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