Passing Parameter(s) to BIOS/UEFI SMI Handlers

There are two ways to pass parameter(s) to SMI handler(s) in BIOS/UEFI:

1. Via the Global Non-Volatile Storage (GNVS). This is a region in the non-volatile storage area. I'm not 100% sure about the physical implementation of the GNVS, but it's part of RAM reserved for Non-Volatile Storage by ACPI BIOS subsystem on the motherboard. [Thanks to Kun-Yi Chen for pointing out].
2. Via General Puupose Registers (GPRs). In this technique physical address pointer is passed via GPR to the SMI handler code. I've been thinking about giving some IDA Pro disassembly for this one. Maybe later. 

There you have it. Next time you encounter a suspicous code with one of the attributes above, it might just be one of them :-).

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