From: Linus Torvalds Date: Thu, 22 Dec 2011 19:36:22 +0000 (-0800) Subject: random: Use arch_get_random_int instead of cycle counter if avail X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=cf833d0b9937874b50ef2867c4e8badfd64948ce;p=GitHub%2FLineageOS%2Fandroid_kernel_samsung_universal7580.git 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" Acked-by: "Theodore Ts'o" Acked-by: Herbert Xu Cc: Matt Mackall Cc: Tony Luck Cc: Eric Dumazet Signed-off-by: H. Peter Anvin --- 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));