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/fs.h>
9#include <linux/secretmem.h>
10
11#define BUILD_ID 3
12
13#define MAX_PHDR_CNT 256
14
15void freader_init_from_file(struct freader *r, void *buf, u32 buf_sz,
16 struct file *file, bool may_fault)
17{
18 memset(r, 0, sizeof(*r));
19 r->buf = buf;
20 r->buf_sz = buf_sz;
21 r->file = file;
22 r->may_fault = may_fault;
23}
24
25void freader_init_from_mem(struct freader *r, const char *data, u64 data_sz)
26{
27 memset(r, 0, sizeof(*r));
28 r->data = data;
29 r->data_sz = data_sz;
30}
31
32static void freader_put_folio(struct freader *r)
33{
34 if (!r->folio)
35 return;
36 kunmap_local(r->addr);
37 folio_put(folio: r->folio);
38 r->folio = NULL;
39}
40
41static int freader_get_folio(struct freader *r, loff_t file_off)
42{
43 /* check if we can just reuse current folio */
44 if (r->folio && file_off >= r->folio_off &&
45 file_off < r->folio_off + folio_size(folio: r->folio))
46 return 0;
47
48 freader_put_folio(r);
49
50 /* only use page cache lookup - fail if not already cached */
51 r->folio = filemap_get_folio(mapping: r->file->f_mapping, index: file_off >> PAGE_SHIFT);
52
53 if (IS_ERR(ptr: r->folio) || !folio_test_uptodate(folio: r->folio)) {
54 if (!IS_ERR(ptr: r->folio))
55 folio_put(folio: r->folio);
56 r->folio = NULL;
57 return -EFAULT;
58 }
59
60 r->folio_off = folio_pos(folio: r->folio);
61 r->addr = kmap_local_folio(folio: r->folio, offset: 0);
62
63 return 0;
64}
65
66const void *freader_fetch(struct freader *r, loff_t file_off, size_t sz)
67{
68 size_t folio_sz;
69
70 /* provided internal temporary buffer should be sized correctly */
71 if (WARN_ON(r->buf && sz > r->buf_sz)) {
72 r->err = -E2BIG;
73 return NULL;
74 }
75
76 if (unlikely(file_off + sz < file_off)) {
77 r->err = -EOVERFLOW;
78 return NULL;
79 }
80
81 /* working with memory buffer is much more straightforward */
82 if (!r->buf) {
83 if (file_off + sz > r->data_sz) {
84 r->err = -ERANGE;
85 return NULL;
86 }
87 return r->data + file_off;
88 }
89
90 /* reject secretmem folios created with memfd_secret() */
91 if (secretmem_mapping(mapping: r->file->f_mapping)) {
92 r->err = -EFAULT;
93 return NULL;
94 }
95
96 /* use __kernel_read() for sleepable context */
97 if (r->may_fault) {
98 ssize_t ret;
99
100 ret = __kernel_read(file: r->file, buf: r->buf, count: sz, pos: &file_off);
101 if (ret != sz) {
102 r->err = (ret < 0) ? ret : -EIO;
103 return NULL;
104 }
105 return r->buf;
106 }
107
108 /* fetch or reuse folio for given file offset */
109 r->err = freader_get_folio(r, file_off);
110 if (r->err)
111 return NULL;
112
113 /* if requested data is crossing folio boundaries, we have to copy
114 * everything into our local buffer to keep a simple linear memory
115 * access interface
116 */
117 folio_sz = folio_size(folio: r->folio);
118 if (file_off + sz > r->folio_off + folio_sz) {
119 u64 part_sz = r->folio_off + folio_sz - file_off, off;
120
121 memcpy(r->buf, r->addr + file_off - r->folio_off, part_sz);
122 off = part_sz;
123
124 while (off < sz) {
125 /* fetch next folio */
126 r->err = freader_get_folio(r, file_off: r->folio_off + folio_sz);
127 if (r->err)
128 return NULL;
129 folio_sz = folio_size(folio: r->folio);
130 part_sz = min_t(u64, sz - off, folio_sz);
131 memcpy(r->buf + off, r->addr, part_sz);
132 off += part_sz;
133 }
134
135 return r->buf;
136 }
137
138 /* if data fits in a single folio, just return direct pointer */
139 return r->addr + (file_off - r->folio_off);
140}
141
142void freader_cleanup(struct freader *r)
143{
144 if (!r->buf)
145 return; /* non-file-backed mode */
146
147 freader_put_folio(r);
148}
149
150/*
151 * Parse build id from the note segment. This logic can be shared between
152 * 32-bit and 64-bit system, because Elf32_Nhdr and Elf64_Nhdr are
153 * identical.
154 */
155static int parse_build_id(struct freader *r, unsigned char *build_id, __u32 *size,
156 loff_t note_off, Elf32_Word note_size)
157{
158 const char note_name[] = "GNU";
159 const size_t note_name_sz = sizeof(note_name);
160 u32 build_id_off, new_off, note_end, name_sz, desc_sz;
161 const Elf32_Nhdr *nhdr;
162 const char *data;
163
164 if (check_add_overflow(note_off, note_size, &note_end))
165 return -EINVAL;
166
167 while (note_end - note_off > sizeof(Elf32_Nhdr) + note_name_sz) {
168 nhdr = freader_fetch(r, file_off: note_off, sz: sizeof(Elf32_Nhdr) + note_name_sz);
169 if (!nhdr)
170 return r->err;
171
172 name_sz = READ_ONCE(nhdr->n_namesz);
173 desc_sz = READ_ONCE(nhdr->n_descsz);
174
175 new_off = note_off + sizeof(Elf32_Nhdr);
176 if (check_add_overflow(new_off, ALIGN(name_sz, 4), &new_off) ||
177 check_add_overflow(new_off, ALIGN(desc_sz, 4), &new_off) ||
178 new_off > note_end)
179 break;
180
181 if (nhdr->n_type == BUILD_ID &&
182 name_sz == note_name_sz &&
183 memcmp(p: nhdr + 1, q: note_name, size: note_name_sz) == 0 &&
184 desc_sz > 0 && desc_sz <= BUILD_ID_SIZE_MAX) {
185 build_id_off = note_off + sizeof(Elf32_Nhdr) + ALIGN(note_name_sz, 4);
186
187 /* freader_fetch() will invalidate nhdr pointer */
188 data = freader_fetch(r, file_off: build_id_off, sz: desc_sz);
189 if (!data)
190 return r->err;
191
192 memcpy(build_id, data, desc_sz);
193 memset(build_id + desc_sz, 0, BUILD_ID_SIZE_MAX - desc_sz);
194 if (size)
195 *size = desc_sz;
196 return 0;
197 }
198
199 note_off = new_off;
200 }
201
202 return -EINVAL;
203}
204
205/* Parse build ID from 32-bit ELF */
206static int get_build_id_32(struct freader *r, unsigned char *build_id, __u32 *size)
207{
208 const Elf32_Ehdr *ehdr;
209 const Elf32_Phdr *phdr;
210 __u32 phnum, phoff, i;
211
212 ehdr = freader_fetch(r, file_off: 0, sz: sizeof(Elf32_Ehdr));
213 if (!ehdr)
214 return r->err;
215
216 /* subsequent freader_fetch() calls invalidate pointers, so remember locally */
217 phnum = READ_ONCE(ehdr->e_phnum);
218 phoff = READ_ONCE(ehdr->e_phoff);
219
220 /* set upper bound on amount of segments (phdrs) we iterate */
221 if (phnum > MAX_PHDR_CNT)
222 phnum = MAX_PHDR_CNT;
223
224 /* check that phoff is not large enough to cause an overflow */
225 if (phoff + phnum * sizeof(Elf32_Phdr) < phoff)
226 return -EINVAL;
227
228 for (i = 0; i < phnum; ++i) {
229 phdr = freader_fetch(r, file_off: phoff + i * sizeof(Elf32_Phdr), sz: sizeof(Elf32_Phdr));
230 if (!phdr)
231 return r->err;
232
233 if (phdr->p_type == PT_NOTE &&
234 !parse_build_id(r, build_id, size, READ_ONCE(phdr->p_offset),
235 READ_ONCE(phdr->p_filesz)))
236 return 0;
237 }
238 return -EINVAL;
239}
240
241/* Parse build ID from 64-bit ELF */
242static int get_build_id_64(struct freader *r, unsigned char *build_id, __u32 *size)
243{
244 const Elf64_Ehdr *ehdr;
245 const Elf64_Phdr *phdr;
246 __u32 phnum, i;
247 __u64 phoff;
248
249 ehdr = freader_fetch(r, file_off: 0, sz: sizeof(Elf64_Ehdr));
250 if (!ehdr)
251 return r->err;
252
253 /* subsequent freader_fetch() calls invalidate pointers, so remember locally */
254 phnum = READ_ONCE(ehdr->e_phnum);
255 phoff = READ_ONCE(ehdr->e_phoff);
256
257 /* set upper bound on amount of segments (phdrs) we iterate */
258 if (phnum > MAX_PHDR_CNT)
259 phnum = MAX_PHDR_CNT;
260
261 /* check that phoff is not large enough to cause an overflow */
262 if (phoff + phnum * sizeof(Elf64_Phdr) < phoff)
263 return -EINVAL;
264
265 for (i = 0; i < phnum; ++i) {
266 phdr = freader_fetch(r, file_off: phoff + i * sizeof(Elf64_Phdr), sz: sizeof(Elf64_Phdr));
267 if (!phdr)
268 return r->err;
269
270 if (phdr->p_type == PT_NOTE &&
271 !parse_build_id(r, build_id, size, READ_ONCE(phdr->p_offset),
272 READ_ONCE(phdr->p_filesz)))
273 return 0;
274 }
275
276 return -EINVAL;
277}
278
279/* enough for Elf64_Ehdr, Elf64_Phdr, and all the smaller requests */
280#define MAX_FREADER_BUF_SZ 64
281
282static int __build_id_parse(struct file *file, unsigned char *build_id,
283 __u32 *size, bool may_fault)
284{
285 const Elf32_Ehdr *ehdr;
286 struct freader r;
287 char buf[MAX_FREADER_BUF_SZ];
288 int ret;
289
290 freader_init_from_file(r: &r, buf, buf_sz: sizeof(buf), file, may_fault);
291
292 /* fetch first 18 bytes of ELF header for checks */
293 ehdr = freader_fetch(r: &r, file_off: 0, offsetofend(Elf32_Ehdr, e_type));
294 if (!ehdr) {
295 ret = r.err;
296 goto out;
297 }
298
299 ret = -EINVAL;
300
301 /* compare magic x7f "ELF" */
302 if (memcmp(p: ehdr->e_ident, ELFMAG, SELFMAG) != 0)
303 goto out;
304
305 /* only support executable file and shared object file */
306 if (ehdr->e_type != ET_EXEC && ehdr->e_type != ET_DYN)
307 goto out;
308
309 if (ehdr->e_ident[EI_CLASS] == ELFCLASS32)
310 ret = get_build_id_32(r: &r, build_id, size);
311 else if (ehdr->e_ident[EI_CLASS] == ELFCLASS64)
312 ret = get_build_id_64(r: &r, build_id, size);
313out:
314 freader_cleanup(r: &r);
315 return ret;
316}
317
318/**
319 * build_id_parse_nofault() - Parse build ID of ELF file mapped to vma
320 * @vma: vma object
321 * @build_id: buffer to store build id, at least BUILD_ID_SIZE long
322 * @size: returns actual build id size in case of success
323 *
324 * Assumes no page fault can be taken, so if relevant portions of ELF file are
325 * not already paged in, fetching of build ID fails.
326 *
327 * Return: 0 on success; negative error, otherwise
328 */
329int build_id_parse_nofault(struct vm_area_struct *vma, unsigned char *build_id, __u32 *size)
330{
331 if (!vma->vm_file)
332 return -EINVAL;
333
334 return __build_id_parse(file: vma->vm_file, build_id, size, may_fault: false /* !may_fault */);
335}
336
337/**
338 * build_id_parse() - Parse build ID of ELF file mapped to VMA
339 * @vma: vma object
340 * @build_id: buffer to store build id, at least BUILD_ID_SIZE long
341 * @size: returns actual build id size in case of success
342 *
343 * Assumes faultable context and can cause page faults to bring in file data
344 * into page cache.
345 *
346 * Return: 0 on success; negative error, otherwise
347 */
348int build_id_parse(struct vm_area_struct *vma, unsigned char *build_id, __u32 *size)
349{
350 if (!vma->vm_file)
351 return -EINVAL;
352
353 return __build_id_parse(file: vma->vm_file, build_id, size, may_fault: true /* may_fault */);
354}
355
356/**
357 * build_id_parse_file() - Parse build ID of ELF file
358 * @file: file object
359 * @build_id: buffer to store build id, at least BUILD_ID_SIZE long
360 * @size: returns actual build id size in case of success
361 *
362 * Assumes faultable context and can cause page faults to bring in file data
363 * into page cache.
364 *
365 * Return: 0 on success; negative error, otherwise
366 */
367int build_id_parse_file(struct file *file, unsigned char *build_id, __u32 *size)
368{
369 return __build_id_parse(file, build_id, size, may_fault: true /* may_fault */);
370}
371
372/**
373 * build_id_parse_buf - Get build ID from a buffer
374 * @buf: ELF note section(s) to parse
375 * @buf_size: Size of @buf in bytes
376 * @build_id: Build ID parsed from @buf, at least BUILD_ID_SIZE_MAX long
377 *
378 * Return: 0 on success, -EINVAL otherwise
379 */
380int build_id_parse_buf(const void *buf, unsigned char *build_id, u32 buf_size)
381{
382 struct freader r;
383 int err;
384
385 freader_init_from_mem(r: &r, data: buf, data_sz: buf_size);
386
387 err = parse_build_id(r: &r, build_id, NULL, note_off: 0, note_size: buf_size);
388
389 freader_cleanup(r: &r);
390 return err;
391}
392
393#if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID) || IS_ENABLED(CONFIG_VMCORE_INFO)
394unsigned char vmlinux_build_id[BUILD_ID_SIZE_MAX] __ro_after_init;
395
396/**
397 * init_vmlinux_build_id - Compute and stash the running kernel's build ID
398 */
399void __init init_vmlinux_build_id(void)
400{
401 extern const void __start_notes;
402 extern const void __stop_notes;
403 unsigned int size = &__stop_notes - &__start_notes;
404
405 build_id_parse_buf(buf: &__start_notes, build_id: vmlinux_build_id, buf_size: size);
406}
407#endif
408

source code of linux/lib/buildid.c