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

From: Pekka Enberg
Date: Tue May 17 2011 - 07:49:25 EST

On Tue, May 17, 2011 at 2:47 PM, Avi Kivity <avi@xxxxxxxxxx> 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.

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