Line data Source code
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 : */
52 0 : u32 prandom_u32_state(struct rnd_state *state)
53 : {
54 : #define TAUSWORTHE(s, a, b, c, d) ((s & c) << d) ^ (((s << a) ^ s) >> b)
55 0 : state->s1 = TAUSWORTHE(state->s1, 6U, 13U, 4294967294U, 18U);
56 0 : state->s2 = TAUSWORTHE(state->s2, 2U, 27U, 4294967288U, 2U);
57 0 : state->s3 = TAUSWORTHE(state->s3, 13U, 21U, 4294967280U, 7U);
58 0 : state->s4 = TAUSWORTHE(state->s4, 3U, 12U, 4294967168U, 13U);
59 :
60 0 : return (state->s1 ^ state->s2 ^ state->s3 ^ state->s4);
61 : }
62 : EXPORT_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 : */
74 0 : void prandom_bytes_state(struct rnd_state *state, void *buf, size_t bytes)
75 : {
76 0 : u8 *ptr = buf;
77 :
78 0 : while (bytes >= sizeof(u32)) {
79 0 : put_unaligned(prandom_u32_state(state), (u32 *) ptr);
80 0 : ptr += sizeof(u32);
81 0 : bytes -= sizeof(u32);
82 : }
83 :
84 0 : if (bytes > 0) {
85 0 : u32 rem = prandom_u32_state(state);
86 0 : do {
87 0 : *ptr++ = (u8) rem;
88 0 : bytes--;
89 0 : rem >>= BITS_PER_BYTE;
90 0 : } while (bytes > 0);
91 : }
92 0 : }
93 : EXPORT_SYMBOL(prandom_bytes_state);
94 :
95 0 : static void prandom_warmup(struct rnd_state *state)
96 : {
97 : /* Calling RNG ten times to satisfy recurrence condition */
98 0 : prandom_u32_state(state);
99 0 : prandom_u32_state(state);
100 0 : prandom_u32_state(state);
101 0 : prandom_u32_state(state);
102 0 : prandom_u32_state(state);
103 0 : prandom_u32_state(state);
104 0 : prandom_u32_state(state);
105 0 : prandom_u32_state(state);
106 0 : prandom_u32_state(state);
107 0 : prandom_u32_state(state);
108 0 : }
109 :
110 0 : void prandom_seed_full_state(struct rnd_state __percpu *pcpu_state)
111 : {
112 0 : int i;
113 :
114 0 : for_each_possible_cpu(i) {
115 0 : struct rnd_state *state = per_cpu_ptr(pcpu_state, i);
116 0 : u32 seeds[4];
117 :
118 0 : get_random_bytes(&seeds, sizeof(seeds));
119 0 : state->s1 = __seed(seeds[0], 2U);
120 0 : state->s2 = __seed(seeds[1], 8U);
121 0 : state->s3 = __seed(seeds[2], 16U);
122 0 : state->s4 = __seed(seeds[3], 128U);
123 :
124 0 : prandom_warmup(state);
125 : }
126 0 : }
127 : EXPORT_SYMBOL(prandom_seed_full_state);
128 :
129 : #ifdef CONFIG_RANDOM32_SELFTEST
130 : static 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 :
140 : static 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 :
248 : static 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 :
258 : static 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 :
269 : static 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 : }
311 : core_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 :
333 : struct siprand_state {
334 : unsigned long v0;
335 : unsigned long v1;
336 : unsigned long v2;
337 : unsigned long v3;
338 : };
339 :
340 : static DEFINE_PER_CPU(struct siprand_state, net_rand_state) __latent_entropy;
341 : DEFINE_PER_CPU(unsigned long, net_rand_noise);
342 : EXPORT_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 : */
363 191239 : static inline u32 siprand_u32(struct siprand_state *s)
364 : {
365 191239 : unsigned long v0 = s->v0, v1 = s->v1, v2 = s->v2, v3 = s->v3;
366 191239 : unsigned long n = raw_cpu_read(net_rand_noise);
367 :
368 191239 : v3 ^= n;
369 191239 : PRND_SIPROUND(v0, v1, v2, v3);
370 191239 : PRND_SIPROUND(v0, v1, v2, v3);
371 191239 : v0 ^= n;
372 191239 : s->v0 = v0; s->v1 = v1; s->v2 = v2; s->v3 = v3;
373 191239 : 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 : */
384 187349 : u32 prandom_u32(void)
385 : {
386 187349 : struct siprand_state *state = get_cpu_ptr(&net_rand_state);
387 188634 : u32 res = siprand_u32(state);
388 :
389 188941 : trace_prandom_u32(res);
390 188309 : put_cpu_ptr(&net_rand_state);
391 188349 : return res;
392 : }
393 : EXPORT_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 : */
400 104 : void prandom_bytes(void *buf, size_t bytes)
401 : {
402 104 : struct siprand_state *state = get_cpu_ptr(&net_rand_state);
403 104 : u8 *ptr = buf;
404 :
405 2564 : while (bytes >= sizeof(u32)) {
406 2460 : put_unaligned(siprand_u32(state), (u32 *)ptr);
407 2460 : ptr += sizeof(u32);
408 2460 : bytes -= sizeof(u32);
409 : }
410 :
411 104 : if (bytes > 0) {
412 0 : u32 rem = siprand_u32(state);
413 :
414 0 : do {
415 0 : *ptr++ = (u8)rem;
416 0 : rem >>= BITS_PER_BYTE;
417 0 : } while (--bytes > 0);
418 : }
419 104 : put_cpu_ptr(&net_rand_state);
420 104 : }
421 : EXPORT_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 : */
432 2 : void prandom_seed(u32 entropy)
433 : {
434 2 : int i;
435 :
436 2 : add_device_randomness(&entropy, sizeof(entropy));
437 :
438 12 : for_each_possible_cpu(i) {
439 8 : struct siprand_state *state = per_cpu_ptr(&net_rand_state, i);
440 8 : unsigned long v0 = state->v0, v1 = state->v1;
441 8 : unsigned long v2 = state->v2, v3 = state->v3;
442 :
443 8 : do {
444 8 : v3 ^= entropy;
445 8 : PRND_SIPROUND(v0, v1, v2, v3);
446 8 : PRND_SIPROUND(v0, v1, v2, v3);
447 8 : v0 ^= entropy;
448 8 : } while (unlikely(!v0 || !v1 || !v2 || !v3));
449 :
450 8 : WRITE_ONCE(state->v0, v0);
451 8 : WRITE_ONCE(state->v1, v1);
452 8 : WRITE_ONCE(state->v2, v2);
453 10 : WRITE_ONCE(state->v3, v3);
454 : }
455 2 : }
456 : EXPORT_SYMBOL(prandom_seed);
457 :
458 : /*
459 : * Generate some initially weak seeding values to allow
460 : * the prandom_u32() engine to be started.
461 : */
462 1 : static int __init prandom_init_early(void)
463 : {
464 1 : int i;
465 1 : unsigned long v0, v1, v2, v3;
466 :
467 1 : if (!arch_get_random_long(&v0))
468 0 : v0 = jiffies;
469 1 : if (!arch_get_random_long(&v1))
470 0 : v1 = random_get_entropy();
471 1 : v2 = v0 ^ PRND_K0;
472 1 : v3 = v1 ^ PRND_K1;
473 :
474 5 : for_each_possible_cpu(i) {
475 4 : struct siprand_state *state;
476 :
477 4 : v3 ^= i;
478 4 : PRND_SIPROUND(v0, v1, v2, v3);
479 4 : PRND_SIPROUND(v0, v1, v2, v3);
480 4 : v0 ^= i;
481 :
482 4 : state = per_cpu_ptr(&net_rand_state, i);
483 4 : state->v0 = v0; state->v1 = v1;
484 4 : state->v2 = v2; state->v3 = v3;
485 : }
486 :
487 1 : return 0;
488 : }
489 : core_initcall(prandom_init_early);
490 :
491 :
492 : /* Stronger reseeding when available, and periodically thereafter. */
493 : static void prandom_reseed(struct timer_list *unused);
494 :
495 : static DEFINE_TIMER(seed_timer, prandom_reseed);
496 :
497 2 : static void prandom_reseed(struct timer_list *unused)
498 : {
499 2 : unsigned long expires;
500 2 : 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 12 : for_each_possible_cpu(i) {
508 8 : struct siprand_state *state;
509 8 : unsigned long v0 = get_random_long(), v2 = v0 ^ PRND_K0;
510 8 : 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 8 : state = per_cpu_ptr(&net_rand_state, i);
539 8 : WRITE_ONCE(state->v0, v0 ? v0 : -1ul);
540 8 : WRITE_ONCE(state->v1, v1 ? v1 : -1ul);
541 8 : WRITE_ONCE(state->v2, v2 ? v2 : -1ul);
542 10 : WRITE_ONCE(state->v3, v3 ? v3 : -1ul);
543 : }
544 :
545 : /* reseed every ~60 seconds, in [40 .. 80) interval with slack */
546 2 : expires = round_jiffies(jiffies + 40 * HZ + prandom_u32_max(40 * HZ));
547 2 : mod_timer(&seed_timer, expires);
548 2 : }
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 : */
555 1 : static void prandom_timer_start(struct random_ready_callback *unused)
556 : {
557 0 : mod_timer(&seed_timer, jiffies);
558 0 : }
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
571 : static 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 : }
612 : core_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 : */
619 1 : static int __init prandom_init_late(void)
620 : {
621 1 : static struct random_ready_callback random_ready = {
622 : .func = prandom_timer_start
623 : };
624 1 : int ret = add_random_ready_callback(&random_ready);
625 :
626 1 : if (ret == -EALREADY) {
627 1 : prandom_timer_start(&random_ready);
628 1 : ret = 0;
629 : }
630 1 : return ret;
631 : }
632 : late_initcall(prandom_init_late);
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