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

[Catalin Marinas]

On Wed, Aug 23, 2023 at 07:16:52PM +0100, Mark Brown wrote:
> On Wed, Aug 23, 2023 at 06:40:40PM +0100, Szabolcs Nagy wrote:
> > i don't know if we can allow disabled gcs thread creation with locked
> > gcs state. (i can see arguments both ways, so further prctl flag may
> > be needed which may be another divergence from x86)
> 
> I think that if we do add a new flag that'd just be new functionality,
> the divergence would be in allowing configuration via clone3() rather
> than the flag.  TBH I'm not sure I see a use case for locking but
> providing a mechanism for getting out of the lock, that seems very
> questionable.

You are right, once the configuration is locked a plain clone() or
clone3() without a GCS pointer should be rejected.

Is there a use-case for the unlocked configuration to allow disabling
the GCS implicitly via a clone syscall?

If we go for extending clone3, I wonder whether we should also introduce
a sigaltstack2/3 ;). I haven't checked what the current patches do and
won't have time until early September (on holiday from the end of today).

-- 
Catalin