Tracking down a UEFI quirk on the Fujitsu LIFEBOOK AH532

Last time, we figured out why not being able to retrieve EFI variables while installing Linux results in an empty UEFI boot menu and an inaccessible BIOS setup menu. Now, we want to discover what is going wrong and what we can do about it.

In the last post, I mentioned that Fujitsu supposedly hardcoded the F2 and F12 boot keys to invoke specific Boot slots. This is a stupid idea because overwriting the Boot slots that the keys refer to will render those keypresses useless.

However, UEFI specified a variable-based way to override boot key mappings (KeyXXXX), and Fujitsu used that to provide the default key mappings for F2 and F12. Of course, if Boot0000 gets overwritten erroneously, that doesn’t mean that the respective Key entry gets updated, which resulted in the issues we have seen.

UEFI provides a limited set of interfaces for accessing variables, with operations that essentially amount to “iterate variable names” (GetNextVariableName), “get variable contents” (GetVariable), and “set variable contents” (SetVariable).

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