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authorLinus Torvalds <torvalds@linux-foundation.org>2011-12-22 11:36:22 -0800
committerH. Peter Anvin <hpa@linux.intel.com>2011-12-29 16:49:45 -0800
commitcf833d0b9937874b50ef2867c4e8badfd64948ce (patch)
treef2eb260e524387c6dce6de17b5c06ec0c34adef7 /drivers
parent5f0a6e2d503896062f641639dacfe5055c2f593b (diff)
random: Use arch_get_random_int instead of cycle counter if avail
We still don't use rdrand in /dev/random, which just seems stupid. We accept the *cycle*counter* as a random input, but we don't accept rdrand? That's just broken. Sure, people can do things in user space (write to /dev/random, use rdrand in addition to /dev/random themselves etc etc), but that *still* seems to be a particularly stupid reason for saying "we shouldn't bother to try to do better in /dev/random". And even if somebody really doesn't trust rdrand as a source of random bytes, it seems singularly stupid to trust the cycle counter *more*. So I'd suggest the attached patch. I'm not going to even bother arguing that we should add more bits to the entropy estimate, because that's not the point - I don't care if /dev/random fills up slowly or not, I think it's just stupid to not use the bits we can get from rdrand and mix them into the strong randomness pool. Link: http://lkml.kernel.org/r/CA%2B55aFwn59N1=m651QAyTy-1gO1noGbK18zwKDwvwqnravA84A@mail.gmail.com Acked-by: "David S. Miller" <davem@davemloft.net> Acked-by: "Theodore Ts'o" <tytso@mit.edu> Acked-by: Herbert Xu <herbert@gondor.apana.org.au> Cc: Matt Mackall <mpm@selenic.com> Cc: Tony Luck <tony.luck@intel.com> Cc: Eric Dumazet <eric.dumazet@gmail.com> Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Diffstat (limited to 'drivers')
-rw-r--r--drivers/char/random.c8
1 files changed, 6 insertions, 2 deletions
diff --git a/drivers/char/random.c b/drivers/char/random.c
index 6035ab8d5ef..85da8740586 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -624,8 +624,8 @@ static struct timer_rand_state input_timer_state;
static void add_timer_randomness(struct timer_rand_state *state, unsigned num)
{
struct {
- cycles_t cycles;
long jiffies;
+ unsigned cycles;
unsigned num;
} sample;
long delta, delta2, delta3;
@@ -637,7 +637,11 @@ static void add_timer_randomness(struct timer_rand_state *state, unsigned num)
goto out;
sample.jiffies = jiffies;
- sample.cycles = get_cycles();
+
+ /* Use arch random value, fall back to cycles */
+ if (!arch_get_random_int(&sample.cycles))
+ sample.cycles = get_cycles();
+
sample.num = num;
mix_pool_bytes(&input_pool, &sample, sizeof(sample));