Re: [PATCH 10/12] crypto: qat - use memzero_explicit() for algs

[Greg KH <gregkh@linuxfoundation.org>]

On Fri, May 06, 2022 at 09:23:25AM +0100, Giovanni Cabiddu wrote:
> Use memzero_explicit(), instead of a memset(.., 0, ..) in the
> implementation of the algorithms, for buffers containing sensitive
> information to ensure they are wiped out before free.
> 
> Cc: stable@vger.kernel.org
> Signed-off-by: Giovanni Cabiddu <giovanni.cabiddu@intel.com>
> Reviewed-by: Adam Guerin <adam.guerin@intel.com>
> Reviewed-by: Wojciech Ziemba <wojciech.ziemba@intel.com>
> ---
>  drivers/crypto/qat/qat_common/qat_algs.c      | 20 +++++++++----------
>  drivers/crypto/qat/qat_common/qat_asym_algs.c | 20 +++++++++----------
>  2 files changed, 20 insertions(+), 20 deletions(-)
> 
> diff --git a/drivers/crypto/qat/qat_common/qat_algs.c b/drivers/crypto/qat/qat_common/qat_algs.c
> index 873533dc43a7..c42df18e02b2 100644
> --- a/drivers/crypto/qat/qat_common/qat_algs.c
> +++ b/drivers/crypto/qat/qat_common/qat_algs.c
> @@ -637,12 +637,12 @@ static int qat_alg_aead_newkey(struct crypto_aead *tfm, const u8 *key,
>  	return 0;
>  
>  out_free_all:
> -	memset(ctx->dec_cd, 0, sizeof(struct qat_alg_cd));
> +	memzero_explicit(ctx->dec_cd, sizeof(struct qat_alg_cd));

This is for structure fields, why does memset() not work properly here?
The compiler should always call this, it doesn't know what
dma_free_coherent() does.  You are referencing this pointer after the
memset() call so all should be working as intended here.

Because of this, I don't see why this change is needed.  Do you have
reports of compilers not calling memset() for all of this properly?

thanks,

greg k-h