Messages in this thread | | | Subject | Re: [PATCH 3.2 41/52] KVM: svm: unconditionally intercept #DB | From | Paolo Bonzini <> | Date | Wed, 25 Nov 2015 12:31:33 +0100 |
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On 24/11/2015 23:33, Ben Hutchings wrote: > 3.2.74-rc1 review patch. If anyone has any objections, please let me know. > > ------------------ > > From: Paolo Bonzini <pbonzini@redhat.com> > > commit cbdb967af3d54993f5814f1cee0ed311a055377d upstream. > > This is needed to avoid the possibility that the guest triggers > an infinite stream of #DB exceptions (CVE-2015-8104). > > VMX is not affected: because it does not save DR6 in the VMCS, > it already intercepts #DB unconditionally. > > Reported-by: Jan Beulich <jbeulich@suse.com> > Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> > [bwh: Backported to 3.2: #DB and #BP did not share a function, and there is > no operation pointer referring to it, so remove update_db_intercept() > entirely]
This is wrong, you still need to check the BP intercept in the (incorrectly named as of 3.2) update_db_intercept function.
Something like:
-static void update_db_intercept(struct kvm_vcpu *vcpu) +static void update_bp_intercept(struct kvm_vcpu *vcpu) { struct vcpu_svm *svm = to_svm(vcpu);
- clr_exception_intercept(svm, DB_VECTOR); clr_exception_intercept(svm, BP_VECTOR); - - if (svm->nmi_singlestep) - set_exception_intercept(svm, DB_VECTOR); - if (vcpu->guest_debug & KVM_GUESTDBG_ENABLE) { - if (vcpu->guest_debug & - (KVM_GUESTDBG_SINGLESTEP | KVM_GUESTDBG_USE_HW_BP)) - set_exception_intercept(svm, DB_VECTOR); if (vcpu->guest_debug & KVM_GUESTDBG_USE_SW_BP) set_exception_intercept(svm, BP_VECTOR); } else vcpu->guest_debug = 0; }
Then the calls in db_interception and enable_nmi_window can be removed, but the one in svm_guest_debug is important.
Paolo
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