task_work: Call tracehook_notify_signal from get_signal on all architectures

Always handle TIF_NOTIFY_SIGNAL in get_signal.  With commit 35d0b389f3
("task_work: unconditionally run task_work from get_signal()") always
calling task_work_run all of the work of tracehook_notify_signal is
already happening except clearing TIF_NOTIFY_SIGNAL.

Factor clear_notify_signal out of tracehook_notify_signal and use it in
get_signal so that get_signal only needs one call of task_work_run.

To keep the semantics in sync update xfer_to_guest_mode_work (which
does not call get_signal) to call tracehook_notify_signal if either
_TIF_SIGPENDING or _TIF_NOTIFY_SIGNAL.

Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lkml.kernel.org/r/20220309162454.123006-8-ebiederm@xmission.com
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

arch/s390/kernel/signal.c

@@ -453,7 +453,7 @@ static void handle_signal(struct ksignal *ksig, sigset_t *oldset,
  * stack-frames in one go after that.
  */
 
-void arch_do_signal_or_restart(struct pt_regs *regs, bool has_signal)
+void arch_do_signal_or_restart(struct pt_regs *regs)
 {
 	struct ksignal ksig;
 	sigset_t *oldset = sigmask_to_save();
@@ -466,7 +466,7 @@ void arch_do_signal_or_restart(struct pt_regs *regs, bool has_signal)
 	current->thread.system_call =
 		test_pt_regs_flag(regs, PIF_SYSCALL) ? regs->int_code : 0;
 
-	if (has_signal && get_signal(&ksig)) {
+	if (get_signal(&ksig)) {
 		/* Whee!  Actually deliver the signal.  */
 		if (current->thread.system_call) {
 			regs->int_code = current->thread.system_call;

arch/x86/kernel/signal.c

@@ -861,11 +861,11 @@ static inline unsigned long get_nr_restart_syscall(const struct pt_regs *regs)
  * want to handle. Thus you cannot kill init even with a SIGKILL even by
  * mistake.
  */
-void arch_do_signal_or_restart(struct pt_regs *regs, bool has_signal)
+void arch_do_signal_or_restart(struct pt_regs *regs)
 {
 	struct ksignal ksig;
 
-	if (has_signal && get_signal(&ksig)) {
+	if (get_signal(&ksig)) {
 		/* Whee! Actually deliver the signal.  */
 		handle_signal(&ksig, regs);
 		return;

include/linux/entry-common.h

@@ -257,7 +257,7 @@ static __always_inline void arch_exit_to_user_mode(void) { }
  *
  * Invoked from exit_to_user_mode_loop().
  */
-void arch_do_signal_or_restart(struct pt_regs *regs, bool has_signal);
+void arch_do_signal_or_restart(struct pt_regs *regs);
 
 /**
  * exit_to_user_mode - Fixup state when exiting to user mode

include/linux/tracehook.h

@@ -106,6 +106,12 @@ static inline void tracehook_notify_resume(struct pt_regs *regs)
 	rseq_handle_notify_resume(NULL, regs);
 }
 
+static inline void clear_notify_signal(void)
+{
+	clear_thread_flag(TIF_NOTIFY_SIGNAL);
+	smp_mb__after_atomic();
+}
+
 /*
  * called by exit_to_user_mode_loop() if ti_work & _TIF_NOTIFY_SIGNAL. This
  * is currently used by TWA_SIGNAL based task_work, which requires breaking
@@ -113,8 +119,7 @@ static inline void tracehook_notify_resume(struct pt_regs *regs)
  */
 static inline void tracehook_notify_signal(void)
 {
-	clear_thread_flag(TIF_NOTIFY_SIGNAL);
+	clear_notify_signal();
-	smp_mb__after_atomic();
 	if (task_work_pending(current))
 		task_work_run();
 }

kernel/entry/common.c

@@ -139,15 +139,7 @@ void noinstr exit_to_user_mode(void)
 }
 
 /* Workaround to allow gradual conversion of architecture code */
-void __weak arch_do_signal_or_restart(struct pt_regs *regs, bool has_signal) { }
+void __weak arch_do_signal_or_restart(struct pt_regs *regs) { }
-
-static void handle_signal_work(struct pt_regs *regs, unsigned long ti_work)
-{
-	if (ti_work & _TIF_NOTIFY_SIGNAL)
-		tracehook_notify_signal();
-
-	arch_do_signal_or_restart(regs, ti_work & _TIF_SIGPENDING);
-}
 
 static unsigned long exit_to_user_mode_loop(struct pt_regs *regs,
 					    unsigned long ti_work)
@@ -170,7 +162,7 @@ static unsigned long exit_to_user_mode_loop(struct pt_regs *regs,
 			klp_update_patch_state(current);
 
 		if (ti_work & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL))
-			handle_signal_work(regs, ti_work);
+			arch_do_signal_or_restart(regs);
 
 		if (ti_work & _TIF_NOTIFY_RESUME)
 			tracehook_notify_resume(regs);

kernel/entry/kvm.c

@@ -8,7 +8,7 @@ static int xfer_to_guest_mode_work(struct kvm_vcpu *vcpu, unsigned long ti_work)
 	do {
 		int ret;
 
-		if (ti_work & _TIF_NOTIFY_SIGNAL)
+		if (ti_work & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL))
 			tracehook_notify_signal();
 
 		if (ti_work & _TIF_SIGPENDING) {

kernel/signal.c

@@ -2626,20 +2626,12 @@ bool get_signal(struct ksignal *ksig)
 	struct signal_struct *signal = current->signal;
 	int signr;
 
+	clear_notify_signal();
 	if (unlikely(task_work_pending(current)))
 		task_work_run();
 
-	/*
-	 * For non-generic architectures, check for TIF_NOTIFY_SIGNAL so
-	 * that the arch handlers don't all have to do it. If we get here
-	 * without TIF_SIGPENDING, just exit after running signal work.
-	 */
-	if (!IS_ENABLED(CONFIG_GENERIC_ENTRY)) {
-		if (test_thread_flag(TIF_NOTIFY_SIGNAL))
-			tracehook_notify_signal();
 	if (!task_sigpending(current))
 		return false;
-	}
 
 	if (unlikely(uprobe_deny_signal()))
 		return false;