tile/ptrace: run seccomp after ptrace

Close the hole where ptrace can change a syscall out from under seccomp.

Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
diff --git a/arch/tile/kernel/ptrace.c b/arch/tile/kernel/ptrace.c
index 8c6d2f2..d89b701 100644
--- a/arch/tile/kernel/ptrace.c
+++ b/arch/tile/kernel/ptrace.c
@@ -255,14 +255,15 @@
 {
 	u32 work = ACCESS_ONCE(current_thread_info()->flags);
 
+	if ((work & _TIF_SYSCALL_TRACE) &&
+	    tracehook_report_syscall_entry(regs)) {
+		regs->regs[TREG_SYSCALL_NR] = -1;
+		return -1;
+	}
+
 	if (secure_computing(NULL) == -1)
 		return -1;
 
-	if (work & _TIF_SYSCALL_TRACE) {
-		if (tracehook_report_syscall_entry(regs))
-			regs->regs[TREG_SYSCALL_NR] = -1;
-	}
-
 	if (work & _TIF_SYSCALL_TRACEPOINT)
 		trace_sys_enter(regs, regs->regs[TREG_SYSCALL_NR]);