KVM: nSVM: always intercept VMLOAD/VMSAVE when nested (CVE-2021-3656)

commit c7dfa4009965a9b2d7b329ee970eb8da0d32f0bc upstream.

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: 0b8ec95268c8 ("KVM: SVM: Enable Virtual VMLOAD VMSAVE feature")
Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 07a52f1bebe00a73958f40e5fb0739fa504df059..425444d080712316da1025fa70171f71dfea031e 100644 (file)
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -516,6 +516,9 @@ static void recalc_intercepts(struct vcpu_svm *svm)
        c->intercept_dr = h->intercept_dr | g->intercept_dr;
        c->intercept_exceptions = h->intercept_exceptions | g->intercept_exceptions;
        c->intercept = h->intercept | g->intercept;
+
+       c->intercept |= (1ULL << INTERCEPT_VMLOAD);
+       c->intercept |= (1ULL << INTERCEPT_VMSAVE);
 }
 
 static inline struct vmcb *get_host_vmcb(struct vcpu_svm *svm)