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
  9#define BUILD_ID 3
 10
 11/*
 12 * Parse build id from the note segment. This logic can be shared between
 13 * 32-bit and 64-bit system, because Elf32_Nhdr and Elf64_Nhdr are
 14 * identical.
 15 */
 16static int parse_build_id_buf(unsigned char *build_id,
 17			      __u32 *size,
 18			      const void *note_start,
 19			      Elf32_Word note_size)
 20{
 21	Elf32_Word note_offs = 0, new_offs;
 22
 23	while (note_offs + sizeof(Elf32_Nhdr) < note_size) {
 24		Elf32_Nhdr *nhdr = (Elf32_Nhdr *)(note_start + note_offs);
 25
 26		if (nhdr->n_type == BUILD_ID &&
 27		    nhdr->n_namesz == sizeof("GNU") &&
 28		    !strcmp((char *)(nhdr + 1), "GNU") &&
 29		    nhdr->n_descsz > 0 &&
 30		    nhdr->n_descsz <= BUILD_ID_SIZE_MAX) {
 31			memcpy(build_id,
 32			       note_start + note_offs +
 33			       ALIGN(sizeof("GNU"), 4) + sizeof(Elf32_Nhdr),
 34			       nhdr->n_descsz);
 35			memset(build_id + nhdr->n_descsz, 0,
 36			       BUILD_ID_SIZE_MAX - nhdr->n_descsz);
 37			if (size)
 38				*size = nhdr->n_descsz;
 39			return 0;
 40		}
 41		new_offs = note_offs + sizeof(Elf32_Nhdr) +
 42			ALIGN(nhdr->n_namesz, 4) + ALIGN(nhdr->n_descsz, 4);
 43		if (new_offs <= note_offs)  /* overflow */
 44			break;
 45		note_offs = new_offs;
 46	}
 47
 48	return -EINVAL;
 49}
 50
 51static inline int parse_build_id(const void *page_addr,
 52				 unsigned char *build_id,
 53				 __u32 *size,
 54				 const void *note_start,
 55				 Elf32_Word note_size)
 56{
 57	/* check for overflow */
 58	if (note_start < page_addr || note_start + note_size < note_start)
 59		return -EINVAL;
 60
 61	/* only supports note that fits in the first page */
 62	if (note_start + note_size > page_addr + PAGE_SIZE)
 63		return -EINVAL;
 64
 65	return parse_build_id_buf(build_id, size, note_start, note_size);
 66}
 67
 68/* Parse build ID from 32-bit ELF */
 69static int get_build_id_32(const void *page_addr, unsigned char *build_id,
 70			   __u32 *size)
 71{
 72	Elf32_Ehdr *ehdr = (Elf32_Ehdr *)page_addr;
 73	Elf32_Phdr *phdr;
 74	int i;
 75
 76	/* only supports phdr that fits in one page */
 77	if (ehdr->e_phnum >
 78	    (PAGE_SIZE - sizeof(Elf32_Ehdr)) / sizeof(Elf32_Phdr))
 79		return -EINVAL;
 80
 81	phdr = (Elf32_Phdr *)(page_addr + sizeof(Elf32_Ehdr));
 82
 83	for (i = 0; i < ehdr->e_phnum; ++i) {
 84		if (phdr[i].p_type == PT_NOTE &&
 85		    !parse_build_id(page_addr, build_id, size,
 86				    page_addr + phdr[i].p_offset,
 87				    phdr[i].p_filesz))
 88			return 0;
 89	}
 90	return -EINVAL;
 91}
 92
 93/* Parse build ID from 64-bit ELF */
 94static int get_build_id_64(const void *page_addr, unsigned char *build_id,
 95			   __u32 *size)
 96{
 97	Elf64_Ehdr *ehdr = (Elf64_Ehdr *)page_addr;
 98	Elf64_Phdr *phdr;
 99	int i;
100
101	/* only supports phdr that fits in one page */
102	if (ehdr->e_phnum >
103	    (PAGE_SIZE - sizeof(Elf64_Ehdr)) / sizeof(Elf64_Phdr))
104		return -EINVAL;
105
106	phdr = (Elf64_Phdr *)(page_addr + sizeof(Elf64_Ehdr));
107
108	for (i = 0; i < ehdr->e_phnum; ++i) {
109		if (phdr[i].p_type == PT_NOTE &&
110		    !parse_build_id(page_addr, build_id, size,
111				    page_addr + phdr[i].p_offset,
112				    phdr[i].p_filesz))
113			return 0;
114	}
115	return -EINVAL;
116}
117
118/*
119 * Parse build ID of ELF file mapped to vma
120 * @vma:      vma object
121 * @build_id: buffer to store build id, at least BUILD_ID_SIZE long
122 * @size:     returns actual build id size in case of success
123 *
124 * Return: 0 on success, -EINVAL otherwise
125 */
126int build_id_parse(struct vm_area_struct *vma, unsigned char *build_id,
127		   __u32 *size)
128{
129	Elf32_Ehdr *ehdr;
130	struct page *page;
131	void *page_addr;
132	int ret;
133
134	/* only works for page backed storage  */
135	if (!vma->vm_file)
136		return -EINVAL;
137
138	page = find_get_page(vma->vm_file->f_mapping, 0);
139	if (!page)
140		return -EFAULT;	/* page not mapped */
141
142	ret = -EINVAL;
143	page_addr = kmap_atomic(page);
144	ehdr = (Elf32_Ehdr *)page_addr;
145
146	/* compare magic x7f "ELF" */
147	if (memcmp(ehdr->e_ident, ELFMAG, SELFMAG) != 0)
148		goto out;
149
150	/* only support executable file and shared object file */
151	if (ehdr->e_type != ET_EXEC && ehdr->e_type != ET_DYN)
152		goto out;
153
154	if (ehdr->e_ident[EI_CLASS] == ELFCLASS32)
155		ret = get_build_id_32(page_addr, build_id, size);
156	else if (ehdr->e_ident[EI_CLASS] == ELFCLASS64)
157		ret = get_build_id_64(page_addr, build_id, size);
158out:
159	kunmap_atomic(page_addr);
160	put_page(page);
161	return ret;
162}
163
164/**
165 * build_id_parse_buf - Get build ID from a buffer
166 * @buf:      ELF note section(s) to parse
167 * @buf_size: Size of @buf in bytes
168 * @build_id: Build ID parsed from @buf, at least BUILD_ID_SIZE_MAX long
169 *
170 * Return: 0 on success, -EINVAL otherwise
171 */
172int build_id_parse_buf(const void *buf, unsigned char *build_id, u32 buf_size)
173{
174	return parse_build_id_buf(build_id, NULL, buf, buf_size);
175}
176
177#if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID) || IS_ENABLED(CONFIG_CRASH_CORE)
178unsigned char vmlinux_build_id[BUILD_ID_SIZE_MAX] __ro_after_init;
179
180/**
181 * init_vmlinux_build_id - Compute and stash the running kernel's build ID
182 */
183void __init init_vmlinux_build_id(void)
184{
185	extern const void __start_notes __weak;
186	extern const void __stop_notes __weak;
187	unsigned int size = &__stop_notes - &__start_notes;
188
189	build_id_parse_buf(&__start_notes, vmlinux_build_id, size);
190}
191#endif