Re: [PATCH v4 24/32] crypto: amcc/aes - switch to AES library for GCM key derivation

From: Christian Lamparter <chunkeey@gmail.com>
To: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: linux-crypto@vger.kernel.org, herbert@gondor.apana.org.au,
	ebiggers@google.com
Subject: Re: [PATCH v4 24/32] crypto: amcc/aes - switch to AES library for GCM key derivation
Date: Sun, 27 Oct 2019 11:08:22 +0100	[thread overview]
Message-ID: <7787734.Led6RIzHno@debian64> (raw)
In-Reply-To: <20190702194150.10405-25-ard.biesheuvel@linaro.org>

Hi,

On Tuesday, July 2, 2019 9:41:42 PM CET Ard Biesheuvel wrote:
> The AMCC code for GCM key derivation allocates a AES cipher to
> perform a single block encryption. So let's switch to the new
> and more lightweight AES library instead.
> 
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> ---
>  drivers/crypto/Kconfig              |  2 +-
>  drivers/crypto/amcc/crypto4xx_alg.c | 24 +++++++-------------
>  2 files changed, 9 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/crypto/Kconfig b/drivers/crypto/Kconfig
> index b30b84089d11..c7ac1e6d23d4 100644
> --- a/drivers/crypto/Kconfig
> +++ b/drivers/crypto/Kconfig
> @@ -311,7 +311,7 @@ config CRYPTO_DEV_PPC4XX
>  	depends on PPC && 4xx
>  	select CRYPTO_HASH
>  	select CRYPTO_AEAD
> -	select CRYPTO_AES
> +	select CRYPTO_LIB_AES

I think that getting rid of CRYPTO_AES was not a good idea here.
Reason being that the crypto4xx driver registers fallbacks to cover
edge-cases for AES-CTR, AES-CCM and AES-GCM modes that the hardware
is incapbale of handling itself.

So without the dependency of CRYPTO_AES, I think there's now a way
to build the crypto4xx module without necessarily having CRYPTO_AES.
And if that's the case then the necessary fallbacks cannot be
instantiated and the driver will not provide the afromentioned modes.

Can somebody clarify?

Regards,
Christian