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// Copyright (c) Meta Platforms, Inc. and affiliates.
// SPDX-License-Identifier: LGPL-2.1-or-later
#include <byteswap.h>
#include <string.h>
#include "elf_notes.h"
#include "util.h"
bool next_elf_note(const void **p, size_t *size, unsigned int align, bool bswap,
GElf_Nhdr *nhdr_ret, const char **name_ret,
const void **desc_ret)
{
uint64_t align_mask = align - 1;
if (*size < sizeof(*nhdr_ret))
return false;
memcpy(nhdr_ret, *p, sizeof(*nhdr_ret));
if (bswap) {
nhdr_ret->n_namesz = bswap_32(nhdr_ret->n_namesz);
nhdr_ret->n_descsz = bswap_32(nhdr_ret->n_descsz);
nhdr_ret->n_type = bswap_32(nhdr_ret->n_type);
}
if (nhdr_ret->n_namesz > *size - sizeof(*nhdr_ret))
return false;
uint64_t aligned_namesz = (nhdr_ret->n_namesz + align_mask) & ~align_mask;
if (nhdr_ret->n_descsz > 0
&& (aligned_namesz > *size - sizeof(*nhdr_ret)
|| nhdr_ret->n_descsz > *size - sizeof(*nhdr_ret) - aligned_namesz))
return false;
*p = (const char *)*p + sizeof(*nhdr_ret);
*size -= sizeof(*nhdr_ret);
*name_ret = *p;
if (aligned_namesz > *size) {
*p = (const char *)*p + *size;
*size = 0;
} else {
*p = (const char *)*p + aligned_namesz;
*size -= aligned_namesz;
}
*desc_ret = *p;
uint64_t aligned_descsz = (nhdr_ret->n_descsz + align_mask) & ~align_mask;
if (aligned_descsz > *size) {
*p = (const char *)*p + *size;
*size = 0;
} else {
*p = (const char *)*p + aligned_descsz;
*size -= aligned_descsz;
}
return true;
}
int find_elf_note(Elf *elf, const char *name, uint32_t type, const void **ret,
size_t *size_ret)
{
size_t phnum;
if (elf_getphdrnum(elf, &phnum))
return -1;
size_t name_size = strlen(name) + 1;
for (size_t i = 0; i < phnum; i++) {
GElf_Phdr phdr_mem, *phdr = gelf_getphdr(elf, i, &phdr_mem);
if (!phdr)
return -1;
if (phdr->p_type != PT_NOTE)
continue;
Elf_Data *data = elf_getdata_rawchunk(elf, phdr->p_offset,
phdr->p_filesz,
note_header_type(phdr->p_align));
if (!data)
return -1;
GElf_Nhdr nhdr;
size_t offset = 0, name_offset, desc_offset;
while (offset < data->d_size &&
(offset = gelf_getnote(data, offset, &nhdr,
&name_offset,
&desc_offset))) {
const char *note_name = (char *)data->d_buf + name_offset;
if (nhdr.n_namesz == name_size
&& memcmp(note_name, name, name_size) == 0
&& nhdr.n_type == type) {
*ret = (char *)data->d_buf + desc_offset;
*size_ret = nhdr.n_descsz;
return 0;
}
}
}
*ret = NULL;
*size_ret = 0;
return 0;
}
size_t parse_gnu_build_id_from_notes(const void *buf, size_t size,
unsigned int align, bool bswap,
const void **ret)
{
GElf_Nhdr nhdr;
const char *name;
const void *desc;
while (next_elf_note(&buf, &size, align, bswap, &nhdr, &name, &desc)) {
if (nhdr.n_namesz == sizeof("GNU")
&& memcmp(name, "GNU", sizeof("GNU")) == 0
&& nhdr.n_type == NT_GNU_BUILD_ID
&& nhdr.n_descsz > 0) {
*ret = desc;
return nhdr.n_descsz;
}
}
*ret = NULL;
return 0;
}
#if _ELFUTILS_PREREQ(0, 175)
ssize_t drgn_elf_gnu_build_id(Elf *elf, const void **ret)
{
GElf_Ehdr ehdr_mem, *ehdr = gelf_getehdr(elf, &ehdr_mem);
if (!ehdr)
return -1;
bool bswap =
(ehdr->e_ident[EI_DATA] == ELFDATA2LSB) != HOST_LITTLE_ENDIAN;
Elf_Data *nhdr8_data = NULL;
size_t num_note_sections = 0;
Elf_Scn *scn = elf_nextscn(elf, NULL);
if (scn) {
do {
GElf_Shdr shdr_mem, *shdr = gelf_getshdr(scn, &shdr_mem);
if (!shdr || shdr->sh_type != SHT_NOTE)
continue;
num_note_sections++;
Elf_Data *data = elf_rawdata(scn, NULL);
if (!data)
continue;
if (data->d_type == ELF_T_NHDR8)
nhdr8_data = data;
unsigned int align = data->d_type == ELF_T_NHDR8 ? 8 : 4;
const void *build_id;
size_t size = parse_gnu_build_id_from_notes(data->d_buf,
data->d_size,
align,
bswap,
&build_id);
if (size) {
*ret = build_id;
return size;
}
} while ((scn = elf_nextscn(elf, scn)));
} else {
size_t phnum;
if (elf_getphdrnum(elf, &phnum))
return -1;
for (size_t i = 0; i < phnum; i++) {
GElf_Phdr phdr_mem, *phdr =
gelf_getphdr(elf, i, &phdr_mem);
if (!phdr || phdr->p_type != PT_NOTE)
continue;
num_note_sections++;
Elf_Data *data =
elf_getdata_rawchunk(elf, phdr->p_offset,
phdr->p_filesz,
note_header_type(phdr->p_align));
if (!data)
continue;
if (data->d_type == ELF_T_NHDR8)
nhdr8_data = data;
unsigned int align = data->d_type == ELF_T_NHDR8 ? 8 : 4;
const void *build_id;
size_t size = parse_gnu_build_id_from_notes(data->d_buf,
data->d_size,
align,
bswap,
&build_id);
if (size) {
*ret = build_id;
return size;
}
}
}
// Before Linux kernel commit f7ba52f302fd ("vmlinux.lds.h: Discard
// .note.gnu.property section") (in v6.4), the vmlinux .notes section
// may specify an 8-byte alignment even though it is actually 4-byte
// aligned. This fix was backported to several stable and longterm
// kernels, but it never made it to the 4.14 and 4.19 longterm branches.
// So, we try to work around this bug here.
//
// If there is only one note section (or segment) and it specifies
// 8-byte alignment, then it might be affected by this bug, so we retry
// with 4-byte alignment.
//
// Whenever we drop Linux 4.14 and 4.19 support, we can probably drop
// this workaround and just use dwelf_elf_gnu_build_id().
if (nhdr8_data && num_note_sections == 1) {
return parse_gnu_build_id_from_notes(nhdr8_data->d_buf,
nhdr8_data->d_size, 4,
bswap, ret);
}
*ret = NULL;
return 0;
}
#endif
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