Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752217Ab2E0Lvb (ORCPT ); Sun, 27 May 2012 07:51:31 -0400 Received: from eusmtp01.atmel.com ([212.144.249.242]:18757 "EHLO eusmtp01.atmel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750975Ab2E0Lv2 (ORCPT ); Sun, 27 May 2012 07:51:28 -0400 Message-ID: <4FC21527.7050705@atmel.com> Date: Sun, 27 May 2012 13:51:03 +0200 From: Nicolas Ferre Organization: atmel User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:12.0) Gecko/20120430 Thunderbird/12.0.1 MIME-Version: 1.0 To: Peter Korsgaard , CC: , , , Subject: Re: [PATCH] hw_random: atmel-rng: fix race condition leading to repeated bits References: <1337937158-9710-1-git-send-email-jacmet@sunsite.dk> In-Reply-To: <1337937158-9710-1-git-send-email-jacmet@sunsite.dk> X-Enigmail-Version: 1.5pre Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit X-Originating-IP: [172.24.48.186] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3264 Lines: 87 On 05/25/2012 11:12 AM, Peter Korsgaard : > Data valid gets cleared by reading the ISR (status register) and NOT from > reading ODATA (data register). A new data word can become available between > checking ISR and reading ODATA, causing us to reuse the same data word next > time atmel_trng_read() gets called, if that happens before the following > data word is ready. > > With this fixed, rngtest no longer complains of 'Continous run' errors. > Before: > > rngtest -c 1000 < /dev/hwrng > rngtest 3 > Copyright (c) 2004 by Henrique de Moraes Holschuh > This is free software; see the source for copying conditions. There is NO warr. > > rngtest: starting FIPS tests... > rngtest: bits received from input: 20000032 > rngtest: FIPS 140-2 successes: 923 > rngtest: FIPS 140-2 failures: 77 > rngtest: FIPS 140-2(2001-10-10) Monobit: 0 > rngtest: FIPS 140-2(2001-10-10) Poker: 0 > rngtest: FIPS 140-2(2001-10-10) Runs: 1 > rngtest: FIPS 140-2(2001-10-10) Long run: 0 > rngtest: FIPS 140-2(2001-10-10) Continuous run: 76 > rngtest: input channel speed: (min=721.402; avg=46003.510; max=49321.338)Kibitss > rngtest: FIPS tests speed: (min=11.442; avg=12.714; max=12.801)Mibits/s > rngtest: Program run time: 1931860 microseconds > > After: > > rngtest -c 1000 < /dev/hwrng > rngtest 3 > Copyright (c) 2004 by Henrique de Moraes Holschuh > This is free software; see the source for copying conditions. There is NO warr. > > rngtest: starting FIPS tests... > rngtest: bits received from input: 20000032 > rngtest: FIPS 140-2 successes: 1000 > rngtest: FIPS 140-2 failures: 0 > rngtest: FIPS 140-2(2001-10-10) Monobit: 0 > rngtest: FIPS 140-2(2001-10-10) Poker: 0 > rngtest: FIPS 140-2(2001-10-10) Runs: 0 > rngtest: FIPS 140-2(2001-10-10) Long run: 0 > rngtest: FIPS 140-2(2001-10-10) Continuous run: 0 > rngtest: input channel speed: (min=777.518; avg=36988.482; max=43115.342)Kibitss > rngtest: FIPS tests speed: (min=11.951; avg=12.715; max=12.887)Mibits/s > rngtest: Program run time: 2035543 microseconds > > Cc: stable@vger.kernel.org > Signed-off-by: Peter Korsgaard > Reported-by: George Pontis Acked-by: Nicolas Ferre Thanks! > --- > drivers/char/hw_random/atmel-rng.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/drivers/char/hw_random/atmel-rng.c b/drivers/char/hw_random/atmel-rng.c > index d7ab920..731c904 100644 > --- a/drivers/char/hw_random/atmel-rng.c > +++ b/drivers/char/hw_random/atmel-rng.c > @@ -36,6 +36,13 @@ static int atmel_trng_read(struct hwrng *rng, void *buf, size_t max, > /* data ready? */ > if (readl(trng->base + TRNG_ISR) & 1) { > *data = readl(trng->base + TRNG_ODATA); > + /* > + ensure data ready is only set again AFTER the next data > + word is ready in case it got set between checking ISR > + and reading ODATA, so we don't risk re-reading the > + same word > + */ > + readl(trng->base + TRNG_ISR); > return 4; > } else > return 0; -- Nicolas Ferre -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/