[PATCH v12 21/39] arm64/gcs: Ensure that new threads have a GCS

[Yury Khrustalev]

On Thu, Aug 29, 2024 at 12:27:37AM +0100, Mark Brown wrote:
> When a new thread is created by a thread with GCS enabled the GCS needs
> to be specified along with the regular stack.
> 
> Unfortunately plain clone() is not extensible and existing clone3()
> users will not specify a stack so all existing code would be broken if
> we mandated specifying the stack explicitly.  For compatibility with
> these cases and also x86 (which did not initially implement clone3()
> support for shadow stacks) if no GCS is specified we will allocate one
> so when a thread is created which has GCS enabled allocate one for it.
> We follow the extensively discussed x86 implementation and allocate
> min(RLIMIT_STACK, 2G).  Since the GCS only stores the call stack and not
> any variables this should be more than sufficient for most applications.
> 
> GCSs allocated via this mechanism will be freed when the thread exits.
> 
> Reviewed-by: Catalin Marinas <catalin.marinas at arm.com>
> Reviewed-by: Thiago Jung Bauermann <thiago.bauermann at linaro.org>
> Signed-off-by: Mark Brown <broonie at kernel.org>

Acked-by: Yury Khrustalev <yury.khrustalev at arm.com>