linux-kernel - Re: [PATCH v4 0/5] /dev/random

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Date:	Tue, 21 Jun 2016 15:19:56 +0200
From:	Tomas Mraz <tmraz@...hat.com>
To:	"Austin S. Hemmelgarn" <ahferroin7@...il.com>,
	Stephan Mueller <smueller@...onox.de>
Cc:	"Theodore Ts'o" <tytso@....edu>,
	David Jaša <djasa@...hat.com>,
	Andi Kleen <andi@...stfloor.org>, sandyinchina@...il.com,
	Jason Cooper <cryptography@...edaemon.net>,
	John Denker <jsd@...n.com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Joe Perches <joe@...ches.com>, Pavel Machek <pavel@....cz>,
	George Spelvin <linux@...izon.com>,
	linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 0/5] /dev/random - a new approach

On Út, 2016-06-21 at 09:05 -0400, Austin S. Hemmelgarn wrote:
> On 2016-06-20 14:32, Stephan Mueller wrote:
> > 
> > [1] http://www.chronox.de/jent/doc/CPU-Jitter-NPTRNG.pdf
> Specific things I notice about this:
> 1. QEMU systems are reporting higher values than almost anything
> else 
> with the same ISA.  This makes sense, but you don't appear to have 
> accounted for the fact that you can't trust almost any of the entropy
> in 
> a VM unless you have absolute trust in the host system, because the
> host 
> system can do whatever the hell it wants to you, including
> manipulating 
> timings directly (with a little patience and some time spent working
> on 
> it, you could probably get those number to show whatever you want
> just 
> by manipulating scheduling parameters on the host OS for the VM
> software).

You have to trust the host for anything, not just for the entropy in
timings. This is completely invalid argument unless you can present a
method that one guest can manipulate timings in other guest in such a
way that _removes_ the inherent entropy from the host.

-- 
Tomas Mraz
No matter how far down the wrong road you've gone, turn back.
                                              Turkish proverb
(You'll never know whether the road is wrong though.)