1 /*-
2 * SPDX-License-Identifier: BSD-2-Clause
3 *
4 * Copyright (c) 2006, David Xu <davidxu@freebsd.org>
5 * All rights reserved.
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 * 1. Redistributions of source code must retain the above copyright
11 * notice unmodified, this list of conditions, and the following
12 * disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 * notice, this list of conditions and the following disclaimer in the
15 * documentation and/or other materials provided with the distribution.
16 *
17 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
18 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
19 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
20 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
21 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
22 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
23 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
24 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
25 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
26 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27 */
28
29 /*
30 * A lockless rwlock for rtld.
31 */
32 #include <sys/mman.h>
33 #include <sys/syscall.h>
34 #include <link.h>
35 #include <stdlib.h>
36 #include <string.h>
37
38 #include "libc_private.h"
39 #include "rtld_lock.h"
40 #include "thr_private.h"
41
42 extern int __libsys_errno;
43
44 static int _thr_rtld_clr_flag(int);
45 static void *_thr_rtld_lock_create(void);
46 static void _thr_rtld_lock_destroy(void *);
47 static void _thr_rtld_lock_release(void *);
48 static void _thr_rtld_rlock_acquire(void *);
49 static int _thr_rtld_set_flag(int);
50 static void _thr_rtld_wlock_acquire(void *);
51
52 struct rtld_lock {
53 struct urwlock lock;
54 char _pad[CACHE_LINE_SIZE - sizeof(struct urwlock)];
55 };
56
57 static struct rtld_lock lock_place[MAX_RTLD_LOCKS] __aligned(CACHE_LINE_SIZE);
58 static int busy_places;
59
60 static void *
_thr_rtld_lock_create(void)61 _thr_rtld_lock_create(void)
62 {
63 int locki;
64 struct rtld_lock *l;
65 static const char fail[] = "_thr_rtld_lock_create failed\n";
66
67 for (locki = 0; locki < MAX_RTLD_LOCKS; locki++) {
68 if ((busy_places & (1 << locki)) == 0)
69 break;
70 }
71 if (locki == MAX_RTLD_LOCKS) {
72 write(2, fail, sizeof(fail) - 1);
73 return (NULL);
74 }
75 busy_places |= (1 << locki);
76
77 l = &lock_place[locki];
78 l->lock.rw_flags = URWLOCK_PREFER_READER;
79 return (l);
80 }
81
82 static void
_thr_rtld_lock_destroy(void * lock)83 _thr_rtld_lock_destroy(void *lock)
84 {
85 int locki;
86 size_t i;
87
88 locki = (struct rtld_lock *)lock - &lock_place[0];
89 for (i = 0; i < sizeof(struct rtld_lock); ++i)
90 ((char *)lock)[i] = 0;
91 busy_places &= ~(1 << locki);
92 }
93
94 #define SAVE_ERRNO() { \
95 if (curthread != _thr_initial) \
96 errsave = curthread->error; \
97 else \
98 errsave = __libsys_errno; \
99 }
100
101 #define RESTORE_ERRNO() { \
102 if (curthread != _thr_initial) \
103 curthread->error = errsave; \
104 else \
105 __libsys_errno = errsave; \
106 }
107
108 static void
_thr_rtld_rlock_acquire(void * lock)109 _thr_rtld_rlock_acquire(void *lock)
110 {
111 struct pthread *curthread;
112 struct rtld_lock *l;
113 int errsave;
114
115 curthread = _get_curthread();
116 SAVE_ERRNO();
117 l = (struct rtld_lock *)lock;
118
119 THR_CRITICAL_ENTER(curthread);
120 while (_thr_rwlock_rdlock(&l->lock, 0, NULL) != 0)
121 ;
122 curthread->rdlock_count++;
123 RESTORE_ERRNO();
124 }
125
126 static void
_thr_rtld_wlock_acquire(void * lock)127 _thr_rtld_wlock_acquire(void *lock)
128 {
129 struct pthread *curthread;
130 struct rtld_lock *l;
131 int errsave;
132
133 curthread = _get_curthread();
134 SAVE_ERRNO();
135 l = (struct rtld_lock *)lock;
136
137 THR_CRITICAL_ENTER(curthread);
138 while (_thr_rwlock_wrlock(&l->lock, NULL) != 0)
139 ;
140 RESTORE_ERRNO();
141 }
142
143 static void
_thr_rtld_lock_release(void * lock)144 _thr_rtld_lock_release(void *lock)
145 {
146 struct pthread *curthread;
147 struct rtld_lock *l;
148 int32_t state;
149 int errsave;
150
151 curthread = _get_curthread();
152 SAVE_ERRNO();
153 l = (struct rtld_lock *)lock;
154
155 state = l->lock.rw_state;
156 if (__predict_false(_thr_after_fork)) {
157 /*
158 * After fork, only this thread is running, there is no
159 * waiters. Keeping waiters recorded in rwlock breaks
160 * wake logic.
161 */
162 atomic_clear_int(&l->lock.rw_state,
163 URWLOCK_WRITE_WAITERS | URWLOCK_READ_WAITERS);
164 l->lock.rw_blocked_readers = 0;
165 l->lock.rw_blocked_writers = 0;
166 }
167 if (_thr_rwlock_unlock(&l->lock) == 0) {
168 if ((state & URWLOCK_WRITE_OWNER) == 0)
169 curthread->rdlock_count--;
170 THR_CRITICAL_LEAVE(curthread);
171 }
172 RESTORE_ERRNO();
173 }
174
175 static int
_thr_rtld_set_flag(int mask __unused)176 _thr_rtld_set_flag(int mask __unused)
177 {
178 /*
179 * The caller's code in rtld-elf is broken, it is not signal safe,
180 * just return zero to fool it.
181 */
182 return (0);
183 }
184
185 static int
_thr_rtld_clr_flag(int mask __unused)186 _thr_rtld_clr_flag(int mask __unused)
187 {
188 return (0);
189 }
190
191 /*
192 * ABI bug workaround: This symbol must be present for rtld to accept
193 * RTLI_VERSION from RtldLockInfo
194 */
195 extern char _pli_rtli_version;
196 char _pli_rtli_version;
197
198 static char *
_thr_dlerror_loc(void)199 _thr_dlerror_loc(void)
200 {
201 struct pthread *curthread;
202
203 curthread = _get_curthread();
204 return (curthread->dlerror_msg);
205 }
206
207 static int *
_thr_dlerror_seen(void)208 _thr_dlerror_seen(void)
209 {
210 struct pthread *curthread;
211
212 curthread = _get_curthread();
213 return (&curthread->dlerror_seen);
214 }
215
216 void
_thr_rtld_init(void)217 _thr_rtld_init(void)
218 {
219 struct RtldLockInfo li;
220 struct pthread *curthread;
221 ucontext_t *uc;
222 int uc_len;
223 char dummy[2] = {};
224
225 curthread = _get_curthread();
226
227 /* force to resolve _umtx_op PLT */
228 _umtx_op_err(&dummy, UMTX_OP_WAKE, 1, 0, 0);
229
230 /* force to resolve errno() PLT */
231 __error();
232
233 /* force to resolve memcpy PLT */
234 memcpy(&dummy[0], &dummy[1], 1);
235
236 mprotect(NULL, 0, 0);
237 _rtld_get_stack_prot();
238 thr_wake(-1);
239
240 li.rtli_version = RTLI_VERSION;
241 li.lock_create = _thr_rtld_lock_create;
242 li.lock_destroy = _thr_rtld_lock_destroy;
243 li.rlock_acquire = _thr_rtld_rlock_acquire;
244 li.wlock_acquire = _thr_rtld_wlock_acquire;
245 li.lock_release = _thr_rtld_lock_release;
246 li.thread_set_flag = _thr_rtld_set_flag;
247 li.thread_clr_flag = _thr_rtld_clr_flag;
248 li.at_fork = NULL;
249 li.dlerror_loc = _thr_dlerror_loc;
250 li.dlerror_loc_sz = sizeof(curthread->dlerror_msg);
251 li.dlerror_seen = _thr_dlerror_seen;
252
253 /*
254 * Preresolve the symbols needed for the fork interposer. We
255 * call _rtld_atfork_pre() and _rtld_atfork_post() with NULL
256 * argument to indicate that no actual locking inside the
257 * functions should happen. Neither rtld compat locks nor
258 * libthr rtld locks cannot work there:
259 * - compat locks do not handle the case of two locks taken
260 * in write mode (the signal mask for the thread is corrupted);
261 * - libthr locks would work, but locked rtld_bind_lock prevents
262 * symbol resolution for _rtld_atfork_post.
263 */
264 _rtld_atfork_pre(NULL);
265 _rtld_atfork_post(NULL);
266 _malloc_prefork();
267 _malloc_postfork();
268 getpid();
269 syscall(SYS_getpid);
270
271 /* mask signals, also force to resolve __sys_sigprocmask PLT */
272 _thr_signal_block(curthread);
273 _rtld_thread_init(&li);
274 _thr_signal_unblock(curthread);
275 _thr_signal_block_check_fast();
276 _thr_signal_block_setup(curthread);
277
278 /* resolve machine depended functions, if any */
279 _thr_resolve_machdep();
280
281 uc_len = __getcontextx_size();
282 uc = alloca(uc_len);
283 getcontext(uc);
284 __fillcontextx2((char *)uc);
285 }
286