On Mon, 8 Sep 2014, Hannes Frederic Sowa wrote:
> On So, 2014-09-07 at 23:23 +0200, Daniel Borkmann wrote:
> > Recently, in commit 13aa93c70e71 ("random: add and use memzero_explicit()
> > for clearing data"), we have found that GCC may optimize some memset()
> > cases away when it detects a stack variable is not being used anymore
> > and going out of scope. This can happen, for example, in cases when we
> > are clearing out sensitive information such as keying material or any
> > e.g. intermediate results from crypto computations, etc.
> >
> > With the help of Coccinelle, we can figure out and fix such occurences
> > in the crypto subsytem as well. Julia Lawall provided the following
> > Coccinelle program:
> >
> > @@
> > type T;
> > identifier x;
> > @@
> >
> > T x;
> > ... when exists
> > when any
> > -memset
> > +memzero_explicit
> > (&x,
> > -0,
> > ...)
> > ... when != x
> > when strict
> >
> > @@
> > type T;
> > identifier x;
> > @@
> >
> > T x[...];
> > ... when exists
> > when any
> > -memset
> > +memzero_explicit
> > (x,
> > -0,
> > ...)
> > ... when != x
> > when strict
>
> I think this Coccinelle patch won't make it completely unnecessary for a
> manual audit as it does not take optimizations (dead code eliminitation)
> into account?
I agree. If you see something else that could be taken into account in
the semantic patch, please let me know.
julia
>
> >
> > Therefore, make use of the drop-in replacement memzero_explicit() for
> > exactly such cases instead of using memset().
> >
> > Signed-off-by: Daniel Borkmann <dborkman@xxxxxxxxxx>
> > Cc: Julia Lawall <julia.lawall@xxxxxxx>
> > Cc: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
> > Cc: Theodore Ts'o <tytso@xxxxxxx>
> > Cc: Hannes Frederic Sowa <hannes@xxxxxxxxxxxxxxxxxxx>
>
> Acked-by: Hannes Frederic Sowa <hannes@xxxxxxxxxxxxxxxxxxx
>
> Thanks,
> Hannes
>
>
>
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