linux-kernel - Re: [PATCH v5 11/37] mm: Define VM_SHADOW

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Date:   Tue, 22 Aug 2023 16:41:32 +0100
From:   Mark Brown <broonie@...nel.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     Catalin Marinas <catalin.marinas@....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>,
        Szabolcs Nagy <Szabolcs.Nagy@....com>,
        "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 v5 11/37] mm: Define VM_SHADOW_STACK for arm64 when we
 support GCS

On Tue, Aug 22, 2023 at 05:21:09PM +0200, David Hildenbrand wrote:
> On 22.08.23 15:56, Mark Brown wrote:

> > @@ -372,7 +372,17 @@ extern unsigned int kobjsize(const void *objp);
> >    * having a PAGE_SIZE guard gap.
> >    */
> >   # define VM_SHADOW_STACK	VM_HIGH_ARCH_5
> > -#else
> > +#endif
> > +
> > +#if defined(CONFIG_ARM64_GCS)
> > +/*
> > + * arm64's Guarded Control Stack implements similar functionality and
> > + * has similar constraints to shadow stacks.
> > + */
> > +# define VM_SHADOW_STACK	VM_HIGH_ARCH_5
> > +#endif

> Shouldn't that all just merged with the previous define(s)?

> Also, I wonder if we now want to have CONFIG_HAVE_ARCH_SHADOW_STACK or
> similar.

I can certainly update it to do that, I was just trying to fit in with
how the code was written on the basis that there was probably a good
reason for it that had been discussed somewhere.  I can send an
incremental patch for this on top of the x86 patches assuming they go in
during the merge window.

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