On Wed, 2018-08-15 at 13:30 -0700, Peter Shier wrote:
> From: Steve Rutherford <srutherford@xxxxxxxxxx>
>
> 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@xxxxxxxxxx>
> Signed-off-by: Peter Shier <pshier@xxxxxxxxxx>
> Signed-off-by: Jim Mattson <jmattson@xxxxxxxxxx>
> ---
> arch/x86/kvm/x86.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 3c83711c0ebe1..953ac519fb984 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -4493,10 +4493,13 @@ long kvm_arch_vm_ioctl(struct file *filp,
> 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;
How about doing it this way instead:
mutex_lock(&kvm->lock);
r = -ENXIO;
if (kvm->arch.vpit)
r = kvm_vm_ioctl_set_pit(kvm, &u.ps);
mutex_unlock(&kvm->lock);
break;
?
This would avoid using a 'goto' + 2 lines shorter.
> }
> case KVM_GET_PIT2: {
> @@ -4516,10 +4519,13 @@ long kvm_arch_vm_ioctl(struct file *filp,
> 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;
... same here.
> }
> case KVM_REINJECT_CONTROL: {
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