[S] Change in coreboot[master]: cpu/x86/smm_stub.S: Add a retpoline around the main C handler

[Jan Samek (Code Review)]

Attention is currently required from: Nico Huber, Martin L Roth, Subrata Banik, Patrick Rudolph, Benjamin Doron, Julius Werner, Maximilian Brune, Arthur Heymans.

Jan Samek has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/67735 )

Change subject: cpu/x86/smm_stub.S: Add a retpoline around the main C handler
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Patch Set 2:

(1 comment)

File src/cpu/x86/smm/smm_stub.S:

https://review.coreboot.org/c/coreboot/+/67735/comment/4cf12ea2_cbeb1423 
PS2, Line 256: 2f
> The `2:` below (f for forward).

OK, thanks for explanation. That was the lack of my knowledge of the forward and backward flags and I misinterpreted these values as hexadecimal offsets (which would have been written differently).