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 <linux/bitops.h>
42#include <linux/slab.h>
43#include <asm/unaligned.h>
44
45/**
46 *	prandom_u32_state - seeded pseudo-random number generator.
47 *	@state: pointer to state structure holding seeded state.
48 *
49 *	This is used for pseudo-randomness with no outside seeding.
50 *	For more random results, use get_random_u32().
51 */
52u32 prandom_u32_state(struct rnd_state *state)
53{
54#define TAUSWORTHE(s, a, b, c, d) ((s & c) << d) ^ (((s << a) ^ s) >> b)
55	state->s1 = TAUSWORTHE(state->s1,  6U, 13U, 4294967294U, 18U);
56	state->s2 = TAUSWORTHE(state->s2,  2U, 27U, 4294967288U,  2U);
57	state->s3 = TAUSWORTHE(state->s3, 13U, 21U, 4294967280U,  7U);
58	state->s4 = TAUSWORTHE(state->s4,  3U, 12U, 4294967168U, 13U);
59
60	return (state->s1 ^ state->s2 ^ state->s3 ^ state->s4);
61}
62EXPORT_SYMBOL(prandom_u32_state);
63
64/**
65 *	prandom_bytes_state - get the requested number of pseudo-random bytes
66 *
67 *	@state: pointer to state structure holding seeded state.
68 *	@buf: where to copy the pseudo-random bytes to
69 *	@bytes: the requested number of bytes
70 *
71 *	This is used for pseudo-randomness with no outside seeding.
72 *	For more random results, use get_random_bytes().
73 */
74void prandom_bytes_state(struct rnd_state *state, void *buf, size_t bytes)
75{
76	u8 *ptr = buf;
77
78	while (bytes >= sizeof(u32)) {
79		put_unaligned(prandom_u32_state(state), (u32 *) ptr);
80		ptr += sizeof(u32);
81		bytes -= sizeof(u32);
82	}
83
84	if (bytes > 0) {
85		u32 rem = prandom_u32_state(state);
86		do {
87			*ptr++ = (u8) rem;
88			bytes--;
89			rem >>= BITS_PER_BYTE;
90		} while (bytes > 0);
91	}
92}
93EXPORT_SYMBOL(prandom_bytes_state);
94
95static void prandom_warmup(struct rnd_state *state)
96{
97	/* Calling RNG ten times to satisfy recurrence condition */
98	prandom_u32_state(state);
99	prandom_u32_state(state);
100	prandom_u32_state(state);
101	prandom_u32_state(state);
102	prandom_u32_state(state);
103	prandom_u32_state(state);
104	prandom_u32_state(state);
105	prandom_u32_state(state);
106	prandom_u32_state(state);
107	prandom_u32_state(state);
108}
109
110void prandom_seed_full_state(struct rnd_state __percpu *pcpu_state)
111{
112	int i;
113
114	for_each_possible_cpu(i) {
115		struct rnd_state *state = per_cpu_ptr(pcpu_state, i);
116		u32 seeds[4];
117
118		get_random_bytes(&seeds, sizeof(seeds));
119		state->s1 = __seed(seeds[0],   2U);
120		state->s2 = __seed(seeds[1],   8U);
121		state->s3 = __seed(seeds[2],  16U);
122		state->s4 = __seed(seeds[3], 128U);
123
124		prandom_warmup(state);
125	}
126}
127EXPORT_SYMBOL(prandom_seed_full_state);
128
129#ifdef CONFIG_RANDOM32_SELFTEST
130static struct prandom_test1 {
131	u32 seed;
132	u32 result;
133} test1[] = {
134	{ 1U, 3484351685U },
135	{ 2U, 2623130059U },
136	{ 3U, 3125133893U },
137	{ 4U,  984847254U },
138};
139
140static struct prandom_test2 {
141	u32 seed;
142	u32 iteration;
143	u32 result;
144} test2[] = {
145	/* Test cases against taus113 from GSL library. */
146	{  931557656U, 959U, 2975593782U },
147	{ 1339693295U, 876U, 3887776532U },
148	{ 1545556285U, 961U, 1615538833U },
149	{  601730776U, 723U, 1776162651U },
150	{ 1027516047U, 687U,  511983079U },
151	{  416526298U, 700U,  916156552U },
152	{ 1395522032U, 652U, 2222063676U },
153	{  366221443U, 617U, 2992857763U },
154	{ 1539836965U, 714U, 3783265725U },
155	{  556206671U, 994U,  799626459U },
156	{  684907218U, 799U,  367789491U },
157	{ 2121230701U, 931U, 2115467001U },
158	{ 1668516451U, 644U, 3620590685U },
159	{  768046066U, 883U, 2034077390U },
160	{ 1989159136U, 833U, 1195767305U },
161	{  536585145U, 996U, 3577259204U },
162	{ 1008129373U, 642U, 1478080776U },
163	{ 1740775604U, 939U, 1264980372U },
164	{ 1967883163U, 508U,   10734624U },
165	{ 1923019697U, 730U, 3821419629U },
166	{  442079932U, 560U, 3440032343U },
167	{ 1961302714U, 845U,  841962572U },
168	{ 2030205964U, 962U, 1325144227U },
169	{ 1160407529U, 507U,  240940858U },
170	{  635482502U, 779U, 4200489746U },
171	{ 1252788931U, 699U,  867195434U },
172	{ 1961817131U, 719U,  668237657U },
173	{ 1071468216U, 983U,  917876630U },
174	{ 1281848367U, 932U, 1003100039U },
175	{  582537119U, 780U, 1127273778U },
176	{ 1973672777U, 853U, 1071368872U },
177	{ 1896756996U, 762U, 1127851055U },
178	{  847917054U, 500U, 1717499075U },
179	{ 1240520510U, 951U, 2849576657U },
180	{ 1685071682U, 567U, 1961810396U },
181	{ 1516232129U, 557U,    3173877U },
182	{ 1208118903U, 612U, 1613145022U },
183	{ 1817269927U, 693U, 4279122573U },
184	{ 1510091701U, 717U,  638191229U },
185	{  365916850U, 807U,  600424314U },
186	{  399324359U, 702U, 1803598116U },
187	{ 1318480274U, 779U, 2074237022U },
188	{  697758115U, 840U, 1483639402U },
189	{ 1696507773U, 840U,  577415447U },
190	{ 2081979121U, 981U, 3041486449U },
191	{  955646687U, 742U, 3846494357U },
192	{ 1250683506U, 749U,  836419859U },
193	{  595003102U, 534U,  366794109U },
194	{   47485338U, 558U, 3521120834U },
195	{  619433479U, 610U, 3991783875U },
196	{  704096520U, 518U, 4139493852U },
197	{ 1712224984U, 606U, 2393312003U },
198	{ 1318233152U, 922U, 3880361134U },
199	{  855572992U, 761U, 1472974787U },
200	{   64721421U, 703U,  683860550U },
201	{  678931758U, 840U,  380616043U },
202	{  692711973U, 778U, 1382361947U },
203	{  677703619U, 530U, 2826914161U },
204	{   92393223U, 586U, 1522128471U },
205	{ 1222592920U, 743U, 3466726667U },
206	{  358288986U, 695U, 1091956998U },
207	{ 1935056945U, 958U,  514864477U },
208	{  735675993U, 990U, 1294239989U },
209	{ 1560089402U, 897U, 2238551287U },
210	{   70616361U, 829U,   22483098U },
211	{  368234700U, 731U, 2913875084U },
212	{   20221190U, 879U, 1564152970U },
213	{  539444654U, 682U, 1835141259U },
214	{ 1314987297U, 840U, 1801114136U },
215	{ 2019295544U, 645U, 3286438930U },
216	{  469023838U, 716U, 1637918202U },
217	{ 1843754496U, 653U, 2562092152U },
218	{  400672036U, 809U, 4264212785U },
219	{  404722249U, 965U, 2704116999U },
220	{  600702209U, 758U,  584979986U },
221	{  519953954U, 667U, 2574436237U },
222	{ 1658071126U, 694U, 2214569490U },
223	{  420480037U, 749U, 3430010866U },
224	{  690103647U, 969U, 3700758083U },
225	{ 1029424799U, 937U, 3787746841U },
226	{ 2012608669U, 506U, 3362628973U },
227	{ 1535432887U, 998U,   42610943U },
228	{ 1330635533U, 857U, 3040806504U },
229	{ 1223800550U, 539U, 3954229517U },
230	{ 1322411537U, 680U, 3223250324U },
231	{ 1877847898U, 945U, 2915147143U },
232	{ 1646356099U, 874U,  965988280U },
233	{  805687536U, 744U, 4032277920U },
234	{ 1948093210U, 633U, 1346597684U },
235	{  392609744U, 783U, 1636083295U },
236	{  690241304U, 770U, 1201031298U },
237	{ 1360302965U, 696U, 1665394461U },
238	{ 1220090946U, 780U, 1316922812U },
239	{  447092251U, 500U, 3438743375U },
240	{ 1613868791U, 592U,  828546883U },
241	{  523430951U, 548U, 2552392304U },
242	{  726692899U, 810U, 1656872867U },
243	{ 1364340021U, 836U, 3710513486U },
244	{ 1986257729U, 931U,  935013962U },
245	{  407983964U, 921U,  728767059U },
246};
247
248static void prandom_state_selftest_seed(struct rnd_state *state, u32 seed)
249{
250#define LCG(x)	 ((x) * 69069U)	/* super-duper LCG */
251	state->s1 = __seed(LCG(seed),        2U);
252	state->s2 = __seed(LCG(state->s1),   8U);
253	state->s3 = __seed(LCG(state->s2),  16U);
254	state->s4 = __seed(LCG(state->s3), 128U);
255}
256
257static int __init prandom_state_selftest(void)
258{
259	int i, j, errors = 0, runs = 0;
260	bool error = false;
261
262	for (i = 0; i < ARRAY_SIZE(test1); i++) {
263		struct rnd_state state;
264
265		prandom_state_selftest_seed(&state, test1[i].seed);
266		prandom_warmup(&state);
267
268		if (test1[i].result != prandom_u32_state(&state))
269			error = true;
270	}
271
272	if (error)
273		pr_warn("prandom: seed boundary self test failed\n");
274	else
275		pr_info("prandom: seed boundary self test passed\n");
276
277	for (i = 0; i < ARRAY_SIZE(test2); i++) {
278		struct rnd_state state;
279
280		prandom_state_selftest_seed(&state, test2[i].seed);
281		prandom_warmup(&state);
282
283		for (j = 0; j < test2[i].iteration - 1; j++)
284			prandom_u32_state(&state);
285
286		if (test2[i].result != prandom_u32_state(&state))
287			errors++;
288
289		runs++;
290		cond_resched();
291	}
292
293	if (errors)
294		pr_warn("prandom: %d/%d self tests failed\n", errors, runs);
295	else
296		pr_info("prandom: %d self tests passed\n", runs);
297	return 0;
298}
299core_initcall(prandom_state_selftest);
300#endif
301