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From:   Horia Geanta <horia.geanta@nxp.com>
To:     Herbert Xu <herbert@gondor.apana.org.au>,
        Ard Biesheuvel <ard.biesheuvel@linaro.org>
CC:     Iuliana Prodan <iuliana.prodan@nxp.com>,
        Eric Biggers <ebiggers@kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Sascha Hauer <s.hauer@pengutronix.de>,
        "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
        <linux-crypto@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        dl-linux-imx <linux-imx@nxp.com>
Subject: Re: [PATCH] crypto: gcm - fix cacheline sharing
Thread-Topic: [PATCH] crypto: gcm - fix cacheline sharing
Thread-Index: AQHVHDJUFTzexZfnZkK5jYnCMHmb4A==
Date:   Thu, 6 Jun 2019 07:10:06 +0000
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On 6/6/2019 9:58 AM, Herbert Xu wrote:=0A=
> On Thu, Jun 06, 2019 at 08:53:10AM +0200, Ard Biesheuvel wrote:=0A=
>>=0A=
>> That same patch 'fixes' CBC, since CBC was never broken to begin with.=
=0A=
>> The CTS driver does not have something like the auth_tag sharing the=0A=
>> same cacheline with the IV, so CBC has always worked fine.=0A=
> =0A=
> CBC is broken.  Any crypto API user is allowed to place the IV=0A=
> in the same position relative to the src/dst buffer.  So the driver=0A=
> must deal with it.=0A=
> =0A=
That's the theory.=0A=
In practice we haven't encountered any issue so far, but yes this case has =
to be=0A=
handled properly.=0A=
=0A=
> It's just that the CTR/ghash combo happened to expose this first.=0A=
> =0A=
Yes, and that's what the patch is fixing.=0A=
=0A=
>> So I guess what you are after is a patch that, instead of dodging the=0A=
>> issue by limiting the copy to CBC, does not perform the copy at all=0A=
>> while anything is mapped for DMA? Then we can leave it up to the NXP=0A=
>> engineers to fix CTR mode.=0A=
> =0A=
> Right, we definitely need to fix it for CBC, probably in the way that=0A=
> you suggested.=0A=
> =0A=
Not really.=0A=
I am in favor of using the HW to update the IV, which would work for all=0A=
skcipher algorithms.=0A=
I have the fix ready, will send it in a couple of days.=0A=
=0A=
Thanks,=0A=
Horia=0A=