linux-kernel - Re: [PATCH 0/4] random,x86,kvm: Add and use MSR_KVM_GET_RNG

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Message-ID: <20140716072315.GW18167@minantech.com>
Date:	Wed, 16 Jul 2014 10:23:16 +0300
From:	Gleb Natapov <gleb@...nel.org>
To:	Daniel Borkmann <dborkman@...hat.com>
Cc:	Andy Lutomirski <luto@...capital.net>, kvm@...r.kernel.org,
	"H. Peter Anvin" <hpa@...or.com>, Theodore Ts'o <tytso@....edu>,
	linux-kernel@...r.kernel.org, Kees Cook <keescook@...omium.org>,
	x86@...nel.org, Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
Subject: Re: [PATCH 0/4] random,x86,kvm: Add and use MSR_KVM_GET_RNG_SEED

On Wed, Jul 16, 2014 at 09:10:27AM +0200, Daniel Borkmann wrote:
> On 07/16/2014 08:41 AM, Gleb Natapov wrote:
> >On Tue, Jul 15, 2014 at 07:48:06PM -0700, Andy Lutomirski wrote:
> >>virtio-rng is both too complicated and insufficient for initial rng
> >>seeding.  It's far too complicated to use for KASLR or any other
> >>early boot random number needs.  It also provides /dev/random-style
> >>bits, which means that making guest boot wait for virtio-rng is
> >>unacceptably slow, and doing it asynchronously means that
> >>/dev/urandom might be predictable when userspace starts.
> >>
> >>This introduces a very simple synchronous mechanism to get
> >>/dev/urandom-style bits.
> >
> >Why can't you use RDRAND instruction for that?
> 
> You mean using it directly? I think simply for the very same reasons
> as in c2557a303a ...
So you trust your hypervisor vendor more than you trust your CPU vendor? :)

--
			Gleb.
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