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