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, §ions_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 } 615