[PATCH v7 21/39] arm64/gcs: Allocate a new GCS for threads with GCS enabled

[Thiago Jung Bauermann]

Mark Brown <broonie at kernel.org> writes:

> When a new thread is created by a thread with GCS enabled the GCS needs
> to be specified along with the regular stack.  clone3() has been
> extended to support this case, allowing userspace to explicitly request
> the size for the GCS to be created, but plain clone() is not extensible
> and existing clone3() users will not specify a size.
>
> 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 thread so when a thread is created which has GCS
                    ~~~~~~

This "thread" seems extraneous in the sentence. Remove it?

> enabled allocate one for it.  We follow the extensively discussed x86
> implementation and allocate min(RLIMIT_STACK, 4G).  Since the GCS only

Isn't it min(RLIMIT_STACK/2, 2G)?

> stores the call stack and not any variables this should be more than
> sufficient for most applications.
>
> GCSs allocated via this mechanism then it will be freed when the thread
> exits.

I'm not sure I parsed this sentence correctly. Is it missing an "If" at
the beginning?

-- 
Thiago