arc4random.c revision 1.44
1 /* $NetBSD: arc4random.c,v 1.44 2025/03/06 00:53:26 riastradh Exp $ */ 2 3 /*- 4 * Copyright (c) 2014 The NetBSD Foundation, Inc. 5 * All rights reserved. 6 * 7 * This code is derived from software contributed to The NetBSD Foundation 8 * by Taylor R. Campbell. 9 * 10 * Redistribution and use in source and binary forms, with or without 11 * modification, are permitted provided that the following conditions 12 * are met: 13 * 1. Redistributions of source code must retain the above copyright 14 * notice, this list of conditions and the following disclaimer. 15 * 2. Redistributions in binary form must reproduce the above copyright 16 * notice, this list of conditions and the following disclaimer in the 17 * documentation and/or other materials provided with the distribution. 18 * 19 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 20 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 21 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 22 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 23 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 24 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 25 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 26 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 27 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 28 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 29 * POSSIBILITY OF SUCH DAMAGE. 30 */ 31 32 /* 33 * Legacy arc4random(3) API from OpenBSD reimplemented using the 34 * ChaCha20 PRF, with per-thread state. 35 * 36 * Security model: 37 * - An attacker who sees some outputs cannot predict past or future 38 * outputs. 39 * - An attacker who sees the PRNG state cannot predict past outputs. 40 * - An attacker who sees a child's PRNG state cannot predict past or 41 * future outputs in the parent, or in other children. 42 * 43 * The arc4random(3) API may abort the process if: 44 * 45 * (a) the crypto self-test fails, 46 * (b) pthread_atfork fails, or 47 * (c) sysctl(KERN_ARND) fails when reseeding the PRNG. 48 * 49 * The crypto self-test and pthread_atfork occur only once, on the 50 * first use of any of the arc4random(3) API. KERN_ARND is unlikely to 51 * fail later unless the kernel is seriously broken. 52 */ 53 54 #include <sys/cdefs.h> 55 __RCSID("$NetBSD: arc4random.c,v 1.44 2025/03/06 00:53:26 riastradh Exp $"); 56 57 #include "namespace.h" 58 #include "reentrant.h" 59 60 #include <sys/bitops.h> 61 #include <sys/endian.h> 62 #include <sys/errno.h> 63 #include <sys/mman.h> 64 #include <sys/sysctl.h> 65 66 #include <assert.h> 67 #include <sha2.h> 68 #include <stdatomic.h> 69 #include <stdbool.h> 70 #include <stdint.h> 71 #include <stdlib.h> 72 #include <string.h> 73 #include <unistd.h> 74 75 #include "arc4random.h" 76 #include "reentrant.h" 77 78 #ifdef __weak_alias 79 __weak_alias(arc4random,_arc4random) 80 __weak_alias(arc4random_addrandom,_arc4random_addrandom) 81 __weak_alias(arc4random_buf,_arc4random_buf) 82 __weak_alias(arc4random_stir,_arc4random_stir) 83 __weak_alias(arc4random_uniform,_arc4random_uniform) 84 #endif 85 86 /* 87 * For standard ChaCha, use le32dec/le32enc. We don't need that for 88 * the purposes of a nondeterministic random number generator -- we 89 * don't need to be bit-for-bit compatible over any wire. 90 */ 91 92 static inline uint32_t 93 crypto_le32dec(const void *p) 94 { 95 uint32_t v; 96 97 (void)memcpy(&v, p, sizeof v); 98 99 return v; 100 } 101 102 static inline void 103 crypto_le32enc(void *p, uint32_t v) 104 { 105 106 (void)memcpy(p, &v, sizeof v); 107 } 108 109 /* ChaCha core */ 110 111 #define crypto_core_OUTPUTBYTES 64 112 #define crypto_core_INPUTBYTES 16 113 #define crypto_core_KEYBYTES 32 114 #define crypto_core_CONSTBYTES 16 115 116 #define crypto_core_ROUNDS 20 117 118 static uint32_t 119 rotate(uint32_t u, unsigned c) 120 { 121 122 return (u << c) | (u >> (32 - c)); 123 } 124 125 #define QUARTERROUND(a, b, c, d) do { \ 126 (a) += (b); (d) ^= (a); (d) = rotate((d), 16); \ 127 (c) += (d); (b) ^= (c); (b) = rotate((b), 12); \ 128 (a) += (b); (d) ^= (a); (d) = rotate((d), 8); \ 129 (c) += (d); (b) ^= (c); (b) = rotate((b), 7); \ 130 } while (0) 131 132 static const uint8_t crypto_core_constant32[16] = "expand 32-byte k"; 133 134 static void 135 crypto_core(uint8_t *out, const uint8_t *in, const uint8_t *k, 136 const uint8_t *c) 137 { 138 uint32_t x0,x1,x2,x3,x4,x5,x6,x7,x8,x9,x10,x11,x12,x13,x14,x15; 139 uint32_t j0,j1,j2,j3,j4,j5,j6,j7,j8,j9,j10,j11,j12,j13,j14,j15; 140 int i; 141 142 j0 = x0 = crypto_le32dec(c + 0); 143 j1 = x1 = crypto_le32dec(c + 4); 144 j2 = x2 = crypto_le32dec(c + 8); 145 j3 = x3 = crypto_le32dec(c + 12); 146 j4 = x4 = crypto_le32dec(k + 0); 147 j5 = x5 = crypto_le32dec(k + 4); 148 j6 = x6 = crypto_le32dec(k + 8); 149 j7 = x7 = crypto_le32dec(k + 12); 150 j8 = x8 = crypto_le32dec(k + 16); 151 j9 = x9 = crypto_le32dec(k + 20); 152 j10 = x10 = crypto_le32dec(k + 24); 153 j11 = x11 = crypto_le32dec(k + 28); 154 j12 = x12 = crypto_le32dec(in + 0); 155 j13 = x13 = crypto_le32dec(in + 4); 156 j14 = x14 = crypto_le32dec(in + 8); 157 j15 = x15 = crypto_le32dec(in + 12); 158 159 for (i = crypto_core_ROUNDS; i > 0; i -= 2) { 160 QUARTERROUND( x0, x4, x8,x12); 161 QUARTERROUND( x1, x5, x9,x13); 162 QUARTERROUND( x2, x6,x10,x14); 163 QUARTERROUND( x3, x7,x11,x15); 164 QUARTERROUND( x0, x5,x10,x15); 165 QUARTERROUND( x1, x6,x11,x12); 166 QUARTERROUND( x2, x7, x8,x13); 167 QUARTERROUND( x3, x4, x9,x14); 168 } 169 170 crypto_le32enc(out + 0, x0 + j0); 171 crypto_le32enc(out + 4, x1 + j1); 172 crypto_le32enc(out + 8, x2 + j2); 173 crypto_le32enc(out + 12, x3 + j3); 174 crypto_le32enc(out + 16, x4 + j4); 175 crypto_le32enc(out + 20, x5 + j5); 176 crypto_le32enc(out + 24, x6 + j6); 177 crypto_le32enc(out + 28, x7 + j7); 178 crypto_le32enc(out + 32, x8 + j8); 179 crypto_le32enc(out + 36, x9 + j9); 180 crypto_le32enc(out + 40, x10 + j10); 181 crypto_le32enc(out + 44, x11 + j11); 182 crypto_le32enc(out + 48, x12 + j12); 183 crypto_le32enc(out + 52, x13 + j13); 184 crypto_le32enc(out + 56, x14 + j14); 185 crypto_le32enc(out + 60, x15 + j15); 186 } 187 188 /* ChaCha self-test */ 189 190 /* 191 * Test vector for ChaCha20 from 192 * <http://tools.ietf.org/html/draft-strombergson-chacha-test-vectors-00>, 193 * test vectors for ChaCha12 and ChaCha8 and for big-endian machines 194 * generated by the same crypto_core code with crypto_core_ROUNDS and 195 * crypto_le32enc/dec varied. 196 */ 197 198 static const uint8_t crypto_core_selftest_vector[64] = { 199 #if _BYTE_ORDER == _LITTLE_ENDIAN 200 # if crypto_core_ROUNDS == 8 201 0x3e,0x00,0xef,0x2f,0x89,0x5f,0x40,0xd6, 202 0x7f,0x5b,0xb8,0xe8,0x1f,0x09,0xa5,0xa1, 203 0x2c,0x84,0x0e,0xc3,0xce,0x9a,0x7f,0x3b, 204 0x18,0x1b,0xe1,0x88,0xef,0x71,0x1a,0x1e, 205 0x98,0x4c,0xe1,0x72,0xb9,0x21,0x6f,0x41, 206 0x9f,0x44,0x53,0x67,0x45,0x6d,0x56,0x19, 207 0x31,0x4a,0x42,0xa3,0xda,0x86,0xb0,0x01, 208 0x38,0x7b,0xfd,0xb8,0x0e,0x0c,0xfe,0x42, 209 # elif crypto_core_ROUNDS == 12 210 0x9b,0xf4,0x9a,0x6a,0x07,0x55,0xf9,0x53, 211 0x81,0x1f,0xce,0x12,0x5f,0x26,0x83,0xd5, 212 0x04,0x29,0xc3,0xbb,0x49,0xe0,0x74,0x14, 213 0x7e,0x00,0x89,0xa5,0x2e,0xae,0x15,0x5f, 214 0x05,0x64,0xf8,0x79,0xd2,0x7a,0xe3,0xc0, 215 0x2c,0xe8,0x28,0x34,0xac,0xfa,0x8c,0x79, 216 0x3a,0x62,0x9f,0x2c,0xa0,0xde,0x69,0x19, 217 0x61,0x0b,0xe8,0x2f,0x41,0x13,0x26,0xbe, 218 # elif crypto_core_ROUNDS == 20 219 0x76,0xb8,0xe0,0xad,0xa0,0xf1,0x3d,0x90, 220 0x40,0x5d,0x6a,0xe5,0x53,0x86,0xbd,0x28, 221 0xbd,0xd2,0x19,0xb8,0xa0,0x8d,0xed,0x1a, 222 0xa8,0x36,0xef,0xcc,0x8b,0x77,0x0d,0xc7, 223 0xda,0x41,0x59,0x7c,0x51,0x57,0x48,0x8d, 224 0x77,0x24,0xe0,0x3f,0xb8,0xd8,0x4a,0x37, 225 0x6a,0x43,0xb8,0xf4,0x15,0x18,0xa1,0x1c, 226 0xc3,0x87,0xb6,0x69,0xb2,0xee,0x65,0x86, 227 # else 228 # error crypto_core_ROUNDS must be 8, 12, or 20. 229 # endif 230 #elif _BYTE_ORDER == _BIG_ENDIAN 231 # if crypto_core_ROUNDS == 8 232 0x9a,0x13,0x07,0xe3,0x38,0x18,0x9e,0x99, 233 0x15,0x37,0x16,0x4d,0x04,0xe6,0x48,0x9a, 234 0x07,0xd6,0xe8,0x7a,0x02,0xf9,0xf5,0xc7, 235 0x3f,0xa9,0xc2,0x0a,0xe1,0xc6,0x62,0xea, 236 0x80,0xaf,0xb6,0x51,0xca,0x52,0x43,0x87, 237 0xe3,0xa6,0xa6,0x61,0x11,0xf5,0xe6,0xcf, 238 0x09,0x0f,0xdc,0x9d,0xc3,0xc3,0xbb,0x43, 239 0xd7,0xfa,0x70,0x42,0xbf,0xa5,0xee,0xa2, 240 # elif crypto_core_ROUNDS == 12 241 0xcf,0x6c,0x16,0x48,0xbf,0xf4,0xba,0x85, 242 0x32,0x69,0xd3,0x98,0xc8,0x7d,0xcd,0x3f, 243 0xdc,0x76,0x6b,0xa2,0x7b,0xcb,0x17,0x4d, 244 0x05,0xda,0xdd,0xd8,0x62,0x54,0xbf,0xe0, 245 0x65,0xed,0x0e,0xf4,0x01,0x7e,0x3c,0x05, 246 0x35,0xb2,0x7a,0x60,0xf3,0x8f,0x12,0x33, 247 0x24,0x60,0xcd,0x85,0xfe,0x4c,0xf3,0x39, 248 0xb1,0x0e,0x3e,0xe0,0xba,0xa6,0x2f,0xa9, 249 # elif crypto_core_ROUNDS == 20 250 0x83,0x8b,0xf8,0x75,0xf7,0xde,0x9d,0x8c, 251 0x33,0x14,0x72,0x28,0xd1,0xbe,0x88,0xe5, 252 0x94,0xb5,0xed,0xb8,0x56,0xb5,0x9e,0x0c, 253 0x64,0x6a,0xaf,0xd9,0xa7,0x49,0x10,0x59, 254 0xba,0x3a,0x82,0xf8,0x4a,0x70,0x9c,0x00, 255 0x82,0x2c,0xae,0xc6,0xd7,0x1c,0x2e,0xda, 256 0x2a,0xfb,0x61,0x70,0x2b,0xd1,0xbf,0x8b, 257 0x95,0xbc,0x23,0xb6,0x4b,0x60,0x02,0xec, 258 # else 259 # error crypto_core_ROUNDS must be 8, 12, or 20. 260 # endif 261 #else 262 # error Byte order must be little-endian or big-endian. 263 #endif 264 }; 265 266 static int 267 crypto_core_selftest(void) 268 { 269 const uint8_t nonce[crypto_core_INPUTBYTES] = {0}; 270 const uint8_t key[crypto_core_KEYBYTES] = {0}; 271 uint8_t block[64]; 272 unsigned i; 273 274 crypto_core(block, nonce, key, crypto_core_constant32); 275 for (i = 0; i < 64; i++) { 276 if (block[i] != crypto_core_selftest_vector[i]) 277 return EIO; 278 } 279 280 return 0; 281 } 282 283 /* PRNG */ 284 285 /* 286 * For a state s, rather than use ChaCha20 as a stream cipher to 287 * generate the concatenation ChaCha20_s(0) || ChaCha20_s(1) || ..., we 288 * split ChaCha20_s(0) into s' || x and yield x for the first request, 289 * split ChaCha20_s'(0) into s'' || y and yield y for the second 290 * request, &c. This provides backtracking resistance: an attacker who 291 * finds s'' can't recover s' or x. 292 */ 293 294 #define crypto_prng_SEEDBYTES crypto_core_KEYBYTES 295 #define crypto_prng_MAXOUTPUTBYTES \ 296 (crypto_core_OUTPUTBYTES - crypto_prng_SEEDBYTES) 297 298 __CTASSERT(sizeof(struct crypto_prng) == crypto_prng_SEEDBYTES); 299 300 static void 301 crypto_prng_seed(struct crypto_prng *prng, const void *seed) 302 { 303 304 (void)memcpy(prng->state, seed, crypto_prng_SEEDBYTES); 305 } 306 307 static void 308 crypto_prng_buf(struct crypto_prng *prng, void *buf, size_t n) 309 { 310 const uint8_t nonce[crypto_core_INPUTBYTES] = {0}; 311 uint8_t output[crypto_core_OUTPUTBYTES]; 312 313 _DIAGASSERT(n <= crypto_prng_MAXOUTPUTBYTES); 314 __CTASSERT(sizeof prng->state + crypto_prng_MAXOUTPUTBYTES 315 <= sizeof output); 316 317 crypto_core(output, nonce, prng->state, crypto_core_constant32); 318 (void)memcpy(prng->state, output, sizeof prng->state); 319 (void)memcpy(buf, output + sizeof prng->state, n); 320 (void)explicit_memset(output, 0, sizeof output); 321 } 322 323 /* One-time stream: expand short single-use secret into long secret */ 324 325 #define crypto_onetimestream_SEEDBYTES crypto_core_KEYBYTES 326 327 static void 328 crypto_onetimestream(const void *seed, void *buf, size_t n) 329 { 330 uint32_t nonce[crypto_core_INPUTBYTES / sizeof(uint32_t)] = {0}; 331 uint8_t block[crypto_core_OUTPUTBYTES]; 332 uint8_t *p8, *p32; 333 const uint8_t *nonce8 = (const uint8_t *)(void *)nonce; 334 size_t ni, nb, nf; 335 336 /* 337 * Guarantee we can generate up to n bytes. We have 338 * 2^(8*INPUTBYTES) possible inputs yielding output of 339 * OUTPUTBYTES*2^(8*INPUTBYTES) bytes. It suffices to require 340 * that sizeof n > (1/CHAR_BIT) log_2 n be less than 341 * (1/CHAR_BIT) log_2 of the total output stream length. We 342 * have 343 * 344 * log_2 (o 2^(8 i)) = log_2 o + log_2 2^(8 i) 345 * = log_2 o + 8 i. 346 */ 347 #ifndef __lint__ 348 __CTASSERT(CHAR_BIT * sizeof n <= (ilog2(crypto_core_OUTPUTBYTES) + 349 8 * crypto_core_INPUTBYTES)); 350 #endif 351 352 p8 = buf; 353 p32 = (uint8_t *)roundup2((uintptr_t)p8, 4); 354 ni = p32 - p8; 355 if (n < ni) 356 ni = n; 357 nb = (n - ni) / sizeof block; 358 nf = (n - ni) % sizeof block; 359 360 _DIAGASSERT(((uintptr_t)p32 & 3) == 0); 361 _DIAGASSERT(ni <= n); 362 _DIAGASSERT(nb <= (n / sizeof block)); 363 _DIAGASSERT(nf <= n); 364 _DIAGASSERT(n == (ni + (nb * sizeof block) + nf)); 365 _DIAGASSERT(ni < 4); 366 _DIAGASSERT(nf < sizeof block); 367 368 if (ni) { 369 crypto_core(block, nonce8, seed, crypto_core_constant32); 370 nonce[0]++; 371 (void)memcpy(p8, block, ni); 372 } 373 while (nb--) { 374 crypto_core(p32, nonce8, seed, crypto_core_constant32); 375 if (++nonce[0] == 0) 376 nonce[1]++; 377 p32 += crypto_core_OUTPUTBYTES; 378 } 379 if (nf) { 380 crypto_core(block, nonce8, seed, crypto_core_constant32); 381 if (++nonce[0] == 0) 382 nonce[1]++; 383 (void)memcpy(p32, block, nf); 384 } 385 386 if (ni | nf) 387 (void)explicit_memset(block, 0, sizeof block); 388 } 389 390 /* 391 * entropy_epoch() 392 * 393 * Return the current entropy epoch, from the sysctl node 394 * kern.entropy.epoch. 395 * 396 * The entropy epoch is never zero. Initially, or on error, it is 397 * (unsigned)-1. It may wrap around but it skips (unsigned)-1 and 398 * 0 when it does. Changes happen less than once per second, so 399 * wraparound will only affect systems after 136 years of uptime. 400 * 401 * XXX This should get it from a page shared read-only by kernel 402 * with userland, but until we implement such a mechanism, this 403 * sysctl -- incurring the cost of a syscall -- will have to 404 * serve. 405 */ 406 static unsigned 407 entropy_epoch(void) 408 { 409 static atomic_int mib0[3]; 410 static atomic_bool initialized = false; 411 int mib[3]; 412 unsigned epoch = (unsigned)-1; 413 size_t epochlen = sizeof(epoch); 414 415 /* 416 * Resolve kern.entropy.epoch if we haven't already. Cache it 417 * for the next caller. Initialization is idempotent, so it's 418 * OK if two threads do it at once. 419 */ 420 if (atomic_load_explicit(&initialized, memory_order_acquire)) { 421 mib[0] = atomic_load_explicit(&mib0[0], memory_order_relaxed); 422 mib[1] = atomic_load_explicit(&mib0[1], memory_order_relaxed); 423 mib[2] = atomic_load_explicit(&mib0[2], memory_order_relaxed); 424 } else { 425 size_t nmib = __arraycount(mib); 426 427 if (sysctlnametomib("kern.entropy.epoch", mib, &nmib) == -1) 428 return (unsigned)-1; 429 if (nmib != __arraycount(mib)) 430 return (unsigned)-1; 431 atomic_store_explicit(&mib0[0], mib[0], memory_order_relaxed); 432 atomic_store_explicit(&mib0[1], mib[1], memory_order_relaxed); 433 atomic_store_explicit(&mib0[2], mib[2], memory_order_relaxed); 434 atomic_store_explicit(&initialized, true, 435 memory_order_release); 436 } 437 438 if (sysctl(mib, __arraycount(mib), &epoch, &epochlen, NULL, 0) == -1) 439 return (unsigned)-1; 440 if (epochlen != sizeof(epoch)) 441 return (unsigned)-1; 442 443 return epoch; 444 } 445 446 /* arc4random state: per-thread, per-process (zeroed in child on fork) */ 447 448 static void 449 arc4random_prng_addrandom(struct arc4random_prng *prng, const void *data, 450 size_t datalen) 451 { 452 const int mib[] = { CTL_KERN, KERN_ARND }; 453 SHA256_CTX ctx; 454 uint8_t buf[crypto_prng_SEEDBYTES]; 455 size_t buflen = sizeof buf; 456 unsigned epoch = entropy_epoch(); 457 458 __CTASSERT(sizeof buf == SHA256_DIGEST_LENGTH); 459 460 SHA256_Init(&ctx); 461 462 crypto_prng_buf(&prng->arc4_prng, buf, sizeof buf); 463 SHA256_Update(&ctx, buf, sizeof buf); 464 465 if (sysctl(mib, (u_int)__arraycount(mib), buf, &buflen, NULL, 0) == -1) 466 abort(); 467 if (buflen != sizeof buf) 468 abort(); 469 SHA256_Update(&ctx, buf, sizeof buf); 470 471 if (data != NULL) 472 SHA256_Update(&ctx, data, datalen); 473 474 SHA256_Final(buf, &ctx); 475 (void)explicit_memset(&ctx, 0, sizeof ctx); 476 477 /* reseed(SHA256(prng() || sysctl(KERN_ARND) || data)) */ 478 crypto_prng_seed(&prng->arc4_prng, buf); 479 (void)explicit_memset(buf, 0, sizeof buf); 480 prng->arc4_epoch = epoch; 481 } 482 483 #ifdef _REENTRANT 484 static struct arc4random_prng * 485 arc4random_prng_create(void) 486 { 487 struct arc4random_prng *prng; 488 const size_t size = roundup(sizeof(*prng), sysconf(_SC_PAGESIZE)); 489 490 prng = mmap(NULL, size, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANON, -1, 491 0); 492 if (prng == MAP_FAILED) 493 goto fail0; 494 if (minherit(prng, size, MAP_INHERIT_ZERO) == -1) 495 goto fail1; 496 497 return prng; 498 499 fail1: (void)munmap(prng, size); 500 fail0: return NULL; 501 } 502 #endif 503 504 #ifdef _REENTRANT 505 static void 506 arc4random_prng_destroy(struct arc4random_prng *prng) 507 { 508 const size_t size = roundup(sizeof(*prng), sysconf(_SC_PAGESIZE)); 509 510 (void)explicit_memset(prng, 0, sizeof(*prng)); 511 (void)munmap(prng, size); 512 } 513 #endif 514 515 /* Library state */ 516 517 struct arc4random_global_state arc4random_global = { 518 #ifdef _REENTRANT 519 .lock = MUTEX_INITIALIZER, 520 #endif 521 .once = ONCE_INITIALIZER, 522 }; 523 524 static void 525 arc4random_atfork_prepare(void) 526 { 527 528 mutex_lock(&arc4random_global.lock); 529 (void)explicit_memset(&arc4random_global.prng, 0, 530 sizeof arc4random_global.prng); 531 } 532 533 static void 534 arc4random_atfork_parent(void) 535 { 536 537 mutex_unlock(&arc4random_global.lock); 538 } 539 540 static void 541 arc4random_atfork_child(void) 542 { 543 544 mutex_unlock(&arc4random_global.lock); 545 } 546 547 #ifdef _REENTRANT 548 static void 549 arc4random_tsd_destructor(void *p) 550 { 551 struct arc4random_prng *const prng = p; 552 553 arc4random_prng_destroy(prng); 554 } 555 #endif 556 557 static void 558 arc4random_initialize(void) 559 { 560 561 /* 562 * If the crypto software is broken, abort -- something is 563 * severely wrong with this process image. 564 */ 565 if (crypto_core_selftest() != 0) 566 abort(); 567 568 /* 569 * Set up a pthread_atfork handler to lock the global state 570 * around fork so that if forked children can't use the 571 * per-thread state, they can take the lock and use the global 572 * state without deadlock. 573 */ 574 if (pthread_atfork(&arc4random_atfork_prepare, 575 &arc4random_atfork_parent, &arc4random_atfork_child) 576 != 0) 577 abort(); 578 579 /* 580 * For multithreaded builds, try to allocate a per-thread PRNG 581 * state to avoid contention due to arc4random. 582 */ 583 #ifdef _REENTRANT 584 if (thr_keycreate(&arc4random_global.thread_key, 585 &arc4random_tsd_destructor) == 0) 586 arc4random_global.per_thread = true; 587 #endif 588 589 /* 590 * Note that the arc4random library state has been initialized 591 * for the sake of automatic tests. 592 */ 593 arc4random_global.initialized = true; 594 } 595 596 static struct arc4random_prng * 597 arc4random_prng_get(void) 598 { 599 struct arc4random_prng *prng = NULL; 600 601 /* Make sure the library is initialized. */ 602 thr_once(&arc4random_global.once, &arc4random_initialize); 603 604 #ifdef _REENTRANT 605 /* Get or create the per-thread PRNG state. */ 606 prng = __predict_true(arc4random_global.per_thread) 607 ? thr_getspecific(arc4random_global.thread_key) 608 : NULL; 609 if (__predict_false(prng == NULL) && arc4random_global.per_thread) { 610 prng = arc4random_prng_create(); 611 thr_setspecific(arc4random_global.thread_key, prng); 612 } 613 #endif 614 615 /* If we can't create it, fall back to the global PRNG. */ 616 if (__predict_false(prng == NULL)) { 617 mutex_lock(&arc4random_global.lock); 618 prng = &arc4random_global.prng; 619 } 620 621 /* Guarantee the PRNG is seeded. */ 622 if (__predict_false(prng->arc4_epoch != entropy_epoch())) 623 arc4random_prng_addrandom(prng, NULL, 0); 624 625 return prng; 626 } 627 628 static void 629 arc4random_prng_put(struct arc4random_prng *prng) 630 { 631 632 /* If we had fallen back to the global PRNG, unlock it. */ 633 if (__predict_false(prng == &arc4random_global.prng)) 634 mutex_unlock(&arc4random_global.lock); 635 } 636 637 /* Public API */ 638 639 uint32_t 640 arc4random(void) 641 { 642 struct arc4random_prng *prng; 643 uint32_t v; 644 645 prng = arc4random_prng_get(); 646 crypto_prng_buf(&prng->arc4_prng, &v, sizeof v); 647 arc4random_prng_put(prng); 648 649 return v; 650 } 651 652 void 653 arc4random_buf(void *buf, size_t len) 654 { 655 struct arc4random_prng *prng; 656 657 if (len <= crypto_prng_MAXOUTPUTBYTES) { 658 prng = arc4random_prng_get(); 659 crypto_prng_buf(&prng->arc4_prng, buf, len); 660 arc4random_prng_put(prng); 661 } else { 662 uint8_t seed[crypto_onetimestream_SEEDBYTES]; 663 664 prng = arc4random_prng_get(); 665 crypto_prng_buf(&prng->arc4_prng, seed, sizeof seed); 666 arc4random_prng_put(prng); 667 668 crypto_onetimestream(seed, buf, len); 669 (void)explicit_memset(seed, 0, sizeof seed); 670 } 671 } 672 673 uint32_t 674 arc4random_uniform(uint32_t bound) 675 { 676 struct arc4random_prng *prng; 677 uint32_t minimum, r; 678 679 /* 680 * We want a uniform random choice in [0, n), and arc4random() 681 * makes a uniform random choice in [0, 2^32). If we reduce 682 * that modulo n, values in [0, 2^32 mod n) will be represented 683 * slightly more than values in [2^32 mod n, n). Instead we 684 * choose only from [2^32 mod n, 2^32) by rejecting samples in 685 * [0, 2^32 mod n), to avoid counting the extra representative 686 * of [0, 2^32 mod n). To compute 2^32 mod n, note that 687 * 688 * 2^32 mod n = 2^32 mod n - 0 689 * = 2^32 mod n - n mod n 690 * = (2^32 - n) mod n, 691 * 692 * the last of which is what we compute in 32-bit arithmetic. 693 */ 694 minimum = (-bound % bound); 695 696 prng = arc4random_prng_get(); 697 do crypto_prng_buf(&prng->arc4_prng, &r, sizeof r); 698 while (__predict_false(r < minimum)); 699 arc4random_prng_put(prng); 700 701 return (r % bound); 702 } 703 704 void 705 arc4random_stir(void) 706 { 707 struct arc4random_prng *prng; 708 709 prng = arc4random_prng_get(); 710 arc4random_prng_addrandom(prng, NULL, 0); 711 arc4random_prng_put(prng); 712 } 713 714 /* 715 * Silly signature here is for hysterical raisins. Should instead be 716 * const void *data and size_t datalen. 717 */ 718 void 719 arc4random_addrandom(u_char *data, int datalen) 720 { 721 struct arc4random_prng *prng; 722 723 _DIAGASSERT(0 <= datalen); 724 725 prng = arc4random_prng_get(); 726 arc4random_prng_addrandom(prng, data, datalen); 727 arc4random_prng_put(prng); 728 } 729 730 #ifdef _ARC4RANDOM_TEST 731 732 #include <sys/wait.h> 733 734 #include <err.h> 735 #include <stdio.h> 736 737 int 738 main(int argc __unused, char **argv __unused) 739 { 740 unsigned char gubbish[] = "random gubbish"; 741 const uint8_t zero64[64] = {0}; 742 uint8_t buf[2048]; 743 unsigned i, a, n; 744 745 /* Test arc4random: should not be deterministic. */ 746 if (printf("arc4random: %08"PRIx32"\n", arc4random()) < 0) 747 err(1, "printf"); 748 749 /* Test stirring: should definitely not be deterministic. */ 750 arc4random_stir(); 751 752 /* Test small buffer. */ 753 arc4random_buf(buf, 8); 754 if (printf("arc4randombuf small:") < 0) 755 err(1, "printf"); 756 for (i = 0; i < 8; i++) 757 if (printf(" %02x", buf[i]) < 0) 758 err(1, "printf"); 759 if (printf("\n") < 0) 760 err(1, "printf"); 761 762 /* Test addrandom: should not make the rest deterministic. */ 763 arc4random_addrandom(gubbish, sizeof gubbish); 764 765 /* Test large buffer. */ 766 arc4random_buf(buf, sizeof buf); 767 if (printf("arc4randombuf_large:") < 0) 768 err(1, "printf"); 769 for (i = 0; i < sizeof buf; i++) 770 if (printf(" %02x", buf[i]) < 0) 771 err(1, "printf"); 772 if (printf("\n") < 0) 773 err(1, "printf"); 774 775 /* Test misaligned small and large. */ 776 for (a = 0; a < 64; a++) { 777 for (n = a; n < sizeof buf; n++) { 778 (void)memset(buf, 0, sizeof buf); 779 arc4random_buf(buf, n - a); 780 if (memcmp(buf + n - a, zero64, a) != 0) 781 errx(1, "arc4random buffer overflow 0"); 782 783 (void)memset(buf, 0, sizeof buf); 784 arc4random_buf(buf + a, n - a); 785 if (memcmp(buf, zero64, a) != 0) 786 errx(1, "arc4random buffer overflow 1"); 787 788 if ((2*a) <= n) { 789 (void)memset(buf, 0, sizeof buf); 790 arc4random_buf(buf + a, n - a - a); 791 if (memcmp(buf + n - a, zero64, a) != 0) 792 errx(1, 793 "arc4random buffer overflow 2"); 794 } 795 } 796 } 797 798 /* Test fork-safety. */ 799 { 800 pid_t pid, rpid; 801 int status; 802 803 pid = fork(); 804 switch (pid) { 805 case -1: 806 err(1, "fork"); 807 case 0: { 808 /* 809 * Verify the epoch has been set to zero by fork. 810 */ 811 struct arc4random_prng *prng = NULL; 812 #ifdef _REENTRANT 813 prng = thr_getspecific(arc4random_global.thread_key); 814 #endif 815 if (prng == NULL) 816 prng = &arc4random_global.prng; 817 _exit(prng->arc4_epoch != 0); 818 } 819 default: 820 rpid = waitpid(pid, &status, 0); 821 if (rpid == -1) 822 err(1, "waitpid"); 823 if (rpid != pid) 824 errx(1, "waitpid returned wrong pid" 825 ": %"PRIdMAX" != %"PRIdMAX, 826 (intmax_t)rpid, 827 (intmax_t)pid); 828 if (WIFEXITED(status)) { 829 if (WEXITSTATUS(status) != 0) 830 errx(1, "child exited with %d", 831 WEXITSTATUS(status)); 832 } else if (WIFSIGNALED(status)) { 833 errx(1, "child terminated on signal %d", 834 WTERMSIG(status)); 835 } else { 836 errx(1, "child died mysteriously: %d", status); 837 } 838 } 839 } 840 841 /* XXX Test multithreaded fork safety...? */ 842 843 return 0; 844 } 845 #endif 846
Indexes created Tue Sep 23 07:09:52 GMT 2025