1/* Support for reading /etc/ld.so.cache files written by Linux ldconfig.
2 Copyright (C) 1996-2020 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <https://www.gnu.org/licenses/>. */
18
19#include <assert.h>
20#include <unistd.h>
21#include <ldsodefs.h>
22#include <sys/mman.h>
23#include <dl-cache.h>
24#include <dl-procinfo.h>
25#include <stdint.h>
26#include <_itoa.h>
27#include <dl-hwcaps.h>
28
29#ifndef _DL_PLATFORMS_COUNT
30# define _DL_PLATFORMS_COUNT 0
31#endif
32
33/* This is the starting address and the size of the mmap()ed file. */
34static struct cache_file *cache;
35static struct cache_file_new *cache_new;
36static size_t cachesize;
37
38/* 1 if cache_data + PTR points into the cache. */
39#define _dl_cache_verify_ptr(ptr) (ptr < cache_data_size)
40
41#define SEARCH_CACHE(cache) \
42/* We use binary search since the table is sorted in the cache file. \
43 The first matching entry in the table is returned. \
44 It is important to use the same algorithm as used while generating \
45 the cache file. */ \
46do \
47 { \
48 left = 0; \
49 right = cache->nlibs - 1; \
50 \
51 while (left <= right) \
52 { \
53 __typeof__ (cache->libs[0].key) key; \
54 \
55 middle = (left + right) / 2; \
56 \
57 key = cache->libs[middle].key; \
58 \
59 /* Make sure string table indices are not bogus before using \
60 them. */ \
61 if (! _dl_cache_verify_ptr (key)) \
62 { \
63 cmpres = 1; \
64 break; \
65 } \
66 \
67 /* Actually compare the entry with the key. */ \
68 cmpres = _dl_cache_libcmp (name, cache_data + key); \
69 if (__glibc_unlikely (cmpres == 0)) \
70 { \
71 /* Found it. LEFT now marks the last entry for which we \
72 know the name is correct. */ \
73 left = middle; \
74 \
75 /* There might be entries with this name before the one we \
76 found. So we have to find the beginning. */ \
77 while (middle > 0) \
78 { \
79 __typeof__ (cache->libs[0].key) key; \
80 \
81 key = cache->libs[middle - 1].key; \
82 /* Make sure string table indices are not bogus before \
83 using them. */ \
84 if (! _dl_cache_verify_ptr (key) \
85 /* Actually compare the entry. */ \
86 || _dl_cache_libcmp (name, cache_data + key) != 0) \
87 break; \
88 --middle; \
89 } \
90 \
91 do \
92 { \
93 int flags; \
94 __typeof__ (cache->libs[0]) *lib = &cache->libs[middle]; \
95 \
96 /* Only perform the name test if necessary. */ \
97 if (middle > left \
98 /* We haven't seen this string so far. Test whether the \
99 index is ok and whether the name matches. Otherwise \
100 we are done. */ \
101 && (! _dl_cache_verify_ptr (lib->key) \
102 || (_dl_cache_libcmp (name, cache_data + lib->key) \
103 != 0))) \
104 break; \
105 \
106 flags = lib->flags; \
107 if (_dl_cache_check_flags (flags) \
108 && _dl_cache_verify_ptr (lib->value)) \
109 { \
110 if (best == NULL || flags == GLRO(dl_correct_cache_id)) \
111 { \
112 HWCAP_CHECK; \
113 best = cache_data + lib->value; \
114 \
115 if (flags == GLRO(dl_correct_cache_id)) \
116 /* We've found an exact match for the shared \
117 object and no general `ELF' release. Stop \
118 searching. */ \
119 break; \
120 } \
121 } \
122 } \
123 while (++middle <= right); \
124 break; \
125 } \
126 \
127 if (cmpres < 0) \
128 left = middle + 1; \
129 else \
130 right = middle - 1; \
131 } \
132 } \
133while (0)
134
135
136int
137_dl_cache_libcmp (const char *p1, const char *p2)
138{
139 while (*p1 != '\0')
140 {
141 if (*p1 >= '0' && *p1 <= '9')
142 {
143 if (*p2 >= '0' && *p2 <= '9')
144 {
145 /* Must compare this numerically. */
146 int val1;
147 int val2;
148
149 val1 = *p1++ - '0';
150 val2 = *p2++ - '0';
151 while (*p1 >= '0' && *p1 <= '9')
152 val1 = val1 * 10 + *p1++ - '0';
153 while (*p2 >= '0' && *p2 <= '9')
154 val2 = val2 * 10 + *p2++ - '0';
155 if (val1 != val2)
156 return val1 - val2;
157 }
158 else
159 return 1;
160 }
161 else if (*p2 >= '0' && *p2 <= '9')
162 return -1;
163 else if (*p1 != *p2)
164 return *p1 - *p2;
165 else
166 {
167 ++p1;
168 ++p2;
169 }
170 }
171 return *p1 - *p2;
172}
173
174
175/* Look up NAME in ld.so.cache and return the file name stored there, or null
176 if none is found. The cache is loaded if it was not already. If loading
177 the cache previously failed there will be no more attempts to load it.
178 The caller is responsible for freeing the returned string. The ld.so.cache
179 may be unmapped at any time by a completing recursive dlopen and
180 this function must take care that it does not return references to
181 any data in the mapping. */
182char *
183_dl_load_cache_lookup (const char *name)
184{
185 int left, right, middle;
186 int cmpres;
187 const char *cache_data;
188 uint32_t cache_data_size;
189 const char *best;
190
191 /* Print a message if the loading of libs is traced. */
192 if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_LIBS))
193 _dl_debug_printf (" search cache=%s\n", LD_SO_CACHE);
194
195 if (cache == NULL)
196 {
197 /* Read the contents of the file. */
198 void *file = _dl_sysdep_read_whole_file (LD_SO_CACHE, &cachesize,
199 PROT_READ);
200
201 /* We can handle three different cache file formats here:
202 - only the new format
203 - the old libc5/glibc2.0/2.1 format
204 - the old format with the new format in it
205 The following checks if the cache contains any of these formats. */
206 if (file != MAP_FAILED && cachesize > sizeof *cache_new
207 && memcmp (file, CACHEMAGIC_VERSION_NEW,
208 sizeof CACHEMAGIC_VERSION_NEW - 1) == 0
209 /* Check for corruption, avoiding overflow. */
210 && ((cachesize - sizeof *cache_new) / sizeof (struct file_entry_new)
211 >= ((struct cache_file_new *) file)->nlibs))
212 {
213 cache_new = file;
214 cache = file;
215 }
216 else if (file != MAP_FAILED && cachesize > sizeof *cache
217 && memcmp (file, CACHEMAGIC, sizeof CACHEMAGIC - 1) == 0
218 /* Check for corruption, avoiding overflow. */
219 && ((cachesize - sizeof *cache) / sizeof (struct file_entry)
220 >= ((struct cache_file *) file)->nlibs))
221 {
222 size_t offset;
223 /* Looks ok. */
224 cache = file;
225
226 /* Check for new version. */
227 offset = ALIGN_CACHE (sizeof (struct cache_file)
228 + cache->nlibs * sizeof (struct file_entry));
229
230 cache_new = (struct cache_file_new *) ((void *) cache + offset);
231 if (cachesize < (offset + sizeof (struct cache_file_new))
232 || memcmp (cache_new->magic, CACHEMAGIC_VERSION_NEW,
233 sizeof CACHEMAGIC_VERSION_NEW - 1) != 0)
234 cache_new = (void *) -1;
235 }
236 else
237 {
238 if (file != MAP_FAILED)
239 __munmap (file, cachesize);
240 cache = (void *) -1;
241 }
242
243 assert (cache != NULL);
244 }
245
246 if (cache == (void *) -1)
247 /* Previously looked for the cache file and didn't find it. */
248 return NULL;
249
250 best = NULL;
251
252 if (cache_new != (void *) -1)
253 {
254 uint64_t platform;
255
256 /* This is where the strings start. */
257 cache_data = (const char *) cache_new;
258
259 /* Now we can compute how large the string table is. */
260 cache_data_size = (const char *) cache + cachesize - cache_data;
261
262 platform = _dl_string_platform (GLRO(dl_platform));
263 if (platform != (uint64_t) -1)
264 platform = 1ULL << platform;
265
266 uint64_t hwcap_mask = GET_HWCAP_MASK();
267
268#define _DL_HWCAP_TLS_MASK (1LL << 63)
269 uint64_t hwcap_exclude = ~((GLRO(dl_hwcap) & hwcap_mask)
270 | _DL_HWCAP_PLATFORM | _DL_HWCAP_TLS_MASK);
271
272 /* Only accept hwcap if it's for the right platform. */
273#define HWCAP_CHECK \
274 if (lib->hwcap & hwcap_exclude) \
275 continue; \
276 if (GLRO(dl_osversion) && lib->osversion > GLRO(dl_osversion)) \
277 continue; \
278 if (_DL_PLATFORMS_COUNT \
279 && (lib->hwcap & _DL_HWCAP_PLATFORM) != 0 \
280 && (lib->hwcap & _DL_HWCAP_PLATFORM) != platform) \
281 continue
282 SEARCH_CACHE (cache_new);
283 }
284 else
285 {
286 /* This is where the strings start. */
287 cache_data = (const char *) &cache->libs[cache->nlibs];
288
289 /* Now we can compute how large the string table is. */
290 cache_data_size = (const char *) cache + cachesize - cache_data;
291
292#undef HWCAP_CHECK
293#define HWCAP_CHECK do {} while (0)
294 SEARCH_CACHE (cache);
295 }
296
297 /* Print our result if wanted. */
298 if (__builtin_expect (GLRO(dl_debug_mask) & DL_DEBUG_LIBS, 0)
299 && best != NULL)
300 _dl_debug_printf (" trying file=%s\n", best);
301
302 if (best == NULL)
303 return NULL;
304
305 /* The double copy is *required* since malloc may be interposed
306 and call dlopen itself whose completion would unmap the data
307 we are accessing. Therefore we must make the copy of the
308 mapping data without using malloc. */
309 char *temp;
310 temp = alloca (strlen (best) + 1);
311 strcpy (temp, best);
312 return __strdup (temp);
313}
314
315#ifndef MAP_COPY
316/* If the system does not support MAP_COPY we cannot leave the file open
317 all the time since this would create problems when the file is replaced.
318 Therefore we provide this function to close the file and open it again
319 once needed. */
320void
321_dl_unload_cache (void)
322{
323 if (cache != NULL && cache != (struct cache_file *) -1)
324 {
325 __munmap (cache, cachesize);
326 cache = NULL;
327 }
328}
329#endif
330