1 /*-
2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
3 *
4 * Copyright 1999, 2000 John D. Polstra.
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, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
17 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
18 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
19 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
21 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
22 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
23 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
24 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
25 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
26 *
27 * from: FreeBSD: src/libexec/rtld-elf/sparc64/lockdflt.c,v 1.3 2002/10/09
28 * $FreeBSD$
29 */
30
31 /*
32 * Thread locking implementation for the dynamic linker.
33 *
34 * We use the "simple, non-scalable reader-preference lock" from:
35 *
36 * J. M. Mellor-Crummey and M. L. Scott. "Scalable Reader-Writer
37 * Synchronization for Shared-Memory Multiprocessors." 3rd ACM Symp. on
38 * Principles and Practice of Parallel Programming, April 1991.
39 *
40 * In this algorithm the lock is a single word. Its low-order bit is
41 * set when a writer holds the lock. The remaining high-order bits
42 * contain a count of readers desiring the lock. The algorithm requires
43 * atomic "compare_and_store" and "add" operations, which we take
44 * from machine/atomic.h.
45 */
46
47 #include <sys/param.h>
48 #include <sys/signalvar.h>
49 #include <signal.h>
50 #include <stdlib.h>
51 #include <time.h>
52
53 #include "debug.h"
54 #include "rtld.h"
55 #include "rtld_machdep.h"
56 #include "rtld_libc.h"
57
58 void _rtld_thread_init(struct RtldLockInfo *) __exported;
59 void _rtld_atfork_pre(int *) __exported;
60 void _rtld_atfork_post(int *) __exported;
61
62 static char def_dlerror_msg[512];
63 static int def_dlerror_seen_val = 1;
64
65 static char *
def_dlerror_loc(void)66 def_dlerror_loc(void)
67 {
68 return (def_dlerror_msg);
69 }
70
71 static int *
def_dlerror_seen(void)72 def_dlerror_seen(void)
73 {
74 return (&def_dlerror_seen_val);
75 }
76
77 #define WAFLAG 0x1 /* A writer holds the lock */
78 #define RC_INCR 0x2 /* Adjusts count of readers desiring lock */
79
80 typedef struct Struct_Lock {
81 volatile u_int lock;
82 void *base;
83 } Lock;
84
85 static sigset_t fullsigmask, oldsigmask;
86 static int thread_flag, wnested;
87 static uint32_t fsigblock;
88
89 static void *
def_lock_create(void)90 def_lock_create(void)
91 {
92 void *base;
93 char *p;
94 uintptr_t r;
95 Lock *l;
96
97 /*
98 * Arrange for the lock to occupy its own cache line. First, we
99 * optimistically allocate just a cache line, hoping that malloc
100 * will give us a well-aligned block of memory. If that doesn't
101 * work, we allocate a larger block and take a well-aligned cache
102 * line from it.
103 */
104 base = xmalloc(CACHE_LINE_SIZE);
105 p = (char *)base;
106 if ((uintptr_t)p % CACHE_LINE_SIZE != 0) {
107 free(base);
108 base = xmalloc(2 * CACHE_LINE_SIZE);
109 p = (char *)base;
110 if ((r = (uintptr_t)p % CACHE_LINE_SIZE) != 0)
111 p += CACHE_LINE_SIZE - r;
112 }
113 l = (Lock *)p;
114 l->base = base;
115 l->lock = 0;
116 return l;
117 }
118
119 static void
def_lock_destroy(void * lock)120 def_lock_destroy(void *lock)
121 {
122 Lock *l = (Lock *)lock;
123
124 free(l->base);
125 }
126
127 static void
def_rlock_acquire(void * lock)128 def_rlock_acquire(void *lock)
129 {
130 Lock *l = (Lock *)lock;
131
132 atomic_add_acq_int(&l->lock, RC_INCR);
133 while (l->lock & WAFLAG)
134 ; /* Spin */
135 }
136
137 static void
sig_fastunblock(void)138 sig_fastunblock(void)
139 {
140 uint32_t oldval;
141
142 assert((fsigblock & ~SIGFASTBLOCK_FLAGS) >= SIGFASTBLOCK_INC);
143 oldval = atomic_fetchadd_32(&fsigblock, -SIGFASTBLOCK_INC);
144 if (oldval == (SIGFASTBLOCK_PEND | SIGFASTBLOCK_INC))
145 __sys_sigfastblock(SIGFASTBLOCK_UNBLOCK, NULL);
146 }
147
148 static void
def_wlock_acquire(void * lock)149 def_wlock_acquire(void *lock)
150 {
151 Lock *l;
152 sigset_t tmp_oldsigmask;
153
154 l = (Lock *)lock;
155 if (ld_fast_sigblock) {
156 for (;;) {
157 atomic_add_32(&fsigblock, SIGFASTBLOCK_INC);
158 if (atomic_cmpset_acq_int(&l->lock, 0, WAFLAG))
159 break;
160 sig_fastunblock();
161 }
162 } else {
163 for (;;) {
164 sigprocmask(SIG_BLOCK, &fullsigmask, &tmp_oldsigmask);
165 if (atomic_cmpset_acq_int(&l->lock, 0, WAFLAG))
166 break;
167 sigprocmask(SIG_SETMASK, &tmp_oldsigmask, NULL);
168 }
169 if (atomic_fetchadd_int(&wnested, 1) == 0)
170 oldsigmask = tmp_oldsigmask;
171 }
172 }
173
174 static void
def_lock_release(void * lock)175 def_lock_release(void *lock)
176 {
177 Lock *l;
178
179 l = (Lock *)lock;
180 if ((l->lock & WAFLAG) == 0)
181 atomic_add_rel_int(&l->lock, -RC_INCR);
182 else {
183 atomic_add_rel_int(&l->lock, -WAFLAG);
184 if (ld_fast_sigblock)
185 sig_fastunblock();
186 else if (atomic_fetchadd_int(&wnested, -1) == 1)
187 sigprocmask(SIG_SETMASK, &oldsigmask, NULL);
188 }
189 }
190
191 static int
def_thread_set_flag(int mask)192 def_thread_set_flag(int mask)
193 {
194 int old_val = thread_flag;
195 thread_flag |= mask;
196 return (old_val);
197 }
198
199 static int
def_thread_clr_flag(int mask)200 def_thread_clr_flag(int mask)
201 {
202 int old_val = thread_flag;
203 thread_flag &= ~mask;
204 return (old_val);
205 }
206
207 /*
208 * Public interface exposed to the rest of the dynamic linker.
209 */
210 struct RtldLockInfo lockinfo;
211 static struct RtldLockInfo deflockinfo;
212
213 static __inline int
thread_mask_set(int mask)214 thread_mask_set(int mask)
215 {
216 return lockinfo.thread_set_flag(mask);
217 }
218
219 static __inline void
thread_mask_clear(int mask)220 thread_mask_clear(int mask)
221 {
222 lockinfo.thread_clr_flag(mask);
223 }
224
225 #define RTLD_LOCK_CNT 3
226 static struct rtld_lock {
227 void *handle;
228 int mask;
229 } rtld_locks[RTLD_LOCK_CNT];
230
231 rtld_lock_t rtld_bind_lock = &rtld_locks[0];
232 rtld_lock_t rtld_libc_lock = &rtld_locks[1];
233 rtld_lock_t rtld_phdr_lock = &rtld_locks[2];
234
235 void
rlock_acquire(rtld_lock_t lock,RtldLockState * lockstate)236 rlock_acquire(rtld_lock_t lock, RtldLockState *lockstate)
237 {
238
239 if (lockstate == NULL)
240 return;
241
242 if (thread_mask_set(lock->mask) & lock->mask) {
243 dbg("rlock_acquire: recursed");
244 lockstate->lockstate = RTLD_LOCK_UNLOCKED;
245 return;
246 }
247 lockinfo.rlock_acquire(lock->handle);
248 lockstate->lockstate = RTLD_LOCK_RLOCKED;
249 }
250
251 void
wlock_acquire(rtld_lock_t lock,RtldLockState * lockstate)252 wlock_acquire(rtld_lock_t lock, RtldLockState *lockstate)
253 {
254
255 if (lockstate == NULL)
256 return;
257
258 if (thread_mask_set(lock->mask) & lock->mask) {
259 dbg("wlock_acquire: recursed");
260 lockstate->lockstate = RTLD_LOCK_UNLOCKED;
261 return;
262 }
263 lockinfo.wlock_acquire(lock->handle);
264 lockstate->lockstate = RTLD_LOCK_WLOCKED;
265 }
266
267 void
lock_release(rtld_lock_t lock,RtldLockState * lockstate)268 lock_release(rtld_lock_t lock, RtldLockState *lockstate)
269 {
270
271 if (lockstate == NULL)
272 return;
273
274 switch (lockstate->lockstate) {
275 case RTLD_LOCK_UNLOCKED:
276 break;
277 case RTLD_LOCK_RLOCKED:
278 case RTLD_LOCK_WLOCKED:
279 thread_mask_clear(lock->mask);
280 lockinfo.lock_release(lock->handle);
281 break;
282 default:
283 assert(0);
284 }
285 }
286
287 void
lock_upgrade(rtld_lock_t lock,RtldLockState * lockstate)288 lock_upgrade(rtld_lock_t lock, RtldLockState *lockstate)
289 {
290
291 if (lockstate == NULL)
292 return;
293
294 lock_release(lock, lockstate);
295 wlock_acquire(lock, lockstate);
296 }
297
298 void
lock_restart_for_upgrade(RtldLockState * lockstate)299 lock_restart_for_upgrade(RtldLockState *lockstate)
300 {
301
302 if (lockstate == NULL)
303 return;
304
305 switch (lockstate->lockstate) {
306 case RTLD_LOCK_UNLOCKED:
307 case RTLD_LOCK_WLOCKED:
308 break;
309 case RTLD_LOCK_RLOCKED:
310 siglongjmp(lockstate->env, 1);
311 break;
312 default:
313 assert(0);
314 }
315 }
316
317 void
dlerror_dflt_init(void)318 dlerror_dflt_init(void)
319 {
320 lockinfo.dlerror_loc = def_dlerror_loc;
321 lockinfo.dlerror_loc_sz = sizeof(def_dlerror_msg);
322 lockinfo.dlerror_seen = def_dlerror_seen;
323 }
324
325 void
lockdflt_init(void)326 lockdflt_init(void)
327 {
328 int i;
329
330 deflockinfo.rtli_version = RTLI_VERSION;
331 deflockinfo.lock_create = def_lock_create;
332 deflockinfo.lock_destroy = def_lock_destroy;
333 deflockinfo.rlock_acquire = def_rlock_acquire;
334 deflockinfo.wlock_acquire = def_wlock_acquire;
335 deflockinfo.lock_release = def_lock_release;
336 deflockinfo.thread_set_flag = def_thread_set_flag;
337 deflockinfo.thread_clr_flag = def_thread_clr_flag;
338 deflockinfo.at_fork = NULL;
339 deflockinfo.dlerror_loc = def_dlerror_loc;
340 deflockinfo.dlerror_loc_sz = sizeof(def_dlerror_msg);
341 deflockinfo.dlerror_seen = def_dlerror_seen;
342
343 for (i = 0; i < RTLD_LOCK_CNT; i++) {
344 rtld_locks[i].mask = (1 << i);
345 rtld_locks[i].handle = NULL;
346 }
347
348 memcpy(&lockinfo, &deflockinfo, sizeof(lockinfo));
349 _rtld_thread_init(NULL);
350 if (ld_fast_sigblock) {
351 __sys_sigfastblock(SIGFASTBLOCK_SETPTR, &fsigblock);
352 } else {
353 /*
354 * Construct a mask to block all signals. Note that
355 * blocked traps mean that the process is terminated
356 * if trap occurs while we are in locked section, with
357 * the default settings for kern.forcesigexit.
358 */
359 sigfillset(&fullsigmask);
360 }
361 }
362
363 /*
364 * Callback function to allow threads implementation to
365 * register their own locking primitives if the default
366 * one is not suitable.
367 * The current context should be the only context
368 * executing at the invocation time.
369 */
370 void
_rtld_thread_init(struct RtldLockInfo * pli)371 _rtld_thread_init(struct RtldLockInfo *pli)
372 {
373 const Obj_Entry *obj;
374 SymLook req;
375 void *locks[RTLD_LOCK_CNT];
376 int flags, i, res;
377
378 if (pli == NULL) {
379 lockinfo.rtli_version = RTLI_VERSION;
380 } else {
381 lockinfo.rtli_version = RTLI_VERSION_ONE;
382 obj = obj_from_addr(pli->lock_create);
383 if (obj != NULL) {
384 symlook_init(&req, "_pli_rtli_version");
385 res = symlook_obj(&req, obj);
386 if (res == 0)
387 lockinfo.rtli_version = pli->rtli_version;
388 }
389 }
390
391 /* disable all locking while this function is running */
392 flags = thread_mask_set(~0);
393
394 if (pli == NULL)
395 pli = &deflockinfo;
396 else if (ld_fast_sigblock) {
397 fsigblock = 0;
398 __sys_sigfastblock(SIGFASTBLOCK_UNSETPTR, NULL);
399 }
400
401 for (i = 0; i < RTLD_LOCK_CNT; i++)
402 if ((locks[i] = pli->lock_create()) == NULL)
403 break;
404
405 if (i < RTLD_LOCK_CNT) {
406 while (--i >= 0)
407 pli->lock_destroy(locks[i]);
408 abort();
409 }
410
411 for (i = 0; i < RTLD_LOCK_CNT; i++) {
412 if (rtld_locks[i].handle == NULL)
413 continue;
414 if (flags & rtld_locks[i].mask)
415 lockinfo.lock_release(rtld_locks[i].handle);
416 lockinfo.lock_destroy(rtld_locks[i].handle);
417 }
418
419 for (i = 0; i < RTLD_LOCK_CNT; i++) {
420 rtld_locks[i].handle = locks[i];
421 if (flags & rtld_locks[i].mask)
422 pli->wlock_acquire(rtld_locks[i].handle);
423 }
424
425 lockinfo.lock_create = pli->lock_create;
426 lockinfo.lock_destroy = pli->lock_destroy;
427 lockinfo.rlock_acquire = pli->rlock_acquire;
428 lockinfo.wlock_acquire = pli->wlock_acquire;
429 lockinfo.lock_release = pli->lock_release;
430 lockinfo.thread_set_flag = pli->thread_set_flag;
431 lockinfo.thread_clr_flag = pli->thread_clr_flag;
432 lockinfo.at_fork = pli->at_fork;
433 if (lockinfo.rtli_version > RTLI_VERSION_ONE && pli != NULL) {
434 strlcpy(pli->dlerror_loc(), lockinfo.dlerror_loc(),
435 lockinfo.dlerror_loc_sz);
436 lockinfo.dlerror_loc = pli->dlerror_loc;
437 lockinfo.dlerror_loc_sz = pli->dlerror_loc_sz;
438 lockinfo.dlerror_seen = pli->dlerror_seen;
439 }
440
441 /* restore thread locking state, this time with new locks */
442 thread_mask_clear(~0);
443 thread_mask_set(flags);
444 dbg("_rtld_thread_init: done");
445 }
446
447 void
_rtld_atfork_pre(int * locks)448 _rtld_atfork_pre(int *locks)
449 {
450 RtldLockState ls[2];
451
452 if (locks == NULL)
453 return;
454
455 /*
456 * Warning: this did not worked well with the rtld compat
457 * locks above, when the thread signal mask was corrupted (set
458 * to all signals blocked) if two locks were taken
459 * simultaneously in the write mode. The caller of the
460 * _rtld_atfork_pre() must provide the working implementation
461 * of the locks anyway, and libthr locks are fine.
462 */
463 wlock_acquire(rtld_phdr_lock, &ls[0]);
464 wlock_acquire(rtld_bind_lock, &ls[1]);
465
466 /* XXXKIB: I am really sorry for this. */
467 locks[0] = ls[1].lockstate;
468 locks[2] = ls[0].lockstate;
469 }
470
471 void
_rtld_atfork_post(int * locks)472 _rtld_atfork_post(int *locks)
473 {
474 RtldLockState ls[2];
475
476 if (locks == NULL)
477 return;
478
479 bzero(ls, sizeof(ls));
480 ls[0].lockstate = locks[2];
481 ls[1].lockstate = locks[0];
482 lock_release(rtld_bind_lock, &ls[1]);
483 lock_release(rtld_phdr_lock, &ls[0]);
484 }
485