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Date:   Wed, 19 Jun 2019 15:37:11 -0700
From:   Eric Biggers <ebiggers@kernel.org>
To:     Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc:     linux-crypto@vger.kernel.org,
        Herbert Xu <herbert@gondor.apana.org.au>, dm-devel@redhat.com,
        linux-fscrypt@vger.kernel.org,
        Gilad Ben-Yossef <gilad@benyossef.com>,
        Milan Broz <gmazyland@gmail.com>
Subject: Re: [PATCH v3 6/6] crypto: arm64/aes - implement accelerated
 ESSIV/CBC mode
Message-ID: <20190619223710.GC33328@gmail.com>
References: <20190619162921.12509-1-ard.biesheuvel@linaro.org>
 <20190619162921.12509-7-ard.biesheuvel@linaro.org>
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On Wed, Jun 19, 2019 at 06:29:21PM +0200, Ard Biesheuvel wrote:
> Add an accelerated version of the 'essiv(cbc(aes),aes,sha256)'
> skcipher, which is used by fscrypt, and in some cases, by dm-crypt.
> This avoids a separate call into the AES cipher for every invocation.
> 
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

I'm not sure we should bother with this, since fscrypt normally uses AES-256-XTS
for contents encryption.  AES-128-CBC-ESSIV support was only added because
people wanted something that is fast on low-powered embedded devices with crypto
accelerators such as CAAM or CESA that don't support XTS.

In the case of Android, the CDD doesn't even allow AES-128-CBC-ESSIV with
file-based encryption (fscrypt).  It's still the default for "full disk
encryption" (which uses dm-crypt), but that's being deprecated.

So maybe dm-crypt users will want this, but I don't think it's very useful for
fscrypt.

- Eric