KVM: Reject device ioctls from processes other than the VM's creator

 - VM ioctls: These query and set attributes that affect an entire virtual

   machine, for example memory layout.  In addition a VM ioctl is used to

   create virtual cpus (vcpus).

   create virtual cpus (vcpus) and devices.

   VM ioctls must be issued from the same process (address space) that was

   used to create the VM.

   the documentation.  Otherwise, the first ioctl after switching threads

   could see a performance impact.

 - device ioctls: These query and set attributes that control the operation

   of a single device.

   device ioctls must be issued from the same process (address space) that

   was used to create the VM.

2. File descriptors

-------------------

open("/dev/kvm") obtains a handle to the kvm subsystem; this handle

can be used to issue system ioctls.  A KVM_CREATE_VM ioctl on this

handle will create a VM file descriptor which can be used to issue VM

ioctls.  A KVM_CREATE_VCPU ioctl on a VM fd will create a virtual cpu

and return a file descriptor pointing to it.  Finally, ioctls on a vcpu

fd can be used to control the vcpu, including the important task of

actually running guest code.

ioctls.  A KVM_CREATE_VCPU or KVM_CREATE_DEVICE ioctl on a VM fd will

create a virtual cpu or device and return a file descriptor pointing to

the new resource.  Finally, ioctls on a vcpu or device fd can be used

to control the vcpu or device.  For vcpus, this includes the important

task of actually running guest code.

In general file descriptors can be migrated among processes by means

of fork() and the SCM_RIGHTS facility of unix domain socket.  These

{

	struct kvm_device *dev = filp->private_data;

	if (dev->kvm->mm != current->mm)

		return -EIO;

	switch (ioctl) {

	case KVM_SET_DEVICE_ATTR:

		return kvm_device_ioctl_attr(dev, dev->ops->set_attr, arg);