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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 | ||
5 | x_n = (s1_n ^ s2_n ^ s3_n) | |
6 | ||
7 | s1_{n+1} = (((s1_n & 4294967294) <<12) ^ (((s1_n <<13) ^ s1_n) >>19)) | |
8 | s2_{n+1} = (((s2_n & 4294967288) << 4) ^ (((s2_n << 2) ^ s2_n) >>25)) | |
9 | s3_{n+1} = (((s3_n & 4294967280) <<17) ^ (((s3_n << 3) ^ s3_n) >>11)) | |
10 | ||
11 | The period of this generator is about 2^88. | |
12 | ||
13 | From: P. L'Ecuyer, "Maximally Equidistributed Combined Tausworthe | |
14 | Generators", Mathematics of Computation, 65, 213 (1996), 203--213. | |
15 | ||
16 | This is available on the net from L'Ecuyer's home page, | |
17 | ||
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. | |
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 | ||
55 | state->s1 = TAUSWORTHE(state->s1, 13, 19, 4294967294UL, 12); | |
56 | state->s2 = TAUSWORTHE(state->s2, 2, 25, 4294967288UL, 4); | |
57 | state->s3 = TAUSWORTHE(state->s3, 3, 11, 4294967280UL, 17); | |
58 | ||
59 | return (state->s1 ^ state->s2 ^ state->s3); | |
60 | } | |
496f2f93 | 61 | EXPORT_SYMBOL(prandom_u32_state); |
aaa248f6 SH |
62 | |
63 | /** | |
496f2f93 | 64 | * prandom_u32 - pseudo random number generator |
aaa248f6 SH |
65 | * |
66 | * A 32 bit pseudo-random number is generated using a fast | |
67 | * algorithm suitable for simulation. This algorithm is NOT | |
68 | * considered safe for cryptographic use. | |
69 | */ | |
496f2f93 | 70 | u32 prandom_u32(void) |
aaa248f6 SH |
71 | { |
72 | unsigned long r; | |
73 | struct rnd_state *state = &get_cpu_var(net_rand_state); | |
496f2f93 | 74 | r = prandom_u32_state(state); |
aaa248f6 SH |
75 | put_cpu_var(state); |
76 | return r; | |
77 | } | |
496f2f93 | 78 | EXPORT_SYMBOL(prandom_u32); |
aaa248f6 | 79 | |
6582c665 AM |
80 | /* |
81 | * prandom_bytes_state - get the requested number of pseudo-random bytes | |
82 | * | |
83 | * @state: pointer to state structure holding seeded state. | |
84 | * @buf: where to copy the pseudo-random bytes to | |
85 | * @bytes: the requested number of bytes | |
86 | * | |
87 | * This is used for pseudo-randomness with no outside seeding. | |
88 | * For more random results, use prandom_bytes(). | |
89 | */ | |
90 | void prandom_bytes_state(struct rnd_state *state, void *buf, int bytes) | |
91 | { | |
92 | unsigned char *p = buf; | |
93 | int i; | |
94 | ||
95 | for (i = 0; i < round_down(bytes, sizeof(u32)); i += sizeof(u32)) { | |
96 | u32 random = prandom_u32_state(state); | |
97 | int j; | |
98 | ||
99 | for (j = 0; j < sizeof(u32); j++) { | |
100 | p[i + j] = random; | |
101 | random >>= BITS_PER_BYTE; | |
102 | } | |
103 | } | |
104 | if (i < bytes) { | |
105 | u32 random = prandom_u32_state(state); | |
106 | ||
107 | for (; i < bytes; i++) { | |
108 | p[i] = random; | |
109 | random >>= BITS_PER_BYTE; | |
110 | } | |
111 | } | |
112 | } | |
113 | EXPORT_SYMBOL(prandom_bytes_state); | |
114 | ||
115 | /** | |
116 | * prandom_bytes - get the requested number of pseudo-random bytes | |
117 | * @buf: where to copy the pseudo-random bytes to | |
118 | * @bytes: the requested number of bytes | |
119 | */ | |
120 | void prandom_bytes(void *buf, int bytes) | |
121 | { | |
122 | struct rnd_state *state = &get_cpu_var(net_rand_state); | |
123 | ||
124 | prandom_bytes_state(state, buf, bytes); | |
125 | put_cpu_var(state); | |
126 | } | |
127 | EXPORT_SYMBOL(prandom_bytes); | |
128 | ||
aaa248f6 | 129 | /** |
496f2f93 | 130 | * prandom_seed - add entropy to pseudo random number generator |
aaa248f6 SH |
131 | * @seed: seed value |
132 | * | |
496f2f93 | 133 | * Add some additional seeding to the prandom pool. |
aaa248f6 | 134 | */ |
496f2f93 | 135 | void prandom_seed(u32 entropy) |
aaa248f6 | 136 | { |
61407f80 AK |
137 | int i; |
138 | /* | |
139 | * No locking on the CPUs, but then somewhat random results are, well, | |
140 | * expected. | |
141 | */ | |
142 | for_each_possible_cpu (i) { | |
143 | struct rnd_state *state = &per_cpu(net_rand_state, i); | |
51c37a70 | 144 | state->s1 = __seed(state->s1 ^ entropy, 2); |
6d319202 | 145 | prandom_u32_state(state); |
61407f80 | 146 | } |
aaa248f6 | 147 | } |
496f2f93 | 148 | EXPORT_SYMBOL(prandom_seed); |
aaa248f6 SH |
149 | |
150 | /* | |
151 | * Generate some initially weak seeding values to allow | |
496f2f93 | 152 | * to start the prandom_u32() engine. |
aaa248f6 | 153 | */ |
496f2f93 | 154 | static int __init prandom_init(void) |
aaa248f6 SH |
155 | { |
156 | int i; | |
157 | ||
158 | for_each_possible_cpu(i) { | |
159 | struct rnd_state *state = &per_cpu(net_rand_state,i); | |
697f8d03 SH |
160 | |
161 | #define LCG(x) ((x) * 69069) /* super-duper LCG */ | |
51c37a70 DB |
162 | state->s1 = __seed(LCG(i + jiffies), 2); |
163 | state->s2 = __seed(LCG(state->s1), 8); | |
164 | state->s3 = __seed(LCG(state->s2), 16); | |
697f8d03 SH |
165 | |
166 | /* "warm it up" */ | |
496f2f93 AM |
167 | prandom_u32_state(state); |
168 | prandom_u32_state(state); | |
169 | prandom_u32_state(state); | |
170 | prandom_u32_state(state); | |
171 | prandom_u32_state(state); | |
172 | prandom_u32_state(state); | |
aaa248f6 SH |
173 | } |
174 | return 0; | |
175 | } | |
496f2f93 | 176 | core_initcall(prandom_init); |
aaa248f6 | 177 | |
6d319202 HFS |
178 | static void __prandom_timer(unsigned long dontcare); |
179 | static DEFINE_TIMER(seed_timer, __prandom_timer, 0, 0); | |
180 | ||
181 | static void __prandom_timer(unsigned long dontcare) | |
182 | { | |
183 | u32 entropy; | |
184 | ||
185 | get_random_bytes(&entropy, sizeof(entropy)); | |
186 | prandom_seed(entropy); | |
187 | /* reseed every ~60 seconds, in [40 .. 80) interval with slack */ | |
188 | seed_timer.expires = jiffies + (40 * HZ + (prandom_u32() % (40 * HZ))); | |
189 | add_timer(&seed_timer); | |
190 | } | |
191 | ||
192 | static void prandom_start_seed_timer(void) | |
193 | { | |
194 | set_timer_slack(&seed_timer, HZ); | |
195 | seed_timer.expires = jiffies + 40 * HZ; | |
196 | add_timer(&seed_timer); | |
197 | } | |
198 | ||
aaa248f6 SH |
199 | /* |
200 | * Generate better values after random number generator | |
421f91d2 | 201 | * is fully initialized. |
aaa248f6 | 202 | */ |
496f2f93 | 203 | static int __init prandom_reseed(void) |
aaa248f6 SH |
204 | { |
205 | int i; | |
aaa248f6 SH |
206 | |
207 | for_each_possible_cpu(i) { | |
208 | struct rnd_state *state = &per_cpu(net_rand_state,i); | |
697f8d03 SH |
209 | u32 seeds[3]; |
210 | ||
211 | get_random_bytes(&seeds, sizeof(seeds)); | |
51c37a70 DB |
212 | state->s1 = __seed(seeds[0], 2); |
213 | state->s2 = __seed(seeds[1], 8); | |
214 | state->s3 = __seed(seeds[2], 16); | |
aaa248f6 | 215 | |
697f8d03 | 216 | /* mix it in */ |
496f2f93 | 217 | prandom_u32_state(state); |
aaa248f6 | 218 | } |
6d319202 | 219 | prandom_start_seed_timer(); |
aaa248f6 SH |
220 | return 0; |
221 | } | |
496f2f93 | 222 | late_initcall(prandom_reseed); |