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).