linux/tools/objtool/elf.c
Josh Poimboeuf 97dab2ae7e objtool: Fix object file corruption
Arnd Bergmann reported that a randconfig build was failing with the
following link error:

  built-in.o: member arch/x86/kernel/time.o in archive is not an object

It turns out the link failed because the time.o file had been corrupted
by objtool:

  nm: arch/x86/kernel/time.o: File format not recognized

In certain rare cases, when a .o file's ORC table is very small, the
.data section size doesn't change because it's page aligned.  Because
all the existing sections haven't changed size, libelf doesn't detect
any section header changes, and so it doesn't update the section header
table properly.  Instead it writes junk in the section header entries
for the new ORC sections.

Make sure libelf properly updates the section header table by setting
the ELF_F_DIRTY flag in the top level elf struct.

Reported-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 627fce1480 ("objtool: Add ORC unwind table generation")
Link: http://lkml.kernel.org/r/e650fd0f2d8a209d1409a9785deb101fdaed55fb.1505459813.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-09-15 11:31:57 +02:00

622 lines
12 KiB
C

/*
* 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"
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 symbol *find_symbol_containing(struct section *sec, unsigned long offset)
{
struct symbol *sym;
list_for_each_entry(sym, &sec->symbol_list, list)
if (sym->type != STT_SECTION &&
offset >= sym->offset && offset < sym->offset + sym->len)
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, &sections_nr)) {
WARN_ELF("elf_getshdrnum");
return -1;
}
if (elf_getshdrstrndx(elf->elf, &shstrndx)) {
WARN_ELF("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) {
WARN_ELF("elf_getscn");
return -1;
}
sec->idx = elf_ndxscn(s);
if (!gelf_getshdr(s, &sec->sh)) {
WARN_ELF("gelf_getshdr");
return -1;
}
sec->name = elf_strptr(elf->elf, shstrndx, sec->sh.sh_name);
if (!sec->name) {
WARN_ELF("elf_strptr");
return -1;
}
if (sec->sh.sh_size != 0) {
sec->data = elf_getdata(s, NULL);
if (!sec->data) {
WARN_ELF("elf_getdata");
return -1;
}
if (sec->data->d_off != 0 ||
sec->data->d_size != sec->sh.sh_size) {
WARN("unexpected data attributes for %s",
sec->name);
return -1;
}
}
sec->len = sec->sh.sh_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->data, i, &sym->sym)) {
WARN_ELF("gelf_getsym");
goto err;
}
sym->name = elf_strptr(elf->elf, symtab->sh.sh_link,
sym->sym.st_name);
if (!sym->name) {
WARN_ELF("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->data, i, &rela->rela)) {
WARN_ELF("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, int flags)
{
struct elf *elf;
Elf_Cmd cmd;
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->fd = open(name, flags);
if (elf->fd == -1) {
perror("open");
goto err;
}
if ((flags & O_ACCMODE) == O_RDONLY)
cmd = ELF_C_READ_MMAP;
else if ((flags & O_ACCMODE) == O_RDWR)
cmd = ELF_C_RDWR;
else /* O_WRONLY */
cmd = ELF_C_WRITE;
elf->elf = elf_begin(elf->fd, cmd, NULL);
if (!elf->elf) {
WARN_ELF("elf_begin");
goto err;
}
if (!gelf_getehdr(elf->elf, &elf->ehdr)) {
WARN_ELF("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;
}
struct section *elf_create_section(struct elf *elf, const char *name,
size_t entsize, int nr)
{
struct section *sec, *shstrtab;
size_t size = entsize * nr;
struct Elf_Scn *s;
Elf_Data *data;
sec = malloc(sizeof(*sec));
if (!sec) {
perror("malloc");
return NULL;
}
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_newscn(elf->elf);
if (!s) {
WARN_ELF("elf_newscn");
return NULL;
}
sec->name = strdup(name);
if (!sec->name) {
perror("strdup");
return NULL;
}
sec->idx = elf_ndxscn(s);
sec->len = size;
sec->changed = true;
sec->data = elf_newdata(s);
if (!sec->data) {
WARN_ELF("elf_newdata");
return NULL;
}
sec->data->d_size = size;
sec->data->d_align = 1;
if (size) {
sec->data->d_buf = malloc(size);
if (!sec->data->d_buf) {
perror("malloc");
return NULL;
}
memset(sec->data->d_buf, 0, size);
}
if (!gelf_getshdr(s, &sec->sh)) {
WARN_ELF("gelf_getshdr");
return NULL;
}
sec->sh.sh_size = size;
sec->sh.sh_entsize = entsize;
sec->sh.sh_type = SHT_PROGBITS;
sec->sh.sh_addralign = 1;
sec->sh.sh_flags = SHF_ALLOC;
/* Add section name to .shstrtab */
shstrtab = find_section_by_name(elf, ".shstrtab");
if (!shstrtab) {
WARN("can't find .shstrtab section");
return NULL;
}
s = elf_getscn(elf->elf, shstrtab->idx);
if (!s) {
WARN_ELF("elf_getscn");
return NULL;
}
data = elf_newdata(s);
if (!data) {
WARN_ELF("elf_newdata");
return NULL;
}
data->d_buf = sec->name;
data->d_size = strlen(name) + 1;
data->d_align = 1;
sec->sh.sh_name = shstrtab->len;
shstrtab->len += strlen(name) + 1;
shstrtab->changed = true;
return sec;
}
struct section *elf_create_rela_section(struct elf *elf, struct section *base)
{
char *relaname;
struct section *sec;
relaname = malloc(strlen(base->name) + strlen(".rela") + 1);
if (!relaname) {
perror("malloc");
return NULL;
}
strcpy(relaname, ".rela");
strcat(relaname, base->name);
sec = elf_create_section(elf, relaname, sizeof(GElf_Rela), 0);
free(relaname);
if (!sec)
return NULL;
base->rela = sec;
sec->base = base;
sec->sh.sh_type = SHT_RELA;
sec->sh.sh_addralign = 8;
sec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx;
sec->sh.sh_info = base->idx;
sec->sh.sh_flags = SHF_INFO_LINK;
return sec;
}
int elf_rebuild_rela_section(struct section *sec)
{
struct rela *rela;
int nr, idx = 0, size;
GElf_Rela *relas;
nr = 0;
list_for_each_entry(rela, &sec->rela_list, list)
nr++;
size = nr * sizeof(*relas);
relas = malloc(size);
if (!relas) {
perror("malloc");
return -1;
}
sec->data->d_buf = relas;
sec->data->d_size = size;
sec->sh.sh_size = size;
idx = 0;
list_for_each_entry(rela, &sec->rela_list, list) {
relas[idx].r_offset = rela->offset;
relas[idx].r_addend = rela->addend;
relas[idx].r_info = GELF_R_INFO(rela->sym->idx, rela->type);
idx++;
}
return 0;
}
int elf_write(struct elf *elf)
{
struct section *sec;
Elf_Scn *s;
/* Update section headers for changed sections: */
list_for_each_entry(sec, &elf->sections, list) {
if (sec->changed) {
s = elf_getscn(elf->elf, sec->idx);
if (!s) {
WARN_ELF("elf_getscn");
return -1;
}
if (!gelf_update_shdr(s, &sec->sh)) {
WARN_ELF("gelf_update_shdr");
return -1;
}
}
}
/* Make sure the new section header entries get updated properly. */
elf_flagelf(elf->elf, ELF_C_SET, ELF_F_DIRTY);
/* Write all changes to the file. */
if (elf_update(elf->elf, ELF_C_WRITE) < 0) {
WARN_ELF("elf_update");
return -1;
}
return 0;
}
void elf_close(struct elf *elf)
{
struct section *sec, *tmpsec;
struct symbol *sym, *tmpsym;
struct rela *rela, *tmprela;
if (elf->elf)
elf_end(elf->elf);
if (elf->fd > 0)
close(elf->fd);
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);
}
free(elf);
}