Adding a runtime service for firmware-based images for a device not known to an operating system

Systems, devices, and methods, including program instructions, are provided for firmware filters and patches. One method embodiment includes executing extended firmware interface (EFI) program instructions during runtime to modify a firmware implementation underlying an interface and invoking the modified firmware implementation, while the original firmware code in non-volatile memory remains unmodified. A further embodiment includes adding a runtime service in an system abstraction layer (SAL) interface and adding a subordinate runtime service that describes a device not known to a firmware image on a system but useable by a particular operating system (OS).