[PATCH] arm64: efi: Make runtime service wrapper more robust

[Kees Cook]

On Mon, Nov 28, 2022 at 10:49:39AM +0100, Ard Biesheuvel wrote:
> Prevent abuse of the runtime service wrapper code by avoiding restoring
> the shadow call stack pointer from the ordinary stack, or the stack
> pointer itself from a GPR. Also, given that the exception recovery
> routine is never called in an ordinary way, it doesn't need BTI landing
> pads so it can be SYM_CODE rather than SYM_FUNC.

Does this mean x18 is now being spilled to the stack? (Do we already
spill it in other places?)

-- 
Kees Cook