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random: If we have arch_get_random_seed*(), try it before blocking

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If we have arch_get_random_seed*(), try to use it for emergency refill
of the entropy pool before giving up and blocking on /dev/random.  It
may or may not work in the moment, but if it does work, it will give
the user better service than blocking will.

Reviewed-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
H. Peter Anvin 2014-03-17 16:36:29 -07:00 committed by Theodore Ts'o
parent 83664a6928
commit 331c6490c7
1 changed files with 33 additions and 0 deletions
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33
drivers/char/random.c
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@ -1294,6 +1294,34 @@ void rand_initialize_disk(struct gendisk *disk)
}
#endif
/*
* Attempt an emergency refill using arch_get_random_seed_long().
*
* As with add_interrupt_randomness() be paranoid and only
* credit the output as 50% entropic.
*/
static int arch_random_refill(void)
{
const unsigned int nlongs = 64; /* Arbitrary number */
unsigned int n = 0;
unsigned int i;
unsigned long buf[nlongs];
for (i = 0; i < nlongs; i++) {
if (arch_get_random_seed_long(&buf[n]))
n++;
}
if (n) {
unsigned int rand_bytes = n * sizeof(unsigned long);
mix_pool_bytes(&input_pool, buf, rand_bytes, NULL);
credit_entropy_bits(&input_pool, rand_bytes*4);
}
return n;
}
static ssize_t
random_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
{
@ -1312,8 +1340,13 @@ random_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
ENTROPY_BITS(&input_pool));
if (n > 0)
return n;
/* Pool is (near) empty. Maybe wait and retry. */
/* First try an emergency refill */
if (arch_random_refill())
continue;
if (file->f_flags & O_NONBLOCK)
return -EAGAIN;