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Peter Anvin" , Andrew Donnellan , Mark Rutland , Arnd Bergmann , Jiaxun Yang , Ryan Roberts , Greg Kroah-Hartman , Mukesh Kumar Chaurasiya , Shrikanth Hegde , Zong Li , Nam Cao , Deepak Gupta , Lukas Gerlach , Rui Qi , Kees Cook , 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 In-Reply-To: References: Date: Thu, 02 Jul 2026 10:12:35 +0200 Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-GUID: DKlldyY4bhkCnlcbefPy2HU56VqtiBGr X-Proofpoint-Spam-Info: AW1haW4tMjYwNzAyMDA3OSBTYWx0ZWRfXyOQuthEL9my+ L3goQ8RSe3aEKWelY2bJXttBAFwFZ3nxAMd4YsPCcEXn38MypvsePfJ6K0Xa0t/CkI83BjCtnVw m6hD2NKtpMS8QTJ1dKDLehpY3uSIRHk= X-Authority-Analysis: v=2.4 cv=edsNubEH c=1 sm=1 tr=0 ts=6a461d79 cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=IkcTkHD0fZMA:10 a=RAioF0-LDSMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=iQ6ETzBq9ecOQQE5vZCe:22 a=H7Grb0cKppj6FskhoBQA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNzAyMDA3OSBTYWx0ZWRfX/oe4D2SHEsm8 fnh8Zogh7aWRM7RCWhvCxl9KxCazzx0GZhXpTwQ6IVs2rk1Lht0I2Pw7XYWwx94bCT3Ez7rq8Dg lg8HV4ioS+8K8e2rqvVEnOYfMVPDiJZERcROKpg9FVgHynbSsV/0kzAosEQ+xeI4rV2SVE0ldfP T/9tPCQSRrH3OFOXXIOJF8xBBCWy/L2bfBCsah4ga0qm4ebPbs3ZjFLYIwziTnpFKZxHXHmd98N MYh5DqQ2fp7GI0HPArVfNFgaDdDflOraiPWOnzhqFhPDp2lG56c8K0xzWRL3jW6kUeiDKuXG+Nk YxA5p0vWRe8IkAgAj8cQkTfxSxUnmjY99x2Cj4BgrgbekYiNXkLROH5O2zrOMUrrb+POiYKlvOZ HnQMDbLmGSoz9dPTQu7oFDFNks2D4/MlmtTaw+2HyBz8naZWPeeOO6fVfljQpTQ/9wmpAyeBa30 MxGwR6nRsgmgvSeCamw== X-Proofpoint-ORIG-GUID: BbxRzj5OULkjMR0AZe7xHLImpWA5FvbD X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.125,FMLib:17.12.100.49 definitions=2026-07-02_01,2026-06-26_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 adultscore=0 impostorscore=0 bulkscore=0 spamscore=0 suspectscore=0 clxscore=1011 lowpriorityscore=0 phishscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2607020079 Michal Such=C3=A1nek 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.