Für das X250 gibt's ein Bios-Update auf 1.23. Changelog:

CHANGES IN THIS RELEASE
  Version 1.23

[Important updates]
- Security fix addresses LEN-8324 System Management Mode (SMM) BIOS Vulnerability
  and some security fixes.
  (Note)
  If the UEFI BIOS has been updated to version 1.23 or higher, it is no longer
  able to roll back to the version before 1.23 for security improvement.


[New functions or enhancements]
- Updated the CPU microcode.
- Updated the Diagnostics module to version 2.09.08.

[Problem fixes]
- Fixed an issue where SRSETUP might set Intel PTT to invalid state.
- Fixed an issue of the Supervisor Password storing failure after the WMI packet
  processing.

Aktualisieren mit USB Stick (nach https://fabio-bregulla.de/lenovo-thinkpad-x250-mit-archlinux/ ):

geteltorito -o bios.img n10ur09w.iso
sudo dd if=bios.img of=/dev/sdX

Download auf der Lenovo-Website.