[PATCH] KVM: ioapic: fix NULL deref ioapic->lock

From: Wanpeng Li
Date: Sat Dec 31 2016 - 22:45:18 EST

From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>

This was reported by syzkaller:

BUG: unable to handle kernel NULL pointer dereference at 00000000000001b0
IP: _raw_spin_lock+0xc/0x30
PGD 3e28eb067
PUD 3f0ac6067
Oops: 0002 [#1] SMP
CPU: 0 PID: 2431 Comm: test Tainted: G OE 4.10.0-rc1+ #3
Call Trace:
? kvm_ioapic_scan_entry+0x3e/0x110 [kvm]
kvm_arch_vcpu_ioctl_run+0x10a8/0x15f0 [kvm]
? pick_next_task_fair+0xe1/0x4e0
? kvm_arch_vcpu_load+0xea/0x260 [kvm]
kvm_vcpu_ioctl+0x33a/0x600 [kvm]
? hrtimer_try_to_cancel+0x29/0x130
? do_nanosleep+0x97/0xf0
? __hrtimer_init+0x90/0x90
? do_nanosleep+0x5b/0xf0
RIP: _raw_spin_lock+0xc/0x30 RSP: ffffa43688973cc0

KVM will skip over create pic/ioapic if there is a created vCPU. However,
there is no guarantee whether ioapic is present when rescan ioapic which
results in NULL dereference ioapic->lock. This patch fix it by adding the
ioapic present check to ioapic scan.

Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Radim KrÄmÃÅ <rkrcmar@xxxxxxxxxx>
Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
arch/x86/kvm/x86.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 51ccfe0..9ca175c 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6556,7 +6556,8 @@ static void vcpu_scan_ioapic(struct kvm_vcpu *vcpu)
else {
if (vcpu->arch.apicv_active)
- kvm_ioapic_scan_entry(vcpu, vcpu->arch.ioapic_handled_vectors);
+ if (ioapic_irqchip(vcpu->kvm))
+ kvm_ioapic_scan_entry(vcpu, vcpu->arch.ioapic_handled_vectors);
bitmap_or((ulong *)eoi_exit_bitmap, vcpu->arch.ioapic_handled_vectors,
vcpu_to_synic(vcpu)->vec_bitmap, 256);