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Subject[PATCH 3.16.y-ckt 079/126] KVM: svm: unconditionally intercept #DB
Date
3.16.7-ckt21 -stable 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>
Signed-off-by: Luis Henriques <luis.henriques@canonical.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 9e59e2d6ba7f..d09bc3e7882c 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1104,6 +1104,7 @@ 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);
@@ -1634,20 +1635,13 @@ 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
@@ -1753,7 +1747,6 @@ 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 &
@@ -3722,7 +3715,6 @@ 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)
@@ -4328,7 +4320,7 @@ 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,

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