1 /*- 2 * Copyright (c) 2017 W. Dean Freeman 3 * Copyright (c) 2013-2015 Mark R V Murray 4 * All rights reserved. 5 * 6 * Redistribution and use in source and binary forms, with or without 7 * modification, are permitted provided that the following conditions 8 * are met: 9 * 1. Redistributions of source code must retain the above copyright 10 * notice, this list of conditions and the following disclaimer 11 * in this position and unchanged. 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 */ 28 29 /* 30 * This implementation of Fortuna is based on the descriptions found in 31 * ISBN 978-0-470-47424-2 "Cryptography Engineering" by Ferguson, Schneier 32 * and Kohno ("FS&K"). 33 */ 34 35 #include <sys/cdefs.h> 36 __FBSDID("$FreeBSD$"); 37 38 #include <sys/param.h> 39 #include <sys/limits.h> 40 41 #ifdef _KERNEL 42 #include <sys/fail.h> 43 #include <sys/kernel.h> 44 #include <sys/lock.h> 45 #include <sys/malloc.h> 46 #include <sys/mutex.h> 47 #include <sys/random.h> 48 #include <sys/sdt.h> 49 #include <sys/sysctl.h> 50 #include <sys/systm.h> 51 52 #include <machine/cpu.h> 53 #else /* !_KERNEL */ 54 #include <inttypes.h> 55 #include <stdbool.h> 56 #include <stdio.h> 57 #include <stdlib.h> 58 #include <string.h> 59 #include <threads.h> 60 61 #include "unit_test.h" 62 #endif /* _KERNEL */ 63 64 #include <crypto/chacha20/chacha.h> 65 #include <crypto/rijndael/rijndael-api-fst.h> 66 #include <crypto/sha2/sha256.h> 67 68 #include <dev/random/hash.h> 69 #include <dev/random/randomdev.h> 70 #ifdef _KERNEL 71 #include <dev/random/random_harvestq.h> 72 #endif 73 #include <dev/random/uint128.h> 74 #include <dev/random/fortuna.h> 75 76 /* Defined in FS&K */ 77 #define RANDOM_FORTUNA_NPOOLS 32 /* The number of accumulation pools */ 78 #define RANDOM_FORTUNA_DEFPOOLSIZE 64 /* The default pool size/length for a (re)seed */ 79 #define RANDOM_FORTUNA_MAX_READ (1 << 20) /* Max bytes from AES before rekeying */ 80 #define RANDOM_FORTUNA_BLOCKS_PER_KEY (1 << 16) /* Max blocks from AES before rekeying */ 81 CTASSERT(RANDOM_FORTUNA_BLOCKS_PER_KEY * RANDOM_BLOCKSIZE == 82 RANDOM_FORTUNA_MAX_READ); 83 84 /* 85 * The allowable range of RANDOM_FORTUNA_DEFPOOLSIZE. The default value is above. 86 * Making RANDOM_FORTUNA_DEFPOOLSIZE too large will mean a long time between reseeds, 87 * and too small may compromise initial security but get faster reseeds. 88 */ 89 #define RANDOM_FORTUNA_MINPOOLSIZE 16 90 #define RANDOM_FORTUNA_MAXPOOLSIZE INT_MAX 91 CTASSERT(RANDOM_FORTUNA_MINPOOLSIZE <= RANDOM_FORTUNA_DEFPOOLSIZE); 92 CTASSERT(RANDOM_FORTUNA_DEFPOOLSIZE <= RANDOM_FORTUNA_MAXPOOLSIZE); 93 94 /* This algorithm (and code) presumes that RANDOM_KEYSIZE is twice as large as RANDOM_BLOCKSIZE */ 95 CTASSERT(RANDOM_BLOCKSIZE == sizeof(uint128_t)); 96 CTASSERT(RANDOM_KEYSIZE == 2*RANDOM_BLOCKSIZE); 97 98 /* Probes for dtrace(1) */ 99 #ifdef _KERNEL 100 SDT_PROVIDER_DECLARE(random); 101 SDT_PROVIDER_DEFINE(random); 102 SDT_PROBE_DEFINE2(random, fortuna, event_processor, debug, "u_int", "struct fs_pool *"); 103 #endif /* _KERNEL */ 104 105 /* 106 * This is the beastie that needs protecting. It contains all of the 107 * state that we are excited about. Exactly one is instantiated. 108 */ 109 static struct fortuna_state { 110 struct fs_pool { /* P_i */ 111 u_int fsp_length; /* Only the first one is used by Fortuna */ 112 struct randomdev_hash fsp_hash; 113 } fs_pool[RANDOM_FORTUNA_NPOOLS]; 114 u_int fs_reseedcount; /* ReseedCnt */ 115 uint128_t fs_counter; /* C */ 116 union randomdev_key fs_key; /* K */ 117 u_int fs_minpoolsize; /* Extras */ 118 /* Extras for the OS */ 119 #ifdef _KERNEL 120 /* For use when 'pacing' the reseeds */ 121 sbintime_t fs_lasttime; 122 #endif 123 /* Reseed lock */ 124 mtx_t fs_mtx; 125 } fortuna_state; 126 127 /* 128 * This knob enables or disables the "Concurrent Reads" Fortuna feature. 129 * 130 * The benefit of Concurrent Reads is improved concurrency in Fortuna. That is 131 * reflected in two related aspects: 132 * 133 * 1. Concurrent full-rate devrandom readers can achieve similar throughput to 134 * a single reader thread (at least up to a modest number of cores; the 135 * non-concurrent design falls over at 2 readers). 136 * 137 * 2. The rand_harvestq process spends much less time spinning when one or more 138 * readers is processing a large request. Partially this is due to 139 * rand_harvestq / ra_event_processor design, which only passes one event at 140 * a time to the underlying algorithm. Each time, Fortuna must take its 141 * global state mutex, potentially blocking on a reader. Our adaptive 142 * mutexes assume that a lock holder currently on CPU will release the lock 143 * quickly, and spin if the owning thread is currently running. 144 * 145 * (There is no reason rand_harvestq necessarily has to use the same lock as 146 * the generator, or that it must necessarily drop and retake locks 147 * repeatedly, but that is the current status quo.) 148 * 149 * The concern is that the reduced lock scope might results in a less safe 150 * random(4) design. However, the reduced-lock scope design is still 151 * fundamentally Fortuna. This is discussed below. 152 * 153 * Fortuna Read() only needs mutual exclusion between readers to correctly 154 * update the shared read-side state: C, the 128-bit counter; and K, the 155 * current cipher/PRF key. 156 * 157 * In the Fortuna design, the global counter C should provide an independent 158 * range of values per request. 159 * 160 * Under lock, we can save a copy of C on the stack, and increment the global C 161 * by the number of blocks a Read request will require. 162 * 163 * Still under lock, we can save a copy of the key K on the stack, and then 164 * perform the usual key erasure K' <- Keystream(C, K, ...). This does require 165 * generating 256 bits (32 bytes) of cryptographic keystream output with the 166 * global lock held, but that's all; none of the API keystream generation must 167 * be performed under lock. 168 * 169 * At this point, we may unlock. 170 * 171 * Some example timelines below (to oversimplify, all requests are in units of 172 * native blocks, and the keysize happens to be equal or less to the native 173 * blocksize of the underlying cipher, and the same sequence of two requests 174 * arrive in the same order). The possibly expensive consumer keystream 175 * generation portion is marked with '**'. 176 * 177 * Status Quo fortuna_read() Reduced-scope locking 178 * ------------------------- --------------------- 179 * C=C_0, K=K_0 C=C_0, K=K_0 180 * <Thr 1 requests N blocks> <Thr 1 requests N blocks> 181 * 1:Lock() 1:Lock() 182 * <Thr 2 requests M blocks> <Thr 2 requests M blocks> 183 * 1:GenBytes() 1:stack_C := C_0 184 * 1: Keystream(C_0, K_0, N) 1:stack_K := K_0 185 * 1: <N blocks generated>** 1:C' := C_0 + N 186 * 1: C' := C_0 + N 1:K' := Keystream(C', K_0, 1) 187 * 1: <- Keystream 1: <1 block generated> 188 * 1: K' := Keystream(C', K_0, 1) 1: C'' := C' + 1 189 * 1: <1 block generated> 1: <- Keystream 190 * 1: C'' := C' + 1 1:Unlock() 191 * 1: <- Keystream 192 * 1: <- GenBytes() 193 * 1:Unlock() 194 * 195 * Just prior to unlock, shared state is identical: 196 * ------------------------------------------------ 197 * C'' == C_0 + N + 1 C'' == C_0 + N + 1 198 * K' == keystream generated from K' == keystream generated from 199 * C_0 + N, K_0. C_0 + N, K_0. 200 * K_0 has been erased. K_0 has been erased. 201 * 202 * After both designs unlock, the 2nd reader is unblocked. 203 * 204 * 2:Lock() 2:Lock() 205 * 2:GenBytes() 2:stack_C' := C'' 206 * 2: Keystream(C'', K', M) 2:stack_K' := K' 207 * 2: <M blocks generated>** 2:C''' := C'' + M 208 * 2: C''' := C'' + M 2:K'' := Keystream(C''', K', 1) 209 * 2: <- Keystream 2: <1 block generated> 210 * 2: K'' := Keystream(C''', K', 1) 2: C'''' := C''' + 1 211 * 2: <1 block generated> 2: <- Keystream 212 * 2: C'''' := C''' + 1 2:Unlock() 213 * 2: <- Keystream 214 * 2: <- GenBytes() 215 * 2:Unlock() 216 * 217 * Just prior to unlock, global state is identical: 218 * ------------------------------------------------------ 219 * 220 * C'''' == (C_0 + N + 1) + M + 1 C'''' == (C_0 + N + 1) + M + 1 221 * K'' == keystream generated from K'' == keystream generated from 222 * C_0 + N + 1 + M, K'. C_0 + N + 1 + M, K'. 223 * K' has been erased. K' has been erased. 224 * 225 * Finally, in the new design, the two consumer threads can finish the 226 * remainder of the generation at any time (including simultaneously): 227 * 228 * 1: GenBytes() 229 * 1: Keystream(stack_C, stack_K, N) 230 * 1: <N blocks generated>** 231 * 1: <- Keystream 232 * 1: <- GenBytes 233 * 1:ExplicitBzero(stack_C, stack_K) 234 * 235 * 2: GenBytes() 236 * 2: Keystream(stack_C', stack_K', M) 237 * 2: <M blocks generated>** 238 * 2: <- Keystream 239 * 2: <- GenBytes 240 * 2:ExplicitBzero(stack_C', stack_K') 241 * 242 * The generated user keystream for both threads is identical between the two 243 * implementations: 244 * 245 * 1: Keystream(C_0, K_0, N) 1: Keystream(stack_C, stack_K, N) 246 * 2: Keystream(C'', K', M) 2: Keystream(stack_C', stack_K', M) 247 * 248 * (stack_C == C_0; stack_K == K_0; stack_C' == C''; stack_K' == K'.) 249 */ 250 static bool fortuna_concurrent_read __read_frequently = true; 251 252 #ifdef _KERNEL 253 static struct sysctl_ctx_list random_clist; 254 RANDOM_CHECK_UINT(fs_minpoolsize, RANDOM_FORTUNA_MINPOOLSIZE, RANDOM_FORTUNA_MAXPOOLSIZE); 255 #else 256 static uint8_t zero_region[RANDOM_ZERO_BLOCKSIZE]; 257 #endif 258 259 static void random_fortuna_pre_read(void); 260 static void random_fortuna_read(uint8_t *, size_t); 261 static bool random_fortuna_seeded(void); 262 static bool random_fortuna_seeded_internal(void); 263 static void random_fortuna_process_event(struct harvest_event *); 264 265 static void random_fortuna_reseed_internal(uint32_t *entropy_data, u_int blockcount); 266 267 #ifdef RANDOM_LOADABLE 268 static 269 #endif 270 const struct random_algorithm random_alg_context = { 271 .ra_ident = "Fortuna", 272 .ra_pre_read = random_fortuna_pre_read, 273 .ra_read = random_fortuna_read, 274 .ra_seeded = random_fortuna_seeded, 275 .ra_event_processor = random_fortuna_process_event, 276 .ra_poolcount = RANDOM_FORTUNA_NPOOLS, 277 }; 278 279 /* ARGSUSED */ 280 static void 281 random_fortuna_init_alg(void *unused __unused) 282 { 283 int i; 284 #ifdef _KERNEL 285 struct sysctl_oid *random_fortuna_o; 286 #endif 287 288 #ifdef RANDOM_LOADABLE 289 p_random_alg_context = &random_alg_context; 290 #endif 291 292 RANDOM_RESEED_INIT_LOCK(); 293 /* 294 * Fortuna parameters. Do not adjust these unless you have 295 * have a very good clue about what they do! 296 */ 297 fortuna_state.fs_minpoolsize = RANDOM_FORTUNA_DEFPOOLSIZE; 298 #ifdef _KERNEL 299 fortuna_state.fs_lasttime = 0; 300 random_fortuna_o = SYSCTL_ADD_NODE(&random_clist, 301 SYSCTL_STATIC_CHILDREN(_kern_random), 302 OID_AUTO, "fortuna", CTLFLAG_RW | CTLFLAG_MPSAFE, 0, 303 "Fortuna Parameters"); 304 SYSCTL_ADD_PROC(&random_clist, 305 SYSCTL_CHILDREN(random_fortuna_o), OID_AUTO, "minpoolsize", 306 CTLTYPE_UINT | CTLFLAG_RWTUN | CTLFLAG_MPSAFE, 307 &fortuna_state.fs_minpoolsize, RANDOM_FORTUNA_DEFPOOLSIZE, 308 random_check_uint_fs_minpoolsize, "IU", 309 "Minimum pool size necessary to cause a reseed"); 310 KASSERT(fortuna_state.fs_minpoolsize > 0, ("random: Fortuna threshold must be > 0 at startup")); 311 312 SYSCTL_ADD_BOOL(&random_clist, SYSCTL_CHILDREN(random_fortuna_o), 313 OID_AUTO, "concurrent_read", CTLFLAG_RDTUN, 314 &fortuna_concurrent_read, 0, "If non-zero, enable " 315 "feature to improve concurrent Fortuna performance."); 316 #endif 317 318 /*- 319 * FS&K - InitializePRNG() 320 * - P_i = \epsilon 321 * - ReseedCNT = 0 322 */ 323 for (i = 0; i < RANDOM_FORTUNA_NPOOLS; i++) { 324 randomdev_hash_init(&fortuna_state.fs_pool[i].fsp_hash); 325 fortuna_state.fs_pool[i].fsp_length = 0; 326 } 327 fortuna_state.fs_reseedcount = 0; 328 /*- 329 * FS&K - InitializeGenerator() 330 * - C = 0 331 * - K = 0 332 */ 333 fortuna_state.fs_counter = UINT128_ZERO; 334 explicit_bzero(&fortuna_state.fs_key, sizeof(fortuna_state.fs_key)); 335 } 336 SYSINIT(random_alg, SI_SUB_RANDOM, SI_ORDER_SECOND, random_fortuna_init_alg, 337 NULL); 338 339 /*- 340 * FS&K - AddRandomEvent() 341 * Process a single stochastic event off the harvest queue 342 */ 343 static void 344 random_fortuna_process_event(struct harvest_event *event) 345 { 346 u_int pl; 347 348 RANDOM_RESEED_LOCK(); 349 /*- 350 * FS&K - P_i = P_i|<harvested stuff> 351 * Accumulate the event into the appropriate pool 352 * where each event carries the destination information. 353 * 354 * The hash_init() and hash_finish() calls are done in 355 * random_fortuna_pre_read(). 356 * 357 * We must be locked against pool state modification which can happen 358 * during accumulation/reseeding and reading/regating. 359 */ 360 pl = event->he_destination % RANDOM_FORTUNA_NPOOLS; 361 /* 362 * If a VM generation ID changes (clone and play or VM rewind), we want 363 * to incorporate that as soon as possible. Override destingation pool 364 * for immediate next use. 365 */ 366 if (event->he_source == RANDOM_PURE_VMGENID) 367 pl = 0; 368 /* 369 * We ignore low entropy static/counter fields towards the end of the 370 * he_event structure in order to increase measurable entropy when 371 * conducting SP800-90B entropy analysis measurements of seed material 372 * fed into PRNG. 373 * -- wdf 374 */ 375 KASSERT(event->he_size <= sizeof(event->he_entropy), 376 ("%s: event->he_size: %hhu > sizeof(event->he_entropy): %zu\n", 377 __func__, event->he_size, sizeof(event->he_entropy))); 378 randomdev_hash_iterate(&fortuna_state.fs_pool[pl].fsp_hash, 379 &event->he_somecounter, sizeof(event->he_somecounter)); 380 randomdev_hash_iterate(&fortuna_state.fs_pool[pl].fsp_hash, 381 event->he_entropy, event->he_size); 382 383 /*- 384 * Don't wrap the length. This is a "saturating" add. 385 * XXX: FIX!!: We don't actually need lengths for anything but fs_pool[0], 386 * but it's been useful debugging to see them all. 387 */ 388 fortuna_state.fs_pool[pl].fsp_length = MIN(RANDOM_FORTUNA_MAXPOOLSIZE, 389 fortuna_state.fs_pool[pl].fsp_length + 390 sizeof(event->he_somecounter) + event->he_size); 391 RANDOM_RESEED_UNLOCK(); 392 } 393 394 /*- 395 * FS&K - Reseed() 396 * This introduces new key material into the output generator. 397 * Additionally it increments the output generator's counter 398 * variable C. When C > 0, the output generator is seeded and 399 * will deliver output. 400 * The entropy_data buffer passed is a very specific size; the 401 * product of RANDOM_FORTUNA_NPOOLS and RANDOM_KEYSIZE. 402 */ 403 static void 404 random_fortuna_reseed_internal(uint32_t *entropy_data, u_int blockcount) 405 { 406 struct randomdev_hash context; 407 uint8_t hash[RANDOM_KEYSIZE]; 408 const void *keymaterial; 409 size_t keysz; 410 bool seeded; 411 412 RANDOM_RESEED_ASSERT_LOCK_OWNED(); 413 414 seeded = random_fortuna_seeded_internal(); 415 if (seeded) { 416 randomdev_getkey(&fortuna_state.fs_key, &keymaterial, &keysz); 417 KASSERT(keysz == RANDOM_KEYSIZE, ("%s: key size %zu not %u", 418 __func__, keysz, (unsigned)RANDOM_KEYSIZE)); 419 } 420 421 /*- 422 * FS&K - K = Hd(K|s) where Hd(m) is H(H(0^512|m)) 423 * - C = C + 1 424 */ 425 randomdev_hash_init(&context); 426 randomdev_hash_iterate(&context, zero_region, RANDOM_ZERO_BLOCKSIZE); 427 if (seeded) 428 randomdev_hash_iterate(&context, keymaterial, keysz); 429 randomdev_hash_iterate(&context, entropy_data, RANDOM_KEYSIZE*blockcount); 430 randomdev_hash_finish(&context, hash); 431 randomdev_hash_init(&context); 432 randomdev_hash_iterate(&context, hash, RANDOM_KEYSIZE); 433 randomdev_hash_finish(&context, hash); 434 randomdev_encrypt_init(&fortuna_state.fs_key, hash); 435 explicit_bzero(hash, sizeof(hash)); 436 /* Unblock the device if this is the first time we are reseeding. */ 437 if (uint128_is_zero(fortuna_state.fs_counter)) 438 randomdev_unblock(); 439 uint128_increment(&fortuna_state.fs_counter); 440 } 441 442 /*- 443 * FS&K - RandomData() (Part 1) 444 * Used to return processed entropy from the PRNG. There is a pre_read 445 * required to be present (but it can be a stub) in order to allow 446 * specific actions at the begin of the read. 447 */ 448 void 449 random_fortuna_pre_read(void) 450 { 451 #ifdef _KERNEL 452 sbintime_t now; 453 #endif 454 struct randomdev_hash context; 455 uint32_t s[RANDOM_FORTUNA_NPOOLS*RANDOM_KEYSIZE_WORDS]; 456 uint8_t temp[RANDOM_KEYSIZE]; 457 u_int i; 458 459 KASSERT(fortuna_state.fs_minpoolsize > 0, ("random: Fortuna threshold must be > 0")); 460 RANDOM_RESEED_LOCK(); 461 #ifdef _KERNEL 462 /* FS&K - Use 'getsbinuptime()' to prevent reseed-spamming. */ 463 now = getsbinuptime(); 464 #endif 465 466 if (fortuna_state.fs_pool[0].fsp_length < fortuna_state.fs_minpoolsize 467 #ifdef _KERNEL 468 /* 469 * FS&K - Use 'getsbinuptime()' to prevent reseed-spamming, but do 470 * not block initial seeding (fs_lasttime == 0). 471 */ 472 || (__predict_true(fortuna_state.fs_lasttime != 0) && 473 now - fortuna_state.fs_lasttime <= SBT_1S/10) 474 #endif 475 ) { 476 RANDOM_RESEED_UNLOCK(); 477 return; 478 } 479 480 #ifdef _KERNEL 481 /* 482 * When set, pretend we do not have enough entropy to reseed yet. 483 */ 484 KFAIL_POINT_CODE(DEBUG_FP, random_fortuna_pre_read, { 485 if (RETURN_VALUE != 0) { 486 RANDOM_RESEED_UNLOCK(); 487 return; 488 } 489 }); 490 #endif 491 492 #ifdef _KERNEL 493 fortuna_state.fs_lasttime = now; 494 #endif 495 496 /* FS&K - ReseedCNT = ReseedCNT + 1 */ 497 fortuna_state.fs_reseedcount++; 498 /* s = \epsilon at start */ 499 for (i = 0; i < RANDOM_FORTUNA_NPOOLS; i++) { 500 /* FS&K - if Divides(ReseedCnt, 2^i) ... */ 501 if ((fortuna_state.fs_reseedcount % (1 << i)) == 0) { 502 /*- 503 * FS&K - temp = (P_i) 504 * - P_i = \epsilon 505 * - s = s|H(temp) 506 */ 507 randomdev_hash_finish(&fortuna_state.fs_pool[i].fsp_hash, temp); 508 randomdev_hash_init(&fortuna_state.fs_pool[i].fsp_hash); 509 fortuna_state.fs_pool[i].fsp_length = 0; 510 randomdev_hash_init(&context); 511 randomdev_hash_iterate(&context, temp, RANDOM_KEYSIZE); 512 randomdev_hash_finish(&context, s + i*RANDOM_KEYSIZE_WORDS); 513 } else 514 break; 515 } 516 #ifdef _KERNEL 517 SDT_PROBE2(random, fortuna, event_processor, debug, fortuna_state.fs_reseedcount, fortuna_state.fs_pool); 518 #endif 519 /* FS&K */ 520 random_fortuna_reseed_internal(s, i); 521 RANDOM_RESEED_UNLOCK(); 522 523 /* Clean up and secure */ 524 explicit_bzero(s, sizeof(s)); 525 explicit_bzero(temp, sizeof(temp)); 526 } 527 528 /* 529 * This is basically GenerateBlocks() from FS&K. 530 * 531 * It differs in two ways: 532 * 533 * 1. Chacha20 is tolerant of non-block-multiple request sizes, so we do not 534 * need to handle any remainder bytes specially and can just pass the length 535 * directly to the PRF construction; and 536 * 537 * 2. Chacha20 is a 512-bit block size cipher (whereas AES has 128-bit block 538 * size, regardless of key size). This means Chacha does not require re-keying 539 * every 1MiB. This is implied by the math in FS&K 9.4 and mentioned 540 * explicitly in the conclusion, "If we had a block cipher with a 256-bit [or 541 * greater] block size, then the collisions would not have been an issue at 542 * all" (p. 144). 543 * 544 * 3. In conventional ("locked") mode, we produce a maximum of PAGE_SIZE output 545 * at a time before dropping the lock, to not bully the lock especially. This 546 * has been the status quo since 2015 (r284959). 547 * 548 * The upstream caller random_fortuna_read is responsible for zeroing out 549 * sensitive buffers provided as parameters to this routine. 550 */ 551 enum { 552 FORTUNA_UNLOCKED = false, 553 FORTUNA_LOCKED = true 554 }; 555 static void 556 random_fortuna_genbytes(uint8_t *buf, size_t bytecount, 557 uint8_t newkey[static RANDOM_KEYSIZE], uint128_t *p_counter, 558 union randomdev_key *p_key, bool locked) 559 { 560 uint8_t remainder_buf[RANDOM_BLOCKSIZE]; 561 size_t chunk_size; 562 563 if (locked) 564 RANDOM_RESEED_ASSERT_LOCK_OWNED(); 565 else 566 RANDOM_RESEED_ASSERT_LOCK_NOT_OWNED(); 567 568 /* 569 * Easy case: don't have to worry about bullying the global mutex, 570 * don't have to worry about rekeying Chacha; API is byte-oriented. 571 */ 572 if (!locked && random_chachamode) { 573 randomdev_keystream(p_key, p_counter, buf, bytecount); 574 return; 575 } 576 577 if (locked) { 578 /* 579 * While holding the global lock, limit PRF generation to 580 * mitigate, but not eliminate, bullying symptoms. 581 */ 582 chunk_size = PAGE_SIZE; 583 } else { 584 /* 585 * 128-bit block ciphers like AES must be re-keyed at 1MB 586 * intervals to avoid unacceptable statistical differentiation 587 * from true random data (FS&K 9.4, p. 143-144). 588 */ 589 MPASS(!random_chachamode); 590 chunk_size = RANDOM_FORTUNA_MAX_READ; 591 } 592 593 chunk_size = MIN(bytecount, chunk_size); 594 if (!random_chachamode) 595 chunk_size = rounddown(chunk_size, RANDOM_BLOCKSIZE); 596 597 while (bytecount >= chunk_size && chunk_size > 0) { 598 randomdev_keystream(p_key, p_counter, buf, chunk_size); 599 600 buf += chunk_size; 601 bytecount -= chunk_size; 602 603 /* We have to rekey if there is any data remaining to be 604 * generated, in two scenarios: 605 * 606 * locked: we need to rekey before we unlock and release the 607 * global state to another consumer; or 608 * 609 * unlocked: we need to rekey because we're in AES mode and are 610 * required to rekey at chunk_size==1MB. But we do not need to 611 * rekey during the last trailing <1MB chunk. 612 */ 613 if (bytecount > 0) { 614 if (locked || chunk_size == RANDOM_FORTUNA_MAX_READ) { 615 randomdev_keystream(p_key, p_counter, newkey, 616 RANDOM_KEYSIZE); 617 randomdev_encrypt_init(p_key, newkey); 618 } 619 620 /* 621 * If we're holding the global lock, yield it briefly 622 * now. 623 */ 624 if (locked) { 625 RANDOM_RESEED_UNLOCK(); 626 RANDOM_RESEED_LOCK(); 627 } 628 629 /* 630 * At the trailing end, scale down chunk_size from 1MB or 631 * PAGE_SIZE to all remaining full blocks (AES) or all 632 * remaining bytes (Chacha). 633 */ 634 if (bytecount < chunk_size) { 635 if (random_chachamode) 636 chunk_size = bytecount; 637 else if (bytecount >= RANDOM_BLOCKSIZE) 638 chunk_size = rounddown(bytecount, 639 RANDOM_BLOCKSIZE); 640 else 641 break; 642 } 643 } 644 } 645 646 /* 647 * Generate any partial AES block remaining into a temporary buffer and 648 * copy the desired substring out. 649 */ 650 if (bytecount > 0) { 651 MPASS(!random_chachamode); 652 653 randomdev_keystream(p_key, p_counter, remainder_buf, 654 sizeof(remainder_buf)); 655 } 656 657 /* 658 * In locked mode, re-key global K before dropping the lock, which we 659 * don't need for memcpy/bzero below. 660 */ 661 if (locked) { 662 randomdev_keystream(p_key, p_counter, newkey, RANDOM_KEYSIZE); 663 randomdev_encrypt_init(p_key, newkey); 664 RANDOM_RESEED_UNLOCK(); 665 } 666 667 if (bytecount > 0) { 668 memcpy(buf, remainder_buf, bytecount); 669 explicit_bzero(remainder_buf, sizeof(remainder_buf)); 670 } 671 } 672 673 674 /* 675 * Handle only "concurrency-enabled" Fortuna reads to simplify logic. 676 * 677 * Caller (random_fortuna_read) is responsible for zeroing out sensitive 678 * buffers provided as parameters to this routine. 679 */ 680 static void 681 random_fortuna_read_concurrent(uint8_t *buf, size_t bytecount, 682 uint8_t newkey[static RANDOM_KEYSIZE]) 683 { 684 union randomdev_key key_copy; 685 uint128_t counter_copy; 686 size_t blockcount; 687 688 MPASS(fortuna_concurrent_read); 689 690 /* 691 * Compute number of blocks required for the PRF request ('delta C'). 692 * We will step the global counter 'C' by this number under lock, and 693 * then actually consume the counter values outside the lock. 694 * 695 * This ensures that contemporaneous but independent requests for 696 * randomness receive distinct 'C' values and thus independent PRF 697 * results. 698 */ 699 if (random_chachamode) { 700 blockcount = howmany(bytecount, CHACHA_BLOCKLEN); 701 } else { 702 blockcount = howmany(bytecount, RANDOM_BLOCKSIZE); 703 704 /* 705 * Need to account for the additional blocks generated by 706 * rekeying when updating the global fs_counter. 707 */ 708 blockcount += RANDOM_KEYS_PER_BLOCK * 709 (blockcount / RANDOM_FORTUNA_BLOCKS_PER_KEY); 710 } 711 712 RANDOM_RESEED_LOCK(); 713 KASSERT(!uint128_is_zero(fortuna_state.fs_counter), ("FS&K: C != 0")); 714 715 /* 716 * Save the original counter and key values that will be used as the 717 * PRF for this particular consumer. 718 */ 719 memcpy(&counter_copy, &fortuna_state.fs_counter, sizeof(counter_copy)); 720 memcpy(&key_copy, &fortuna_state.fs_key, sizeof(key_copy)); 721 722 /* 723 * Step the counter as if we had generated 'bytecount' blocks for this 724 * consumer. I.e., ensure that the next consumer gets an independent 725 * range of counter values once we drop the global lock. 726 */ 727 uint128_add64(&fortuna_state.fs_counter, blockcount); 728 729 /* 730 * We still need to Rekey the global 'K' between independent calls; 731 * this is no different from conventional Fortuna. Note that 732 * 'randomdev_keystream()' will step the fs_counter 'C' appropriately 733 * for the blocks needed for the 'newkey'. 734 * 735 * (This is part of PseudoRandomData() in FS&K, 9.4.4.) 736 */ 737 randomdev_keystream(&fortuna_state.fs_key, &fortuna_state.fs_counter, 738 newkey, RANDOM_KEYSIZE); 739 randomdev_encrypt_init(&fortuna_state.fs_key, newkey); 740 741 /* 742 * We have everything we need to generate a unique PRF for this 743 * consumer without touching global state. 744 */ 745 RANDOM_RESEED_UNLOCK(); 746 747 random_fortuna_genbytes(buf, bytecount, newkey, &counter_copy, 748 &key_copy, FORTUNA_UNLOCKED); 749 RANDOM_RESEED_ASSERT_LOCK_NOT_OWNED(); 750 751 explicit_bzero(&counter_copy, sizeof(counter_copy)); 752 explicit_bzero(&key_copy, sizeof(key_copy)); 753 } 754 755 /*- 756 * FS&K - RandomData() (Part 2) 757 * Main read from Fortuna, continued. May be called multiple times after 758 * the random_fortuna_pre_read() above. 759 * 760 * The supplied buf MAY not be a multiple of RANDOM_BLOCKSIZE in size; it is 761 * the responsibility of the algorithm to accommodate partial block reads, if a 762 * block output mode is used. 763 */ 764 void 765 random_fortuna_read(uint8_t *buf, size_t bytecount) 766 { 767 uint8_t newkey[RANDOM_KEYSIZE]; 768 769 if (fortuna_concurrent_read) { 770 random_fortuna_read_concurrent(buf, bytecount, newkey); 771 goto out; 772 } 773 774 RANDOM_RESEED_LOCK(); 775 KASSERT(!uint128_is_zero(fortuna_state.fs_counter), ("FS&K: C != 0")); 776 777 random_fortuna_genbytes(buf, bytecount, newkey, 778 &fortuna_state.fs_counter, &fortuna_state.fs_key, FORTUNA_LOCKED); 779 /* Returns unlocked */ 780 RANDOM_RESEED_ASSERT_LOCK_NOT_OWNED(); 781 782 out: 783 explicit_bzero(newkey, sizeof(newkey)); 784 } 785 786 #ifdef _KERNEL 787 static bool block_seeded_status = false; 788 SYSCTL_BOOL(_kern_random, OID_AUTO, block_seeded_status, CTLFLAG_RWTUN, 789 &block_seeded_status, 0, 790 "If non-zero, pretend Fortuna is in an unseeded state. By setting " 791 "this as a tunable, boot can be tested as if the random device is " 792 "unavailable."); 793 #endif 794 795 static bool 796 random_fortuna_seeded_internal(void) 797 { 798 return (!uint128_is_zero(fortuna_state.fs_counter)); 799 } 800 801 static bool 802 random_fortuna_seeded(void) 803 { 804 805 #ifdef _KERNEL 806 if (block_seeded_status) 807 return (false); 808 #endif 809 810 if (__predict_true(random_fortuna_seeded_internal())) 811 return (true); 812 813 /* 814 * Maybe we have enough entropy in the zeroth pool but just haven't 815 * kicked the initial seed step. Do so now. 816 */ 817 random_fortuna_pre_read(); 818 819 return (random_fortuna_seeded_internal()); 820 } 821