[RFC 2/5] aarch64: check if clone3 supports shadow stack

[Mark Brown]

On Tue, Jun 10, 2025 at 02:34:28PM -0300, Adhemerval Zanella Netto wrote:
> On 10/06/25 12:13, Yury Khrustalev wrote:

Adding Catalin.

> > Rely on the version of the currently running kernel and use
> > existing mechanism to determine this version (same that was
> > used for checks related to SVE).

> Since this is WIP feature, this would be simpler if kernel advertise it through
> a new HWCAP bits.  The kernel parsing is somewhat fragile and thinking
> twice we should have done it as well for the SVE issue that required to add
> this back on 2e94e2f5d2bf2de124c8ad7da85463355e54ccb2.

> The powerpc did a similar thing with PPC_FEATURE2_HTM_NOSC to avoid some
> performance issues with the initial HTM enablement on pthread (which made
> us tune it better, check f0458cf4f9ff3d870c43b624e6dccaaf657d5e83).

That's technically easy enough to do on arm64 and did come up before,
it's just mildly annoying.  The main reason I held off was that this
also affects x86 (which has had shadow stack support for even longer)
and at current rate of progress likely also RISC-V so a per arch thing
didn't seem ideal.  I'll need to investigate what the tasteful thing is
on x86.

It does also feel like we should have a better solution for clone3() in
general...
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