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McKenney" , Boqun Feng , Thomas Gleixner , Dmitry Vyukov , Alexander Potapenko Cc: linux-kernel@vger.kernel.org, Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Aleksei Nikiforov , linux-s390@vger.kernel.org, Ilya Leoshkevich Subject: [PATCH] rseq: Out-of-line rseq_exit_user_update() for KMSAN Date: Tue, 18 Aug 2026 20:12:49 +0200 Message-ID: <20260818181328.2963038-1-iii@linux.ibm.com> X-Mailer: git-send-email 2.55.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-GUID: Rth__ZDKU1atolB_Z0s1vOlrITZsLJUu X-Proofpoint-ORIG-GUID: 9HoS9nQBnbhUbhGlj_iOHJoLT0nHkEYy X-Proofpoint-Spam-Info: AW1haW4tMjYwODE4MDEzMyBTYWx0ZWRfX+9YABC+a0Of+ S7reecgzODwjaSFKb050v0CduCMPIReXYNOd5h/2xF/CJPQgG7Z1ffaJoBDl5nWBzYlpegBY2Yx jizlc6sdLwFiwxeFQw6YDtUFCDtYkrA= X-Authority-Analysis: v=2.4 cv=WtQb99fv c=1 sm=1 tr=0 ts=6a84a0f5 cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=Sv0fKeRqtYgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=iQ6ETzBq9ecOQQE5vZCe:22 a=VnNF1IyMAAAA:8 a=4DPV4PFdrL5DSAU6TMgA:9 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwODE4MDEzMyBTYWx0ZWRfX86URenIvRDuT fMyqxpwgobcIVhcHbk5bFaAtstqWeXYvHrndrq3Uz254smpKO/r73ncQrkACoYUOVtq44QSy2aR TvxoDSVH5mCUO6q0md8MZXzT1dkse9jKVJEIjtGuth6OJ6XemGP9XujUbDKvIL0cfZEupMKOlB9 kKIIomphd+XnDw9+uHvg6/fSaMoEzqYJx8zY11t0zdDekB2UE0nx0GJd8ltpm9OceqG0o4Qzm7q orwckRw2K+aYVBZSyoXCVOqUjpW81xnJa0ja2OoNLQpzPatR1yFaZem6TWyNSehLFc1n7qHfbcw /AJPT8IdP/AeDJajT1MwSAI0kmS9MS3ikxsEk5ZnaMrT7Y4eFr0IZRuz6JS+F2jrhzvFNVh8ejW EiRVDS42lq/faoTSnycawWoerTsMN3LRqBr1zfYFkU98CV7hB6h3GtnCbtvibyxHG5JgFbOSlpk tooONN79X0m0Gjene/A== 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=2026-08-18_03,2026-08-18_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 spamscore=0 malwarescore=0 suspectscore=0 phishscore=0 lowpriorityscore=0 clxscore=1011 adultscore=0 priorityscore=1501 impostorscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2608180133 KMSAN produces the following false positive on s390x: [ 4.232136] Kernel panic - not syncing: kmsan.panic set ... [ 4.232339] CPU: 7 UID: 0 PID: 1 Comm: virtme-init Tainted: G B N 7.2.0-rc6-virtme #27 PREEMPTLAZY [ 4.232676] Tainted: [B]=BAD_PAGE, [N]=TEST [ 4.232808] Hardware name: IBM 3931 A01 701 (KVM/Linux) [ 4.232971] Call Trace: [ 4.233065] [<000002dcfb993140>] vpanic+0xb50/0x1080 [ 4.239698] [<000002dcfb9925ec>] panic+0x22c/0x230 [ 4.239879] [<000002dcfcec5d32>] kmsan_report+0x322/0x330 [ 4.240081] [<000002dcfcec3592>] kmsan_internal_check_memory+0x222/0x280 [ 4.240304] [<000002dcffe3444e>] irqentry_exit+0x50e/0x8f0 [ 4.240522] [<000002dcffe33454>] __do_pgm_check+0x1b4/0x2b0 [ 4.240740] [<000002dcffe75304>] pgm_check_handler+0x114/0x160 The reason is that the following call chain inlined into the noinstr irqentry_exit() function: irqentry_exit() irqentry_exit_to_user_mode() irqentry_exit_to_user_mode_prepare() __exit_to_user_mode_prepare() exit_to_user_mode_loop() rseq_exit_to_user_mode_restart() __rseq_exit_to_user_mode_restart() rseq_exit_user_update() does not set KMSAN shadow on struct rseq_ids, which is then verified by rseq_exit_user_update() rseq_update_usr() rseq_set_ids_get_csaddr() unsafe_put_user() regardless of presence of KMSAN instrumentation. Fix by out-of-lining rseq_exit_user_update() and compiling the out-of-lined version with KMSAN instrumentation. This should affect other architectures as well, but whether one actually sees it depends on the leftover shadow of struct rseq_ids stack location: s390 is not special here. Fixes: 05b44aef709c ("rseq: Implement fast path for exit to user") Signed-off-by: Ilya Leoshkevich --- include/linux/rseq_entry.h | 9 ++++++++- kernel/rseq.c | 7 +++++++ 2 files changed, 15 insertions(+), 1 deletion(-) diff --git a/include/linux/rseq_entry.h b/include/linux/rseq_entry.h index ed9da6e41a2aa..a396050f771cc 100644 --- a/include/linux/rseq_entry.h +++ b/include/linux/rseq_entry.h @@ -595,7 +595,8 @@ static rseq_inline bool rseq_update_usr(struct task_struct *t, struct pt_regs *r * tells the caller to loop back into exit_to_user_mode_loop(). The rseq * slow path there will handle the failure. */ -static __always_inline bool rseq_exit_user_update(struct pt_regs *regs, struct task_struct *t) +static __always_inline bool rseq_exit_user_update_inline(struct pt_regs *regs, + struct task_struct *t) { /* * Page faults need to be disabled as this is called with @@ -647,6 +648,12 @@ static __always_inline bool rseq_exit_user_update(struct pt_regs *regs, struct t return false; } +#ifdef CONFIG_KMSAN +bool rseq_exit_user_update(struct pt_regs *regs, struct task_struct *t); +#else +#define rseq_exit_user_update rseq_exit_user_update_inline +#endif + static __always_inline bool __rseq_exit_to_user_mode_restart(struct pt_regs *regs) { struct task_struct *t = current; diff --git a/kernel/rseq.c b/kernel/rseq.c index e75e3a5e312c8..be759d7d266b5 100644 --- a/kernel/rseq.c +++ b/kernel/rseq.c @@ -329,6 +329,13 @@ void __rseq_handle_slowpath(struct pt_regs *regs) rseq_slowpath_update_usr(regs); } +#if defined(CONFIG_KMSAN) && defined(CONFIG_GENERIC_ENTRY) +bool rseq_exit_user_update(struct pt_regs *regs, struct task_struct *t) +{ + return rseq_exit_user_update_inline(regs, t); +} +#endif + void __rseq_signal_deliver(int sig, struct pt_regs *regs) { rseq_stat_inc(rseq_stats.signal); -- 2.55.0