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Linux/lib/random32.c

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  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  *      @entropy: entropy value
175  *
176  *      Add some additional entropy 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(struct timer_list *unused);
217 
218 static DEFINE_TIMER(seed_timer, __prandom_timer);
219 
220 static void __prandom_timer(struct timer_list *unused)
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
466 

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