[linux-2.6-block.git] / lib / buildid.c

// 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>
#include <linux/secretmem.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);

	/* reject secretmem folios created with memfd_secret() */
	if (secretmem_mapping(r->file->f_mapping))
		return -EFAULT;

	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, &note_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
Commit	Line	Data
	1	// SPDX-License-Identifier: GPL-2.0
	2
	3	#include <linux/buildid.h>
	4	#include <linux/cache.h>
	5	#include <linux/elf.h>
	6	#include <linux/kernel.h>
	7	#include <linux/pagemap.h>
	8	#include <linux/secretmem.h>
	9
	10	#define BUILD_ID 3
	11
	12	#define MAX_PHDR_CNT 256
	13
	14	struct freader {
	15	void *buf;
	16	u32 buf_sz;
	17	int err;
	18	union {
	19	struct {
	20	struct file *file;
	21	struct folio *folio;
	22	void *addr;
	23	loff_t folio_off;
	24	bool may_fault;
	25	};
	26	struct {
	27	const char *data;
	28	u64 data_sz;
	29	};
	30	};
	31	};
	32
	33	static void freader_init_from_file(struct freader r, void buf, u32 buf_sz,
	34	struct file *file, bool may_fault)
	35	{
	36	memset(r, 0, sizeof(*r));
	37	r->buf = buf;
	38	r->buf_sz = buf_sz;
	39	r->file = file;
	40	r->may_fault = may_fault;
	41	}
	42
	43	static void freader_init_from_mem(struct freader r, const char data, u64 data_sz)
	44	{
	45	memset(r, 0, sizeof(*r));
	46	r->data = data;
	47	r->data_sz = data_sz;
	48	}
	49
	50	static void freader_put_folio(struct freader *r)
	51	{
	52	if (!r->folio)
	53	return;
	54	kunmap_local(r->addr);
	55	folio_put(r->folio);
	56	r->folio = NULL;
	57	}
	58
	59	static int freader_get_folio(struct freader *r, loff_t file_off)
	60	{
	61	/* check if we can just reuse current folio */
	62	if (r->folio && file_off >= r->folio_off &&
	63	file_off < r->folio_off + folio_size(r->folio))
	64	return 0;
	65
	66	freader_put_folio(r);
	67
	68	/* reject secretmem folios created with memfd_secret() */
	69	if (secretmem_mapping(r->file->f_mapping))
	70	return -EFAULT;
	71
	72	r->folio = filemap_get_folio(r->file->f_mapping, file_off >> PAGE_SHIFT);
	73
	74	/* if sleeping is allowed, wait for the page, if necessary */
	75	if (r->may_fault && (IS_ERR(r->folio) \|\| !folio_test_uptodate(r->folio))) {
	76	filemap_invalidate_lock_shared(r->file->f_mapping);
	77	r->folio = read_cache_folio(r->file->f_mapping, file_off >> PAGE_SHIFT,
	78	NULL, r->file);
	79	filemap_invalidate_unlock_shared(r->file->f_mapping);
	80	}
	81
	82	if (IS_ERR(r->folio) \|\| !folio_test_uptodate(r->folio)) {
	83	if (!IS_ERR(r->folio))
	84	folio_put(r->folio);
	85	r->folio = NULL;
	86	return -EFAULT;
	87	}
	88
	89	r->folio_off = folio_pos(r->folio);
	90	r->addr = kmap_local_folio(r->folio, 0);
	91
	92	return 0;
	93	}
	94
	95	static const void freader_fetch(struct freader r, loff_t file_off, size_t sz)
	96	{
	97	size_t folio_sz;
	98
	99	/* provided internal temporary buffer should be sized correctly */
	100	if (WARN_ON(r->buf && sz > r->buf_sz)) {
	101	r->err = -E2BIG;
	102	return NULL;
	103	}
	104
	105	if (unlikely(file_off + sz < file_off)) {
	106	r->err = -EOVERFLOW;
	107	return NULL;
	108	}
	109
	110	/* working with memory buffer is much more straightforward */
	111	if (!r->buf) {
	112	if (file_off + sz > r->data_sz) {
	113	r->err = -ERANGE;
	114	return NULL;
	115	}
	116	return r->data + file_off;
	117	}
	118
	119	/* fetch or reuse folio for given file offset */
	120	r->err = freader_get_folio(r, file_off);
	121	if (r->err)
	122	return NULL;
	123
	124	/* if requested data is crossing folio boundaries, we have to copy
	125	* everything into our local buffer to keep a simple linear memory
	126	* access interface
	127	*/
	128	folio_sz = folio_size(r->folio);
	129	if (file_off + sz > r->folio_off + folio_sz) {
	130	int part_sz = r->folio_off + folio_sz - file_off;
	131
	132	/* copy the part that resides in the current folio */
	133	memcpy(r->buf, r->addr + (file_off - r->folio_off), part_sz);
	134
	135	/* fetch next folio */
	136	r->err = freader_get_folio(r, r->folio_off + folio_sz);
	137	if (r->err)
	138	return NULL;
	139
	140	/* copy the rest of requested data */
	141	memcpy(r->buf + part_sz, r->addr, sz - part_sz);
	142
	143	return r->buf;
	144	}
	145
	146	/* if data fits in a single folio, just return direct pointer */
	147	return r->addr + (file_off - r->folio_off);
	148	}
	149
	150	static void freader_cleanup(struct freader *r)
	151	{
	152	if (!r->buf)
	153	return; /* non-file-backed mode */
	154
	155	freader_put_folio(r);
	156	}
	157
	158	/*
	159	* Parse build id from the note segment. This logic can be shared between
	160	* 32-bit and 64-bit system, because Elf32_Nhdr and Elf64_Nhdr are
	161	* identical.
	162	*/
	163	static int parse_build_id(struct freader r, unsigned char build_id, __u32 *size,
	164	loff_t note_off, Elf32_Word note_size)
	165	{
	166	const char note_name[] = "GNU";
	167	const size_t note_name_sz = sizeof(note_name);
	168	u32 build_id_off, new_off, note_end, name_sz, desc_sz;
	169	const Elf32_Nhdr *nhdr;
	170	const char *data;
	171
	172	if (check_add_overflow(note_off, note_size, &note_end))
	173	return -EINVAL;
	174
	175	while (note_end - note_off > sizeof(Elf32_Nhdr) + note_name_sz) {
	176	nhdr = freader_fetch(r, note_off, sizeof(Elf32_Nhdr) + note_name_sz);
	177	if (!nhdr)
	178	return r->err;
	179
	180	name_sz = READ_ONCE(nhdr->n_namesz);
	181	desc_sz = READ_ONCE(nhdr->n_descsz);
	182
	183	new_off = note_off + sizeof(Elf32_Nhdr);
	184	if (check_add_overflow(new_off, ALIGN(name_sz, 4), &new_off) \|\|
	185	check_add_overflow(new_off, ALIGN(desc_sz, 4), &new_off) \|\|
	186	new_off > note_end)
	187	break;
	188
	189	if (nhdr->n_type == BUILD_ID &&
	190	name_sz == note_name_sz &&
	191	memcmp(nhdr + 1, note_name, note_name_sz) == 0 &&
	192	desc_sz > 0 && desc_sz <= BUILD_ID_SIZE_MAX) {
	193	build_id_off = note_off + sizeof(Elf32_Nhdr) + ALIGN(note_name_sz, 4);
	194
	195	/* freader_fetch() will invalidate nhdr pointer */
	196	data = freader_fetch(r, build_id_off, desc_sz);
	197	if (!data)
	198	return r->err;
	199
	200	memcpy(build_id, data, desc_sz);
	201	memset(build_id + desc_sz, 0, BUILD_ID_SIZE_MAX - desc_sz);
	202	if (size)
	203	*size = desc_sz;
	204	return 0;
	205	}
	206
	207	note_off = new_off;
	208	}
	209
	210	return -EINVAL;
	211	}
	212
	213	/* Parse build ID from 32-bit ELF */
	214	static int get_build_id_32(struct freader r, unsigned char build_id, __u32 *size)
	215	{
	216	const Elf32_Ehdr *ehdr;
	217	const Elf32_Phdr *phdr;
	218	__u32 phnum, phoff, i;
	219
	220	ehdr = freader_fetch(r, 0, sizeof(Elf32_Ehdr));
	221	if (!ehdr)
	222	return r->err;
	223
	224	/* subsequent freader_fetch() calls invalidate pointers, so remember locally */
	225	phnum = READ_ONCE(ehdr->e_phnum);
	226	phoff = READ_ONCE(ehdr->e_phoff);
	227
	228	/* set upper bound on amount of segments (phdrs) we iterate */
	229	if (phnum > MAX_PHDR_CNT)
	230	phnum = MAX_PHDR_CNT;
	231
	232	/* check that phoff is not large enough to cause an overflow */
	233	if (phoff + phnum * sizeof(Elf32_Phdr) < phoff)
	234	return -EINVAL;
	235
	236	for (i = 0; i < phnum; ++i) {
	237	phdr = freader_fetch(r, phoff + i * sizeof(Elf32_Phdr), sizeof(Elf32_Phdr));
	238	if (!phdr)
	239	return r->err;
	240
	241	if (phdr->p_type == PT_NOTE &&
	242	!parse_build_id(r, build_id, size, READ_ONCE(phdr->p_offset),
	243	READ_ONCE(phdr->p_filesz)))
	244	return 0;
	245	}
	246	return -EINVAL;
	247	}
	248
	249	/* Parse build ID from 64-bit ELF */
	250	static int get_build_id_64(struct freader r, unsigned char build_id, __u32 *size)
	251	{
	252	const Elf64_Ehdr *ehdr;
	253	const Elf64_Phdr *phdr;
	254	__u32 phnum, i;
	255	__u64 phoff;
	256
	257	ehdr = freader_fetch(r, 0, sizeof(Elf64_Ehdr));
	258	if (!ehdr)
	259	return r->err;
	260
	261	/* subsequent freader_fetch() calls invalidate pointers, so remember locally */
	262	phnum = READ_ONCE(ehdr->e_phnum);
	263	phoff = READ_ONCE(ehdr->e_phoff);
	264
	265	/* set upper bound on amount of segments (phdrs) we iterate */
	266	if (phnum > MAX_PHDR_CNT)
	267	phnum = MAX_PHDR_CNT;
	268
	269	/* check that phoff is not large enough to cause an overflow */
	270	if (phoff + phnum * sizeof(Elf64_Phdr) < phoff)
	271	return -EINVAL;
	272
	273	for (i = 0; i < phnum; ++i) {
	274	phdr = freader_fetch(r, phoff + i * sizeof(Elf64_Phdr), sizeof(Elf64_Phdr));
	275	if (!phdr)
	276	return r->err;
	277
	278	if (phdr->p_type == PT_NOTE &&
	279	!parse_build_id(r, build_id, size, READ_ONCE(phdr->p_offset),
	280	READ_ONCE(phdr->p_filesz)))
	281	return 0;
	282	}
	283
	284	return -EINVAL;
	285	}
	286
	287	/* enough for Elf64_Ehdr, Elf64_Phdr, and all the smaller requests */
	288	#define MAX_FREADER_BUF_SZ 64
	289
	290	static int __build_id_parse(struct vm_area_struct vma, unsigned char build_id,
	291	__u32 *size, bool may_fault)
	292	{
	293	const Elf32_Ehdr *ehdr;
	294	struct freader r;
	295	char buf[MAX_FREADER_BUF_SZ];
	296	int ret;
	297
	298	/* only works for page backed storage */
	299	if (!vma->vm_file)
	300	return -EINVAL;
	301
	302	freader_init_from_file(&r, buf, sizeof(buf), vma->vm_file, may_fault);
	303
	304	/* fetch first 18 bytes of ELF header for checks */
	305	ehdr = freader_fetch(&r, 0, offsetofend(Elf32_Ehdr, e_type));
	306	if (!ehdr) {
	307	ret = r.err;
	308	goto out;
	309	}
	310
	311	ret = -EINVAL;
	312
	313	/* compare magic x7f "ELF" */
	314	if (memcmp(ehdr->e_ident, ELFMAG, SELFMAG) != 0)
	315	goto out;
	316
	317	/* only support executable file and shared object file */
	318	if (ehdr->e_type != ET_EXEC && ehdr->e_type != ET_DYN)
	319	goto out;
	320
	321	if (ehdr->e_ident[EI_CLASS] == ELFCLASS32)
	322	ret = get_build_id_32(&r, build_id, size);
	323	else if (ehdr->e_ident[EI_CLASS] == ELFCLASS64)
	324	ret = get_build_id_64(&r, build_id, size);
	325	out:
	326	freader_cleanup(&r);
	327	return ret;
	328	}
	329
	330	/*
	331	* Parse build ID of ELF file mapped to vma
	332	* @vma: vma object
	333	* @build_id: buffer to store build id, at least BUILD_ID_SIZE long
	334	* @size: returns actual build id size in case of success
	335	*
	336	* Assumes no page fault can be taken, so if relevant portions of ELF file are
	337	* not already paged in, fetching of build ID fails.
	338	*
	339	* Return: 0 on success; negative error, otherwise
	340	*/
	341	int build_id_parse_nofault(struct vm_area_struct vma, unsigned char build_id, __u32 *size)
	342	{
	343	return __build_id_parse(vma, build_id, size, false /* !may_fault */);
	344	}
	345
	346	/*
	347	* Parse build ID of ELF file mapped to VMA
	348	* @vma: vma object
	349	* @build_id: buffer to store build id, at least BUILD_ID_SIZE long
	350	* @size: returns actual build id size in case of success
	351	*
	352	* Assumes faultable context and can cause page faults to bring in file data
	353	* into page cache.
	354	*
	355	* Return: 0 on success; negative error, otherwise
	356	*/
	357	int build_id_parse(struct vm_area_struct vma, unsigned char build_id, __u32 *size)
	358	{
	359	return __build_id_parse(vma, build_id, size, true /* may_fault */);
	360	}
	361
	362	/**
	363	* build_id_parse_buf - Get build ID from a buffer
	364	* @buf: ELF note section(s) to parse
	365	* @buf_size: Size of @buf in bytes
	366	* @build_id: Build ID parsed from @buf, at least BUILD_ID_SIZE_MAX long
	367	*
	368	* Return: 0 on success, -EINVAL otherwise
	369	*/
	370	int build_id_parse_buf(const void buf, unsigned char build_id, u32 buf_size)
	371	{
	372	struct freader r;
	373	int err;
	374
	375	freader_init_from_mem(&r, buf, buf_size);
	376
	377	err = parse_build_id(&r, build_id, NULL, 0, buf_size);
	378
	379	freader_cleanup(&r);
	380	return err;
	381	}
	382
	383	#if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID) \|\| IS_ENABLED(CONFIG_VMCORE_INFO)
	384	unsigned char vmlinux_build_id[BUILD_ID_SIZE_MAX] __ro_after_init;
	385
	386	/**
	387	* init_vmlinux_build_id - Compute and stash the running kernel's build ID
	388	*/
	389	void __init init_vmlinux_build_id(void)
	390	{
	391	extern const void __start_notes;
	392	extern const void __stop_notes;
	393	unsigned int size = &__stop_notes - &__start_notes;
	394
	395	build_id_parse_buf(&__start_notes, vmlinux_build_id, size);
	396	}
	397	#endif