/usr/s390x-linux-gnu/lib/libubsan.so.1 is in libubsan1-s390x-cross 8-20180414-1ubuntu2cross1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/s390x-linux-gnu/lib/libubsan.so.1.0.0
/usr/s390x-linux-gnu/lib/libubsan.so.1.0.0