Re: [PATCH 2/4] iio: magnetometer: ak8974: add_device_randomness(fw + serial)

[Jonathan Cameron <jic23@kernel.org>]

On Sun, 20 Aug 2017 13:10:58 +0200
Linus Walleij <linus.walleij@linaro.org> wrote:

> On Sun, Aug 20, 2017 at 12:22 PM, Jonathan Cameron <jic23@kernel.org> wrote:
> > On Thu, 17 Aug 2017 15:56:11 +0200
> > Michał Mirosław <mirq-linux@rere.qmqm.pl> wrote:  
> >> Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>  
> >
> > Hmm. I wondered about the firmware version as a source of randomness, but
> > will leave it in here.  
> (...)
> >> +             add_device_randomness(&fw, sizeof(fw));  
> >
> > The firmware version seems rather to guessable to really count as randomness.
> > presumably it would constant for a particular batch of chips.  
> 
> That is true, this should go, not for security reasons but because it doesn't
> add much device-unique randomness.
Dropped the fw one...

J
> 
> Nothing we add with add_device_randomness() actually affects the entropy
> pool trust, it is just icing making it - maybe - even more random, so adding
> 256 zeroes is fine for the trust, just pointless and taking time for no good.
> 
> Yours,
> Linus Walleij
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