[PATCH v4 03/36] arm64/gcs: Document the ABI for Guarded Control Stacks

[Mark Brown]

On Tue, Oct 03, 2023 at 09:45:56AM +0100, Szabolcs Nagy wrote:

> clone3 seems to have features that are only available in clone3 and
> not exposed (reasonably) in libc apis so ppl will use clone3 directly
> and those will be hard to fix for gcs (you have to convince upstream
> to add future arm64 arch specific changes that they cannot test).

Ah, I hadn't realised that there were things that weren't available via
libc - that does change the calculation a bit here.  I would hope that
anything we do for clone3() would work just as well for x86 so the test
side should be a bit easier there than if it were a future arm64 thing,
though obviously it wouldn't be mandatory on x86 in the way that Catalin
wanted it for arm64.

> where this analysis might be wrong is that raw clone3 is more likely
> used as fork/vfork without a new stack and thus no gcs issue.

> even if we have time to fix code, we don't want too many ifdef hacks
> just for gcs so it matters how many projects are affected.

My impression was that raw usage of the APIs was a specialist enough
thing that this was viable, ICBW though - I might not have been
searching well enough (clone is an annoying term to search for!).
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