linux-kernel - Re: [RFC/PATCH 0/3] Add devicetree scanning for randomness

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Date:	Mon, 17 Feb 2014 15:54:19 +0000
From:	Grant Likely <grant.likely@...aro.org>
To:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	Jason Cooper <jason@...edaemon.net>
Cc:	Arnd Bergmann <arnd@...db.de>, keescook@...omium.org,
	devicetree@...r.kernel.org, Laura Abbott <lauraa@...eaurora.org>,
	linux-kernel@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
	Kumar Gala <galak@...eaurora.org>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC/PATCH 0/3] Add devicetree scanning for randomness

On Wed, 12 Feb 2014 11:20:00 -0700, Jason Gunthorpe <jgunthorpe@...idianresearch.com> wrote:
> On Wed, Feb 12, 2014 at 12:45:54PM -0500, Jason Cooper wrote:
> 
> > The bootloader would then load this file into ram, and pass the
> > address/size to the kernel either via dt, or commandline.  kaslr (run in
> > the decompressor) would consume some of this randomness, and then
> > random.c would consume the rest in a non-crediting initialization.
> 
> Sure is a neat idea, but I think in general it would probably be smart
> to include the entire FDT blob in the early random pool, that way you
> get MACs and other machine unique data too.

I applied a patch that did exactly that (109b623629), and then reverted
it (b920ecc82) shortly thereafter because add_device_randomness() is
a rather slow function and FDTs can get large. I'd like to see someone
do a reasonable analysis on the cost of using an FDT for randomness
before I reapply a patch doing something similar. An awful lot of the
FDT data is not very random, but there are certainly portions of it that
are appropriate for the random pool.

g.
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