Commit b42506c6 authored by Paolo Bonzini's avatar Paolo Bonzini Committed by Ben Hutchings

KVM: svm: unconditionally intercept #DB

commit cbdb967a 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: default avatarJan Beulich <jbeulich@suse.com>
Signed-off-by: default avatarPaolo 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: default avatarBen Hutchings <ben@decadent.org.uk>
parent 1a513170
...@@ -1015,6 +1015,7 @@ static void init_vmcb(struct vcpu_svm *svm) ...@@ -1015,6 +1015,7 @@ static void init_vmcb(struct vcpu_svm *svm)
set_exception_intercept(svm, UD_VECTOR); set_exception_intercept(svm, UD_VECTOR);
set_exception_intercept(svm, MC_VECTOR); set_exception_intercept(svm, MC_VECTOR);
set_exception_intercept(svm, AC_VECTOR); set_exception_intercept(svm, AC_VECTOR);
set_exception_intercept(svm, DB_VECTOR);
set_intercept(svm, INTERCEPT_INTR); set_intercept(svm, INTERCEPT_INTR);
set_intercept(svm, INTERCEPT_NMI); set_intercept(svm, INTERCEPT_NMI);
...@@ -1550,20 +1551,13 @@ static void svm_set_segment(struct kvm_vcpu *vcpu, ...@@ -1550,20 +1551,13 @@ static void svm_set_segment(struct kvm_vcpu *vcpu,
mark_dirty(svm->vmcb, VMCB_SEG); 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); struct vcpu_svm *svm = to_svm(vcpu);
clr_exception_intercept(svm, DB_VECTOR);
clr_exception_intercept(svm, BP_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_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) if (vcpu->guest_debug & KVM_GUESTDBG_USE_SW_BP)
set_exception_intercept(svm, BP_VECTOR); set_exception_intercept(svm, BP_VECTOR);
} else } else
...@@ -1581,7 +1575,7 @@ static void svm_guest_debug(struct kvm_vcpu *vcpu, struct kvm_guest_debug *dbg) ...@@ -1581,7 +1575,7 @@ static void svm_guest_debug(struct kvm_vcpu *vcpu, struct kvm_guest_debug *dbg)
mark_dirty(svm->vmcb, VMCB_DR); 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) static void new_asid(struct vcpu_svm *svm, struct svm_cpu_data *sd)
...@@ -1655,7 +1649,6 @@ static int db_interception(struct vcpu_svm *svm) ...@@ -1655,7 +1649,6 @@ static int db_interception(struct vcpu_svm *svm)
if (!(svm->vcpu.guest_debug & KVM_GUESTDBG_SINGLESTEP)) if (!(svm->vcpu.guest_debug & KVM_GUESTDBG_SINGLESTEP))
svm->vmcb->save.rflags &= svm->vmcb->save.rflags &=
~(X86_EFLAGS_TF | X86_EFLAGS_RF); ~(X86_EFLAGS_TF | X86_EFLAGS_RF);
update_db_intercept(&svm->vcpu);
} }
if (svm->vcpu.guest_debug & if (svm->vcpu.guest_debug &
...@@ -3557,7 +3550,6 @@ static void enable_nmi_window(struct kvm_vcpu *vcpu) ...@@ -3557,7 +3550,6 @@ static void enable_nmi_window(struct kvm_vcpu *vcpu)
*/ */
svm->nmi_singlestep = true; svm->nmi_singlestep = true;
svm->vmcb->save.rflags |= (X86_EFLAGS_TF | X86_EFLAGS_RF); 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) static int svm_set_tss_addr(struct kvm *kvm, unsigned int addr)
......
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