Re: [PATCH] static_call,x86: Robustify trampoline patching

Peter Zijlstra
2021-10-31T20:11:54Z

On Sun, Oct 31, 2021 at 05:44:04PM +0100, Ard Biesheuvel wrote:

> > Is is also a terriblly gross hack. I really want the clang-cfi stuff to
> > improve, not add layers of hacks on top of it.
>
> I'm just as annoyed as you are about the apparent need for this.
> However, emitting an alias at build time is far better IMHO than
> adding a magic byte sequence and having to check it at runtime.

Oh, I'm keeping that magic sequence :-) That's hardening in general, and
I don't want to ever want to debug a wrong poke like that again.

Adding an extra label fixes this thing, but there's still the other
cases where we need/want/desire a *real* function pointer.

I'm very close to saying that anything that mucks up function pointers
like this is a complete non-starter. Let's start re-start this whole CFI
endeavour from the start.