[PATCH 3/6] kernel: split syscall restart from signal handling

Jens Axboe
2020-10-05T15:05:10Z

Move the restart syscall logic into a separate generic entry helper,
and handle that part separately from signal checking and delivery.

This is in preparation for being able to do syscall restarting
independently from handling signals.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
arch/x86/kernel/signal.c | 32 ++++++++++++++++++--------------
include/linux/entry-common.h | 14 ++++++++++++--
kernel/entry/common.c | 11 ++++++++---
3 files changed, 38 insertions(+), 19 deletions(-)

diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index be0d7d4152ec..5dc1eeaf0866 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -799,21 +799,8 @@ static inline unsigned long get_nr_restart_syscall(const struct pt_regs *regs)
#endif
}

-/*
- * Note that 'init' is a special process: it doesn't get signals it doesn't
- * want to handle. Thus you cannot kill init even with a SIGKILL even by
- * mistake.
- */
-void arch_do_signal(struct pt_regs *regs)
+void arch_restart_syscall(struct pt_regs *regs)
{
- struct ksignal ksig;
-
- if (get_signal(&ksig)) {
- /* Whee! Actually deliver the signal. */
- handle_signal(&ksig, regs);
- return;
- }
-
/* Did we come from a system call? */
if (syscall_get_nr(current, regs) >= 0) {
/* Restart the system call - no handlers present */
@@ -831,12 +818,29 @@ void arch_do_signal(struct pt_regs *regs)
break;
}
}
+}
+
+/*
+ * Note that 'init' is a special process: it doesn't get signals it doesn't
+ * want to handle. Thus you cannot kill init even with a SIGKILL even by
+ * mistake.
+ */
+bool arch_do_signal(struct pt_regs *regs)
+{
+ struct ksignal ksig;
+
+ if (get_signal(&ksig)) {
+ /* Whee! Actually deliver the signal. */
+ handle_signal(&ksig, regs);
+ return true;
+ }

/*
* If there's no signal to deliver, we just put the saved sigmask
* back.
*/
restore_saved_sigmask();
+ return false;
}

void signal_fault(struct pt_regs *regs, void __user *frame, char *where)
diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h
index 159c7476b11b..ccfcc4769925 100644
--- a/include/linux/entry-common.h
+++ b/include/linux/entry-common.h
@@ -262,9 +262,19 @@ static __always_inline void arch_exit_to_user_mode(void) { }
* arch_do_signal - Architecture specific signal delivery function
* @regs: Pointer to currents pt_regs
*
- * Invoked from exit_to_user_mode_loop().
+ * Invoked from exit_to_user_mode_loop(). Returns true if a signal was
+ * handled.
*/
-void arch_do_signal(struct pt_regs *regs);
+bool arch_do_signal(struct pt_regs *regs);
+
+/**
+ * arch_restart_syscall - Architecture specific syscall restarting
+ * @regs: Pointer to currents pt_regs
+ *
+ * Invoked from exit_to_user_mode_loop(), if we need to restart the current
+ * system call.
+ */
+void arch_restart_syscall(struct pt_regs *regs);

/**
* arch_syscall_exit_tracehook - Wrapper around tracehook_report_syscall_exit()
diff --git a/kernel/entry/common.c b/kernel/entry/common.c
index d20ab4ac7183..0c0cc3cf3eba 100644
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -135,11 +135,13 @@ static __always_inline void exit_to_user_mode(void)
}

/* Workaround to allow gradual conversion of architecture code */
-void __weak arch_do_signal(struct pt_regs *regs) { }
+bool __weak arch_do_signal(struct pt_regs *regs) { return true; }

static unsigned long exit_to_user_mode_loop(struct pt_regs *regs,
unsigned long ti_work)
{
+ bool restart_sys = ti_work & _TIF_SIGPENDING;
+
/*
* Before returning to user space ensure that all pending work
* items have been completed.
@@ -157,8 +159,8 @@ static unsigned long exit_to_user_mode_loop(struct pt_regs *regs,
if (ti_work & _TIF_PATCH_PENDING)
klp_update_patch_state(current);

- if (ti_work & _TIF_SIGPENDING)
- arch_do_signal(regs);
+ if ((ti_work & _TIF_SIGPENDING) && arch_do_signal(regs))
+ restart_sys = false;

if (ti_work & _TIF_NOTIFY_RESUME) {
tracehook_notify_resume(regs);
@@ -177,6 +179,9 @@ static unsigned long exit_to_user_mode_loop(struct pt_regs *regs,
ti_work = READ_ONCE(current_thread_info()->flags);
}

+ if (restart_sys)
+ arch_restart_syscall(regs);
+
/* Return the latest work state for arch_exit_to_user_mode() */
return ti_work;
}
--
2.28.0