Commit 1d17e808 authored by Linus Torvalds's avatar Linus Torvalds
Browse files

Merge tag 'core-rseq-2025-09-29' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 

Pull rseq updates from Thomas Gleixner:
 "Two fixes for RSEQ:

   - Protect the event mask modification against the membarrier() IPI as
     otherwise the RmW operation is unprotected and events might be lost

   - Fix the weak symbol reference in rseq selftests

     The current weak RSEQ symbols definitions which were added to allow
     static linkage are not working correctly as they effectively
     re-define the glibc symbols leading to multiple versions of the
     symbols when compiled with -fno-common.

     Mark them as 'extern' to convert them from weak symbol definitions
     to weak symbol references. That works with static and dynamic
     linkage independent of -fcommon and -fno-common"

* tag 'core-rseq-2025-09-29' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  rseq/selftests: Use weak symbol reference, not definition, to link with glibc
  rseq: Protect event mask against membarrier IPI
parents 7601d18b a001cd24

include/linux/rseq.h

+8 −3
Original line number Diff line number Diff line
@@ -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();

	scoped_guard(RSEQ_EVENT_GUARD)

		__set_bit(RSEQ_EVENT_SIGNAL_BIT, &current->rseq_event_mask);

	preempt_enable();

	rseq_handle_notify_resume(ksig, regs);

}

kernel/rseq.c

+5 −5
Original line number Diff line number Diff line
@@ -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();

	scoped_guard(RSEQ_EVENT_GUARD) {

		event_mask = t->rseq_event_mask;

		t->rseq_event_mask = 0;

	preempt_enable();

	}



	return !!event_mask;

}

tools/testing/selftests/rseq/rseq.c

+4 −4
Original line number Diff line number Diff line
@@ -40,9 +40,9 @@ 
 * Define weak versions to play nice with binaries that are statically linked

 * against a libc that doesn't support registering its own rseq.

 */

__weak ptrdiff_t __rseq_offset;

__weak unsigned int __rseq_size;

__weak unsigned int __rseq_flags;

extern __weak ptrdiff_t __rseq_offset;

extern __weak unsigned int __rseq_size;

extern __weak unsigned int __rseq_flags;



static const ptrdiff_t *libc_rseq_offset_p = &__rseq_offset;

static const unsigned int *libc_rseq_size_p = &__rseq_size;
@@ -209,7 +209,7 @@ void rseq_init(void) 
	 * libc not having registered a restartable sequence.  Try to find the

	 * symbols if that's the case.

	 */

	if (!*libc_rseq_size_p) {

	if (!libc_rseq_size_p || !*libc_rseq_size_p) {

		libc_rseq_offset_p = dlsym(RTLD_NEXT, "__rseq_offset");

		libc_rseq_size_p = dlsym(RTLD_NEXT, "__rseq_size");

		libc_rseq_flags_p = dlsym(RTLD_NEXT, "__rseq_flags");