linux-kernel - Re: [PATCH v10 05/16] arm64: ptrace: Move rseq_syscall() before audit_syscall

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Message-ID: <28e54f74-9b3d-4c3c-9172-ceb429e7fcbe@arm.com>
Date: Tue, 27 Jan 2026 10:44:17 +0100
From: Kevin Brodsky <kevin.brodsky@....com>
To: Will Deacon <will@...nel.org>, Jinjie Ruan <ruanjinjie@...wei.com>
Cc: catalin.marinas@....com, oleg@...hat.com, tglx@...utronix.de,
 peterz@...radead.org, luto@...nel.org, shuah@...nel.org, kees@...nel.org,
 wad@...omium.org, macro@...am.me.uk, charlie@...osinc.com,
 akpm@...ux-foundation.org, ldv@...ace.io, anshuman.khandual@....com,
 mark.rutland@....com, thuth@...hat.com, song@...nel.org,
 ryan.roberts@....com, ada.coupriediaz@....com, broonie@...nel.org,
 liqiang01@...inos.cn, pengcan@...inos.cn, kmal@...k.li, dvyukov@...gle.com,
 richard.weiyang@...il.com, reddybalavignesh9979@...il.com,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v10 05/16] arm64: ptrace: Move rseq_syscall() before
 audit_syscall_exit()

On 26/01/2026 20:02, Will Deacon wrote:
> On Mon, Dec 22, 2025 at 07:47:26PM +0800, Jinjie Ruan wrote:
>> [...]
>>
>> To make it more reasonable and in preparation for moving arm64 over to
>> the generic entry code, move rseq_syscall() ahead before
>> audit_syscall_exit().
> I've been struggling a bit to see how this helps to align with the
> generic code.

rseq_syscall(), or rather rseq_debug_syscall_return() since eaa9088d568c
("rseq: Use static branch for syscall exit debug when
GENERIC_IRQ_ENTRY=y"), is called first in the generic
syscall_exit_to_user_mode_work(), so the aim of that patch is to align
the order of calls with generic entry.

>  I'm also concerned that rseq_debug_update_user_cs()
> operates on instruction_pointer(regs) which is something that can be
> chaned by ptrace.

Isn't that true regardless of where rseq_syscall() is called on the
syscall exit path, though?

> So, I'm not saying this is wrong, but it feels like a user-visible
> change that needs better justification.

This seems to hang on whether the force_sig(SIGSEGV) that rseq_syscall()
might issue interacts in any way with the tracing calls. My feeling is
that it doesn't, but I haven't confirmed it. Worth noting this is only
relevant if rseq debugging is enabled, so any potential user-visible
effect is limited.

- Kevin