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 if (sec->sh.sh_size != 0) { 179 sec->data = elf_getdata(s, NULL); 180 if (!sec->data) { 181 WARN_ELF("elf_getdata"); 182 return -1; 183 } 184 if (sec->data->d_off != 0 || 185 sec->data->d_size != sec->sh.sh_size) { 186 WARN("unexpected data attributes for %s", 187 sec->name); 188 return -1; 189 } 190 } 191 sec->len = sec->sh.sh_size; 192 } 193 194 /* sanity check, one more call to elf_nextscn() should return NULL */ 195 if (elf_nextscn(elf->elf, s)) { 196 WARN("section entry mismatch"); 197 return -1; 198 } 199 200 return 0; 201 } 202 203 static int read_symbols(struct elf *elf) 204 { 205 struct section *symtab; 206 struct symbol *sym; 207 struct list_head *entry, *tmp; 208 int symbols_nr, i; 209 210 symtab = find_section_by_name(elf, ".symtab"); 211 if (!symtab) { 212 WARN("missing symbol table"); 213 return -1; 214 } 215 216 symbols_nr = symtab->sh.sh_size / symtab->sh.sh_entsize; 217 218 for (i = 0; i < symbols_nr; i++) { 219 sym = malloc(sizeof(*sym)); 220 if (!sym) { 221 perror("malloc"); 222 return -1; 223 } 224 memset(sym, 0, sizeof(*sym)); 225 226 sym->idx = i; 227 228 if (!gelf_getsym(symtab->data, i, &sym->sym)) { 229 WARN_ELF("gelf_getsym"); 230 goto err; 231 } 232 233 sym->name = elf_strptr(elf->elf, symtab->sh.sh_link, 234 sym->sym.st_name); 235 if (!sym->name) { 236 WARN_ELF("elf_strptr"); 237 goto err; 238 } 239 240 sym->type = GELF_ST_TYPE(sym->sym.st_info); 241 sym->bind = GELF_ST_BIND(sym->sym.st_info); 242 243 if (sym->sym.st_shndx > SHN_UNDEF && 244 sym->sym.st_shndx < SHN_LORESERVE) { 245 sym->sec = find_section_by_index(elf, 246 sym->sym.st_shndx); 247 if (!sym->sec) { 248 WARN("couldn't find section for symbol %s", 249 sym->name); 250 goto err; 251 } 252 if (sym->type == STT_SECTION) { 253 sym->name = sym->sec->name; 254 sym->sec->sym = sym; 255 } 256 } else 257 sym->sec = find_section_by_index(elf, 0); 258 259 sym->offset = sym->sym.st_value; 260 sym->len = sym->sym.st_size; 261 262 /* sorted insert into a per-section list */ 263 entry = &sym->sec->symbol_list; 264 list_for_each_prev(tmp, &sym->sec->symbol_list) { 265 struct symbol *s; 266 267 s = list_entry(tmp, struct symbol, list); 268 269 if (sym->offset > s->offset) { 270 entry = tmp; 271 break; 272 } 273 274 if (sym->offset == s->offset && sym->len >= s->len) { 275 entry = tmp; 276 break; 277 } 278 } 279 list_add(&sym->list, entry); 280 hash_add(sym->sec->symbol_hash, &sym->hash, sym->idx); 281 } 282 283 return 0; 284 285 err: 286 free(sym); 287 return -1; 288 } 289 290 static int read_relas(struct elf *elf) 291 { 292 struct section *sec; 293 struct rela *rela; 294 int i; 295 unsigned int symndx; 296 297 list_for_each_entry(sec, &elf->sections, list) { 298 if (sec->sh.sh_type != SHT_RELA) 299 continue; 300 301 sec->base = find_section_by_name(elf, sec->name + 5); 302 if (!sec->base) { 303 WARN("can't find base section for rela section %s", 304 sec->name); 305 return -1; 306 } 307 308 sec->base->rela = sec; 309 310 for (i = 0; i < sec->sh.sh_size / sec->sh.sh_entsize; i++) { 311 rela = malloc(sizeof(*rela)); 312 if (!rela) { 313 perror("malloc"); 314 return -1; 315 } 316 memset(rela, 0, sizeof(*rela)); 317 318 if (!gelf_getrela(sec->data, i, &rela->rela)) { 319 WARN_ELF("gelf_getrela"); 320 return -1; 321 } 322 323 rela->type = GELF_R_TYPE(rela->rela.r_info); 324 rela->addend = rela->rela.r_addend; 325 rela->offset = rela->rela.r_offset; 326 symndx = GELF_R_SYM(rela->rela.r_info); 327 rela->sym = find_symbol_by_index(elf, symndx); 328 if (!rela->sym) { 329 WARN("can't find rela entry symbol %d for %s", 330 symndx, sec->name); 331 return -1; 332 } 333 334 list_add_tail(&rela->list, &sec->rela_list); 335 hash_add(sec->rela_hash, &rela->hash, rela->offset); 336 337 } 338 } 339 340 return 0; 341 } 342 343 struct elf *elf_open(const char *name, int flags) 344 { 345 struct elf *elf; 346 Elf_Cmd cmd; 347 348 elf_version(EV_CURRENT); 349 350 elf = malloc(sizeof(*elf)); 351 if (!elf) { 352 perror("malloc"); 353 return NULL; 354 } 355 memset(elf, 0, sizeof(*elf)); 356 357 INIT_LIST_HEAD(&elf->sections); 358 359 elf->fd = open(name, flags); 360 if (elf->fd == -1) { 361 perror("open"); 362 goto err; 363 } 364 365 if ((flags & O_ACCMODE) == O_RDONLY) 366 cmd = ELF_C_READ_MMAP; 367 else if ((flags & O_ACCMODE) == O_RDWR) 368 cmd = ELF_C_RDWR; 369 else /* O_WRONLY */ 370 cmd = ELF_C_WRITE; 371 372 elf->elf = elf_begin(elf->fd, cmd, NULL); 373 if (!elf->elf) { 374 WARN_ELF("elf_begin"); 375 goto err; 376 } 377 378 if (!gelf_getehdr(elf->elf, &elf->ehdr)) { 379 WARN_ELF("gelf_getehdr"); 380 goto err; 381 } 382 383 if (read_sections(elf)) 384 goto err; 385 386 if (read_symbols(elf)) 387 goto err; 388 389 if (read_relas(elf)) 390 goto err; 391 392 return elf; 393 394 err: 395 elf_close(elf); 396 return NULL; 397 } 398 399 struct section *elf_create_section(struct elf *elf, const char *name, 400 size_t entsize, int nr) 401 { 402 struct section *sec, *shstrtab; 403 size_t size = entsize * nr; 404 struct Elf_Scn *s; 405 Elf_Data *data; 406 407 sec = malloc(sizeof(*sec)); 408 if (!sec) { 409 perror("malloc"); 410 return NULL; 411 } 412 memset(sec, 0, sizeof(*sec)); 413 414 INIT_LIST_HEAD(&sec->symbol_list); 415 INIT_LIST_HEAD(&sec->rela_list); 416 hash_init(sec->rela_hash); 417 hash_init(sec->symbol_hash); 418 419 list_add_tail(&sec->list, &elf->sections); 420 421 s = elf_newscn(elf->elf); 422 if (!s) { 423 WARN_ELF("elf_newscn"); 424 return NULL; 425 } 426 427 sec->name = strdup(name); 428 if (!sec->name) { 429 perror("strdup"); 430 return NULL; 431 } 432 433 sec->idx = elf_ndxscn(s); 434 sec->len = size; 435 sec->changed = true; 436 437 sec->data = elf_newdata(s); 438 if (!sec->data) { 439 WARN_ELF("elf_newdata"); 440 return NULL; 441 } 442 443 sec->data->d_size = size; 444 sec->data->d_align = 1; 445 446 if (size) { 447 sec->data->d_buf = malloc(size); 448 if (!sec->data->d_buf) { 449 perror("malloc"); 450 return NULL; 451 } 452 memset(sec->data->d_buf, 0, size); 453 } 454 455 if (!gelf_getshdr(s, &sec->sh)) { 456 WARN_ELF("gelf_getshdr"); 457 return NULL; 458 } 459 460 sec->sh.sh_size = size; 461 sec->sh.sh_entsize = entsize; 462 sec->sh.sh_type = SHT_PROGBITS; 463 sec->sh.sh_addralign = 1; 464 sec->sh.sh_flags = SHF_ALLOC; 465 466 467 /* Add section name to .shstrtab */ 468 shstrtab = find_section_by_name(elf, ".shstrtab"); 469 if (!shstrtab) { 470 WARN("can't find .shstrtab section"); 471 return NULL; 472 } 473 474 s = elf_getscn(elf->elf, shstrtab->idx); 475 if (!s) { 476 WARN_ELF("elf_getscn"); 477 return NULL; 478 } 479 480 data = elf_newdata(s); 481 if (!data) { 482 WARN_ELF("elf_newdata"); 483 return NULL; 484 } 485 486 data->d_buf = sec->name; 487 data->d_size = strlen(name) + 1; 488 data->d_align = 1; 489 490 sec->sh.sh_name = shstrtab->len; 491 492 shstrtab->len += strlen(name) + 1; 493 shstrtab->changed = true; 494 495 return sec; 496 } 497 498 struct section *elf_create_rela_section(struct elf *elf, struct section *base) 499 { 500 char *relaname; 501 struct section *sec; 502 503 relaname = malloc(strlen(base->name) + strlen(".rela") + 1); 504 if (!relaname) { 505 perror("malloc"); 506 return NULL; 507 } 508 strcpy(relaname, ".rela"); 509 strcat(relaname, base->name); 510 511 sec = elf_create_section(elf, relaname, sizeof(GElf_Rela), 0); 512 free(relaname); 513 if (!sec) 514 return NULL; 515 516 base->rela = sec; 517 sec->base = base; 518 519 sec->sh.sh_type = SHT_RELA; 520 sec->sh.sh_addralign = 8; 521 sec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx; 522 sec->sh.sh_info = base->idx; 523 sec->sh.sh_flags = SHF_INFO_LINK; 524 525 return sec; 526 } 527 528 int elf_rebuild_rela_section(struct section *sec) 529 { 530 struct rela *rela; 531 int nr, idx = 0, size; 532 GElf_Rela *relas; 533 534 nr = 0; 535 list_for_each_entry(rela, &sec->rela_list, list) 536 nr++; 537 538 size = nr * sizeof(*relas); 539 relas = malloc(size); 540 if (!relas) { 541 perror("malloc"); 542 return -1; 543 } 544 545 sec->data->d_buf = relas; 546 sec->data->d_size = size; 547 548 sec->sh.sh_size = size; 549 550 idx = 0; 551 list_for_each_entry(rela, &sec->rela_list, list) { 552 relas[idx].r_offset = rela->offset; 553 relas[idx].r_addend = rela->addend; 554 relas[idx].r_info = GELF_R_INFO(rela->sym->idx, rela->type); 555 idx++; 556 } 557 558 return 0; 559 } 560 561 int elf_write(struct elf *elf) 562 { 563 struct section *sec; 564 Elf_Scn *s; 565 566 /* Update section headers for changed sections: */ 567 list_for_each_entry(sec, &elf->sections, list) { 568 if (sec->changed) { 569 s = elf_getscn(elf->elf, sec->idx); 570 if (!s) { 571 WARN_ELF("elf_getscn"); 572 return -1; 573 } 574 if (!gelf_update_shdr(s, &sec->sh)) { 575 WARN_ELF("gelf_update_shdr"); 576 return -1; 577 } 578 } 579 } 580 581 /* Make sure the new section header entries get updated properly. */ 582 elf_flagelf(elf->elf, ELF_C_SET, ELF_F_DIRTY); 583 584 /* Write all changes to the file. */ 585 if (elf_update(elf->elf, ELF_C_WRITE) < 0) { 586 WARN_ELF("elf_update"); 587 return -1; 588 } 589 590 return 0; 591 } 592 593 void elf_close(struct elf *elf) 594 { 595 struct section *sec, *tmpsec; 596 struct symbol *sym, *tmpsym; 597 struct rela *rela, *tmprela; 598 599 if (elf->elf) 600 elf_end(elf->elf); 601 602 if (elf->fd > 0) 603 close(elf->fd); 604 605 list_for_each_entry_safe(sec, tmpsec, &elf->sections, list) { 606 list_for_each_entry_safe(sym, tmpsym, &sec->symbol_list, list) { 607 list_del(&sym->list); 608 hash_del(&sym->hash); 609 free(sym); 610 } 611 list_for_each_entry_safe(rela, tmprela, &sec->rela_list, list) { 612 list_del(&rela->list); 613 hash_del(&rela->hash); 614 free(rela); 615 } 616 list_del(&sec->list); 617 free(sec); 618 } 619 620 free(elf); 621 } 622