Enforcing limitations on hardware drivers. The method includes from a system kernel, assigning I/O resources to the system's root bus. From the root bus, the method further includes assigning a subset of the I/O resources to a device bus. Assigning a subset of the I/O resources to a device bus includes limiting the device bus to only be able to assign I/O resources that are assigned to it by the root bus. From the device bus, the method includes assigning I/O resources to a device through a device interface.