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From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
To: Horia Geanta <horia.geanta@nxp.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>,
	Sascha Hauer <s.hauer@pengutronix.de>,
	"linux-crypto@vger.kernel.org" <linux-crypto@vger.kernel.org>,
	"kernel@pengutronix.de" <kernel@pengutronix.de>,
	"stable@vger.kernel.org" <stable@vger.kernel.org>
Subject: Re: [PATCH] crypto: caam - Do not overwrite IV
Date: Mon, 11 Feb 2019 18:28:36 +0100	[thread overview]
Message-ID: <CAKv+Gu9nzpefv=TVh23dqk6etgvZS_KUfHsaJ=hjwwtjckT8Gw@mail.gmail.com> (raw)
In-Reply-To: <VI1PR0402MB34851754919DFF6FD0FDA57D98640@VI1PR0402MB3485.eurprd04.prod.outlook.com>

On Mon, 11 Feb 2019 at 16:13, Horia Geanta <horia.geanta@nxp.com> wrote:
>
> On 2/8/2019 1:45 PM, Herbert Xu wrote:
> > On Fri, Feb 08, 2019 at 08:41:37AM +0000, Horia Geanta wrote:
> >>
> >> So if there is a real intention to support offloading skcipher, as this old
> >> commit suggests:
> >>
> >> 84c911523020 ("[CRYPTO] gcm: Add support for async ciphers")
> >>     This patch adds the necessary changes for GCM to be used with async
> >>     ciphers.  This would allow it to be used with hardware devices that
> >>     support CTR.
> >>
> >> then we must take special care when building skcipher req->src and avoid having
> >> it's first entry (auth_tag[16] in crypto_gcm_req_priv_ctx structure) sharing a
> >> cache line with req->iv.
> >
> > Could you prepare a patch for this?
> >
> Yes, will do.
>
> Note that I am seeing the same issue on CCM.
>
> Also for GCM, besides auth_tag there is iauth_tag[16] buffer that is added in a
> 1-entry S/G in gcm_hash_len():
>         sg_init_one(&pctx->sg, pctx->iauth_tag, 16);
>

Yes, but I suppose the issue only occurs when writing data from the
device, no? AFAICT, iauth_tag[] is passed into the device but never
updated by it.

> It looks like there other places where this happens, for e.g. "tail" member of
> poly_req (crypto/cacha20poly1305.c) in poly_tail():
>         sg_set_buf(preq->src, &preq->tail, sizeof(preq->tail));
>

Same here. If it never occurs in the destination of the scatterlist,
it should be safe for non-cache coherent DMA (since DMA to the device
does not involve cache invalidation)

However, it would be nice if we could test this in some way ...

      reply	other threads:[~2019-02-11 17:28 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-01-31  6:12 [PATCH] crypto: caam - Do not overwrite IV Sascha Hauer
2019-02-04 12:26 ` Horia Geanta
2019-02-05  8:31   ` Sascha Hauer
2019-02-05 11:49     ` Horia Geanta
2019-02-08  7:16   ` Herbert Xu
2019-02-08  8:41     ` Horia Geanta
2019-02-08  8:55       ` Ard Biesheuvel
2019-02-08 11:44         ` Herbert Xu
2019-02-12  9:13         ` Ard Biesheuvel
2019-02-13 20:48           ` Horia Geanta
2019-02-13 21:15             ` Ard Biesheuvel
2019-02-08 11:45       ` Herbert Xu
2019-02-11 15:13         ` Horia Geanta
2019-02-11 17:28           ` Ard Biesheuvel [this message]

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