[PATCH v3 2/7] crypto: aead - disallow en/decrypt for non-task or non-softirq context

[Eric Biggers]

On Wed, May 12, 2021 at 08:44:34PM +0200, Ard Biesheuvel wrote:
> In order to ensure that kernel mode SIMD routines will not need a scalar
> fallback if they run with softirqs disabled, disallow any use of the
> AEAD encrypt and decrypt routines from outside of task or softirq context.
> 
> Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
> ---
>  crypto/aead.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/crypto/aead.c b/crypto/aead.c
> index 16991095270d..b5304b3d3314 100644
> --- a/crypto/aead.c
> +++ b/crypto/aead.c
> @@ -87,6 +87,11 @@ int crypto_aead_encrypt(struct aead_request *req)
>  	unsigned int cryptlen = req->cryptlen;
>  	int ret;
>  
> +	if (!(alg->cra_flags & CRYPTO_ALG_ASYNC) &&
> +	    WARN_ONCE(!in_task() && !in_serving_softirq(),
> +		      "synchronous call from invalid context\n"))
> +		return -EBUSY;
> +
>  	crypto_stats_get(alg);
>  	if (crypto_aead_get_flags(aead) & CRYPTO_TFM_NEED_KEY)
>  		ret = -ENOKEY;
> @@ -104,6 +109,11 @@ int crypto_aead_decrypt(struct aead_request *req)
>  	unsigned int cryptlen = req->cryptlen;
>  	int ret;
>  
> +	if (!(alg->cra_flags & CRYPTO_ALG_ASYNC) &&
> +	    WARN_ONCE(!in_task() && !in_serving_softirq(),
> +		      "synchronous call from invalid context\n"))
> +		return -EBUSY;
> +
>  	crypto_stats_get(alg);
>  	if (crypto_aead_get_flags(aead) & CRYPTO_TFM_NEED_KEY)
>  		ret = -ENOKEY;

This probably should go after crypto_stats_get() so that the error gets counted
in the stats (if stats are enabled) -- analogous to how the ENOKEY error is
counted.

Likewise for the skcipher patch.

- Eric