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

[Thiago Jung Bauermann]

Mark Brown <broonie@xxxxxxxxxx> 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@xxxxxxxxxx>

-- 
Thiago