[linux-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>

#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, &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
bd7525da JO	1	// SPDX-License-Identifier: GPL-2.0
	2
	3	#include <linux/buildid.h>
83cc6fa0	4	#include <linux/cache.h>
bd7525da	5	#include <linux/elf.h>
7eaf3cf3	6	#include <linux/kernel.h>
bd7525da JO	7	#include <linux/pagemap.h>
	8
	9	#define BUILD_ID 3
7eaf3cf3	10
4e9d360c AN	11	#define MAX_PHDR_CNT 256
4e9d360c AN	12
de3ec364 AN	13	struct freader {
	14	void *buf;
	15	u32 buf_sz;
	16	int err;
	17	union {
	18	struct {
ad41251c	19	struct file *file;
de3ec364 AN	20	struct folio *folio;
	21	void *addr;
	22	loff_t folio_off;
ad41251c	23	bool may_fault;
de3ec364 AN	24	};
	25	struct {
	26	const char *data;
	27	u64 data_sz;
	28	};
	29	};
	30	};
	31
	32	static void freader_init_from_file(struct freader r, void buf, u32 buf_sz,
ad41251c	33	struct file *file, bool may_fault)
de3ec364 AN	34	{
	35	memset(r, 0, sizeof(*r));
	36	r->buf = buf;
	37	r->buf_sz = buf_sz;
ad41251c AN	38	r->file = file;
ad41251c AN	39	r->may_fault = may_fault;
de3ec364 AN	40	}
	41
	42	static void freader_init_from_mem(struct freader r, const char data, u64 data_sz)
	43	{
	44	memset(r, 0, sizeof(*r));
	45	r->data = data;
	46	r->data_sz = data_sz;
	47	}
	48
	49	static void freader_put_folio(struct freader *r)
	50	{
	51	if (!r->folio)
	52	return;
	53	kunmap_local(r->addr);
	54	folio_put(r->folio);
	55	r->folio = NULL;
	56	}
	57
	58	static int freader_get_folio(struct freader *r, loff_t file_off)
	59	{
	60	/* check if we can just reuse current folio */
	61	if (r->folio && file_off >= r->folio_off &&
	62	file_off < r->folio_off + folio_size(r->folio))
	63	return 0;
	64
	65	freader_put_folio(r);
	66
ad41251c AN	67	r->folio = filemap_get_folio(r->file->f_mapping, file_off >> PAGE_SHIFT);
	68
	69	/* if sleeping is allowed, wait for the page, if necessary */
	70	if (r->may_fault && (IS_ERR(r->folio) \|\| !folio_test_uptodate(r->folio))) {
	71	filemap_invalidate_lock_shared(r->file->f_mapping);
	72	r->folio = read_cache_folio(r->file->f_mapping, file_off >> PAGE_SHIFT,
	73	NULL, r->file);
	74	filemap_invalidate_unlock_shared(r->file->f_mapping);
	75	}
	76
de3ec364 AN	77	if (IS_ERR(r->folio) \|\| !folio_test_uptodate(r->folio)) {
	78	if (!IS_ERR(r->folio))
	79	folio_put(r->folio);
	80	r->folio = NULL;
	81	return -EFAULT;
	82	}
	83
	84	r->folio_off = folio_pos(r->folio);
	85	r->addr = kmap_local_folio(r->folio, 0);
	86
	87	return 0;
	88	}
	89
	90	static const void freader_fetch(struct freader r, loff_t file_off, size_t sz)
	91	{
	92	size_t folio_sz;
	93
	94	/* provided internal temporary buffer should be sized correctly */
	95	if (WARN_ON(r->buf && sz > r->buf_sz)) {
	96	r->err = -E2BIG;
	97	return NULL;
	98	}
	99
	100	if (unlikely(file_off + sz < file_off)) {
	101	r->err = -EOVERFLOW;
	102	return NULL;
	103	}
	104
	105	/* working with memory buffer is much more straightforward */
	106	if (!r->buf) {
	107	if (file_off + sz > r->data_sz) {
	108	r->err = -ERANGE;
	109	return NULL;
	110	}
	111	return r->data + file_off;
	112	}
	113
	114	/* fetch or reuse folio for given file offset */
	115	r->err = freader_get_folio(r, file_off);
	116	if (r->err)
	117	return NULL;
	118
	119	/* if requested data is crossing folio boundaries, we have to copy
	120	* everything into our local buffer to keep a simple linear memory
	121	* access interface
	122	*/
	123	folio_sz = folio_size(r->folio);
	124	if (file_off + sz > r->folio_off + folio_sz) {
	125	int part_sz = r->folio_off + folio_sz - file_off;
	126
	127	/* copy the part that resides in the current folio */
	128	memcpy(r->buf, r->addr + (file_off - r->folio_off), part_sz);
	129
	130	/* fetch next folio */
	131	r->err = freader_get_folio(r, r->folio_off + folio_sz);
	132	if (r->err)
	133	return NULL;
	134
	135	/* copy the rest of requested data */
	136	memcpy(r->buf + part_sz, r->addr, sz - part_sz);
	137
	138	return r->buf;
	139	}
	140
141	/* if data fits in a single folio, just return direct pointer */
142	return r->addr + (file_off - r->folio_off);
143	}
144
145	static void freader_cleanup(struct freader *r)
146	{
147	if (!r->buf)
148	return; /* non-file-backed mode */
149
150	freader_put_folio(r);
151	}
152
bd7525da JO	153	/*
	154	* Parse build id from the note segment. This logic can be shared between
	155	* 32-bit and 64-bit system, because Elf32_Nhdr and Elf64_Nhdr are
	156	* identical.
	157	*/
cdbb44f9 AN	158	static int parse_build_id(struct freader r, unsigned char build_id, __u32 *size,
cdbb44f9 AN	159	loff_t note_off, Elf32_Word note_size)
bd7525da	160	{
905415ff AN	161	const char note_name[] = "GNU";
905415ff AN	162	const size_t note_name_sz = sizeof(note_name);
de3ec364 AN	163	u32 build_id_off, new_off, note_end, name_sz, desc_sz;
de3ec364 AN	164	const Elf32_Nhdr *nhdr;
905415ff AN	165	const char *data;
905415ff AN	166
cdbb44f9 AN	167	if (check_add_overflow(note_off, note_size, &note_end))
	168	return -EINVAL;
	169
de3ec364 AN	170	while (note_end - note_off > sizeof(Elf32_Nhdr) + note_name_sz) {
	171	nhdr = freader_fetch(r, note_off, sizeof(Elf32_Nhdr) + note_name_sz);
	172	if (!nhdr)
	173	return r->err;
905415ff AN	174
	175	name_sz = READ_ONCE(nhdr->n_namesz);
	176	desc_sz = READ_ONCE(nhdr->n_descsz);
	177
	178	new_off = note_off + sizeof(Elf32_Nhdr);
	179	if (check_add_overflow(new_off, ALIGN(name_sz, 4), &new_off) \|\|
	180	check_add_overflow(new_off, ALIGN(desc_sz, 4), &new_off) \|\|
de3ec364	181	new_off > note_end)
905415ff	182	break;
bd7525da JO	183
bd7525da JO	184	if (nhdr->n_type == BUILD_ID &&
905415ff AN	185	name_sz == note_name_sz &&
	186	memcmp(nhdr + 1, note_name, note_name_sz) == 0 &&
	187	desc_sz > 0 && desc_sz <= BUILD_ID_SIZE_MAX) {
de3ec364 AN	188	build_id_off = note_off + sizeof(Elf32_Nhdr) + ALIGN(note_name_sz, 4);
	189
	190	/* freader_fetch() will invalidate nhdr pointer */
	191	data = freader_fetch(r, build_id_off, desc_sz);
	192	if (!data)
	193	return r->err;
	194
905415ff AN	195	memcpy(build_id, data, desc_sz);
905415ff AN	196	memset(build_id + desc_sz, 0, BUILD_ID_SIZE_MAX - desc_sz);
921f88fc	197	if (size)
905415ff	198	*size = desc_sz;
bd7525da JO	199	return 0;
bd7525da JO	200	}
905415ff AN	201
905415ff AN	202	note_off = new_off;
bd7525da	203	}
7eaf3cf3	204
bd7525da JO	205	return -EINVAL;
	206	}
	207
	208	/* Parse build ID from 32-bit ELF */
de3ec364	209	static int get_build_id_32(struct freader r, unsigned char build_id, __u32 *size)
bd7525da	210	{
de3ec364 AN	211	const Elf32_Ehdr *ehdr;
de3ec364 AN	212	const Elf32_Phdr *phdr;
d4deb824	213	__u32 phnum, phoff, i;
de3ec364 AN	214
	215	ehdr = freader_fetch(r, 0, sizeof(Elf32_Ehdr));
	216	if (!ehdr)
	217	return r->err;
bd7525da	218
de3ec364	219	/* subsequent freader_fetch() calls invalidate pointers, so remember locally */
905415ff	220	phnum = READ_ONCE(ehdr->e_phnum);
d4deb824 AN	221	phoff = READ_ONCE(ehdr->e_phoff);
d4deb824 AN	222
4e9d360c AN	223	/* set upper bound on amount of segments (phdrs) we iterate */
	224	if (phnum > MAX_PHDR_CNT)
	225	phnum = MAX_PHDR_CNT;
bd7525da	226
d4deb824 AN	227	/* check that phoff is not large enough to cause an overflow */
	228	if (phoff + phnum * sizeof(Elf32_Phdr) < phoff)
	229	return -EINVAL;
	230
905415ff	231	for (i = 0; i < phnum; ++i) {
d4deb824	232	phdr = freader_fetch(r, phoff + i * sizeof(Elf32_Phdr), sizeof(Elf32_Phdr));
de3ec364 AN	233	if (!phdr)
	234	return r->err;
	235
	236	if (phdr->p_type == PT_NOTE &&
	237	!parse_build_id(r, build_id, size, READ_ONCE(phdr->p_offset),
	238	READ_ONCE(phdr->p_filesz)))
bd7525da JO	239	return 0;
	240	}
	241	return -EINVAL;
	242	}
	243
	244	/* Parse build ID from 64-bit ELF */
de3ec364	245	static int get_build_id_64(struct freader r, unsigned char build_id, __u32 *size)
bd7525da	246	{
de3ec364 AN	247	const Elf64_Ehdr *ehdr;
	248	const Elf64_Phdr *phdr;
	249	__u32 phnum, i;
d4deb824	250	__u64 phoff;
de3ec364 AN	251
	252	ehdr = freader_fetch(r, 0, sizeof(Elf64_Ehdr));
	253	if (!ehdr)
	254	return r->err;
bd7525da	255
de3ec364	256	/* subsequent freader_fetch() calls invalidate pointers, so remember locally */
905415ff	257	phnum = READ_ONCE(ehdr->e_phnum);
d4deb824 AN	258	phoff = READ_ONCE(ehdr->e_phoff);
d4deb824 AN	259
4e9d360c AN	260	/* set upper bound on amount of segments (phdrs) we iterate */
	261	if (phnum > MAX_PHDR_CNT)
	262	phnum = MAX_PHDR_CNT;
bd7525da	263
d4deb824 AN	264	/* check that phoff is not large enough to cause an overflow */
	265	if (phoff + phnum * sizeof(Elf64_Phdr) < phoff)
	266	return -EINVAL;
	267
905415ff	268	for (i = 0; i < phnum; ++i) {
d4deb824	269	phdr = freader_fetch(r, phoff + i * sizeof(Elf64_Phdr), sizeof(Elf64_Phdr));
de3ec364 AN	270	if (!phdr)
	271	return r->err;
	272
	273	if (phdr->p_type == PT_NOTE &&
	274	!parse_build_id(r, build_id, size, READ_ONCE(phdr->p_offset),
	275	READ_ONCE(phdr->p_filesz)))
bd7525da JO	276	return 0;
bd7525da JO	277	}
de3ec364	278
bd7525da JO	279	return -EINVAL;
	280	}
	281
de3ec364 AN	282	/* enough for Elf64_Ehdr, Elf64_Phdr, and all the smaller requests */
	283	#define MAX_FREADER_BUF_SZ 64
	284
ad41251c AN	285	static int __build_id_parse(struct vm_area_struct vma, unsigned char build_id,
ad41251c AN	286	__u32 *size, bool may_fault)
bd7525da	287	{
de3ec364 AN	288	const Elf32_Ehdr *ehdr;
	289	struct freader r;
	290	char buf[MAX_FREADER_BUF_SZ];
bd7525da JO	291	int ret;
	292
	293	/* only works for page backed storage */
	294	if (!vma->vm_file)
	295	return -EINVAL;
	296
ad41251c	297	freader_init_from_file(&r, buf, sizeof(buf), vma->vm_file, may_fault);
de3ec364 AN	298
	299	/* fetch first 18 bytes of ELF header for checks */
	300	ehdr = freader_fetch(&r, 0, offsetofend(Elf32_Ehdr, e_type));
	301	if (!ehdr) {
	302	ret = r.err;
	303	goto out;
905415ff	304	}
bd7525da JO	305
bd7525da JO	306	ret = -EINVAL;
bd7525da JO	307
	308	/* compare magic x7f "ELF" */
	309	if (memcmp(ehdr->e_ident, ELFMAG, SELFMAG) != 0)
	310	goto out;
	311
	312	/* only support executable file and shared object file */
	313	if (ehdr->e_type != ET_EXEC && ehdr->e_type != ET_DYN)
	314	goto out;
	315
	316	if (ehdr->e_ident[EI_CLASS] == ELFCLASS32)
de3ec364	317	ret = get_build_id_32(&r, build_id, size);
bd7525da	318	else if (ehdr->e_ident[EI_CLASS] == ELFCLASS64)
de3ec364	319	ret = get_build_id_64(&r, build_id, size);
bd7525da	320	out:
de3ec364	321	freader_cleanup(&r);
bd7525da JO	322	return ret;
bd7525da JO	323	}
7eaf3cf3	324
ad41251c AN	325	/*
	326	* Parse build ID of ELF file mapped to vma
	327	* @vma: vma object
	328	* @build_id: buffer to store build id, at least BUILD_ID_SIZE long
	329	* @size: returns actual build id size in case of success
	330	*
	331	* Assumes no page fault can be taken, so if relevant portions of ELF file are
	332	* not already paged in, fetching of build ID fails.
	333	*
	334	* Return: 0 on success; negative error, otherwise
	335	*/
	336	int build_id_parse_nofault(struct vm_area_struct vma, unsigned char build_id, __u32 *size)
	337	{
	338	return __build_id_parse(vma, build_id, size, false /* !may_fault */);
	339	}
	340
45b8fc30 AN	341	/*
	342	* Parse build ID of ELF file mapped to VMA
	343	* @vma: vma object
	344	* @build_id: buffer to store build id, at least BUILD_ID_SIZE long
	345	* @size: returns actual build id size in case of success
	346	*
	347	* Assumes faultable context and can cause page faults to bring in file data
	348	* into page cache.
	349	*
	350	* Return: 0 on success; negative error, otherwise
	351	*/
	352	int build_id_parse(struct vm_area_struct vma, unsigned char build_id, __u32 *size)
	353	{
ad41251c	354	return __build_id_parse(vma, build_id, size, true /* may_fault */);
45b8fc30 AN	355	}
45b8fc30 AN	356
7eaf3cf3 SB	357	/**
7eaf3cf3 SB	358	* build_id_parse_buf - Get build ID from a buffer
70e79866	359	* @buf: ELF note section(s) to parse
7eaf3cf3 SB	360	* @buf_size: Size of @buf in bytes
	361	* @build_id: Build ID parsed from @buf, at least BUILD_ID_SIZE_MAX long
	362	*
	363	* Return: 0 on success, -EINVAL otherwise
	364	*/
	365	int build_id_parse_buf(const void buf, unsigned char build_id, u32 buf_size)
	366	{
de3ec364 AN	367	struct freader r;
	368	int err;
	369
	370	freader_init_from_mem(&r, buf, buf_size);
	371
	372	err = parse_build_id(&r, build_id, NULL, 0, buf_size);
	373
	374	freader_cleanup(&r);
	375	return err;
7eaf3cf3	376	}
83cc6fa0	377
443cbaf9	378	#if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID) \|\| IS_ENABLED(CONFIG_VMCORE_INFO)
83cc6fa0 SB	379	unsigned char vmlinux_build_id[BUILD_ID_SIZE_MAX] __ro_after_init;
	380
	381	/**
	382	* init_vmlinux_build_id - Compute and stash the running kernel's build ID
	383	*/
	384	void __init init_vmlinux_build_id(void)
	385	{
377d9095 AB	386	extern const void __start_notes;
377d9095 AB	387	extern const void __stop_notes;
83cc6fa0 SB	388	unsigned int size = &__stop_notes - &__start_notes;
	389
	390	build_id_parse_buf(&__start_notes, vmlinux_build_id, size);
	391	}
22f4e66d	392	#endif