Commit | Line | Data |
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aaa248f6 SH |
1 | /* |
2 | This is a maximally equidistributed combined Tausworthe generator | |
3 | based on code from GNU Scientific Library 1.5 (30 Jun 2004) | |
4 | ||
a98814ce | 5 | lfsr113 version: |
aaa248f6 | 6 | |
a98814ce | 7 | x_n = (s1_n ^ s2_n ^ s3_n ^ s4_n) |
aaa248f6 | 8 | |
a98814ce DB |
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)) | |
aaa248f6 | 13 | |
a98814ce | 14 | The period of this generator is about 2^113 (see erratum paper). |
aaa248f6 | 15 | |
a98814ce DB |
16 | From: P. L'Ecuyer, "Maximally Equidistributed Combined Tausworthe |
17 | Generators", Mathematics of Computation, 65, 213 (1996), 203--213: | |
aaa248f6 SH |
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 | |
a98814ce | 32 | s1 > 1, s2 > 7, s3 > 15, s4 > 127. |
aaa248f6 SH |
33 | |
34 | */ | |
35 | ||
36 | #include <linux/types.h> | |
37 | #include <linux/percpu.h> | |
8bc3bcc9 | 38 | #include <linux/export.h> |
f6a57033 | 39 | #include <linux/jiffies.h> |
aaa248f6 SH |
40 | #include <linux/random.h> |
41 | ||
aaa248f6 SH |
42 | static DEFINE_PER_CPU(struct rnd_state, net_rand_state); |
43 | ||
5960164f | 44 | /** |
496f2f93 | 45 | * prandom_u32_state - seeded pseudo-random number generator. |
5960164f JE |
46 | * @state: pointer to state structure holding seeded state. |
47 | * | |
48 | * This is used for pseudo-randomness with no outside seeding. | |
496f2f93 | 49 | * For more random results, use prandom_u32(). |
5960164f | 50 | */ |
496f2f93 | 51 | u32 prandom_u32_state(struct rnd_state *state) |
aaa248f6 SH |
52 | { |
53 | #define TAUSWORTHE(s,a,b,c,d) ((s&c)<<d) ^ (((s <<a) ^ s)>>b) | |
54 | ||
a98814ce DB |
55 | state->s1 = TAUSWORTHE(state->s1, 6U, 13U, 4294967294U, 18U); |
56 | state->s2 = TAUSWORTHE(state->s2, 2U, 27U, 4294967288U, 2U); | |
57 | state->s3 = TAUSWORTHE(state->s3, 13U, 21U, 4294967280U, 7U); | |
58 | state->s4 = TAUSWORTHE(state->s4, 3U, 12U, 4294967168U, 13U); | |
aaa248f6 | 59 | |
a98814ce | 60 | return (state->s1 ^ state->s2 ^ state->s3 ^ state->s4); |
aaa248f6 | 61 | } |
496f2f93 | 62 | EXPORT_SYMBOL(prandom_u32_state); |
aaa248f6 SH |
63 | |
64 | /** | |
496f2f93 | 65 | * prandom_u32 - pseudo random number generator |
aaa248f6 SH |
66 | * |
67 | * A 32 bit pseudo-random number is generated using a fast | |
68 | * algorithm suitable for simulation. This algorithm is NOT | |
69 | * considered safe for cryptographic use. | |
70 | */ | |
496f2f93 | 71 | u32 prandom_u32(void) |
aaa248f6 SH |
72 | { |
73 | unsigned long r; | |
74 | struct rnd_state *state = &get_cpu_var(net_rand_state); | |
496f2f93 | 75 | r = prandom_u32_state(state); |
aaa248f6 SH |
76 | put_cpu_var(state); |
77 | return r; | |
78 | } | |
496f2f93 | 79 | EXPORT_SYMBOL(prandom_u32); |
aaa248f6 | 80 | |
6582c665 AM |
81 | /* |
82 | * prandom_bytes_state - get the requested number of pseudo-random bytes | |
83 | * | |
84 | * @state: pointer to state structure holding seeded state. | |
85 | * @buf: where to copy the pseudo-random bytes to | |
86 | * @bytes: the requested number of bytes | |
87 | * | |
88 | * This is used for pseudo-randomness with no outside seeding. | |
89 | * For more random results, use prandom_bytes(). | |
90 | */ | |
91 | void prandom_bytes_state(struct rnd_state *state, void *buf, int bytes) | |
92 | { | |
93 | unsigned char *p = buf; | |
94 | int i; | |
95 | ||
96 | for (i = 0; i < round_down(bytes, sizeof(u32)); i += sizeof(u32)) { | |
97 | u32 random = prandom_u32_state(state); | |
98 | int j; | |
99 | ||
100 | for (j = 0; j < sizeof(u32); j++) { | |
101 | p[i + j] = random; | |
102 | random >>= BITS_PER_BYTE; | |
103 | } | |
104 | } | |
105 | if (i < bytes) { | |
106 | u32 random = prandom_u32_state(state); | |
107 | ||
108 | for (; i < bytes; i++) { | |
109 | p[i] = random; | |
110 | random >>= BITS_PER_BYTE; | |
111 | } | |
112 | } | |
113 | } | |
114 | EXPORT_SYMBOL(prandom_bytes_state); | |
115 | ||
116 | /** | |
117 | * prandom_bytes - get the requested number of pseudo-random bytes | |
118 | * @buf: where to copy the pseudo-random bytes to | |
119 | * @bytes: the requested number of bytes | |
120 | */ | |
121 | void prandom_bytes(void *buf, int bytes) | |
122 | { | |
123 | struct rnd_state *state = &get_cpu_var(net_rand_state); | |
124 | ||
125 | prandom_bytes_state(state, buf, bytes); | |
126 | put_cpu_var(state); | |
127 | } | |
128 | EXPORT_SYMBOL(prandom_bytes); | |
129 | ||
a98814ce DB |
130 | static void prandom_warmup(struct rnd_state *state) |
131 | { | |
132 | /* Calling RNG ten times to satify recurrence condition */ | |
133 | prandom_u32_state(state); | |
134 | prandom_u32_state(state); | |
135 | prandom_u32_state(state); | |
136 | prandom_u32_state(state); | |
137 | prandom_u32_state(state); | |
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 | } | |
144 | ||
aaa248f6 | 145 | /** |
496f2f93 | 146 | * prandom_seed - add entropy to pseudo random number generator |
aaa248f6 SH |
147 | * @seed: seed value |
148 | * | |
496f2f93 | 149 | * Add some additional seeding to the prandom pool. |
aaa248f6 | 150 | */ |
496f2f93 | 151 | void prandom_seed(u32 entropy) |
aaa248f6 | 152 | { |
61407f80 AK |
153 | int i; |
154 | /* | |
155 | * No locking on the CPUs, but then somewhat random results are, well, | |
156 | * expected. | |
157 | */ | |
158 | for_each_possible_cpu (i) { | |
159 | struct rnd_state *state = &per_cpu(net_rand_state, i); | |
a98814ce DB |
160 | |
161 | state->s1 = __seed(state->s1 ^ entropy, 2U); | |
162 | prandom_warmup(state); | |
61407f80 | 163 | } |
aaa248f6 | 164 | } |
496f2f93 | 165 | EXPORT_SYMBOL(prandom_seed); |
aaa248f6 SH |
166 | |
167 | /* | |
168 | * Generate some initially weak seeding values to allow | |
496f2f93 | 169 | * to start the prandom_u32() engine. |
aaa248f6 | 170 | */ |
496f2f93 | 171 | static int __init prandom_init(void) |
aaa248f6 SH |
172 | { |
173 | int i; | |
174 | ||
175 | for_each_possible_cpu(i) { | |
176 | struct rnd_state *state = &per_cpu(net_rand_state,i); | |
697f8d03 | 177 | |
a98814ce DB |
178 | #define LCG(x) ((x) * 69069U) /* super-duper LCG */ |
179 | state->s1 = __seed(LCG((i + jiffies) ^ random_get_entropy()), 2U); | |
180 | state->s2 = __seed(LCG(state->s1), 8U); | |
181 | state->s3 = __seed(LCG(state->s2), 16U); | |
182 | state->s4 = __seed(LCG(state->s3), 128U); | |
183 | ||
184 | prandom_warmup(state); | |
aaa248f6 SH |
185 | } |
186 | return 0; | |
187 | } | |
496f2f93 | 188 | core_initcall(prandom_init); |
aaa248f6 | 189 | |
6d319202 HFS |
190 | static void __prandom_timer(unsigned long dontcare); |
191 | static DEFINE_TIMER(seed_timer, __prandom_timer, 0, 0); | |
192 | ||
193 | static void __prandom_timer(unsigned long dontcare) | |
194 | { | |
195 | u32 entropy; | |
196 | ||
197 | get_random_bytes(&entropy, sizeof(entropy)); | |
198 | prandom_seed(entropy); | |
199 | /* reseed every ~60 seconds, in [40 .. 80) interval with slack */ | |
200 | seed_timer.expires = jiffies + (40 * HZ + (prandom_u32() % (40 * HZ))); | |
201 | add_timer(&seed_timer); | |
202 | } | |
203 | ||
204 | static void prandom_start_seed_timer(void) | |
205 | { | |
206 | set_timer_slack(&seed_timer, HZ); | |
207 | seed_timer.expires = jiffies + 40 * HZ; | |
208 | add_timer(&seed_timer); | |
209 | } | |
210 | ||
aaa248f6 SH |
211 | /* |
212 | * Generate better values after random number generator | |
421f91d2 | 213 | * is fully initialized. |
aaa248f6 | 214 | */ |
4af712e8 | 215 | static void __prandom_reseed(bool late) |
aaa248f6 SH |
216 | { |
217 | int i; | |
4af712e8 HFS |
218 | unsigned long flags; |
219 | static bool latch = false; | |
220 | static DEFINE_SPINLOCK(lock); | |
221 | ||
222 | /* only allow initial seeding (late == false) once */ | |
223 | spin_lock_irqsave(&lock, flags); | |
224 | if (latch && !late) | |
225 | goto out; | |
226 | latch = true; | |
aaa248f6 SH |
227 | |
228 | for_each_possible_cpu(i) { | |
229 | struct rnd_state *state = &per_cpu(net_rand_state,i); | |
a98814ce | 230 | u32 seeds[4]; |
697f8d03 SH |
231 | |
232 | get_random_bytes(&seeds, sizeof(seeds)); | |
a98814ce DB |
233 | state->s1 = __seed(seeds[0], 2U); |
234 | state->s2 = __seed(seeds[1], 8U); | |
235 | state->s3 = __seed(seeds[2], 16U); | |
236 | state->s4 = __seed(seeds[3], 128U); | |
aaa248f6 | 237 | |
a98814ce | 238 | prandom_warmup(state); |
aaa248f6 | 239 | } |
4af712e8 HFS |
240 | out: |
241 | spin_unlock_irqrestore(&lock, flags); | |
242 | } | |
243 | ||
244 | void prandom_reseed_late(void) | |
245 | { | |
246 | __prandom_reseed(true); | |
247 | } | |
248 | ||
249 | static int __init prandom_reseed(void) | |
250 | { | |
251 | __prandom_reseed(false); | |
6d319202 | 252 | prandom_start_seed_timer(); |
aaa248f6 SH |
253 | return 0; |
254 | } | |
496f2f93 | 255 | late_initcall(prandom_reseed); |