[PATCH v7 26/39] arm64/ptrace: Expose GCS via ptrace and core files

[Mark Brown]

On Sat, Dec 09, 2023 at 08:49:02PM -0300, Thiago Jung Bauermann wrote:
> Mark Brown <broonie at kernel.org> writes:

> > Provide a new register type NT_ARM_GCS reporting the current GCS mode
> > and pointer for EL0.  Due to the interactions with allocation and
> > deallocation of Guarded Control Stacks we do not permit any changes to
> > the GCS mode via ptrace, only GCSPR_EL0 may be changed.

> The code allows disabling GCS. Is that unintended?

No, it's intentional - ptrace has a lot of control over the process,
there's not a huge point trying to protect against it doing a disable.
The reason we prevent enabling is the allocation of a GCS along with
enable, the complexity of doing that on a remote process seemed
unjustified.  If clone3() ends up allowing manual allocation and
placement that'll likely be revised.
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