From mboxrd@z Thu Jan  1 00:00:00 1970
From: Michael Ellerman <mpe@ellerman.id.au>
Subject: Re: [PATCH v2] arch: Reserve map_shadow_stack() syscall number for
 all architectures
Date: Fri, 15 Sep 2023 13:23:43 +1000
Message-ID: <878r986rwg.fsf@mail.lhotse>
References: <20230914185804.2000497-1-sohil.mehta@intel.com>
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To: Sohil Mehta <sohil.mehta@intel.com>, linux-api@vger.kernel.org, linux-arch@vger.kernel.org
Cc: Sohil Mehta <sohil.mehta@intel.com>, Richard Henderson <richard.henderson@linaro.org>, Ivan Kokshaysky <ink@jurassic.park.msu.ru>, Matt Turner <mattst88@gmail.com>, Russell King <linux@armlinux.org.uk>, Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will@kernel.org>, Geert Uytterhoeven <geert@linux-m68k.org>, Michal Simek <monstr@monstr.eu>, Thomas Bogendoerfer <tsbogend@alpha.franken.de>, "James E . J . Bottomley" <James.Bottomley@HansenPartnership.com>, Helge Deller <deller@gmx.de>, Nicholas Piggin <npiggin@gmail.com>, Christophe Leroy <christophe.leroy@csgroup.eu>, Heiko Carstens <hca@linux.ibm.com>, Vasily Gorbik <gor@linux.ibm.com>, Alexander Gordeev <agordeev@linux.ibm.com>, Christian Borntraeger <borntraeger@linux.ibm.com>, Sv

Sohil Mehta <sohil.mehta@intel.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@ellerman.id.au> (powerpc)

cheers