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Sun, 08 Nov 2026 05:27:01 -0800 (PST) Received: from Terra.tail0ac356.ts.net ([198.176.50.208]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3b1278918f4sm2949795a91.6.2026.11.08.05.26.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 08 Nov 2026 05:27:00 -0800 (PST) From: Weiming Shi To: Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , K Prateek Nayak Cc: linux-kernel@vger.kernel.org, Marco Elver , Mathieu Desnoyers , co+cab19e2ebe4d535a@bugs.sh, Xiang Mei , Weiming Shi , stable@vger.kernel.org Subject: [PATCH v2] sched/mmcid: Synchronize exec MM teardown with affinity updates Date: Sun, 8 Nov 2026 05:26:35 -0800 Message-ID: <20261108132634.2650642-2-bestswngs@gmail.com> X-Mailer: git-send-email 2.56.0 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit set_cpus_allowed_common() passes a remote task's p->mm to mm_update_cpus_allowed(), but the scheduler locks do not stabilize that pointer against exec. A same-owner sched_setaffinity() can race the target replacing and freeing its old mm. Current kernels are only incidentally serialized by futex_exec_done() taking p->pi_lock when CONFIG_FUTEX=y; valid CONFIG_FUTEX=n builds remain vulnerable. BUG: KASAN: slab-use-after-free in set_cpus_allowed_common (kernel/sched/core.c:10835 kernel/sched/core.c:2829) Read of size 4 at addr ffff88810991b04c by task poc/5127 Call Trace: set_cpus_allowed_common (kernel/sched/core.c:10835 kernel/sched/core.c:2829) set_cpus_allowed_fair (kernel/sched/fair.c:10046) __set_cpus_allowed_ptr_locked (kernel/sched/core.c:2842 kernel/sched/core.c:3224) __set_cpus_allowed_ptr (kernel/sched/core.c:3258) __sched_setaffinity (kernel/sched/syscalls.c:1161) sched_setaffinity (kernel/sched/syscalls.c:1239) __x64_sys_sched_setaffinity (kernel/sched/syscalls.c:1275) do_syscall_64 (arch/x86/entry/syscall_64.c:84) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121) Freed by task 5128: kmem_cache_free (mm/slub.c:6757) __mmput (kernel/fork.c:1204) mmput (kernel/fork.c:1215) setup_new_exec (fs/exec.c:1395) load_elf_binary (fs/binfmt_elf.c:1024) bprm_execve (fs/exec.c:1865) do_execveat_common.isra.0 (fs/exec.c:1963) __x64_sys_execve (fs/exec.c:2036) do_syscall_64 (arch/x86/entry/syscall_64.c:84) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121) After exec publishes the new p->mm, acquire and release the task's runqueue lock before the old mm can be dropped. Affinity updates already hold that lock across set_cpus_allowed_common(), so the barrier waits for any update that loaded the old mm. Updates that start afterwards observe the new mm. This keeps allowed-mask updates synchronous, including transient affinity expansions, without changing the MM-CID fork, exit, or scheduling paths. This change was developed with assistance from an LLM. Fixes: 7e019dcc470f ("sched: Improve cache locality of RSEQ concurrency IDs for intermittent workloads") Cc: stable@vger.kernel.org Reported-by: Signed-off-by: Weiming Shi --- Changes in v2: - Replace the schedule-in deferral with an exec-side runqueue-lock barrier. - Keep affinity expansions synchronous, including expansions narrowed before the next schedule-in. - Avoid changes to the MM-CID fork, exit, and scheduling state machine. fs/exec.c | 1 + include/linux/sched.h | 2 ++ kernel/sched/core.c | 6 ++++++ 3 files changed, 9 insertions(+) diff --git a/fs/exec.c b/fs/exec.c index 8d2b14e1d455..2e1cac6a3de7 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -905,6 +905,7 @@ static int exec_mmap(struct linux_binprm *bprm) BUG_ON(active_mm != old_mm); /* Defer teardown to setup_new_exec(), outside the exec locks. */ bprm->old_mm = old_mm; + sched_mm_cid_exec_mmap(tsk); } else { mmdrop_lazy_tlb(active_mm); } diff --git a/include/linux/sched.h b/include/linux/sched.h index 1c93da75226e..9b3d4d609273 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -2358,6 +2358,7 @@ static __always_inline void alloc_tag_restore(struct alloc_tag *tag, struct allo #ifdef CONFIG_SCHED_MM_CID void sched_mm_cid_before_execve(struct task_struct *t); void sched_mm_cid_after_execve(struct task_struct *t); +void sched_mm_cid_exec_mmap(struct task_struct *t); void sched_mm_cid_exit(struct task_struct *t); static __always_inline int task_mm_cid(struct task_struct *t) { @@ -2366,6 +2367,7 @@ static __always_inline int task_mm_cid(struct task_struct *t) #else static inline void sched_mm_cid_before_execve(struct task_struct *t) { } static inline void sched_mm_cid_after_execve(struct task_struct *t) { } +static inline void sched_mm_cid_exec_mmap(struct task_struct *t) { } static inline void sched_mm_cid_exit(struct task_struct *t) { } static __always_inline int task_mm_cid(struct task_struct *t) { diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 04b62c16fa8c..c9fc8c1cd46f 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -11128,6 +11128,12 @@ void sched_mm_cid_after_execve(struct task_struct *t) sched_mm_cid_fork(t); } +/* Wait for affinity updates that may still be using the old MM. */ +void sched_mm_cid_exec_mmap(struct task_struct *t) +{ + guard(task_rq_lock)(t); +} + static void mm_cid_work_fn(struct work_struct *work) { struct mm_struct *mm = container_of(work, struct mm_struct, mm_cid.work); -- 2.56.0