linux-kernel - Re: random: Providing a seed value to VM guests

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Message-ID: <20140501203910.GB25829@thunk.org>
Date:	Thu, 1 May 2014 20:39:10 +0000
From:	tytso@....edu
To:	Andy Lutomirski <luto@...capital.net>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	kvm list <kvm@...r.kernel.org>,
	Florian Weimer <fweimer@...hat.com>,
	Kees Cook <kees@...flux.net>
Subject: Re: random: Providing a seed value to VM guests

On Thu, May 01, 2014 at 01:32:55PM -0700, Andy Lutomirski wrote:
> On Thu, May 1, 2014 at 1:30 PM, H. Peter Anvin <hpa@...or.com> wrote:
> > RDSEED is not synchronous.  It is, however, nonblocking.
> 
> What I mean is: IIUC it's reasonable to call RDSEED a few times in a
> loop and hope it works.  It makes no sense to do that with
> /dev/random.

RDSEED is allowed to return an error if there is insufficient entropy.
So long as the caller understands that this is an emulated
instruction, I don't see a problem.

						- Ted
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