linux/lib/random32.c
Andi Kleen 61407f80f7 [NET]: srandom32 fixes for networking v2
- Let it update the state of all CPUs. The network stack goes
into pains to feed the current IP addresses in, but it is not very
effective if that is only done for some random CPU instead of all.
So change it to feed bits into all CPUs.  I decided to do that lockless 
because well somewhat random results are ok.

v2: Drop rename so that this patch doesn't depend on x86 maintainers

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
2008-04-03 14:07:02 -07:00

149 lines
3.7 KiB
C

/*
This is a maximally equidistributed combined Tausworthe generator
based on code from GNU Scientific Library 1.5 (30 Jun 2004)
x_n = (s1_n ^ s2_n ^ s3_n)
s1_{n+1} = (((s1_n & 4294967294) <<12) ^ (((s1_n <<13) ^ s1_n) >>19))
s2_{n+1} = (((s2_n & 4294967288) << 4) ^ (((s2_n << 2) ^ s2_n) >>25))
s3_{n+1} = (((s3_n & 4294967280) <<17) ^ (((s3_n << 3) ^ s3_n) >>11))
The period of this generator is about 2^88.
From: P. L'Ecuyer, "Maximally Equidistributed Combined Tausworthe
Generators", Mathematics of Computation, 65, 213 (1996), 203--213.
This is available on the net from L'Ecuyer's home page,
http://www.iro.umontreal.ca/~lecuyer/myftp/papers/tausme.ps
ftp://ftp.iro.umontreal.ca/pub/simulation/lecuyer/papers/tausme.ps
There is an erratum in the paper "Tables of Maximally
Equidistributed Combined LFSR Generators", Mathematics of
Computation, 68, 225 (1999), 261--269:
http://www.iro.umontreal.ca/~lecuyer/myftp/papers/tausme2.ps
... the k_j most significant bits of z_j must be non-
zero, for each j. (Note: this restriction also applies to the
computer code given in [4], but was mistakenly not mentioned in
that paper.)
This affects the seeding procedure by imposing the requirement
s1 > 1, s2 > 7, s3 > 15.
*/
#include <linux/types.h>
#include <linux/percpu.h>
#include <linux/module.h>
#include <linux/jiffies.h>
#include <linux/random.h>
struct rnd_state {
u32 s1, s2, s3;
};
static DEFINE_PER_CPU(struct rnd_state, net_rand_state);
static u32 __random32(struct rnd_state *state)
{
#define TAUSWORTHE(s,a,b,c,d) ((s&c)<<d) ^ (((s <<a) ^ s)>>b)
state->s1 = TAUSWORTHE(state->s1, 13, 19, 4294967294UL, 12);
state->s2 = TAUSWORTHE(state->s2, 2, 25, 4294967288UL, 4);
state->s3 = TAUSWORTHE(state->s3, 3, 11, 4294967280UL, 17);
return (state->s1 ^ state->s2 ^ state->s3);
}
static void __set_random32(struct rnd_state *state, unsigned long s)
{
if (s == 0)
s = 1; /* default seed is 1 */
#define LCG(n) (69069 * n)
state->s1 = LCG(s);
state->s2 = LCG(state->s1);
state->s3 = LCG(state->s2);
/* "warm it up" */
__random32(state);
__random32(state);
__random32(state);
__random32(state);
__random32(state);
__random32(state);
}
/**
* random32 - pseudo random number generator
*
* A 32 bit pseudo-random number is generated using a fast
* algorithm suitable for simulation. This algorithm is NOT
* considered safe for cryptographic use.
*/
u32 random32(void)
{
unsigned long r;
struct rnd_state *state = &get_cpu_var(net_rand_state);
r = __random32(state);
put_cpu_var(state);
return r;
}
EXPORT_SYMBOL(random32);
/**
* srandom32 - add entropy to pseudo random number generator
* @seed: seed value
*
* Add some additional seeding to the random32() pool.
*/
void srandom32(u32 entropy)
{
int i;
/*
* No locking on the CPUs, but then somewhat random results are, well,
* expected.
*/
for_each_possible_cpu (i) {
struct rnd_state *state = &per_cpu(net_rand_state, i);
__set_random32(state, state->s1 ^ entropy);
}
}
EXPORT_SYMBOL(srandom32);
/*
* Generate some initially weak seeding values to allow
* to start the random32() engine.
*/
static int __init random32_init(void)
{
int i;
for_each_possible_cpu(i) {
struct rnd_state *state = &per_cpu(net_rand_state,i);
__set_random32(state, i + jiffies);
}
return 0;
}
core_initcall(random32_init);
/*
* Generate better values after random number generator
* is fully initalized.
*/
static int __init random32_reseed(void)
{
int i;
unsigned long seed;
for_each_possible_cpu(i) {
struct rnd_state *state = &per_cpu(net_rand_state,i);
get_random_bytes(&seed, sizeof(seed));
__set_random32(state, seed);
}
return 0;
}
late_initcall(random32_reseed);