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
58void _rtld_thread_init(struct RtldLockInfo *) __exported;
59void _rtld_atfork_pre(int *) __exported;
60void _rtld_atfork_post(int *) __exported;
61
62static char def_dlerror_msg[512];
63static int def_dlerror_seen_val = 1;
64
65static char *
66def_dlerror_loc(void)
67{
68	return (def_dlerror_msg);
69}
70
71static int *
72def_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
80typedef struct Struct_Lock {
81	volatile u_int lock;
82	void *base;
83} Lock;
84
85static sigset_t fullsigmask, oldsigmask;
86static int thread_flag, wnested;
87static uint32_t fsigblock;
88
89static void *
90def_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
119static void
120def_lock_destroy(void *lock)
121{
122    Lock *l = (Lock *)lock;
123
124    free(l->base);
125}
126
127static void
128def_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
137static void
138sig_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
148static void
149def_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
174static void
175def_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
191static int
192def_thread_set_flag(int mask)
193{
194	int old_val = thread_flag;
195	thread_flag |= mask;
196	return (old_val);
197}
198
199static int
200def_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 */
210struct RtldLockInfo lockinfo;
211static struct RtldLockInfo deflockinfo;
212
213static __inline int
214thread_mask_set(int mask)
215{
216	return lockinfo.thread_set_flag(mask);
217}
218
219static __inline void
220thread_mask_clear(int mask)
221{
222	lockinfo.thread_clr_flag(mask);
223}
224
225#define	RTLD_LOCK_CNT	3
226static struct rtld_lock {
227	void	*handle;
228	int	 mask;
229} rtld_locks[RTLD_LOCK_CNT];
230
231rtld_lock_t	rtld_bind_lock = &rtld_locks[0];
232rtld_lock_t	rtld_libc_lock = &rtld_locks[1];
233rtld_lock_t	rtld_phdr_lock = &rtld_locks[2];
234
235void
236rlock_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
251void
252wlock_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
267void
268lock_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
287void
288lock_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
298void
299lock_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
317void
318dlerror_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
325void
326lockdflt_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 */
370void
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
447void
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
471void
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