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Tue, 1 Sep 2026 09:17:22 +0000 (GMT) Content-Type: text/plain; charset=utf-8 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3864.600.51.1.1\)) Subject: Re: [PATCH] powerpc/entry: Clear TIF_SYSCALL_RET before syscall error return From: Venkat In-Reply-To: <20260828053811.1042300-1-sshegde@linux.ibm.com> Date: Tue, 1 Sep 2026 14:47:10 +0530 Cc: tglx@kernel.org, maddy@linux.ibm.com, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, chleroy@kernel.org, sbhat@linux.ibm.com, mkchauras@gmail.com Content-Transfer-Encoding: quoted-printable Message-Id: <51BB4B46-5227-4FE6-A368-A05E45CA4915@linux.ibm.com> References: <20260828053811.1042300-1-sshegde@linux.ibm.com> To: Shrikanth Hegde X-Mailer: Apple Mail (2.3864.600.51.1.1) X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-GUID: v7kA_hfiVqwZZueVb-2Av2MN1UpneIZ4 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwOTAxMDA4MCBTYWx0ZWRfXxgo11J9td64p xwQ85WOSAFWgbz3P258pYKaymgxOGjIahzKvxMKeAxVArVKV4B+g6cnIpYOEUzPECouPD4+Lvna FT4Ll9+4totAcrQ3YQN/KHYdsrISqAHBcBVQtFvLkCimmgMf0mRQWQ9+qMtgB87Ub7YCcVNXd9K 56jkqGNTvOd796pzU4IwDr7hnvsFCbexc9Yn/fAgVJ9xfyz6MqhyCiBNe9gBBJ6vkElElL2oAKm a+z9ladbu7n2Hr5QfCLPj87cBBAU0ILHzMHCjyTJt4c+TL/zjLmMCNr9U04ggRqfgzNEglzoQ8m Zdx/hdEk+p4aNiTGbVRAHBUHwMsFYTOzSpHJG+ND/z6o3HDz6o4Wp9S1YG1r9HIJgJwbqN8ki6y 8kcoThj0fSwKVgGcYAKXjGPefj3ApKUhIGX656SA9bAFPN6oEQEMHPnBAgyeaz+BNaoPBbdiA/5 6f68MpfGrSliZ95coww== X-Proofpoint-ORIG-GUID: 0OnnASqNBx2GEwqB5pYim-XRWPOggbg3 X-Proofpoint-Spam-Info: AW1haW4tMjYwOTAxMDA4MCBTYWx0ZWRfX0D8oKDWmy931 YkV/VChb5SvWyyN+tZd9h+L6HMT3Clp5fkhBqHomyXIy2TDwc79pKwZYNzqJSwZziO57esidXM0 OEJpThLrZ1KQBGG71nyc7irYC59aDm0= X-Authority-Analysis: v=2.4 cv=B92JFutM c=1 sm=1 tr=0 ts=6a969828 cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=IkcTkHD0fZMA:10 a=VdqzKS8jKosA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=V8glGbnc2Ofi9Qvn3v5h:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=jdSCQhKvPWLdp4stf3gA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-09-01_02,2026-08-31_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 adultscore=0 spamscore=0 clxscore=1015 suspectscore=0 phishscore=0 lowpriorityscore=0 bulkscore=0 priorityscore=1501 impostorscore=0 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2609010080 > On 28 Aug 2026, at 11:08=E2=80=AFAM, Shrikanth Hegde = wrote: >=20 > Shivaprasad reported a boot failure due to userspace processes crash = on > abort() from libc.so.6. It was bisected to merge request > commit '3424d8c18a7d ("Merge tag 'core-entry-2026-08-17' of=20 > git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip")' >=20 > Upon checking the merge, when = syscall_enter_from_user_mode_randomize_stack > fails, which could happen when a tracer like seccomp or ptrace = intercepts > and skips the syscall, the code returns to userspace immediately = without > clearing the intermediate flag which was set. >=20 > When the next syscall is made, it immediately aborts the valid syscall > since the flag is still set. Hence clear the flag on occurrence of = first > failure. >=20 > Reported-by: Shivaprasad G Bhat > Closes: = https://lore.kernel.org/all/e301014d-568f-4ed5-bc64-b8a85ca0b1e1@linux.ibm= .com/ > Fixes: 3424d8c18a7d ("Merge tag 'core-entry-2026-08-17' of = git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip") > Signed-off-by: Shrikanth Hegde > --- Tested-by: Venkat Rao Bagalkote Regards, Venkat. > PS: I have kept the block below since earlier code was checking it > regardless of result of syscall_enter_from_user_mode. If it turns out > to be a redundant, it can be removed later. >=20 > arch/powerpc/kernel/syscall.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) >=20 > diff --git a/arch/powerpc/kernel/syscall.c = b/arch/powerpc/kernel/syscall.c > index 4916c205c4bb..fbefe1927b10 100644 > --- a/arch/powerpc/kernel/syscall.c > +++ b/arch/powerpc/kernel/syscall.c > @@ -18,8 +18,10 @@ notrace long system_call_exception(struct pt_regs = *regs, unsigned long r0) > long ret; > syscall_fn f; >=20 > - if (unlikely(!syscall_enter_from_user_mode_randomize_stack(regs, = &r0))) > + if (unlikely(!syscall_enter_from_user_mode_randomize_stack(regs, = &r0))) { > + clear_thread_flag(TIF_SYSCALL_RET); > return syscall_get_error(current, regs); > + } >=20 > if (unlikely(test_and_clear_thread_flag(TIF_SYSCALL_RET))) > return syscall_get_error(current, regs); > --=20 > 2.47.3 >=20