name(elf, ".shstrtab");
 468         if (!shstrtab) {
 469                 WARN("can't find .shstrtab section");
 470                 return NULL;
 471         }
 472
 473         s = elf_getscn(elf->elf, shstrtab->idx);
 474         if (!s) {
 475                 WARN_ELF("elf_getscn");
 476                 return NULL;
 477         }
 478
 479         data = elf_newdata(s);
 480         if (!data) {
 481                 WARN_ELF("elf_newdata");
 482                 return NULL;
 483         }
 484
 485         data->d_buf = sec->name;
 486         data->d_size = strlen(name) + 1;
 487         data->d_align = 1;
 488
 489         sec->sh.sh_name = shstrtab->len;
 490
 491         shstrtab->len += strlen(name) + 1;
 492         shstrtab->changed = true;
 493
 494         return sec;
 495 }
 496
 497 struct section *elf_create_rela_section(struct elf *elf, struct section *base)
 498 {
 499         char *relaname;
 500         struct section *sec;
 501
 502         relaname = malloc(strlen(base->name) + strlen(".rela") + 1);
 503         if (!relaname) {
 504                 perror("malloc");
 505                 return NULL;
 506         }
 507         strcpy(relaname, ".rela");
 508         strcat(relaname, base->name);
 509
 510         sec = elf_create_section(elf, relaname, sizeof(GElf_Rela), 0);
 511         if (!sec)
 512                 return NULL;
 513
 514         base->rela = sec;
 515         sec->base = base;
 516
 517         sec->sh.sh_type = SHT_RELA;
 518         sec->sh.sh_addralign = 8;
 519         sec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx;
 520         sec->sh.sh_info = base->idx;
 521         sec->sh.sh_flags = SHF_INFO_LINK;
 522
 523         return sec;
 524 }
 525
 526 int elf_rebuild_rela_section(struct section *sec)
 527 {
 528         struct rela *rela;
 529         int nr, idx = 0, size;
 530         GElf_Rela *relas;
 531
 532         nr = 0;
 533         list_for_each_entry(rela, &sec->rela_list, list)
 534                 nr++;
 535
 536         size = nr * sizeof(*relas);
 537         relas = malloc(size);
 538         if (!relas) {
 539                 perror("malloc");
 540                 return -1;
 541         }
 542
 543         sec->data->d_buf = relas;
 544         sec->data->d_size = size;
 545
 546         sec->sh.sh_size = size;
 547
 548         idx = 0;
 549         list_for_each_entry(rela, &sec->rela_list, list) {
 550                 relas[idx].r_offset = rela->offset;
 551                 relas[idx].r_addend = rela->addend;
 552                 relas[idx].r_info = GELF_R_INFO(rela->sym->idx, rela->type);
 553                 idx++;
 554         }
 555
 556         return 0;
 557 }
 558
 559 int elf_write(struct elf *elf)
 560 {
 561         struct section *sec;
 562         Elf_Scn *s;
 563
 564         list_for_each_entry(sec, &elf->sections, list) {
 565                 if (sec->changed) {
 566                         s = elf_getscn(elf->elf, sec->idx);
 567                         if (!s) {
 568                                 WARN_ELF("elf_getscn");
 569                                 return -1;
 570                         }
 571                         if (!gelf_update_shdr (s, &sec->sh)) {
 572                                 WARN_ELF("gelf_update_shdr");
 573                                 return -1;
 574                         }
 575                 }
 576         }
 577
 578         if (elf_update(elf->elf, ELF_C_WRITE) < 0) {
 579                 WARN_ELF("elf_update");
 580                 return -1;
 581         }
 582
 583         return 0;
 584 }
 585
 586 void elf_close(struct elf *elf)
 587 {
 588         struct section *sec, *tmpsec;
 589         struct symbol *sym, *tmpsym;
 590         struct rela *rela, *tmprela;
 591
 592         if (elf->elf)
 593                 elf_end(elf->elf);
 594
 595         if (elf->fd > 0)
 596                 close(elf->fd);
 597
 598         list_for_each_entry_safe(sec, tmpsec, &elf->sections, list) {
 599                 list_for_each_entry_safe(sym, tmpsym, &sec->symbol_list, list) {
 600                         list_del(&sym->list);
 601                         hash_del(&sym->hash);
 602                         free(sym);
 603                 }
 604                 list_for_each_entry_safe(rela, tmprela, &sec->rela_list, list) {
 605                         list_del(&rela->list);
 606                         hash_del(&rela->hash);
 607                         free(rela);
 608                 }
 609                 list_del(&sec->list);
 610                 free(sec);
 611         }
 612
 613         free(elf);
 614 }