https://forums.freebsd.org/threads/freebsd-zfs-on-uefi-support-just-landed.54744/
https://svnweb.freebsd.org/base?view=revision&revision=294068
Add EFI ZFS boot support: This builds on the modular EFI loader support added r294060 adding a module to provide ZFS boot support on EFI systems. It should be noted that EFI uses a fixed size memory block for all allocations performed by the loader so it may be necessary to tune this size. For example when building an image which uses mfs_root e.g. mfsbsd, adding the following to /etc/make.conf would be needed to prevent EFI from running out of memory when loading the mfs_root image.
EFI_STAGING_SIZE=128
Firmware Security 