linux-kernel - Re: [PATCH v7 02/39] prctl: arch-agnostic prctl for shadow stack

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Message-ID: <d723fdb4-9be9-4846-a49d-6bd00602afb3@sirena.org.uk>
Date:   Wed, 13 Dec 2023 13:49:29 +0000
From:   Mark Brown <broonie@...nel.org>
To:     "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
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Subject: Re: [PATCH v7 02/39] prctl: arch-agnostic prctl for shadow stack

On Tue, Dec 12, 2023 at 09:22:59PM +0000, Edgecombe, Rick P wrote:
> On Tue, 2023-12-12 at 20:26 +0000, Mark Brown wrote:

> > In general if things have a need to get at prctl()s via ptrace we
> > should
> > just fix that, at least for arm64 there's things like the vector
> > lengths
> > that are currently controlled via prctl(), but it shouldn't be a
> > blocker
> > for the locking specifically.

> ptrace arch_prctl() is a bit odd. Not all values of 'option' are
> supported because ptrace arch_prctl's have to operate cross task. Some
> have extra code to support doing this, and some only know how to
> operate on the current task, so return an error in the ptrace case.

It feels like x86 is doing some things via arch_prctl() rather than
implementing specific ptrace() interfaces for them, there's a lot of
stuff where ptrace isn't a great fit for due to it's concept that it's
going to work with an array of registers so that's understandable.

> I guess a benefit would be that there could be some arch agnostic
> ptrace userspace code. And I'd also guess (really a guess) that most
> ptracing code has some arch awareness already, but the other way is
> probably non-zero. Same for shadow stack enabling code. Then on the
> kernel side we'd have to add and support a ptrace prctl() solution.

> Is it worth the effort? I don't have a strong opinion.

I don't have a strong enough opinion on it to start working on it
immediately at any rate.

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