[PATCH 3.4 089/107] KVM: svm: unconditionally intercept #DB

lizf
2016-03-16T08:19:20Z

From: Paolo Bonzini <pbonzini@redhat.com>

3.4.111-rc1 review patch. If anyone has any objections, please let me know.

------------------

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, with thanks to Paolo:
- update_db_bp_intercept() was called update_db_intercept()
- The remaining call is in svm_guest_debug() rather than through svm_x86_ops]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Zefan Li <lizefan@huawei.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 56dd88a..6201ca0 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1082,6 +1082,7 @@ 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);
@@ -1637,20 +1638,13 @@ static void svm_set_segment(struct kvm_vcpu *vcpu,
mark_dirty(svm->vmcb, VMCB_SEG);
}

-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
@@ -1668,7 +1662,7 @@ static void svm_guest_debug(struct kvm_vcpu *vcpu, struct kvm_guest_debug *dbg)

mark_dirty(svm->vmcb, VMCB_DR);

- update_db_intercept(vcpu);
+ update_bp_intercept(vcpu);
}

static void new_asid(struct vcpu_svm *svm, struct svm_cpu_data *sd)
@@ -1742,7 +1736,6 @@ 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_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_intercept(vcpu);
}

static int svm_set_tss_addr(struct kvm *kvm, unsigned int addr)
--
1.9.1