Re: [Patch][Fix] crypto: arm{,64} neon: memzero_explicit aes-cbc key

[Will Deacon]

[+Ard]

On Fri, Mar 13, 2020 at 12:02:58PM +0100, Torsten Duwe wrote:
> From: Torsten Duwe <duwe@xxxxxxx>
> 
> 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@xxxxxxx>
> ---
> 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@xxxxxxxxxx>

Will