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 = base; 106 if ((uintptr_t)p % CACHE_LINE_SIZE != 0) { 107 free(base); 108 base = xmalloc(2 * CACHE_LINE_SIZE); 109 p = 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; 123 124 free(l->base); 125 } 126 127 static void 128 sig_fastunblock(void) 129 { 130 uint32_t oldval; 131 132 assert((fsigblock & ~SIGFASTBLOCK_FLAGS) >= SIGFASTBLOCK_INC); 133 oldval = atomic_fetchadd_32(&fsigblock, -SIGFASTBLOCK_INC); 134 if (oldval == (SIGFASTBLOCK_PEND | SIGFASTBLOCK_INC)) 135 __sys_sigfastblock(SIGFASTBLOCK_UNBLOCK, NULL); 136 } 137 138 static bool 139 def_lock_acquire_set(Lock *l, bool wlock) 140 { 141 if (wlock) { 142 if (atomic_cmpset_acq_int(&l->lock, 0, WAFLAG)) 143 return (true); 144 } else { 145 atomic_add_acq_int(&l->lock, RC_INCR); 146 if ((l->lock & WAFLAG) == 0) 147 return (true); 148 atomic_add_int(&l->lock, -RC_INCR); 149 } 150 return (false); 151 } 152 153 static void 154 def_lock_acquire(Lock *l, bool wlock) 155 { 156 sigset_t tmp_oldsigmask; 157 158 if (ld_fast_sigblock) { 159 for (;;) { 160 atomic_add_32(&fsigblock, SIGFASTBLOCK_INC); 161 if (def_lock_acquire_set(l, wlock)) 162 break; 163 sig_fastunblock(); 164 } 165 } else { 166 for (;;) { 167 sigprocmask(SIG_BLOCK, &fullsigmask, &tmp_oldsigmask); 168 if (def_lock_acquire_set(l, wlock)) 169 break; 170 sigprocmask(SIG_SETMASK, &tmp_oldsigmask, NULL); 171 } 172 if (atomic_fetchadd_int(&wnested, 1) == 0) 173 oldsigmask = tmp_oldsigmask; 174 } 175 } 176 177 static void 178 def_rlock_acquire(void *lock) 179 { 180 def_lock_acquire(lock, false); 181 } 182 183 static void 184 def_wlock_acquire(void *lock) 185 { 186 def_lock_acquire(lock, true); 187 } 188 189 static void 190 def_lock_release(void *lock) 191 { 192 Lock *l = lock; 193 194 atomic_add_rel_int(&l->lock, -((l->lock & WAFLAG) == 0 ? 195 RC_INCR : WAFLAG)); 196 if (ld_fast_sigblock) 197 sig_fastunblock(); 198 else if (atomic_fetchadd_int(&wnested, -1) == 1) 199 sigprocmask(SIG_SETMASK, &oldsigmask, NULL); 200 } 201 202 static int 203 def_thread_set_flag(int mask) 204 { 205 int old_val = thread_flag; 206 207 thread_flag |= mask; 208 return (old_val); 209 } 210 211 static int 212 def_thread_clr_flag(int mask) 213 { 214 int old_val = thread_flag; 215 216 thread_flag &= ~mask; 217 return (old_val); 218 } 219 220 /* 221 * Public interface exposed to the rest of the dynamic linker. 222 */ 223 struct RtldLockInfo lockinfo; 224 static struct RtldLockInfo deflockinfo; 225 226 static __inline int 227 thread_mask_set(int mask) 228 { 229 return (lockinfo.thread_set_flag(mask)); 230 } 231 232 static __inline void 233 thread_mask_clear(int mask) 234 { 235 lockinfo.thread_clr_flag(mask); 236 } 237 238 #define RTLD_LOCK_CNT 3 239 static struct rtld_lock { 240 void *handle; 241 int mask; 242 } rtld_locks[RTLD_LOCK_CNT]; 243 244 rtld_lock_t rtld_bind_lock = &rtld_locks[0]; 245 rtld_lock_t rtld_libc_lock = &rtld_locks[1]; 246 rtld_lock_t rtld_phdr_lock = &rtld_locks[2]; 247 248 void 249 rlock_acquire(rtld_lock_t lock, RtldLockState *lockstate) 250 { 251 252 if (lockstate == NULL) 253 return; 254 255 if (thread_mask_set(lock->mask) & lock->mask) { 256 dbg("rlock_acquire: recursed"); 257 lockstate->lockstate = RTLD_LOCK_UNLOCKED; 258 return; 259 } 260 lockinfo.rlock_acquire(lock->handle); 261 lockstate->lockstate = RTLD_LOCK_RLOCKED; 262 } 263 264 void 265 wlock_acquire(rtld_lock_t lock, RtldLockState *lockstate) 266 { 267 268 if (lockstate == NULL) 269 return; 270 271 if (thread_mask_set(lock->mask) & lock->mask) { 272 dbg("wlock_acquire: recursed"); 273 lockstate->lockstate = RTLD_LOCK_UNLOCKED; 274 return; 275 } 276 lockinfo.wlock_acquire(lock->handle); 277 lockstate->lockstate = RTLD_LOCK_WLOCKED; 278 } 279 280 void 281 lock_release(rtld_lock_t lock, RtldLockState *lockstate) 282 { 283 284 if (lockstate == NULL) 285 return; 286 287 switch (lockstate->lockstate) { 288 case RTLD_LOCK_UNLOCKED: 289 break; 290 case RTLD_LOCK_RLOCKED: 291 case RTLD_LOCK_WLOCKED: 292 thread_mask_clear(lock->mask); 293 lockinfo.lock_release(lock->handle); 294 break; 295 default: 296 assert(0); 297 } 298 } 299 300 void 301 lock_upgrade(rtld_lock_t lock, RtldLockState *lockstate) 302 { 303 304 if (lockstate == NULL) 305 return; 306 307 lock_release(lock, lockstate); 308 wlock_acquire(lock, lockstate); 309 } 310 311 void 312 lock_restart_for_upgrade(RtldLockState *lockstate) 313 { 314 315 if (lockstate == NULL) 316 return; 317 318 switch (lockstate->lockstate) { 319 case RTLD_LOCK_UNLOCKED: 320 case RTLD_LOCK_WLOCKED: 321 break; 322 case RTLD_LOCK_RLOCKED: 323 siglongjmp(lockstate->env, 1); 324 break; 325 default: 326 assert(0); 327 } 328 } 329 330 void 331 dlerror_dflt_init(void) 332 { 333 lockinfo.dlerror_loc = def_dlerror_loc; 334 lockinfo.dlerror_loc_sz = sizeof(def_dlerror_msg); 335 lockinfo.dlerror_seen = def_dlerror_seen; 336 } 337 338 void 339 lockdflt_init(void) 340 { 341 int i; 342 343 deflockinfo.rtli_version = RTLI_VERSION; 344 deflockinfo.lock_create = def_lock_create; 345 deflockinfo.lock_destroy = def_lock_destroy; 346 deflockinfo.rlock_acquire = def_rlock_acquire; 347 deflockinfo.wlock_acquire = def_wlock_acquire; 348 deflockinfo.lock_release = def_lock_release; 349 deflockinfo.thread_set_flag = def_thread_set_flag; 350 deflockinfo.thread_clr_flag = def_thread_clr_flag; 351 deflockinfo.at_fork = NULL; 352 deflockinfo.dlerror_loc = def_dlerror_loc; 353 deflockinfo.dlerror_loc_sz = sizeof(def_dlerror_msg); 354 deflockinfo.dlerror_seen = def_dlerror_seen; 355 356 for (i = 0; i < RTLD_LOCK_CNT; i++) { 357 rtld_locks[i].mask = (1 << i); 358 rtld_locks[i].handle = NULL; 359 } 360 361 memcpy(&lockinfo, &deflockinfo, sizeof(lockinfo)); 362 _rtld_thread_init(NULL); 363 if (ld_fast_sigblock) { 364 __sys_sigfastblock(SIGFASTBLOCK_SETPTR, &fsigblock); 365 } else { 366 /* 367 * Construct a mask to block all signals. Note that 368 * blocked traps mean that the process is terminated 369 * if trap occurs while we are in locked section, with 370 * the default settings for kern.forcesigexit. 371 */ 372 sigfillset(&fullsigmask); 373 } 374 } 375 376 /* 377 * Callback function to allow threads implementation to 378 * register their own locking primitives if the default 379 * one is not suitable. 380 * The current context should be the only context 381 * executing at the invocation time. 382 */ 383 void 384 _rtld_thread_init(struct RtldLockInfo *pli) 385 { 386 const Obj_Entry *obj; 387 SymLook req; 388 void *locks[RTLD_LOCK_CNT]; 389 int flags, i, res; 390 391 if (pli == NULL) { 392 lockinfo.rtli_version = RTLI_VERSION; 393 } else { 394 lockinfo.rtli_version = RTLI_VERSION_ONE; 395 obj = obj_from_addr(pli->lock_create); 396 if (obj != NULL) { 397 symlook_init(&req, "_pli_rtli_version"); 398 res = symlook_obj(&req, obj); 399 if (res == 0) 400 lockinfo.rtli_version = pli->rtli_version; 401 } 402 } 403 404 /* disable all locking while this function is running */ 405 flags = thread_mask_set(~0); 406 407 if (pli == NULL) 408 pli = &deflockinfo; 409 else if (ld_fast_sigblock) { 410 fsigblock = 0; 411 __sys_sigfastblock(SIGFASTBLOCK_UNSETPTR, NULL); 412 } 413 414 for (i = 0; i < RTLD_LOCK_CNT; i++) 415 if ((locks[i] = pli->lock_create()) == NULL) 416 break; 417 418 if (i < RTLD_LOCK_CNT) { 419 while (--i >= 0) 420 pli->lock_destroy(locks[i]); 421 abort(); 422 } 423 424 for (i = 0; i < RTLD_LOCK_CNT; i++) { 425 if (rtld_locks[i].handle == NULL) 426 continue; 427 if (flags & rtld_locks[i].mask) 428 lockinfo.lock_release(rtld_locks[i].handle); 429 lockinfo.lock_destroy(rtld_locks[i].handle); 430 } 431 432 for (i = 0; i < RTLD_LOCK_CNT; i++) { 433 rtld_locks[i].handle = locks[i]; 434 if (flags & rtld_locks[i].mask) 435 pli->wlock_acquire(rtld_locks[i].handle); 436 } 437 438 lockinfo.lock_create = pli->lock_create; 439 lockinfo.lock_destroy = pli->lock_destroy; 440 lockinfo.rlock_acquire = pli->rlock_acquire; 441 lockinfo.wlock_acquire = pli->wlock_acquire; 442 lockinfo.lock_release = pli->lock_release; 443 lockinfo.thread_set_flag = pli->thread_set_flag; 444 lockinfo.thread_clr_flag = pli->thread_clr_flag; 445 lockinfo.at_fork = pli->at_fork; 446 if (lockinfo.rtli_version > RTLI_VERSION_ONE && pli != NULL) { 447 strlcpy(pli->dlerror_loc(), lockinfo.dlerror_loc(), 448 lockinfo.dlerror_loc_sz); 449 lockinfo.dlerror_loc = pli->dlerror_loc; 450 lockinfo.dlerror_loc_sz = pli->dlerror_loc_sz; 451 lockinfo.dlerror_seen = pli->dlerror_seen; 452 } 453 454 /* restore thread locking state, this time with new locks */ 455 thread_mask_clear(~0); 456 thread_mask_set(flags); 457 dbg("_rtld_thread_init: done"); 458 } 459 460 void 461 _rtld_atfork_pre(int *locks) 462 { 463 RtldLockState ls[2]; 464 465 if (locks == NULL) 466 return; 467 468 /* 469 * Warning: this did not worked well with the rtld compat 470 * locks above, when the thread signal mask was corrupted (set 471 * to all signals blocked) if two locks were taken 472 * simultaneously in the write mode. The caller of the 473 * _rtld_atfork_pre() must provide the working implementation 474 * of the locks anyway, and libthr locks are fine. 475 */ 476 wlock_acquire(rtld_phdr_lock, &ls[0]); 477 wlock_acquire(rtld_bind_lock, &ls[1]); 478 479 /* XXXKIB: I am really sorry for this. */ 480 locks[0] = ls[1].lockstate; 481 locks[2] = ls[0].lockstate; 482 } 483 484 void 485 _rtld_atfork_post(int *locks) 486 { 487 RtldLockState ls[2]; 488 489 if (locks == NULL) 490 return; 491 492 bzero(ls, sizeof(ls)); 493 ls[0].lockstate = locks[2]; 494 ls[1].lockstate = locks[0]; 495 lock_release(rtld_bind_lock, &ls[1]); 496 lock_release(rtld_phdr_lock, &ls[0]); 497 } 498