[PATCH 07/12] random: use the arch-specific rng in xfer_secondary_pool

Theodore Ts'o
2012-07-06T22:45:11Z

If the CPU supports a hardware random number generator, use it in
xfer_secondary_pool(), where it will significantly improve things and
where we can afford it.

Also, remove the use of the arch-specific rng in
add_timer_randomness(), since the call is significantly slower than
get_cycles(), and we're much better off using it in
xfer_secondary_pool() anyway.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: stable@vger.kernel.org
---
drivers/char/random.c | 23 ++++++++++++++---------
1 file changed, 14 insertions(+), 9 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index e867409..c39bdc4 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -702,11 +702,7 @@ static void add_timer_randomness(struct timer_rand_state *state, unsigned num)
goto out;

sample.jiffies = jiffies;
-
- /* Use arch random value, fall back to cycles */
- if (!arch_get_random_int(&sample.cycles))
- sample.cycles = get_cycles();
-
+ sample.cycles = get_cycles();
sample.num = num;
mix_pool_bytes(&input_pool, &sample, sizeof(sample), NULL);

@@ -838,7 +834,11 @@ static ssize_t extract_entropy(struct entropy_store *r, void *buf,
*/
static void xfer_secondary_pool(struct entropy_store *r, size_t nbytes)
{
- __u32 tmp[OUTPUT_POOL_WORDS];
+ union {
+ __u32 tmp[OUTPUT_POOL_WORDS];
+ long hwrand[4];
+ } u;
+ int i;

if (r->pull && r->entropy_count < nbytes * 8 &&
r->entropy_count < r->poolinfo->POOLBITS) {
@@ -849,17 +849,22 @@ static void xfer_secondary_pool(struct entropy_store *r, size_t nbytes)
/* pull at least as many as BYTES as wakeup BITS */
bytes = max_t(int, bytes, random_read_wakeup_thresh / 8);
/* but never more than the buffer size */
- bytes = min_t(int, bytes, sizeof(tmp));
+ bytes = min_t(int, bytes, sizeof(u.tmp));

DEBUG_ENT("going to reseed %s with %d bits "
"(%d of %d requested)\n",
r->name, bytes * 8, nbytes * 8, r->entropy_count);

- bytes = extract_entropy(r->pull, tmp, bytes,
+ bytes = extract_entropy(r->pull, u.tmp, bytes,
random_read_wakeup_thresh / 8, rsvd);
- mix_pool_bytes(r, tmp, bytes, NULL);
+ mix_pool_bytes(r, u.tmp, bytes, NULL);
credit_entropy_bits(r, bytes*8);
}
+ for (i = 0; i < 4; i++)
+ if (arch_get_random_long(&u.hwrand[i]))
+ break;
+ if (i)
+ mix_pool_bytes(r, &u.hwrand, sizeof(u.hwrand), 0);
}

/*
--
1.7.11.1.108.gb129051