linux-kernel - Re: [PATCH] random: add and use memzero

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Date:	Mon, 1 Dec 2014 13:27:39 +0300
From:	Dan Carpenter <dan.carpenter@...cle.com>
To:	Daniel Borkmann <dborkman@...hat.com>
Cc:	tytso@....edu, zatimend@...mail.co.uk,
	linux-kernel@...r.kernel.org,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Kees Cook <keescook@...omium.org>,
	Julia Lawall <julia.lawall@...6.fr>
Subject: Re: [PATCH] random: add and use memzero_explicit() for clearing data

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
> 

What???

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
drivers.

regards,
dan carpnter

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