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Commit cbdb967a authored by Paolo Bonzini's avatar Paolo Bonzini
Browse files

KVM: svm: unconditionally intercept #DB 



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: default avatarJan Beulich <jbeulich@suse.com>
Cc: stable@vger.kernel.org
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 54a20552

arch/x86/kvm/svm.c

+3 −11
Original line number Diff line number Diff line
@@ -1020,6 +1020,7 @@ static void init_vmcb(struct vcpu_svm *svm) 
	set_exception_intercept(svm, UD_VECTOR);

	set_exception_intercept(svm, MC_VECTOR);

	set_exception_intercept(svm, AC_VECTOR);

	set_exception_intercept(svm, DB_VECTOR);



	set_intercept(svm, INTERCEPT_INTR);

	set_intercept(svm, INTERCEPT_NMI);
@@ -1554,20 +1555,13 @@ static void svm_set_segment(struct kvm_vcpu *vcpu, 
	mark_dirty(svm->vmcb, VMCB_SEG);

}



static void update_db_bp_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
@@ -1673,7 +1667,6 @@ static int db_interception(struct vcpu_svm *svm) 
		if (!(svm->vcpu.guest_debug & KVM_GUESTDBG_SINGLESTEP))

			svm->vmcb->save.rflags &=

				~(X86_EFLAGS_TF | X86_EFLAGS_RF);

		update_db_bp_intercept(&svm->vcpu);

	}



	if (svm->vcpu.guest_debug &
@@ -3661,7 +3654,6 @@ static void enable_nmi_window(struct kvm_vcpu *vcpu) 
	 */

	svm->nmi_singlestep = true;

	svm->vmcb->save.rflags |= (X86_EFLAGS_TF | X86_EFLAGS_RF);

	update_db_bp_intercept(vcpu);

}



static int svm_set_tss_addr(struct kvm *kvm, unsigned int addr)
@@ -4287,7 +4279,7 @@ static struct kvm_x86_ops svm_x86_ops = { 
	.vcpu_load = svm_vcpu_load,

	.vcpu_put = svm_vcpu_put,



	.update_db_bp_intercept = update_db_bp_intercept,

	.update_db_bp_intercept = update_bp_intercept,

	.get_msr = svm_get_msr,

	.set_msr = svm_set_msr,

	.get_segment_base = svm_get_segment_base,