[PATCH 5.0 103/122] KVM: lapic: Check for in-kernel LAPIC before deferencing apic pointer

Greg Kroah-Hartman
2019-05-06T14:39:05Z

From: Sean Christopherson <sean.j.christopherson@intel.com>

commit b904cb8dff824b79233e82c078837627ebd52717 upstream.

...to avoid dereferencing a null pointer when querying the per-vCPU
timer advance.

Fixes: 39497d7660d98 ("KVM: lapic: Track lapic timer advance per vCPU")
Reported-by: syzbot+f7e65445a40d3e0e4ebf@syzkaller.appspotmail.com
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/x86/kvm/lapic.c | 3 ---
arch/x86/kvm/x86.c | 3 ++-
2 files changed, 2 insertions(+), 4 deletions(-)

--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1504,9 +1504,6 @@ void wait_lapic_expire(struct kvm_vcpu *
u32 timer_advance_ns = apic->lapic_timer.timer_advance_ns;
u64 guest_tsc, tsc_deadline, ns;

- if (!lapic_in_kernel(vcpu))
- return;
-
if (apic->lapic_timer.expired_tscdeadline == 0)
return;

--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7886,7 +7886,8 @@ static int vcpu_enter_guest(struct kvm_v
}

trace_kvm_entry(vcpu->vcpu_id);
- if (vcpu->arch.apic->lapic_timer.timer_advance_ns)
+ if (lapic_in_kernel(vcpu) &&
+ vcpu->arch.apic->lapic_timer.timer_advance_ns)
wait_lapic_expire(vcpu);
guest_enter_irqoff();