[patch 13/18] entry: Make trace_syscall_enter() return type bool

In preparation of converting the return value of
syscall_enter_from_user_mode[_work]() bool, rework trace_syscall_enter() to

 - update the syscall number via a pointer argument

 - Return True if the syscall number is != -1, False otherwise

That aligns with ptrace_report_syscall_permit_enter() and
seccomp_permit_syscall().

The only difference is that this also returns False, when the syscall
number was already -1 to begin with, but there is not much which can be
done about that. As the architecture has to preset the return value to
-ENOSYS anyway, that results in the correct return value for such an
invalid syscall.

Signed-off-by: Thomas Gleixner <[email protected]>
---
 include/linux/entry-common.h  |    8 +++++---
 kernel/entry/syscall-common.c |    7 ++++---
 2 files changed, 9 insertions(+), 6 deletions(-)

--- a/include/linux/entry-common.h
+++ b/include/linux/entry-common.h
@@ -58,7 +58,7 @@ static __always_inline bool arch_ptrace_
 #endif
 
 bool syscall_user_dispatch(struct pt_regs *regs);
-long trace_syscall_enter(struct pt_regs *regs, long syscall);
+bool trace_syscall_enter(struct pt_regs *regs, long *syscall);
 void trace_syscall_exit(struct pt_regs *regs, long ret);
 
 static inline void syscall_enter_audit(struct pt_regs *regs, long syscall)
@@ -108,8 +108,10 @@ static __always_inline long syscall_trac
 	/* Either of the above might have changed the syscall number */
 	syscall = syscall_get_nr(current, regs);
 
-	if (unlikely(work & SYSCALL_WORK_SYSCALL_TRACEPOINT))
-		syscall = trace_syscall_enter(regs, syscall);
+	if (unlikely(work & SYSCALL_WORK_SYSCALL_TRACEPOINT)) {
+		if (!trace_syscall_enter(regs, &syscall))
+			return -1L;
+	}
 
 	syscall_enter_audit(regs, syscall);
 
--- a/kernel/entry/syscall-common.c
+++ b/kernel/entry/syscall-common.c
@@ -7,14 +7,15 @@
 
 /* Out of line to prevent tracepoint code duplication */
 
-long trace_syscall_enter(struct pt_regs *regs, long syscall)
+bool trace_syscall_enter(struct pt_regs *regs, long *syscall)
 {
-	trace_sys_enter(regs, syscall);
+	trace_sys_enter(regs, *syscall);
 	/*
 	 * Probes or BPF hooks in the tracepoint may have changed the
 	 * system call number. Reread it.
 	 */
-	return syscall_get_nr(current, regs);
+	*syscall = syscall_get_nr(current, regs);
+	return *syscall != -1L;
 }
 
 void trace_syscall_exit(struct pt_regs *regs, long ret)