linux-kernel - Re: [PATCH] nvmem: sunxi-sid: SID content is not a valid source of randomness

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Date:   Fri, 28 Oct 2016 14:37:20 +0200
From:   LABBE Corentin <clabbe.montjoie@...il.com>
To:     Jean-Francois Moine <moinejf@...e.fr>
Cc:     Maxime Ripard <maxime.ripard@...e-electrons.com>, wens@...e.org,
        srinivas.kandagatla@...aro.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-crypto@...r.kernel.org
Subject: Re: [PATCH] nvmem: sunxi-sid: SID content is not a valid source of
 randomness

On Tue, Oct 25, 2016 at 09:06:34AM +0200, Jean-Francois Moine wrote:
> On Tue, 25 Oct 2016 07:38:55 +0200
> LABBE Corentin <clabbe.montjoie@...il.com> wrote:
> 
> > > On Sat, Oct 22, 2016 at 03:53:28PM +0200, Corentin Labbe wrote:
> > > > Since SID's content is constant over reboot,
> > > 
> > > That's not true, at least not across all the Allwinner SoCs, and
> > > especially not on the A10 and A20 that this driver supports.
> > > 
> > 
> > On my cubieboard2 (A20)
> > hexdump -C /sys/devices/platform/soc\@01c00000/1c23800.eeprom/sunxi-sid0/nvmem 
> > 00000000  16 51 66 83 80 48 50 72  56 54 48 48 03 c2 75 72  |.Qf..HPrVTHH..ur|
> > 00000010  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
> > *
> > 00000100  16 51 66 83 80 48 50 72  56 54 48 48 03 c2 75 72  |.Qf..HPrVTHH..ur|
> > 00000110  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
> > *
> > 00000200
> > cubiedev ~ # reboot
> > cubiedev ~ # hexdump -C /sys/devices/platform/soc\@01c00000/1c23800.eeprom/sunxi-sid0/nvmem 
> > 00000000  16 51 66 83 80 48 50 72  56 54 48 48 03 c2 75 72  |.Qf..HPrVTHH..ur|
> > 00000010  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
> > *
> > 00000100  16 51 66 83 80 48 50 72  56 54 48 48 03 c2 75 72  |.Qf..HPrVTHH..ur|
> > 00000110  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
> > *
> > 00000200
> > 
> > So clearly for me its constant.
> 
> Even after power off/power on?

Yes, even after remove of any power supply.