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 /*
13 * Parse build id from the note segment. This logic can be shared between
14 * 32-bit and 64-bit system, because Elf32_Nhdr and Elf64_Nhdr are
15 * identical.
16 */
parse_build_id_buf(unsigned char * build_id,__u32 * size,const void * note_start,Elf32_Word note_size)17 static int parse_build_id_buf(unsigned char *build_id,
18 __u32 *size,
19 const void *note_start,
20 Elf32_Word note_size)
21 {
22 const char note_name[] = "GNU";
23 const size_t note_name_sz = sizeof(note_name);
24 u64 note_off = 0, new_off, name_sz, desc_sz;
25 const char *data;
26
27 while (note_off + sizeof(Elf32_Nhdr) < note_size &&
28 note_off + sizeof(Elf32_Nhdr) > note_off /* overflow */) {
29 Elf32_Nhdr *nhdr = (Elf32_Nhdr *)(note_start + note_off);
30
31 name_sz = READ_ONCE(nhdr->n_namesz);
32 desc_sz = READ_ONCE(nhdr->n_descsz);
33
34 new_off = note_off + sizeof(Elf32_Nhdr);
35 if (check_add_overflow(new_off, ALIGN(name_sz, 4), &new_off) ||
36 check_add_overflow(new_off, ALIGN(desc_sz, 4), &new_off) ||
37 new_off > note_size)
38 break;
39
40 if (nhdr->n_type == BUILD_ID &&
41 name_sz == note_name_sz &&
42 memcmp(nhdr + 1, note_name, note_name_sz) == 0 &&
43 desc_sz > 0 && desc_sz <= BUILD_ID_SIZE_MAX) {
44 data = note_start + note_off + sizeof(Elf32_Nhdr) + ALIGN(note_name_sz, 4);
45 memcpy(build_id, data, desc_sz);
46 memset(build_id + desc_sz, 0, BUILD_ID_SIZE_MAX - desc_sz);
47 if (size)
48 *size = desc_sz;
49 return 0;
50 }
51
52 note_off = new_off;
53 }
54
55 return -EINVAL;
56 }
57
parse_build_id(const void * page_addr,unsigned char * build_id,__u32 * size,const void * note_start,Elf32_Word note_size)58 static inline int parse_build_id(const void *page_addr,
59 unsigned char *build_id,
60 __u32 *size,
61 const void *note_start,
62 Elf32_Word note_size)
63 {
64 /* check for overflow */
65 if (note_start < page_addr || note_start + note_size < note_start)
66 return -EINVAL;
67
68 /* only supports note that fits in the first page */
69 if (note_start + note_size > page_addr + PAGE_SIZE)
70 return -EINVAL;
71
72 return parse_build_id_buf(build_id, size, note_start, note_size);
73 }
74
75 /* Parse build ID from 32-bit ELF */
get_build_id_32(const void * page_addr,unsigned char * build_id,__u32 * size)76 static int get_build_id_32(const void *page_addr, unsigned char *build_id,
77 __u32 *size)
78 {
79 Elf32_Ehdr *ehdr = (Elf32_Ehdr *)page_addr;
80 Elf32_Phdr *phdr;
81 __u32 i, phnum;
82
83 /*
84 * FIXME
85 * Neither ELF spec nor ELF loader require that program headers
86 * start immediately after ELF header.
87 */
88 if (ehdr->e_phoff != sizeof(Elf32_Ehdr))
89 return -EINVAL;
90
91 phnum = READ_ONCE(ehdr->e_phnum);
92 /* only supports phdr that fits in one page */
93 if (phnum > (PAGE_SIZE - sizeof(Elf32_Ehdr)) / sizeof(Elf32_Phdr))
94 return -EINVAL;
95
96 phdr = (Elf32_Phdr *)(page_addr + sizeof(Elf32_Ehdr));
97
98 for (i = 0; i < phnum; ++i) {
99 if (phdr[i].p_type == PT_NOTE &&
100 !parse_build_id(page_addr, build_id, size,
101 page_addr + READ_ONCE(phdr[i].p_offset),
102 READ_ONCE(phdr[i].p_filesz)))
103 return 0;
104 }
105 return -EINVAL;
106 }
107
108 /* Parse build ID from 64-bit ELF */
get_build_id_64(const void * page_addr,unsigned char * build_id,__u32 * size)109 static int get_build_id_64(const void *page_addr, unsigned char *build_id,
110 __u32 *size)
111 {
112 Elf64_Ehdr *ehdr = (Elf64_Ehdr *)page_addr;
113 Elf64_Phdr *phdr;
114 __u32 i, phnum;
115
116 /*
117 * FIXME
118 * Neither ELF spec nor ELF loader require that program headers
119 * start immediately after ELF header.
120 */
121 if (ehdr->e_phoff != sizeof(Elf64_Ehdr))
122 return -EINVAL;
123
124 phnum = READ_ONCE(ehdr->e_phnum);
125 /* only supports phdr that fits in one page */
126 if (phnum > (PAGE_SIZE - sizeof(Elf64_Ehdr)) / sizeof(Elf64_Phdr))
127 return -EINVAL;
128
129 phdr = (Elf64_Phdr *)(page_addr + sizeof(Elf64_Ehdr));
130
131 for (i = 0; i < phnum; ++i) {
132 if (phdr[i].p_type == PT_NOTE &&
133 !parse_build_id(page_addr, build_id, size,
134 page_addr + READ_ONCE(phdr[i].p_offset),
135 READ_ONCE(phdr[i].p_filesz)))
136 return 0;
137 }
138 return -EINVAL;
139 }
140
141 /*
142 * Parse build ID of ELF file mapped to vma
143 * @vma: vma object
144 * @build_id: buffer to store build id, at least BUILD_ID_SIZE long
145 * @size: returns actual build id size in case of success
146 *
147 * Return: 0 on success, -EINVAL otherwise
148 */
build_id_parse(struct vm_area_struct * vma,unsigned char * build_id,__u32 * size)149 int build_id_parse(struct vm_area_struct *vma, unsigned char *build_id,
150 __u32 *size)
151 {
152 Elf32_Ehdr *ehdr;
153 struct page *page;
154 void *page_addr;
155 int ret;
156
157 /* only works for page backed storage */
158 if (!vma->vm_file)
159 return -EINVAL;
160
161 /* reject secretmem folios created with memfd_secret() */
162 if (vma_is_secretmem(vma))
163 return -EFAULT;
164
165 page = find_get_page(vma->vm_file->f_mapping, 0);
166 if (!page)
167 return -EFAULT; /* page not mapped */
168 if (!PageUptodate(page)) {
169 put_page(page);
170 return -EFAULT;
171 }
172
173 ret = -EINVAL;
174 page_addr = kmap_atomic(page);
175 ehdr = (Elf32_Ehdr *)page_addr;
176
177 /* compare magic x7f "ELF" */
178 if (memcmp(ehdr->e_ident, ELFMAG, SELFMAG) != 0)
179 goto out;
180
181 /* only support executable file and shared object file */
182 if (ehdr->e_type != ET_EXEC && ehdr->e_type != ET_DYN)
183 goto out;
184
185 if (ehdr->e_ident[EI_CLASS] == ELFCLASS32)
186 ret = get_build_id_32(page_addr, build_id, size);
187 else if (ehdr->e_ident[EI_CLASS] == ELFCLASS64)
188 ret = get_build_id_64(page_addr, build_id, size);
189 out:
190 kunmap_atomic(page_addr);
191 put_page(page);
192 return ret;
193 }
194
195 /**
196 * build_id_parse_buf - Get build ID from a buffer
197 * @buf: ELF note section(s) to parse
198 * @buf_size: Size of @buf in bytes
199 * @build_id: Build ID parsed from @buf, at least BUILD_ID_SIZE_MAX long
200 *
201 * Return: 0 on success, -EINVAL otherwise
202 */
build_id_parse_buf(const void * buf,unsigned char * build_id,u32 buf_size)203 int build_id_parse_buf(const void *buf, unsigned char *build_id, u32 buf_size)
204 {
205 return parse_build_id_buf(build_id, NULL, buf, buf_size);
206 }
207
208 #if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID) || IS_ENABLED(CONFIG_CRASH_CORE)
209 unsigned char vmlinux_build_id[BUILD_ID_SIZE_MAX] __ro_after_init;
210
211 /**
212 * init_vmlinux_build_id - Compute and stash the running kernel's build ID
213 */
init_vmlinux_build_id(void)214 void __init init_vmlinux_build_id(void)
215 {
216 extern const void __start_notes __weak;
217 extern const void __stop_notes __weak;
218 unsigned int size = &__stop_notes - &__start_notes;
219
220 build_id_parse_buf(&__start_notes, vmlinux_build_id, size);
221 }
222 #endif
223