From: Sven Schnelle <svens@linux.ibm.com>
To: "Michal Suchánek" <msuchanek@suse.de>
Cc: Peter Zijlstra <peterz@infradead.org>,
Jonathan Corbet <corbet@lwn.net>,
Shuah Khan <skhan@linuxfoundation.org>,
Huacai Chen <chenhuacai@kernel.org>,
WANG Xuerui <kernel@xen0n.name>,
Madhavan Srinivasan <maddy@linux.ibm.com>,
Michael Ellerman <mpe@ellerman.id.au>,
Nicholas Piggin <npiggin@gmail.com>,
"Christophe Leroy (CS GROUP)" <chleroy@kernel.org>,
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Albert Ou <aou@eecs.berkeley.edu>,
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Alexander Gordeev <agordeev@linux.ibm.com>,
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Lukas Gerlach <lukas.gerlach@cispa.de>,
Rui Qi <qirui.001@bytedance.com>, Kees Cook <kees@kernel.org>,
linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
loongarch@lists.linux.dev, linuxppc-dev@lists.ozlabs.org,
linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org
Subject: Re: [RFC] entry: Untangle the return value of syscall_enter_from_user_mode from syscall NR
Date: Thu, 02 Jul 2026 10:12:35 +0200 [thread overview]
Message-ID: <yt9dechlbyj0.fsf@linux.ibm.com> (raw)
In-Reply-To: <akVRcPsD_R_CE1qW@kunlun.suse.cz>
Michal Suchánek <msuchanek@suse.de> writes:
> The return value of syscall_enter_from_user_mode is used both for the
> adjusted syscall number and the indicator that a syscall should be
> skipped.
>
> As seccomp can be invoked on any syscall, including invalid ones this
> somewhat undermines seccomp.
>
> While the seccomp variants that terminate the process do not need to
> care about this for the filter that sets the syscall return value this
> disctinction is required.
>
> Pass the syscall number as a pointer to the inline entry functions, and
> use the return value exclusively for the indication that the syscall is
> already handled.
>
> This should avoid the need for the s390 PIF_SYSCALL_RET_SET which is the
> workaround for exactly this deficiency.
I'm not sure whether PIF_SYSCALL_RET_SET can be removed - the syscall
return might still get set by PTRACE_SET_SYSCALL_INFO when the tracee is
stopped. This might be a positive number which can't be distinguished
from a syscall number. But maybe i'm missing something? It's been quite
a while since I touched all that ptrace stuff.
next prev parent reply other threads:[~2026-07-02 8:14 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-01 17:42 [RFC] entry: Untangle the return value of syscall_enter_from_user_mode from syscall NR Michal Suchánek
2026-07-01 18:29 ` H. Peter Anvin
2026-07-02 9:30 ` Michal Suchánek
2026-07-02 21:49 ` Thomas Gleixner
2026-07-02 8:12 ` Sven Schnelle [this message]
2026-07-02 9:12 ` Michal Suchánek
2026-07-02 12:01 ` Sven Schnelle
2026-07-02 12:13 ` Michal Suchánek
2026-07-02 11:24 ` Thomas Gleixner
2026-07-02 11:45 ` Michal Suchánek
2026-07-02 20:45 ` Thomas Gleixner
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