linux-kernel - Re: [PATCH v10 38/40] kselftest/arm64: Add a GCS stress test

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Message-ID: <87y157cz2h.fsf@linaro.org>
Date: Thu, 08 Aug 2024 03:23:50 -0300
From: Thiago Jung Bauermann <thiago.bauermann@...aro.org>
To: Mark Brown <broonie@...nel.org>
Cc: Catalin Marinas <catalin.marinas@....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>,
  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>,
  Kees Cook <kees@...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>,  Florian Weimer <fweimer@...hat.com>,
  Christian Brauner <brauner@...nel.org>,  Ross Burton
 <ross.burton@....com>,  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 v10 38/40] kselftest/arm64: Add a GCS stress test

Mark Brown <broonie@...nel.org> writes:

> On Wed, Aug 07, 2024 at 07:39:54PM -0300, Thiago Jung Bauermann wrote:
> 
>> # # Thread-4870: Failed to enable GCS
>
> which is printed if a basic PR_SET_SHADOW_STACK_STATUS fails immediately
> the program starts executing:
>
> function _start
>         // Run with GCS
>         mov     x0, PR_SET_SHADOW_STACK_STATUS
>         mov     x1, PR_SHADOW_STACK_ENABLE
>         mov     x2, xzr
>         mov     x3, xzr
>         mov     x4, xzr
>         mov     x5, xzr
>         mov     x8, #__NR_prctl
>         svc     #0
>         cbz     x0, 1f
>         puts    "Failed to enable GCS\n"
>         b       abort
>
> the defines for which all seem up to date (and unlikely to fail in
> system or config specific fashions).  What happens if you try to execute
> the gcs-stress-thread binary directly, does strace show anything
> interesting?  If you instrument arch_set_shadow_stack_status() in the
> kernel does it show anything?

Thank you for the pointer. It turned out that I accidentally ran the
selftests binaries from the v9 version instead of the v10 version, and
the gcs-stress-thread binary failed because it was using the old value
for PR_SET_SHADOW_STACK_STATUS.

Using the v10 version of the selftests the gcs-stress test passes. Sorry
for the false alarm.

Tested-by: Thiago Jung Bauermann <thiago.bauermann@...aro.org>

-- 
Thiago