Re: [PATCH v2] crypto: memzero_explicit - make sure to clear out sensitive data

[Hannes Frederic Sowa <hannes@stressinduktion.org>]

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?

> 
> Therefore, make use of the drop-in replacement memzero_explicit() for
> exactly such cases instead of using memset().
> 
> Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
> Cc: Julia Lawall <julia.lawall@lip6.fr>
> Cc: Herbert Xu <herbert@gondor.apana.org.au>
> Cc: Theodore Ts'o <tytso@mit.edu>
> Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>

Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org

Thanks,
Hannes