Root/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
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
44static void __init prandom_state_selftest(void);
45#endif
46
47static 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 */
56u32 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}
67EXPORT_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 */
76u32 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}
84EXPORT_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 */
96void 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}
119EXPORT_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 */
126void 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}
133EXPORT_SYMBOL(prandom_bytes);
134
135static 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
150static 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 */
173void 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}
187EXPORT_SYMBOL(prandom_seed);
188
189/*
190 * Generate some initially weak seeding values to allow
191 * to start the prandom_u32() engine.
192 */
193static 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}
209core_initcall(prandom_init);
210
211static void __prandom_timer(unsigned long dontcare);
212static DEFINE_TIMER(seed_timer, __prandom_timer, 0, 0);
213
214static 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
229static 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 */
240static 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    /* only allow initial seeding (late == false) once */
248    spin_lock_irqsave(&lock, flags);
249    if (latch && !late)
250        goto out;
251    latch = true;
252
253    for_each_possible_cpu(i) {
254        struct rnd_state *state = &per_cpu(net_rand_state,i);
255        u32 seeds[4];
256
257        get_random_bytes(&seeds, sizeof(seeds));
258        state->s1 = __seed(seeds[0], 2U);
259        state->s2 = __seed(seeds[1], 8U);
260        state->s3 = __seed(seeds[2], 16U);
261        state->s4 = __seed(seeds[3], 128U);
262
263        prandom_warmup(state);
264    }
265out:
266    spin_unlock_irqrestore(&lock, flags);
267}
268
269void prandom_reseed_late(void)
270{
271    __prandom_reseed(true);
272}
273
274static int __init prandom_reseed(void)
275{
276    __prandom_reseed(false);
277    __prandom_start_seed_timer();
278    return 0;
279}
280late_initcall(prandom_reseed);
281
282#ifdef CONFIG_RANDOM32_SELFTEST
283static struct prandom_test1 {
284    u32 seed;
285    u32 result;
286} test1[] = {
287    { 1U, 3484351685U },
288    { 2U, 2623130059U },
289    { 3U, 3125133893U },
290    { 4U, 984847254U },
291};
292
293static struct prandom_test2 {
294    u32 seed;
295    u32 iteration;
296    u32 result;
297} test2[] = {
298    /* Test cases against taus113 from GSL library. */
299    { 931557656U, 959U, 2975593782U },
300    { 1339693295U, 876U, 3887776532U },
301    { 1545556285U, 961U, 1615538833U },
302    { 601730776U, 723U, 1776162651U },
303    { 1027516047U, 687U, 511983079U },
304    { 416526298U, 700U, 916156552U },
305    { 1395522032U, 652U, 2222063676U },
306    { 366221443U, 617U, 2992857763U },
307    { 1539836965U, 714U, 3783265725U },
308    { 556206671U, 994U, 799626459U },
309    { 684907218U, 799U, 367789491U },
310    { 2121230701U, 931U, 2115467001U },
311    { 1668516451U, 644U, 3620590685U },
312    { 768046066U, 883U, 2034077390U },
313    { 1989159136U, 833U, 1195767305U },
314    { 536585145U, 996U, 3577259204U },
315    { 1008129373U, 642U, 1478080776U },
316    { 1740775604U, 939U, 1264980372U },
317    { 1967883163U, 508U, 10734624U },
318    { 1923019697U, 730U, 3821419629U },
319    { 442079932U, 560U, 3440032343U },
320    { 1961302714U, 845U, 841962572U },
321    { 2030205964U, 962U, 1325144227U },
322    { 1160407529U, 507U, 240940858U },
323    { 635482502U, 779U, 4200489746U },
324    { 1252788931U, 699U, 867195434U },
325    { 1961817131U, 719U, 668237657U },
326    { 1071468216U, 983U, 917876630U },
327    { 1281848367U, 932U, 1003100039U },
328    { 582537119U, 780U, 1127273778U },
329    { 1973672777U, 853U, 1071368872U },
330    { 1896756996U, 762U, 1127851055U },
331    { 847917054U, 500U, 1717499075U },
332    { 1240520510U, 951U, 2849576657U },
333    { 1685071682U, 567U, 1961810396U },
334    { 1516232129U, 557U, 3173877U },
335    { 1208118903U, 612U, 1613145022U },
336    { 1817269927U, 693U, 4279122573U },
337    { 1510091701U, 717U, 638191229U },
338    { 365916850U, 807U, 600424314U },
339    { 399324359U, 702U, 1803598116U },
340    { 1318480274U, 779U, 2074237022U },
341    { 697758115U, 840U, 1483639402U },
342    { 1696507773U, 840U, 577415447U },
343    { 2081979121U, 981U, 3041486449U },
344    { 955646687U, 742U, 3846494357U },
345    { 1250683506U, 749U, 836419859U },
346    { 595003102U, 534U, 366794109U },
347    { 47485338U, 558U, 3521120834U },
348    { 619433479U, 610U, 3991783875U },
349    { 704096520U, 518U, 4139493852U },
350    { 1712224984U, 606U, 2393312003U },
351    { 1318233152U, 922U, 3880361134U },
352    { 855572992U, 761U, 1472974787U },
353    { 64721421U, 703U, 683860550U },
354    { 678931758U, 840U, 380616043U },
355    { 692711973U, 778U, 1382361947U },
356    { 677703619U, 530U, 2826914161U },
357    { 92393223U, 586U, 1522128471U },
358    { 1222592920U, 743U, 3466726667U },
359    { 358288986U, 695U, 1091956998U },
360    { 1935056945U, 958U, 514864477U },
361    { 735675993U, 990U, 1294239989U },
362    { 1560089402U, 897U, 2238551287U },
363    { 70616361U, 829U, 22483098U },
364    { 368234700U, 731U, 2913875084U },
365    { 20221190U, 879U, 1564152970U },
366    { 539444654U, 682U, 1835141259U },
367    { 1314987297U, 840U, 1801114136U },
368    { 2019295544U, 645U, 3286438930U },
369    { 469023838U, 716U, 1637918202U },
370    { 1843754496U, 653U, 2562092152U },
371    { 400672036U, 809U, 4264212785U },
372    { 404722249U, 965U, 2704116999U },
373    { 600702209U, 758U, 584979986U },
374    { 519953954U, 667U, 2574436237U },
375    { 1658071126U, 694U, 2214569490U },
376    { 420480037U, 749U, 3430010866U },
377    { 690103647U, 969U, 3700758083U },
378    { 1029424799U, 937U, 3787746841U },
379    { 2012608669U, 506U, 3362628973U },
380    { 1535432887U, 998U, 42610943U },
381    { 1330635533U, 857U, 3040806504U },
382    { 1223800550U, 539U, 3954229517U },
383    { 1322411537U, 680U, 3223250324U },
384    { 1877847898U, 945U, 2915147143U },
385    { 1646356099U, 874U, 965988280U },
386    { 805687536U, 744U, 4032277920U },
387    { 1948093210U, 633U, 1346597684U },
388    { 392609744U, 783U, 1636083295U },
389    { 690241304U, 770U, 1201031298U },
390    { 1360302965U, 696U, 1665394461U },
391    { 1220090946U, 780U, 1316922812U },
392    { 447092251U, 500U, 3438743375U },
393    { 1613868791U, 592U, 828546883U },
394    { 523430951U, 548U, 2552392304U },
395    { 726692899U, 810U, 1656872867U },
396    { 1364340021U, 836U, 3710513486U },
397    { 1986257729U, 931U, 935013962U },
398    { 407983964U, 921U, 728767059U },
399};
400
401static void __init prandom_state_selftest(void)
402{
403    int i, j, errors = 0, runs = 0;
404    bool error = false;
405
406    for (i = 0; i < ARRAY_SIZE(test1); i++) {
407        struct rnd_state state;
408
409        prandom_seed_very_weak(&state, test1[i].seed);
410        prandom_warmup(&state);
411
412        if (test1[i].result != prandom_u32_state(&state))
413            error = true;
414    }
415
416    if (error)
417        pr_warn("prandom: seed boundary self test failed\n");
418    else
419        pr_info("prandom: seed boundary self test passed\n");
420
421    for (i = 0; i < ARRAY_SIZE(test2); i++) {
422        struct rnd_state state;
423
424        prandom_seed_very_weak(&state, test2[i].seed);
425        prandom_warmup(&state);
426
427        for (j = 0; j < test2[i].iteration - 1; j++)
428            prandom_u32_state(&state);
429
430        if (test2[i].result != prandom_u32_state(&state))
431            errors++;
432
433        runs++;
434        cond_resched();
435    }
436
437    if (errors)
438        pr_warn("prandom: %d/%d self tests failed\n", errors, runs);
439    else
440        pr_info("prandom: %d self tests passed\n", runs);
441}
442#endif
443

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