[OpenBIOS] l440gx write to NVRAM: ah ha!

[Ronald G. Minnich]

such fun. There is a PAL (or PLD) on the motherboard called a BUD. The bud
is a chunk of glue that takes care of stuff not in the various chipsets. 

The BUD has two interrupt lines it controls, one called SMI_L. 

IF you write to the NVRAM, BUD yanks SMI_L and the interrupt handler (in
this case in the BIOS) is tasked with responding with a magic word or
having put a magic word at some magic place in memory. This is the 'key'.
No key, no write. Tough for you. 

This little detail is only documented in the l440gx+ baseboard tps,
#245151-001, version 1.0, march 1999, and not in any of the other five
manuals I have on this chipset! 

Security through obscurity, I guess.

ron

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