lib/random32.c

   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  * lfsr113 version:
   6  *
   7  * x_n = (s1_n ^ s2_n ^ s3_n ^ s4_n)
   8  *
   9  * s1_{n+1} = (((s1_n & 4294967294) << 18) ^ (((s1_n <<  6) ^ s1_n) >> 13))
  10  * s2_{n+1} = (((s2_n & 4294967288) <<  2) ^ (((s2_n <<  2) ^ s2_n) >> 27))
  11  * s3_{n+1} = (((s3_n & 4294967280) <<  7) ^ (((s3_n << 13) ^ s3_n) >> 21))
  12  * s4_{n+1} = (((s4_n & 4294967168) << 13) ^ (((s4_n <<  3) ^ s4_n) >> 12))
  13  *
  14  * The period of this generator is about 2^113 (see erratum paper).
  15  *
  16  * From: P. L'Ecuyer, "Maximally Equidistributed Combined Tausworthe
  17  * Generators", Mathematics of Computation, 65, 213 (1996), 203--213:
  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 Equidistributed
  22  * Combined LFSR Generators", Mathematics of Computation, 68, 225 (1999),
  23  * 261--269: http://www.iro.umontreal.ca/~lecuyer/myftp/papers/tausme2.ps
  24  *
  25  *      ... the k_j most significant bits of z_j must be non-zero,
  26  *      for each j. (Note: this restriction also applies to the
  27  *      computer code given in [4], but was mistakenly not mentioned
  28  *      in that paper.)
  29  *
  30  * This affects the seeding procedure by imposing the requirement
  31  * s1 > 1, s2 > 7, s3 > 15, s4 > 127.
  32  */
  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
  41 #ifdef CONFIG_RANDOM32_SELFTEST
  42 static void __init prandom_state_selftest(void);
  43 #endif
  44
  45 static DEFINE_PER_CPU(struct rnd_state, net_rand_state);
  46
  47 /**
  48  *      prandom_u32_state - seeded pseudo-random number generator.
  49  *      @state: pointer to state structure holding seeded state.
  50  *
  51  *      This is used for pseudo-randomness with no outside seeding.
  52  *      For more random results, use prandom_u32().
  53  */
  54 u32 prandom_u32_state(struct rnd_state *state)
  55 {
  56 #define TAUSWORTHE(s,a,b,c,d) ((s&c)<<d) ^ (((s <<a) ^ s)>>b)
  57
  58         state->s1 = TAUSWORTHE(state->s1,  6U, 13U, 4294967294U, 18U);
  59         state->s2 = TAUSWORTHE(state->s2,  2U, 27U, 4294967288U,  2U);
  60         state->s3 = TAUSWORTHE(state->s3, 13U, 21U, 4294967280U,  7U);
  61         state->s4 = TAUSWORTHE(state->s4,  3U, 12U, 4294967168U, 13U);
  62
  63         return (state->s1 ^ state->s2 ^ state->s3 ^ state->s4);
  64 }
  65 EXPORT_SYMBOL(prandom_u32_state);
  66
  67 /**
  68  *      prandom_u32 - pseudo random number generator
  69  *
  70  *      A 32 bit pseudo-random number is generated using a fast
  71  *      algorithm suitable for simulation. This algorithm is NOT
  72  *      considered safe for cryptographic use.
  73  */
  74 u32 prandom_u32(void)
  75 {
  76         struct rnd_state *state = &get_cpu_var(net_rand_state);
  77         u32 res;
  78
  79         res = prandom_u32_state(state);
  80         put_cpu_var(state);
  81
  82         return res;
  83 }
  84 EXPORT_SYMBOL(prandom_u32);
  85
  86 /**
  87  *      prandom_bytes_state - get the requested number of pseudo-random bytes
  88  *
  89  *      @state: pointer to state structure holding seeded state.
  90  *      @buf: where to copy the pseudo-random bytes to
  91  *      @bytes: the requested number of bytes
  92  *
  93  *      This is used for pseudo-randomness with no outside seeding.
  94  *      For more random results, use prandom_bytes().
  95  */
  96 void prandom_bytes_state(struct rnd_state *state, void *buf, int bytes)
  97 {
  98         unsigned char *p = buf;
  99         int i;
 100
 101         for (i = 0; i < round_down(bytes, sizeof(u32)); i += sizeof(u32)) {
 102                 u32 random = prandom_u32_state(state);
 103                 int j;
 104
 105                 for (j = 0; j < sizeof(u32); j++) {
 106                         p[i + j] = random;
 107                         random >>= BITS_PER_BYTE;
 108                 }
 109         }
 110         if (i < bytes) {
 111                 u32 random = prandom_u32_state(state);
 112
 113                 for (; i < bytes; i++) {
 114                         p[i] = random;
 115                         random >>= BITS_PER_BYTE;
 116                 }
 117         }
 118 }
 119 EXPORT_SYMBOL(prandom_bytes_state);
 120
 121 /**
 122  *      prandom_bytes - get the requested number of pseudo-random bytes
 123  *      @buf: where to copy the pseudo-random bytes to
 124  *      @bytes: the requested number of bytes
 125  */
 126 void prandom_bytes(void *buf, int bytes)
 127 {
 128         struct rnd_state *state = &get_cpu_var(net_rand_state);
 129
 130         prandom_bytes_state(state, buf, bytes);
 131         put_cpu_var(state);
 132 }
 133 EXPORT_SYMBOL(prandom_bytes);
 134
 135 static void prandom_warmup(struct rnd_state *state)
 136 {
 137         /* Calling RNG ten times to satify recurrence condition */
 138         prandom_u32_state(state);
 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 }
 149
 150 static void prandom_seed_very_weak(struct rnd_state *state, u32 seed)
 151 {
 152         /* Note: This sort of seeding is ONLY used in test cases and
 153          * during boot at the time from core_initcall until late_initcall
 154          * as we don't have a stronger entropy source available yet.
 155          * After late_initcall, we reseed entire state, we have to (!),
 156          * otherwise an attacker just needs to search 32 bit space to
 157          * probe for our internal 128 bit state if he knows a couple
 158          * of prandom32 outputs!
 159          */
 160 #define LCG(x)  ((x) * 69069U)  /* super-duper LCG */
 161         state->s1 = __seed(LCG(seed),        2U);
 162         state->s2 = __seed(LCG(state->s1),   8U);
 163         state->s3 = __seed(LCG(state->s2),  16U);
 164         state->s4 = __seed(LCG(state->s3), 128U);
 165 }
 166
 167 /**
 168  *      prandom_seed - add entropy to pseudo random number generator
 169  *      @seed: seed value
 170  *
 171  *      Add some additional seeding to the prandom pool.
 172  */
 173 void prandom_seed(u32 entropy)
 174 {
 175         int i;
 176         /*
 177          * No locking on the CPUs, but then somewhat random results are, well,
 178          * expected.
 179          */
 180         for_each_possible_cpu (i) {
 181                 struct rnd_state *state = &per_cpu(net_rand_state, i);
 182
 183                 state->s1 = __seed(state->s1 ^ entropy, 2U);
 184                 prandom_warmup(state);
 185         }
 186 }
 187 EXPORT_SYMBOL(prandom_seed);
 188
 189 /*
 190  *      Generate some initially weak seeding values to allow
 191  *      to start the prandom_u32() engine.
 192  */
 193 static int __init prandom_init(void)
 194 {
 195         int i;
 196
 197 #ifdef CONFIG_RANDOM32_SELFTEST
 198         prandom_state_selftest();
 199 #endif
 200
 201         for_each_possible_cpu(i) {
 202                 struct rnd_state *state = &per_cpu(net_rand_state,i);
 203
 204                 prandom_seed_very_weak(state, (i + jiffies) ^ random_get_entropy());
 205                 prandom_warmup(state);
 206         }
 207
 208         return 0;
 209 }
 210 core_initcall(prandom_init);
 211
 212 static void __prandom_timer(unsigned long dontcare);
 213 static DEFINE_TIMER(seed_timer, __prandom_timer, 0, 0);
 214
 215 static void __prandom_timer(unsigned long dontcare)
 216 {
 217         u32 entropy;
 218         unsigned long expires;
 219
 220         get_random_bytes(&entropy, sizeof(entropy));
 221         prandom_seed(entropy);
 222
 223         /* reseed every ~60 seconds, in [40 .. 80) interval with slack */
 224         expires = 40 + (prandom_u32() % 40);
 225         seed_timer.expires = jiffies + msecs_to_jiffies(expires * MSEC_PER_SEC);
 226
 227         add_timer(&seed_timer);
 228 }
 229
 230 static void __init __prandom_start_seed_timer(void)
 231 {
 232         set_timer_slack(&seed_timer, HZ);
 233         seed_timer.expires = jiffies + msecs_to_jiffies(40 * MSEC_PER_SEC);
 234         add_timer(&seed_timer);
 235 }
 236
 237 /*
 238  *      Generate better values after random number generator
 239  *      is fully initialized.
 240  */
 241 static void __prandom_reseed(bool late)
 242 {
 243         int i;
 244         unsigned long flags;
 245         static bool latch = false;
 246         static DEFINE_SPINLOCK(lock);
 247
 248         /* Asking for random bytes might result in bytes getting
 249          * moved into the nonblocking pool and thus marking it
 250          * as initialized. In this case we would double back into
 251          * this function and attempt to do a late reseed.
 252          * Ignore the pointless attempt to reseed again if we're
 253          * already waiting for bytes when the nonblocking pool
 254          * got initialized.
 255          */
 256
 257         /* only allow initial seeding (late == false) once */
 258         if (!spin_trylock_irqsave(&lock, flags))
 259                 return;
 260
 261         if (latch && !late)
 262                 goto out;
 263
 264         latch = true;
 265
 266         for_each_possible_cpu(i) {
 267                 struct rnd_state *state = &per_cpu(net_rand_state,i);
 268                 u32 seeds[4];
 269
 270                 get_random_bytes(&seeds, sizeof(seeds));
 271                 state->s1 = __seed(seeds[0],   2U);
 272                 state->s2 = __seed(seeds[1],   8U);
 273                 state->s3 = __seed(seeds[2],  16U);
 274                 state->s4 = __seed(seeds[3], 128U);
 275
 276                 prandom_warmup(state);
 277         }
 278 out:
 279         spin_unlock_irqrestore(&lock, flags);
 280 }
 281
 282 void prandom_reseed_late(void)
 283 {
 284         __prandom_reseed(true);
 285 }
 286
 287 static int __init prandom_reseed(void)
 288 {
 289         __prandom_reseed(false);
 290         __prandom_start_seed_timer();
 291         return 0;
 292 }
 293 late_initcall(prandom_reseed);
 294
 295 #ifdef CONFIG_RANDOM32_SELFTEST
 296 static struct prandom_test1 {
 297         u32 seed;
 298         u32 result;
 299 } test1[] = {
 300         { 1U, 3484351685U },
 301         { 2U, 2623130059U },
 302         { 3U, 3125133893U },
 303         { 4U,  984847254U },
 304 };
 305
 306 static struct prandom_test2 {
 307         u32 seed;
 308         u32 iteration;
 309         u32 result;
 310 } test2[] = {
 311         /* Test cases against taus113 from GSL library. */
 312         {  931557656U, 959U, 2975593782U },
 313         { 1339693295U, 876U, 3887776532U },
 314         { 1545556285U, 961U, 1615538833U },
 315         {  601730776U, 723U, 1776162651U },
 316         { 1027516047U, 687U,  511983079U },
 317         {  416526298U, 700U,  916156552U },
 318         { 1395522032U, 652U, 2222063676U },
 319         {  366221443U, 617U, 2992857763U },
 320         { 1539836965U, 714U, 3783265725U },
 321         {  556206671U, 994U,  799626459U },
 322         {  684907218U, 799U,  367789491U },
 323         { 2121230701U, 931U, 2115467001U },
 324         { 1668516451U, 644U, 3620590685U },
 325         {  768046066U, 883U, 2034077390U },
 326         { 1989159136U, 833U, 1195767305U },
 327         {  536585145U, 996U, 3577259204U },
 328         { 1008129373U, 642U, 1478080776U },
 329         { 1740775604U, 939U, 1264980372U },
 330         { 1967883163U, 508U,   10734624U },
 331         { 1923019697U, 730U, 3821419629U },
 332         {  442079932U, 560U, 3440032343U },
 333         { 1961302714U, 845U,  841962572U },
 334         { 2030205964U, 962U, 1325144227U },
 335         { 1160407529U, 507U,  240940858U },
 336         {  635482502U, 779U, 4200489746U },
 337         { 1252788931U, 699U,  867195434U },
 338         { 1961817131U, 719U,  668237657U },
 339         { 1071468216U, 983U,  917876630U },
 340         { 1281848367U, 932U, 1003100039U },
 341         {  582537119U, 780U, 1127273778U },
 342         { 1973672777U, 853U, 1071368872U },
 343         { 1896756996U, 762U, 1127851055U },
 344         {  847917054U, 500U, 1717499075U },
 345         { 1240520510U, 951U, 2849576657U },
 346         { 1685071682U, 567U, 1961810396U },
 347         { 1516232129U, 557U,    3173877U },
 348         { 1208118903U, 612U, 1613145022U },
 349         { 1817269927U, 693U, 4279122573U },
 350         { 1510091701U, 717U,  638191229U },
 351         {  365916850U, 807U,  600424314U },
 352         {  399324359U, 702U, 1803598116U },
 353         { 1318480274U, 779U, 2074237022U },
 354         {  697758115U, 840U, 1483639402U },
 355         { 1696507773U, 840U,  577415447U },
 356         { 2081979121U, 981U, 3041486449U },
 357         {  955646687U, 742U, 3846494357U },
 358         { 1250683506U, 749U,  836419859U },
 359         {  595003102U, 534U,  366794109U },
 360         {   47485338U, 558U, 3521120834U },
 361         {  619433479U, 610U, 3991783875U },
 362         {  704096520U, 518U, 4139493852U },
 363         { 1712224984U, 606U, 2393312003U },
 364         { 1318233152U, 922U, 3880361134U },
 365         {  855572992U, 761U, 1472974787U },
 366         {   64721421U, 703U,  683860550U },
 367         {  678931758U, 840U,  380616043U },
 368         {  692711973U, 778U, 1382361947U },
 369         {  677703619U, 530U, 2826914161U },
 370         {   92393223U, 586U, 1522128471U },
 371         { 1222592920U, 743U, 3466726667U },
 372         {  358288986U, 695U, 1091956998U },
 373         { 1935056945U, 958U,  514864477U },
 374         {  735675993U, 990U, 1294239989U },
 375         { 1560089402U, 897U, 2238551287U },
 376         {   70616361U, 829U,   22483098U },
 377         {  368234700U, 731U, 2913875084U },
 378         {   20221190U, 879U, 1564152970U },
 379         {  539444654U, 682U, 1835141259U },
 380         { 1314987297U, 840U, 1801114136U },
 381         { 2019295544U, 645U, 3286438930U },
 382         {  469023838U, 716U, 1637918202U },
 383         { 1843754496U, 653U, 2562092152U },
 384         {  400672036U, 809U, 4264212785U },
 385         {  404722249U, 965U, 2704116999U },
 386         {  600702209U, 758U,  584979986U },
 387         {  519953954U, 667U, 2574436237U },
 388         { 1658071126U, 694U, 2214569490U },
 389         {  420480037U, 749U, 3430010866U },
 390         {  690103647U, 969U, 3700758083U },
 391         { 1029424799U, 937U, 3787746841U },
 392         { 2012608669U, 506U, 3362628973U },
 393         { 1535432887U, 998U,   42610943U },
 394         { 1330635533U, 857U, 3040806504U },
 395         { 1223800550U, 539U, 3954229517U },
 396         { 1322411537U, 680U, 3223250324U },
 397         { 1877847898U, 945U, 2915147143U },
 398         { 1646356099U, 874U,  965988280U },
 399         {  805687536U, 744U, 4032277920U },
 400         { 1948093210U, 633U, 1346597684U },
 401         {  392609744U, 783U, 1636083295U },
 402         {  690241304U, 770U, 1201031298U },
 403         { 1360302965U, 696U, 1665394461U },
 404         { 1220090946U, 780U, 1316922812U },
 405         {  447092251U, 500U, 3438743375U },
 406         { 1613868791U, 592U,  828546883U },
 407         {  523430951U, 548U, 2552392304U },
 408         {  726692899U, 810U, 1656872867U },
 409         { 1364340021U, 836U, 3710513486U },
 410         { 1986257729U, 931U,  935013962U },
 411         {  407983964U, 921U,  728767059U },
 412 };
 413
 414 static void __init prandom_state_selftest(void)
 415 {
 416         int i, j, errors = 0, runs = 0;
 417         bool error = false;
 418
 419         for (i = 0; i < ARRAY_SIZE(test1); i++) {
 420                 struct rnd_state state;
 421
 422                 prandom_seed_very_weak(&state, test1[i].seed);
 423                 prandom_warmup(&state);
 424
 425                 if (test1[i].result != prandom_u32_state(&state))
 426                         error = true;
 427         }
 428
 429         if (error)
 430                 pr_warn("prandom: seed boundary self test failed\n");
 431         else
 432                 pr_info("prandom: seed boundary self test passed\n");
 433
 434         for (i = 0; i < ARRAY_SIZE(test2); i++) {
 435                 struct rnd_state state;
 436
 437                 prandom_seed_very_weak(&state, test2[i].seed);
 438                 prandom_warmup(&state);
 439
 440                 for (j = 0; j < test2[i].iteration - 1; j++)
 441                         prandom_u32_state(&state);
 442
 443                 if (test2[i].result != prandom_u32_state(&state))
 444                         errors++;
 445
 446                 runs++;
 447                 cond_resched();
 448         }
 449
 450         if (errors)
 451                 pr_warn("prandom: %d/%d self tests failed\n", errors, runs);
 452         else
 453                 pr_info("prandom: %d self tests passed\n", runs);
 454 }
 455 #endif