On 20/11/18 02:39, Wanpeng Li wrote: > Reported by syzkaller: > > BUG: unable to handle kernel NULL pointer dereference at 0000000000000014 > PGD 800000040410c067 P4D 800000040410c067 PUD 40410d067 PMD 0 > Oops: 0000 [#1] PREEMPT SMP PTI > CPU: 3 PID: 2567 Comm: poc Tainted: G OE 4.19.0-rc5 #16 > RIP: 0010:kvm_pv_send_ipi+0x94/0x350 [kvm] > Call Trace: > kvm_emulate_hypercall+0x3cc/0x700 [kvm] > handle_vmcall+0xe/0x10 [kvm_intel] > vmx_handle_exit+0xc1/0x11b0 [kvm_intel] > vcpu_enter_guest+0x9fb/0x1910 [kvm] > kvm_arch_vcpu_ioctl_run+0x35c/0x610 [kvm] > kvm_vcpu_ioctl+0x3e9/0x6d0 [kvm] > do_vfs_ioctl+0xa5/0x690 > ksys_ioctl+0x6d/0x80 > __x64_sys_ioctl+0x1a/0x20 > do_syscall_64+0x83/0x6e0 > entry_SYSCALL_64_after_hwframe+0x49/0xbe > > The reason is that the apic map has not yet been initialized, the testcase > triggers pv_send_ipi interface by vmcall which results in kvm->arch.apic_map > is dereferenced. This patch fixes it by checking whether or not apic map is > NULL and bailing out immediately if that is the case. > > Fixes: 4180bf1b65 (KVM: X86: Implement "send IPI" hypercall) > Reported-by: Wei Wu <ww9210@xxxxxxxxx> > Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx> > Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx> > Cc: Wei Wu <ww9210@xxxxxxxxx> > Signed-off-by: Wanpeng Li <wanpengli@xxxxxxxxxxx> > --- > arch/x86/kvm/lapic.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c > index 3cd227f..09e3a12 100644 > --- a/arch/x86/kvm/lapic.c > +++ b/arch/x86/kvm/lapic.c > @@ -576,6 +576,11 @@ int kvm_pv_send_ipi(struct kvm *kvm, unsigned long ipi_bitmap_low, > rcu_read_lock(); > map = rcu_dereference(kvm->arch.apic_map); > > + if (unlikely(!map)) { > + count = -EOPNOTSUPP; > + goto out; > + } > + > if (min > map->max_apic_id) > goto out; > /* Bits above cluster_size are masked in the caller. */ > Queued, thanks. Paolo