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

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Message-ID: <20140212185156.GP27395@titan.lakedaemon.net>
Date:	Wed, 12 Feb 2014 13:51:56 -0500
From:	Jason Cooper <jason@...edaemon.net>
To:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc:	devicetree@...r.kernel.org, Laura Abbott <lauraa@...eaurora.org>,
	keescook@...omium.org, Arnd Bergmann <arnd@...db.de>,
	linux-kernel@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
	Kumar Gala <galak@...eaurora.org>,
	Grant Likely <grant.likely@...aro.org>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [RFC/PATCH 0/3] Add devicetree scanning for randomness

On Wed, Feb 12, 2014 at 11:20:00AM -0700, Jason Gunthorpe 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.

Sure.

> From there it is a small step to encourage bootloaders to include
> boot-time-variable data in the DT like like 'boot time of day', 'cycle
> counter', 'random blob', etc.

I like it.

> Then you just need the bootloader to dump the random-seed file into a
> DT property.

Yes, see my response to Arnd re the binding.  I'm also interested in
making it easier for devices already in the field.  iow, without
upgrading the bootloader.

> Or have the bootloader fetch randomness from any HWRNG it has a driver
> for. (eg a TPM)

Depends on who you're protecting against.  I'd prefer to have that
called out as a separate blob in the DT so the kernel could decide
whether to trust it explicitly, or mix it like random.c already does
with RDRAND.

thx,

Jason.
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