I have just finished to write a wikipage to help people to implement and debug UEFI Runtime drivers based on the Tianocore project (Open Source implementation of the UEFI spec).

To validate the UEFI Runtime drivers, I have been using the Linux kernel with EFI Stub support (https://wiki.linaro.org/LEG/Engineering/Kernel/UEFI/EFIstub):

Linux kernel available here: https://git.linaro.org/people/leif.lindholm/linux.git/shortlog/refs/heads/uefi-for-next

The wikipage: https://sourceforge.net/apps/mediawiki/tianocore/index.php?title=ArmPkg/Runtime