linux-kernel - Re: [musl] Re: [PATCH v8 00/38] arm64/gcs: Provide support for GCS in userspace

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Message-ID: <d334e9b9-659c-476f-b28d-42d3ac3dc591@sirena.org.uk>
Date: Thu, 14 Mar 2024 14:03:30 +0000
From: Mark Brown <broonie@...nel.org>
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Subject: Re: [musl] Re: [PATCH v8 00/38] arm64/gcs: Provide support for GCS
 in userspace

On Sat, Mar 02, 2024 at 03:57:02PM +0100, Szabolcs Nagy wrote:
> * Mark Brown <broonie@...nel.org> [2024-02-21 17:36:12 +0000]:

> > > I said NOP but there's no reason it strictly needs to be a NOP. It
> > > could instead do something reasonable to convey the state of racing
> > > with shadow stack being disabled.

> > This feels like it's getting complicated and I fear it may be an uphill
> > struggle to get such code merged, at least for arm64.  My instinct is

> the aarch64 behaviour is already nop
> for gcs instructions when gcs is disabled.
> the isa was designed so async disable is
> possible.

Yeah, we'd need to handle GCSPR_EL0 somehow (currently it's inaccessible
when GCS is disabled) and userspace would need to take care it's not
doing something that could get stuck if for example a pop didn't
actually *do* anything.

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