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Linux/include/linux/prandom.h

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  1 /* SPDX-License-Identifier: GPL-2.0 */
  2 /*
  3  * include/linux/prandom.h
  4  *
  5  * Include file for the fast pseudo-random 32-bit
  6  * generation.
  7  */
  8 #ifndef _LINUX_PRANDOM_H
  9 #define _LINUX_PRANDOM_H
 10 
 11 #include <linux/types.h>
 12 #include <linux/percpu.h>
 13 
 14 u32 prandom_u32(void);
 15 void prandom_bytes(void *buf, size_t nbytes);
 16 void prandom_seed(u32 seed);
 17 void prandom_reseed_late(void);
 18 
 19 DECLARE_PER_CPU(unsigned long, net_rand_noise);
 20 
 21 #define PRANDOM_ADD_NOISE(a, b, c, d) \
 22         prandom_u32_add_noise((unsigned long)(a), (unsigned long)(b), \
 23                               (unsigned long)(c), (unsigned long)(d))
 24 
 25 #if BITS_PER_LONG == 64
 26 /*
 27  * The core SipHash round function.  Each line can be executed in
 28  * parallel given enough CPU resources.
 29  */
 30 #define PRND_SIPROUND(v0, v1, v2, v3) ( \
 31         v0 += v1, v1 = rol64(v1, 13),  v2 += v3, v3 = rol64(v3, 16), \
 32         v1 ^= v0, v0 = rol64(v0, 32),  v3 ^= v2,                     \
 33         v0 += v3, v3 = rol64(v3, 21),  v2 += v1, v1 = rol64(v1, 17), \
 34         v3 ^= v0,                      v1 ^= v2, v2 = rol64(v2, 32)  \
 35 )
 36 
 37 #define PRND_K0 (0x736f6d6570736575 ^ 0x6c7967656e657261)
 38 #define PRND_K1 (0x646f72616e646f6d ^ 0x7465646279746573)
 39 
 40 #elif BITS_PER_LONG == 32
 41 /*
 42  * On 32-bit machines, we use HSipHash, a reduced-width version of SipHash.
 43  * This is weaker, but 32-bit machines are not used for high-traffic
 44  * applications, so there is less output for an attacker to analyze.
 45  */
 46 #define PRND_SIPROUND(v0, v1, v2, v3) ( \
 47         v0 += v1, v1 = rol32(v1,  5),  v2 += v3, v3 = rol32(v3,  8), \
 48         v1 ^= v0, v0 = rol32(v0, 16),  v3 ^= v2,                     \
 49         v0 += v3, v3 = rol32(v3,  7),  v2 += v1, v1 = rol32(v1, 13), \
 50         v3 ^= v0,                      v1 ^= v2, v2 = rol32(v2, 16)  \
 51 )
 52 #define PRND_K0 0x6c796765
 53 #define PRND_K1 0x74656462
 54 
 55 #else
 56 #error Unsupported BITS_PER_LONG
 57 #endif
 58 
 59 static inline void prandom_u32_add_noise(unsigned long a, unsigned long b,
 60                                          unsigned long c, unsigned long d)
 61 {
 62         /*
 63          * This is not used cryptographically; it's just
 64          * a convenient 4-word hash function. (3 xor, 2 add, 2 rol)
 65          */
 66         a ^= raw_cpu_read(net_rand_noise);
 67         PRND_SIPROUND(a, b, c, d);
 68         raw_cpu_write(net_rand_noise, d);
 69 }
 70 
 71 struct rnd_state {
 72         __u32 s1, s2, s3, s4;
 73 };
 74 
 75 u32 prandom_u32_state(struct rnd_state *state);
 76 void prandom_bytes_state(struct rnd_state *state, void *buf, size_t nbytes);
 77 void prandom_seed_full_state(struct rnd_state __percpu *pcpu_state);
 78 
 79 #define prandom_init_once(pcpu_state)                   \
 80         DO_ONCE(prandom_seed_full_state, (pcpu_state))
 81 
 82 /**
 83  * prandom_u32_max - returns a pseudo-random number in interval [0, ep_ro)
 84  * @ep_ro: right open interval endpoint
 85  *
 86  * Returns a pseudo-random number that is in interval [0, ep_ro). Note
 87  * that the result depends on PRNG being well distributed in [0, ~0U]
 88  * u32 space. Here we use maximally equidistributed combined Tausworthe
 89  * generator, that is, prandom_u32(). This is useful when requesting a
 90  * random index of an array containing ep_ro elements, for example.
 91  *
 92  * Returns: pseudo-random number in interval [0, ep_ro)
 93  */
 94 static inline u32 prandom_u32_max(u32 ep_ro)
 95 {
 96         return (u32)(((u64) prandom_u32() * ep_ro) >> 32);
 97 }
 98 
 99 /*
100  * Handle minimum values for seeds
101  */
102 static inline u32 __seed(u32 x, u32 m)
103 {
104         return (x < m) ? x + m : x;
105 }
106 
107 /**
108  * prandom_seed_state - set seed for prandom_u32_state().
109  * @state: pointer to state structure to receive the seed.
110  * @seed: arbitrary 64-bit value to use as a seed.
111  */
112 static inline void prandom_seed_state(struct rnd_state *state, u64 seed)
113 {
114         u32 i = ((seed >> 32) ^ (seed << 10) ^ seed) & 0xffffffffUL;
115 
116         state->s1 = __seed(i,   2U);
117         state->s2 = __seed(i,   8U);
118         state->s3 = __seed(i,  16U);
119         state->s4 = __seed(i, 128U);
120         PRANDOM_ADD_NOISE(state, i, 0, 0);
121 }
122 
123 /* Pseudo random number generator from numerical recipes. */
124 static inline u32 next_pseudo_random32(u32 seed)
125 {
126         return seed * 1664525 + 1013904223;
127 }
128 
129 #endif
130 

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