linux-kernel - Re: [PATCH v3 00/03]: hwrng: an in-kernel rngd

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Date:	Mon, 14 Apr 2014 09:09:14 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Torsten Duwe <duwe@....de>
CC:	Andy Lutomirski <luto@...capital.net>,
	"Theodore Ts'o" <tytso@....edu>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Matt Mackall <mpm@...enic.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Arnd Bergmann <arnd@...db.de>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Satoru Takeuchi <satoru.takeuchi@...il.com>,
	ingo.tuchscherer@...ibm.com, linux-kernel@...r.kernel.org,
	Hans-Georg Markgraf <MGRF@...ibm.com>,
	Gerald Schaefer <gerald.schaefer@...ibm.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Joe Perches <joe@...ches.com>
Subject: Re: [PATCH v3 00/03]: hwrng: an in-kernel rngd

I think the default should be zero, so each hwrng driver maintainer would have to consider what guarantees that particular driver can give.  If anything 50% ought to be the maximum.

On April 14, 2014 9:02:11 AM PDT, Torsten Duwe <duwe@....de> wrote:
>More or less a resend of v2.
>
>On Wed, Mar 26, 2014 at 06:03:37PM -0700, H. Peter Anvin wrote:
>> I'm wondering more about the default.  We default to 50% for
>arch_get_random_seed, and this is supposed to be the default for in
>effect unverified hwrngs...
>
>Done. 50% is now the default, that's the only change from v2.
>
>Andy: the printk you pointed out already limits itself to 1/10s,
>which is half the default rate limit. Also, as Peter already
>wrote, we're dealing with true HWRNGs here; if such a device
>does not produce a single byte within 10 seconds something _is_
>severely broken and, like a dying disk, worth to be logged.
>Here's one of the better circuits I found:
>http://www.maximintegrated.com/app-notes/index.mvp/id/3469
>or offline:
>http://pdfserv.maximintegrated.com/en/an/AN3469.pdf
>Disclaimer: I'm not endorsing Maxim, it's just that paper
>that hits the spot IMHO.
>
>Anything wrong with feeding those bits into the input pool?
>Any other comments on the code?
>
>	Torsten

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