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Two fixes for RSEQ:

Browse Source 
1) Protect the event mask modification against the membarrier() IPI as
      otherwise the RmW operation is unprotected and events might be lost.
 
   2) 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 the 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.
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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
This commit is contained in:
Linus Torvalds 2025-09-30 15:06:33 -07:00
commit 1d17e808cf
3 changed files with 17 additions and 12 deletions
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11
include/linux/rseq.h
View File

@ -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);
}

10
kernel/rseq.c
View File

@ -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;
}

8
tools/testing/selftests/rseq/rseq.c
View File

@ -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");