xref: /openbmc/linux/lib/random32.c (revision dbf563ee) 
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * This is a maximally equidistributed combined Tausworthe generator
4  * based on code from GNU Scientific Library 1.5 (30 Jun 2004)
5  *
6  * lfsr113 version:
7  *
8  * x_n = (s1_n ^ s2_n ^ s3_n ^ s4_n)
9  *
10  * s1_{n+1} = (((s1_n & 4294967294) << 18) ^ (((s1_n <<  6) ^ s1_n) >> 13))
11  * s2_{n+1} = (((s2_n & 4294967288) <<  2) ^ (((s2_n <<  2) ^ s2_n) >> 27))
12  * s3_{n+1} = (((s3_n & 4294967280) <<  7) ^ (((s3_n << 13) ^ s3_n) >> 21))
13  * s4_{n+1} = (((s4_n & 4294967168) << 13) ^ (((s4_n <<  3) ^ s4_n) >> 12))
14  *
15  * The period of this generator is about 2^113 (see erratum paper).
16  *
17  * From: P. L'Ecuyer, "Maximally Equidistributed Combined Tausworthe
18  * Generators", Mathematics of Computation, 65, 213 (1996), 203--213:
19  * http://www.iro.umontreal.ca/~lecuyer/myftp/papers/tausme.ps
20  * ftp://ftp.iro.umontreal.ca/pub/simulation/lecuyer/papers/tausme.ps
21  *
22  * There is an erratum in the paper "Tables of Maximally Equidistributed
23  * Combined LFSR Generators", Mathematics of Computation, 68, 225 (1999),
24  * 261--269: http://www.iro.umontreal.ca/~lecuyer/myftp/papers/tausme2.ps
25  *
26  *      ... the k_j most significant bits of z_j must be non-zero,
27  *      for each j. (Note: this restriction also applies to the
28  *      computer code given in [4], but was mistakenly not mentioned
29  *      in that paper.)
30  *
31  * This affects the seeding procedure by imposing the requirement
32  * s1 > 1, s2 > 7, s3 > 15, s4 > 127.
33  */
34 
35 #include <linux/types.h>
36 #include <linux/percpu.h>
37 #include <linux/export.h>
38 #include <linux/jiffies.h>
39 #include <linux/random.h>
40 #include <linux/sched.h>
41 #include <asm/unaligned.h>
42 #include <trace/events/random.h>
43 
44 #ifdef CONFIG_RANDOM32_SELFTEST
45 static void __init prandom_state_selftest(void);
46 #else
47 static inline void prandom_state_selftest(void)
48 {
49 }
50 #endif
51 
52 DEFINE_PER_CPU(struct rnd_state, net_rand_state)  __latent_entropy;
53 
54 /**
55  *	prandom_u32_state - seeded pseudo-random number generator.
56  *	@state: pointer to state structure holding seeded state.
57  *
58  *	This is used for pseudo-randomness with no outside seeding.
59  *	For more random results, use prandom_u32().
60  */
61 u32 prandom_u32_state(struct rnd_state *state)
62 {
63 #define TAUSWORTHE(s, a, b, c, d) ((s & c) << d) ^ (((s << a) ^ s) >> b)
64 	state->s1 = TAUSWORTHE(state->s1,  6U, 13U, 4294967294U, 18U);
65 	state->s2 = TAUSWORTHE(state->s2,  2U, 27U, 4294967288U,  2U);
66 	state->s3 = TAUSWORTHE(state->s3, 13U, 21U, 4294967280U,  7U);
67 	state->s4 = TAUSWORTHE(state->s4,  3U, 12U, 4294967168U, 13U);
68 
69 	return (state->s1 ^ state->s2 ^ state->s3 ^ state->s4);
70 }
71 EXPORT_SYMBOL(prandom_u32_state);
72 
73 /**
74  *	prandom_u32 - pseudo random number generator
75  *
76  *	A 32 bit pseudo-random number is generated using a fast
77  *	algorithm suitable for simulation. This algorithm is NOT
78  *	considered safe for cryptographic use.
79  */
80 u32 prandom_u32(void)
81 {
82 	struct rnd_state *state = &get_cpu_var(net_rand_state);
83 	u32 res;
84 
85 	res = prandom_u32_state(state);
86 	trace_prandom_u32(res);
87 	put_cpu_var(net_rand_state);
88 
89 	return res;
90 }
91 EXPORT_SYMBOL(prandom_u32);
92 
93 /**
94  *	prandom_bytes_state - get the requested number of pseudo-random bytes
95  *
96  *	@state: pointer to state structure holding seeded state.
97  *	@buf: where to copy the pseudo-random bytes to
98  *	@bytes: the requested number of bytes
99  *
100  *	This is used for pseudo-randomness with no outside seeding.
101  *	For more random results, use prandom_bytes().
102  */
103 void prandom_bytes_state(struct rnd_state *state, void *buf, size_t bytes)
104 {
105 	u8 *ptr = buf;
106 
107 	while (bytes >= sizeof(u32)) {
108 		put_unaligned(prandom_u32_state(state), (u32 *) ptr);
109 		ptr += sizeof(u32);
110 		bytes -= sizeof(u32);
111 	}
112 
113 	if (bytes > 0) {
114 		u32 rem = prandom_u32_state(state);
115 		do {
116 			*ptr++ = (u8) rem;
117 			bytes--;
118 			rem >>= BITS_PER_BYTE;
119 		} while (bytes > 0);
120 	}
121 }
122 EXPORT_SYMBOL(prandom_bytes_state);
123 
124 /**
125  *	prandom_bytes - get the requested number of pseudo-random bytes
126  *	@buf: where to copy the pseudo-random bytes to
127  *	@bytes: the requested number of bytes
128  */
129 void prandom_bytes(void *buf, size_t bytes)
130 {
131 	struct rnd_state *state = &get_cpu_var(net_rand_state);
132 
133 	prandom_bytes_state(state, buf, bytes);
134 	put_cpu_var(net_rand_state);
135 }
136 EXPORT_SYMBOL(prandom_bytes);
137 
138 static void prandom_warmup(struct rnd_state *state)
139 {
140 	/* Calling RNG ten times to satisfy recurrence condition */
141 	prandom_u32_state(state);
142 	prandom_u32_state(state);
143 	prandom_u32_state(state);
144 	prandom_u32_state(state);
145 	prandom_u32_state(state);
146 	prandom_u32_state(state);
147 	prandom_u32_state(state);
148 	prandom_u32_state(state);
149 	prandom_u32_state(state);
150 	prandom_u32_state(state);
151 }
152 
153 static u32 __extract_hwseed(void)
154 {
155 	unsigned int val = 0;
156 
157 	(void)(arch_get_random_seed_int(&val) ||
158 	       arch_get_random_int(&val));
159 
160 	return val;
161 }
162 
163 static void prandom_seed_early(struct rnd_state *state, u32 seed,
164 			       bool mix_with_hwseed)
165 {
166 #define LCG(x)	 ((x) * 69069U)	/* super-duper LCG */
167 #define HWSEED() (mix_with_hwseed ? __extract_hwseed() : 0)
168 	state->s1 = __seed(HWSEED() ^ LCG(seed),        2U);
169 	state->s2 = __seed(HWSEED() ^ LCG(state->s1),   8U);
170 	state->s3 = __seed(HWSEED() ^ LCG(state->s2),  16U);
171 	state->s4 = __seed(HWSEED() ^ LCG(state->s3), 128U);
172 }
173 
174 /**
175  *	prandom_seed - add entropy to pseudo random number generator
176  *	@entropy: entropy value
177  *
178  *	Add some additional entropy to the prandom pool.
179  */
180 void prandom_seed(u32 entropy)
181 {
182 	int i;
183 	/*
184 	 * No locking on the CPUs, but then somewhat random results are, well,
185 	 * expected.
186 	 */
187 	for_each_possible_cpu(i) {
188 		struct rnd_state *state = &per_cpu(net_rand_state, i);
189 
190 		state->s1 = __seed(state->s1 ^ entropy, 2U);
191 		prandom_warmup(state);
192 	}
193 }
194 EXPORT_SYMBOL(prandom_seed);
195 
196 /*
197  *	Generate some initially weak seeding values to allow
198  *	to start the prandom_u32() engine.
199  */
200 static int __init prandom_init(void)
201 {
202 	int i;
203 
204 	prandom_state_selftest();
205 
206 	for_each_possible_cpu(i) {
207 		struct rnd_state *state = &per_cpu(net_rand_state, i);
208 		u32 weak_seed = (i + jiffies) ^ random_get_entropy();
209 
210 		prandom_seed_early(state, weak_seed, true);
211 		prandom_warmup(state);
212 	}
213 
214 	return 0;
215 }
216 core_initcall(prandom_init);
217 
218 static void __prandom_timer(struct timer_list *unused);
219 
220 static DEFINE_TIMER(seed_timer, __prandom_timer);
221 
222 static void __prandom_timer(struct timer_list *unused)
223 {
224 	u32 entropy;
225 	unsigned long expires;
226 
227 	get_random_bytes(&entropy, sizeof(entropy));
228 	prandom_seed(entropy);
229 
230 	/* reseed every ~60 seconds, in [40 .. 80) interval with slack */
231 	expires = 40 + prandom_u32_max(40);
232 	seed_timer.expires = jiffies + msecs_to_jiffies(expires * MSEC_PER_SEC);
233 
234 	add_timer(&seed_timer);
235 }
236 
237 static void __init __prandom_start_seed_timer(void)
238 {
239 	seed_timer.expires = jiffies + msecs_to_jiffies(40 * MSEC_PER_SEC);
240 	add_timer(&seed_timer);
241 }
242 
243 void prandom_seed_full_state(struct rnd_state __percpu *pcpu_state)
244 {
245 	int i;
246 
247 	for_each_possible_cpu(i) {
248 		struct rnd_state *state = per_cpu_ptr(pcpu_state, i);
249 		u32 seeds[4];
250 
251 		get_random_bytes(&seeds, sizeof(seeds));
252 		state->s1 = __seed(seeds[0],   2U);
253 		state->s2 = __seed(seeds[1],   8U);
254 		state->s3 = __seed(seeds[2],  16U);
255 		state->s4 = __seed(seeds[3], 128U);
256 
257 		prandom_warmup(state);
258 	}
259 }
260 EXPORT_SYMBOL(prandom_seed_full_state);
261 
262 /*
263  *	Generate better values after random number generator
264  *	is fully initialized.
265  */
266 static void __prandom_reseed(bool late)
267 {
268 	unsigned long flags;
269 	static bool latch = false;
270 	static DEFINE_SPINLOCK(lock);
271 
272 	/* Asking for random bytes might result in bytes getting
273 	 * moved into the nonblocking pool and thus marking it
274 	 * as initialized. In this case we would double back into
275 	 * this function and attempt to do a late reseed.
276 	 * Ignore the pointless attempt to reseed again if we're
277 	 * already waiting for bytes when the nonblocking pool
278 	 * got initialized.
279 	 */
280 
281 	/* only allow initial seeding (late == false) once */
282 	if (!spin_trylock_irqsave(&lock, flags))
283 		return;
284 
285 	if (latch && !late)
286 		goto out;
287 
288 	latch = true;
289 	prandom_seed_full_state(&net_rand_state);
290 out:
291 	spin_unlock_irqrestore(&lock, flags);
292 }
293 
294 void prandom_reseed_late(void)
295 {
296 	__prandom_reseed(true);
297 }
298 
299 static int __init prandom_reseed(void)
300 {
301 	__prandom_reseed(false);
302 	__prandom_start_seed_timer();
303 	return 0;
304 }
305 late_initcall(prandom_reseed);
306 
307 #ifdef CONFIG_RANDOM32_SELFTEST
308 static struct prandom_test1 {
309 	u32 seed;
310 	u32 result;
311 } test1[] = {
312 	{ 1U, 3484351685U },
313 	{ 2U, 2623130059U },
314 	{ 3U, 3125133893U },
315 	{ 4U,  984847254U },
316 };
317 
318 static struct prandom_test2 {
319 	u32 seed;
320 	u32 iteration;
321 	u32 result;
322 } test2[] = {
323 	/* Test cases against taus113 from GSL library. */
324 	{  931557656U, 959U, 2975593782U },
325 	{ 1339693295U, 876U, 3887776532U },
326 	{ 1545556285U, 961U, 1615538833U },
327 	{  601730776U, 723U, 1776162651U },
328 	{ 1027516047U, 687U,  511983079U },
329 	{  416526298U, 700U,  916156552U },
330 	{ 1395522032U, 652U, 2222063676U },
331 	{  366221443U, 617U, 2992857763U },
332 	{ 1539836965U, 714U, 3783265725U },
333 	{  556206671U, 994U,  799626459U },
334 	{  684907218U, 799U,  367789491U },
335 	{ 2121230701U, 931U, 2115467001U },
336 	{ 1668516451U, 644U, 3620590685U },
337 	{  768046066U, 883U, 2034077390U },
338 	{ 1989159136U, 833U, 1195767305U },
339 	{  536585145U, 996U, 3577259204U },
340 	{ 1008129373U, 642U, 1478080776U },
341 	{ 1740775604U, 939U, 1264980372U },
342 	{ 1967883163U, 508U,   10734624U },
343 	{ 1923019697U, 730U, 3821419629U },
344 	{  442079932U, 560U, 3440032343U },
345 	{ 1961302714U, 845U,  841962572U },
346 	{ 2030205964U, 962U, 1325144227U },
347 	{ 1160407529U, 507U,  240940858U },
348 	{  635482502U, 779U, 4200489746U },
349 	{ 1252788931U, 699U,  867195434U },
350 	{ 1961817131U, 719U,  668237657U },
351 	{ 1071468216U, 983U,  917876630U },
352 	{ 1281848367U, 932U, 1003100039U },
353 	{  582537119U, 780U, 1127273778U },
354 	{ 1973672777U, 853U, 1071368872U },
355 	{ 1896756996U, 762U, 1127851055U },
356 	{  847917054U, 500U, 1717499075U },
357 	{ 1240520510U, 951U, 2849576657U },
358 	{ 1685071682U, 567U, 1961810396U },
359 	{ 1516232129U, 557U,    3173877U },
360 	{ 1208118903U, 612U, 1613145022U },
361 	{ 1817269927U, 693U, 4279122573U },
362 	{ 1510091701U, 717U,  638191229U },
363 	{  365916850U, 807U,  600424314U },
364 	{  399324359U, 702U, 1803598116U },
365 	{ 1318480274U, 779U, 2074237022U },
366 	{  697758115U, 840U, 1483639402U },
367 	{ 1696507773U, 840U,  577415447U },
368 	{ 2081979121U, 981U, 3041486449U },
369 	{  955646687U, 742U, 3846494357U },
370 	{ 1250683506U, 749U,  836419859U },
371 	{  595003102U, 534U,  366794109U },
372 	{   47485338U, 558U, 3521120834U },
373 	{  619433479U, 610U, 3991783875U },
374 	{  704096520U, 518U, 4139493852U },
375 	{ 1712224984U, 606U, 2393312003U },
376 	{ 1318233152U, 922U, 3880361134U },
377 	{  855572992U, 761U, 1472974787U },
378 	{   64721421U, 703U,  683860550U },
379 	{  678931758U, 840U,  380616043U },
380 	{  692711973U, 778U, 1382361947U },
381 	{  677703619U, 530U, 2826914161U },
382 	{   92393223U, 586U, 1522128471U },
383 	{ 1222592920U, 743U, 3466726667U },
384 	{  358288986U, 695U, 1091956998U },
385 	{ 1935056945U, 958U,  514864477U },
386 	{  735675993U, 990U, 1294239989U },
387 	{ 1560089402U, 897U, 2238551287U },
388 	{   70616361U, 829U,   22483098U },
389 	{  368234700U, 731U, 2913875084U },
390 	{   20221190U, 879U, 1564152970U },
391 	{  539444654U, 682U, 1835141259U },
392 	{ 1314987297U, 840U, 1801114136U },
393 	{ 2019295544U, 645U, 3286438930U },
394 	{  469023838U, 716U, 1637918202U },
395 	{ 1843754496U, 653U, 2562092152U },
396 	{  400672036U, 809U, 4264212785U },
397 	{  404722249U, 965U, 2704116999U },
398 	{  600702209U, 758U,  584979986U },
399 	{  519953954U, 667U, 2574436237U },
400 	{ 1658071126U, 694U, 2214569490U },
401 	{  420480037U, 749U, 3430010866U },
402 	{  690103647U, 969U, 3700758083U },
403 	{ 1029424799U, 937U, 3787746841U },
404 	{ 2012608669U, 506U, 3362628973U },
405 	{ 1535432887U, 998U,   42610943U },
406 	{ 1330635533U, 857U, 3040806504U },
407 	{ 1223800550U, 539U, 3954229517U },
408 	{ 1322411537U, 680U, 3223250324U },
409 	{ 1877847898U, 945U, 2915147143U },
410 	{ 1646356099U, 874U,  965988280U },
411 	{  805687536U, 744U, 4032277920U },
412 	{ 1948093210U, 633U, 1346597684U },
413 	{  392609744U, 783U, 1636083295U },
414 	{  690241304U, 770U, 1201031298U },
415 	{ 1360302965U, 696U, 1665394461U },
416 	{ 1220090946U, 780U, 1316922812U },
417 	{  447092251U, 500U, 3438743375U },
418 	{ 1613868791U, 592U,  828546883U },
419 	{  523430951U, 548U, 2552392304U },
420 	{  726692899U, 810U, 1656872867U },
421 	{ 1364340021U, 836U, 3710513486U },
422 	{ 1986257729U, 931U,  935013962U },
423 	{  407983964U, 921U,  728767059U },
424 };
425 
426 static void __init prandom_state_selftest(void)
427 {
428 	int i, j, errors = 0, runs = 0;
429 	bool error = false;
430 
431 	for (i = 0; i < ARRAY_SIZE(test1); i++) {
432 		struct rnd_state state;
433 
434 		prandom_seed_early(&state, test1[i].seed, false);
435 		prandom_warmup(&state);
436 
437 		if (test1[i].result != prandom_u32_state(&state))
438 			error = true;
439 	}
440 
441 	if (error)
442 		pr_warn("prandom: seed boundary self test failed\n");
443 	else
444 		pr_info("prandom: seed boundary self test passed\n");
445 
446 	for (i = 0; i < ARRAY_SIZE(test2); i++) {
447 		struct rnd_state state;
448 
449 		prandom_seed_early(&state, test2[i].seed, false);
450 		prandom_warmup(&state);
451 
452 		for (j = 0; j < test2[i].iteration - 1; j++)
453 			prandom_u32_state(&state);
454 
455 		if (test2[i].result != prandom_u32_state(&state))
456 			errors++;
457 
458 		runs++;
459 		cond_resched();
460 	}
461 
462 	if (errors)
463 		pr_warn("prandom: %d/%d self tests failed\n", errors, runs);
464 	else
465 		pr_info("prandom: %d self tests passed\n", runs);
466 }
467 #endif
468