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/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
  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  */
  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  */
  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  */
 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  */
 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
 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
 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
 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  */
 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  */
 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(unsigned long dontcare);
 217
 218 static DEFINE_TIMER(seed_timer, __prandom_timer, 0, 0);
 219
 220 static void __prandom_timer(unsigned long dontcare)
 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
 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
 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  */
 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
 292 void prandom_reseed_late(void)
 293 {
 294         __prandom_reseed(true);
 295 }
 296
 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
 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