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

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Date:	Tue, 17 May 2011 14:49:20 +0300
From:	Pekka Enberg <penberg@...nel.org>
To:	Avi Kivity <avi@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>, "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

On Tue, May 17, 2011 at 2:47 PM, Avi Kivity <avi@...hat.com> wrote:
> On 05/17/2011 02:44 PM, Avi Kivity wrote:
>>
>> On 05/17/2011 02:38 PM, Ingo Molnar wrote:
>>>
>>> >
>>> >  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?
>>
>> Yes.
>>
>
> btw, KVM support is required anyway, you can't set random bits in cr4 (from
> either the guest or host userspace) - kvm needs to understand them.

Yeah, I was wondering how the CR4 hack would actually enable
something. :-) Please CC me if you do add such an ioctl() and we'll
make the native KVM tool use it by default.

                        Pekka
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