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

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Message-Id: <231994b0-ca11-4347-8d93-ce66fdbe3d25@app.fastmail.com>
Date:   Tue, 03 Oct 2023 18:54:59 +0200
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Sohil Mehta" <sohil.mehta@...el.com>, linux-api@...r.kernel.org,
        Linux-Arch <linux-arch@...r.kernel.org>
Cc:     "Richard Henderson" <richard.henderson@...aro.org>,
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Subject: Re: [PATCH v2] arch: Reserve map_shadow_stack() syscall number for all
 architectures

On Tue, Oct 3, 2023, at 18:35, Sohil Mehta wrote:
> On 9/14/2023 11:58 AM, Sohil Mehta 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@...el.com>
>> ---
>
> Gentle ping...
>
> Are there any additional comments? It applies cleanly on 6.6-rc4.
>
> Or does it seem ready to be merged? It has the following
> acknowledgements until now:
>
> Reviewed-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
> Acked-by: Michael Ellerman <mpe@...erman.id.au> (powerpc)
>

Reviewed-by: Arnd Bergmann <arnd@...db.de>

If you like, I can pick this up for 6.7 through the asm-generic
tree. If you think this should be part of 6.6, I would suggest
to merge it through the tree that originally contained the
syscall code.

      Arnd