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The current state of UEFI and Linux

Filed under
Linux

Executive summary: Most things work fine.

Things we know are broken:

* Some Samsung laptops. The samsung-laptop driver is a slightly weird thing. By 2010 (when it first appeared) most vendors had moved over to using some level of firmware abstraction, either using ACPI or WMI. Samsung still seemed to be stuck around a decade earlier - they were providing a region of memory at a known address, and you'd read that address to find a bunch of offsets. Then you'd write magic values based on those offsets to magic system IO ports based on those offsets and something would happen. Those writes were triggering System Management Mode, a special x86 CPU mode where the processor executes code from memory that the OS can't see, without telling the OS that it's doing so. There's nothing especially new in this (SMM first appeared in the 386sl back in 1990), but it also means that you depend on the system vendor not changing the interface without telling you. Turns out that Samsung apparently changed their platform interface when they moved to UEFI, but didn't actually do anything to prevent old drivers from breaking things -

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