// 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
#define MAX_PHDR_CNT 256
struct freader {
void *buf;
u32 buf_sz;
int err;
union {
struct {
struct file *file;
struct folio *folio;
void *addr;
loff_t folio_off;
bool may_fault;
};
struct {
const char *data;
u64 data_sz;
};
};
};
static void freader_init_from_file(struct freader *r, void *buf, u32 buf_sz,
struct file *file, bool may_fault)
{
memset(r, 0, sizeof(*r));
r->buf = buf;
r->buf_sz = buf_sz;
r->file = file;
r->may_fault = may_fault;
}
static void freader_init_from_mem(struct freader *r, const char *data, u64 data_sz)
{
memset(r, 0, sizeof(*r));
r->data = data;
r->data_sz = data_sz;
}
static void freader_put_folio(struct freader *r)
{
if (!r->folio)
return;
kunmap_local(r->addr);
folio_put(r->folio);
r->folio = NULL;
}
static int freader_get_folio(struct freader *r, loff_t file_off)
{
/* check if we can just reuse current folio */
if (r->folio && file_off >= r->folio_off &&
file_off < r->folio_off + folio_size(r->folio))
return 0;
freader_put_folio(r);
r->folio = filemap_get_folio(r->file->f_mapping, file_off >> PAGE_SHIFT);
/* if sleeping is allowed, wait for the page, if necessary */
if (r->may_fault && (IS_ERR(r->folio) || !folio_test_uptodate(r->folio))) {
filemap_invalidate_lock_shared(r->file->f_mapping);
r->folio = read_cache_folio(r->file->f_mapping, file_off >> PAGE_SHIFT,
NULL, r->file);
filemap_invalidate_unlock_shared(r->file->f_mapping);
}
if (IS_ERR(r->folio) || !folio_test_uptodate(r->folio)) {
if (!IS_ERR(r->folio))
folio_put(r->folio);
r->folio = NULL;
return -EFAULT;
}
r->folio_off = folio_pos(r->folio);
r->addr = kmap_local_folio(r->folio, 0);
return 0;
}
static const void *freader_fetch(struct freader *r, loff_t file_off, size_t sz)
{
size_t folio_sz;
/* provided internal temporary buffer should be sized correctly */
if (WARN_ON(r->buf && sz > r->buf_sz)) {
r->err = -E2BIG;
return NULL;
}
if (unlikely(file_off + sz < file_off)) {
r->err = -EOVERFLOW;
return NULL;
}
/* working with memory buffer is much more straightforward */
if (!r->buf) {
if (file_off + sz > r->data_sz) {
r->err = -ERANGE;
return NULL;
}
return r->data + file_off;
}
/* fetch or reuse folio for given file offset */
r->err = freader_get_folio(r, file_off);
if (r->err)
return NULL;
/* if requested data is crossing folio boundaries, we have to copy
* everything into our local buffer to keep a simple linear memory
* access interface
*/
folio_sz = folio_size(r->folio);
if (file_off + sz > r->folio_off + folio_sz) {
int part_sz = r->folio_off + folio_sz - file_off;
/* copy the part that resides in the current folio */
memcpy(r->buf, r->addr + (file_off - r->folio_off), part_sz);
/* fetch next folio */
r->err = freader_get_folio(r, r->folio_off + folio_sz);
if (r->err)
return NULL;
/* copy the rest of requested data */
memcpy(r->buf + part_sz, r->addr, sz - part_sz);
return r->buf;
}
/* if data fits in a single folio, just return direct pointer */
return r->addr + (file_off - r->folio_off);
}
static void freader_cleanup(struct freader *r)
{
if (!r->buf)
return; /* non-file-backed mode */
freader_put_folio(r);
}
/*
* 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(struct freader *r, unsigned char *build_id, __u32 *size,
loff_t note_off, Elf32_Word note_size)
{
const char note_name[] = "GNU";
const size_t note_name_sz = sizeof(note_name);
u32 build_id_off, new_off, note_end, name_sz, desc_sz;
const Elf32_Nhdr *nhdr;
const char *data;
if (check_add_overflow(note_off, note_size, ¬e_end))
return -EINVAL;
while (note_end - note_off > sizeof(Elf32_Nhdr) + note_name_sz) {
nhdr = freader_fetch(r, note_off, sizeof(Elf32_Nhdr) + note_name_sz);
if (!nhdr)
return r->err;
name_sz = READ_ONCE(nhdr->n_namesz);
desc_sz = READ_ONCE(nhdr->n_descsz);
new_off = note_off + sizeof(Elf32_Nhdr);
if (check_add_overflow(new_off, ALIGN(name_sz, 4), &new_off) ||
check_add_overflow(new_off, ALIGN(desc_sz, 4), &new_off) ||
new_off > note_end)
break;
if (nhdr->n_type == BUILD_ID &&
name_sz == note_name_sz &&
memcmp(nhdr + 1, note_name, note_name_sz) == 0 &&
desc_sz > 0 && desc_sz <= BUILD_ID_SIZE_MAX) {
build_id_off = note_off + sizeof(Elf32_Nhdr) + ALIGN(note_name_sz, 4);
/* freader_fetch() will invalidate nhdr pointer */
data = freader_fetch(r, build_id_off, desc_sz);
if (!data)
return r->err;
memcpy(build_id, data, desc_sz);
memset(build_id + desc_sz, 0, BUILD_ID_SIZE_MAX - desc_sz);
if (size)
*size = desc_sz;
return 0;
}
note_off = new_off;
}
return -EINVAL;
}
/* Parse build ID from 32-bit ELF */
static int get_build_id_32(struct freader *r, unsigned char *build_id, __u32 *size)
{
const Elf32_Ehdr *ehdr;
const Elf32_Phdr *phdr;
__u32 phnum, phoff, i;
ehdr = freader_fetch(r, 0, sizeof(Elf32_Ehdr));
if (!ehdr)
return r->err;
/* subsequent freader_fetch() calls invalidate pointers, so remember locally */
phnum = READ_ONCE(ehdr->e_phnum);
phoff = READ_ONCE(ehdr->e_phoff);
/* set upper bound on amount of segments (phdrs) we iterate */
if (phnum > MAX_PHDR_CNT)
phnum = MAX_PHDR_CNT;
/* check that phoff is not large enough to cause an overflow */
if (phoff + phnum * sizeof(Elf32_Phdr) < phoff)
return -EINVAL;
for (i = 0; i < phnum; ++i) {
phdr = freader_fetch(r, phoff + i * sizeof(Elf32_Phdr), sizeof(Elf32_Phdr));
if (!phdr)
return r->err;
if (phdr->p_type == PT_NOTE &&
!parse_build_id(r, build_id, size, READ_ONCE(phdr->p_offset),
READ_ONCE(phdr->p_filesz)))
return 0;
}
return -EINVAL;
}
/* Parse build ID from 64-bit ELF */
static int get_build_id_64(struct freader *r, unsigned char *build_id, __u32 *size)
{
const Elf64_Ehdr *ehdr;
const Elf64_Phdr *phdr;
__u32 phnum, i;
__u64 phoff;
ehdr = freader_fetch(r, 0, sizeof(Elf64_Ehdr));
if (!ehdr)
return r->err;
/* subsequent freader_fetch() calls invalidate pointers, so remember locally */
phnum = READ_ONCE(ehdr->e_phnum);
phoff = READ_ONCE(ehdr->e_phoff);
/* set upper bound on amount of segments (phdrs) we iterate */
if (phnum > MAX_PHDR_CNT)
phnum = MAX_PHDR_CNT;
/* check that phoff is not large enough to cause an overflow */
if (phoff + phnum * sizeof(Elf64_Phdr) < phoff)
return -EINVAL;
for (i = 0; i < phnum; ++i) {
phdr = freader_fetch(r, phoff + i * sizeof(Elf64_Phdr), sizeof(Elf64_Phdr));
if (!phdr)
return r->err;
if (phdr->p_type == PT_NOTE &&
!parse_build_id(r, build_id, size, READ_ONCE(phdr->p_offset),
READ_ONCE(phdr->p_filesz)))
return 0;
}
return -EINVAL;
}
/* enough for Elf64_Ehdr, Elf64_Phdr, and all the smaller requests */
#define MAX_FREADER_BUF_SZ 64
static int __build_id_parse(struct vm_area_struct *vma, unsigned char *build_id,
__u32 *size, bool may_fault)
{
const Elf32_Ehdr *ehdr;
struct freader r;
char buf[MAX_FREADER_BUF_SZ];
int ret;
/* only works for page backed storage */
if (!vma->vm_file)
return -EINVAL;
freader_init_from_file(&r, buf, sizeof(buf), vma->vm_file, may_fault);
/* fetch first 18 bytes of ELF header for checks */
ehdr = freader_fetch(&r, 0, offsetofend(Elf32_Ehdr, e_type));
if (!ehdr) {
ret = r.err;
goto out;
}
ret = -EINVAL;
/* 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(&r, build_id, size);
else if (ehdr->e_ident[EI_CLASS] == ELFCLASS64)
ret = get_build_id_64(&r, build_id, size);
out:
freader_cleanup(&r);
return ret;
}
/*
* 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
*
* Assumes no page fault can be taken, so if relevant portions of ELF file are
* not already paged in, fetching of build ID fails.
*
* Return: 0 on success; negative error, otherwise
*/
int build_id_parse_nofault(struct vm_area_struct *vma, unsigned char *build_id, __u32 *size)
{
return __build_id_parse(vma, build_id, size, false /* !may_fault */);
}
/*
* 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
*
* Assumes faultable context and can cause page faults to bring in file data
* into page cache.
*
* Return: 0 on success; negative error, otherwise
*/
int build_id_parse(struct vm_area_struct *vma, unsigned char *build_id, __u32 *size)
{
return __build_id_parse(vma, build_id, size, true /* may_fault */);
}
/**
* 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)
{
struct freader r;
int err;
freader_init_from_mem(&r, buf, buf_size);
err = parse_build_id(&r, build_id, NULL, 0, buf_size);
freader_cleanup(&r);
return err;
}
#if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID) || IS_ENABLED(CONFIG_VMCORE_INFO)
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;
extern const void __stop_notes;
unsigned int size = &__stop_notes - &__start_notes;
build_id_parse_buf(&__start_notes, vmlinux_build_id, size);
}
#endif
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