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 #include <trace/events/random.h>
  43
  44 /**
  45  *      prandom_u32_state - seeded pseudo-random number generator.
  46  *      @state: pointer to state structure holding seeded state.
  47  *
  48  *      This is used for pseudo-randomness with no outside seeding.
  49  *      For more random results, use prandom_u32().
  50  */
  51 u32 prandom_u32_state(struct rnd_state *state)
  52 {
  53 #define TAUSWORTHE(s, a, b, c, d) ((s & c) << d) ^ (((s << a) ^ s) >> b)
  54         state->s1 = TAUSWORTHE(state->s1,  6U, 13U, 4294967294U, 18U);
  55         state->s2 = TAUSWORTHE(state->s2,  2U, 27U, 4294967288U,  2U);
  56         state->s3 = TAUSWORTHE(state->s3, 13U, 21U, 4294967280U,  7U);
  57         state->s4 = TAUSWORTHE(state->s4,  3U, 12U, 4294967168U, 13U);
  58
  59         return (state->s1 ^ state->s2 ^ state->s3 ^ state->s4);
  60 }
  61 EXPORT_SYMBOL(prandom_u32_state);
  62
  63 /**
  64  *      prandom_bytes_state - get the requested number of pseudo-random bytes
  65  *
  66  *      @state: pointer to state structure holding seeded state.
  67  *      @buf: where to copy the pseudo-random bytes to
  68  *      @bytes: the requested number of bytes
  69  *
  70  *      This is used for pseudo-randomness with no outside seeding.
  71  *      For more random results, use prandom_bytes().
  72  */
  73 void prandom_bytes_state(struct rnd_state *state, void *buf, size_t bytes)
  74 {
  75         u8 *ptr = buf;
  76
  77         while (bytes >= sizeof(u32)) {
  78                 put_unaligned(prandom_u32_state(state), (u32 *) ptr);
  79                 ptr += sizeof(u32);
  80                 bytes -= sizeof(u32);
  81         }
  82
  83         if (bytes > 0) {
  84                 u32 rem = prandom_u32_state(state);
  85                 do {
  86                         *ptr++ = (u8) rem;
  87                         bytes--;
  88                         rem >>= BITS_PER_BYTE;
  89                 } while (bytes > 0);
  90         }
  91 }
  92 EXPORT_SYMBOL(prandom_bytes_state);
  93
  94 static void prandom_warmup(struct rnd_state *state)
  95 {
  96         /* Calling RNG ten times to satisfy recurrence condition */
  97         prandom_u32_state(state);
  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 }
 108
 109 void prandom_seed_full_state(struct rnd_state __percpu *pcpu_state)
 110 {
 111         int i;
 112
 113         for_each_possible_cpu(i) {
 114                 struct rnd_state *state = per_cpu_ptr(pcpu_state, i);
 115                 u32 seeds[4];
 116
 117                 get_random_bytes(&seeds, sizeof(seeds));
 118                 state->s1 = __seed(seeds[0],   2U);
 119                 state->s2 = __seed(seeds[1],   8U);
 120                 state->s3 = __seed(seeds[2],  16U);
 121                 state->s4 = __seed(seeds[3], 128U);
 122
 123                 prandom_warmup(state);
 124         }
 125 }
 126 EXPORT_SYMBOL(prandom_seed_full_state);
 127
 128 #ifdef CONFIG_RANDOM32_SELFTEST
 129 static struct prandom_test1 {
 130         u32 seed;
 131         u32 result;
 132 } test1[] = {
 133         { 1U, 3484351685U },
 134         { 2U, 2623130059U },
 135         { 3U, 3125133893U },
 136         { 4U,  984847254U },
 137 };
 138
 139 static struct prandom_test2 {
 140         u32 seed;
 141         u32 iteration;
 142         u32 result;
 143 } test2[] = {
 144         /* Test cases against taus113 from GSL library. */
 145         {  931557656U, 959U, 2975593782U },
 146         { 1339693295U, 876U, 3887776532U },
 147         { 1545556285U, 961U, 1615538833U },
 148         {  601730776U, 723U, 1776162651U },
 149         { 1027516047U, 687U,  511983079U },
 150         {  416526298U, 700U,  916156552U },
 151         { 1395522032U, 652U, 2222063676U },
 152         {  366221443U, 617U, 2992857763U },
 153         { 1539836965U, 714U, 3783265725U },
 154         {  556206671U, 994U,  799626459U },
 155         {  684907218U, 799U,  367789491U },
 156         { 2121230701U, 931U, 2115467001U },
 157         { 1668516451U, 644U, 3620590685U },
 158         {  768046066U, 883U, 2034077390U },
 159         { 1989159136U, 833U, 1195767305U },
 160         {  536585145U, 996U, 3577259204U },
 161         { 1008129373U, 642U, 1478080776U },
 162         { 1740775604U, 939U, 1264980372U },
 163         { 1967883163U, 508U,   10734624U },
 164         { 1923019697U, 730U, 3821419629U },
 165         {  442079932U, 560U, 3440032343U },
 166         { 1961302714U, 845U,  841962572U },
 167         { 2030205964U, 962U, 1325144227U },
 168         { 1160407529U, 507U,  240940858U },
 169         {  635482502U, 779U, 4200489746U },
 170         { 1252788931U, 699U,  867195434U },
 171         { 1961817131U, 719U,  668237657U },
 172         { 1071468216U, 983U,  917876630U },
 173         { 1281848367U, 932U, 1003100039U },
 174         {  582537119U, 780U, 1127273778U },
 175         { 1973672777U, 853U, 1071368872U },
 176         { 1896756996U, 762U, 1127851055U },
 177         {  847917054U, 500U, 1717499075U },
 178         { 1240520510U, 951U, 2849576657U },
 179         { 1685071682U, 567U, 1961810396U },
 180         { 1516232129U, 557U,    3173877U },
 181         { 1208118903U, 612U, 1613145022U },
 182         { 1817269927U, 693U, 4279122573U },
 183         { 1510091701U, 717U,  638191229U },
 184         {  365916850U, 807U,  600424314U },
 185         {  399324359U, 702U, 1803598116U },
 186         { 1318480274U, 779U, 2074237022U },
 187         {  697758115U, 840U, 1483639402U },
 188         { 1696507773U, 840U,  577415447U },
 189         { 2081979121U, 981U, 3041486449U },
 190         {  955646687U, 742U, 3846494357U },
 191         { 1250683506U, 749U,  836419859U },
 192         {  595003102U, 534U,  366794109U },
 193         {   47485338U, 558U, 3521120834U },
 194         {  619433479U, 610U, 3991783875U },
 195         {  704096520U, 518U, 4139493852U },
 196         { 1712224984U, 606U, 2393312003U },
 197         { 1318233152U, 922U, 3880361134U },
 198         {  855572992U, 761U, 1472974787U },
 199         {   64721421U, 703U,  683860550U },
 200         {  678931758U, 840U,  380616043U },
 201         {  692711973U, 778U, 1382361947U },
 202         {  677703619U, 530U, 2826914161U },
 203         {   92393223U, 586U, 1522128471U },
 204         { 1222592920U, 743U, 3466726667U },
 205         {  358288986U, 695U, 1091956998U },
 206         { 1935056945U, 958U,  514864477U },
 207         {  735675993U, 990U, 1294239989U },
 208         { 1560089402U, 897U, 2238551287U },
 209         {   70616361U, 829U,   22483098U },
 210         {  368234700U, 731U, 2913875084U },
 211         {   20221190U, 879U, 1564152970U },
 212         {  539444654U, 682U, 1835141259U },
 213         { 1314987297U, 840U, 1801114136U },
 214         { 2019295544U, 645U, 3286438930U },
 215         {  469023838U, 716U, 1637918202U },
 216         { 1843754496U, 653U, 2562092152U },
 217         {  400672036U, 809U, 4264212785U },
 218         {  404722249U, 965U, 2704116999U },
 219         {  600702209U, 758U,  584979986U },
 220         {  519953954U, 667U, 2574436237U },
 221         { 1658071126U, 694U, 2214569490U },
 222         {  420480037U, 749U, 3430010866U },
 223         {  690103647U, 969U, 3700758083U },
 224         { 1029424799U, 937U, 3787746841U },
 225         { 2012608669U, 506U, 3362628973U },
 226         { 1535432887U, 998U,   42610943U },
 227         { 1330635533U, 857U, 3040806504U },
 228         { 1223800550U, 539U, 3954229517U },
 229         { 1322411537U, 680U, 3223250324U },
 230         { 1877847898U, 945U, 2915147143U },
 231         { 1646356099U, 874U,  965988280U },
 232         {  805687536U, 744U, 4032277920U },
 233         { 1948093210U, 633U, 1346597684U },
 234         {  392609744U, 783U, 1636083295U },
 235         {  690241304U, 770U, 1201031298U },
 236         { 1360302965U, 696U, 1665394461U },
 237         { 1220090946U, 780U, 1316922812U },
 238         {  447092251U, 500U, 3438743375U },
 239         { 1613868791U, 592U,  828546883U },
 240         {  523430951U, 548U, 2552392304U },
 241         {  726692899U, 810U, 1656872867U },
 242         { 1364340021U, 836U, 3710513486U },
 243         { 1986257729U, 931U,  935013962U },
 244         {  407983964U, 921U,  728767059U },
 245 };
 246
 247 static u32 __extract_hwseed(void)
 248 {
 249         unsigned int val = 0;
 250
 251         (void)(arch_get_random_seed_int(&val) ||
 252                arch_get_random_int(&val));
 253
 254         return val;
 255 }
 256
 257 static void prandom_seed_early(struct rnd_state *state, u32 seed,
 258                                bool mix_with_hwseed)
 259 {
 260 #define LCG(x)   ((x) * 69069U) /* super-duper LCG */
 261 #define HWSEED() (mix_with_hwseed ? __extract_hwseed() : 0)
 262         state->s1 = __seed(HWSEED() ^ LCG(seed),        2U);
 263         state->s2 = __seed(HWSEED() ^ LCG(state->s1),   8U);
 264         state->s3 = __seed(HWSEED() ^ LCG(state->s2),  16U);
 265         state->s4 = __seed(HWSEED() ^ LCG(state->s3), 128U);
 266 }
 267
 268 static int __init prandom_state_selftest(void)
 269 {
 270         int i, j, errors = 0, runs = 0;
 271         bool error = false;
 272
 273         for (i = 0; i < ARRAY_SIZE(test1); i++) {
 274                 struct rnd_state state;
 275
 276                 prandom_seed_early(&state, test1[i].seed, false);
 277                 prandom_warmup(&state);
 278
 279                 if (test1[i].result != prandom_u32_state(&state))
 280                         error = true;
 281         }
 282
 283         if (error)
 284                 pr_warn("prandom: seed boundary self test failed\n");
 285         else
 286                 pr_info("prandom: seed boundary self test passed\n");
 287
 288         for (i = 0; i < ARRAY_SIZE(test2); i++) {
 289                 struct rnd_state state;
 290
 291                 prandom_seed_early(&state, test2[i].seed, false);
 292                 prandom_warmup(&state);
 293
 294                 for (j = 0; j < test2[i].iteration - 1; j++)
 295                         prandom_u32_state(&state);
 296
 297                 if (test2[i].result != prandom_u32_state(&state))
 298                         errors++;
 299
 300                 runs++;
 301                 cond_resched();
 302         }
 303
 304         if (errors)
 305                 pr_warn("prandom: %d/%d self tests failed\n", errors, runs);
 306         else
 307                 pr_info("prandom: %d self tests passed\n", runs);
 308         return 0;
 309 }
 310 core_initcall(prandom_state_selftest);
 311 #endif
 312
 313 /*
 314  * The prandom_u32() implementation is now completely separate from the
 315  * prandom_state() functions, which are retained (for now) for compatibility.
 316  *
 317  * Because of (ab)use in the networking code for choosing random TCP/UDP port
 318  * numbers, which open DoS possibilities if guessable, we want something
 319  * stronger than a standard PRNG.  But the performance requirements of
 320  * the network code do not allow robust crypto for this application.
 321  *
 322  * So this is a homebrew Junior Spaceman implementation, based on the
 323  * lowest-latency trustworthy crypto primitive available, SipHash.
 324  * (The authors of SipHash have not been consulted about this abuse of
 325  * their work.)
 326  *
 327  * Standard SipHash-2-4 uses 2n+4 rounds to hash n words of input to
 328  * one word of output.  This abbreviated version uses 2 rounds per word
 329  * of output.
 330  */
 331
 332 struct siprand_state {
 333         unsigned long v0;
 334         unsigned long v1;
 335         unsigned long v2;
 336         unsigned long v3;
 337 };
 338
 339 static DEFINE_PER_CPU(struct siprand_state, net_rand_state) __latent_entropy;
 340
 341 /*
 342  * This is the core CPRNG function.  As "pseudorandom", this is not used
 343  * for truly valuable things, just intended to be a PITA to guess.
 344  * For maximum speed, we do just two SipHash rounds per word.  This is
 345  * the same rate as 4 rounds per 64 bits that SipHash normally uses,
 346  * so hopefully it's reasonably secure.
 347  *
 348  * There are two changes from the official SipHash finalization:
 349  * - We omit some constants XORed with v2 in the SipHash spec as irrelevant;
 350  *   they are there only to make the output rounds distinct from the input
 351  *   rounds, and this application has no input rounds.
 352  * - Rather than returning v0^v1^v2^v3, return v1+v3.
 353  *   If you look at the SipHash round, the last operation on v3 is
 354  *   "v3 ^= v0", so "v0 ^ v3" just undoes that, a waste of time.
 355  *   Likewise "v1 ^= v2".  (The rotate of v2 makes a difference, but
 356  *   it still cancels out half of the bits in v2 for no benefit.)
 357  *   Second, since the last combining operation was xor, continue the
 358  *   pattern of alternating xor/add for a tiny bit of extra non-linearity.
 359  */
 360 static inline u32 siprand_u32(struct siprand_state *s)
 361 {
 362         unsigned long v0 = s->v0, v1 = s->v1, v2 = s->v2, v3 = s->v3;
 363
 364         PRND_SIPROUND(v0, v1, v2, v3);
 365         PRND_SIPROUND(v0, v1, v2, v3);
 366         s->v0 = v0;  s->v1 = v1;  s->v2 = v2;  s->v3 = v3;
 367         return v1 + v3;
 368 }
 369
 370
 371 /**
 372  *      prandom_u32 - pseudo random number generator
 373  *
 374  *      A 32 bit pseudo-random number is generated using a fast
 375  *      algorithm suitable for simulation. This algorithm is NOT
 376  *      considered safe for cryptographic use.
 377  */
 378 u32 prandom_u32(void)
 379 {
 380         struct siprand_state *state = get_cpu_ptr(&net_rand_state);
 381         u32 res = siprand_u32(state);
 382
 383         trace_prandom_u32(res);
 384         put_cpu_ptr(&net_rand_state);
 385         return res;
 386 }
 387 EXPORT_SYMBOL(prandom_u32);
 388
 389 /**
 390  *      prandom_bytes - get the requested number of pseudo-random bytes
 391  *      @buf: where to copy the pseudo-random bytes to
 392  *      @bytes: the requested number of bytes
 393  */
 394 void prandom_bytes(void *buf, size_t bytes)
 395 {
 396         struct siprand_state *state = get_cpu_ptr(&net_rand_state);
 397         u8 *ptr = buf;
 398
 399         while (bytes >= sizeof(u32)) {
 400                 put_unaligned(siprand_u32(state), (u32 *)ptr);
 401                 ptr += sizeof(u32);
 402                 bytes -= sizeof(u32);
 403         }
 404
 405         if (bytes > 0) {
 406                 u32 rem = siprand_u32(state);
 407
 408                 do {
 409                         *ptr++ = (u8)rem;
 410                         rem >>= BITS_PER_BYTE;
 411                 } while (--bytes > 0);
 412         }
 413         put_cpu_ptr(&net_rand_state);
 414 }
 415 EXPORT_SYMBOL(prandom_bytes);
 416
 417 /**
 418  *      prandom_seed - add entropy to pseudo random number generator
 419  *      @entropy: entropy value
 420  *
 421  *      Add some additional seed material to the prandom pool.
 422  *      The "entropy" is actually our IP address (the only caller is
 423  *      the network code), not for unpredictability, but to ensure that
 424  *      different machines are initialized differently.
 425  */
 426 void prandom_seed(u32 entropy)
 427 {
 428         int i;
 429
 430         add_device_randomness(&entropy, sizeof(entropy));
 431
 432         for_each_possible_cpu(i) {
 433                 struct siprand_state *state = per_cpu_ptr(&net_rand_state, i);
 434                 unsigned long v0 = state->v0, v1 = state->v1;
 435                 unsigned long v2 = state->v2, v3 = state->v3;
 436
 437                 do {
 438                         v3 ^= entropy;
 439                         PRND_SIPROUND(v0, v1, v2, v3);
 440                         PRND_SIPROUND(v0, v1, v2, v3);
 441                         v0 ^= entropy;
 442                 } while (unlikely(!v0 || !v1 || !v2 || !v3));
 443
 444                 WRITE_ONCE(state->v0, v0);
 445                 WRITE_ONCE(state->v1, v1);
 446                 WRITE_ONCE(state->v2, v2);
 447                 WRITE_ONCE(state->v3, v3);
 448         }
 449 }
 450 EXPORT_SYMBOL(prandom_seed);
 451
 452 /*
 453  *      Generate some initially weak seeding values to allow
 454  *      the prandom_u32() engine to be started.
 455  */
 456 static int __init prandom_init_early(void)
 457 {
 458         int i;
 459         unsigned long v0, v1, v2, v3;
 460
 461         if (!arch_get_random_long(&v0))
 462                 v0 = jiffies;
 463         if (!arch_get_random_long(&v1))
 464                 v1 = random_get_entropy();
 465         v2 = v0 ^ PRND_K0;
 466         v3 = v1 ^ PRND_K1;
 467
 468         for_each_possible_cpu(i) {
 469                 struct siprand_state *state;
 470
 471                 v3 ^= i;
 472                 PRND_SIPROUND(v0, v1, v2, v3);
 473                 PRND_SIPROUND(v0, v1, v2, v3);
 474                 v0 ^= i;
 475
 476                 state = per_cpu_ptr(&net_rand_state, i);
 477                 state->v0 = v0;  state->v1 = v1;
 478                 state->v2 = v2;  state->v3 = v3;
 479         }
 480
 481         return 0;
 482 }
 483 core_initcall(prandom_init_early);
 484
 485
 486 /* Stronger reseeding when available, and periodically thereafter. */
 487 static void prandom_reseed(struct timer_list *unused);
 488
 489 static DEFINE_TIMER(seed_timer, prandom_reseed);
 490
 491 static void prandom_reseed(struct timer_list *unused)
 492 {
 493         unsigned long expires;
 494         int i;
 495
 496         /*
 497          * Reinitialize each CPU's PRNG with 128 bits of key.
 498          * No locking on the CPUs, but then somewhat random results are,
 499          * well, expected.
 500          */
 501         for_each_possible_cpu(i) {
 502                 struct siprand_state *state;
 503                 unsigned long v0 = get_random_long(), v2 = v0 ^ PRND_K0;
 504                 unsigned long v1 = get_random_long(), v3 = v1 ^ PRND_K1;
 505 #if BITS_PER_LONG == 32
 506                 int j;
 507
 508                 /*
 509                  * On 32-bit machines, hash in two extra words to
 510                  * approximate 128-bit key length.  Not that the hash
 511                  * has that much security, but this prevents a trivial
 512                  * 64-bit brute force.
 513                  */
 514                 for (j = 0; j < 2; j++) {
 515                         unsigned long m = get_random_long();
 516
 517                         v3 ^= m;
 518                         PRND_SIPROUND(v0, v1, v2, v3);
 519                         PRND_SIPROUND(v0, v1, v2, v3);
 520                         v0 ^= m;
 521                 }
 522 #endif
 523                 /*
 524                  * Probably impossible in practice, but there is a
 525                  * theoretical risk that a race between this reseeding
 526                  * and the target CPU writing its state back could
 527                  * create the all-zero SipHash fixed point.
 528                  *
 529                  * To ensure that never happens, ensure the state
 530                  * we write contains no zero words.
 531                  */
 532                 state = per_cpu_ptr(&net_rand_state, i);
 533                 WRITE_ONCE(state->v0, v0 ? v0 : -1ul);
 534                 WRITE_ONCE(state->v1, v1 ? v1 : -1ul);
 535                 WRITE_ONCE(state->v2, v2 ? v2 : -1ul);
 536                 WRITE_ONCE(state->v3, v3 ? v3 : -1ul);
 537         }
 538
 539         /* reseed every ~60 seconds, in [40 .. 80) interval with slack */
 540         expires = round_jiffies(jiffies + 40 * HZ + prandom_u32_max(40 * HZ));
 541         mod_timer(&seed_timer, expires);
 542 }
 543
 544 /*
 545  * The random ready callback can be called from almost any interrupt.
 546  * To avoid worrying about whether it's safe to delay that interrupt
 547  * long enough to seed all CPUs, just schedule an immediate timer event.
 548  */
 549 static void prandom_timer_start(struct random_ready_callback *unused)
 550 {
 551         mod_timer(&seed_timer, jiffies);
 552 }
 553
 554 /*
 555  * Start periodic full reseeding as soon as strong
 556  * random numbers are available.
 557  */
 558 static int __init prandom_init_late(void)
 559 {
 560         static struct random_ready_callback random_ready = {
 561                 .func = prandom_timer_start
 562         };
 563         int ret = add_random_ready_callback(&random_ready);
 564
 565         if (ret == -EALREADY) {
 566                 prandom_timer_start(&random_ready);
 567                 ret = 0;
 568         }
 569         return ret;
 570 }
 571 late_initcall(prandom_init_late);