2018-08-29 17:54-0700, Peter Shier:
> 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.
>From what you describe, it seems that the problems is the timer
interrupt started in
kvm_vm_ioctl_set_pit2() ->
kvm_pit_load_count() ->
pit_load_count() ->
create_pit_timer() ->
hrtimer_start()
that immediately fires
pit_timer_fn() ->
pit_do_work() ->
kvm_set_irq()
and the irq routes there are not set up properly.
I don't see what we race with, though:
create_pit_timer() checks ioapic_in_kernel() before creating the timer,
so the whole KVM_CREATE_IRQCHIP must have finished and routing is
kvm_setup_default_irq_routing() if the timer fires.
The only other way to change the routing is through KVM_SET_GSI_ROUTING,
but that doesn't have kvm->lock protection, so it shouldn't matter.
Isn't the bug somewhere else?
Thanks.
> 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 | 14 ++++++++------
> 1 file changed, 8 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 506bd2b4b8bb7..188bc3fc907f1 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -4518,10 +4518,11 @@ 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;
> - r = kvm_vm_ioctl_set_pit(kvm, &u.ps);
> + if (kvm->arch.vpit)
> + r = kvm_vm_ioctl_set_pit(kvm, &u.ps);
> + mutex_unlock(&kvm->lock);
> break;
> }
> case KVM_GET_PIT2: {
> @@ -4541,10 +4542,11 @@ 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;
> - r = kvm_vm_ioctl_set_pit2(kvm, &u.ps2);
> + if (kvm->arch.vpit)
> + r = kvm_vm_ioctl_set_pit2(kvm, &u.ps2);
> + mutex_unlock(&kvm->lock);
> break;
> }
> case KVM_REINJECT_CONTROL: {
> --
> 2.19.0.rc0.228.g281dcd1b4d0-goog
