linux-kernel - Re: [PATCH v2 0/4] Enable SMEP CPU Feature

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Date:	Tue, 17 May 2011 13:38:51 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Avi Kivity <avi@...hat.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Fenghua Yu <fenghua.yu@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Asit K Mallick <asit.k.mallick@...el.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Pekka Enberg <penberg@...helsinki.fi>
Subject: Re: [PATCH v2 0/4] Enable SMEP CPU Feature


* Avi Kivity <avi@...hat.com> wrote:

> On 05/17/2011 01:46 PM, Ingo Molnar wrote:
> >>
> >>  We could support it as a non-default feature, but that reduces its utility.
> >
> >It would be a nice touch for tools/kvm/: we would use KVM_GET_SREGS and
> >KVM_GET_SREGS to twiddle CR4.SMEP, even without the guest explicitly doing it.
> >
> >A quick glance suggests that it could be done straight away in
> >tools/kvm/kvm-cpu.c::kvm_cpu__setup_sregs() during vcpu setup, and hopefully
> >that cr4 value survives boot and ends up in the guest kernel's mmu_cr4_features
> >mask shadow register.
> 
> Depends if the guest uses a read-modify-write pattern or not.  We could do it 
> transparently in kvm.ko, since the real cr4 need not corresponds to the guest 
> notion (for example, we often set cr0.wp or cr0.ts even though the guest 
> wants them clear).

Oh, being transparent is a nice touch when it comes to security measures 
(catching attackers who think there's no SMEP and such) - but that would need 
KVM support and a new ioctl to configure it, right?

Thanks,

	Ingo
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