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bd7525da JO |
1 | // SPDX-License-Identifier: GPL-2.0 |
2 | ||
3 | #include <linux/buildid.h> | |
4 | #include <linux/elf.h> | |
5 | #include <linux/pagemap.h> | |
6 | ||
7 | #define BUILD_ID 3 | |
8 | /* | |
9 | * Parse build id from the note segment. This logic can be shared between | |
10 | * 32-bit and 64-bit system, because Elf32_Nhdr and Elf64_Nhdr are | |
11 | * identical. | |
12 | */ | |
13 | static inline int parse_build_id(void *page_addr, | |
14 | unsigned char *build_id, | |
921f88fc | 15 | __u32 *size, |
bd7525da JO |
16 | void *note_start, |
17 | Elf32_Word note_size) | |
18 | { | |
19 | Elf32_Word note_offs = 0, new_offs; | |
20 | ||
21 | /* check for overflow */ | |
22 | if (note_start < page_addr || note_start + note_size < note_start) | |
23 | return -EINVAL; | |
24 | ||
25 | /* only supports note that fits in the first page */ | |
26 | if (note_start + note_size > page_addr + PAGE_SIZE) | |
27 | return -EINVAL; | |
28 | ||
29 | while (note_offs + sizeof(Elf32_Nhdr) < note_size) { | |
30 | Elf32_Nhdr *nhdr = (Elf32_Nhdr *)(note_start + note_offs); | |
31 | ||
32 | if (nhdr->n_type == BUILD_ID && | |
33 | nhdr->n_namesz == sizeof("GNU") && | |
34 | nhdr->n_descsz > 0 && | |
35 | nhdr->n_descsz <= BUILD_ID_SIZE_MAX) { | |
36 | memcpy(build_id, | |
37 | note_start + note_offs + | |
38 | ALIGN(sizeof("GNU"), 4) + sizeof(Elf32_Nhdr), | |
39 | nhdr->n_descsz); | |
40 | memset(build_id + nhdr->n_descsz, 0, | |
41 | BUILD_ID_SIZE_MAX - nhdr->n_descsz); | |
921f88fc JO |
42 | if (size) |
43 | *size = nhdr->n_descsz; | |
bd7525da JO |
44 | return 0; |
45 | } | |
46 | new_offs = note_offs + sizeof(Elf32_Nhdr) + | |
47 | ALIGN(nhdr->n_namesz, 4) + ALIGN(nhdr->n_descsz, 4); | |
48 | if (new_offs <= note_offs) /* overflow */ | |
49 | break; | |
50 | note_offs = new_offs; | |
51 | } | |
52 | return -EINVAL; | |
53 | } | |
54 | ||
55 | /* Parse build ID from 32-bit ELF */ | |
921f88fc JO |
56 | static int get_build_id_32(void *page_addr, unsigned char *build_id, |
57 | __u32 *size) | |
bd7525da JO |
58 | { |
59 | Elf32_Ehdr *ehdr = (Elf32_Ehdr *)page_addr; | |
60 | Elf32_Phdr *phdr; | |
61 | int i; | |
62 | ||
63 | /* only supports phdr that fits in one page */ | |
64 | if (ehdr->e_phnum > | |
65 | (PAGE_SIZE - sizeof(Elf32_Ehdr)) / sizeof(Elf32_Phdr)) | |
66 | return -EINVAL; | |
67 | ||
68 | phdr = (Elf32_Phdr *)(page_addr + sizeof(Elf32_Ehdr)); | |
69 | ||
70 | for (i = 0; i < ehdr->e_phnum; ++i) { | |
71 | if (phdr[i].p_type == PT_NOTE && | |
921f88fc | 72 | !parse_build_id(page_addr, build_id, size, |
bd7525da JO |
73 | page_addr + phdr[i].p_offset, |
74 | phdr[i].p_filesz)) | |
75 | return 0; | |
76 | } | |
77 | return -EINVAL; | |
78 | } | |
79 | ||
80 | /* Parse build ID from 64-bit ELF */ | |
921f88fc JO |
81 | static int get_build_id_64(void *page_addr, unsigned char *build_id, |
82 | __u32 *size) | |
bd7525da JO |
83 | { |
84 | Elf64_Ehdr *ehdr = (Elf64_Ehdr *)page_addr; | |
85 | Elf64_Phdr *phdr; | |
86 | int i; | |
87 | ||
88 | /* only supports phdr that fits in one page */ | |
89 | if (ehdr->e_phnum > | |
90 | (PAGE_SIZE - sizeof(Elf64_Ehdr)) / sizeof(Elf64_Phdr)) | |
91 | return -EINVAL; | |
92 | ||
93 | phdr = (Elf64_Phdr *)(page_addr + sizeof(Elf64_Ehdr)); | |
94 | ||
95 | for (i = 0; i < ehdr->e_phnum; ++i) { | |
96 | if (phdr[i].p_type == PT_NOTE && | |
921f88fc | 97 | !parse_build_id(page_addr, build_id, size, |
bd7525da JO |
98 | page_addr + phdr[i].p_offset, |
99 | phdr[i].p_filesz)) | |
100 | return 0; | |
101 | } | |
102 | return -EINVAL; | |
103 | } | |
104 | ||
921f88fc JO |
105 | /* |
106 | * Parse build ID of ELF file mapped to vma | |
107 | * @vma: vma object | |
108 | * @build_id: buffer to store build id, at least BUILD_ID_SIZE long | |
109 | * @size: returns actual build id size in case of success | |
110 | * | |
111 | * Returns 0 on success, otherwise error (< 0). | |
112 | */ | |
113 | int build_id_parse(struct vm_area_struct *vma, unsigned char *build_id, | |
114 | __u32 *size) | |
bd7525da JO |
115 | { |
116 | Elf32_Ehdr *ehdr; | |
117 | struct page *page; | |
118 | void *page_addr; | |
119 | int ret; | |
120 | ||
121 | /* only works for page backed storage */ | |
122 | if (!vma->vm_file) | |
123 | return -EINVAL; | |
124 | ||
125 | page = find_get_page(vma->vm_file->f_mapping, 0); | |
126 | if (!page) | |
127 | return -EFAULT; /* page not mapped */ | |
128 | ||
129 | ret = -EINVAL; | |
130 | page_addr = kmap_atomic(page); | |
131 | ehdr = (Elf32_Ehdr *)page_addr; | |
132 | ||
133 | /* compare magic x7f "ELF" */ | |
134 | if (memcmp(ehdr->e_ident, ELFMAG, SELFMAG) != 0) | |
135 | goto out; | |
136 | ||
137 | /* only support executable file and shared object file */ | |
138 | if (ehdr->e_type != ET_EXEC && ehdr->e_type != ET_DYN) | |
139 | goto out; | |
140 | ||
141 | if (ehdr->e_ident[EI_CLASS] == ELFCLASS32) | |
921f88fc | 142 | ret = get_build_id_32(page_addr, build_id, size); |
bd7525da | 143 | else if (ehdr->e_ident[EI_CLASS] == ELFCLASS64) |
921f88fc | 144 | ret = get_build_id_64(page_addr, build_id, size); |
bd7525da JO |
145 | out: |
146 | kunmap_atomic(page_addr); | |
147 | put_page(page); | |
148 | return ret; | |
149 | } |