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, 0, 303 "Fortuna Parameters"); 304 SYSCTL_ADD_PROC(&random_clist, 305 SYSCTL_CHILDREN(random_fortuna_o), OID_AUTO, 306 "minpoolsize", CTLTYPE_UINT | CTLFLAG_RWTUN, 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 * We ignore low entropy static/counter fields towards the end of the 363 * he_event structure in order to increase measurable entropy when 364 * conducting SP800-90B entropy analysis measurements of seed material 365 * fed into PRNG. 366 * -- wdf 367 */ 368 KASSERT(event->he_size <= sizeof(event->he_entropy), 369 ("%s: event->he_size: %hhu > sizeof(event->he_entropy): %zu\n", 370 __func__, event->he_size, sizeof(event->he_entropy))); 371 randomdev_hash_iterate(&fortuna_state.fs_pool[pl].fsp_hash, 372 &event->he_somecounter, sizeof(event->he_somecounter)); 373 randomdev_hash_iterate(&fortuna_state.fs_pool[pl].fsp_hash, 374 event->he_entropy, event->he_size); 375 376 /*- 377 * Don't wrap the length. This is a "saturating" add. 378 * XXX: FIX!!: We don't actually need lengths for anything but fs_pool[0], 379 * but it's been useful debugging to see them all. 380 */ 381 fortuna_state.fs_pool[pl].fsp_length = MIN(RANDOM_FORTUNA_MAXPOOLSIZE, 382 fortuna_state.fs_pool[pl].fsp_length + 383 sizeof(event->he_somecounter) + event->he_size); 384 RANDOM_RESEED_UNLOCK(); 385 } 386 387 /*- 388 * FS&K - Reseed() 389 * This introduces new key material into the output generator. 390 * Additionally it increments the output generator's counter 391 * variable C. When C > 0, the output generator is seeded and 392 * will deliver output. 393 * The entropy_data buffer passed is a very specific size; the 394 * product of RANDOM_FORTUNA_NPOOLS and RANDOM_KEYSIZE. 395 */ 396 static void 397 random_fortuna_reseed_internal(uint32_t *entropy_data, u_int blockcount) 398 { 399 struct randomdev_hash context; 400 uint8_t hash[RANDOM_KEYSIZE]; 401 const void *keymaterial; 402 size_t keysz; 403 bool seeded; 404 405 RANDOM_RESEED_ASSERT_LOCK_OWNED(); 406 407 seeded = random_fortuna_seeded_internal(); 408 if (seeded) { 409 randomdev_getkey(&fortuna_state.fs_key, &keymaterial, &keysz); 410 KASSERT(keysz == RANDOM_KEYSIZE, ("%s: key size %zu not %u", 411 __func__, keysz, (unsigned)RANDOM_KEYSIZE)); 412 } 413 414 /*- 415 * FS&K - K = Hd(K|s) where Hd(m) is H(H(0^512|m)) 416 * - C = C + 1 417 */ 418 randomdev_hash_init(&context); 419 randomdev_hash_iterate(&context, zero_region, RANDOM_ZERO_BLOCKSIZE); 420 if (seeded) 421 randomdev_hash_iterate(&context, keymaterial, keysz); 422 randomdev_hash_iterate(&context, entropy_data, RANDOM_KEYSIZE*blockcount); 423 randomdev_hash_finish(&context, hash); 424 randomdev_hash_init(&context); 425 randomdev_hash_iterate(&context, hash, RANDOM_KEYSIZE); 426 randomdev_hash_finish(&context, hash); 427 randomdev_encrypt_init(&fortuna_state.fs_key, hash); 428 explicit_bzero(hash, sizeof(hash)); 429 /* Unblock the device if this is the first time we are reseeding. */ 430 if (uint128_is_zero(fortuna_state.fs_counter)) 431 randomdev_unblock(); 432 uint128_increment(&fortuna_state.fs_counter); 433 } 434 435 /*- 436 * FS&K - RandomData() (Part 1) 437 * Used to return processed entropy from the PRNG. There is a pre_read 438 * required to be present (but it can be a stub) in order to allow 439 * specific actions at the begin of the read. 440 */ 441 void 442 random_fortuna_pre_read(void) 443 { 444 #ifdef _KERNEL 445 sbintime_t now; 446 #endif 447 struct randomdev_hash context; 448 uint32_t s[RANDOM_FORTUNA_NPOOLS*RANDOM_KEYSIZE_WORDS]; 449 uint8_t temp[RANDOM_KEYSIZE]; 450 u_int i; 451 452 KASSERT(fortuna_state.fs_minpoolsize > 0, ("random: Fortuna threshold must be > 0")); 453 RANDOM_RESEED_LOCK(); 454 #ifdef _KERNEL 455 /* FS&K - Use 'getsbinuptime()' to prevent reseed-spamming. */ 456 now = getsbinuptime(); 457 #endif 458 459 if (fortuna_state.fs_pool[0].fsp_length < fortuna_state.fs_minpoolsize 460 #ifdef _KERNEL 461 /* 462 * FS&K - Use 'getsbinuptime()' to prevent reseed-spamming, but do 463 * not block initial seeding (fs_lasttime == 0). 464 */ 465 || (__predict_true(fortuna_state.fs_lasttime != 0) && 466 now - fortuna_state.fs_lasttime <= SBT_1S/10) 467 #endif 468 ) { 469 RANDOM_RESEED_UNLOCK(); 470 return; 471 } 472 473 #ifdef _KERNEL 474 /* 475 * When set, pretend we do not have enough entropy to reseed yet. 476 */ 477 KFAIL_POINT_CODE(DEBUG_FP, random_fortuna_pre_read, { 478 if (RETURN_VALUE != 0) { 479 RANDOM_RESEED_UNLOCK(); 480 return; 481 } 482 }); 483 #endif 484 485 #ifdef _KERNEL 486 fortuna_state.fs_lasttime = now; 487 #endif 488 489 /* FS&K - ReseedCNT = ReseedCNT + 1 */ 490 fortuna_state.fs_reseedcount++; 491 /* s = \epsilon at start */ 492 for (i = 0; i < RANDOM_FORTUNA_NPOOLS; i++) { 493 /* FS&K - if Divides(ReseedCnt, 2^i) ... */ 494 if ((fortuna_state.fs_reseedcount % (1 << i)) == 0) { 495 /*- 496 * FS&K - temp = (P_i) 497 * - P_i = \epsilon 498 * - s = s|H(temp) 499 */ 500 randomdev_hash_finish(&fortuna_state.fs_pool[i].fsp_hash, temp); 501 randomdev_hash_init(&fortuna_state.fs_pool[i].fsp_hash); 502 fortuna_state.fs_pool[i].fsp_length = 0; 503 randomdev_hash_init(&context); 504 randomdev_hash_iterate(&context, temp, RANDOM_KEYSIZE); 505 randomdev_hash_finish(&context, s + i*RANDOM_KEYSIZE_WORDS); 506 } else 507 break; 508 } 509 #ifdef _KERNEL 510 SDT_PROBE2(random, fortuna, event_processor, debug, fortuna_state.fs_reseedcount, fortuna_state.fs_pool); 511 #endif 512 /* FS&K */ 513 random_fortuna_reseed_internal(s, i); 514 RANDOM_RESEED_UNLOCK(); 515 516 /* Clean up and secure */ 517 explicit_bzero(s, sizeof(s)); 518 explicit_bzero(temp, sizeof(temp)); 519 } 520 521 /* 522 * This is basically GenerateBlocks() from FS&K. 523 * 524 * It differs in two ways: 525 * 526 * 1. Chacha20 is tolerant of non-block-multiple request sizes, so we do not 527 * need to handle any remainder bytes specially and can just pass the length 528 * directly to the PRF construction; and 529 * 530 * 2. Chacha20 is a 512-bit block size cipher (whereas AES has 128-bit block 531 * size, regardless of key size). This means Chacha does not require re-keying 532 * every 1MiB. This is implied by the math in FS&K 9.4 and mentioned 533 * explicitly in the conclusion, "If we had a block cipher with a 256-bit [or 534 * greater] block size, then the collisions would not have been an issue at 535 * all" (p. 144). 536 * 537 * 3. In conventional ("locked") mode, we produce a maximum of PAGE_SIZE output 538 * at a time before dropping the lock, to not bully the lock especially. This 539 * has been the status quo since 2015 (r284959). 540 * 541 * The upstream caller random_fortuna_read is responsible for zeroing out 542 * sensitive buffers provided as parameters to this routine. 543 */ 544 enum { 545 FORTUNA_UNLOCKED = false, 546 FORTUNA_LOCKED = true 547 }; 548 static void 549 random_fortuna_genbytes(uint8_t *buf, size_t bytecount, 550 uint8_t newkey[static RANDOM_KEYSIZE], uint128_t *p_counter, 551 union randomdev_key *p_key, bool locked) 552 { 553 uint8_t remainder_buf[RANDOM_BLOCKSIZE]; 554 size_t chunk_size; 555 556 if (locked) 557 RANDOM_RESEED_ASSERT_LOCK_OWNED(); 558 else 559 RANDOM_RESEED_ASSERT_LOCK_NOT_OWNED(); 560 561 /* 562 * Easy case: don't have to worry about bullying the global mutex, 563 * don't have to worry about rekeying Chacha; API is byte-oriented. 564 */ 565 if (!locked && random_chachamode) { 566 randomdev_keystream(p_key, p_counter, buf, bytecount); 567 return; 568 } 569 570 if (locked) { 571 /* 572 * While holding the global lock, limit PRF generation to 573 * mitigate, but not eliminate, bullying symptoms. 574 */ 575 chunk_size = PAGE_SIZE; 576 } else { 577 /* 578 * 128-bit block ciphers like AES must be re-keyed at 1MB 579 * intervals to avoid unacceptable statistical differentiation 580 * from true random data (FS&K 9.4, p. 143-144). 581 */ 582 MPASS(!random_chachamode); 583 chunk_size = RANDOM_FORTUNA_MAX_READ; 584 } 585 586 chunk_size = MIN(bytecount, chunk_size); 587 if (!random_chachamode) 588 chunk_size = rounddown(chunk_size, RANDOM_BLOCKSIZE); 589 590 while (bytecount >= chunk_size && chunk_size > 0) { 591 randomdev_keystream(p_key, p_counter, buf, chunk_size); 592 593 buf += chunk_size; 594 bytecount -= chunk_size; 595 596 /* We have to rekey if there is any data remaining to be 597 * generated, in two scenarios: 598 * 599 * locked: we need to rekey before we unlock and release the 600 * global state to another consumer; or 601 * 602 * unlocked: we need to rekey because we're in AES mode and are 603 * required to rekey at chunk_size==1MB. But we do not need to 604 * rekey during the last trailing <1MB chunk. 605 */ 606 if (bytecount > 0) { 607 if (locked || chunk_size == RANDOM_FORTUNA_MAX_READ) { 608 randomdev_keystream(p_key, p_counter, newkey, 609 RANDOM_KEYSIZE); 610 randomdev_encrypt_init(p_key, newkey); 611 } 612 613 /* 614 * If we're holding the global lock, yield it briefly 615 * now. 616 */ 617 if (locked) { 618 RANDOM_RESEED_UNLOCK(); 619 RANDOM_RESEED_LOCK(); 620 } 621 622 /* 623 * At the trailing end, scale down chunk_size from 1MB or 624 * PAGE_SIZE to all remaining full blocks (AES) or all 625 * remaining bytes (Chacha). 626 */ 627 if (bytecount < chunk_size) { 628 if (random_chachamode) 629 chunk_size = bytecount; 630 else if (bytecount >= RANDOM_BLOCKSIZE) 631 chunk_size = rounddown(bytecount, 632 RANDOM_BLOCKSIZE); 633 else 634 break; 635 } 636 } 637 } 638 639 /* 640 * Generate any partial AES block remaining into a temporary buffer and 641 * copy the desired substring out. 642 */ 643 if (bytecount > 0) { 644 MPASS(!random_chachamode); 645 646 randomdev_keystream(p_key, p_counter, remainder_buf, 647 sizeof(remainder_buf)); 648 } 649 650 /* 651 * In locked mode, re-key global K before dropping the lock, which we 652 * don't need for memcpy/bzero below. 653 */ 654 if (locked) { 655 randomdev_keystream(p_key, p_counter, newkey, RANDOM_KEYSIZE); 656 randomdev_encrypt_init(p_key, newkey); 657 RANDOM_RESEED_UNLOCK(); 658 } 659 660 if (bytecount > 0) { 661 memcpy(buf, remainder_buf, bytecount); 662 explicit_bzero(remainder_buf, sizeof(remainder_buf)); 663 } 664 } 665 666 667 /* 668 * Handle only "concurrency-enabled" Fortuna reads to simplify logic. 669 * 670 * Caller (random_fortuna_read) is responsible for zeroing out sensitive 671 * buffers provided as parameters to this routine. 672 */ 673 static void 674 random_fortuna_read_concurrent(uint8_t *buf, size_t bytecount, 675 uint8_t newkey[static RANDOM_KEYSIZE]) 676 { 677 union randomdev_key key_copy; 678 uint128_t counter_copy; 679 size_t blockcount; 680 681 MPASS(fortuna_concurrent_read); 682 683 /* 684 * Compute number of blocks required for the PRF request ('delta C'). 685 * We will step the global counter 'C' by this number under lock, and 686 * then actually consume the counter values outside the lock. 687 * 688 * This ensures that contemporaneous but independent requests for 689 * randomness receive distinct 'C' values and thus independent PRF 690 * results. 691 */ 692 if (random_chachamode) { 693 blockcount = howmany(bytecount, CHACHA_BLOCKLEN); 694 } else { 695 blockcount = howmany(bytecount, RANDOM_BLOCKSIZE); 696 697 /* 698 * Need to account for the additional blocks generated by 699 * rekeying when updating the global fs_counter. 700 */ 701 blockcount += RANDOM_KEYS_PER_BLOCK * 702 (blockcount / RANDOM_FORTUNA_BLOCKS_PER_KEY); 703 } 704 705 RANDOM_RESEED_LOCK(); 706 KASSERT(!uint128_is_zero(fortuna_state.fs_counter), ("FS&K: C != 0")); 707 708 /* 709 * Save the original counter and key values that will be used as the 710 * PRF for this particular consumer. 711 */ 712 memcpy(&counter_copy, &fortuna_state.fs_counter, sizeof(counter_copy)); 713 memcpy(&key_copy, &fortuna_state.fs_key, sizeof(key_copy)); 714 715 /* 716 * Step the counter as if we had generated 'bytecount' blocks for this 717 * consumer. I.e., ensure that the next consumer gets an independent 718 * range of counter values once we drop the global lock. 719 */ 720 uint128_add64(&fortuna_state.fs_counter, blockcount); 721 722 /* 723 * We still need to Rekey the global 'K' between independent calls; 724 * this is no different from conventional Fortuna. Note that 725 * 'randomdev_keystream()' will step the fs_counter 'C' appropriately 726 * for the blocks needed for the 'newkey'. 727 * 728 * (This is part of PseudoRandomData() in FS&K, 9.4.4.) 729 */ 730 randomdev_keystream(&fortuna_state.fs_key, &fortuna_state.fs_counter, 731 newkey, RANDOM_KEYSIZE); 732 randomdev_encrypt_init(&fortuna_state.fs_key, newkey); 733 734 /* 735 * We have everything we need to generate a unique PRF for this 736 * consumer without touching global state. 737 */ 738 RANDOM_RESEED_UNLOCK(); 739 740 random_fortuna_genbytes(buf, bytecount, newkey, &counter_copy, 741 &key_copy, FORTUNA_UNLOCKED); 742 RANDOM_RESEED_ASSERT_LOCK_NOT_OWNED(); 743 744 explicit_bzero(&counter_copy, sizeof(counter_copy)); 745 explicit_bzero(&key_copy, sizeof(key_copy)); 746 } 747 748 /*- 749 * FS&K - RandomData() (Part 2) 750 * Main read from Fortuna, continued. May be called multiple times after 751 * the random_fortuna_pre_read() above. 752 * 753 * The supplied buf MAY not be a multiple of RANDOM_BLOCKSIZE in size; it is 754 * the responsibility of the algorithm to accommodate partial block reads, if a 755 * block output mode is used. 756 */ 757 void 758 random_fortuna_read(uint8_t *buf, size_t bytecount) 759 { 760 uint8_t newkey[RANDOM_KEYSIZE]; 761 762 if (fortuna_concurrent_read) { 763 random_fortuna_read_concurrent(buf, bytecount, newkey); 764 goto out; 765 } 766 767 RANDOM_RESEED_LOCK(); 768 KASSERT(!uint128_is_zero(fortuna_state.fs_counter), ("FS&K: C != 0")); 769 770 random_fortuna_genbytes(buf, bytecount, newkey, 771 &fortuna_state.fs_counter, &fortuna_state.fs_key, FORTUNA_LOCKED); 772 /* Returns unlocked */ 773 RANDOM_RESEED_ASSERT_LOCK_NOT_OWNED(); 774 775 out: 776 explicit_bzero(newkey, sizeof(newkey)); 777 } 778 779 #ifdef _KERNEL 780 static bool block_seeded_status = false; 781 SYSCTL_BOOL(_kern_random, OID_AUTO, block_seeded_status, CTLFLAG_RWTUN, 782 &block_seeded_status, 0, 783 "If non-zero, pretend Fortuna is in an unseeded state. By setting " 784 "this as a tunable, boot can be tested as if the random device is " 785 "unavailable."); 786 #endif 787 788 static bool 789 random_fortuna_seeded_internal(void) 790 { 791 return (!uint128_is_zero(fortuna_state.fs_counter)); 792 } 793 794 static bool 795 random_fortuna_seeded(void) 796 { 797 798 #ifdef _KERNEL 799 if (block_seeded_status) 800 return (false); 801 #endif 802 803 if (__predict_true(random_fortuna_seeded_internal())) 804 return (true); 805 806 /* 807 * Maybe we have enough entropy in the zeroth pool but just haven't 808 * kicked the initial seed step. Do so now. 809 */ 810 random_fortuna_pre_read(); 811 812 return (random_fortuna_seeded_internal()); 813 } 814