[M] Change in coreboot[main]: cpu/x86: Support SMBASE relocation-only use-case

[Felix Held (Code Review)]

Attention is currently required from: Angel Pons, Benjamin Doron, Dinesh Gehlot, Eran Mitrani, Fred Reitberger, Jason Glenesk, Kapil Porwal, Martin L Roth, Matt DeVillier, Matt DeVillier, Maulik Vaghela, Raul Rangel, Subrata Banik, Tarun, Tarun Tuli, ron minnich.

Felix Held has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/70376?usp=email )

Change subject: cpu/x86: Support SMBASE relocation-only use-case
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Patch Set 7:

(1 comment)

Patchset:

PS7:
> It's a fair concern, but if we want to use payload SMI handlers, the payload must put code in SMM. […]

ah, ok, that special hob being within smram/tseg and not just being a regular hob makes me a bit less concerned about the security aspects of that part.
i still don't see why a payload should install the smi handler which should only contain the small amount of smm code needed to make the hardware work; putting more code than necessary into the smi handler increases the chance of possible attack surfaces. another thing i'm concerned about there is the possibility to use that to put proprietary code into smm which i consider a rather bad idea in terms of security and reviewability of the code that stays active after the handoff from the firmware to the os. might be worth discussing this at a leadership meeting; not sure though if i'll manage to attend the one in two days