linux-kernel - Re: [BUG/PATCH] kernel RNG and its secrets

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Date:	Mon, 27 Apr 2015 21:10:14 +0200
From:	Stephan Mueller <smueller@...onox.de>
To:	Daniel Borkmann <daniel@...earbox.net>
Cc:	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	mancha <mancha1@...o.com>, tytso@....edu,
	linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
	herbert@...dor.apana.org.au, dborkman@...hat.com
Subject: Re: [BUG/PATCH] kernel RNG and its secrets

Am Freitag, 10. April 2015, 16:50:22 schrieb Stephan Mueller:

Hi Stephan,

>Am Freitag, 10. April 2015, 16:46:04 schrieb Daniel Borkmann:
>
>Hi Daniel,
>
>>On 04/10/2015 04:36 PM, Stephan Mueller wrote:
>>> Am Freitag, 10. April 2015, 16:26:00 schrieb Hannes Frederic Sowa:
>>...
>>
>>>> I suspected a problem in how volatile with non-present output args could
>>>> be different, but this seems not to be the case.
>>>> 
>>>> I would contact llvm/clang mailing list and ask. Maybe there is a
>>>> problem? It seems kind of strange to me...
>>
>>+1
>>
>>> Do you really think this is a compiler issue?
>>
>>If clang/LLVM advertises "GCC compatibility", then this would
>>certainly be a different behavior.
>
>As you wish. I will contact the clang folks. As the proposed fix is not super
>urgend, I think we can leave it until I got word from clang.

I posted the issue on the clang mailing list on April 10 -- no word so far. I 
would interpret this as a sign that it is a no-issue for them.

Thus, I propose we update our memzero_explicit implementation to use

__asm__ __volatile__("" : "=r" (s) : "0" (s) : "memory");

Concerns?

Ciao
Stephan
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