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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, | |
15 | void *note_start, | |
16 | Elf32_Word note_size) | |
17 | { | |
18 | Elf32_Word note_offs = 0, new_offs; | |
19 | ||
20 | /* check for overflow */ | |
21 | if (note_start < page_addr || note_start + note_size < note_start) | |
22 | return -EINVAL; | |
23 | ||
24 | /* only supports note that fits in the first page */ | |
25 | if (note_start + note_size > page_addr + PAGE_SIZE) | |
26 | return -EINVAL; | |
27 | ||
28 | while (note_offs + sizeof(Elf32_Nhdr) < note_size) { | |
29 | Elf32_Nhdr *nhdr = (Elf32_Nhdr *)(note_start + note_offs); | |
30 | ||
31 | if (nhdr->n_type == BUILD_ID && | |
32 | nhdr->n_namesz == sizeof("GNU") && | |
33 | nhdr->n_descsz > 0 && | |
34 | nhdr->n_descsz <= BUILD_ID_SIZE_MAX) { | |
35 | memcpy(build_id, | |
36 | note_start + note_offs + | |
37 | ALIGN(sizeof("GNU"), 4) + sizeof(Elf32_Nhdr), | |
38 | nhdr->n_descsz); | |
39 | memset(build_id + nhdr->n_descsz, 0, | |
40 | BUILD_ID_SIZE_MAX - nhdr->n_descsz); | |
41 | return 0; | |
42 | } | |
43 | new_offs = note_offs + sizeof(Elf32_Nhdr) + | |
44 | ALIGN(nhdr->n_namesz, 4) + ALIGN(nhdr->n_descsz, 4); | |
45 | if (new_offs <= note_offs) /* overflow */ | |
46 | break; | |
47 | note_offs = new_offs; | |
48 | } | |
49 | return -EINVAL; | |
50 | } | |
51 | ||
52 | /* Parse build ID from 32-bit ELF */ | |
53 | static int get_build_id_32(void *page_addr, unsigned char *build_id) | |
54 | { | |
55 | Elf32_Ehdr *ehdr = (Elf32_Ehdr *)page_addr; | |
56 | Elf32_Phdr *phdr; | |
57 | int i; | |
58 | ||
59 | /* only supports phdr that fits in one page */ | |
60 | if (ehdr->e_phnum > | |
61 | (PAGE_SIZE - sizeof(Elf32_Ehdr)) / sizeof(Elf32_Phdr)) | |
62 | return -EINVAL; | |
63 | ||
64 | phdr = (Elf32_Phdr *)(page_addr + sizeof(Elf32_Ehdr)); | |
65 | ||
66 | for (i = 0; i < ehdr->e_phnum; ++i) { | |
67 | if (phdr[i].p_type == PT_NOTE && | |
68 | !parse_build_id(page_addr, build_id, | |
69 | page_addr + phdr[i].p_offset, | |
70 | phdr[i].p_filesz)) | |
71 | return 0; | |
72 | } | |
73 | return -EINVAL; | |
74 | } | |
75 | ||
76 | /* Parse build ID from 64-bit ELF */ | |
77 | static int get_build_id_64(void *page_addr, unsigned char *build_id) | |
78 | { | |
79 | Elf64_Ehdr *ehdr = (Elf64_Ehdr *)page_addr; | |
80 | Elf64_Phdr *phdr; | |
81 | int i; | |
82 | ||
83 | /* only supports phdr that fits in one page */ | |
84 | if (ehdr->e_phnum > | |
85 | (PAGE_SIZE - sizeof(Elf64_Ehdr)) / sizeof(Elf64_Phdr)) | |
86 | return -EINVAL; | |
87 | ||
88 | phdr = (Elf64_Phdr *)(page_addr + sizeof(Elf64_Ehdr)); | |
89 | ||
90 | for (i = 0; i < ehdr->e_phnum; ++i) { | |
91 | if (phdr[i].p_type == PT_NOTE && | |
92 | !parse_build_id(page_addr, build_id, | |
93 | page_addr + phdr[i].p_offset, | |
94 | phdr[i].p_filesz)) | |
95 | return 0; | |
96 | } | |
97 | return -EINVAL; | |
98 | } | |
99 | ||
100 | /* Parse build ID of ELF file mapped to vma */ | |
101 | int build_id_parse(struct vm_area_struct *vma, unsigned char *build_id) | |
102 | { | |
103 | Elf32_Ehdr *ehdr; | |
104 | struct page *page; | |
105 | void *page_addr; | |
106 | int ret; | |
107 | ||
108 | /* only works for page backed storage */ | |
109 | if (!vma->vm_file) | |
110 | return -EINVAL; | |
111 | ||
112 | page = find_get_page(vma->vm_file->f_mapping, 0); | |
113 | if (!page) | |
114 | return -EFAULT; /* page not mapped */ | |
115 | ||
116 | ret = -EINVAL; | |
117 | page_addr = kmap_atomic(page); | |
118 | ehdr = (Elf32_Ehdr *)page_addr; | |
119 | ||
120 | /* compare magic x7f "ELF" */ | |
121 | if (memcmp(ehdr->e_ident, ELFMAG, SELFMAG) != 0) | |
122 | goto out; | |
123 | ||
124 | /* only support executable file and shared object file */ | |
125 | if (ehdr->e_type != ET_EXEC && ehdr->e_type != ET_DYN) | |
126 | goto out; | |
127 | ||
128 | if (ehdr->e_ident[EI_CLASS] == ELFCLASS32) | |
129 | ret = get_build_id_32(page_addr, build_id); | |
130 | else if (ehdr->e_ident[EI_CLASS] == ELFCLASS64) | |
131 | ret = get_build_id_64(page_addr, build_id); | |
132 | out: | |
133 | kunmap_atomic(page_addr); | |
134 | put_page(page); | |
135 | return ret; | |
136 | } |