From a17f2f2c89494c0974529579f3552ecbd1bc2d52 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.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c index 07a52f1bebe0..425444d08071 100644 --- 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)