Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:5 as permitted sender) client-ip=2620:137:e000::3:5;
Date:   Fri, 6 Oct 2023 13:17:01 +0100
From:   Mark Brown <broonie@kernel.org>
To:     Catalin Marinas <catalin.marinas@arm.com>
Cc:     Szabolcs Nagy <Szabolcs.Nagy@arm.com>,
        Will Deacon <will@kernel.org>,
        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>,
        "H.J. Lu" <hjl.tools@gmail.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        linux-arm-kernel@lists.infradead.org, linux-doc@vger.kernel.org,
        kvmarm@lists.linux.dev, linux-fsdevel@vger.kernel.org,
        linux-arch@vger.kernel.org, linux-mm@kvack.org,
        linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-riscv@lists.infradead.org
Subject: Re: [PATCH v4 03/36] arm64/gcs: Document the ABI for Guarded Control
 Stacks
Message-ID: <638a7be5-6662-471d-a3ce-0de0ac768e99@sirena.org.uk>
References: <aaea542c-929c-4c9b-8caa-ca67e0eb9c1e@sirena.org.uk>
 <ZOTnL1SDJWZjHPUW@arm.com>
 <43ec219d-bf20-47b8-a5f8-32bc3b64d487@sirena.org.uk>
 <ZOXa98SqwYPwxzNP@arm.com>
 <ZOYFazB1gYjzDRdA@arm.com>
 <ZRWw7aa3C0LlMPTH@arm.com>
 <38edb5c3-367e-4ab7-8cb7-aa1a5c0e330c@sirena.org.uk>
 <ZRvUxLgMse8QYlGS@arm.com>
 <a7d2fd66-c06b-4033-bca2-4b14afc4904f@sirena.org.uk>
 <ZR7w/mr0xZbpIPc5@arm.com>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha512;
        protocol="application/pgp-signature"; boundary="fv2LrnWqf0aiVt0H"
Content-Disposition: inline
In-Reply-To: <ZR7w/mr0xZbpIPc5@arm.com>
Precedence: bulk


--fv2LrnWqf0aiVt0H
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline

On Thu, Oct 05, 2023 at 06:23:10PM +0100, Catalin Marinas wrote:

> It's not just the default size that I dislike (I think the x86
> RLIMIT_STACK or clone3() stack_size is probably good enough) but the
> kernel allocating the shadow stack and inserting it into the user
> address space. The actual thread stack is managed by the user but the
> shadow stack is not (and we don't do this very often). Anyway, I don't
> have a better solution for direct uses of clone() or clone3(), other
> than running those threads with the shadow stack disabled. Not sure
> that's desirable.

Running threads with the shadow stack disabled if they don't explicitly
request it feels like it's asking for trouble - as well as the escape
route from the protection it'd provide I'd expect there to be trouble
for things that do stack pivots, potentially random issues if there's a
mix of ways threads are started.  It's going to be a tradeoff whatever
we do.

--fv2LrnWqf0aiVt0H
Content-Type: application/pgp-signature; name="signature.asc"

-----BEGIN PGP SIGNATURE-----

iQEzBAABCgAdFiEEreZoqmdXGLWf4p/qJNaLcl1Uh9AFAmUf+rwACgkQJNaLcl1U
h9AHQQf7BUjbkJGRbqVL5lGyELqXE64nUXJxqNVQXzkHQ1ujZqDV/cLF9uojqJh6
yo1MngEonxyKeJjgqupcA6TzR0LGD9KvuzahtnPwSfluLAxLQG5iY2L+sA2Tdwb4
kPqoRiUS0++v1w/Oud9y0kcF6an3/im18MenqLAPGtnHPH+xE3EHipQsrYN53Fos
vsFAhXwuDhqGVonMiS+J1OxVsYZ9cRcVlStwZI0JbcCPGjS/vMUsCiE1j8ERuLYr
ZUNLyxMMQy35iW2uIdk67nRdv03mjTOw9yYr3akjxNW5eJeFrc804fBdZZ7YqrEE
Ju28oLb7xq1zQUOX3lYKlNKWsex4KA==
=iNQp
-----END PGP SIGNATURE-----

--fv2LrnWqf0aiVt0H--