linux-kernel - Re: [PATCH 1/2] Initial support for Allwinner's Security ID fuses

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Message-ID: <519DCEE9.6070208@schinagl.nl>
Date:	Thu, 23 May 2013 10:10:17 +0200
From:	Oliver Schinagl <oliver+list@...inagl.nl>
To:	Linus Walleij <linus.walleij@...aro.org>
CC:	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Arnd Bergmann <arnd@...b.de>,
	Greg KH <gregkh@...uxfoundation.org>,
	Oliver Schinagl <oliver@...inagl.nl>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/2] Initial support for Allwinner's Security ID fuses

On 05/23/13 09:56, Linus Walleij wrote:
> On Fri, May 17, 2013 at 3:35 PM, Oliver Schinagl
> <oliver+list@...inagl.nl> wrote:
>
> (...)
>> While initially these fuses are used to somewhat determin the chipID, these
>> appear to be writeable by the user and thus can be used for other purpouses.
>> For example storing a 128 bit root key, a unique serial number, which could
>> then even be used as a MAC address.
> (...)
> Then follows some code to read out the keys from sysfs I guess..
>> +static int __init sid_probe(struct platform_device *pdev)
>
> It's really simple to actually make the kernel use this to seed the
> entropy pool.
>
> #include <linux/random.h>
> add_device_randomness(u8 *, num);
>
> If you know after probe that you can read out a number of bytes
> of device-unique data, I think you should add those bytes to the
> entropy pool like this.
While that is a great idea, we can't guarantee device uniqueness. We've 
already seen some chips that where 'forgotten' to program and default 
set to all 0. I guess that doesn't have to be a bad thing.

Then, i'm not sure if the driver is the best for this to be loaded? 
Maxime, what do you think? Personally I would feel more in having this 
in the mach-sunxi/core.c bit, but then again, this is currently a module 
and wouldn't be useful to have there. Maxime is far more knowledgeable 
to answer that.

It should probably be noted, that the sunxi series have a hardware 
crypto engine, with hardware random seed generator, one for a later project.
>
> Yours,
> Linus Walleij
>

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