Received-SPF: pass (google.com: domain of linux-kernel+bounces-73873-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:4601:e00::3 as permitted sender) client-ip=2604:1380:4601:e00::3;
Date: Wed, 21 Feb 2024 00:44:43 +0000
From: Mark Brown <broonie@kernel.org>
To: "Edgecombe, Rick P" <rick.p.edgecombe@intel.com>
Cc: "dalias@libc.org" <dalias@libc.org>,
	"linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
	"suzuki.poulose@arm.com" <suzuki.poulose@arm.com>,
	"Szabolcs.Nagy@arm.com" <Szabolcs.Nagy@arm.com>,
	"musl@lists.openwall.com" <musl@lists.openwall.com>,
	"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
	"linux-riscv@lists.infradead.org" <linux-riscv@lists.infradead.org>,
	"kvmarm@lists.linux.dev" <kvmarm@lists.linux.dev>,
	"corbet@lwn.net" <corbet@lwn.net>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"catalin.marinas@arm.com" <catalin.marinas@arm.com>,
	"oliver.upton@linux.dev" <oliver.upton@linux.dev>,
	"palmer@dabbelt.com" <palmer@dabbelt.com>,
	"debug@rivosinc.com" <debug@rivosinc.com>,
	"aou@eecs.berkeley.edu" <aou@eecs.berkeley.edu>,
	"shuah@kernel.org" <shuah@kernel.org>,
	"arnd@arndb.de" <arnd@arndb.de>, "maz@kernel.org" <maz@kernel.org>,
	"oleg@redhat.com" <oleg@redhat.com>,
	"fweimer@redhat.com" <fweimer@redhat.com>,
	"keescook@chromium.org" <keescook@chromium.org>,
	"james.morse@arm.com" <james.morse@arm.com>,
	"ebiederm@xmission.com" <ebiederm@xmission.com>,
	"will@kernel.org" <will@kernel.org>,
	"brauner@kernel.org" <brauner@kernel.org>,
	"hjl.tools@gmail.com" <hjl.tools@gmail.com>,
	"linux-kselftest@vger.kernel.org" <linux-kselftest@vger.kernel.org>,
	"paul.walmsley@sifive.com" <paul.walmsley@sifive.com>,
	"ardb@kernel.org" <ardb@kernel.org>,
	"linux-arm-kernel@lists.infradead.org" <linux-arm-kernel@lists.infradead.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	"thiago.bauermann@linaro.org" <thiago.bauermann@linaro.org>,
	"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
	"sorear@fastmail.com" <sorear@fastmail.com>,
	"linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>
Subject: Re: [musl] Re: [PATCH v8 00/38] arm64/gcs: Provide support for GCS
 in userspace
Message-ID: <cffc9c7e-ba1c-4894-a455-8b2d687182cd@sirena.org.uk>
References: <20240203-arm64-gcs-v8-0-c9fec77673ef@kernel.org>
 <22a53b78-10d7-4a5a-a01e-b2f3a8c22e94@app.fastmail.com>
 <4c7bdf8fde9cc45174f10b9221fa58ffb450b755.camel@intel.com>
 <20240220185714.GO4163@brightrain.aerifal.cx>
 <9fc9c45ff6e14df80ad023e66ff7a978bd4ec91c.camel@intel.com>
 <20240220235415.GP4163@brightrain.aerifal.cx>
 <a57d6c7eada4b9a7c35addbc8556f5b53a0c3e6f.camel@intel.com>
Precedence: bulk
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha512;
	protocol="application/pgp-signature"; boundary="zmCyS0Odp0mOsqor"
Content-Disposition: inline
In-Reply-To: <a57d6c7eada4b9a7c35addbc8556f5b53a0c3e6f.camel@intel.com>


--zmCyS0Odp0mOsqor
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline

On Wed, Feb 21, 2024 at 12:35:48AM +0000, Edgecombe, Rick P wrote:

> doing. But those threads might be using shadow stack instructions
> (INCSSP, RSTORSSP, etc). These are a collection of instructions that
> allow limited control of the SSP. When shadow stack gets disabled,
> these suddenly turn into #UD generating instructions. So any other
> threads executing those instructions when shadow stack got disabled
> would be in for a nasty surprise.

> Glibc's permissive mode (that disables shadow stack when dlopen()ing a
> DSO that doesn't support shadow stack) is quite limited because of
> this. There was a POC for working around it, but I'll stop there for
> now, to not spam you with the details. I'm not sure of arm and risc-v
> details on this specific corner, but for x86.

We have the same issue with disabling GCS causing GCS instructions to
become undefined.

--zmCyS0Odp0mOsqor
Content-Type: application/pgp-signature; name="signature.asc"

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

iQEzBAABCgAdFiEEreZoqmdXGLWf4p/qJNaLcl1Uh9AFAmXVR3oACgkQJNaLcl1U
h9BO9Qf/bgPI/9ROkHiV6cP5ag9FVPBuoU4y8o043FWrLxXipYjgLbjIps3r7NYd
VLNWiX+sScsGrwtujlkAC3JYU0QAro+3+MY0cp+MjZopgqrEpOHlREM+dZO4FSB+
BH4GTQgpADdgkbaukCb71Yd8D8HkPkpjvvsEGO6Kv2Bq4kMF6w2sd5O/llI+5BPN
0v1hps6/0VWFICJibmb4hRIRPMjb91mxGQRdpF8OTCgHa0w4UXaTHLttIE3iqCd4
nyeOZPkoIxUv3fYTVZjAqm6emWXXodOaOQrOtjTM1shBFck2DtY+hJJopNkuwE2j
qeuz0TLv83oNLhiCiSUgT5gKjQrvdA==
=VhGm
-----END PGP SIGNATURE-----

--zmCyS0Odp0mOsqor--