linux-kernel - Re: [PATCH v8 04/12] arm64: ptrace: Move rseq_syscall() before audit_syscall

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Message-ID: <5997e6bb-4d69-46a7-821f-72d470f6ddff@arm.com>
Date: Thu, 27 Nov 2025 14:28:45 +0100
From: Kevin Brodsky <kevin.brodsky@....com>
To: Jinjie Ruan <ruanjinjie@...wei.com>, catalin.marinas@....com,
 will@...nel.org, oleg@...hat.com, tglx@...utronix.de, peterz@...radead.org,
 luto@...nel.org, shuah@...nel.org, kees@...nel.org, wad@...omium.org,
 charlie@...osinc.com, akpm@...ux-foundation.org, ldv@...ace.io,
 macro@...am.me.uk, deller@....de, mark.rutland@....com, efault@....de,
 song@...nel.org, mbenes@...e.cz, ryan.roberts@....com,
 ada.coupriediaz@....com, anshuman.khandual@....com, broonie@...nel.org,
 pengcan@...inos.cn, dvyukov@...gle.com, kmal@...k.li,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v8 04/12] arm64: ptrace: Move rseq_syscall() before
 audit_syscall_exit()

On 26/11/2025 08:14, Jinjie Ruan wrote:
> commit a9f3a74a29af ("entry: Provide generic syscall exit function")
> introduce generic syscall exit function and call rseq_syscall()
> before audit_syscall_exit() and arch_syscall_exit_tracehook().
>
> And commit b74406f37737 ("arm: Add syscall detection for restartable
> sequences") add rseq support for arm32, which also call rseq_syscall()
> before audit_syscall_exit() and tracehook_report_syscall().
>
> However, commit 409d5db49867c ("arm64: rseq: Implement backend rseq
> calls and select HAVE_RSEQ") implement arm64 rseq and call
> rseq_syscall() after audit_syscall_exit() and tracehook_report_syscall().
>
> So compared to the generic entry and arm32 code, arm64 terminates
> the process a bit later if the syscall is issued within
> a restartable sequence.
>
> But as commit b74406f37737 ("arm: Add syscall detection for restartable
> sequences") said, syscalls are not allowed inside restartable sequences,
> so should call rseq_syscall() at the very beginning of system call
> exiting path for CONFIG_DEBUG_RSEQ=y kernel. This could help us to detect
> whether there is a syscall issued inside restartable sequences.
>
> It makes sense to raise SIGSEGV via rseq_syscall() before auditing
> and ptrace syscall exit, because this guarantees that the process is
> already in an error state with SIGSEGV pending when those later steps
> run. Although it makes no practical difference to signal delivery (signals
> are processed at the very end in arm64_exit_to_user_mode()), the ordering
> is more logical: detect and flag the error first, then proceed with
> the remaining work.

Thanks for providing this separate patch with a detailed rationale!

> 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().
>
> Signed-off-by: Jinjie Ruan <ruanjinjie@...wei.com>

Reviewed-by: Kevin Brodsky <kevin.brodsky@....com>