lib/random32.c

   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/prandom.h>
  40 #include <linux/sched.h>
  41 #include <linux/bitops.h>
  42 #include <linux/slab.h>
  43 #include <linux/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  */
  52 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         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 }
  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 get_random_bytes().
  73  */
  74 void 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 }
  93 EXPORT_SYMBOL(prandom_bytes_state);
  94
  95 static 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
 110 void 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 }
 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 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
 257 static 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 }
 299 core_initcall(prandom_state_selftest);
 300 #endif