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

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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
parent 7601d18be0 a001cd248a
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");