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Linux/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 #include <asm/unaligned.h>
 41 
 42 #ifdef CONFIG_RANDOM32_SELFTEST
 43 static void __init prandom_state_selftest(void);
 44 #else
 45 static inline void prandom_state_selftest(void)
 46 {
 47 }
 48 #endif
 49 
 50 static DEFINE_PER_CPU(struct rnd_state, net_rand_state) __latent_entropy;
 51 
 52 /**
 53  *      prandom_u32_state - seeded pseudo-random number generator.
 54  *      @state: pointer to state structure holding seeded state.
 55  *
 56  *      This is used for pseudo-randomness with no outside seeding.
 57  *      For more random results, use prandom_u32().
 58  */
 59 u32 prandom_u32_state(struct rnd_state *state)
 60 {
 61 #define TAUSWORTHE(s, a, b, c, d) ((s & c) << d) ^ (((s << a) ^ s) >> b)
 62         state->s1 = TAUSWORTHE(state->s1,  6U, 13U, 4294967294U, 18U);
 63         state->s2 = TAUSWORTHE(state->s2,  2U, 27U, 4294967288U,  2U);
 64         state->s3 = TAUSWORTHE(state->s3, 13U, 21U, 4294967280U,  7U);
 65         state->s4 = TAUSWORTHE(state->s4,  3U, 12U, 4294967168U, 13U);
 66 
 67         return (state->s1 ^ state->s2 ^ state->s3 ^ state->s4);
 68 }
 69 EXPORT_SYMBOL(prandom_u32_state);
 70 
 71 /**
 72  *      prandom_u32 - pseudo random number generator
 73  *
 74  *      A 32 bit pseudo-random number is generated using a fast
 75  *      algorithm suitable for simulation. This algorithm is NOT
 76  *      considered safe for cryptographic use.
 77  */
 78 u32 prandom_u32(void)
 79 {
 80         struct rnd_state *state = &get_cpu_var(net_rand_state);
 81         u32 res;
 82 
 83         res = prandom_u32_state(state);
 84         put_cpu_var(net_rand_state);
 85 
 86         return res;
 87 }
 88 EXPORT_SYMBOL(prandom_u32);
 89 
 90 /**
 91  *      prandom_bytes_state - get the requested number of pseudo-random bytes
 92  *
 93  *      @state: pointer to state structure holding seeded state.
 94  *      @buf: where to copy the pseudo-random bytes to
 95  *      @bytes: the requested number of bytes
 96  *
 97  *      This is used for pseudo-randomness with no outside seeding.
 98  *      For more random results, use prandom_bytes().
 99  */
100 void prandom_bytes_state(struct rnd_state *state, void *buf, size_t bytes)
101 {
102         u8 *ptr = buf;
103 
104         while (bytes >= sizeof(u32)) {
105                 put_unaligned(prandom_u32_state(state), (u32 *) ptr);
106                 ptr += sizeof(u32);
107                 bytes -= sizeof(u32);
108         }
109 
110         if (bytes > 0) {
111                 u32 rem = prandom_u32_state(state);
112                 do {
113                         *ptr++ = (u8) rem;
114                         bytes--;
115                         rem >>= BITS_PER_BYTE;
116                 } while (bytes > 0);
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, size_t 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(net_rand_state);
132 }
133 EXPORT_SYMBOL(prandom_bytes);
134 
135 static void prandom_warmup(struct rnd_state *state)
136 {
137         /* Calling RNG ten times to satisfy 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 u32 __extract_hwseed(void)
151 {
152         unsigned int val = 0;
153 
154         (void)(arch_get_random_seed_int(&val) ||
155                arch_get_random_int(&val));
156 
157         return val;
158 }
159 
160 static void prandom_seed_early(struct rnd_state *state, u32 seed,
161                                bool mix_with_hwseed)
162 {
163 #define LCG(x)   ((x) * 69069U) /* super-duper LCG */
164 #define HWSEED() (mix_with_hwseed ? __extract_hwseed() : 0)
165         state->s1 = __seed(HWSEED() ^ LCG(seed),        2U);
166         state->s2 = __seed(HWSEED() ^ LCG(state->s1),   8U);
167         state->s3 = __seed(HWSEED() ^ LCG(state->s2),  16U);
168         state->s4 = __seed(HWSEED() ^ LCG(state->s3), 128U);
169 }
170 
171 /**
172  *      prandom_seed - add entropy to pseudo random number generator
173  *      @seed: seed value
174  *
175  *      Add some additional seeding to the prandom pool.
176  */
177 void prandom_seed(u32 entropy)
178 {
179         int i;
180         /*
181          * No locking on the CPUs, but then somewhat random results are, well,
182          * expected.
183          */
184         for_each_possible_cpu(i) {
185                 struct rnd_state *state = &per_cpu(net_rand_state, i);
186 
187                 state->s1 = __seed(state->s1 ^ entropy, 2U);
188                 prandom_warmup(state);
189         }
190 }
191 EXPORT_SYMBOL(prandom_seed);
192 
193 /*
194  *      Generate some initially weak seeding values to allow
195  *      to start the prandom_u32() engine.
196  */
197 static int __init prandom_init(void)
198 {
199         int i;
200 
201         prandom_state_selftest();
202 
203         for_each_possible_cpu(i) {
204                 struct rnd_state *state = &per_cpu(net_rand_state, i);
205                 u32 weak_seed = (i + jiffies) ^ random_get_entropy();
206 
207                 prandom_seed_early(state, weak_seed, true);
208                 prandom_warmup(state);
209         }
210 
211         return 0;
212 }
213 core_initcall(prandom_init);
214 
215 static void __prandom_timer(unsigned long dontcare);
216 
217 static DEFINE_TIMER(seed_timer, __prandom_timer, 0, 0);
218 
219 static void __prandom_timer(unsigned long dontcare)
220 {
221         u32 entropy;
222         unsigned long expires;
223 
224         get_random_bytes(&entropy, sizeof(entropy));
225         prandom_seed(entropy);
226 
227         /* reseed every ~60 seconds, in [40 .. 80) interval with slack */
228         expires = 40 + prandom_u32_max(40);
229         seed_timer.expires = jiffies + msecs_to_jiffies(expires * MSEC_PER_SEC);
230 
231         add_timer(&seed_timer);
232 }
233 
234 static void __init __prandom_start_seed_timer(void)
235 {
236         seed_timer.expires = jiffies + msecs_to_jiffies(40 * MSEC_PER_SEC);
237         add_timer(&seed_timer);
238 }
239 
240 void prandom_seed_full_state(struct rnd_state __percpu *pcpu_state)
241 {
242         int i;
243 
244         for_each_possible_cpu(i) {
245                 struct rnd_state *state = per_cpu_ptr(pcpu_state, i);
246                 u32 seeds[4];
247 
248                 get_random_bytes(&seeds, sizeof(seeds));
249                 state->s1 = __seed(seeds[0],   2U);
250                 state->s2 = __seed(seeds[1],   8U);
251                 state->s3 = __seed(seeds[2],  16U);
252                 state->s4 = __seed(seeds[3], 128U);
253 
254                 prandom_warmup(state);
255         }
256 }
257 EXPORT_SYMBOL(prandom_seed_full_state);
258 
259 /*
260  *      Generate better values after random number generator
261  *      is fully initialized.
262  */
263 static void __prandom_reseed(bool late)
264 {
265         unsigned long flags;
266         static bool latch = false;
267         static DEFINE_SPINLOCK(lock);
268 
269         /* Asking for random bytes might result in bytes getting
270          * moved into the nonblocking pool and thus marking it
271          * as initialized. In this case we would double back into
272          * this function and attempt to do a late reseed.
273          * Ignore the pointless attempt to reseed again if we're
274          * already waiting for bytes when the nonblocking pool
275          * got initialized.
276          */
277 
278         /* only allow initial seeding (late == false) once */
279         if (!spin_trylock_irqsave(&lock, flags))
280                 return;
281 
282         if (latch && !late)
283                 goto out;
284 
285         latch = true;
286         prandom_seed_full_state(&net_rand_state);
287 out:
288         spin_unlock_irqrestore(&lock, flags);
289 }
290 
291 void prandom_reseed_late(void)
292 {
293         __prandom_reseed(true);
294 }
295 
296 static int __init prandom_reseed(void)
297 {
298         __prandom_reseed(false);
299         __prandom_start_seed_timer();
300         return 0;
301 }
302 late_initcall(prandom_reseed);
303 
304 #ifdef CONFIG_RANDOM32_SELFTEST
305 static struct prandom_test1 {
306         u32 seed;
307         u32 result;
308 } test1[] = {
309         { 1U, 3484351685U },
310         { 2U, 2623130059U },
311         { 3U, 3125133893U },
312         { 4U,  984847254U },
313 };
314 
315 static struct prandom_test2 {
316         u32 seed;
317         u32 iteration;
318         u32 result;
319 } test2[] = {
320         /* Test cases against taus113 from GSL library. */
321         {  931557656U, 959U, 2975593782U },
322         { 1339693295U, 876U, 3887776532U },
323         { 1545556285U, 961U, 1615538833U },
324         {  601730776U, 723U, 1776162651U },
325         { 1027516047U, 687U,  511983079U },
326         {  416526298U, 700U,  916156552U },
327         { 1395522032U, 652U, 2222063676U },
328         {  366221443U, 617U, 2992857763U },
329         { 1539836965U, 714U, 3783265725U },
330         {  556206671U, 994U,  799626459U },
331         {  684907218U, 799U,  367789491U },
332         { 2121230701U, 931U, 2115467001U },
333         { 1668516451U, 644U, 3620590685U },
334         {  768046066U, 883U, 2034077390U },
335         { 1989159136U, 833U, 1195767305U },
336         {  536585145U, 996U, 3577259204U },
337         { 1008129373U, 642U, 1478080776U },
338         { 1740775604U, 939U, 1264980372U },
339         { 1967883163U, 508U,   10734624U },
340         { 1923019697U, 730U, 3821419629U },
341         {  442079932U, 560U, 3440032343U },
342         { 1961302714U, 845U,  841962572U },
343         { 2030205964U, 962U, 1325144227U },
344         { 1160407529U, 507U,  240940858U },
345         {  635482502U, 779U, 4200489746U },
346         { 1252788931U, 699U,  867195434U },
347         { 1961817131U, 719U,  668237657U },
348         { 1071468216U, 983U,  917876630U },
349         { 1281848367U, 932U, 1003100039U },
350         {  582537119U, 780U, 1127273778U },
351         { 1973672777U, 853U, 1071368872U },
352         { 1896756996U, 762U, 1127851055U },
353         {  847917054U, 500U, 1717499075U },
354         { 1240520510U, 951U, 2849576657U },
355         { 1685071682U, 567U, 1961810396U },
356         { 1516232129U, 557U,    3173877U },
357         { 1208118903U, 612U, 1613145022U },
358         { 1817269927U, 693U, 4279122573U },
359         { 1510091701U, 717U,  638191229U },
360         {  365916850U, 807U,  600424314U },
361         {  399324359U, 702U, 1803598116U },
362         { 1318480274U, 779U, 2074237022U },
363         {  697758115U, 840U, 1483639402U },
364         { 1696507773U, 840U,  577415447U },
365         { 2081979121U, 981U, 3041486449U },
366         {  955646687U, 742U, 3846494357U },
367         { 1250683506U, 749U,  836419859U },
368         {  595003102U, 534U,  366794109U },
369         {   47485338U, 558U, 3521120834U },
370         {  619433479U, 610U, 3991783875U },
371         {  704096520U, 518U, 4139493852U },
372         { 1712224984U, 606U, 2393312003U },
373         { 1318233152U, 922U, 3880361134U },
374         {  855572992U, 761U, 1472974787U },
375         {   64721421U, 703U,  683860550U },
376         {  678931758U, 840U,  380616043U },
377         {  692711973U, 778U, 1382361947U },
378         {  677703619U, 530U, 2826914161U },
379         {   92393223U, 586U, 1522128471U },
380         { 1222592920U, 743U, 3466726667U },
381         {  358288986U, 695U, 1091956998U },
382         { 1935056945U, 958U,  514864477U },
383         {  735675993U, 990U, 1294239989U },
384         { 1560089402U, 897U, 2238551287U },
385         {   70616361U, 829U,   22483098U },
386         {  368234700U, 731U, 2913875084U },
387         {   20221190U, 879U, 1564152970U },
388         {  539444654U, 682U, 1835141259U },
389         { 1314987297U, 840U, 1801114136U },
390         { 2019295544U, 645U, 3286438930U },
391         {  469023838U, 716U, 1637918202U },
392         { 1843754496U, 653U, 2562092152U },
393         {  400672036U, 809U, 4264212785U },
394         {  404722249U, 965U, 2704116999U },
395         {  600702209U, 758U,  584979986U },
396         {  519953954U, 667U, 2574436237U },
397         { 1658071126U, 694U, 2214569490U },
398         {  420480037U, 749U, 3430010866U },
399         {  690103647U, 969U, 3700758083U },
400         { 1029424799U, 937U, 3787746841U },
401         { 2012608669U, 506U, 3362628973U },
402         { 1535432887U, 998U,   42610943U },
403         { 1330635533U, 857U, 3040806504U },
404         { 1223800550U, 539U, 3954229517U },
405         { 1322411537U, 680U, 3223250324U },
406         { 1877847898U, 945U, 2915147143U },
407         { 1646356099U, 874U,  965988280U },
408         {  805687536U, 744U, 4032277920U },
409         { 1948093210U, 633U, 1346597684U },
410         {  392609744U, 783U, 1636083295U },
411         {  690241304U, 770U, 1201031298U },
412         { 1360302965U, 696U, 1665394461U },
413         { 1220090946U, 780U, 1316922812U },
414         {  447092251U, 500U, 3438743375U },
415         { 1613868791U, 592U,  828546883U },
416         {  523430951U, 548U, 2552392304U },
417         {  726692899U, 810U, 1656872867U },
418         { 1364340021U, 836U, 3710513486U },
419         { 1986257729U, 931U,  935013962U },
420         {  407983964U, 921U,  728767059U },
421 };
422 
423 static void __init prandom_state_selftest(void)
424 {
425         int i, j, errors = 0, runs = 0;
426         bool error = false;
427 
428         for (i = 0; i < ARRAY_SIZE(test1); i++) {
429                 struct rnd_state state;
430 
431                 prandom_seed_early(&state, test1[i].seed, false);
432                 prandom_warmup(&state);
433 
434                 if (test1[i].result != prandom_u32_state(&state))
435                         error = true;
436         }
437 
438         if (error)
439                 pr_warn("prandom: seed boundary self test failed\n");
440         else
441                 pr_info("prandom: seed boundary self test passed\n");
442 
443         for (i = 0; i < ARRAY_SIZE(test2); i++) {
444                 struct rnd_state state;
445 
446                 prandom_seed_early(&state, test2[i].seed, false);
447                 prandom_warmup(&state);
448 
449                 for (j = 0; j < test2[i].iteration - 1; j++)
450                         prandom_u32_state(&state);
451 
452                 if (test2[i].result != prandom_u32_state(&state))
453                         errors++;
454 
455                 runs++;
456                 cond_resched();
457         }
458 
459         if (errors)
460                 pr_warn("prandom: %d/%d self tests failed\n", errors, runs);
461         else
462                 pr_info("prandom: %d self tests passed\n", runs);
463 }
464 #endif
465 

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