Re: [PATCH 4.14.y] KVM: nSVM: always intercept VMLOAD/VMSAVE when nested (CVE-2021-3656)

[Greg KH]

On Mon, Aug 16, 2021 at 04:02:36PM +0200, Paolo Bonzini wrote:
> From: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
> 
> [ upstream commit c7dfa4009965a9b2d7b329ee970eb8da0d32f0bc ]
> 
> If L1 disables VMLOAD/VMSAVE intercepts, and doesn't enable
> Virtual VMLOAD/VMSAVE (currently not supported for the nested hypervisor),
> then VMLOAD/VMSAVE must operate on the L1 physical memory, which is only
> possible by making L0 intercept these instructions.
> 
> Failure to do so allowed the nested guest to run VMLOAD/VMSAVE unintercepted,
> and thus read/write portions of the host physical memory.
> 
> Fixes: 89c8a4984fc9 ("KVM: SVM: Enable Virtual VMLOAD VMSAVE feature")
> 
> Suggested-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Signed-off-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> ---
> 	The above upstream SHA1 is still on its way to Linus

Ah, missed this down here, I read top-to-bottom and stopped at the
second line :)

Anyway, will wait for Linus to pick these up first.

thanks,

greg k-h