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

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Date:   Fri, 15 Sep 2023 13:23:43 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Sohil Mehta <sohil.mehta@...el.com>, linux-api@...r.kernel.org,
        linux-arch@...r.kernel.org
Cc:     Sohil Mehta <sohil.mehta@...el.com>,
        Richard Henderson <richard.henderson@...aro.org>,
        Ivan Kokshaysky <ink@...assic.park.msu.ru>,
        Matt Turner <mattst88@...il.com>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Michal Simek <monstr@...str.eu>,
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Subject: Re: [PATCH v2] arch: Reserve map_shadow_stack() syscall number for
 all architectures

Sohil Mehta <sohil.mehta@...el.com> 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 <mpe@...erman.id.au> (powerpc)

cheers