121 lines
3.4 KiB
C
121 lines
3.4 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* include/linux/prandom.h
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*
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* Include file for the fast pseudo-random 32-bit
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* generation.
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*/
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#ifndef _LINUX_PRANDOM_H
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#define _LINUX_PRANDOM_H
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#include <linux/types.h>
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#include <linux/percpu.h>
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#include <linux/siphash.h>
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u32 prandom_u32(void);
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void prandom_bytes(void *buf, size_t nbytes);
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void prandom_seed(u32 seed);
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void prandom_reseed_late(void);
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DECLARE_PER_CPU(unsigned long, net_rand_noise);
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#define PRANDOM_ADD_NOISE(a, b, c, d) \
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prandom_u32_add_noise((unsigned long)(a), (unsigned long)(b), \
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(unsigned long)(c), (unsigned long)(d))
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#if BITS_PER_LONG == 64
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/*
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* The core SipHash round function. Each line can be executed in
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* parallel given enough CPU resources.
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*/
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#define PRND_SIPROUND(v0, v1, v2, v3) SIPHASH_PERMUTATION(v0, v1, v2, v3)
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#define PRND_K0 (SIPHASH_CONST_0 ^ SIPHASH_CONST_2)
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#define PRND_K1 (SIPHASH_CONST_1 ^ SIPHASH_CONST_3)
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#elif BITS_PER_LONG == 32
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/*
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* On 32-bit machines, we use HSipHash, a reduced-width version of SipHash.
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* This is weaker, but 32-bit machines are not used for high-traffic
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* applications, so there is less output for an attacker to analyze.
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*/
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#define PRND_SIPROUND(v0, v1, v2, v3) HSIPHASH_PERMUTATION(v0, v1, v2, v3)
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#define PRND_K0 (HSIPHASH_CONST_0 ^ HSIPHASH_CONST_2)
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#define PRND_K1 (HSIPHASH_CONST_1 ^ HSIPHASH_CONST_3)
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#else
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#error Unsupported BITS_PER_LONG
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#endif
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static inline void prandom_u32_add_noise(unsigned long a, unsigned long b,
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unsigned long c, unsigned long d)
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{
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/*
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* This is not used cryptographically; it's just
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* a convenient 4-word hash function. (3 xor, 2 add, 2 rol)
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*/
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a ^= raw_cpu_read(net_rand_noise);
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PRND_SIPROUND(a, b, c, d);
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raw_cpu_write(net_rand_noise, d);
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}
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struct rnd_state {
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__u32 s1, s2, s3, s4;
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};
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u32 prandom_u32_state(struct rnd_state *state);
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void prandom_bytes_state(struct rnd_state *state, void *buf, size_t nbytes);
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void prandom_seed_full_state(struct rnd_state __percpu *pcpu_state);
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#define prandom_init_once(pcpu_state) \
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DO_ONCE(prandom_seed_full_state, (pcpu_state))
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/**
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* prandom_u32_max - returns a pseudo-random number in interval [0, ep_ro)
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* @ep_ro: right open interval endpoint
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*
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* Returns a pseudo-random number that is in interval [0, ep_ro). Note
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* that the result depends on PRNG being well distributed in [0, ~0U]
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* u32 space. Here we use maximally equidistributed combined Tausworthe
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* generator, that is, prandom_u32(). This is useful when requesting a
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* random index of an array containing ep_ro elements, for example.
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*
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* Returns: pseudo-random number in interval [0, ep_ro)
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*/
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static inline u32 prandom_u32_max(u32 ep_ro)
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{
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return (u32)(((u64) prandom_u32() * ep_ro) >> 32);
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}
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/*
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* Handle minimum values for seeds
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*/
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static inline u32 __seed(u32 x, u32 m)
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{
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return (x < m) ? x + m : x;
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}
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/**
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* prandom_seed_state - set seed for prandom_u32_state().
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* @state: pointer to state structure to receive the seed.
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* @seed: arbitrary 64-bit value to use as a seed.
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*/
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static inline void prandom_seed_state(struct rnd_state *state, u64 seed)
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{
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u32 i = ((seed >> 32) ^ (seed << 10) ^ seed) & 0xffffffffUL;
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state->s1 = __seed(i, 2U);
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state->s2 = __seed(i, 8U);
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state->s3 = __seed(i, 16U);
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state->s4 = __seed(i, 128U);
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PRANDOM_ADD_NOISE(state, i, 0, 0);
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}
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/* Pseudo random number generator from numerical recipes. */
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static inline u32 next_pseudo_random32(u32 seed)
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{
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return seed * 1664525 + 1013904223;
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}
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#endif
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