Re: [PATCH RFC RFT v2 5/5] kselftest/clone3: Test shadow stack support

Mark Brown
2023-11-20T15:48:02Z

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On Fri, Nov 17, 2023 at 01:12:46PM -0800, Deepak Gupta wrote:
> On Tue, Nov 14, 2023 at 11:11:58PM +0000, Edgecombe, Rick P wrote:

> > It seems like there will be a need for some generic method of checking
> > if shadow stack is enabled. Maybe a more generic compiler
> > intrinsic/builtin or glibc API (something unrelated to SSP)?

> Exposing a new file under procfs would be useful?
> Something like "/proc/sys/vm/user_shadow_stack_supported"

> `map_shadow_stack` can return MAP_FAILED for other reasons.
> I think `kselftests` are fine but I don't want people to pick up this
> as test code and run with it in production :-)

> So kernel providing a way to indicate whether it supports shadow stack
> mappings in user mode via procfs would be useful and arch agnostic.

I can see that might be useful for some higher level code that wants to
tune the size and nothing else. I'd be tempted to do it through adding
a tuneable for the maximum default shadow stack size (x86 currently uses
4G) just so it's *vaguely* useful rather than just a file. I question
the utility of that but just a plain file doesn't feel quite idiomatic.

In any case it feels like it's off topic for this series and should be
done separately.

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