linux-kernel - Re: [PATCH v3 00/36] arm64/gcs: Provide support for GCS in userspace

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Message-ID: <09b7a94d-cc88-4372-85de-52db26bc2daf@sirena.org.uk>
Date:   Tue, 1 Aug 2023 16:09:58 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Will Deacon <will@...nel.org>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        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 v3 00/36] arm64/gcs: Provide support for GCS in userspace

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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