Re: [PATCH v2 1/6] kvm: s390: Reject setting flic pfault attributes on ucontrol VMs

[Hariharan Mari <hari55@linux.ibm.com>]

On 2024-12-16 10:21, Christoph Schlameuss wrote:
> Prevent null pointer dereference when processing the
> KVM_DEV_FLIC_APF_ENABLE and KVM_DEV_FLIC_APF_DISABLE_WAIT ioctls in the
> interrupt controller.
> 
> Fixes: 3c038e6be0e2 ("KVM: async_pf: Async page fault support on s390")
> Reported-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
> Signed-off-by: Christoph Schlameuss <schlameuss@linux.ibm.com>

Tested-by: Hariharan Mari <hari55@linux.ibm.com>
> ---
>  Documentation/virt/kvm/devices/s390_flic.rst | 4 ++++
>  arch/s390/kvm/interrupt.c                    | 4 ++++
>  2 files changed, 8 insertions(+)
> 
> diff --git a/Documentation/virt/kvm/devices/s390_flic.rst
> b/Documentation/virt/kvm/devices/s390_flic.rst
> index ea96559ba501..b784f8016748 100644
> --- a/Documentation/virt/kvm/devices/s390_flic.rst
> +++ b/Documentation/virt/kvm/devices/s390_flic.rst
> @@ -58,11 +58,15 @@ Groups:
>      Enables async page faults for the guest. So in case of a major 
> page fault
>      the host is allowed to handle this async and continues the guest.
> 
> +    -EINVAL is returned when called on the FLIC of a ucontrol VM.
> +
>    KVM_DEV_FLIC_APF_DISABLE_WAIT
>      Disables async page faults for the guest and waits until already 
> pending
>      async page faults are done. This is necessary to trigger a
> completion interrupt
>      for every init interrupt before migrating the interrupt list.
> 
> +    -EINVAL is returned when called on the FLIC of a ucontrol VM.
> +
>    KVM_DEV_FLIC_ADAPTER_REGISTER
>      Register an I/O adapter interrupt source. Takes a 
> kvm_s390_io_adapter
>      describing the adapter to register::
> diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
> index ea8dce299954..22d73c13e555 100644
> --- a/arch/s390/kvm/interrupt.c
> +++ b/arch/s390/kvm/interrupt.c
> @@ -2678,9 +2678,13 @@ static int flic_set_attr(struct kvm_device
> *dev, struct kvm_device_attr *attr)
>  		kvm_s390_clear_float_irqs(dev->kvm);
>  		break;
>  	case KVM_DEV_FLIC_APF_ENABLE:
> +		if (kvm_is_ucontrol(dev->kvm))
> +			return -EINVAL;
>  		dev->kvm->arch.gmap->pfault_enabled = 1;
>  		break;
>  	case KVM_DEV_FLIC_APF_DISABLE_WAIT:
> +		if (kvm_is_ucontrol(dev->kvm))
> +			return -EINVAL;
>  		dev->kvm->arch.gmap->pfault_enabled = 0;
>  		/*
>  		 * Make sure no async faults are in transition when