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

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Message-ID: <b6b654d6-9f77-463e-bbe9-58e8135536ff@sirena.org.uk>
Date:   Wed, 23 Aug 2023 16:50:10 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Catalin Marinas <catalin.marinas@....com>
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 02:11:07PM +0100, Catalin Marinas wrote:

> Yes, this should work. Any invocation of clone() or clone3() without a
> shadow stack would disable GCS. What about the reverse, should GCS be
> enabled for a thread even if the clone3() caller has GCS disabled? I
> guess we shouldn't since GCS enabling depends on the prctl() state set
> previously.

It has a fairly obvious intended meaning so we could do it easily enough
but OTOH allowing it opens up the idea of people wanting to specify GCS
flags which starts to seem like more trouble than it's worth compared to
just having them do the prctl() in the new thread.

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