/* * elf.c - ELF access library * * Adapted from kpatch (https://github.com/dynup/kpatch): * Copyright (C) 2013-2015 Josh Poimboeuf <jpoimboe@redhat.com> * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com> * * This program is free software; you can redistribute it and/or * modify it under the terms of the GNU General Public License * as published by the Free Software Foundation; either version 2 * of the License, or (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, see <http://www.gnu.org/licenses/>. */ #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <unistd.h> #include "elf.h" #include "warn.h" /* * Fallback for systems without this "read, mmaping if possible" cmd. */ #ifndef ELF_C_READ_MMAP #define ELF_C_READ_MMAP ELF_C_READ #endif struct section *find_section_by_name(struct elf *elf, const char *name) { struct section *sec; list_for_each_entry(sec, &elf->sections, list) if (!strcmp(sec->name, name)) return sec; return NULL; } static struct section *find_section_by_index(struct elf *elf, unsigned int idx) { struct section *sec; list_for_each_entry(sec, &elf->sections, list) if (sec->idx == idx) return sec; return NULL; } static struct symbol *find_symbol_by_index(struct elf *elf, unsigned int idx) { struct section *sec; struct symbol *sym; list_for_each_entry(sec, &elf->sections, list) hash_for_each_possible(sec->symbol_hash, sym, hash, idx) if (sym->idx == idx) return sym; return NULL; } struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset) { struct symbol *sym; list_for_each_entry(sym, &sec->symbol_list, list) if (sym->type != STT_SECTION && sym->offset == offset) return sym; return NULL; } struct rela *find_rela_by_dest_range(struct section *sec, unsigned long offset, unsigned int len) { struct rela *rela; unsigned long o; if (!sec->rela) return NULL; for (o = offset; o < offset + len; o++) hash_for_each_possible(sec->rela->rela_hash, rela, hash, o) if (rela->offset == o) return rela; return NULL; } struct rela *find_rela_by_dest(struct section *sec, unsigned long offset) { return find_rela_by_dest_range(sec, offset, 1); } struct symbol *find_containing_func(struct section *sec, unsigned long offset) { struct symbol *func; list_for_each_entry(func, &sec->symbol_list, list) if (func->type == STT_FUNC && offset >= func->offset && offset < func->offset + func->len) return func; return NULL; } static int read_sections(struct elf *elf) { Elf_Scn *s = NULL; struct section *sec; size_t shstrndx, sections_nr; int i; if (elf_getshdrnum(elf->elf, §ions_nr)) { perror("elf_getshdrnum"); return -1; } if (elf_getshdrstrndx(elf->elf, &shstrndx)) { perror("elf_getshdrstrndx"); return -1; } for (i = 0; i < sections_nr; i++) { sec = malloc(sizeof(*sec)); if (!sec) { perror("malloc"); return -1; } memset(sec, 0, sizeof(*sec)); INIT_LIST_HEAD(&sec->symbol_list); INIT_LIST_HEAD(&sec->rela_list); hash_init(sec->rela_hash); hash_init(sec->symbol_hash); list_add_tail(&sec->list, &elf->sections); s = elf_getscn(elf->elf, i); if (!s) { perror("elf_getscn"); return -1; } sec->idx = elf_ndxscn(s); if (!gelf_getshdr(s, &sec->sh)) { perror("gelf_getshdr"); return -1; } sec->name = elf_strptr(elf->elf, shstrndx, sec->sh.sh_name); if (!sec->name) { perror("elf_strptr"); return -1; } sec->elf_data = elf_getdata(s, NULL); if (!sec->elf_data) { perror("elf_getdata"); return -1; } if (sec->elf_data->d_off != 0 || sec->elf_data->d_size != sec->sh.sh_size) { WARN("unexpected data attributes for %s", sec->name); return -1; } sec->data = (unsigned long)sec->elf_data->d_buf; sec->len = sec->elf_data->d_size; } /* sanity check, one more call to elf_nextscn() should return NULL */ if (elf_nextscn(elf->elf, s)) { WARN("section entry mismatch"); return -1; } return 0; } static int read_symbols(struct elf *elf) { struct section *symtab; struct symbol *sym; struct list_head *entry, *tmp; int symbols_nr, i; symtab = find_section_by_name(elf, ".symtab"); if (!symtab) { WARN("missing symbol table"); return -1; } symbols_nr = symtab->sh.sh_size / symtab->sh.sh_entsize; for (i = 0; i < symbols_nr; i++) { sym = malloc(sizeof(*sym)); if (!sym) { perror("malloc"); return -1; } memset(sym, 0, sizeof(*sym)); sym->idx = i; if (!gelf_getsym(symtab->elf_data, i, &sym->sym)) { perror("gelf_getsym"); goto err; } sym->name = elf_strptr(elf->elf, symtab->sh.sh_link, sym->sym.st_name); if (!sym->name) { perror("elf_strptr"); goto err; } sym->type = GELF_ST_TYPE(sym->sym.st_info); sym->bind = GELF_ST_BIND(sym->sym.st_info); if (sym->sym.st_shndx > SHN_UNDEF && sym->sym.st_shndx < SHN_LORESERVE) { sym->sec = find_section_by_index(elf, sym->sym.st_shndx); if (!sym->sec) { WARN("couldn't find section for symbol %s", sym->name); goto err; } if (sym->type == STT_SECTION) { sym->name = sym->sec->name; sym->sec->sym = sym; } } else sym->sec = find_section_by_index(elf, 0); sym->offset = sym->sym.st_value; sym->len = sym->sym.st_size; /* sorted insert into a per-section list */ entry = &sym->sec->symbol_list; list_for_each_prev(tmp, &sym->sec->symbol_list) { struct symbol *s; s = list_entry(tmp, struct symbol, list); if (sym->offset > s->offset) { entry = tmp; break; } if (sym->offset == s->offset && sym->len >= s->len) { entry = tmp; break; } } list_add(&sym->list, entry); hash_add(sym->sec->symbol_hash, &sym->hash, sym->idx); } return 0; err: free(sym); return -1; } static int read_relas(struct elf *elf) { struct section *sec; struct rela *rela; int i; unsigned int symndx; list_for_each_entry(sec, &elf->sections, list) { if (sec->sh.sh_type != SHT_RELA) continue; sec->base = find_section_by_name(elf, sec->name + 5); if (!sec->base) { WARN("can't find base section for rela section %s", sec->name); return -1; } sec->base->rela = sec; for (i = 0; i < sec->sh.sh_size / sec->sh.sh_entsize; i++) { rela = malloc(sizeof(*rela)); if (!rela) { perror("malloc"); return -1; } memset(rela, 0, sizeof(*rela)); if (!gelf_getrela(sec->elf_data, i, &rela->rela)) { perror("gelf_getrela"); return -1; } rela->type = GELF_R_TYPE(rela->rela.r_info); rela->addend = rela->rela.r_addend; rela->offset = rela->rela.r_offset; symndx = GELF_R_SYM(rela->rela.r_info); rela->sym = find_symbol_by_index(elf, symndx); if (!rela->sym) { WARN("can't find rela entry symbol %d for %s", symndx, sec->name); return -1; } list_add_tail(&rela->list, &sec->rela_list); hash_add(sec->rela_hash, &rela->hash, rela->offset); } } return 0; } struct elf *elf_open(const char *name) { struct elf *elf; elf_version(EV_CURRENT); elf = malloc(sizeof(*elf)); if (!elf) { perror("malloc"); return NULL; } memset(elf, 0, sizeof(*elf)); INIT_LIST_HEAD(&elf->sections); elf->name = strdup(name); if (!elf->name) { perror("strdup"); goto err; } elf->fd = open(name, O_RDONLY); if (elf->fd == -1) { perror("open"); goto err; } elf->elf = elf_begin(elf->fd, ELF_C_READ_MMAP, NULL); if (!elf->elf) { perror("elf_begin"); goto err; } if (!gelf_getehdr(elf->elf, &elf->ehdr)) { perror("gelf_getehdr"); goto err; } if (read_sections(elf)) goto err; if (read_symbols(elf)) goto err; if (read_relas(elf)) goto err; return elf; err: elf_close(elf); return NULL; } void elf_close(struct elf *elf) { struct section *sec, *tmpsec; struct symbol *sym, *tmpsym; struct rela *rela, *tmprela; list_for_each_entry_safe(sec, tmpsec, &elf->sections, list) { list_for_each_entry_safe(sym, tmpsym, &sec->symbol_list, list) { list_del(&sym->list); hash_del(&sym->hash); free(sym); } list_for_each_entry_safe(rela, tmprela, &sec->rela_list, list) { list_del(&rela->list); hash_del(&rela->hash); free(rela); } list_del(&sec->list); free(sec); } if (elf->name) free(elf->name); if (elf->fd > 0) close(elf->fd); if (elf->elf) elf_end(elf->elf); free(elf); }