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random32: move the pseudo-random 32-bit definitions to prandom.h
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The addition of percpu.h to the list of includes in random.h revealed
some circular dependencies on arm64 and possibly other platforms.  This
include was added solely for the pseudo-random definitions, which have
nothing to do with the rest of the definitions in this file but are
still there for legacy reasons.

This patch moves the pseudo-random parts to linux/prandom.h and the
percpu.h include with it, which is now guarded by _LINUX_PRANDOM_H and
protected against recursive inclusion.

A further cleanup step would be to remove this from <linux/random.h>
entirely, and make people who use the prandom infrastructure include
just the new header file.  That's a bit of a churn patch, but grepping
for "prandom_" and "next_pseudo_random32" "struct rnd_state" should
catch most users.

But it turns out that that nice cleanup step is fairly painful, because
a _lot_ of code currently seems to depend on the implicit include of
<linux/random.h>, which can currently come in a lot of ways, including
such fairly core headfers as <linux/net.h>.

So the "nice cleanup" part may or may never happen.

Fixes: 1c9df90 ("random: fix circular include dependency on arm64 after addition of percpu.h")
Tested-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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torvalds committed Aug 4, 2020
1 parent 2baa85d commit c0842fb
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Showing 2 changed files with 82 additions and 62 deletions.
78 changes: 78 additions & 0 deletions include/linux/prandom.h
Original file line number Diff line number Diff line change
@@ -0,0 +1,78 @@
/* 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>

u32 prandom_u32(void);
void prandom_bytes(void *buf, size_t nbytes);
void prandom_seed(u32 seed);
void prandom_reseed_late(void);

struct rnd_state {
__u32 s1, s2, s3, s4;
};

DECLARE_PER_CPU(struct rnd_state, net_rand_state);

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;

state->s1 = __seed(i, 2U);
state->s2 = __seed(i, 8U);
state->s3 = __seed(i, 16U);
state->s4 = __seed(i, 128U);
}

/* Pseudo random number generator from numerical recipes. */
static inline u32 next_pseudo_random32(u32 seed)
{
return seed * 1664525 + 1013904223;
}

#endif
66 changes: 4 additions & 62 deletions include/linux/random.h
Original file line number Diff line number Diff line change
Expand Up @@ -11,7 +11,6 @@
#include <linux/kernel.h>
#include <linux/list.h>
#include <linux/once.h>
#include <asm/percpu.h>

#include <uapi/linux/random.h>

Expand Down Expand Up @@ -111,63 +110,12 @@ declare_get_random_var_wait(long)

unsigned long randomize_page(unsigned long start, unsigned long range);

u32 prandom_u32(void);
void prandom_bytes(void *buf, size_t nbytes);
void prandom_seed(u32 seed);
void prandom_reseed_late(void);

struct rnd_state {
__u32 s1, s2, s3, s4;
};

DECLARE_PER_CPU(struct rnd_state, net_rand_state);

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.
* This is designed to be standalone for just prandom
* users, but for now we include it from <linux/random.h>
* for legacy reasons.
*/
static inline void prandom_seed_state(struct rnd_state *state, u64 seed)
{
u32 i = (seed >> 32) ^ (seed << 10) ^ seed;

state->s1 = __seed(i, 2U);
state->s2 = __seed(i, 8U);
state->s3 = __seed(i, 16U);
state->s4 = __seed(i, 128U);
}
#include <linux/prandom.h>

#ifdef CONFIG_ARCH_RANDOM
# include <asm/archrandom.h>
Expand Down Expand Up @@ -210,10 +158,4 @@ static inline bool __init arch_get_random_long_early(unsigned long *v)
}
#endif

/* Pseudo random number generator from numerical recipes. */
static inline u32 next_pseudo_random32(u32 seed)
{
return seed * 1664525 + 1013904223;
}

#endif /* _LINUX_RANDOM_H */

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