From c7dfa4009965a9b2d7b329ee970eb8da0d32f0bc 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) 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 --- 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 28381ca..e551547 100644 --- a/arch/x86/kvm/svm/nested.c +++ b/arch/x86/kvm/svm/nested.c @@ -158,6 +158,9 @@ void recalc_intercepts(struct vcpu_svm *svm) /* If SMI is not intercepted, ignore guest SMI intercept as well */ if (!intercept_smi) vmcb_clr_intercept(c, INTERCEPT_SMI); + + vmcb_set_intercept(c, INTERCEPT_VMLOAD); + vmcb_set_intercept(c, INTERCEPT_VMSAVE); } static void copy_vmcb_control_area(struct vmcb_control_area *dst, -- 2.7.4