KVM: Remove CREATE_IRQCHIP/SET_PIT2 race

Fixes a NULL pointer dereference, caused by the PIT firing an interrupt
before the interrupt table has been initialized.

SET_PIT2 can race with the creation of the IRQchip. In particular,
if SET_PIT2 is called with a low PIT timer period (after the creation of
the IOAPIC, but before the instantiation of the irq routes), the PIT can
fire an interrupt at an uninitialized table.

Signed-off-by: Steve Rutherford <srutherford@google.com>
Signed-off-by: Jon Cargille <jcargill@google.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Message-Id: <20200416191152.259434-1-jcargill@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 027dfd2..3cc3f67 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5049,10 +5049,13 @@ set_identity_unlock:
                r = -EFAULT;
                if (copy_from_user(&u.ps, argp, sizeof(u.ps)))
                        goto out;
+               mutex_lock(&kvm->lock);
                r = -ENXIO;
                if (!kvm->arch.vpit)
-                       goto out;
+                       goto set_pit_out;
                r = kvm_vm_ioctl_set_pit(kvm, &u.ps);
+set_pit_out:
+               mutex_unlock(&kvm->lock);
                break;
        }
        case KVM_GET_PIT2: {
@@ -5072,10 +5075,13 @@ set_identity_unlock:
                r = -EFAULT;
                if (copy_from_user(&u.ps2, argp, sizeof(u.ps2)))
                        goto out;
+               mutex_lock(&kvm->lock);
                r = -ENXIO;
                if (!kvm->arch.vpit)
-                       goto out;
+                       goto set_pit2_out;
                r = kvm_vm_ioctl_set_pit2(kvm, &u.ps2);
+set_pit2_out:
+               mutex_unlock(&kvm->lock);
                break;
        }
        case KVM_REINJECT_CONTROL: {