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  */
parse_build_id_buf(unsigned char * build_id,__u32 * size,const void * note_start,Elf32_Word note_size)16 static 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 
parse_build_id(const void * page_addr,unsigned char * build_id,__u32 * size,const void * note_start,Elf32_Word note_size)51 static 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 */
get_build_id_32(const void * page_addr,unsigned char * build_id,__u32 * size)69 static 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 */
get_build_id_64(const void * page_addr,unsigned char * build_id,__u32 * size)94 static 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  */
build_id_parse(struct vm_area_struct * vma,unsigned char * build_id,__u32 * size)126 int 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);
158 out:
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  */
build_id_parse_buf(const void * buf,unsigned char * build_id,u32 buf_size)172 int 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)
178 unsigned 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  */
init_vmlinux_build_id(void)183 void __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
192