linux-kernel - Re: [PATCH v2] RANDOM: ATH9K RNG delivers zero bits of entropy

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Date:	Mon, 8 Aug 2016 22:04:52 +0000
From:	Jason Cooper <jason@...edaemon.net>
To:	Stephan Mueller <smueller@...onox.de>
Cc:	"Pan, Miaoqing" <miaoqing@....qualcomm.com>,
	Ted Tso <tytso@....edu>,
	"Sepehrdad, Pouyan" <pouyans@....qualcomm.com>,
	"herbert@...dor.apana.org.au" <herbert@...dor.apana.org.au>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
	ath9k-devel <ath9k-devel@....qualcomm.com>,
	"linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
	"ath9k-devel@...ts.ath9k.org" <ath9k-devel@...ts.ath9k.org>,
	Kalle Valo <kvalo@...eaurora.org>
Subject: Re: [PATCH v2] RANDOM: ATH9K RNG delivers zero bits of entropy

Hi Stephan,

On Mon, Aug 08, 2016 at 05:29:30PM +0000, Jason Cooper wrote:
> On Mon, Aug 08, 2016 at 08:41:36AM +0200, Stephan Mueller wrote:
...
> > If you think that this patch is a challenge because your driver starts to 
> > spin, please help and offer another solution.
> 
> Well, I don't buy the reasoning listed above for not using the hwrng
> framework.  Interrupt timings were never designed to be a source of entropy
> either.  We need to grab it where ever we can find it, especially on
> embedded systems.  Documentation/hw_random.txt even says:
> 
> """
> This data is NOT CHECKED by any fitness tests, and could potentially be
> bogus (if the hardware is faulty or has been tampered with).
> """
> 
> I really don't think there's a problem with adding these sorts of
> sources under char/hw_random/.  I think the only thing we would be
> concerned about, other than the already addressed entropy estimation,
> would be constraining the data rate.

Further research yields char/hw_random/timeriomem-rng.c

It could use an update to ->read() vice data_{present,read}(), but it's
functionally exactly what the ath9k rng is doing. :)

thx,

Jason.