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Date:   Tue, 1 Aug 2023 16:09:58 +0100
From:   Mark Brown <broonie@kernel.org>
To:     Will Deacon <will@kernel.org>
Cc:     Catalin Marinas <catalin.marinas@arm.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Andrew Morton <akpm@linux-foundation.org>,
        Marc Zyngier <maz@kernel.org>,
        Oliver Upton <oliver.upton@linux.dev>,
        James Morse <james.morse@arm.com>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        Arnd Bergmann <arnd@arndb.de>, Oleg Nesterov <oleg@redhat.com>,
        Eric Biederman <ebiederm@xmission.com>,
        Kees Cook <keescook@chromium.org>,
        Shuah Khan <shuah@kernel.org>,
        "Rick P. Edgecombe" <rick.p.edgecombe@intel.com>,
        Deepak Gupta <debug@rivosinc.com>,
        Ard Biesheuvel <ardb@kernel.org>,
        Szabolcs Nagy <Szabolcs.Nagy@arm.com>,
        "H.J. Lu" <hjl.tools@gmail.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
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        linux-riscv@lists.infradead.org
Subject: Re: [PATCH v3 00/36] arm64/gcs: Provide support for GCS in userspace
Message-ID: <09b7a94d-cc88-4372-85de-52db26bc2daf@sirena.org.uk>
References: <20230731-arm64-gcs-v3-0-cddf9f980d98@kernel.org>
 <20230801141319.GC26253@willie-the-truck>
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On Tue, Aug 01, 2023 at 03:13:20PM +0100, Will Deacon wrote:
> On Mon, Jul 31, 2023 at 02:43:09PM +0100, Mark Brown wrote:

> > The arm64 Guarded Control Stack (GCS) feature provides support for
> > hardware protected stacks of return addresses, intended to provide
> > hardening against return oriented programming (ROP) attacks and to make
> > it easier to gather call stacks for applications such as profiling.

> Why is this better than Clang's software shadow stack implementation? It
> would be nice to see some justification behind adding all this, rather
> than it being an architectural tick-box exercise.

Mainly that it's hardware enforced (as the quoted paragraph says).  This
makes it harder to attack, and hopefully it's also a bit faster (how
measurable that might be will be an open question, but even NOPs in
function entry/exit tend to get noticed).

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