From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754563Ab2HMWEI (ORCPT ); Mon, 13 Aug 2012 18:04:08 -0400 Received: from mail-yw0-f46.google.com ([209.85.213.46]:58152 "EHLO mail-yw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754540Ab2HMWEC (ORCPT ); Mon, 13 Aug 2012 18:04:02 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Greg KH , 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: [ 16/44] random: Use arch_get_random_int instead of cycle counter if avail Date: Mon, 13 Aug 2012 15:02:23 -0700 Message-Id: <20120813220143.578443311@linuxfoundation.org> X-Mailer: git-send-email 1.7.10.1.362.g242cab3 In-Reply-To: <20120813220142.113186818@linuxfoundation.org> References: <20120813220142.113186818@linuxfoundation.org> User-Agent: quilt/0.60-20.5 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Greg KH 3.0-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: Greg Kroah-Hartman --- drivers/char/random.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -624,8 +624,8 @@ static struct timer_rand_state input_tim 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 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));