aboutsummaryrefslogtreecommitdiffstats
path: root/lib/random32.c
blob: be9f242a420754c44c7788178ad4ae023a0fbf99 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
// SPDX-License-Identifier: GPL-2.0
/*
 * This is a maximally equidistributed combined Tausworthe generator
 * based on code from GNU Scientific Library 1.5 (30 Jun 2004)
 *
 * lfsr113 version:
 *
 * x_n = (s1_n ^ s2_n ^ s3_n ^ s4_n)
 *
 * s1_{n+1} = (((s1_n & 4294967294) << 18) ^ (((s1_n <<  6) ^ s1_n) >> 13))
 * s2_{n+1} = (((s2_n & 4294967288) <<  2) ^ (((s2_n <<  2) ^ s2_n) >> 27))
 * s3_{n+1} = (((s3_n & 4294967280) <<  7) ^ (((s3_n << 13) ^ s3_n) >> 21))
 * s4_{n+1} = (((s4_n & 4294967168) << 13) ^ (((s4_n <<  3) ^ s4_n) >> 12))
 *
 * The period of this generator is about 2^113 (see erratum paper).
 *
 * From: P. L'Ecuyer, "Maximally Equidistributed Combined Tausworthe
 * Generators", Mathematics of Computation, 65, 213 (1996), 203--213:
 * http://www.iro.umontreal.ca/~lecuyer/myftp/papers/tausme.ps
 * ftp://ftp.iro.umontreal.ca/pub/simulation/lecuyer/papers/tausme.ps
 *
 * There is an erratum in the paper "Tables of Maximally Equidistributed
 * Combined LFSR Generators", Mathematics of Computation, 68, 225 (1999),
 * 261--269: http://www.iro.umontreal.ca/~lecuyer/myftp/papers/tausme2.ps
 *
 *      ... the k_j most significant bits of z_j must be non-zero,
 *      for each j. (Note: this restriction also applies to the
 *      computer code given in [4], but was mistakenly not mentioned
 *      in that paper.)
 *
 * This affects the seeding procedure by imposing the requirement
 * s1 > 1, s2 > 7, s3 > 15, s4 > 127.
 */

#include <linux/types.h>
#include <linux/percpu.h>
#include <linux/export.h>
#include <linux/jiffies.h>
#include <linux/random.h>
#include <linux/sched.h>
#include <asm/unaligned.h>
#include <trace/events/random.h>

/**
 *	prandom_u32_state - seeded pseudo-random number generator.
 *	@state: pointer to state structure holding seeded state.
 *
 *	This is used for pseudo-randomness with no outside seeding.
 *	For more random results, use prandom_u32().
 */
u32 prandom_u32_state(struct rnd_state *state)
{
#define TAUSWORTHE(s, a, b, c, d) ((s & c) << d) ^ (((s << a) ^ s) >> b)
	state->s1 = TAUSWORTHE(state->s1,  6U, 13U, 4294967294U, 18U);
	state->s2 = TAUSWORTHE(state->s2,  2U, 27U, 4294967288U,  2U);
	state->s3 = TAUSWORTHE(state->s3, 13U, 21U, 4294967280U,  7U);
	state->s4 = TAUSWORTHE(state->s4,  3U, 12U, 4294967168U, 13U);

	return (state->s1 ^ state->s2 ^ state->s3 ^ state->s4);
}
EXPORT_SYMBOL(prandom_u32_state);

/**
 *	prandom_bytes_state - get the requested number of pseudo-random bytes
 *
 *	@state: pointer to state structure holding seeded state.
 *	@buf: where to copy the pseudo-random bytes to
 *	@bytes: the requested number of bytes
 *
 *	This is used for pseudo-randomness with no outside seeding.
 *	For more random results, use prandom_bytes().
 */
void prandom_bytes_state(struct rnd_state *state, void *buf, size_t bytes)
{
	u8 *ptr = buf;

	while (bytes >= sizeof(u32)) {
		put_unaligned(prandom_u32_state(state), (u32 *) ptr);
		ptr += sizeof(u32);
		bytes -= sizeof(u32);
	}

	if (bytes > 0) {
		u32 rem = prandom_u32_state(state);
		do {
			*ptr++ = (u8) rem;
			bytes--;
			rem >>= BITS_PER_BYTE;
		} while (bytes > 0);
	}
}
EXPORT_SYMBOL(prandom_bytes_state);

static void prandom_warmup(struct rnd_state *state)
{
	/* Calling RNG ten times to satisfy recurrence condition */
	prandom_u32_state(state);
	prandom_u32_state(state);
	prandom_u32_state(state);
	prandom_u32_state(state);
	prandom_u32_state(state);
	prandom_u32_state(state);
	prandom_u32_state(state);
	prandom_u32_state(state);
	prandom_u32_state(state);
	prandom_u32_state(state);
}

void prandom_seed_full_state(struct rnd_state __percpu *pcpu_state)
{
	int i;

	for_each_possible_cpu(i) {
		struct rnd_state *state = per_cpu_ptr(pcpu_state, i);
		u32 seeds[4];

		get_random_bytes(&seeds, sizeof(seeds));
		state->s1 = __seed(seeds[0],   2U);
		state->s2 = __seed(seeds[1],   8U);
		state->s3 = __seed(seeds[2],  16U);
		state->s4 = __seed(seeds[3], 128U);

		prandom_warmup(state);
	}
}
EXPORT_SYMBOL(prandom_seed_full_state);

#ifdef CONFIG_RANDOM32_SELFTEST
static struct prandom_test1 {
	u32 seed;
	u32 result;
} test1[] = {
	{ 1U, 3484351685U },
	{ 2U, 2623130059U },
	{ 3U, 3125133893U },
	{ 4U,  984847254U },
};

static struct prandom_test2 {
	u32 seed;
	u32 iteration;
	u32 result;
} test2[] = {
	/* Test cases against taus113 from GSL library. */
	{  931557656U, 959U, 2975593782U },
	{ 1339693295U, 876U, 3887776532U },
	{ 1545556285U, 961U, 1615538833U },
	{  601730776U, 723U, 1776162651U },
	{ 1027516047U, 687U,  511983079U },
	{  416526298U, 700U,  916156552U },
	{ 1395522032U, 652U, 2222063676U },
	{  366221443U, 617U, 2992857763U },
	{ 1539836965U, 714U, 3783265725U },
	{  556206671U, 994U,  799626459U },
	{  684907218U, 799U,  367789491U },
	{ 2121230701U, 931U, 2115467001U },
	{ 1668516451U, 644U, 3620590685U },
	{  768046066U, 883U, 2034077390U },
	{ 1989159136U, 833U, 1195767305U },
	{  536585145U, 996U, 3577259204U },
	{ 1008129373U, 642U, 1478080776U },
	{ 1740775604U, 939U, 1264980372U },
	{ 1967883163U, 508U,   10734624U },
	{ 1923019697U, 730U, 3821419629U },
	{  442079932U, 560U, 3440032343U },
	{ 1961302714U, 845U,  841962572U },
	{ 2030205964U, 962U, 1325144227U },
	{ 1160407529U, 507U,  240940858U },
	{  635482502U, 779U, 4200489746U },
	{ 1252788931U, 699U,  867195434U },
	{ 1961817131U, 719U,  668237657U },
	{ 1071468216U, 983U,  917876630U },
	{ 1281848367U, 932U, 1003100039U },
	{  582537119U, 780U, 1127273778U },
	{ 1973672777U, 853U, 1071368872U },
	{ 1896756996U, 762U, 1127851055U },
	{  847917054U, 500U, 1717499075U },
	{ 1240520510U, 951U, 2849576657U },
	{ 1685071682U, 567U, 1961810396U },
	{ 1516232129U, 557U,    3173877U },
	{ 1208118903U, 612U, 1613145022U },
	{ 1817269927U, 693U, 4279122573U },
	{ 1510091701U, 717U,  638191229U },
	{  365916850U, 807U,  600424314U },
	{  399324359U, 702U, 1803598116U },
	{ 1318480274U, 779U, 2074237022U },
	{  697758115U, 840U, 1483639402U },
	{ 1696507773U, 840U,  577415447U },
	{ 2081979121U, 981U, 3041486449U },
	{  955646687U, 742U, 3846494357U },
	{ 1250683506U, 749U,  836419859U },
	{  595003102U, 534U,  366794109U },
	{   47485338U, 558U, 3521120834U },
	{  619433479U, 610U, 3991783875U },
	{  704096520U, 518U, 4139493852U },
	{ 1712224984U, 606U, 2393312003U },
	{ 1318233152U, 922U, 3880361134U },
	{  855572992U, 761U, 1472974787U },
	{   64721421U, 703U,  683860550U },
	{  678931758U, 840U,  380616043U },
	{  692711973U, 778U, 1382361947U },
	{  677703619U, 530U, 2826914161U },
	{   92393223U, 586U, 1522128471U },
	{ 1222592920U, 743U, 3466726667U },
	{  358288986U, 695U, 1091956998U },
	{ 1935056945U, 958U,  514864477U },
	{  735675993U, 990U, 1294239989U },
	{ 1560089402U, 897U, 2238551287U },
	{   70616361U, 829U,   22483098U },
	{  368234700U, 731U, 2913875084U },
	{   20221190U, 879U, 1564152970U },
	{  539444654U, 682U, 1835141259U },
	{ 1314987297U, 840U, 1801114136U },
	{ 2019295544U, 645U, 3286438930U },
	{  469023838U, 716U, 1637918202U },
	{ 1843754496U, 653U, 2562092152U },
	{  400672036U, 809U, 4264212785U },
	{  404722249U, 965U, 2704116999U },
	{  600702209U, 758U,  584979986U },
	{  519953954U, 667U, 2574436237U },
	{ 1658071126U, 694U, 2214569490U },
	{  420480037U, 749U, 3430010866U },
	{  690103647U, 969U, 3700758083U },
	{ 1029424799U, 937U, 3787746841U },
	{ 2012608669U, 506U, 3362628973U },
	{ 1535432887U, 998U,   42610943U },
	{ 1330635533U, 857U, 3040806504U },
	{ 1223800550U, 539U, 3954229517U },
	{ 1322411537U, 680U, 3223250324U },
	{ 1877847898U, 945U, 2915147143U },
	{ 1646356099U, 874U,  965988280U },
	{  805687536U, 744U, 4032277920U },
	{ 1948093210U, 633U, 1346597684U },
	{  392609744U, 783U, 1636083295U },
	{  690241304U, 770U, 1201031298U },
	{ 1360302965U, 696U, 1665394461U },
	{ 1220090946U, 780U, 1316922812U },
	{  447092251U, 500U, 3438743375U },
	{ 1613868791U, 592U,  828546883U },
	{  523430951U, 548U, 2552392304U },
	{  726692899U, 810U, 1656872867U },
	{ 1364340021U, 836U, 3710513486U },
	{ 1986257729U, 931U,  935013962U },
	{  407983964U, 921U,  728767059U },
};

static u32 __extract_hwseed(void)
{
	unsigned int val = 0;

	(void)(arch_get_random_seed_int(&val) ||
	       arch_get_random_int(&val));

	return val;
}

static void prandom_seed_early(struct rnd_state *state, u32 seed,
			       bool mix_with_hwseed)
{
#define LCG(x)	 ((x) * 69069U)	/* super-duper LCG */
#define HWSEED() (mix_with_hwseed ? __extract_hwseed() : 0)
	state->s1 = __seed(HWSEED() ^ LCG(seed),        2U);
	state->s2 = __seed(HWSEED() ^ LCG(state->s1),   8U);
	state->s3 = __seed(HWSEED() ^ LCG(state->s2),  16U);
	state->s4 = __seed(HWSEED() ^ LCG(state->s3), 128U);
}

static int __init prandom_state_selftest(void)
{
	int i, j, errors = 0, runs = 0;
	bool error = false;

	for (i = 0; i < ARRAY_SIZE(test1); i++) {
		struct rnd_state state;

		prandom_seed_early(&state, test1[i].seed, false);
		prandom_warmup(&state);

		if (test1[i].result != prandom_u32_state(&state))
			error = true;
	}

	if (error)
		pr_warn("prandom: seed boundary self test failed\n");
	else
		pr_info("prandom: seed boundary self test passed\n");

	for (i = 0; i < ARRAY_SIZE(test2); i++) {
		struct rnd_state state;

		prandom_seed_early(&state, test2[i].seed, false);
		prandom_warmup(&state);

		for (j = 0; j < test2[i].iteration - 1; j++)
			prandom_u32_state(&state);

		if (test2[i].result != prandom_u32_state(&state))
			errors++;

		runs++;
		cond_resched();
	}

	if (errors)
		pr_warn("prandom: %d/%d self tests failed\n", errors, runs);
	else
		pr_info("prandom: %d self tests passed\n", runs);
	return 0;
}
core_initcall(prandom_state_selftest);
#endif

/*
 * The prandom_u32() implementation is now completely separate from the
 * prandom_state() functions, which are retained (for now) for compatibility.
 *
 * Because of (ab)use in the networking code for choosing random TCP/UDP port
 * numbers, which open DoS possibilities if guessable, we want something
 * stronger than a standard PRNG.  But the performance requirements of
 * the network code do not allow robust crypto for this application.
 *
 * So this is a homebrew Junior Spaceman implementation, based on the
 * lowest-latency trustworthy crypto primitive available, SipHash.
 * (The authors of SipHash have not been consulted about this abuse of
 * their work.)
 *
 * Standard SipHash-2-4 uses 2n+4 rounds to hash n words of input to
 * one word of output.  This abbreviated version uses 2 rounds per word
 * of output.
 */

struct siprand_state {
	unsigned long v0;
	unsigned long v1;
	unsigned long v2;
	unsigned long v3;
};

static DEFINE_PER_CPU(struct siprand_state, net_rand_state) __latent_entropy;

/*
 * This is the core CPRNG function.  As "pseudorandom", this is not used
 * for truly valuable things, just intended to be a PITA to guess.
 * For maximum speed, we do just two SipHash rounds per word.  This is
 * the same rate as 4 rounds per 64 bits that SipHash normally uses,
 * so hopefully it's reasonably secure.
 *
 * There are two changes from the official SipHash finalization:
 * - We omit some constants XORed with v2 in the SipHash spec as irrelevant;
 *   they are there only to make the output rounds distinct from the input
 *   rounds, and this application has no input rounds.
 * - Rather than returning v0^v1^v2^v3, return v1+v3.
 *   If you look at the SipHash round, the last operation on v3 is
 *   "v3 ^= v0", so "v0 ^ v3" just undoes that, a waste of time.
 *   Likewise "v1 ^= v2".  (The rotate of v2 makes a difference, but
 *   it still cancels out half of the bits in v2 for no benefit.)
 *   Second, since the last combining operation was xor, continue the
 *   pattern of alternating xor/add for a tiny bit of extra non-linearity.
 */
static inline u32 siprand_u32(struct siprand_state *s)
{
	unsigned long v0 = s->v0, v1 = s->v1, v2 = s->v2, v3 = s->v3;

	PRND_SIPROUND(v0, v1, v2, v3);
	PRND_SIPROUND(v0, v1, v2, v3);
	s->v0 = v0;  s->v1 = v1;  s->v2 = v2;  s->v3 = v3;
	return v1 + v3;
}


/**
 *	prandom_u32 - pseudo random number generator
 *
 *	A 32 bit pseudo-random number is generated using a fast
 *	algorithm suitable for simulation. This algorithm is NOT
 *	considered safe for cryptographic use.
 */
u32 prandom_u32(void)
{
	struct siprand_state *state = get_cpu_ptr(&net_rand_state);
	u32 res = siprand_u32(state);

	trace_prandom_u32(res);
	put_cpu_ptr(&net_rand_state);
	return res;
}
EXPORT_SYMBOL(prandom_u32);

/**
 *	prandom_bytes - get the requested number of pseudo-random bytes
 *	@buf: where to copy the pseudo-random bytes to
 *	@bytes: the requested number of bytes
 */
void prandom_bytes(void *buf, size_t bytes)
{
	struct siprand_state *state = get_cpu_ptr(&net_rand_state);
	u8 *ptr = buf;

	while (bytes >= sizeof(u32)) {
		put_unaligned(siprand_u32(state), (u32 *)ptr);
		ptr += sizeof(u32);
		bytes -= sizeof(u32);
	}

	if (bytes > 0) {
		u32 rem = siprand_u32(state);

		do {
			*ptr++ = (u8)rem;
			rem >>= BITS_PER_BYTE;
		} while (--bytes > 0);
	}
	put_cpu_ptr(&net_rand_state);
}
EXPORT_SYMBOL(prandom_bytes);

/**
 *	prandom_seed - add entropy to pseudo random number generator
 *	@entropy: entropy value
 *
 *	Add some additional seed material to the prandom pool.
 *	The "entropy" is actually our IP address (the only caller is
 *	the network code), not for unpredictability, but to ensure that
 *	different machines are initialized differently.
 */
void prandom_seed(u32 entropy)
{
	int i;

	add_device_randomness(&entropy, sizeof(entropy));

	for_each_possible_cpu(i) {
		struct siprand_state *state = per_cpu_ptr(&net_rand_state, i);
		unsigned long v0 = state->v0, v1 = state->v1;
		unsigned long v2 = state->v2, v3 = state->v3;

		do {
			v3 ^= entropy;
			PRND_SIPROUND(v0, v1, v2, v3);
			PRND_SIPROUND(v0, v1, v2, v3);
			v0 ^= entropy;
		} while (unlikely(!v0 || !v1 || !v2 || !v3));

		WRITE_ONCE(state->v0, v0);
		WRITE_ONCE(state->v1, v1);
		WRITE_ONCE(state->v2, v2);
		WRITE_ONCE(state->v3, v3);
	}
}
EXPORT_SYMBOL(prandom_seed);

/*
 *	Generate some initially weak seeding values to allow
 *	the prandom_u32() engine to be started.
 */
static int __init prandom_init_early(void)
{
	int i;
	unsigned long v0, v1, v2, v3;

	if (!arch_get_random_long(&v0))
		v0 = jiffies;
	if (!arch_get_random_long(&v1))
		v1 = random_get_entropy();
	v2 = v0 ^ PRND_K0;
	v3 = v1 ^ PRND_K1;

	for_each_possible_cpu(i) {
		struct siprand_state *state;

		v3 ^= i;
		PRND_SIPROUND(v0, v1, v2, v3);
		PRND_SIPROUND(v0, v1, v2, v3);
		v0 ^= i;

		state = per_cpu_ptr(&net_rand_state, i);
		state->v0 = v0;  state->v1 = v1;
		state->v2 = v2;  state->v3 = v3;
	}

	return 0;
}
core_initcall(prandom_init_early);


/* Stronger reseeding when available, and periodically thereafter. */
static void prandom_reseed(struct timer_list *unused);

static DEFINE_TIMER(seed_timer, prandom_reseed);

static void prandom_reseed(struct timer_list *unused)
{
	unsigned long expires;
	int i;

	/*
	 * Reinitialize each CPU's PRNG with 128 bits of key.
	 * No locking on the CPUs, but then somewhat random results are,
	 * well, expected.
	 */
	for_each_possible_cpu(i) {
		struct siprand_state *state;
		unsigned long v0 = get_random_long(), v2 = v0 ^ PRND_K0;
		unsigned long v1 = get_random_long(), v3 = v1 ^ PRND_K1;
#if BITS_PER_LONG == 32
		int j;

		/*
		 * On 32-bit machines, hash in two extra words to
		 * approximate 128-bit key length.  Not that the hash
		 * has that much security, but this prevents a trivial
		 * 64-bit brute force.
		 */
		for (j = 0; j < 2; j++) {
			unsigned long m = get_random_long();

			v3 ^= m;
			PRND_SIPROUND(v0, v1, v2, v3);
			PRND_SIPROUND(v0, v1, v2, v3);
			v0 ^= m;
		}
#endif
		/*
		 * Probably impossible in practice, but there is a
		 * theoretical risk that a race between this reseeding
		 * and the target CPU writing its state back could
		 * create the all-zero SipHash fixed point.
		 *
		 * To ensure that never happens, ensure the state
		 * we write contains no zero words.
		 */
		state = per_cpu_ptr(&net_rand_state, i);
		WRITE_ONCE(state->v0, v0 ? v0 : -1ul);
		WRITE_ONCE(state->v1, v1 ? v1 : -1ul);
		WRITE_ONCE(state->v2, v2 ? v2 : -1ul);
		WRITE_ONCE(state->v3, v3 ? v3 : -1ul);
	}

	/* reseed every ~60 seconds, in [40 .. 80) interval with slack */
	expires = round_jiffies(jiffies + 40 * HZ + prandom_u32_max(40 * HZ));
	mod_timer(&seed_timer, expires);
}

/*
 * The random ready callback can be called from almost any interrupt.
 * To avoid worrying about whether it's safe to delay that interrupt
 * long enough to seed all CPUs, just schedule an immediate timer event.
 */
static void prandom_timer_start(struct random_ready_callback *unused)
{
	mod_timer(&seed_timer, jiffies);
}

/*
 * Start periodic full reseeding as soon as strong
 * random numbers are available.
 */
static int __init prandom_init_late(void)
{
	static struct random_ready_callback random_ready = {
		.func = prandom_timer_start
	};
	int ret = add_random_ready_callback(&random_ready);

	if (ret == -EALREADY) {
		prandom_timer_start(&random_ready);
		ret = 0;
	}
	return ret;
}
late_initcall(prandom_init_late);

Privacy Policy