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 * 66 def_dlerror_loc(void) 67 { 68 return (def_dlerror_msg); 69 } 70 71 static int * 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 * 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 120 def_lock_destroy(void *lock) 121 { 122 Lock *l = (Lock *)lock; 123 124 free(l->base); 125 } 126 127 static void 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 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 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 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 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 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 214 thread_mask_set(int mask) 215 { 216 return lockinfo.thread_set_flag(mask); 217 } 218 219 static __inline void 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 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 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 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 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 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 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 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 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 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 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