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// SPDX-License-Identifier: GPL-2.0
#include <linux/buildid.h>
#include <linux/cache.h>
#include <linux/elf.h>
#include <linux/kernel.h>
#include <linux/pagemap.h>
#define BUILD_ID 3
/*
* Parse build id from the note segment. This logic can be shared between
* 32-bit and 64-bit system, because Elf32_Nhdr and Elf64_Nhdr are
* identical.
*/
static int parse_build_id_buf(unsigned char *build_id,
__u32 *size,
const void *note_start,
Elf32_Word note_size)
{
Elf32_Word note_offs = 0, new_offs;
while (note_offs + sizeof(Elf32_Nhdr) < note_size) {
Elf32_Nhdr *nhdr = (Elf32_Nhdr *)(note_start + note_offs);
if (nhdr->n_type == BUILD_ID &&
nhdr->n_namesz == sizeof("GNU") &&
!strcmp((char *)(nhdr + 1), "GNU") &&
nhdr->n_descsz > 0 &&
nhdr->n_descsz <= BUILD_ID_SIZE_MAX) {
memcpy(build_id,
note_start + note_offs +
ALIGN(sizeof("GNU"), 4) + sizeof(Elf32_Nhdr),
nhdr->n_descsz);
memset(build_id + nhdr->n_descsz, 0,
BUILD_ID_SIZE_MAX - nhdr->n_descsz);
if (size)
*size = nhdr->n_descsz;
return 0;
}
new_offs = note_offs + sizeof(Elf32_Nhdr) +
ALIGN(nhdr->n_namesz, 4) + ALIGN(nhdr->n_descsz, 4);
if (new_offs <= note_offs) /* overflow */
break;
note_offs = new_offs;
}
return -EINVAL;
}
static inline int parse_build_id(void *page_addr,
unsigned char *build_id,
__u32 *size,
void *note_start,
Elf32_Word note_size)
{
/* check for overflow */
if (note_start < page_addr || note_start + note_size < note_start)
return -EINVAL;
/* only supports note that fits in the first page */
if (note_start + note_size > page_addr + PAGE_SIZE)
return -EINVAL;
return parse_build_id_buf(build_id, size, note_start, note_size);
}
/* Parse build ID from 32-bit ELF */
static int get_build_id_32(void *page_addr, unsigned char *build_id,
__u32 *size)
{
Elf32_Ehdr *ehdr = (Elf32_Ehdr *)page_addr;
Elf32_Phdr *phdr;
int i;
/* only supports phdr that fits in one page */
if (ehdr->e_phnum >
(PAGE_SIZE - sizeof(Elf32_Ehdr)) / sizeof(Elf32_Phdr))
return -EINVAL;
phdr = (Elf32_Phdr *)(page_addr + sizeof(Elf32_Ehdr));
for (i = 0; i < ehdr->e_phnum; ++i) {
if (phdr[i].p_type == PT_NOTE &&
!parse_build_id(page_addr, build_id, size,
page_addr + phdr[i].p_offset,
phdr[i].p_filesz))
return 0;
}
return -EINVAL;
}
/* Parse build ID from 64-bit ELF */
static int get_build_id_64(void *page_addr, unsigned char *build_id,
__u32 *size)
{
Elf64_Ehdr *ehdr = (Elf64_Ehdr *)page_addr;
Elf64_Phdr *phdr;
int i;
/* only supports phdr that fits in one page */
if (ehdr->e_phnum >
(PAGE_SIZE - sizeof(Elf64_Ehdr)) / sizeof(Elf64_Phdr))
return -EINVAL;
phdr = (Elf64_Phdr *)(page_addr + sizeof(Elf64_Ehdr));
for (i = 0; i < ehdr->e_phnum; ++i) {
if (phdr[i].p_type == PT_NOTE &&
!parse_build_id(page_addr, build_id, size,
page_addr + phdr[i].p_offset,
phdr[i].p_filesz))
return 0;
}
return -EINVAL;
}
/*
* Parse build ID of ELF file mapped to vma
* @vma: vma object
* @build_id: buffer to store build id, at least BUILD_ID_SIZE long
* @size: returns actual build id size in case of success
*
* Returns 0 on success, otherwise error (< 0).
*/
int build_id_parse(struct vm_area_struct *vma, unsigned char *build_id,
__u32 *size)
{
Elf32_Ehdr *ehdr;
struct page *page;
void *page_addr;
int ret;
/* only works for page backed storage */
if (!vma->vm_file)
return -EINVAL;
page = find_get_page(vma->vm_file->f_mapping, 0);
if (!page)
return -EFAULT; /* page not mapped */
ret = -EINVAL;
page_addr = kmap_atomic(page);
ehdr = (Elf32_Ehdr *)page_addr;
/* compare magic x7f "ELF" */
if (memcmp(ehdr->e_ident, ELFMAG, SELFMAG) != 0)
goto out;
/* only support executable file and shared object file */
if (ehdr->e_type != ET_EXEC && ehdr->e_type != ET_DYN)
goto out;
if (ehdr->e_ident[EI_CLASS] == ELFCLASS32)
ret = get_build_id_32(page_addr, build_id, size);
else if (ehdr->e_ident[EI_CLASS] == ELFCLASS64)
ret = get_build_id_64(page_addr, build_id, size);
out:
kunmap_atomic(page_addr);
put_page(page);
return ret;
}
/**
* build_id_parse_buf - Get build ID from a buffer
* @buf: Elf note section(s) to parse
* @buf_size: Size of @buf in bytes
* @build_id: Build ID parsed from @buf, at least BUILD_ID_SIZE_MAX long
*
* Return: 0 on success, -EINVAL otherwise
*/
int build_id_parse_buf(const void *buf, unsigned char *build_id, u32 buf_size)
{
return parse_build_id_buf(build_id, NULL, buf, buf_size);
}
#if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID)
unsigned char vmlinux_build_id[BUILD_ID_SIZE_MAX] __ro_after_init;
/**
* init_vmlinux_build_id - Compute and stash the running kernel's build ID
*/
void __init init_vmlinux_build_id(void)
{
extern const void __start_notes __weak;
extern const void __stop_notes __weak;
unsigned int size = &__stop_notes - &__start_notes;
build_id_parse_buf(&__start_notes, vmlinux_build_id, size);
}
#endif
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