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 rela *find_rela_by_dest_range(struct section *sec, unsigned long offset, 82 unsigned int len) 83 { 84 struct rela *rela; 85 unsigned long o; 86 87 if (!sec->rela) 88 return NULL; 89 90 for (o = offset; o < offset + len; o++) 91 hash_for_each_possible(sec->rela->rela_hash, rela, hash, o) 92 if (rela->offset == o) 93 return rela; 94 95 return NULL; 96 } 97 98 struct rela *find_rela_by_dest(struct section *sec, unsigned long offset) 99 { 100 return find_rela_by_dest_range(sec, offset, 1); 101 } 102 103 struct symbol *find_containing_func(struct section *sec, unsigned long offset) 104 { 105 struct symbol *func; 106 107 list_for_each_entry(func, &sec->symbol_list, list) 108 if (func->type == STT_FUNC && offset >= func->offset && 109 offset < func->offset + func->len) 110 return func; 111 112 return NULL; 113 } 114 115 static int read_sections(struct elf *elf) 116 { 117 Elf_Scn *s = NULL; 118 struct section *sec; 119 size_t shstrndx, sections_nr; 120 int i; 121 122 if (elf_getshdrnum(elf->elf, §ions_nr)) { 123 perror("elf_getshdrnum"); 124 return -1; 125 } 126 127 if (elf_getshdrstrndx(elf->elf, &shstrndx)) { 128 perror("elf_getshdrstrndx"); 129 return -1; 130 } 131 132 for (i = 0; i < sections_nr; i++) { 133 sec = malloc(sizeof(*sec)); 134 if (!sec) { 135 perror("malloc"); 136 return -1; 137 } 138 memset(sec, 0, sizeof(*sec)); 139 140 INIT_LIST_HEAD(&sec->symbol_list); 141 INIT_LIST_HEAD(&sec->rela_list); 142 hash_init(sec->rela_hash); 143 hash_init(sec->symbol_hash); 144 145 list_add_tail(&sec->list, &elf->sections); 146 147 s = elf_getscn(elf->elf, i); 148 if (!s) { 149 perror("elf_getscn"); 150 return -1; 151 } 152 153 sec->idx = elf_ndxscn(s); 154 155 if (!gelf_getshdr(s, &sec->sh)) { 156 perror("gelf_getshdr"); 157 return -1; 158 } 159 160 sec->name = elf_strptr(elf->elf, shstrndx, sec->sh.sh_name); 161 if (!sec->name) { 162 perror("elf_strptr"); 163 return -1; 164 } 165 166 sec->elf_data = elf_getdata(s, NULL); 167 if (!sec->elf_data) { 168 perror("elf_getdata"); 169 return -1; 170 } 171 172 if (sec->elf_data->d_off != 0 || 173 sec->elf_data->d_size != sec->sh.sh_size) { 174 WARN("unexpected data attributes for %s", sec->name); 175 return -1; 176 } 177 178 sec->data = (unsigned long)sec->elf_data->d_buf; 179 sec->len = sec->elf_data->d_size; 180 } 181 182 /* sanity check, one more call to elf_nextscn() should return NULL */ 183 if (elf_nextscn(elf->elf, s)) { 184 WARN("section entry mismatch"); 185 return -1; 186 } 187 188 return 0; 189 } 190 191 static int read_symbols(struct elf *elf) 192 { 193 struct section *symtab; 194 struct symbol *sym; 195 struct list_head *entry, *tmp; 196 int symbols_nr, i; 197 198 symtab = find_section_by_name(elf, ".symtab"); 199 if (!symtab) { 200 WARN("missing symbol table"); 201 return -1; 202 } 203 204 symbols_nr = symtab->sh.sh_size / symtab->sh.sh_entsize; 205 206 for (i = 0; i < symbols_nr; i++) { 207 sym = malloc(sizeof(*sym)); 208 if (!sym) { 209 perror("malloc"); 210 return -1; 211 } 212 memset(sym, 0, sizeof(*sym)); 213 214 sym->idx = i; 215 216 if (!gelf_getsym(symtab->elf_data, i, &sym->sym)) { 217 perror("gelf_getsym"); 218 goto err; 219 } 220 221 sym->name = elf_strptr(elf->elf, symtab->sh.sh_link, 222 sym->sym.st_name); 223 if (!sym->name) { 224 perror("elf_strptr"); 225 goto err; 226 } 227 228 sym->type = GELF_ST_TYPE(sym->sym.st_info); 229 sym->bind = GELF_ST_BIND(sym->sym.st_info); 230 231 if (sym->sym.st_shndx > SHN_UNDEF && 232 sym->sym.st_shndx < SHN_LORESERVE) { 233 sym->sec = find_section_by_index(elf, 234 sym->sym.st_shndx); 235 if (!sym->sec) { 236 WARN("couldn't find section for symbol %s", 237 sym->name); 238 goto err; 239 } 240 if (sym->type == STT_SECTION) { 241 sym->name = sym->sec->name; 242 sym->sec->sym = sym; 243 } 244 } else 245 sym->sec = find_section_by_index(elf, 0); 246 247 sym->offset = sym->sym.st_value; 248 sym->len = sym->sym.st_size; 249 250 /* sorted insert into a per-section list */ 251 entry = &sym->sec->symbol_list; 252 list_for_each_prev(tmp, &sym->sec->symbol_list) { 253 struct symbol *s; 254 255 s = list_entry(tmp, struct symbol, list); 256 257 if (sym->offset > s->offset) { 258 entry = tmp; 259 break; 260 } 261 262 if (sym->offset == s->offset && sym->len >= s->len) { 263 entry = tmp; 264 break; 265 } 266 } 267 list_add(&sym->list, entry); 268 hash_add(sym->sec->symbol_hash, &sym->hash, sym->idx); 269 } 270 271 return 0; 272 273 err: 274 free(sym); 275 return -1; 276 } 277 278 static int read_relas(struct elf *elf) 279 { 280 struct section *sec; 281 struct rela *rela; 282 int i; 283 unsigned int symndx; 284 285 list_for_each_entry(sec, &elf->sections, list) { 286 if (sec->sh.sh_type != SHT_RELA) 287 continue; 288 289 sec->base = find_section_by_name(elf, sec->name + 5); 290 if (!sec->base) { 291 WARN("can't find base section for rela section %s", 292 sec->name); 293 return -1; 294 } 295 296 sec->base->rela = sec; 297 298 for (i = 0; i < sec->sh.sh_size / sec->sh.sh_entsize; i++) { 299 rela = malloc(sizeof(*rela)); 300 if (!rela) { 301 perror("malloc"); 302 return -1; 303 } 304 memset(rela, 0, sizeof(*rela)); 305 306 if (!gelf_getrela(sec->elf_data, i, &rela->rela)) { 307 perror("gelf_getrela"); 308 return -1; 309 } 310 311 rela->type = GELF_R_TYPE(rela->rela.r_info); 312 rela->addend = rela->rela.r_addend; 313 rela->offset = rela->rela.r_offset; 314 symndx = GELF_R_SYM(rela->rela.r_info); 315 rela->sym = find_symbol_by_index(elf, symndx); 316 if (!rela->sym) { 317 WARN("can't find rela entry symbol %d for %s", 318 symndx, sec->name); 319 return -1; 320 } 321 322 list_add_tail(&rela->list, &sec->rela_list); 323 hash_add(sec->rela_hash, &rela->hash, rela->offset); 324 325 } 326 } 327 328 return 0; 329 } 330 331 struct elf *elf_open(const char *name) 332 { 333 struct elf *elf; 334 335 elf_version(EV_CURRENT); 336 337 elf = malloc(sizeof(*elf)); 338 if (!elf) { 339 perror("malloc"); 340 return NULL; 341 } 342 memset(elf, 0, sizeof(*elf)); 343 344 INIT_LIST_HEAD(&elf->sections); 345 346 elf->name = strdup(name); 347 if (!elf->name) { 348 perror("strdup"); 349 goto err; 350 } 351 352 elf->fd = open(name, O_RDONLY); 353 if (elf->fd == -1) { 354 perror("open"); 355 goto err; 356 } 357 358 elf->elf = elf_begin(elf->fd, ELF_C_READ_MMAP, NULL); 359 if (!elf->elf) { 360 perror("elf_begin"); 361 goto err; 362 } 363 364 if (!gelf_getehdr(elf->elf, &elf->ehdr)) { 365 perror("gelf_getehdr"); 366 goto err; 367 } 368 369 if (read_sections(elf)) 370 goto err; 371 372 if (read_symbols(elf)) 373 goto err; 374 375 if (read_relas(elf)) 376 goto err; 377 378 return elf; 379 380 err: 381 elf_close(elf); 382 return NULL; 383 } 384 385 void elf_close(struct elf *elf) 386 { 387 struct section *sec, *tmpsec; 388 struct symbol *sym, *tmpsym; 389 struct rela *rela, *tmprela; 390 391 list_for_each_entry_safe(sec, tmpsec, &elf->sections, list) { 392 list_for_each_entry_safe(sym, tmpsym, &sec->symbol_list, list) { 393 list_del(&sym->list); 394 hash_del(&sym->hash); 395 free(sym); 396 } 397 list_for_each_entry_safe(rela, tmprela, &sec->rela_list, list) { 398 list_del(&rela->list); 399 hash_del(&rela->hash); 400 free(rela); 401 } 402 list_del(&sec->list); 403 free(sec); 404 } 405 if (elf->name) 406 free(elf->name); 407 if (elf->fd > 0) 408 close(elf->fd); 409 if (elf->elf) 410 elf_end(elf->elf); 411 free(elf); 412 } 413