linux-kernel - Re: [PATCH v4 03/36] arm64/gcs: Document the ABI for Guarded Control Stacks

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Message-ID: <ZOY3lz+Zyhd5ZyQ9@arm.com>
Date:   Wed, 23 Aug 2023 17:45:11 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Mark Brown <broonie@...nel.org>
Cc:     Szabolcs Nagy <Szabolcs.Nagy@....com>,
        Will Deacon <will@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Marc Zyngier <maz@...nel.org>,
        Oliver Upton <oliver.upton@...ux.dev>,
        James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Arnd Bergmann <arnd@...db.de>, Oleg Nesterov <oleg@...hat.com>,
        Eric Biederman <ebiederm@...ssion.com>,
        Kees Cook <keescook@...omium.org>,
        Shuah Khan <shuah@...nel.org>,
        "Rick P. Edgecombe" <rick.p.edgecombe@...el.com>,
        Deepak Gupta <debug@...osinc.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        "H.J. Lu" <hjl.tools@...il.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org,
        kvmarm@...ts.linux.dev, linux-fsdevel@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-mm@...ck.org,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v4 03/36] arm64/gcs: Document the ABI for Guarded Control
 Stacks

On Wed, Aug 23, 2023 at 01:51:35PM +0100, Mark Brown wrote:
> On Wed, Aug 23, 2023 at 11:09:59AM +0100, Szabolcs Nagy wrote:
> > The 08/22/2023 18:53, Mark Brown wrote:
> > > My sense is that they deployment story is going to be smoother with
> > > defaults being provided since it avoids dealing with the issue of what
> > > to do if userspace creates a thread without a GCS in a GCS enabled
> > > process but like I say I'd be totally happy to extend clone3().  I will
> > > put some patches together for that (probably once the x86 stuff lands).
> > > Given the size of this series it might be better split out for
> > > manageability if nothing else.
> 
> > i would make thread without gcs to implicitly disable gcs, since
> > that's what's bw compat with clones outside of libc (the libc can
> > guarantee gcs allocation when gcs is enabled).
> 
> That'd create a pretty substantial divergence with the x86 patches if
> they land this time around, there's not enough time to rework them now -
> I suppose it'd mainly bite people implementing libc type stuff but
> still, doesn't feel great.

I don't mind the divergence in this area if the libc folks are ok with
it. x86 can eventually use the clone3() interface if they want more
flexibility, they'll just have to continue supporting the old one. I
think we already diverge around the prctl().

-- 
Catalin