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Date:   Mon, 6 Jul 2020 19:32:48 +0200
From:   Corentin Labbe <clabbe.montjoie@gmail.com>
To:     Ard Biesheuvel <ardb@kernel.org>
Cc:     linux-crypto@vger.kernel.org,
        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 04/13] crypto: sun4i - permit asynchronous skcipher as
 fallback
Message-ID: <20200706173248.GA25769@Red>
References: <20200630121907.24274-1-ardb@kernel.org>
 <20200630121907.24274-5-ardb@kernel.org>
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On Tue, Jun 30, 2020 at 02:18:58PM +0200, Ard Biesheuvel wrote:
> Even though the sun4i 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>
> ---
>  drivers/crypto/allwinner/sun4i-ss/sun4i-ss-cipher.c | 46 ++++++++++----------
>  drivers/crypto/allwinner/sun4i-ss/sun4i-ss.h        |  3 +-
>  2 files changed, 25 insertions(+), 24 deletions(-)
> 

Tested-by: Corentin Labbe <clabbe.montjoie@gmail.com>