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Linux/lib/random32.c

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  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
 22    Equidistributed Combined LFSR Generators", Mathematics of
 23    Computation, 68, 225 (1999), 261--269:
 24    http://www.iro.umontreal.ca/~lecuyer/myftp/papers/tausme2.ps
 25 
 26         ... the k_j most significant bits of z_j must be non-
 27         zero, for each j. (Note: this restriction also applies to the
 28         computer code given in [4], but was mistakenly not mentioned in
 29         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 
 36 #include <linux/types.h>
 37 #include <linux/percpu.h>
 38 #include <linux/export.h>
 39 #include <linux/jiffies.h>
 40 #include <linux/random.h>
 41 #include <linux/sched.h>
 42 
 43 #ifdef CONFIG_RANDOM32_SELFTEST
 44 static void __init prandom_state_selftest(void);
 45 #endif
 46 
 47 static DEFINE_PER_CPU(struct rnd_state, net_rand_state);
 48 
 49 /**
 50  *      prandom_u32_state - seeded pseudo-random number generator.
 51  *      @state: pointer to state structure holding seeded state.
 52  *
 53  *      This is used for pseudo-randomness with no outside seeding.
 54  *      For more random results, use prandom_u32().
 55  */
 56 u32 prandom_u32_state(struct rnd_state *state)
 57 {
 58 #define TAUSWORTHE(s,a,b,c,d) ((s&c)<<d) ^ (((s <<a) ^ s)>>b)
 59 
 60         state->s1 = TAUSWORTHE(state->s1,  6U, 13U, 4294967294U, 18U);
 61         state->s2 = TAUSWORTHE(state->s2,  2U, 27U, 4294967288U,  2U);
 62         state->s3 = TAUSWORTHE(state->s3, 13U, 21U, 4294967280U,  7U);
 63         state->s4 = TAUSWORTHE(state->s4,  3U, 12U, 4294967168U, 13U);
 64 
 65         return (state->s1 ^ state->s2 ^ state->s3 ^ state->s4);
 66 }
 67 EXPORT_SYMBOL(prandom_u32_state);
 68 
 69 /**
 70  *      prandom_u32 - pseudo random number generator
 71  *
 72  *      A 32 bit pseudo-random number is generated using a fast
 73  *      algorithm suitable for simulation. This algorithm is NOT
 74  *      considered safe for cryptographic use.
 75  */
 76 u32 prandom_u32(void)
 77 {
 78         unsigned long r;
 79         struct rnd_state *state = &get_cpu_var(net_rand_state);
 80         r = prandom_u32_state(state);
 81         put_cpu_var(state);
 82         return r;
 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         return 0;
208 }
209 core_initcall(prandom_init);
210 
211 static void __prandom_timer(unsigned long dontcare);
212 static DEFINE_TIMER(seed_timer, __prandom_timer, 0, 0);
213 
214 static void __prandom_timer(unsigned long dontcare)
215 {
216         u32 entropy;
217         unsigned long expires;
218 
219         get_random_bytes(&entropy, sizeof(entropy));
220         prandom_seed(entropy);
221 
222         /* reseed every ~60 seconds, in [40 .. 80) interval with slack */
223         expires = 40 + (prandom_u32() % 40);
224         seed_timer.expires = jiffies + msecs_to_jiffies(expires * MSEC_PER_SEC);
225 
226         add_timer(&seed_timer);
227 }
228 
229 static void __init __prandom_start_seed_timer(void)
230 {
231         set_timer_slack(&seed_timer, HZ);
232         seed_timer.expires = jiffies + msecs_to_jiffies(40 * MSEC_PER_SEC);
233         add_timer(&seed_timer);
234 }
235 
236 /*
237  *      Generate better values after random number generator
238  *      is fully initialized.
239  */
240 static void __prandom_reseed(bool late)
241 {
242         int i;
243         unsigned long flags;
244         static bool latch = false;
245         static DEFINE_SPINLOCK(lock);
246 
247         /* Asking for random bytes might result in bytes getting
248          * moved into the nonblocking pool and thus marking it
249          * as initialized. In this case we would double back into
250          * this function and attempt to do a late reseed.
251          * Ignore the pointless attempt to reseed again if we're
252          * already waiting for bytes when the nonblocking pool
253          * got initialized.
254          */
255 
256         /* only allow initial seeding (late == false) once */
257         if (!spin_trylock_irqsave(&lock, flags))
258                 return;
259 
260         if (latch && !late)
261                 goto out;
262         latch = true;
263 
264         for_each_possible_cpu(i) {
265                 struct rnd_state *state = &per_cpu(net_rand_state,i);
266                 u32 seeds[4];
267 
268                 get_random_bytes(&seeds, sizeof(seeds));
269                 state->s1 = __seed(seeds[0],   2U);
270                 state->s2 = __seed(seeds[1],   8U);
271                 state->s3 = __seed(seeds[2],  16U);
272                 state->s4 = __seed(seeds[3], 128U);
273 
274                 prandom_warmup(state);
275         }
276 out:
277         spin_unlock_irqrestore(&lock, flags);
278 }
279 
280 void prandom_reseed_late(void)
281 {
282         __prandom_reseed(true);
283 }
284 
285 static int __init prandom_reseed(void)
286 {
287         __prandom_reseed(false);
288         __prandom_start_seed_timer();
289         return 0;
290 }
291 late_initcall(prandom_reseed);
292 
293 #ifdef CONFIG_RANDOM32_SELFTEST
294 static struct prandom_test1 {
295         u32 seed;
296         u32 result;
297 } test1[] = {
298         { 1U, 3484351685U },
299         { 2U, 2623130059U },
300         { 3U, 3125133893U },
301         { 4U,  984847254U },
302 };
303 
304 static struct prandom_test2 {
305         u32 seed;
306         u32 iteration;
307         u32 result;
308 } test2[] = {
309         /* Test cases against taus113 from GSL library. */
310         {  931557656U, 959U, 2975593782U },
311         { 1339693295U, 876U, 3887776532U },
312         { 1545556285U, 961U, 1615538833U },
313         {  601730776U, 723U, 1776162651U },
314         { 1027516047U, 687U,  511983079U },
315         {  416526298U, 700U,  916156552U },
316         { 1395522032U, 652U, 2222063676U },
317         {  366221443U, 617U, 2992857763U },
318         { 1539836965U, 714U, 3783265725U },
319         {  556206671U, 994U,  799626459U },
320         {  684907218U, 799U,  367789491U },
321         { 2121230701U, 931U, 2115467001U },
322         { 1668516451U, 644U, 3620590685U },
323         {  768046066U, 883U, 2034077390U },
324         { 1989159136U, 833U, 1195767305U },
325         {  536585145U, 996U, 3577259204U },
326         { 1008129373U, 642U, 1478080776U },
327         { 1740775604U, 939U, 1264980372U },
328         { 1967883163U, 508U,   10734624U },
329         { 1923019697U, 730U, 3821419629U },
330         {  442079932U, 560U, 3440032343U },
331         { 1961302714U, 845U,  841962572U },
332         { 2030205964U, 962U, 1325144227U },
333         { 1160407529U, 507U,  240940858U },
334         {  635482502U, 779U, 4200489746U },
335         { 1252788931U, 699U,  867195434U },
336         { 1961817131U, 719U,  668237657U },
337         { 1071468216U, 983U,  917876630U },
338         { 1281848367U, 932U, 1003100039U },
339         {  582537119U, 780U, 1127273778U },
340         { 1973672777U, 853U, 1071368872U },
341         { 1896756996U, 762U, 1127851055U },
342         {  847917054U, 500U, 1717499075U },
343         { 1240520510U, 951U, 2849576657U },
344         { 1685071682U, 567U, 1961810396U },
345         { 1516232129U, 557U,    3173877U },
346         { 1208118903U, 612U, 1613145022U },
347         { 1817269927U, 693U, 4279122573U },
348         { 1510091701U, 717U,  638191229U },
349         {  365916850U, 807U,  600424314U },
350         {  399324359U, 702U, 1803598116U },
351         { 1318480274U, 779U, 2074237022U },
352         {  697758115U, 840U, 1483639402U },
353         { 1696507773U, 840U,  577415447U },
354         { 2081979121U, 981U, 3041486449U },
355         {  955646687U, 742U, 3846494357U },
356         { 1250683506U, 749U,  836419859U },
357         {  595003102U, 534U,  366794109U },
358         {   47485338U, 558U, 3521120834U },
359         {  619433479U, 610U, 3991783875U },
360         {  704096520U, 518U, 4139493852U },
361         { 1712224984U, 606U, 2393312003U },
362         { 1318233152U, 922U, 3880361134U },
363         {  855572992U, 761U, 1472974787U },
364         {   64721421U, 703U,  683860550U },
365         {  678931758U, 840U,  380616043U },
366         {  692711973U, 778U, 1382361947U },
367         {  677703619U, 530U, 2826914161U },
368         {   92393223U, 586U, 1522128471U },
369         { 1222592920U, 743U, 3466726667U },
370         {  358288986U, 695U, 1091956998U },
371         { 1935056945U, 958U,  514864477U },
372         {  735675993U, 990U, 1294239989U },
373         { 1560089402U, 897U, 2238551287U },
374         {   70616361U, 829U,   22483098U },
375         {  368234700U, 731U, 2913875084U },
376         {   20221190U, 879U, 1564152970U },
377         {  539444654U, 682U, 1835141259U },
378         { 1314987297U, 840U, 1801114136U },
379         { 2019295544U, 645U, 3286438930U },
380         {  469023838U, 716U, 1637918202U },
381         { 1843754496U, 653U, 2562092152U },
382         {  400672036U, 809U, 4264212785U },
383         {  404722249U, 965U, 2704116999U },
384         {  600702209U, 758U,  584979986U },
385         {  519953954U, 667U, 2574436237U },
386         { 1658071126U, 694U, 2214569490U },
387         {  420480037U, 749U, 3430010866U },
388         {  690103647U, 969U, 3700758083U },
389         { 1029424799U, 937U, 3787746841U },
390         { 2012608669U, 506U, 3362628973U },
391         { 1535432887U, 998U,   42610943U },
392         { 1330635533U, 857U, 3040806504U },
393         { 1223800550U, 539U, 3954229517U },
394         { 1322411537U, 680U, 3223250324U },
395         { 1877847898U, 945U, 2915147143U },
396         { 1646356099U, 874U,  965988280U },
397         {  805687536U, 744U, 4032277920U },
398         { 1948093210U, 633U, 1346597684U },
399         {  392609744U, 783U, 1636083295U },
400         {  690241304U, 770U, 1201031298U },
401         { 1360302965U, 696U, 1665394461U },
402         { 1220090946U, 780U, 1316922812U },
403         {  447092251U, 500U, 3438743375U },
404         { 1613868791U, 592U,  828546883U },
405         {  523430951U, 548U, 2552392304U },
406         {  726692899U, 810U, 1656872867U },
407         { 1364340021U, 836U, 3710513486U },
408         { 1986257729U, 931U,  935013962U },
409         {  407983964U, 921U,  728767059U },
410 };
411 
412 static void __init prandom_state_selftest(void)
413 {
414         int i, j, errors = 0, runs = 0;
415         bool error = false;
416 
417         for (i = 0; i < ARRAY_SIZE(test1); i++) {
418                 struct rnd_state state;
419 
420                 prandom_seed_very_weak(&state, test1[i].seed);
421                 prandom_warmup(&state);
422 
423                 if (test1[i].result != prandom_u32_state(&state))
424                         error = true;
425         }
426 
427         if (error)
428                 pr_warn("prandom: seed boundary self test failed\n");
429         else
430                 pr_info("prandom: seed boundary self test passed\n");
431 
432         for (i = 0; i < ARRAY_SIZE(test2); i++) {
433                 struct rnd_state state;
434 
435                 prandom_seed_very_weak(&state, test2[i].seed);
436                 prandom_warmup(&state);
437 
438                 for (j = 0; j < test2[i].iteration - 1; j++)
439                         prandom_u32_state(&state);
440 
441                 if (test2[i].result != prandom_u32_state(&state))
442                         errors++;
443 
444                 runs++;
445                 cond_resched();
446         }
447 
448         if (errors)
449                 pr_warn("prandom: %d/%d self tests failed\n", errors, runs);
450         else
451                 pr_info("prandom: %d self tests passed\n", runs);
452 }
453 #endif
454 

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