linux-kernel - Re: [PATCH 1/8] Replace memset() with memzero

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Message-ID: <YZOpl5mVVcG/s9w1@kroah.com>
Date:   Tue, 16 Nov 2021 13:52:39 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Sandy Harris <sandyinchina@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Herbert Xu <herbert@...dor.apana.org.au>
Subject: Re: [PATCH 1/8] Replace memset() with memzero_explicit()

On Tue, Nov 16, 2021 at 12:50:58PM +0100, Greg Kroah-Hartman wrote:
> On Tue, Nov 16, 2021 at 07:25:22PM +0800, Sandy Harris wrote:
> > Replace memset(address,0,bytes) which may be optimised away
> > with memzero_explicit(address,bytes) which resists
> > such optimisation
> > 
> > ---
> >  crypto/des_generic.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/crypto/des_generic.c b/crypto/des_generic.c
> > index c85354a5e94c..105a32e7afea 100644
> > --- a/crypto/des_generic.c
> > +++ b/crypto/des_generic.c
> > @@ -30,7 +30,7 @@ static int des_setkey(struct crypto_tfm *tfm, const u8 *key,
> >              err = 0;
> >      }
> >      if (err)
> > -        memset(dctx, 0, sizeof(*dctx));
> > +        memzero_explicit(dctx, sizeof(*dctx));
> >      return err;
> >  }
> > 
> > @@ -62,7 +62,7 @@ static int des3_ede_setkey(struct crypto_tfm *tfm,
> > const u8 *key,
> >              err = 0;
> >      }
> >      if (err)
> > -        memset(dctx, 0, sizeof(*dctx));
> > +        memzero_explicit(dctx, sizeof(*dctx));
> >      return err;
> >  }
> > 
> 
> Have you looked at the output of the compiler to see if this really is
> needed or not?

Oh wait, that's not a stack variable, how would this be optimized away
at all?  If it is, that's a HUGE compiler bug.

Is that really happening here?

thanks,

greg k-h