The patch below does not apply to the 6.6-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y git checkout FETCH_HEAD git cherry-pick -x 6eb350a2233100a283f882c023e5ad426d0ed63b # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2025101555-glimpse-gauntlet-5c2a@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 6eb350a2233100a283f882c023e5ad426d0ed63b Mon Sep 17 00:00:00 2001 From: Thomas Gleixner tglx@linutronix.de Date: Wed, 13 Aug 2025 17:02:30 +0200 Subject: [PATCH] rseq: Protect event mask against membarrier IPI

rseq_need_restart() reads and clears task::rseq_event_mask with preemption disabled to guard against the scheduler.

But membarrier() uses an IPI and sets the PREEMPT bit in the event mask from the IPI, which leaves that RMW operation unprotected.

Use guard(irq) if CONFIG_MEMBARRIER is enabled to fix that.

Fixes: 2a36ab717e8f ("rseq/membarrier: Add MEMBARRIER_CMD_PRIVATE_EXPEDITED_RSEQ") Signed-off-by: Thomas Gleixner tglx@linutronix.de Reviewed-by: Boqun Feng boqun.feng@gmail.com Reviewed-by: Mathieu Desnoyers mathieu.desnoyers@efficios.com Cc: stable@vger.kernel.org

diff --git a/include/linux/rseq.h b/include/linux/rseq.h index bc8af3eb5598..1fbeb61babeb 100644 --- a/include/linux/rseq.h +++ b/include/linux/rseq.h @@ -7,6 +7,12 @@ #include <linux/preempt.h> #include <linux/sched.h>

+#ifdef CONFIG_MEMBARRIER +# define RSEQ_EVENT_GUARD irq +#else +# define RSEQ_EVENT_GUARD preempt +#endif + /* * Map the event mask on the user-space ABI enum rseq_cs_flags * for direct mask checks. @@ -41,9 +47,8 @@ static inline void rseq_handle_notify_resume(struct ksignal *ksig, static inline void rseq_signal_deliver(struct ksignal *ksig, struct pt_regs *regs) { - preempt_disable(); - __set_bit(RSEQ_EVENT_SIGNAL_BIT, &current->rseq_event_mask); - preempt_enable(); + scoped_guard(RSEQ_EVENT_GUARD) + __set_bit(RSEQ_EVENT_SIGNAL_BIT, &current->rseq_event_mask); rseq_handle_notify_resume(ksig, regs); }

diff --git a/kernel/rseq.c b/kernel/rseq.c index b7a1ec327e81..2452b7366b00 100644 --- a/kernel/rseq.c +++ b/kernel/rseq.c @@ -342,12 +342,12 @@ static int rseq_need_restart(struct task_struct *t, u32 cs_flags)

/* * Load and clear event mask atomically with respect to - * scheduler preemption. + * scheduler preemption and membarrier IPIs. */ - preempt_disable(); - event_mask = t->rseq_event_mask; - t->rseq_event_mask = 0; - preempt_enable(); + scoped_guard(RSEQ_EVENT_GUARD) { + event_mask = t->rseq_event_mask; + t->rseq_event_mask = 0; + }

return !!event_mask; }