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![Andrii Nakryiko](/assets/img/avatar_default.png)
Fix too eager assumption that SHT_GNU_verdef ELF section is going to be
present whenever binary has SHT_GNU_versym section. It seems like either
SHT_GNU_verdef or SHT_GNU_verneed can be used, so failing on missing
SHT_GNU_verdef actually breaks use cases in production.
One specific reported issue, which was used to manually test this fix,
was trying to attach to `readline` function in BASH binary.
Fixes: bb7fa09399
("libbpf: Support symbol versioning for uprobe")
Reported-by: Liam Wisehart <liamwisehart@meta.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Tested-by: Manu Bretelle <chantr4@gmail.com>
Reviewed-by: Fangrui Song <maskray@google.com>
Acked-by: Hengqi Chen <hengqi.chen@gmail.com>
Link: https://lore.kernel.org/bpf/20231016182840.4033346-1-andrii@kernel.org
559 lines
13 KiB
C
559 lines
13 KiB
C
// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)
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#ifndef _GNU_SOURCE
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#define _GNU_SOURCE
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#endif
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#include <libelf.h>
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#include <gelf.h>
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#include <fcntl.h>
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#include <linux/kernel.h>
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#include "libbpf_internal.h"
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#include "str_error.h"
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#define STRERR_BUFSIZE 128
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/* A SHT_GNU_versym section holds 16-bit words. This bit is set if
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* the symbol is hidden and can only be seen when referenced using an
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* explicit version number. This is a GNU extension.
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*/
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#define VERSYM_HIDDEN 0x8000
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/* This is the mask for the rest of the data in a word read from a
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* SHT_GNU_versym section.
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*/
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#define VERSYM_VERSION 0x7fff
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int elf_open(const char *binary_path, struct elf_fd *elf_fd)
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{
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char errmsg[STRERR_BUFSIZE];
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int fd, ret;
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Elf *elf;
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if (elf_version(EV_CURRENT) == EV_NONE) {
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pr_warn("elf: failed to init libelf for %s\n", binary_path);
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return -LIBBPF_ERRNO__LIBELF;
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}
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fd = open(binary_path, O_RDONLY | O_CLOEXEC);
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if (fd < 0) {
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ret = -errno;
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pr_warn("elf: failed to open %s: %s\n", binary_path,
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libbpf_strerror_r(ret, errmsg, sizeof(errmsg)));
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return ret;
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}
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elf = elf_begin(fd, ELF_C_READ_MMAP, NULL);
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if (!elf) {
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pr_warn("elf: could not read elf from %s: %s\n", binary_path, elf_errmsg(-1));
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close(fd);
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return -LIBBPF_ERRNO__FORMAT;
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}
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elf_fd->fd = fd;
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elf_fd->elf = elf;
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return 0;
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}
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void elf_close(struct elf_fd *elf_fd)
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{
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if (!elf_fd)
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return;
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elf_end(elf_fd->elf);
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close(elf_fd->fd);
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}
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/* Return next ELF section of sh_type after scn, or first of that type if scn is NULL. */
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static Elf_Scn *elf_find_next_scn_by_type(Elf *elf, int sh_type, Elf_Scn *scn)
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{
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while ((scn = elf_nextscn(elf, scn)) != NULL) {
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GElf_Shdr sh;
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if (!gelf_getshdr(scn, &sh))
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continue;
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if (sh.sh_type == sh_type)
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return scn;
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}
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return NULL;
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}
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struct elf_sym {
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const char *name;
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GElf_Sym sym;
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GElf_Shdr sh;
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int ver;
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bool hidden;
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};
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struct elf_sym_iter {
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Elf *elf;
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Elf_Data *syms;
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Elf_Data *versyms;
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Elf_Data *verdefs;
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size_t nr_syms;
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size_t strtabidx;
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size_t verdef_strtabidx;
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size_t next_sym_idx;
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struct elf_sym sym;
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int st_type;
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};
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static int elf_sym_iter_new(struct elf_sym_iter *iter,
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Elf *elf, const char *binary_path,
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int sh_type, int st_type)
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{
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Elf_Scn *scn = NULL;
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GElf_Ehdr ehdr;
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GElf_Shdr sh;
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memset(iter, 0, sizeof(*iter));
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if (!gelf_getehdr(elf, &ehdr)) {
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pr_warn("elf: failed to get ehdr from %s: %s\n", binary_path, elf_errmsg(-1));
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return -EINVAL;
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}
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scn = elf_find_next_scn_by_type(elf, sh_type, NULL);
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if (!scn) {
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pr_debug("elf: failed to find symbol table ELF sections in '%s'\n",
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binary_path);
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return -ENOENT;
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}
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if (!gelf_getshdr(scn, &sh))
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return -EINVAL;
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iter->strtabidx = sh.sh_link;
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iter->syms = elf_getdata(scn, 0);
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if (!iter->syms) {
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pr_warn("elf: failed to get symbols for symtab section in '%s': %s\n",
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binary_path, elf_errmsg(-1));
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return -EINVAL;
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}
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iter->nr_syms = iter->syms->d_size / sh.sh_entsize;
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iter->elf = elf;
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iter->st_type = st_type;
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/* Version symbol table is meaningful to dynsym only */
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if (sh_type != SHT_DYNSYM)
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return 0;
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scn = elf_find_next_scn_by_type(elf, SHT_GNU_versym, NULL);
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if (!scn)
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return 0;
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iter->versyms = elf_getdata(scn, 0);
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scn = elf_find_next_scn_by_type(elf, SHT_GNU_verdef, NULL);
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if (!scn)
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return 0;
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iter->verdefs = elf_getdata(scn, 0);
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if (!iter->verdefs || !gelf_getshdr(scn, &sh)) {
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pr_warn("elf: failed to get verdef ELF section in '%s'\n", binary_path);
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return -EINVAL;
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}
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iter->verdef_strtabidx = sh.sh_link;
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return 0;
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}
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static struct elf_sym *elf_sym_iter_next(struct elf_sym_iter *iter)
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{
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struct elf_sym *ret = &iter->sym;
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GElf_Sym *sym = &ret->sym;
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const char *name = NULL;
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GElf_Versym versym;
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Elf_Scn *sym_scn;
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size_t idx;
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for (idx = iter->next_sym_idx; idx < iter->nr_syms; idx++) {
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if (!gelf_getsym(iter->syms, idx, sym))
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continue;
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if (GELF_ST_TYPE(sym->st_info) != iter->st_type)
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continue;
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name = elf_strptr(iter->elf, iter->strtabidx, sym->st_name);
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if (!name)
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continue;
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sym_scn = elf_getscn(iter->elf, sym->st_shndx);
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if (!sym_scn)
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continue;
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if (!gelf_getshdr(sym_scn, &ret->sh))
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continue;
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iter->next_sym_idx = idx + 1;
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ret->name = name;
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ret->ver = 0;
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ret->hidden = false;
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if (iter->versyms) {
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if (!gelf_getversym(iter->versyms, idx, &versym))
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continue;
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ret->ver = versym & VERSYM_VERSION;
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ret->hidden = versym & VERSYM_HIDDEN;
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}
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return ret;
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}
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return NULL;
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}
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static const char *elf_get_vername(struct elf_sym_iter *iter, int ver)
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{
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GElf_Verdaux verdaux;
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GElf_Verdef verdef;
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int offset;
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if (!iter->verdefs)
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return NULL;
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offset = 0;
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while (gelf_getverdef(iter->verdefs, offset, &verdef)) {
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if (verdef.vd_ndx != ver) {
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if (!verdef.vd_next)
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break;
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offset += verdef.vd_next;
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continue;
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}
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if (!gelf_getverdaux(iter->verdefs, offset + verdef.vd_aux, &verdaux))
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break;
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return elf_strptr(iter->elf, iter->verdef_strtabidx, verdaux.vda_name);
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}
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return NULL;
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}
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static bool symbol_match(struct elf_sym_iter *iter, int sh_type, struct elf_sym *sym,
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const char *name, size_t name_len, const char *lib_ver)
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{
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const char *ver_name;
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/* Symbols are in forms of func, func@LIB_VER or func@@LIB_VER
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* make sure the func part matches the user specified name
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*/
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if (strncmp(sym->name, name, name_len) != 0)
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return false;
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/* ...but we don't want a search for "foo" to match 'foo2" also, so any
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* additional characters in sname should be of the form "@@LIB".
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*/
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if (sym->name[name_len] != '\0' && sym->name[name_len] != '@')
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return false;
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/* If user does not specify symbol version, then we got a match */
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if (!lib_ver)
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return true;
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/* If user specifies symbol version, for dynamic symbols,
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* get version name from ELF verdef section for comparison.
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*/
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if (sh_type == SHT_DYNSYM) {
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ver_name = elf_get_vername(iter, sym->ver);
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if (!ver_name)
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return false;
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return strcmp(ver_name, lib_ver) == 0;
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}
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/* For normal symbols, it is already in form of func@LIB_VER */
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return strcmp(sym->name, name) == 0;
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}
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/* Transform symbol's virtual address (absolute for binaries and relative
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* for shared libs) into file offset, which is what kernel is expecting
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* for uprobe/uretprobe attachment.
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* See Documentation/trace/uprobetracer.rst for more details. This is done
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* by looking up symbol's containing section's header and using iter's virtual
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* address (sh_addr) and corresponding file offset (sh_offset) to transform
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* sym.st_value (virtual address) into desired final file offset.
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*/
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static unsigned long elf_sym_offset(struct elf_sym *sym)
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{
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return sym->sym.st_value - sym->sh.sh_addr + sym->sh.sh_offset;
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}
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/* Find offset of function name in the provided ELF object. "binary_path" is
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* the path to the ELF binary represented by "elf", and only used for error
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* reporting matters. "name" matches symbol name or name@@LIB for library
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* functions.
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*/
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long elf_find_func_offset(Elf *elf, const char *binary_path, const char *name)
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{
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int i, sh_types[2] = { SHT_DYNSYM, SHT_SYMTAB };
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const char *at_symbol, *lib_ver;
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bool is_shared_lib;
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long ret = -ENOENT;
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size_t name_len;
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GElf_Ehdr ehdr;
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if (!gelf_getehdr(elf, &ehdr)) {
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pr_warn("elf: failed to get ehdr from %s: %s\n", binary_path, elf_errmsg(-1));
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ret = -LIBBPF_ERRNO__FORMAT;
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goto out;
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}
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/* for shared lib case, we do not need to calculate relative offset */
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is_shared_lib = ehdr.e_type == ET_DYN;
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/* Does name specify "@@LIB_VER" or "@LIB_VER" ? */
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at_symbol = strchr(name, '@');
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if (at_symbol) {
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name_len = at_symbol - name;
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/* skip second @ if it's @@LIB_VER case */
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if (at_symbol[1] == '@')
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at_symbol++;
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lib_ver = at_symbol + 1;
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} else {
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name_len = strlen(name);
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lib_ver = NULL;
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}
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/* Search SHT_DYNSYM, SHT_SYMTAB for symbol. This search order is used because if
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* a binary is stripped, it may only have SHT_DYNSYM, and a fully-statically
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* linked binary may not have SHT_DYMSYM, so absence of a section should not be
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* reported as a warning/error.
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*/
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for (i = 0; i < ARRAY_SIZE(sh_types); i++) {
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struct elf_sym_iter iter;
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struct elf_sym *sym;
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int last_bind = -1;
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int cur_bind;
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ret = elf_sym_iter_new(&iter, elf, binary_path, sh_types[i], STT_FUNC);
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if (ret == -ENOENT)
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continue;
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if (ret)
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goto out;
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while ((sym = elf_sym_iter_next(&iter))) {
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if (!symbol_match(&iter, sh_types[i], sym, name, name_len, lib_ver))
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continue;
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cur_bind = GELF_ST_BIND(sym->sym.st_info);
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if (ret > 0) {
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/* handle multiple matches */
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if (elf_sym_offset(sym) == ret) {
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/* same offset, no problem */
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continue;
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} else if (last_bind != STB_WEAK && cur_bind != STB_WEAK) {
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/* Only accept one non-weak bind. */
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pr_warn("elf: ambiguous match for '%s', '%s' in '%s'\n",
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sym->name, name, binary_path);
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ret = -LIBBPF_ERRNO__FORMAT;
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goto out;
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} else if (cur_bind == STB_WEAK) {
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/* already have a non-weak bind, and
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* this is a weak bind, so ignore.
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*/
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continue;
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}
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}
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ret = elf_sym_offset(sym);
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last_bind = cur_bind;
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}
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if (ret > 0)
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break;
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}
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if (ret > 0) {
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pr_debug("elf: symbol address match for '%s' in '%s': 0x%lx\n", name, binary_path,
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ret);
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} else {
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if (ret == 0) {
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pr_warn("elf: '%s' is 0 in symtab for '%s': %s\n", name, binary_path,
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is_shared_lib ? "should not be 0 in a shared library" :
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"try using shared library path instead");
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ret = -ENOENT;
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} else {
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pr_warn("elf: failed to find symbol '%s' in '%s'\n", name, binary_path);
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}
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}
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out:
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return ret;
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}
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/* Find offset of function name in ELF object specified by path. "name" matches
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* symbol name or name@@LIB for library functions.
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*/
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long elf_find_func_offset_from_file(const char *binary_path, const char *name)
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{
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struct elf_fd elf_fd;
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long ret = -ENOENT;
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ret = elf_open(binary_path, &elf_fd);
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if (ret)
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return ret;
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ret = elf_find_func_offset(elf_fd.elf, binary_path, name);
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elf_close(&elf_fd);
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return ret;
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}
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struct symbol {
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const char *name;
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int bind;
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int idx;
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};
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static int symbol_cmp(const void *a, const void *b)
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{
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const struct symbol *sym_a = a;
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const struct symbol *sym_b = b;
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return strcmp(sym_a->name, sym_b->name);
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}
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/*
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* Return offsets in @poffsets for symbols specified in @syms array argument.
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* On success returns 0 and offsets are returned in allocated array with @cnt
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* size, that needs to be released by the caller.
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*/
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int elf_resolve_syms_offsets(const char *binary_path, int cnt,
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const char **syms, unsigned long **poffsets)
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{
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int sh_types[2] = { SHT_DYNSYM, SHT_SYMTAB };
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int err = 0, i, cnt_done = 0;
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unsigned long *offsets;
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struct symbol *symbols;
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struct elf_fd elf_fd;
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err = elf_open(binary_path, &elf_fd);
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if (err)
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return err;
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offsets = calloc(cnt, sizeof(*offsets));
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symbols = calloc(cnt, sizeof(*symbols));
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if (!offsets || !symbols) {
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err = -ENOMEM;
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goto out;
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}
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for (i = 0; i < cnt; i++) {
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symbols[i].name = syms[i];
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symbols[i].idx = i;
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}
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qsort(symbols, cnt, sizeof(*symbols), symbol_cmp);
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for (i = 0; i < ARRAY_SIZE(sh_types); i++) {
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struct elf_sym_iter iter;
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struct elf_sym *sym;
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err = elf_sym_iter_new(&iter, elf_fd.elf, binary_path, sh_types[i], STT_FUNC);
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if (err == -ENOENT)
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continue;
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if (err)
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goto out;
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while ((sym = elf_sym_iter_next(&iter))) {
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unsigned long sym_offset = elf_sym_offset(sym);
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int bind = GELF_ST_BIND(sym->sym.st_info);
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struct symbol *found, tmp = {
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.name = sym->name,
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};
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unsigned long *offset;
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found = bsearch(&tmp, symbols, cnt, sizeof(*symbols), symbol_cmp);
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if (!found)
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continue;
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offset = &offsets[found->idx];
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if (*offset > 0) {
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/* same offset, no problem */
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if (*offset == sym_offset)
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continue;
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/* handle multiple matches */
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if (found->bind != STB_WEAK && bind != STB_WEAK) {
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/* Only accept one non-weak bind. */
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pr_warn("elf: ambiguous match found '%s@%lu' in '%s' previous offset %lu\n",
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sym->name, sym_offset, binary_path, *offset);
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err = -ESRCH;
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goto out;
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} else if (bind == STB_WEAK) {
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/* already have a non-weak bind, and
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* this is a weak bind, so ignore.
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*/
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continue;
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}
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} else {
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cnt_done++;
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}
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*offset = sym_offset;
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found->bind = bind;
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}
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}
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if (cnt != cnt_done) {
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err = -ENOENT;
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goto out;
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}
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*poffsets = offsets;
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|
|
out:
|
|
free(symbols);
|
|
if (err)
|
|
free(offsets);
|
|
elf_close(&elf_fd);
|
|
return err;
|
|
}
|
|
|
|
/*
|
|
* Return offsets in @poffsets for symbols specified by @pattern argument.
|
|
* On success returns 0 and offsets are returned in allocated @poffsets
|
|
* array with the @pctn size, that needs to be released by the caller.
|
|
*/
|
|
int elf_resolve_pattern_offsets(const char *binary_path, const char *pattern,
|
|
unsigned long **poffsets, size_t *pcnt)
|
|
{
|
|
int sh_types[2] = { SHT_SYMTAB, SHT_DYNSYM };
|
|
unsigned long *offsets = NULL;
|
|
size_t cap = 0, cnt = 0;
|
|
struct elf_fd elf_fd;
|
|
int err = 0, i;
|
|
|
|
err = elf_open(binary_path, &elf_fd);
|
|
if (err)
|
|
return err;
|
|
|
|
for (i = 0; i < ARRAY_SIZE(sh_types); i++) {
|
|
struct elf_sym_iter iter;
|
|
struct elf_sym *sym;
|
|
|
|
err = elf_sym_iter_new(&iter, elf_fd.elf, binary_path, sh_types[i], STT_FUNC);
|
|
if (err == -ENOENT)
|
|
continue;
|
|
if (err)
|
|
goto out;
|
|
|
|
while ((sym = elf_sym_iter_next(&iter))) {
|
|
if (!glob_match(sym->name, pattern))
|
|
continue;
|
|
|
|
err = libbpf_ensure_mem((void **) &offsets, &cap, sizeof(*offsets),
|
|
cnt + 1);
|
|
if (err)
|
|
goto out;
|
|
|
|
offsets[cnt++] = elf_sym_offset(sym);
|
|
}
|
|
|
|
/* If we found anything in the first symbol section,
|
|
* do not search others to avoid duplicates.
|
|
*/
|
|
if (cnt)
|
|
break;
|
|
}
|
|
|
|
if (cnt) {
|
|
*poffsets = offsets;
|
|
*pcnt = cnt;
|
|
} else {
|
|
err = -ENOENT;
|
|
}
|
|
|
|
out:
|
|
if (err)
|
|
free(offsets);
|
|
elf_close(&elf_fd);
|
|
return err;
|
|
}
|