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Date: Tue, 26 Jun 2018 21:54:53 +0100
From: David CARLIER <devnexen@...il.com>
To: musl@...ts.openwall.com
Subject: Re: [PATCH] proposal adding explicit_bzero

Sure I do agree. Thanks.

On Tue, 26 Jun 2018 at 21:53, Rich Felker <dalias@...c.org> wrote:

> On Tue, Jun 26, 2018 at 09:48:47PM +0100, David CARLIER wrote:
> > Yes true sorry :-|.
>
> No problem. Do you agree with my proposed fix and want me to make that
> change and apply it?
>
> Rich
>
>
> > On Tue, 26 Jun 2018 at 21:43, Rich Felker <dalias@...c.org> wrote:
> >
> > > On Fri, Jun 15, 2018 at 01:37:43PM +0000, David CARLIER wrote:
> > > > Hi dear lists,
> > > > this is my first message so forgive me if this idea had already been
> > > rejected.
> > >
> > > It's definitely not rejected outright, and I think the consensus is
> > > to adopt it. But..
> > >
> > > > From c0a16cf96b96b009097d6ed656a2a7b8969e8399 Mon Sep 17 00:00:00
> 2001
> > > > From: David Carlier <dcarlier@...lias.info>
> > > > Date: Fri, 15 Jun 2018 13:30:09 +0000
> > > > Subject: [PATCH] string: adding simple explicit_bzero implementation.
> > > >
> > > > glibc implementing it and modern security based code starting
> > > > using it widely, here a simple implementation using memory barrier.
> > > > ---
> > > >  include/string.h            | 1 +
> > > >  src/string/explicit_bzero.c | 8 ++++++++
> > > >  2 files changed, 9 insertions(+)
> > > >  create mode 100644 src/string/explicit_bzero.c
> > > >
> > > > diff --git a/include/string.h b/include/string.h
> > > > index ce1dc300..795a2abc 100644
> > > > --- a/include/string.h
> > > > +++ b/include/string.h
> > > > @@ -82,6 +82,7 @@ void *memccpy (void *__restrict, const void
> > > *__restrict, int, size_t);
> > > >  char *strsep(char **, const char *);
> > > >  size_t strlcat (char *, const char *, size_t);
> > > >  size_t strlcpy (char *, const char *, size_t);
> > > > +void explicit_bzero (void *, size_t);
> > > >  #endif
> > > >
> > > >  #ifdef _GNU_SOURCE
> > > > diff --git a/src/string/explicit_bzero.c
> b/src/string/explicit_bzero.c
> > > > new file mode 100644
> > > > index 00000000..47dba3c7
> > > > --- /dev/null
> > > > +++ b/src/string/explicit_bzero.c
> > > > @@ -0,0 +1,8 @@
> > > > +#define _BSD_SOURCE
> > > > +#include <string.h>
> > > > +
> > > > +void explicit_bzero(void *d, size_t n)
> > > > +{
> > > > +     memset(d, 0, n);
> > > > +     __asm__ volatile("": "r="(d) :: "memory");
> > > > +}
> > > > --
> > >
> > > The constraint here looks wrong. Normally = is written before the
> > > type, not after; I'm not sure if all compiler versions accept the
> > > unusual form with it after. But more importantly you have it as an
> > > output constraint, where it's essentially a dead store, such that the
> > > asm block does nothing to make explicit_bzero force the memset to
> > > happen.
> > >
> > > I think you meant for the constraint to be an input constraint "r"(d).
> > > Does that sound right?
> > >
> > > Rich
> > >
>

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