[PATCH v13 22/40] arm64/gcs: Ensure that new threads have a GCS

[Catalin Marinas]

On Tue, Oct 01, 2024 at 11:59:01PM +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/2, 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.

I think Szabolcs mentioned a GCS leak with v12:

https://lore.kernel.org/r/ZtrihWQFyb2/XrQV@arm.com

(and in some private messages IIRC)

Has this been identified? The changelog only mentions a leak in v8.

-- 
Catalin