Patch "KVM: svm: unconditionally intercept #DB" has been added to the 4.3-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    KVM: svm: unconditionally intercept #DB

to the 4.3-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     kvm-svm-unconditionally-intercept-db.patch
and it can be found in the queue-4.3 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From cbdb967af3d54993f5814f1cee0ed311a055377d Mon Sep 17 00:00:00 2001
From: Paolo Bonzini <pbonzini@redhat.com>
Date: Tue, 10 Nov 2015 09:14:39 +0100
Subject: KVM: svm: unconditionally intercept #DB

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/x86/kvm/svm.c |   14 +++-----------
 1 file changed, 3 insertions(+), 11 deletions(-)

--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1108,6 +1108,7 @@ static void init_vmcb(struct vcpu_svm *s
 	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);
@@ -1642,20 +1643,13 @@ static void svm_set_segment(struct kvm_v
 	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
@@ -1761,7 +1755,6 @@ static int db_interception(struct vcpu_s
 		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 &
@@ -3761,7 +3754,6 @@ static void enable_nmi_window(struct kvm
 	 */
 	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)
@@ -4383,7 +4375,7 @@ 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,


Patches currently in stable-queue which might be from pbonzini@redhat.com are

queue-4.3/kvm-x86-correctly-print-ac-in-traces.patch
queue-4.3/kvm-vmx-fix-smep-and-smap-without-ept.patch
queue-4.3/kvm-x86-expose-msr_tsc_aux-to-userspace.patch
queue-4.3/kvm-svm-unconditionally-intercept-db.patch