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