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

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Message-ID: <CALCETrUe_pFgn27HP4JQ7XpUVJJJoj1PXU5PnznRCEY7mCaaWg@mail.gmail.com>
Date:	Thu, 1 May 2014 15:32:02 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	"Theodore Ts'o" <tytso@....edu>,
	Andy Lutomirski <luto@...capital.net>,
	"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 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.

--Andy
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