linux-kernel - Re: [PATCH] random: mix in architectural randomness in extract

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Message-ID: <5013530D.5080001@zytor.com>
Date:	Fri, 27 Jul 2012 19:48:45 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	"Theodore Ts'o" <tytso@....edu>, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>, w@....edu, ewust@...ch.edu,
	zakir@...ch.edu, greg@...ah.com, mpm@...enic.com,
	nadiah@...ucsd.edu, jhalderm@...ch.edu, tglx@...utronix.de,
	davem@...emloft.net, stable@...r.kernel.org,
	DJ Johnston <dj.johnston@...el.com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>
Subject: Re: [PATCH] random: mix in architectural randomness in extract_buf()

On 07/27/2012 07:39 PM, Theodore Ts'o wrote:
> Ok, I'll add this patch to the random tree.  I've modified the commit
> message a bit since the speed advertisement of RDRAND is rather
> pointless --- processes aren't generating session keys or long term
> keys at a high rate, and programs can't count on /dev/random being
> super fast and having unlimited entropy, since for most platforms and
> even most x86 CPU's deployed in service today, this isn't true --- and
> making your userspace program depond upon /dev/random in such a way
> that it only works on Ivy Bridge CPU's might be good for Intel from a
> vendor lock-in perspective, but it's really bad, non-portable
> programming style.
>
> Also, in the future arch_get_random_long() will almost certainly be
> hooked up for other architectures, so putting an extended
> advertisement for RDRAND really isn't appropriate.

Thanks.  /dev/random vs /dev/urandom is orthogonal to this; as you note 
we still haven't changed the entropy accounting.  I am thinking that 
that is probably better left to rngd at least until RDSEED is available 
(or the equivalent on other hardware.)

	-hpa


-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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