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