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

[Giovanni Cabiddu <giovanni.cabiddu@intel.com>]

On Fri, May 06, 2022 at 11:22:39AM +0200, Greg KH wrote:
> 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?
Apologies, I had a wrong assumption.
Based on a comment in the memzero_explicit() documentation I assumed it
should be always used to zero sensitive data.

     * memzero_explicit - Fill a region of memory (e.g. sensitive
     *			  keying data) with 0s.

I'm going to drop this patch.

Thanks,

-- 
Giovanni