efi application to update the proc microcode

[Raphael G <raphael.glon@corp.ovh.com>]

Hello,

We are currently attempting to find an 'OS-independent' way of applying 
some updated microcode early during the efi boot sequence (note we 
cannot flash the motherboard firmware directly since we have not yet 
been provided with the latest constructor firmwares)

Would it somehow be possible, for motherboards booting in uefi mode, to 
chain an efi application that would apply some microcode bin (in a uefi 
capsule or not) on flight before chaining to the next efi app (the os one) ?

Or do you have any other generic way to do this, regardless of the final 
operating system ?

We have found some interesting hints in edk2 framework, that seem 
promising (IntelSiliconPkg)

https://github.com/tianocore/edk2/tree/master/IntelSiliconPkg

but so far we have not managed to make it work, so any help/solution 
would be great :)

If possible we do not want to persist anything in any non volatile 
storage at all, just apply it at the right time (we commented the flags 
persist_across_reset+trigger_reset in the capsule fdf for this, not sure 
this was the right thing to do)

# #####################

workflow example: whatever.efi -> chain microcodeupdate.efi (apply 
ucode) -> chain final_os.efi

#!ipxe
echo Fetch images and capsule
imgfetch http://${server}/microcode_efi/MicrocodeUpdateDxe.efi
imgfetch http://${server}/microcode_efi/MICROCODECAPSULE.Cap
chain MicrocodeUpdateDxe.efi MICROCODECAPSULE.Cap || goto fail

[...]


Regards,