arc4random.c revision 1.35
1 /* $NetBSD: arc4random.c,v 1.35 2024/08/26 15:19:22 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 or thr_keycreate fail, or 47 * (c) sysctl(KERN_ARND) fails when reseeding the PRNG. 48 * 49 * The crypto self-test, pthread_atfork, and thr_keycreate occur only 50 * once, on the first use of any of the arc4random(3) API. KERN_ARND 51 * is unlikely to fail later unless the kernel is seriously broken. 52 */ 53 54 #include <sys/cdefs.h> 55 __RCSID("$NetBSD: arc4random.c,v 1.35 2024/08/26 15:19:22 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 #ifdef __weak_alias 76 __weak_alias(arc4random,_arc4random) 77 __weak_alias(arc4random_addrandom,_arc4random_addrandom) 78 __weak_alias(arc4random_buf,_arc4random_buf) 79 __weak_alias(arc4random_stir,_arc4random_stir) 80 __weak_alias(arc4random_uniform,_arc4random_uniform) 81 #endif 82 83 /* 84 * For standard ChaCha, use le32dec/le32enc. We don't need that for 85 * the purposes of a nondeterministic random number generator -- we 86 * don't need to be bit-for-bit compatible over any wire. 87 */ 88 89 static inline uint32_t 90 crypto_le32dec(const void *p) 91 { 92 uint32_t v; 93 94 (void)memcpy(&v, p, sizeof v); 95 96 return v; 97 } 98 99 static inline void 100 crypto_le32enc(void *p, uint32_t v) 101 { 102 103 (void)memcpy(p, &v, sizeof v); 104 } 105 106 /* ChaCha core */ 107 108 #define crypto_core_OUTPUTBYTES 64 109 #define crypto_core_INPUTBYTES 16 110 #define crypto_core_KEYBYTES 32 111 #define crypto_core_CONSTBYTES 16 112 113 #define crypto_core_ROUNDS 20 114 115 static uint32_t 116 rotate(uint32_t u, unsigned c) 117 { 118 119 return (u << c) | (u >> (32 - c)); 120 } 121 122 #define QUARTERROUND(a, b, c, d) do { \ 123 (a) += (b); (d) ^= (a); (d) = rotate((d), 16); \ 124 (c) += (d); (b) ^= (c); (b) = rotate((b), 12); \ 125 (a) += (b); (d) ^= (a); (d) = rotate((d), 8); \ 126 (c) += (d); (b) ^= (c); (b) = rotate((b), 7); \ 127 } while (0) 128 129 static const uint8_t crypto_core_constant32[16] = "expand 32-byte k"; 130 131 static void 132 crypto_core(uint8_t *out, const uint8_t *in, const uint8_t *k, 133 const uint8_t *c) 134 { 135 uint32_t x0,x1,x2,x3,x4,x5,x6,x7,x8,x9,x10,x11,x12,x13,x14,x15; 136 uint32_t j0,j1,j2,j3,j4,j5,j6,j7,j8,j9,j10,j11,j12,j13,j14,j15; 137 int i; 138 139 j0 = x0 = crypto_le32dec(c + 0); 140 j1 = x1 = crypto_le32dec(c + 4); 141 j2 = x2 = crypto_le32dec(c + 8); 142 j3 = x3 = crypto_le32dec(c + 12); 143 j4 = x4 = crypto_le32dec(k + 0); 144 j5 = x5 = crypto_le32dec(k + 4); 145 j6 = x6 = crypto_le32dec(k + 8); 146 j7 = x7 = crypto_le32dec(k + 12); 147 j8 = x8 = crypto_le32dec(k + 16); 148 j9 = x9 = crypto_le32dec(k + 20); 149 j10 = x10 = crypto_le32dec(k + 24); 150 j11 = x11 = crypto_le32dec(k + 28); 151 j12 = x12 = crypto_le32dec(in + 0); 152 j13 = x13 = crypto_le32dec(in + 4); 153 j14 = x14 = crypto_le32dec(in + 8); 154 j15 = x15 = crypto_le32dec(in + 12); 155 156 for (i = crypto_core_ROUNDS; i > 0; i -= 2) { 157 QUARTERROUND( x0, x4, x8,x12); 158 QUARTERROUND( x1, x5, x9,x13); 159 QUARTERROUND( x2, x6,x10,x14); 160 QUARTERROUND( x3, x7,x11,x15); 161 QUARTERROUND( x0, x5,x10,x15); 162 QUARTERROUND( x1, x6,x11,x12); 163 QUARTERROUND( x2, x7, x8,x13); 164 QUARTERROUND( x3, x4, x9,x14); 165 } 166 167 crypto_le32enc(out + 0, x0 + j0); 168 crypto_le32enc(out + 4, x1 + j1); 169 crypto_le32enc(out + 8, x2 + j2); 170 crypto_le32enc(out + 12, x3 + j3); 171 crypto_le32enc(out + 16, x4 + j4); 172 crypto_le32enc(out + 20, x5 + j5); 173 crypto_le32enc(out + 24, x6 + j6); 174 crypto_le32enc(out + 28, x7 + j7); 175 crypto_le32enc(out + 32, x8 + j8); 176 crypto_le32enc(out + 36, x9 + j9); 177 crypto_le32enc(out + 40, x10 + j10); 178 crypto_le32enc(out + 44, x11 + j11); 179 crypto_le32enc(out + 48, x12 + j12); 180 crypto_le32enc(out + 52, x13 + j13); 181 crypto_le32enc(out + 56, x14 + j14); 182 crypto_le32enc(out + 60, x15 + j15); 183 } 184 185 /* ChaCha self-test */ 186 187 #ifdef _DIAGNOSTIC 188 189 /* 190 * Test vector for ChaCha20 from 191 * <http://tools.ietf.org/html/draft-strombergson-chacha-test-vectors-00>, 192 * test vectors for ChaCha12 and ChaCha8 and for big-endian machines 193 * generated by the same crypto_core code with crypto_core_ROUNDS and 194 * crypto_le32enc/dec varied. 195 */ 196 197 static const uint8_t crypto_core_selftest_vector[64] = { 198 #if _BYTE_ORDER == _LITTLE_ENDIAN 199 # if crypto_core_ROUNDS == 8 200 0x3e,0x00,0xef,0x2f,0x89,0x5f,0x40,0xd6, 201 0x7f,0x5b,0xb8,0xe8,0x1f,0x09,0xa5,0xa1, 202 0x2c,0x84,0x0e,0xc3,0xce,0x9a,0x7f,0x3b, 203 0x18,0x1b,0xe1,0x88,0xef,0x71,0x1a,0x1e, 204 0x98,0x4c,0xe1,0x72,0xb9,0x21,0x6f,0x41, 205 0x9f,0x44,0x53,0x67,0x45,0x6d,0x56,0x19, 206 0x31,0x4a,0x42,0xa3,0xda,0x86,0xb0,0x01, 207 0x38,0x7b,0xfd,0xb8,0x0e,0x0c,0xfe,0x42, 208 # elif crypto_core_ROUNDS == 12 209 0x9b,0xf4,0x9a,0x6a,0x07,0x55,0xf9,0x53, 210 0x81,0x1f,0xce,0x12,0x5f,0x26,0x83,0xd5, 211 0x04,0x29,0xc3,0xbb,0x49,0xe0,0x74,0x14, 212 0x7e,0x00,0x89,0xa5,0x2e,0xae,0x15,0x5f, 213 0x05,0x64,0xf8,0x79,0xd2,0x7a,0xe3,0xc0, 214 0x2c,0xe8,0x28,0x34,0xac,0xfa,0x8c,0x79, 215 0x3a,0x62,0x9f,0x2c,0xa0,0xde,0x69,0x19, 216 0x61,0x0b,0xe8,0x2f,0x41,0x13,0x26,0xbe, 217 # elif crypto_core_ROUNDS == 20 218 0x76,0xb8,0xe0,0xad,0xa0,0xf1,0x3d,0x90, 219 0x40,0x5d,0x6a,0xe5,0x53,0x86,0xbd,0x28, 220 0xbd,0xd2,0x19,0xb8,0xa0,0x8d,0xed,0x1a, 221 0xa8,0x36,0xef,0xcc,0x8b,0x77,0x0d,0xc7, 222 0xda,0x41,0x59,0x7c,0x51,0x57,0x48,0x8d, 223 0x77,0x24,0xe0,0x3f,0xb8,0xd8,0x4a,0x37, 224 0x6a,0x43,0xb8,0xf4,0x15,0x18,0xa1,0x1c, 225 0xc3,0x87,0xb6,0x69,0xb2,0xee,0x65,0x86, 226 # else 227 # error crypto_core_ROUNDS must be 8, 12, or 20. 228 # endif 229 #elif _BYTE_ORDER == _BIG_ENDIAN 230 # if crypto_core_ROUNDS == 8 231 0x9a,0x13,0x07,0xe3,0x38,0x18,0x9e,0x99, 232 0x15,0x37,0x16,0x4d,0x04,0xe6,0x48,0x9a, 233 0x07,0xd6,0xe8,0x7a,0x02,0xf9,0xf5,0xc7, 234 0x3f,0xa9,0xc2,0x0a,0xe1,0xc6,0x62,0xea, 235 0x80,0xaf,0xb6,0x51,0xca,0x52,0x43,0x87, 236 0xe3,0xa6,0xa6,0x61,0x11,0xf5,0xe6,0xcf, 237 0x09,0x0f,0xdc,0x9d,0xc3,0xc3,0xbb,0x43, 238 0xd7,0xfa,0x70,0x42,0xbf,0xa5,0xee,0xa2, 239 # elif crypto_core_ROUNDS == 12 240 0xcf,0x6c,0x16,0x48,0xbf,0xf4,0xba,0x85, 241 0x32,0x69,0xd3,0x98,0xc8,0x7d,0xcd,0x3f, 242 0xdc,0x76,0x6b,0xa2,0x7b,0xcb,0x17,0x4d, 243 0x05,0xda,0xdd,0xd8,0x62,0x54,0xbf,0xe0, 244 0x65,0xed,0x0e,0xf4,0x01,0x7e,0x3c,0x05, 245 0x35,0xb2,0x7a,0x60,0xf3,0x8f,0x12,0x33, 246 0x24,0x60,0xcd,0x85,0xfe,0x4c,0xf3,0x39, 247 0xb1,0x0e,0x3e,0xe0,0xba,0xa6,0x2f,0xa9, 248 # elif crypto_core_ROUNDS == 20 249 0x83,0x8b,0xf8,0x75,0xf7,0xde,0x9d,0x8c, 250 0x33,0x14,0x72,0x28,0xd1,0xbe,0x88,0xe5, 251 0x94,0xb5,0xed,0xb8,0x56,0xb5,0x9e,0x0c, 252 0x64,0x6a,0xaf,0xd9,0xa7,0x49,0x10,0x59, 253 0xba,0x3a,0x82,0xf8,0x4a,0x70,0x9c,0x00, 254 0x82,0x2c,0xae,0xc6,0xd7,0x1c,0x2e,0xda, 255 0x2a,0xfb,0x61,0x70,0x2b,0xd1,0xbf,0x8b, 256 0x95,0xbc,0x23,0xb6,0x4b,0x60,0x02,0xec, 257 # else 258 # error crypto_core_ROUNDS must be 8, 12, or 20. 259 # endif 260 #else 261 # error Byte order must be little-endian or big-endian. 262 #endif 263 }; 264 265 static int 266 crypto_core_selftest(void) 267 { 268 const uint8_t nonce[crypto_core_INPUTBYTES] = {0}; 269 const uint8_t key[crypto_core_KEYBYTES] = {0}; 270 uint8_t block[64]; 271 unsigned i; 272 273 crypto_core(block, nonce, key, crypto_core_constant32); 274 for (i = 0; i < 64; i++) { 275 if (block[i] != crypto_core_selftest_vector[i]) 276 return EIO; 277 } 278 279 return 0; 280 } 281 282 #else /* !_DIAGNOSTIC */ 283 284 static int 285 crypto_core_selftest(void) 286 { 287 288 return 0; 289 } 290 291 #endif 292 293 /* PRNG */ 294 295 /* 296 * For a state s, rather than use ChaCha20 as a stream cipher to 297 * generate the concatenation ChaCha20_s(0) || ChaCha20_s(1) || ..., we 298 * split ChaCha20_s(0) into s' || x and yield x for the first request, 299 * split ChaCha20_s'(0) into s'' || y and yield y for the second 300 * request, &c. This provides backtracking resistance: an attacker who 301 * finds s'' can't recover s' or x. 302 */ 303 304 #define crypto_prng_SEEDBYTES crypto_core_KEYBYTES 305 #define crypto_prng_MAXOUTPUTBYTES \ 306 (crypto_core_OUTPUTBYTES - crypto_prng_SEEDBYTES) 307 308 struct crypto_prng { 309 uint8_t state[crypto_prng_SEEDBYTES]; 310 }; 311 312 static void 313 crypto_prng_seed(struct crypto_prng *prng, const void *seed) 314 { 315 316 (void)memcpy(prng->state, seed, crypto_prng_SEEDBYTES); 317 } 318 319 static void 320 crypto_prng_buf(struct crypto_prng *prng, void *buf, size_t n) 321 { 322 const uint8_t nonce[crypto_core_INPUTBYTES] = {0}; 323 uint8_t output[crypto_core_OUTPUTBYTES]; 324 325 _DIAGASSERT(n <= crypto_prng_MAXOUTPUTBYTES); 326 __CTASSERT(sizeof prng->state + crypto_prng_MAXOUTPUTBYTES 327 <= sizeof output); 328 329 crypto_core(output, nonce, prng->state, crypto_core_constant32); 330 (void)memcpy(prng->state, output, sizeof prng->state); 331 (void)memcpy(buf, output + sizeof prng->state, n); 332 (void)explicit_memset(output, 0, sizeof output); 333 } 334 335 /* One-time stream: expand short single-use secret into long secret */ 336 337 #define crypto_onetimestream_SEEDBYTES crypto_core_KEYBYTES 338 339 static void 340 crypto_onetimestream(const void *seed, void *buf, size_t n) 341 { 342 uint32_t nonce[crypto_core_INPUTBYTES / sizeof(uint32_t)] = {0}; 343 uint8_t block[crypto_core_OUTPUTBYTES]; 344 uint8_t *p8, *p32; 345 const uint8_t *nonce8 = (const uint8_t *)(void *)nonce; 346 size_t ni, nb, nf; 347 348 /* 349 * Guarantee we can generate up to n bytes. We have 350 * 2^(8*INPUTBYTES) possible inputs yielding output of 351 * OUTPUTBYTES*2^(8*INPUTBYTES) bytes. It suffices to require 352 * that sizeof n > (1/CHAR_BIT) log_2 n be less than 353 * (1/CHAR_BIT) log_2 of the total output stream length. We 354 * have 355 * 356 * log_2 (o 2^(8 i)) = log_2 o + log_2 2^(8 i) 357 * = log_2 o + 8 i. 358 */ 359 #ifndef __lint__ 360 __CTASSERT(CHAR_BIT * sizeof n <= (ilog2(crypto_core_OUTPUTBYTES) + 361 8 * crypto_core_INPUTBYTES)); 362 #endif 363 364 p8 = buf; 365 p32 = (uint8_t *)roundup2((uintptr_t)p8, 4); 366 ni = p32 - p8; 367 if (n < ni) 368 ni = n; 369 nb = (n - ni) / sizeof block; 370 nf = (n - ni) % sizeof block; 371 372 _DIAGASSERT(((uintptr_t)p32 & 3) == 0); 373 _DIAGASSERT(ni <= n); 374 _DIAGASSERT(nb <= (n / sizeof block)); 375 _DIAGASSERT(nf <= n); 376 _DIAGASSERT(n == (ni + (nb * sizeof block) + nf)); 377 _DIAGASSERT(ni < 4); 378 _DIAGASSERT(nf < sizeof block); 379 380 if (ni) { 381 crypto_core(block, nonce8, seed, crypto_core_constant32); 382 nonce[0]++; 383 (void)memcpy(p8, block, ni); 384 } 385 while (nb--) { 386 crypto_core(p32, nonce8, seed, crypto_core_constant32); 387 if (++nonce[0] == 0) 388 nonce[1]++; 389 p32 += crypto_core_OUTPUTBYTES; 390 } 391 if (nf) { 392 crypto_core(block, nonce8, seed, crypto_core_constant32); 393 if (++nonce[0] == 0) 394 nonce[1]++; 395 (void)memcpy(p32, block, nf); 396 } 397 398 if (ni | nf) 399 (void)explicit_memset(block, 0, sizeof block); 400 } 401 402 /* 403 * entropy_epoch() 404 * 405 * Return the current entropy epoch, from the sysctl node 406 * kern.entropy.epoch. 407 * 408 * The entropy epoch is never zero. Initially, or on error, it is 409 * (unsigned)-1. It may wrap around but it skips (unsigned)-1 and 410 * 0 when it does. Changes happen less than once per second, so 411 * wraparound will only affect systems after 136 years of uptime. 412 * 413 * XXX This should get it from a page shared read-only by kernel 414 * with userland, but until we implement such a mechanism, this 415 * sysctl -- incurring the cost of a syscall -- will have to 416 * serve. 417 */ 418 static unsigned 419 entropy_epoch(void) 420 { 421 static atomic_int mib0[3]; 422 static atomic_bool initialized = false; 423 int mib[3]; 424 unsigned epoch = -1; 425 size_t epochlen = sizeof(epoch); 426 427 /* 428 * Resolve kern.entropy.epoch if we haven't already. Cache it 429 * for the next caller. Initialization is idempotent, so it's 430 * OK if two threads do it at once. 431 */ 432 if (atomic_load_explicit(&initialized, memory_order_acquire)) { 433 mib[0] = atomic_load_explicit(&mib0[0], memory_order_relaxed); 434 mib[1] = atomic_load_explicit(&mib0[1], memory_order_relaxed); 435 mib[2] = atomic_load_explicit(&mib0[2], memory_order_relaxed); 436 } else { 437 size_t nmib = __arraycount(mib); 438 439 if (sysctlnametomib("kern.entropy.epoch", mib, &nmib) == -1) 440 return -1; 441 if (nmib != __arraycount(mib)) 442 return -1; 443 atomic_store_explicit(&mib0[0], mib[0], memory_order_relaxed); 444 atomic_store_explicit(&mib0[1], mib[1], memory_order_relaxed); 445 atomic_store_explicit(&mib0[2], mib[2], memory_order_relaxed); 446 atomic_store_explicit(&initialized, true, 447 memory_order_release); 448 } 449 450 if (sysctl(mib, __arraycount(mib), &epoch, &epochlen, NULL, 0) == -1) 451 return -1; 452 if (epochlen != sizeof(epoch)) 453 return -1; 454 455 return epoch; 456 } 457 458 /* arc4random state: per-thread, per-process (zeroed in child on fork) */ 459 460 struct arc4random_prng { 461 struct crypto_prng arc4_prng; 462 unsigned arc4_epoch; 463 }; 464 465 static void 466 arc4random_prng_addrandom(struct arc4random_prng *prng, const void *data, 467 size_t datalen) 468 { 469 const int mib[] = { CTL_KERN, KERN_ARND }; 470 SHA256_CTX ctx; 471 uint8_t buf[crypto_prng_SEEDBYTES]; 472 size_t buflen = sizeof buf; 473 unsigned epoch = entropy_epoch(); 474 475 __CTASSERT(sizeof buf == SHA256_DIGEST_LENGTH); 476 477 SHA256_Init(&ctx); 478 479 crypto_prng_buf(&prng->arc4_prng, buf, sizeof buf); 480 SHA256_Update(&ctx, buf, sizeof buf); 481 482 if (sysctl(mib, (u_int)__arraycount(mib), buf, &buflen, NULL, 0) == -1) 483 abort(); 484 if (buflen != sizeof buf) 485 abort(); 486 SHA256_Update(&ctx, buf, sizeof buf); 487 488 if (data != NULL) 489 SHA256_Update(&ctx, data, datalen); 490 491 SHA256_Final(buf, &ctx); 492 (void)explicit_memset(&ctx, 0, sizeof ctx); 493 494 /* reseed(SHA256(prng() || sysctl(KERN_ARND) || data)) */ 495 crypto_prng_seed(&prng->arc4_prng, buf); 496 (void)explicit_memset(buf, 0, sizeof buf); 497 prng->arc4_epoch = epoch; 498 } 499 500 #ifdef _REENTRANT 501 static struct arc4random_prng * 502 arc4random_prng_create(void) 503 { 504 struct arc4random_prng *prng; 505 const size_t size = roundup(sizeof(*prng), sysconf(_SC_PAGESIZE)); 506 507 prng = mmap(NULL, size, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANON, -1, 508 0); 509 if (prng == MAP_FAILED) 510 goto fail0; 511 if (minherit(prng, size, MAP_INHERIT_ZERO) == -1) 512 goto fail1; 513 514 return prng; 515 516 fail1: (void)munmap(prng, size); 517 fail0: return NULL; 518 } 519 #endif 520 521 #ifdef _REENTRANT 522 static void 523 arc4random_prng_destroy(struct arc4random_prng *prng) 524 { 525 const size_t size = roundup(sizeof(*prng), sysconf(_SC_PAGESIZE)); 526 527 (void)explicit_memset(prng, 0, sizeof(*prng)); 528 (void)munmap(prng, size); 529 } 530 #endif 531 532 /* Library state */ 533 534 static struct arc4random_global { 535 #ifdef _REENTRANT 536 mutex_t lock; 537 thread_key_t thread_key; 538 #endif 539 struct arc4random_prng prng; 540 bool initialized; 541 } arc4random_global = { 542 #ifdef _REENTRANT 543 .lock = MUTEX_INITIALIZER, 544 #endif 545 .initialized = false, 546 }; 547 548 static void 549 arc4random_atfork_prepare(void) 550 { 551 552 mutex_lock(&arc4random_global.lock); 553 (void)explicit_memset(&arc4random_global.prng, 0, 554 sizeof arc4random_global.prng); 555 } 556 557 static void 558 arc4random_atfork_parent(void) 559 { 560 561 mutex_unlock(&arc4random_global.lock); 562 } 563 564 static void 565 arc4random_atfork_child(void) 566 { 567 568 mutex_unlock(&arc4random_global.lock); 569 } 570 571 #ifdef _REENTRANT 572 static void 573 arc4random_tsd_destructor(void *p) 574 { 575 struct arc4random_prng *const prng = p; 576 577 arc4random_prng_destroy(prng); 578 } 579 #endif 580 581 static void 582 arc4random_initialize(void) 583 { 584 585 mutex_lock(&arc4random_global.lock); 586 if (!arc4random_global.initialized) { 587 if (crypto_core_selftest() != 0) 588 abort(); 589 if (pthread_atfork(&arc4random_atfork_prepare, 590 &arc4random_atfork_parent, &arc4random_atfork_child) 591 != 0) 592 abort(); 593 #ifdef _REENTRANT 594 if (thr_keycreate(&arc4random_global.thread_key, 595 &arc4random_tsd_destructor) != 0) 596 abort(); 597 #endif 598 arc4random_global.initialized = true; 599 } 600 mutex_unlock(&arc4random_global.lock); 601 } 602 603 static struct arc4random_prng * 604 arc4random_prng_get(void) 605 { 606 struct arc4random_prng *prng = NULL; 607 608 /* Make sure the library is initialized. */ 609 if (__predict_false(!arc4random_global.initialized)) 610 arc4random_initialize(); 611 612 #ifdef _REENTRANT 613 /* Get or create the per-thread PRNG state. */ 614 prng = thr_getspecific(arc4random_global.thread_key); 615 if (__predict_false(prng == NULL)) { 616 prng = arc4random_prng_create(); 617 thr_setspecific(arc4random_global.thread_key, prng); 618 } 619 #endif 620 621 /* If we can't create it, fall back to the global PRNG. */ 622 if (__predict_false(prng == NULL)) { 623 mutex_lock(&arc4random_global.lock); 624 prng = &arc4random_global.prng; 625 } 626 627 /* Guarantee the PRNG is seeded. */ 628 if (__predict_false(prng->arc4_epoch != entropy_epoch())) 629 arc4random_prng_addrandom(prng, NULL, 0); 630 631 return prng; 632 } 633 634 static void 635 arc4random_prng_put(struct arc4random_prng *prng) 636 { 637 638 /* If we had fallen back to the global PRNG, unlock it. */ 639 if (__predict_false(prng == &arc4random_global.prng)) 640 mutex_unlock(&arc4random_global.lock); 641 } 642 643 /* Public API */ 644 645 uint32_t 646 arc4random(void) 647 { 648 struct arc4random_prng *prng; 649 uint32_t v; 650 651 prng = arc4random_prng_get(); 652 crypto_prng_buf(&prng->arc4_prng, &v, sizeof v); 653 arc4random_prng_put(prng); 654 655 return v; 656 } 657 658 void 659 arc4random_buf(void *buf, size_t len) 660 { 661 struct arc4random_prng *prng; 662 663 if (len <= crypto_prng_MAXOUTPUTBYTES) { 664 prng = arc4random_prng_get(); 665 crypto_prng_buf(&prng->arc4_prng, buf, len); 666 arc4random_prng_put(prng); 667 } else { 668 uint8_t seed[crypto_onetimestream_SEEDBYTES]; 669 670 prng = arc4random_prng_get(); 671 crypto_prng_buf(&prng->arc4_prng, seed, sizeof seed); 672 arc4random_prng_put(prng); 673 674 crypto_onetimestream(seed, buf, len); 675 (void)explicit_memset(seed, 0, sizeof seed); 676 } 677 } 678 679 uint32_t 680 arc4random_uniform(uint32_t bound) 681 { 682 struct arc4random_prng *prng; 683 uint32_t minimum, r; 684 685 /* 686 * We want a uniform random choice in [0, n), and arc4random() 687 * makes a uniform random choice in [0, 2^32). If we reduce 688 * that modulo n, values in [0, 2^32 mod n) will be represented 689 * slightly more than values in [2^32 mod n, n). Instead we 690 * choose only from [2^32 mod n, 2^32) by rejecting samples in 691 * [0, 2^32 mod n), to avoid counting the extra representative 692 * of [0, 2^32 mod n). To compute 2^32 mod n, note that 693 * 694 * 2^32 mod n = 2^32 mod n - 0 695 * = 2^32 mod n - n mod n 696 * = (2^32 - n) mod n, 697 * 698 * the last of which is what we compute in 32-bit arithmetic. 699 */ 700 minimum = (-bound % bound); 701 702 prng = arc4random_prng_get(); 703 do crypto_prng_buf(&prng->arc4_prng, &r, sizeof r); 704 while (__predict_false(r < minimum)); 705 arc4random_prng_put(prng); 706 707 return (r % bound); 708 } 709 710 void 711 arc4random_stir(void) 712 { 713 struct arc4random_prng *prng; 714 715 prng = arc4random_prng_get(); 716 arc4random_prng_addrandom(prng, NULL, 0); 717 arc4random_prng_put(prng); 718 } 719 720 /* 721 * Silly signature here is for hysterical raisins. Should instead be 722 * const void *data and size_t datalen. 723 */ 724 void 725 arc4random_addrandom(u_char *data, int datalen) 726 { 727 struct arc4random_prng *prng; 728 729 _DIAGASSERT(0 <= datalen); 730 731 prng = arc4random_prng_get(); 732 arc4random_prng_addrandom(prng, data, datalen); 733 arc4random_prng_put(prng); 734 } 735 736 #ifdef _ARC4RANDOM_TEST 737 738 #include <sys/wait.h> 739 740 #include <err.h> 741 #include <stdio.h> 742 743 int 744 main(int argc __unused, char **argv __unused) 745 { 746 unsigned char gubbish[] = "random gubbish"; 747 const uint8_t zero64[64] = {0}; 748 uint8_t buf[2048]; 749 unsigned i, a, n; 750 751 /* Test arc4random: should not be deterministic. */ 752 if (printf("arc4random: %08"PRIx32"\n", arc4random()) < 0) 753 err(1, "printf"); 754 755 /* Test stirring: should definitely not be deterministic. */ 756 arc4random_stir(); 757 758 /* Test small buffer. */ 759 arc4random_buf(buf, 8); 760 if (printf("arc4randombuf small:") < 0) 761 err(1, "printf"); 762 for (i = 0; i < 8; i++) 763 if (printf(" %02x", buf[i]) < 0) 764 err(1, "printf"); 765 if (printf("\n") < 0) 766 err(1, "printf"); 767 768 /* Test addrandom: should not make the rest deterministic. */ 769 arc4random_addrandom(gubbish, sizeof gubbish); 770 771 /* Test large buffer. */ 772 arc4random_buf(buf, sizeof buf); 773 if (printf("arc4randombuf_large:") < 0) 774 err(1, "printf"); 775 for (i = 0; i < sizeof buf; i++) 776 if (printf(" %02x", buf[i]) < 0) 777 err(1, "printf"); 778 if (printf("\n") < 0) 779 err(1, "printf"); 780 781 /* Test misaligned small and large. */ 782 for (a = 0; a < 64; a++) { 783 for (n = a; n < sizeof buf; n++) { 784 (void)memset(buf, 0, sizeof buf); 785 arc4random_buf(buf, n - a); 786 if (memcmp(buf + n - a, zero64, a) != 0) 787 errx(1, "arc4random buffer overflow 0"); 788 789 (void)memset(buf, 0, sizeof buf); 790 arc4random_buf(buf + a, n - a); 791 if (memcmp(buf, zero64, a) != 0) 792 errx(1, "arc4random buffer overflow 1"); 793 794 if ((2*a) <= n) { 795 (void)memset(buf, 0, sizeof buf); 796 arc4random_buf(buf + a, n - a - a); 797 if (memcmp(buf + n - a, zero64, a) != 0) 798 errx(1, 799 "arc4random buffer overflow 2"); 800 } 801 } 802 } 803 804 /* Test fork-safety. */ 805 { 806 pid_t pid, rpid; 807 int status; 808 809 pid = fork(); 810 switch (pid) { 811 case -1: 812 err(1, "fork"); 813 case 0: 814 _exit(arc4random_prng_get()->arc4_seeded); 815 default: 816 rpid = waitpid(pid, &status, 0); 817 if (rpid == -1) 818 err(1, "waitpid"); 819 if (rpid != pid) 820 errx(1, "waitpid returned wrong pid" 821 ": %"PRIdMAX" != %"PRIdMAX, 822 (intmax_t)rpid, 823 (intmax_t)pid); 824 if (WIFEXITED(status)) { 825 if (WEXITSTATUS(status) != 0) 826 errx(1, "child exited with %d", 827 WEXITSTATUS(status)); 828 } else if (WIFSIGNALED(status)) { 829 errx(1, "child terminated on signal %d", 830 WTERMSIG(status)); 831 } else { 832 errx(1, "child died mysteriously: %d", status); 833 } 834 } 835 } 836 837 /* XXX Test multithreaded fork safety...? */ 838 839 return 0; 840 } 841 #endif 842
Indexes created Mon Sep 22 13:09:51 GMT 2025