Re: [PATCH 07/12] crypto: qat - set to zero DH parameters before free

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

On Fri, May 06, 2022 at 11:23:50AM +0200, Greg KH wrote:
> On Fri, May 06, 2022 at 09:23:22AM +0100, Giovanni Cabiddu wrote:
> > Set to zero the DH context buffers containing the DH key before they are
> > freed.
> 
> That says what, but not why.
> 
> > Cc: stable@vger.kernel.org
> > Fixes: c9839143ebbf ("crypto: qat - Add DH support")
> > 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_asym_algs.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/drivers/crypto/qat/qat_common/qat_asym_algs.c b/drivers/crypto/qat/qat_common/qat_asym_algs.c
> > index d75eb77c9fb9..2fec89b8a188 100644
> > --- a/drivers/crypto/qat/qat_common/qat_asym_algs.c
> > +++ b/drivers/crypto/qat/qat_common/qat_asym_algs.c
> > @@ -421,14 +421,17 @@ static int qat_dh_set_params(struct qat_dh_ctx *ctx, struct dh *params)
> >  static void qat_dh_clear_ctx(struct device *dev, struct qat_dh_ctx *ctx)
> >  {
> >  	if (ctx->g) {
> > +		memzero_explicit(ctx->g, ctx->p_size);
> >  		dma_free_coherent(dev, ctx->p_size, ctx->g, ctx->dma_g);
> 
> Why is a memset() not sufficient here?
Based on the previous conversation a memset() should be sufficient.

> And what is this solving?  Who would get this stale data?
This is to make sure the buffer containing sensitive data (i.e. a key)
is not leaked out by a subsequent allocation.
I will clarify it in the commit message.

Thanks,

-- 
Giovanni