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

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Message-ID: <5362CEBC.9090705@zytor.com>
Date:	Thu, 01 May 2014 15:46:20 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andy Lutomirski <luto@...capital.net>,
	"Theodore Ts'o" <tytso@....edu>,
	"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 05/01/2014 03:32 PM, Andy Lutomirski wrote:
> On Thu, May 1, 2014 at 3:28 PM,  <tytso@....edu> wrote:
>> On Thu, May 01, 2014 at 02:06:13PM -0700, Andy Lutomirski wrote:
>>>
>>> I still don't see the point.  What does this do better than virtio-rng?
>>
>> I believe you had been complaining about how complicated it was to set
>> up virtio?  And this complexity is also an issue if we want to use it
>> to initialize the RNG used for the kernel text ASLR --- which has to
>> be done very early in the boot process, and where making something as
>> simple as possible is a Good Thing.
> 
> It's complicated, so it won't be up until much later in the boot
> process.  This is completely fine for /dev/random, but it's a problem
> for /dev/urandom, ASLR, and such.
> 
>>
>> And since we would want to use RDRAND/RDSEED if it is available
>> *anyway*, perhaps in combination with other things, why not use the
>> RDRAND/RDSEED interface?
> 
> Because it's awkward.  I don't think it simplifies anything.
> 

It greatly simplifies discovery, which is a Big Deal[TM] in early code.

	-hpa


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