random32.c 18 KB

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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. #include <linux/types.h>
  35. #include <linux/percpu.h>
  36. #include <linux/export.h>
  37. #include <linux/jiffies.h>
  38. #include <linux/random.h>
  39. #include <linux/sched.h>
  40. #include <linux/bitops.h>
  41. #include <asm/unaligned.h>
  42. #include <trace/events/random.h>
  43. /**
  44. * prandom_u32_state - seeded pseudo-random number generator.
  45. * @state: pointer to state structure holding seeded state.
  46. *
  47. * This is used for pseudo-randomness with no outside seeding.
  48. * For more random results, use prandom_u32().
  49. */
  50. u32 prandom_u32_state(struct rnd_state *state)
  51. {
  52. #define TAUSWORTHE(s, a, b, c, d) ((s & c) << d) ^ (((s << a) ^ s) >> b)
  53. state->s1 = TAUSWORTHE(state->s1, 6U, 13U, 4294967294U, 18U);
  54. state->s2 = TAUSWORTHE(state->s2, 2U, 27U, 4294967288U, 2U);
  55. state->s3 = TAUSWORTHE(state->s3, 13U, 21U, 4294967280U, 7U);
  56. state->s4 = TAUSWORTHE(state->s4, 3U, 12U, 4294967168U, 13U);
  57. return (state->s1 ^ state->s2 ^ state->s3 ^ state->s4);
  58. }
  59. EXPORT_SYMBOL(prandom_u32_state);
  60. /**
  61. * prandom_bytes_state - get the requested number of pseudo-random bytes
  62. *
  63. * @state: pointer to state structure holding seeded state.
  64. * @buf: where to copy the pseudo-random bytes to
  65. * @bytes: the requested number of bytes
  66. *
  67. * This is used for pseudo-randomness with no outside seeding.
  68. * For more random results, use prandom_bytes().
  69. */
  70. void prandom_bytes_state(struct rnd_state *state, void *buf, size_t bytes)
  71. {
  72. u8 *ptr = buf;
  73. while (bytes >= sizeof(u32)) {
  74. put_unaligned(prandom_u32_state(state), (u32 *) ptr);
  75. ptr += sizeof(u32);
  76. bytes -= sizeof(u32);
  77. }
  78. if (bytes > 0) {
  79. u32 rem = prandom_u32_state(state);
  80. do {
  81. *ptr++ = (u8) rem;
  82. bytes--;
  83. rem >>= BITS_PER_BYTE;
  84. } while (bytes > 0);
  85. }
  86. }
  87. EXPORT_SYMBOL(prandom_bytes_state);
  88. static void prandom_warmup(struct rnd_state *state)
  89. {
  90. /* Calling RNG ten times to satisfy recurrence condition */
  91. prandom_u32_state(state);
  92. prandom_u32_state(state);
  93. prandom_u32_state(state);
  94. prandom_u32_state(state);
  95. prandom_u32_state(state);
  96. prandom_u32_state(state);
  97. prandom_u32_state(state);
  98. prandom_u32_state(state);
  99. prandom_u32_state(state);
  100. prandom_u32_state(state);
  101. }
  102. void prandom_seed_full_state(struct rnd_state __percpu *pcpu_state)
  103. {
  104. int i;
  105. for_each_possible_cpu(i) {
  106. struct rnd_state *state = per_cpu_ptr(pcpu_state, i);
  107. u32 seeds[4];
  108. get_random_bytes(&seeds, sizeof(seeds));
  109. state->s1 = __seed(seeds[0], 2U);
  110. state->s2 = __seed(seeds[1], 8U);
  111. state->s3 = __seed(seeds[2], 16U);
  112. state->s4 = __seed(seeds[3], 128U);
  113. prandom_warmup(state);
  114. }
  115. }
  116. EXPORT_SYMBOL(prandom_seed_full_state);
  117. #ifdef CONFIG_RANDOM32_SELFTEST
  118. static struct prandom_test1 {
  119. u32 seed;
  120. u32 result;
  121. } test1[] = {
  122. { 1U, 3484351685U },
  123. { 2U, 2623130059U },
  124. { 3U, 3125133893U },
  125. { 4U, 984847254U },
  126. };
  127. static struct prandom_test2 {
  128. u32 seed;
  129. u32 iteration;
  130. u32 result;
  131. } test2[] = {
  132. /* Test cases against taus113 from GSL library. */
  133. { 931557656U, 959U, 2975593782U },
  134. { 1339693295U, 876U, 3887776532U },
  135. { 1545556285U, 961U, 1615538833U },
  136. { 601730776U, 723U, 1776162651U },
  137. { 1027516047U, 687U, 511983079U },
  138. { 416526298U, 700U, 916156552U },
  139. { 1395522032U, 652U, 2222063676U },
  140. { 366221443U, 617U, 2992857763U },
  141. { 1539836965U, 714U, 3783265725U },
  142. { 556206671U, 994U, 799626459U },
  143. { 684907218U, 799U, 367789491U },
  144. { 2121230701U, 931U, 2115467001U },
  145. { 1668516451U, 644U, 3620590685U },
  146. { 768046066U, 883U, 2034077390U },
  147. { 1989159136U, 833U, 1195767305U },
  148. { 536585145U, 996U, 3577259204U },
  149. { 1008129373U, 642U, 1478080776U },
  150. { 1740775604U, 939U, 1264980372U },
  151. { 1967883163U, 508U, 10734624U },
  152. { 1923019697U, 730U, 3821419629U },
  153. { 442079932U, 560U, 3440032343U },
  154. { 1961302714U, 845U, 841962572U },
  155. { 2030205964U, 962U, 1325144227U },
  156. { 1160407529U, 507U, 240940858U },
  157. { 635482502U, 779U, 4200489746U },
  158. { 1252788931U, 699U, 867195434U },
  159. { 1961817131U, 719U, 668237657U },
  160. { 1071468216U, 983U, 917876630U },
  161. { 1281848367U, 932U, 1003100039U },
  162. { 582537119U, 780U, 1127273778U },
  163. { 1973672777U, 853U, 1071368872U },
  164. { 1896756996U, 762U, 1127851055U },
  165. { 847917054U, 500U, 1717499075U },
  166. { 1240520510U, 951U, 2849576657U },
  167. { 1685071682U, 567U, 1961810396U },
  168. { 1516232129U, 557U, 3173877U },
  169. { 1208118903U, 612U, 1613145022U },
  170. { 1817269927U, 693U, 4279122573U },
  171. { 1510091701U, 717U, 638191229U },
  172. { 365916850U, 807U, 600424314U },
  173. { 399324359U, 702U, 1803598116U },
  174. { 1318480274U, 779U, 2074237022U },
  175. { 697758115U, 840U, 1483639402U },
  176. { 1696507773U, 840U, 577415447U },
  177. { 2081979121U, 981U, 3041486449U },
  178. { 955646687U, 742U, 3846494357U },
  179. { 1250683506U, 749U, 836419859U },
  180. { 595003102U, 534U, 366794109U },
  181. { 47485338U, 558U, 3521120834U },
  182. { 619433479U, 610U, 3991783875U },
  183. { 704096520U, 518U, 4139493852U },
  184. { 1712224984U, 606U, 2393312003U },
  185. { 1318233152U, 922U, 3880361134U },
  186. { 855572992U, 761U, 1472974787U },
  187. { 64721421U, 703U, 683860550U },
  188. { 678931758U, 840U, 380616043U },
  189. { 692711973U, 778U, 1382361947U },
  190. { 677703619U, 530U, 2826914161U },
  191. { 92393223U, 586U, 1522128471U },
  192. { 1222592920U, 743U, 3466726667U },
  193. { 358288986U, 695U, 1091956998U },
  194. { 1935056945U, 958U, 514864477U },
  195. { 735675993U, 990U, 1294239989U },
  196. { 1560089402U, 897U, 2238551287U },
  197. { 70616361U, 829U, 22483098U },
  198. { 368234700U, 731U, 2913875084U },
  199. { 20221190U, 879U, 1564152970U },
  200. { 539444654U, 682U, 1835141259U },
  201. { 1314987297U, 840U, 1801114136U },
  202. { 2019295544U, 645U, 3286438930U },
  203. { 469023838U, 716U, 1637918202U },
  204. { 1843754496U, 653U, 2562092152U },
  205. { 400672036U, 809U, 4264212785U },
  206. { 404722249U, 965U, 2704116999U },
  207. { 600702209U, 758U, 584979986U },
  208. { 519953954U, 667U, 2574436237U },
  209. { 1658071126U, 694U, 2214569490U },
  210. { 420480037U, 749U, 3430010866U },
  211. { 690103647U, 969U, 3700758083U },
  212. { 1029424799U, 937U, 3787746841U },
  213. { 2012608669U, 506U, 3362628973U },
  214. { 1535432887U, 998U, 42610943U },
  215. { 1330635533U, 857U, 3040806504U },
  216. { 1223800550U, 539U, 3954229517U },
  217. { 1322411537U, 680U, 3223250324U },
  218. { 1877847898U, 945U, 2915147143U },
  219. { 1646356099U, 874U, 965988280U },
  220. { 805687536U, 744U, 4032277920U },
  221. { 1948093210U, 633U, 1346597684U },
  222. { 392609744U, 783U, 1636083295U },
  223. { 690241304U, 770U, 1201031298U },
  224. { 1360302965U, 696U, 1665394461U },
  225. { 1220090946U, 780U, 1316922812U },
  226. { 447092251U, 500U, 3438743375U },
  227. { 1613868791U, 592U, 828546883U },
  228. { 523430951U, 548U, 2552392304U },
  229. { 726692899U, 810U, 1656872867U },
  230. { 1364340021U, 836U, 3710513486U },
  231. { 1986257729U, 931U, 935013962U },
  232. { 407983964U, 921U, 728767059U },
  233. };
  234. static u32 __extract_hwseed(void)
  235. {
  236. unsigned int val = 0;
  237. (void)(arch_get_random_seed_int(&val) ||
  238. arch_get_random_int(&val));
  239. return val;
  240. }
  241. static void prandom_seed_early(struct rnd_state *state, u32 seed,
  242. bool mix_with_hwseed)
  243. {
  244. #define LCG(x) ((x) * 69069U) /* super-duper LCG */
  245. #define HWSEED() (mix_with_hwseed ? __extract_hwseed() : 0)
  246. state->s1 = __seed(HWSEED() ^ LCG(seed), 2U);
  247. state->s2 = __seed(HWSEED() ^ LCG(state->s1), 8U);
  248. state->s3 = __seed(HWSEED() ^ LCG(state->s2), 16U);
  249. state->s4 = __seed(HWSEED() ^ LCG(state->s3), 128U);
  250. }
  251. static int __init prandom_state_selftest(void)
  252. {
  253. int i, j, errors = 0, runs = 0;
  254. bool error = false;
  255. for (i = 0; i < ARRAY_SIZE(test1); i++) {
  256. struct rnd_state state;
  257. prandom_seed_early(&state, test1[i].seed, false);
  258. prandom_warmup(&state);
  259. if (test1[i].result != prandom_u32_state(&state))
  260. error = true;
  261. }
  262. if (error)
  263. pr_warn("prandom: seed boundary self test failed\n");
  264. else
  265. pr_info("prandom: seed boundary self test passed\n");
  266. for (i = 0; i < ARRAY_SIZE(test2); i++) {
  267. struct rnd_state state;
  268. prandom_seed_early(&state, test2[i].seed, false);
  269. prandom_warmup(&state);
  270. for (j = 0; j < test2[i].iteration - 1; j++)
  271. prandom_u32_state(&state);
  272. if (test2[i].result != prandom_u32_state(&state))
  273. errors++;
  274. runs++;
  275. cond_resched();
  276. }
  277. if (errors)
  278. pr_warn("prandom: %d/%d self tests failed\n", errors, runs);
  279. else
  280. pr_info("prandom: %d self tests passed\n", runs);
  281. return 0;
  282. }
  283. core_initcall(prandom_state_selftest);
  284. #endif
  285. /*
  286. * The prandom_u32() implementation is now completely separate from the
  287. * prandom_state() functions, which are retained (for now) for compatibility.
  288. *
  289. * Because of (ab)use in the networking code for choosing random TCP/UDP port
  290. * numbers, which open DoS possibilities if guessable, we want something
  291. * stronger than a standard PRNG. But the performance requirements of
  292. * the network code do not allow robust crypto for this application.
  293. *
  294. * So this is a homebrew Junior Spaceman implementation, based on the
  295. * lowest-latency trustworthy crypto primitive available, SipHash.
  296. * (The authors of SipHash have not been consulted about this abuse of
  297. * their work.)
  298. *
  299. * Standard SipHash-2-4 uses 2n+4 rounds to hash n words of input to
  300. * one word of output. This abbreviated version uses 2 rounds per word
  301. * of output.
  302. */
  303. struct siprand_state {
  304. unsigned long v0;
  305. unsigned long v1;
  306. unsigned long v2;
  307. unsigned long v3;
  308. };
  309. static DEFINE_PER_CPU(struct siprand_state, net_rand_state) __latent_entropy;
  310. DEFINE_PER_CPU(unsigned long, net_rand_noise);
  311. EXPORT_PER_CPU_SYMBOL(net_rand_noise);
  312. /*
  313. * This is the core CPRNG function. As "pseudorandom", this is not used
  314. * for truly valuable things, just intended to be a PITA to guess.
  315. * For maximum speed, we do just two SipHash rounds per word. This is
  316. * the same rate as 4 rounds per 64 bits that SipHash normally uses,
  317. * so hopefully it's reasonably secure.
  318. *
  319. * There are two changes from the official SipHash finalization:
  320. * - We omit some constants XORed with v2 in the SipHash spec as irrelevant;
  321. * they are there only to make the output rounds distinct from the input
  322. * rounds, and this application has no input rounds.
  323. * - Rather than returning v0^v1^v2^v3, return v1+v3.
  324. * If you look at the SipHash round, the last operation on v3 is
  325. * "v3 ^= v0", so "v0 ^ v3" just undoes that, a waste of time.
  326. * Likewise "v1 ^= v2". (The rotate of v2 makes a difference, but
  327. * it still cancels out half of the bits in v2 for no benefit.)
  328. * Second, since the last combining operation was xor, continue the
  329. * pattern of alternating xor/add for a tiny bit of extra non-linearity.
  330. */
  331. static inline u32 siprand_u32(struct siprand_state *s)
  332. {
  333. unsigned long v0 = s->v0, v1 = s->v1, v2 = s->v2, v3 = s->v3;
  334. unsigned long n = raw_cpu_read(net_rand_noise);
  335. v3 ^= n;
  336. PRND_SIPROUND(v0, v1, v2, v3);
  337. PRND_SIPROUND(v0, v1, v2, v3);
  338. v0 ^= n;
  339. s->v0 = v0; s->v1 = v1; s->v2 = v2; s->v3 = v3;
  340. return v1 + v3;
  341. }
  342. /**
  343. * prandom_u32 - pseudo random number generator
  344. *
  345. * A 32 bit pseudo-random number is generated using a fast
  346. * algorithm suitable for simulation. This algorithm is NOT
  347. * considered safe for cryptographic use.
  348. */
  349. u32 prandom_u32(void)
  350. {
  351. struct siprand_state *state = get_cpu_ptr(&net_rand_state);
  352. u32 res = siprand_u32(state);
  353. trace_prandom_u32(res);
  354. put_cpu_ptr(&net_rand_state);
  355. return res;
  356. }
  357. EXPORT_SYMBOL(prandom_u32);
  358. /**
  359. * prandom_bytes - get the requested number of pseudo-random bytes
  360. * @buf: where to copy the pseudo-random bytes to
  361. * @bytes: the requested number of bytes
  362. */
  363. void prandom_bytes(void *buf, size_t bytes)
  364. {
  365. struct siprand_state *state = get_cpu_ptr(&net_rand_state);
  366. u8 *ptr = buf;
  367. while (bytes >= sizeof(u32)) {
  368. put_unaligned(siprand_u32(state), (u32 *)ptr);
  369. ptr += sizeof(u32);
  370. bytes -= sizeof(u32);
  371. }
  372. if (bytes > 0) {
  373. u32 rem = siprand_u32(state);
  374. do {
  375. *ptr++ = (u8)rem;
  376. rem >>= BITS_PER_BYTE;
  377. } while (--bytes > 0);
  378. }
  379. put_cpu_ptr(&net_rand_state);
  380. }
  381. EXPORT_SYMBOL(prandom_bytes);
  382. /**
  383. * prandom_seed - add entropy to pseudo random number generator
  384. * @entropy: entropy value
  385. *
  386. * Add some additional seed material to the prandom pool.
  387. * The "entropy" is actually our IP address (the only caller is
  388. * the network code), not for unpredictability, but to ensure that
  389. * different machines are initialized differently.
  390. */
  391. void prandom_seed(u32 entropy)
  392. {
  393. int i;
  394. add_device_randomness(&entropy, sizeof(entropy));
  395. for_each_possible_cpu(i) {
  396. struct siprand_state *state = per_cpu_ptr(&net_rand_state, i);
  397. unsigned long v0 = state->v0, v1 = state->v1;
  398. unsigned long v2 = state->v2, v3 = state->v3;
  399. do {
  400. v3 ^= entropy;
  401. PRND_SIPROUND(v0, v1, v2, v3);
  402. PRND_SIPROUND(v0, v1, v2, v3);
  403. v0 ^= entropy;
  404. } while (unlikely(!v0 || !v1 || !v2 || !v3));
  405. WRITE_ONCE(state->v0, v0);
  406. WRITE_ONCE(state->v1, v1);
  407. WRITE_ONCE(state->v2, v2);
  408. WRITE_ONCE(state->v3, v3);
  409. }
  410. }
  411. EXPORT_SYMBOL(prandom_seed);
  412. /*
  413. * Generate some initially weak seeding values to allow
  414. * the prandom_u32() engine to be started.
  415. */
  416. static int __init prandom_init_early(void)
  417. {
  418. int i;
  419. unsigned long v0, v1, v2, v3;
  420. if (!arch_get_random_long(&v0))
  421. v0 = jiffies;
  422. if (!arch_get_random_long(&v1))
  423. v1 = random_get_entropy();
  424. v2 = v0 ^ PRND_K0;
  425. v3 = v1 ^ PRND_K1;
  426. for_each_possible_cpu(i) {
  427. struct siprand_state *state;
  428. v3 ^= i;
  429. PRND_SIPROUND(v0, v1, v2, v3);
  430. PRND_SIPROUND(v0, v1, v2, v3);
  431. v0 ^= i;
  432. state = per_cpu_ptr(&net_rand_state, i);
  433. state->v0 = v0; state->v1 = v1;
  434. state->v2 = v2; state->v3 = v3;
  435. }
  436. return 0;
  437. }
  438. core_initcall(prandom_init_early);
  439. /* Stronger reseeding when available, and periodically thereafter. */
  440. static void prandom_reseed(struct timer_list *unused);
  441. static DEFINE_TIMER(seed_timer, prandom_reseed);
  442. static void prandom_reseed(struct timer_list *unused)
  443. {
  444. unsigned long expires;
  445. int i;
  446. /*
  447. * Reinitialize each CPU's PRNG with 128 bits of key.
  448. * No locking on the CPUs, but then somewhat random results are,
  449. * well, expected.
  450. */
  451. for_each_possible_cpu(i) {
  452. struct siprand_state *state;
  453. unsigned long v0 = get_random_long(), v2 = v0 ^ PRND_K0;
  454. unsigned long v1 = get_random_long(), v3 = v1 ^ PRND_K1;
  455. #if BITS_PER_LONG == 32
  456. int j;
  457. /*
  458. * On 32-bit machines, hash in two extra words to
  459. * approximate 128-bit key length. Not that the hash
  460. * has that much security, but this prevents a trivial
  461. * 64-bit brute force.
  462. */
  463. for (j = 0; j < 2; j++) {
  464. unsigned long m = get_random_long();
  465. v3 ^= m;
  466. PRND_SIPROUND(v0, v1, v2, v3);
  467. PRND_SIPROUND(v0, v1, v2, v3);
  468. v0 ^= m;
  469. }
  470. #endif
  471. /*
  472. * Probably impossible in practice, but there is a
  473. * theoretical risk that a race between this reseeding
  474. * and the target CPU writing its state back could
  475. * create the all-zero SipHash fixed point.
  476. *
  477. * To ensure that never happens, ensure the state
  478. * we write contains no zero words.
  479. */
  480. state = per_cpu_ptr(&net_rand_state, i);
  481. WRITE_ONCE(state->v0, v0 ? v0 : -1ul);
  482. WRITE_ONCE(state->v1, v1 ? v1 : -1ul);
  483. WRITE_ONCE(state->v2, v2 ? v2 : -1ul);
  484. WRITE_ONCE(state->v3, v3 ? v3 : -1ul);
  485. }
  486. /* reseed every ~60 seconds, in [40 .. 80) interval with slack */
  487. expires = round_jiffies(jiffies + 40 * HZ + prandom_u32_max(40 * HZ));
  488. mod_timer(&seed_timer, expires);
  489. }
  490. /*
  491. * The random ready callback can be called from almost any interrupt.
  492. * To avoid worrying about whether it's safe to delay that interrupt
  493. * long enough to seed all CPUs, just schedule an immediate timer event.
  494. */
  495. static void prandom_timer_start(struct random_ready_callback *unused)
  496. {
  497. mod_timer(&seed_timer, jiffies);
  498. }
  499. #ifdef CONFIG_RANDOM32_SELFTEST
  500. /* Principle: True 32-bit random numbers will all have 16 differing bits on
  501. * average. For each 32-bit number, there are 601M numbers differing by 16
  502. * bits, and 89% of the numbers differ by at least 12 bits. Note that more
  503. * than 16 differing bits also implies a correlation with inverted bits. Thus
  504. * we take 1024 random numbers and compare each of them to the other ones,
  505. * counting the deviation of correlated bits to 16. Constants report 32,
  506. * counters 32-log2(TEST_SIZE), and pure randoms, around 6 or lower. With the
  507. * u32 total, TEST_SIZE may be as large as 4096 samples.
  508. */
  509. #define TEST_SIZE 1024
  510. static int __init prandom32_state_selftest(void)
  511. {
  512. unsigned int x, y, bits, samples;
  513. u32 xor, flip;
  514. u32 total;
  515. u32 *data;
  516. data = kmalloc(sizeof(*data) * TEST_SIZE, GFP_KERNEL);
  517. if (!data)
  518. return 0;
  519. for (samples = 0; samples < TEST_SIZE; samples++)
  520. data[samples] = prandom_u32();
  521. flip = total = 0;
  522. for (x = 0; x < samples; x++) {
  523. for (y = 0; y < samples; y++) {
  524. if (x == y)
  525. continue;
  526. xor = data[x] ^ data[y];
  527. flip |= xor;
  528. bits = hweight32(xor);
  529. total += (bits - 16) * (bits - 16);
  530. }
  531. }
  532. /* We'll return the average deviation as 2*sqrt(corr/samples), which
  533. * is also sqrt(4*corr/samples) which provides a better resolution.
  534. */
  535. bits = int_sqrt(total / (samples * (samples - 1)) * 4);
  536. if (bits > 6)
  537. pr_warn("prandom32: self test failed (at least %u bits"
  538. " correlated, fixed_mask=%#x fixed_value=%#x\n",
  539. bits, ~flip, data[0] & ~flip);
  540. else
  541. pr_info("prandom32: self test passed (less than %u bits"
  542. " correlated)\n",
  543. bits+1);
  544. kfree(data);
  545. return 0;
  546. }
  547. core_initcall(prandom32_state_selftest);
  548. #endif /* CONFIG_RANDOM32_SELFTEST */
  549. /*
  550. * Start periodic full reseeding as soon as strong
  551. * random numbers are available.
  552. */
  553. static int __init prandom_init_late(void)
  554. {
  555. static struct random_ready_callback random_ready = {
  556. .func = prandom_timer_start
  557. };
  558. int ret = add_random_ready_callback(&random_ready);
  559. if (ret == -EALREADY) {
  560. prandom_timer_start(&random_ready);
  561. ret = 0;
  562. }
  563. return ret;
  564. }
  565. late_initcall(prandom_init_late);