From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932820Ab2HGDvA (ORCPT ); Mon, 6 Aug 2012 23:51:00 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:59730 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757346Ab2HGDic (ORCPT ); Mon, 6 Aug 2012 23:38:32 -0400 Message-Id: <20120807032757.729008929@decadent.org.uk> User-Agent: quilt/0.60-1 Date: Tue, 07 Aug 2012 04:28:06 +0100 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, "David S. Miller" , "Theodore Tso" , Herbert Xu , Matt Mackall , Tony Luck , Eric Dumazet , "H. Peter Anvin" Subject: [ 11/70] random: Use arch_get_random_int instead of cycle counter if avail In-Reply-To: <20120807032755.803571133@decadent.org.uk> X-SA-Exim-Connect-IP: 2001:470:1f08:1539:21c:bfff:fe03:f805 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.2-stable review patch. If anyone has any objections, please let me know. ------------------ From: Linus Torvalds commit cf833d0b9937874b50ef2867c4e8badfd64948ce upstream. 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 Signed-off-by: Ben Hutchings --- drivers/char/random.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 6035ab8..85da874 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));