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

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Message-ID: <5362998D.3030102@zytor.com>
Date:	Thu, 01 May 2014 11:59:25 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andy Lutomirski <luto@...capital.net>,
	"Theodore Ts'o" <tytso@....edu>,
	Florian Weimer <fweimer@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Kees Cook <kees@...flux.net>, kvm list <kvm@...r.kernel.org>
Subject: random: Providing a seed value to VM guests

On 05/01/2014 11:53 AM, Andy Lutomirski wrote:
> 
> A CPUID leaf or an MSR advertised by a CPUID leaf has another
> advantage: it's easy to use in the ASLR code -- I don't think there's
> a real IDT, so there's nothing like rdmsr_safe available.  It also
> avoids doing anything complicated with the boot process to allow the
> same seed to be used for ASLR and random.c; it can just be invoked
> twice on boot.
> 

At that point we are talking an x86-specific interface, and so we might
as well simply emulate RDRAND (urandom) and RDSEED (random) if the CPU
doesn't support them.  I believe KVM already has a way to report CPUID
features that are "emulated but supported anyway", i.e. they work but
are slow.

> What's the right forum for this?  This thread is probably not it.

Change the subject line?

	-hpa


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