From 639a033fd765ed473dfee27028df5ccbe1038a2e Mon Sep 17 00:00:00 2001 From: Maxim Levitsky Date: Mon, 19 Jul 2021 16:05:00 +0300 Subject: [PATCH] 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: 89c8a4984fc9 ("KVM: SVM: Enable Virtual VMLOAD VMSAVE feature") Suggested-by: Paolo Bonzini Signed-off-by: Maxim Levitsky Signed-off-by: Paolo Bonzini Signed-off-by: Greg Kroah-Hartman --- arch/x86/kvm/svm/nested.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c index 7f3b55561ae82..61f4186442352 100644 --- a/arch/x86/kvm/svm/nested.c +++ b/arch/x86/kvm/svm/nested.c @@ -149,6 +149,9 @@ void recalc_intercepts(struct vcpu_svm *svm) for (i = 0; i < MAX_INTERCEPT; i++) c->intercepts[i] |= g->intercepts[i]; + + vmcb_set_intercept(c, INTERCEPT_VMLOAD); + vmcb_set_intercept(c, INTERCEPT_VMSAVE); } static void copy_vmcb_control_area(struct vmcb_control_area *dst,