Re: [PATCH 03/15] KVM: SVM: Inject #UD on RDTSCP when it should be disabled in the guest

From: Reiji Watanabe
Date: Wed May 05 2021 - 00:28:00 EST

On Tue, May 4, 2021 at 10:17 AM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
> Intercept RDTSCP to inject #UD if RDTSC is disabled in the guest.
> Note, SVM does not support intercepting RDPID. Unlike VMX's
> ENABLE_RDTSCP control, RDTSCP interception does not apply to RDPID. This
> is a benign virtualization hole as the host kernel (incorrectly) sets
> MSR_TSC_AUX if RDTSCP is supported, and KVM loads the guest's MSR_TSC_AUX
> into hardware if RDTSCP is supported in the host, i.e. KVM will not leak
> the host's MSR_TSC_AUX to the guest.
> But, when the kernel bug is fixed, KVM will start leaking the host's
> MSR_TSC_AUX if RDPID is supported in hardware, but RDTSCP isn't available
> for whatever reason. This leak will be remedied in a future commit.
> Fixes: 46896c73c1a4 ("KVM: svm: add support for RDTSCP")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>

Reviewed-by: Reiji Watanabe <reijiw@xxxxxxxxxx>