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