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Date:   Tue, 17 Mar 2020 22:17:43 +0000
From:   Will Deacon <will@kernel.org>
To:     Torsten Duwe <duwe@lst.de>
Cc:     Catalin Marinas <catalin.marinas@arm.com>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        "David S. Miller" <davem@davemloft.net>,
        Russell King <linux@armlinux.org.uk>,
        linux-crypto@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-kernel@vger.kernel.org, ardb@kernel.org
Subject: Re: [Patch][Fix] crypto: arm{,64} neon: memzero_explicit aes-cbc key
Message-ID: <20200317221743.GD20788@willie-the-truck>
References: <20200313110258.94A0668C4E@verein.lst.de>
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[+Ard]

On Fri, Mar 13, 2020 at 12:02:58PM +0100, Torsten Duwe wrote:
> From: Torsten Duwe <duwe@suse.de>
> 
> At function exit, do not leave the expanded key in the rk struct
> which got allocated on the stack.
> 
> Signed-off-by: Torsten Duwe <duwe@suse.de>
> ---
> Another small fix from our FIPS evaluation. I hope you don't mind I merged
> arm32 and arm64 into one patch -- this is really simple.
> --- a/arch/arm/crypto/aes-neonbs-glue.c
> +++ b/arch/arm/crypto/aes-neonbs-glue.c
> @@ -138,6 +138,7 @@ static int aesbs_cbc_setkey(struct crypto_skcipher *tfm, const u8 *in_key,
>  	kernel_neon_begin();
>  	aesbs_convert_key(ctx->key.rk, rk.key_enc, ctx->key.rounds);
>  	kernel_neon_end();
> +	memzero_explicit(&rk, sizeof(rk));
>  
>  	return crypto_cipher_setkey(ctx->enc_tfm, in_key, key_len);
>  }
> diff --git a/arch/arm64/crypto/aes-neonbs-glue.c b/arch/arm64/crypto/aes-neonbs-glue.c
> index e3e27349a9fe..c0b980503643 100644
> --- a/arch/arm64/crypto/aes-neonbs-glue.c
> +++ b/arch/arm64/crypto/aes-neonbs-glue.c
> @@ -151,6 +151,7 @@ static int aesbs_cbc_setkey(struct crypto_skcipher *tfm, const u8 *in_key,
>  	kernel_neon_begin();
>  	aesbs_convert_key(ctx->key.rk, rk.key_enc, ctx->key.rounds);
>  	kernel_neon_end();
> +	memzero_explicit(&rk, sizeof(rk));
>  
>  	return 0;
>  }

I'm certainly not a crypto person, but this looks sensible to me and I
couldn't find any other similar stack variable usage under
arch/arm64/crypto/ at a quick glance.

Acked-by: Will Deacon <will@kernel.org>

Will