MIPS: Give __secure_computing() access to syscall arguments.

KProbes of __seccomp_filter() are not very useful without access to
the syscall arguments.

Do what x86 does, and populate a struct seccomp_data to be passed to
__secure_computing().  This allows samples/bpf/tracex5 to extract a
sensible trace.
Signed-off-by: David Daney <david.daney@cavium.com>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Matt Redfearn <matt.redfearn@imgtec.com>
Cc: netdev@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/16368/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/kernel/ptrace.c

@@ -868,8 +868,26 @@ asmlinkage long syscall_trace_enter(struct pt_regs *regs, long syscall)
 	    tracehook_report_syscall_entry(regs))
 		return -1;
 
-	if (secure_computing(NULL) == -1)
-		return -1;
+#ifdef CONFIG_SECCOMP
+	if (unlikely(test_thread_flag(TIF_SECCOMP))) {
+		int ret, i;
+		struct seccomp_data sd;
+
+		sd.nr = syscall;
+		sd.arch = syscall_get_arch();
+		for (i = 0; i < 6; i++) {
+			unsigned long v, r;
+
+			r = mips_get_syscall_arg(&v, current, regs, i);
+			sd.args[i] = r ? 0 : v;
+		}
+		sd.instruction_pointer = KSTK_EIP(current);
+
+		ret = __secure_computing(&sd);
+		if (ret == -1)
+			return ret;
+	}
+#endif
 
 	if (unlikely(test_thread_flag(TIF_SYSCALL_TRACEPOINT)))
 		trace_sys_enter(regs, regs->regs[2]);