These patches have been in my personal queue for about two years, and have already been incorporated into the Ubuntu packaged version of sbsigntool.
Patch #1 and #2 fixes some generic issues, and patch #3 introduces the ARM and AArch64 magic values in the PE/COFF header check, which is all that is needed to get sbsign to sign ARM images.
Ard Biesheuvel (3): sbsigntool: remove doubly defined IMAGE_FILE_MACHINE_AMD64 sbsigntool: fix handling of zero sized sections sbsigntool: add support for ARM and Aarch64 PE/COFF images
src/coff/pe.h | 2 +- src/image.c | 48 +++++++++++--------- 2 files changed, 27 insertions(+), 23 deletions(-)