[linux] 01/02: [x86] KVM: svm: unconditionally intercept #DB (CVE-2015-8104)

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carnil pushed a commit to branch jessie-security
in repository linux.

commit 2e524ddf86cfad3431a77a96d3348d4113866288
Author: Salvatore Bonaccorso <carnil at debian.org>
Date:   Sun Nov 15 10:01:47 2015 +0100

    [x86] KVM: svm: unconditionally intercept #DB (CVE-2015-8104)
---
 debian/changelog                                   |  6 ++
 .../x86/kvm-svm-unconditionally-intercept-DB.patch | 80 ++++++++++++++++++++++
 debian/patches/series                              |  1 +
 3 files changed, 87 insertions(+)

diff --git a/debian/changelog b/debian/changelog
index f29ed37..9637f9f 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -1,3 +1,9 @@
+linux (3.16.7-ckt11-1+deb8u7) UNRELEASED; urgency=medium
+
+  * [x86] KVM: svm: unconditionally intercept #DB (CVE-2015-8104)
+
+ -- Salvatore Bonaccorso <carnil at debian.org>  Sun, 15 Nov 2015 10:01:10 +0100
+
 linux (3.16.7-ckt11-1+deb8u6) jessie-security; urgency=medium
 
   [ Salvatore Bonaccorso ]
diff --git a/debian/patches/bugfix/x86/kvm-svm-unconditionally-intercept-DB.patch b/debian/patches/bugfix/x86/kvm-svm-unconditionally-intercept-DB.patch
new file mode 100644
index 0000000..efa115e
--- /dev/null
+++ b/debian/patches/bugfix/x86/kvm-svm-unconditionally-intercept-DB.patch
@@ -0,0 +1,80 @@
+From: Paolo Bonzini <pbonzini at redhat.com>
+Date: Tue, 10 Nov 2015 09:14:39 +0100
+Subject: KVM: svm: unconditionally intercept #DB
+Origin: https://git.kernel.org/linus/cbdb967af3d54993f5814f1cee0ed311a055377d
+
+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 at suse.com>
+Cc: stable at vger.kernel.org
+Signed-off-by: Paolo Bonzini <pbonzini at redhat.com>
+---
+ arch/x86/kvm/svm.c | 14 +++-----------
+ 1 file changed, 3 insertions(+), 11 deletions(-)
+
+diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
+index 1839264..1cc1ffc 100644
+--- a/arch/x86/kvm/svm.c
++++ b/arch/x86/kvm/svm.c
+@@ -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,
+-- 
+2.6.2
+
diff --git a/debian/patches/series b/debian/patches/series
index 221f89c..86b08a5 100644
--- a/debian/patches/series
+++ b/debian/patches/series
@@ -659,3 +659,4 @@ bugfix/all/usbvision-fix-overflow-of-interfaces-array.patch
 bugfix/all/rds-fix-race-condition-when-sending-a-message-on-unbound-socket.patch
 bugfix/x86/kvm-x86-vmx-avoid-guest-host-dos-by-intercepting-ac.patch
 bugfix/x86/kvm-x86-svm-intercept-ac-to-avoid-guest-host-exploit.patch
+bugfix/x86/kvm-svm-unconditionally-intercept-DB.patch

-- 
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