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

From: Michael Ellerman <[email-masked]>
Date: Fri, 15 Sep 2023 13:23:43 +1000

Sohil Mehta <[email-masked]> writes:
> 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.

Mapping it to sys_map_shadow_stack() would work fine, but I'm happy with
sys_ni_syscall as I don't see powerpc implementing map_shadow_stack()
any time soon.

Acked-by: Michael Ellerman <[email-masked]> (powerpc)

cheers