Re: [PATCH v2] arch: Reserve map_shadow_stack() syscall number for all architectures

Geert Uytterhoeven
2023-10-03T17:20:14Z

On Thu, Sep 14, 2023 at 8:59 PM Sohil Mehta <sohil.mehta@intel.com> wrote:
> commit c35559f94ebc ("x86/shstk: Introduce map_shadow_stack syscall")
> recently added support for map_shadow_stack() but it is limited to x86
> only for now. There is a possibility that other architectures (namely,
> arm64 and RISC-V), that are implementing equivalent support for shadow
> stacks, might need to add support for it.
>
> Independent of that, reserving arch-specific syscall numbers in the
> syscall tables of all architectures is good practice and would help
> avoid future conflicts. map_shadow_stack() is marked as a conditional
> syscall in sys_ni.c. Adding it to the syscall tables of other
> architectures is harmless and would return ENOSYS when exercised.
>
> Note, map_shadow_stack() was assigned #453 during the merge process
> since #452 was taken by fchmodat2().
>
> For Powerpc, map it to sys_ni_syscall() as is the norm for Powerpc
> syscall tables.
>
> For Alpha, map_shadow_stack() takes up #563 as Alpha still diverges from
> the common syscall numbering system in the other architectures.
>
> Link: https://lore.kernel.org/lkml/20230515212255.GA562920@debug.ba.rivosinc.com/
> Link: https://lore.kernel.org/lkml/b402b80b-a7c6-4ef0-b977-c0f5f582b78a@sirena.org.uk/
>
> Signed-off-by: Sohil Mehta <sohil.mehta@intel.com>

> arch/m68k/kernel/syscalls/syscall.tbl | 1 +

Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>

Gr{oetje,eeting}s,

Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

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