Re: [PATCH] random: add and use memzero_explicit() for clearing data

From: Daniel Borkmann
Date: Mon Dec 01 2014 - 06:05:29 EST

On 12/01/2014 11:27 AM, Dan Carpenter wrote:
On Mon, Aug 25, 2014 at 10:01:39PM +0200, Daniel Borkmann wrote:
zatimend has reported that in his environment (3.16/gcc4.8.3/corei7)
memset() calls which clear out sensitive data in extract_{buf,entropy,
entropy_user}() in random driver are being optimized away by gcc.

Add a helper memzero_explicit() (similarly as explicit_bzero() variants)
that can be used in such cases where a variable with sensitive data is
being cleared out in the end. Other use cases might also be in crypto
code. [ I have put this into lib/string.c though, as it's always built-in
and doesn't need any dependencies then. ]

Fixes kernel bugzilla: 82041


That's not ok. We totally rely on memset to work. Every single memset
that I have added was absolutely necessary. This should be fixed
so that memset works instead of adding a work around for specific

Well, BSD has helpers such as bzero_explicit() for such cases to work
around this, which memzero_explicit() similarly does; see also [1].

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at