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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 <asm/unaligned.h>
43#include <trace/events/random.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 prandom_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 prandom_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 u32 __extract_hwseed(void)
249{
250 unsigned int val = 0;
251
252 (void)(arch_get_random_seed_int(&val) ||
253 arch_get_random_int(&val));
254
255 return val;
256}
257
258static void prandom_seed_early(struct rnd_state *state, u32 seed,
259 bool mix_with_hwseed)
260{
261#define LCG(x) ((x) * 69069U) /* super-duper LCG */
262#define HWSEED() (mix_with_hwseed ? __extract_hwseed() : 0)
263 state->s1 = __seed(HWSEED() ^ LCG(seed), 2U);
264 state->s2 = __seed(HWSEED() ^ LCG(state->s1), 8U);
265 state->s3 = __seed(HWSEED() ^ LCG(state->s2), 16U);
266 state->s4 = __seed(HWSEED() ^ LCG(state->s3), 128U);
267}
268
269static int __init prandom_state_selftest(void)
270{
271 int i, j, errors = 0, runs = 0;
272 bool error = false;
273
274 for (i = 0; i < ARRAY_SIZE(test1); i++) {
275 struct rnd_state state;
276
277 prandom_seed_early(&state, test1[i].seed, false);
278 prandom_warmup(&state);
279
280 if (test1[i].result != prandom_u32_state(&state))
281 error = true;
282 }
283
284 if (error)
285 pr_warn("prandom: seed boundary self test failed\n");
286 else
287 pr_info("prandom: seed boundary self test passed\n");
288
289 for (i = 0; i < ARRAY_SIZE(test2); i++) {
290 struct rnd_state state;
291
292 prandom_seed_early(&state, test2[i].seed, false);
293 prandom_warmup(&state);
294
295 for (j = 0; j < test2[i].iteration - 1; j++)
296 prandom_u32_state(&state);
297
298 if (test2[i].result != prandom_u32_state(&state))
299 errors++;
300
301 runs++;
302 cond_resched();
303 }
304
305 if (errors)
306 pr_warn("prandom: %d/%d self tests failed\n", errors, runs);
307 else
308 pr_info("prandom: %d self tests passed\n", runs);
309 return 0;
310}
311core_initcall(prandom_state_selftest);
312#endif
313
314/*
315 * The prandom_u32() implementation is now completely separate from the
316 * prandom_state() functions, which are retained (for now) for compatibility.
317 *
318 * Because of (ab)use in the networking code for choosing random TCP/UDP port
319 * numbers, which open DoS possibilities if guessable, we want something
320 * stronger than a standard PRNG. But the performance requirements of
321 * the network code do not allow robust crypto for this application.
322 *
323 * So this is a homebrew Junior Spaceman implementation, based on the
324 * lowest-latency trustworthy crypto primitive available, SipHash.
325 * (The authors of SipHash have not been consulted about this abuse of
326 * their work.)
327 *
328 * Standard SipHash-2-4 uses 2n+4 rounds to hash n words of input to
329 * one word of output. This abbreviated version uses 2 rounds per word
330 * of output.
331 */
332
333struct siprand_state {
334 unsigned long v0;
335 unsigned long v1;
336 unsigned long v2;
337 unsigned long v3;
338};
339
340static DEFINE_PER_CPU(struct siprand_state, net_rand_state) __latent_entropy;
341DEFINE_PER_CPU(unsigned long, net_rand_noise);
342EXPORT_PER_CPU_SYMBOL(net_rand_noise);
343
344/*
345 * This is the core CPRNG function. As "pseudorandom", this is not used
346 * for truly valuable things, just intended to be a PITA to guess.
347 * For maximum speed, we do just two SipHash rounds per word. This is
348 * the same rate as 4 rounds per 64 bits that SipHash normally uses,
349 * so hopefully it's reasonably secure.
350 *
351 * There are two changes from the official SipHash finalization:
352 * - We omit some constants XORed with v2 in the SipHash spec as irrelevant;
353 * they are there only to make the output rounds distinct from the input
354 * rounds, and this application has no input rounds.
355 * - Rather than returning v0^v1^v2^v3, return v1+v3.
356 * If you look at the SipHash round, the last operation on v3 is
357 * "v3 ^= v0", so "v0 ^ v3" just undoes that, a waste of time.
358 * Likewise "v1 ^= v2". (The rotate of v2 makes a difference, but
359 * it still cancels out half of the bits in v2 for no benefit.)
360 * Second, since the last combining operation was xor, continue the
361 * pattern of alternating xor/add for a tiny bit of extra non-linearity.
362 */
363static inline u32 siprand_u32(struct siprand_state *s)
364{
365 unsigned long v0 = s->v0, v1 = s->v1, v2 = s->v2, v3 = s->v3;
366 unsigned long n = raw_cpu_read(net_rand_noise);
367
368 v3 ^= n;
369 PRND_SIPROUND(v0, v1, v2, v3);
370 PRND_SIPROUND(v0, v1, v2, v3);
371 v0 ^= n;
372 s->v0 = v0; s->v1 = v1; s->v2 = v2; s->v3 = v3;
373 return v1 + v3;
374}
375
376
377/**
378 * prandom_u32 - pseudo random number generator
379 *
380 * A 32 bit pseudo-random number is generated using a fast
381 * algorithm suitable for simulation. This algorithm is NOT
382 * considered safe for cryptographic use.
383 */
384u32 prandom_u32(void)
385{
386 struct siprand_state *state = get_cpu_ptr(&net_rand_state);
387 u32 res = siprand_u32(state);
388
389 trace_prandom_u32(res);
390 put_cpu_ptr(&net_rand_state);
391 return res;
392}
393EXPORT_SYMBOL(prandom_u32);
394
395/**
396 * prandom_bytes - get the requested number of pseudo-random bytes
397 * @buf: where to copy the pseudo-random bytes to
398 * @bytes: the requested number of bytes
399 */
400void prandom_bytes(void *buf, size_t bytes)
401{
402 struct siprand_state *state = get_cpu_ptr(&net_rand_state);
403 u8 *ptr = buf;
404
405 while (bytes >= sizeof(u32)) {
406 put_unaligned(siprand_u32(state), (u32 *)ptr);
407 ptr += sizeof(u32);
408 bytes -= sizeof(u32);
409 }
410
411 if (bytes > 0) {
412 u32 rem = siprand_u32(state);
413
414 do {
415 *ptr++ = (u8)rem;
416 rem >>= BITS_PER_BYTE;
417 } while (--bytes > 0);
418 }
419 put_cpu_ptr(&net_rand_state);
420}
421EXPORT_SYMBOL(prandom_bytes);
422
423/**
424 * prandom_seed - add entropy to pseudo random number generator
425 * @entropy: entropy value
426 *
427 * Add some additional seed material to the prandom pool.
428 * The "entropy" is actually our IP address (the only caller is
429 * the network code), not for unpredictability, but to ensure that
430 * different machines are initialized differently.
431 */
432void prandom_seed(u32 entropy)
433{
434 int i;
435
436 add_device_randomness(&entropy, sizeof(entropy));
437
438 for_each_possible_cpu(i) {
439 struct siprand_state *state = per_cpu_ptr(&net_rand_state, i);
440 unsigned long v0 = state->v0, v1 = state->v1;
441 unsigned long v2 = state->v2, v3 = state->v3;
442
443 do {
444 v3 ^= entropy;
445 PRND_SIPROUND(v0, v1, v2, v3);
446 PRND_SIPROUND(v0, v1, v2, v3);
447 v0 ^= entropy;
448 } while (unlikely(!v0 || !v1 || !v2 || !v3));
449
450 WRITE_ONCE(state->v0, v0);
451 WRITE_ONCE(state->v1, v1);
452 WRITE_ONCE(state->v2, v2);
453 WRITE_ONCE(state->v3, v3);
454 }
455}
456EXPORT_SYMBOL(prandom_seed);
457
458/*
459 * Generate some initially weak seeding values to allow
460 * the prandom_u32() engine to be started.
461 */
462static int __init prandom_init_early(void)
463{
464 int i;
465 unsigned long v0, v1, v2, v3;
466
467 if (!arch_get_random_long(&v0))
468 v0 = jiffies;
469 if (!arch_get_random_long(&v1))
470 v1 = random_get_entropy();
471 v2 = v0 ^ PRND_K0;
472 v3 = v1 ^ PRND_K1;
473
474 for_each_possible_cpu(i) {
475 struct siprand_state *state;
476
477 v3 ^= i;
478 PRND_SIPROUND(v0, v1, v2, v3);
479 PRND_SIPROUND(v0, v1, v2, v3);
480 v0 ^= i;
481
482 state = per_cpu_ptr(&net_rand_state, i);
483 state->v0 = v0; state->v1 = v1;
484 state->v2 = v2; state->v3 = v3;
485 }
486
487 return 0;
488}
489core_initcall(prandom_init_early);
490
491
492/* Stronger reseeding when available, and periodically thereafter. */
493static void prandom_reseed(struct timer_list *unused);
494
495static DEFINE_TIMER(seed_timer, prandom_reseed);
496
497static void prandom_reseed(struct timer_list *unused)
498{
499 unsigned long expires;
500 int i;
501
502 /*
503 * Reinitialize each CPU's PRNG with 128 bits of key.
504 * No locking on the CPUs, but then somewhat random results are,
505 * well, expected.
506 */
507 for_each_possible_cpu(i) {
508 struct siprand_state *state;
509 unsigned long v0 = get_random_long(), v2 = v0 ^ PRND_K0;
510 unsigned long v1 = get_random_long(), v3 = v1 ^ PRND_K1;
511#if BITS_PER_LONG == 32
512 int j;
513
514 /*
515 * On 32-bit machines, hash in two extra words to
516 * approximate 128-bit key length. Not that the hash
517 * has that much security, but this prevents a trivial
518 * 64-bit brute force.
519 */
520 for (j = 0; j < 2; j++) {
521 unsigned long m = get_random_long();
522
523 v3 ^= m;
524 PRND_SIPROUND(v0, v1, v2, v3);
525 PRND_SIPROUND(v0, v1, v2, v3);
526 v0 ^= m;
527 }
528#endif
529 /*
530 * Probably impossible in practice, but there is a
531 * theoretical risk that a race between this reseeding
532 * and the target CPU writing its state back could
533 * create the all-zero SipHash fixed point.
534 *
535 * To ensure that never happens, ensure the state
536 * we write contains no zero words.
537 */
538 state = per_cpu_ptr(&net_rand_state, i);
539 WRITE_ONCE(state->v0, v0 ? v0 : -1ul);
540 WRITE_ONCE(state->v1, v1 ? v1 : -1ul);
541 WRITE_ONCE(state->v2, v2 ? v2 : -1ul);
542 WRITE_ONCE(state->v3, v3 ? v3 : -1ul);
543 }
544
545 /* reseed every ~60 seconds, in [40 .. 80) interval with slack */
546 expires = round_jiffies(jiffies + 40 * HZ + prandom_u32_max(40 * HZ));
547 mod_timer(&seed_timer, expires);
548}
549
550/*
551 * The random ready callback can be called from almost any interrupt.
552 * To avoid worrying about whether it's safe to delay that interrupt
553 * long enough to seed all CPUs, just schedule an immediate timer event.
554 */
555static void prandom_timer_start(struct random_ready_callback *unused)
556{
557 mod_timer(&seed_timer, jiffies);
558}
559
560#ifdef CONFIG_RANDOM32_SELFTEST
561/* Principle: True 32-bit random numbers will all have 16 differing bits on
562 * average. For each 32-bit number, there are 601M numbers differing by 16
563 * bits, and 89% of the numbers differ by at least 12 bits. Note that more
564 * than 16 differing bits also implies a correlation with inverted bits. Thus
565 * we take 1024 random numbers and compare each of them to the other ones,
566 * counting the deviation of correlated bits to 16. Constants report 32,
567 * counters 32-log2(TEST_SIZE), and pure randoms, around 6 or lower. With the
568 * u32 total, TEST_SIZE may be as large as 4096 samples.
569 */
570#define TEST_SIZE 1024
571static int __init prandom32_state_selftest(void)
572{
573 unsigned int x, y, bits, samples;
574 u32 xor, flip;
575 u32 total;
576 u32 *data;
577
578 data = kmalloc(sizeof(*data) * TEST_SIZE, GFP_KERNEL);
579 if (!data)
580 return 0;
581
582 for (samples = 0; samples < TEST_SIZE; samples++)
583 data[samples] = prandom_u32();
584
585 flip = total = 0;
586 for (x = 0; x < samples; x++) {
587 for (y = 0; y < samples; y++) {
588 if (x == y)
589 continue;
590 xor = data[x] ^ data[y];
591 flip |= xor;
592 bits = hweight32(xor);
593 total += (bits - 16) * (bits - 16);
594 }
595 }
596
597 /* We'll return the average deviation as 2*sqrt(corr/samples), which
598 * is also sqrt(4*corr/samples) which provides a better resolution.
599 */
600 bits = int_sqrt(total / (samples * (samples - 1)) * 4);
601 if (bits > 6)
602 pr_warn("prandom32: self test failed (at least %u bits"
603 " correlated, fixed_mask=%#x fixed_value=%#x\n",
604 bits, ~flip, data[0] & ~flip);
605 else
606 pr_info("prandom32: self test passed (less than %u bits"
607 " correlated)\n",
608 bits+1);
609 kfree(data);
610 return 0;
611}
612core_initcall(prandom32_state_selftest);
613#endif /* CONFIG_RANDOM32_SELFTEST */
614
615/*
616 * Start periodic full reseeding as soon as strong
617 * random numbers are available.
618 */
619static int __init prandom_init_late(void)
620{
621 static struct random_ready_callback random_ready = {
622 .func = prandom_timer_start
623 };
624 int ret = add_random_ready_callback(&random_ready);
625
626 if (ret == -EALREADY) {
627 prandom_timer_start(&random_ready);
628 ret = 0;
629 }
630 return ret;
631}
632late_initcall(prandom_init_late);
1/*
2 This is a maximally equidistributed combined Tausworthe generator
3 based on code from GNU Scientific Library 1.5 (30 Jun 2004)
4
5 x_n = (s1_n ^ s2_n ^ s3_n)
6
7 s1_{n+1} = (((s1_n & 4294967294) <<12) ^ (((s1_n <<13) ^ s1_n) >>19))
8 s2_{n+1} = (((s2_n & 4294967288) << 4) ^ (((s2_n << 2) ^ s2_n) >>25))
9 s3_{n+1} = (((s3_n & 4294967280) <<17) ^ (((s3_n << 3) ^ s3_n) >>11))
10
11 The period of this generator is about 2^88.
12
13 From: P. L'Ecuyer, "Maximally Equidistributed Combined Tausworthe
14 Generators", Mathematics of Computation, 65, 213 (1996), 203--213.
15
16 This is available on the net from L'Ecuyer's home page,
17
18 http://www.iro.umontreal.ca/~lecuyer/myftp/papers/tausme.ps
19 ftp://ftp.iro.umontreal.ca/pub/simulation/lecuyer/papers/tausme.ps
20
21 There is an erratum in the paper "Tables of Maximally
22 Equidistributed Combined LFSR Generators", Mathematics of
23 Computation, 68, 225 (1999), 261--269:
24 http://www.iro.umontreal.ca/~lecuyer/myftp/papers/tausme2.ps
25
26 ... the k_j most significant bits of z_j must be non-
27 zero, for each j. (Note: this restriction also applies to the
28 computer code given in [4], but was mistakenly not mentioned in
29 that paper.)
30
31 This affects the seeding procedure by imposing the requirement
32 s1 > 1, s2 > 7, s3 > 15.
33
34*/
35
36#include <linux/types.h>
37#include <linux/percpu.h>
38#include <linux/module.h>
39#include <linux/jiffies.h>
40#include <linux/random.h>
41
42static DEFINE_PER_CPU(struct rnd_state, net_rand_state);
43
44/**
45 * prandom32 - seeded pseudo-random number generator.
46 * @state: pointer to state structure holding seeded state.
47 *
48 * This is used for pseudo-randomness with no outside seeding.
49 * For more random results, use random32().
50 */
51u32 prandom32(struct rnd_state *state)
52{
53#define TAUSWORTHE(s,a,b,c,d) ((s&c)<<d) ^ (((s <<a) ^ s)>>b)
54
55 state->s1 = TAUSWORTHE(state->s1, 13, 19, 4294967294UL, 12);
56 state->s2 = TAUSWORTHE(state->s2, 2, 25, 4294967288UL, 4);
57 state->s3 = TAUSWORTHE(state->s3, 3, 11, 4294967280UL, 17);
58
59 return (state->s1 ^ state->s2 ^ state->s3);
60}
61EXPORT_SYMBOL(prandom32);
62
63/**
64 * random32 - pseudo random number generator
65 *
66 * A 32 bit pseudo-random number is generated using a fast
67 * algorithm suitable for simulation. This algorithm is NOT
68 * considered safe for cryptographic use.
69 */
70u32 random32(void)
71{
72 unsigned long r;
73 struct rnd_state *state = &get_cpu_var(net_rand_state);
74 r = prandom32(state);
75 put_cpu_var(state);
76 return r;
77}
78EXPORT_SYMBOL(random32);
79
80/**
81 * srandom32 - add entropy to pseudo random number generator
82 * @seed: seed value
83 *
84 * Add some additional seeding to the random32() pool.
85 */
86void srandom32(u32 entropy)
87{
88 int i;
89 /*
90 * No locking on the CPUs, but then somewhat random results are, well,
91 * expected.
92 */
93 for_each_possible_cpu (i) {
94 struct rnd_state *state = &per_cpu(net_rand_state, i);
95 state->s1 = __seed(state->s1 ^ entropy, 1);
96 }
97}
98EXPORT_SYMBOL(srandom32);
99
100/*
101 * Generate some initially weak seeding values to allow
102 * to start the random32() engine.
103 */
104static int __init random32_init(void)
105{
106 int i;
107
108 for_each_possible_cpu(i) {
109 struct rnd_state *state = &per_cpu(net_rand_state,i);
110
111#define LCG(x) ((x) * 69069) /* super-duper LCG */
112 state->s1 = __seed(LCG(i + jiffies), 1);
113 state->s2 = __seed(LCG(state->s1), 7);
114 state->s3 = __seed(LCG(state->s2), 15);
115
116 /* "warm it up" */
117 prandom32(state);
118 prandom32(state);
119 prandom32(state);
120 prandom32(state);
121 prandom32(state);
122 prandom32(state);
123 }
124 return 0;
125}
126core_initcall(random32_init);
127
128/*
129 * Generate better values after random number generator
130 * is fully initialized.
131 */
132static int __init random32_reseed(void)
133{
134 int i;
135
136 for_each_possible_cpu(i) {
137 struct rnd_state *state = &per_cpu(net_rand_state,i);
138 u32 seeds[3];
139
140 get_random_bytes(&seeds, sizeof(seeds));
141 state->s1 = __seed(seeds[0], 1);
142 state->s2 = __seed(seeds[1], 7);
143 state->s3 = __seed(seeds[2], 15);
144
145 /* mix it in */
146 prandom32(state);
147 }
148 return 0;
149}
150late_initcall(random32_reseed);