[PATCH 4.19 21/46] KVM: X86: Fix NULL deref in vcpu_scan_ioapic

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

4.19-stable review patch.  If anyone has any objections, please let me know.

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

From: Wanpeng Li <wanpengli@tencent.com>

commit dcbd3e49c2f0b2c2d8a321507ff8f3de4af76d7c upstream.

Reported by syzkaller:

    CPU: 1 PID: 5962 Comm: syz-executor118 Not tainted 4.20.0-rc6+ #374
    Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
    RIP: 0010:kvm_apic_hw_enabled arch/x86/kvm/lapic.h:169 [inline]
    RIP: 0010:vcpu_scan_ioapic arch/x86/kvm/x86.c:7449 [inline]
    RIP: 0010:vcpu_enter_guest arch/x86/kvm/x86.c:7602 [inline]
    RIP: 0010:vcpu_run arch/x86/kvm/x86.c:7874 [inline]
    RIP: 0010:kvm_arch_vcpu_ioctl_run+0x5296/0x7320 arch/x86/kvm/x86.c:8074
    Call Trace:
	 kvm_vcpu_ioctl+0x5c8/0x1150 arch/x86/kvm/../../../virt/kvm/kvm_main.c:2596
	 vfs_ioctl fs/ioctl.c:46 [inline]
	 file_ioctl fs/ioctl.c:509 [inline]
	 do_vfs_ioctl+0x1de/0x1790 fs/ioctl.c:696
	 ksys_ioctl+0xa9/0xd0 fs/ioctl.c:713
	 __do_sys_ioctl fs/ioctl.c:720 [inline]
	 __se_sys_ioctl fs/ioctl.c:718 [inline]
	 __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
	 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
	 entry_SYSCALL_64_after_hwframe+0x49/0xbe

The reason is that the testcase writes hyperv synic HV_X64_MSR_SINT14 msr
and triggers scan ioapic logic to load synic vectors into EOI exit bitmap.
However, irqchip is not initialized by this simple testcase, ioapic/apic
objects should not be accessed.

This patch fixes it by also considering whether or not apic is present.

Reported-by: syzbot+39810e6c400efadfef71@syzkaller.appspotmail.com
Cc: stable@vger.kernel.org
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/x86/kvm/x86.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7304,7 +7304,7 @@ void kvm_make_scan_ioapic_request(struct
 
 static void vcpu_scan_ioapic(struct kvm_vcpu *vcpu)
 {
-	if (!kvm_apic_hw_enabled(vcpu->arch.apic))
+	if (!kvm_apic_present(vcpu))
 		return;
 
 	bitmap_zero(vcpu->arch.ioapic_handled_vectors, 256);