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Date:   Mon, 6 Jul 2020 17:05:39 +0100
From:   Jamie Iles <jamie@jamieiles.com>
To:     Ard Biesheuvel <ardb@kernel.org>
Cc:     linux-crypto@vger.kernel.org,
        Corentin Labbe <clabbe.montjoie@gmail.com>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        "David S. Miller" <davem@davemloft.net>,
        Maxime Ripard <mripard@kernel.org>,
        Chen-Yu Tsai <wens@csie.org>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Ayush Sawal <ayush.sawal@chelsio.com>,
        Vinay Kumar Yadav <vinay.yadav@chelsio.com>,
        Rohit Maheshwari <rohitm@chelsio.com>,
        Shawn Guo <shawnguo@kernel.org>,
        Sascha Hauer <s.hauer@pengutronix.de>,
        Pengutronix Kernel Team <kernel@pengutronix.de>,
        Fabio Estevam <festevam@gmail.com>,
        NXP Linux Team <linux-imx@nxp.com>,
        Jamie Iles <jamie@jamieiles.com>,
        Eric Biggers <ebiggers@google.com>,
        Tero Kristo <t-kristo@ti.com>,
        Matthias Brugger <matthias.bgg@gmail.com>
Subject: Re: [PATCH v3 10/13] crypto: picoxcell - permit asynchronous
 skcipher as fallback
Message-ID: <20200706160539.GE84554@willow>
References: <20200630121907.24274-1-ardb@kernel.org>
 <20200630121907.24274-11-ardb@kernel.org>
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On Tue, Jun 30, 2020 at 02:19:04PM +0200, Ard Biesheuvel wrote:
> Even though the picoxcell driver implements asynchronous versions of
> ecb(aes) and cbc(aes), the fallbacks it allocates are required to be
> synchronous. Given that SIMD based software implementations are usually
> asynchronous as well, even though they rarely complete asynchronously
> (this typically only happens in cases where the request was made from
> softirq context, while SIMD was already in use in the task context that
> it interrupted), these implementations are disregarded, and either the
> generic C version or another table based version implemented in assembler
> is selected instead.
> 
> Since falling back to synchronous AES is not only a performance issue, but
> potentially a security issue as well (due to the fact that table based AES
> is not time invariant), let's fix this, by allocating an ordinary skcipher
> as the fallback, and invoke it with the completion routine that was given
> to the outer request.
> 
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

Thanks Ard!

Reviewed-by: Jamie Iles <jamie@jamieiles.com>