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

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Date:	Mon, 27 Apr 2015 22:34:30 +0200
From:	Daniel Borkmann <daniel@...earbox.net>
To:	Stephan Mueller <smueller@...onox.de>
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

On 04/27/2015 09:10 PM, Stephan Mueller wrote:
...
> 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.

Hm. ;)

Here's a bug report on the topic, gcc vs llvm:

   https://llvm.org/bugs/show_bug.cgi?id=15495

Lets add a new barrier macro to linux/compiler{,-gcc}.h, f.e.

   #define barrier_data(ptr) __asm__ __volatile__("" : : "r" (ptr) : "memory")

or the version Mancha proposed. You could wrap that ...

   #define OPTIMIZER_HIDE(ptr)   barrier_data(ptr)

... and use that one for memzero_explicit() instead:

   void memzero_explicit(void *s, size_t count)
   {
      memset(s, 0, count);
      OPTIMIZER_HIDE(s);
   }

It certainly needs comments explaining in what situations to use
which OPTIMIZER_HIDE* variants, etc.

Do you want to send a patch?
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