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

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Date:   Mon,  6 May 2019 16:32:41 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        syzbot+f7e65445a40d3e0e4ebf@...kaller.appspotmail.com,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH 5.0 103/122] KVM: lapic: Check for in-kernel LAPIC before deferencing apic pointer

From: Sean Christopherson <sean.j.christopherson@...el.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@...kaller.appspotmail.com
Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.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();