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 <linux/bitops.h>
42 #include <linux/slab.h>
43 #include <linux/notifier.h>
44 #include <asm/unaligned.h>
45
46 /**
47 * prandom_u32_state - seeded pseudo-random number generator.
48 * @state: pointer to state structure holding seeded state.
49 *
50 * This is used for pseudo-randomness with no outside seeding.
51 * For more random results, use prandom_u32().
52 */
prandom_u32_state(struct rnd_state * state)53 u32 prandom_u32_state(struct rnd_state *state)
54 {
55 #define TAUSWORTHE(s, a, b, c, d) ((s & c) << d) ^ (((s << a) ^ s) >> b)
56 state->s1 = TAUSWORTHE(state->s1, 6U, 13U, 4294967294U, 18U);
57 state->s2 = TAUSWORTHE(state->s2, 2U, 27U, 4294967288U, 2U);
58 state->s3 = TAUSWORTHE(state->s3, 13U, 21U, 4294967280U, 7U);
59 state->s4 = TAUSWORTHE(state->s4, 3U, 12U, 4294967168U, 13U);
60
61 return (state->s1 ^ state->s2 ^ state->s3 ^ state->s4);
62 }
63 EXPORT_SYMBOL(prandom_u32_state);
64
65 /**
66 * prandom_bytes_state - get the requested number of pseudo-random bytes
67 *
68 * @state: pointer to state structure holding seeded state.
69 * @buf: where to copy the pseudo-random bytes to
70 * @bytes: the requested number of bytes
71 *
72 * This is used for pseudo-randomness with no outside seeding.
73 * For more random results, use prandom_bytes().
74 */
prandom_bytes_state(struct rnd_state * state,void * buf,size_t bytes)75 void prandom_bytes_state(struct rnd_state *state, void *buf, size_t bytes)
76 {
77 u8 *ptr = buf;
78
79 while (bytes >= sizeof(u32)) {
80 put_unaligned(prandom_u32_state(state), (u32 *) ptr);
81 ptr += sizeof(u32);
82 bytes -= sizeof(u32);
83 }
84
85 if (bytes > 0) {
86 u32 rem = prandom_u32_state(state);
87 do {
88 *ptr++ = (u8) rem;
89 bytes--;
90 rem >>= BITS_PER_BYTE;
91 } while (bytes > 0);
92 }
93 }
94 EXPORT_SYMBOL(prandom_bytes_state);
95
prandom_warmup(struct rnd_state * state)96 static void prandom_warmup(struct rnd_state *state)
97 {
98 /* Calling RNG ten times to satisfy recurrence condition */
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 prandom_u32_state(state);
109 }
110
prandom_seed_full_state(struct rnd_state __percpu * pcpu_state)111 void prandom_seed_full_state(struct rnd_state __percpu *pcpu_state)
112 {
113 int i;
114
115 for_each_possible_cpu(i) {
116 struct rnd_state *state = per_cpu_ptr(pcpu_state, i);
117 u32 seeds[4];
118
119 get_random_bytes(&seeds, sizeof(seeds));
120 state->s1 = __seed(seeds[0], 2U);
121 state->s2 = __seed(seeds[1], 8U);
122 state->s3 = __seed(seeds[2], 16U);
123 state->s4 = __seed(seeds[3], 128U);
124
125 prandom_warmup(state);
126 }
127 }
128 EXPORT_SYMBOL(prandom_seed_full_state);
129
130 #ifdef CONFIG_RANDOM32_SELFTEST
131 static struct prandom_test1 {
132 u32 seed;
133 u32 result;
134 } test1[] = {
135 { 1U, 3484351685U },
136 { 2U, 2623130059U },
137 { 3U, 3125133893U },
138 { 4U, 984847254U },
139 };
140
141 static struct prandom_test2 {
142 u32 seed;
143 u32 iteration;
144 u32 result;
145 } test2[] = {
146 /* Test cases against taus113 from GSL library. */
147 { 931557656U, 959U, 2975593782U },
148 { 1339693295U, 876U, 3887776532U },
149 { 1545556285U, 961U, 1615538833U },
150 { 601730776U, 723U, 1776162651U },
151 { 1027516047U, 687U, 511983079U },
152 { 416526298U, 700U, 916156552U },
153 { 1395522032U, 652U, 2222063676U },
154 { 366221443U, 617U, 2992857763U },
155 { 1539836965U, 714U, 3783265725U },
156 { 556206671U, 994U, 799626459U },
157 { 684907218U, 799U, 367789491U },
158 { 2121230701U, 931U, 2115467001U },
159 { 1668516451U, 644U, 3620590685U },
160 { 768046066U, 883U, 2034077390U },
161 { 1989159136U, 833U, 1195767305U },
162 { 536585145U, 996U, 3577259204U },
163 { 1008129373U, 642U, 1478080776U },
164 { 1740775604U, 939U, 1264980372U },
165 { 1967883163U, 508U, 10734624U },
166 { 1923019697U, 730U, 3821419629U },
167 { 442079932U, 560U, 3440032343U },
168 { 1961302714U, 845U, 841962572U },
169 { 2030205964U, 962U, 1325144227U },
170 { 1160407529U, 507U, 240940858U },
171 { 635482502U, 779U, 4200489746U },
172 { 1252788931U, 699U, 867195434U },
173 { 1961817131U, 719U, 668237657U },
174 { 1071468216U, 983U, 917876630U },
175 { 1281848367U, 932U, 1003100039U },
176 { 582537119U, 780U, 1127273778U },
177 { 1973672777U, 853U, 1071368872U },
178 { 1896756996U, 762U, 1127851055U },
179 { 847917054U, 500U, 1717499075U },
180 { 1240520510U, 951U, 2849576657U },
181 { 1685071682U, 567U, 1961810396U },
182 { 1516232129U, 557U, 3173877U },
183 { 1208118903U, 612U, 1613145022U },
184 { 1817269927U, 693U, 4279122573U },
185 { 1510091701U, 717U, 638191229U },
186 { 365916850U, 807U, 600424314U },
187 { 399324359U, 702U, 1803598116U },
188 { 1318480274U, 779U, 2074237022U },
189 { 697758115U, 840U, 1483639402U },
190 { 1696507773U, 840U, 577415447U },
191 { 2081979121U, 981U, 3041486449U },
192 { 955646687U, 742U, 3846494357U },
193 { 1250683506U, 749U, 836419859U },
194 { 595003102U, 534U, 366794109U },
195 { 47485338U, 558U, 3521120834U },
196 { 619433479U, 610U, 3991783875U },
197 { 704096520U, 518U, 4139493852U },
198 { 1712224984U, 606U, 2393312003U },
199 { 1318233152U, 922U, 3880361134U },
200 { 855572992U, 761U, 1472974787U },
201 { 64721421U, 703U, 683860550U },
202 { 678931758U, 840U, 380616043U },
203 { 692711973U, 778U, 1382361947U },
204 { 677703619U, 530U, 2826914161U },
205 { 92393223U, 586U, 1522128471U },
206 { 1222592920U, 743U, 3466726667U },
207 { 358288986U, 695U, 1091956998U },
208 { 1935056945U, 958U, 514864477U },
209 { 735675993U, 990U, 1294239989U },
210 { 1560089402U, 897U, 2238551287U },
211 { 70616361U, 829U, 22483098U },
212 { 368234700U, 731U, 2913875084U },
213 { 20221190U, 879U, 1564152970U },
214 { 539444654U, 682U, 1835141259U },
215 { 1314987297U, 840U, 1801114136U },
216 { 2019295544U, 645U, 3286438930U },
217 { 469023838U, 716U, 1637918202U },
218 { 1843754496U, 653U, 2562092152U },
219 { 400672036U, 809U, 4264212785U },
220 { 404722249U, 965U, 2704116999U },
221 { 600702209U, 758U, 584979986U },
222 { 519953954U, 667U, 2574436237U },
223 { 1658071126U, 694U, 2214569490U },
224 { 420480037U, 749U, 3430010866U },
225 { 690103647U, 969U, 3700758083U },
226 { 1029424799U, 937U, 3787746841U },
227 { 2012608669U, 506U, 3362628973U },
228 { 1535432887U, 998U, 42610943U },
229 { 1330635533U, 857U, 3040806504U },
230 { 1223800550U, 539U, 3954229517U },
231 { 1322411537U, 680U, 3223250324U },
232 { 1877847898U, 945U, 2915147143U },
233 { 1646356099U, 874U, 965988280U },
234 { 805687536U, 744U, 4032277920U },
235 { 1948093210U, 633U, 1346597684U },
236 { 392609744U, 783U, 1636083295U },
237 { 690241304U, 770U, 1201031298U },
238 { 1360302965U, 696U, 1665394461U },
239 { 1220090946U, 780U, 1316922812U },
240 { 447092251U, 500U, 3438743375U },
241 { 1613868791U, 592U, 828546883U },
242 { 523430951U, 548U, 2552392304U },
243 { 726692899U, 810U, 1656872867U },
244 { 1364340021U, 836U, 3710513486U },
245 { 1986257729U, 931U, 935013962U },
246 { 407983964U, 921U, 728767059U },
247 };
248
__extract_hwseed(void)249 static u32 __extract_hwseed(void)
250 {
251 unsigned int val = 0;
252
253 (void)(arch_get_random_seed_int(&val) ||
254 arch_get_random_int(&val));
255
256 return val;
257 }
258
prandom_seed_early(struct rnd_state * state,u32 seed,bool mix_with_hwseed)259 static void prandom_seed_early(struct rnd_state *state, u32 seed,
260 bool mix_with_hwseed)
261 {
262 #define LCG(x) ((x) * 69069U) /* super-duper LCG */
263 #define HWSEED() (mix_with_hwseed ? __extract_hwseed() : 0)
264 state->s1 = __seed(HWSEED() ^ LCG(seed), 2U);
265 state->s2 = __seed(HWSEED() ^ LCG(state->s1), 8U);
266 state->s3 = __seed(HWSEED() ^ LCG(state->s2), 16U);
267 state->s4 = __seed(HWSEED() ^ LCG(state->s3), 128U);
268 }
269
prandom_state_selftest(void)270 static int __init prandom_state_selftest(void)
271 {
272 int i, j, errors = 0, runs = 0;
273 bool error = false;
274
275 for (i = 0; i < ARRAY_SIZE(test1); i++) {
276 struct rnd_state state;
277
278 prandom_seed_early(&state, test1[i].seed, false);
279 prandom_warmup(&state);
280
281 if (test1[i].result != prandom_u32_state(&state))
282 error = true;
283 }
284
285 if (error)
286 pr_warn("prandom: seed boundary self test failed\n");
287 else
288 pr_info("prandom: seed boundary self test passed\n");
289
290 for (i = 0; i < ARRAY_SIZE(test2); i++) {
291 struct rnd_state state;
292
293 prandom_seed_early(&state, test2[i].seed, false);
294 prandom_warmup(&state);
295
296 for (j = 0; j < test2[i].iteration - 1; j++)
297 prandom_u32_state(&state);
298
299 if (test2[i].result != prandom_u32_state(&state))
300 errors++;
301
302 runs++;
303 cond_resched();
304 }
305
306 if (errors)
307 pr_warn("prandom: %d/%d self tests failed\n", errors, runs);
308 else
309 pr_info("prandom: %d self tests passed\n", runs);
310 return 0;
311 }
312 core_initcall(prandom_state_selftest);
313 #endif
314
315 /*
316 * The prandom_u32() implementation is now completely separate from the
317 * prandom_state() functions, which are retained (for now) for compatibility.
318 *
319 * Because of (ab)use in the networking code for choosing random TCP/UDP port
320 * numbers, which open DoS possibilities if guessable, we want something
321 * stronger than a standard PRNG. But the performance requirements of
322 * the network code do not allow robust crypto for this application.
323 *
324 * So this is a homebrew Junior Spaceman implementation, based on the
325 * lowest-latency trustworthy crypto primitive available, SipHash.
326 * (The authors of SipHash have not been consulted about this abuse of
327 * their work.)
328 *
329 * Standard SipHash-2-4 uses 2n+4 rounds to hash n words of input to
330 * one word of output. This abbreviated version uses 2 rounds per word
331 * of output.
332 */
333
334 struct siprand_state {
335 unsigned long v0;
336 unsigned long v1;
337 unsigned long v2;
338 unsigned long v3;
339 };
340
341 static DEFINE_PER_CPU(struct siprand_state, net_rand_state) __latent_entropy;
342
343 /*
344 * This is the core CPRNG function. As "pseudorandom", this is not used
345 * for truly valuable things, just intended to be a PITA to guess.
346 * For maximum speed, we do just two SipHash rounds per word. This is
347 * the same rate as 4 rounds per 64 bits that SipHash normally uses,
348 * so hopefully it's reasonably secure.
349 *
350 * There are two changes from the official SipHash finalization:
351 * - We omit some constants XORed with v2 in the SipHash spec as irrelevant;
352 * they are there only to make the output rounds distinct from the input
353 * rounds, and this application has no input rounds.
354 * - Rather than returning v0^v1^v2^v3, return v1+v3.
355 * If you look at the SipHash round, the last operation on v3 is
356 * "v3 ^= v0", so "v0 ^ v3" just undoes that, a waste of time.
357 * Likewise "v1 ^= v2". (The rotate of v2 makes a difference, but
358 * it still cancels out half of the bits in v2 for no benefit.)
359 * Second, since the last combining operation was xor, continue the
360 * pattern of alternating xor/add for a tiny bit of extra non-linearity.
361 */
siprand_u32(struct siprand_state * s)362 static inline u32 siprand_u32(struct siprand_state *s)
363 {
364 unsigned long v0 = s->v0, v1 = s->v1, v2 = s->v2, v3 = s->v3;
365
366 PRND_SIPROUND(v0, v1, v2, v3);
367 PRND_SIPROUND(v0, v1, v2, v3);
368 s->v0 = v0; s->v1 = v1; s->v2 = v2; s->v3 = v3;
369 return v1 + v3;
370 }
371
372
373 /**
374 * prandom_u32 - pseudo random number generator
375 *
376 * A 32 bit pseudo-random number is generated using a fast
377 * algorithm suitable for simulation. This algorithm is NOT
378 * considered safe for cryptographic use.
379 */
prandom_u32(void)380 u32 prandom_u32(void)
381 {
382 struct siprand_state *state = get_cpu_ptr(&net_rand_state);
383 u32 res = siprand_u32(state);
384
385 put_cpu_ptr(&net_rand_state);
386 return res;
387 }
388 EXPORT_SYMBOL(prandom_u32);
389
390 /**
391 * prandom_bytes - get the requested number of pseudo-random bytes
392 * @buf: where to copy the pseudo-random bytes to
393 * @bytes: the requested number of bytes
394 */
prandom_bytes(void * buf,size_t bytes)395 void prandom_bytes(void *buf, size_t bytes)
396 {
397 struct siprand_state *state = get_cpu_ptr(&net_rand_state);
398 u8 *ptr = buf;
399
400 while (bytes >= sizeof(u32)) {
401 put_unaligned(siprand_u32(state), (u32 *)ptr);
402 ptr += sizeof(u32);
403 bytes -= sizeof(u32);
404 }
405
406 if (bytes > 0) {
407 u32 rem = siprand_u32(state);
408
409 do {
410 *ptr++ = (u8)rem;
411 rem >>= BITS_PER_BYTE;
412 } while (--bytes > 0);
413 }
414 put_cpu_ptr(&net_rand_state);
415 }
416 EXPORT_SYMBOL(prandom_bytes);
417
418 /**
419 * prandom_seed - add entropy to pseudo random number generator
420 * @entropy: entropy value
421 *
422 * Add some additional seed material to the prandom pool.
423 * The "entropy" is actually our IP address (the only caller is
424 * the network code), not for unpredictability, but to ensure that
425 * different machines are initialized differently.
426 */
prandom_seed(u32 entropy)427 void prandom_seed(u32 entropy)
428 {
429 int i;
430
431 add_device_randomness(&entropy, sizeof(entropy));
432
433 for_each_possible_cpu(i) {
434 struct siprand_state *state = per_cpu_ptr(&net_rand_state, i);
435 unsigned long v0 = state->v0, v1 = state->v1;
436 unsigned long v2 = state->v2, v3 = state->v3;
437
438 do {
439 v3 ^= entropy;
440 PRND_SIPROUND(v0, v1, v2, v3);
441 PRND_SIPROUND(v0, v1, v2, v3);
442 v0 ^= entropy;
443 } while (unlikely(!v0 || !v1 || !v2 || !v3));
444
445 WRITE_ONCE(state->v0, v0);
446 WRITE_ONCE(state->v1, v1);
447 WRITE_ONCE(state->v2, v2);
448 WRITE_ONCE(state->v3, v3);
449 }
450 }
451 EXPORT_SYMBOL(prandom_seed);
452
453 /*
454 * Generate some initially weak seeding values to allow
455 * the prandom_u32() engine to be started.
456 */
prandom_init_early(void)457 static int __init prandom_init_early(void)
458 {
459 int i;
460 unsigned long v0, v1, v2, v3;
461
462 if (!arch_get_random_long(&v0))
463 v0 = jiffies;
464 if (!arch_get_random_long(&v1))
465 v1 = random_get_entropy();
466 v2 = v0 ^ PRND_K0;
467 v3 = v1 ^ PRND_K1;
468
469 for_each_possible_cpu(i) {
470 struct siprand_state *state;
471
472 v3 ^= i;
473 PRND_SIPROUND(v0, v1, v2, v3);
474 PRND_SIPROUND(v0, v1, v2, v3);
475 v0 ^= i;
476
477 state = per_cpu_ptr(&net_rand_state, i);
478 state->v0 = v0; state->v1 = v1;
479 state->v2 = v2; state->v3 = v3;
480 }
481
482 return 0;
483 }
484 core_initcall(prandom_init_early);
485
486
487 /* Stronger reseeding when available, and periodically thereafter. */
488 static void prandom_reseed(struct timer_list *unused);
489
490 static DEFINE_TIMER(seed_timer, prandom_reseed);
491
prandom_reseed(struct timer_list * unused)492 static void prandom_reseed(struct timer_list *unused)
493 {
494 unsigned long expires;
495 int i;
496
497 /*
498 * Reinitialize each CPU's PRNG with 128 bits of key.
499 * No locking on the CPUs, but then somewhat random results are,
500 * well, expected.
501 */
502 for_each_possible_cpu(i) {
503 struct siprand_state *state;
504 unsigned long v0 = get_random_long(), v2 = v0 ^ PRND_K0;
505 unsigned long v1 = get_random_long(), v3 = v1 ^ PRND_K1;
506 #if BITS_PER_LONG == 32
507 int j;
508
509 /*
510 * On 32-bit machines, hash in two extra words to
511 * approximate 128-bit key length. Not that the hash
512 * has that much security, but this prevents a trivial
513 * 64-bit brute force.
514 */
515 for (j = 0; j < 2; j++) {
516 unsigned long m = get_random_long();
517
518 v3 ^= m;
519 PRND_SIPROUND(v0, v1, v2, v3);
520 PRND_SIPROUND(v0, v1, v2, v3);
521 v0 ^= m;
522 }
523 #endif
524 /*
525 * Probably impossible in practice, but there is a
526 * theoretical risk that a race between this reseeding
527 * and the target CPU writing its state back could
528 * create the all-zero SipHash fixed point.
529 *
530 * To ensure that never happens, ensure the state
531 * we write contains no zero words.
532 */
533 state = per_cpu_ptr(&net_rand_state, i);
534 WRITE_ONCE(state->v0, v0 ? v0 : -1ul);
535 WRITE_ONCE(state->v1, v1 ? v1 : -1ul);
536 WRITE_ONCE(state->v2, v2 ? v2 : -1ul);
537 WRITE_ONCE(state->v3, v3 ? v3 : -1ul);
538 }
539
540 /* reseed every ~60 seconds, in [40 .. 80) interval with slack */
541 expires = round_jiffies(jiffies + 40 * HZ + prandom_u32_max(40 * HZ));
542 mod_timer(&seed_timer, expires);
543 }
544
545 /*
546 * The random ready callback can be called from almost any interrupt.
547 * To avoid worrying about whether it's safe to delay that interrupt
548 * long enough to seed all CPUs, just schedule an immediate timer event.
549 */
prandom_timer_start(struct notifier_block * nb,unsigned long action,void * data)550 static int prandom_timer_start(struct notifier_block *nb,
551 unsigned long action, void *data)
552 {
553 mod_timer(&seed_timer, jiffies);
554 return 0;
555 }
556
557 /*
558 * Start periodic full reseeding as soon as strong
559 * random numbers are available.
560 */
prandom_init_late(void)561 static int __init prandom_init_late(void)
562 {
563 static struct notifier_block random_ready = {
564 .notifier_call = prandom_timer_start
565 };
566 int ret = register_random_ready_notifier(&random_ready);
567
568 if (ret == -EALREADY) {
569 prandom_timer_start(&random_ready, 0, NULL);
570 ret = 0;
571 }
572 return ret;
573 }
574 late_initcall(prandom_init_late);
575