--- /dev/null
+From 1bd54d851f50dea6af30c3e6ff4f3e9aab5558f9 Mon Sep 17 00:00:00 2001
+From: He Zhe <zhe.he@windriver.com>
+Date: Fri, 17 Aug 2018 22:42:28 +0800
+Subject: kgdboc: Passing ekgdboc to command line causes panic
+
+From: He Zhe <zhe.he@windriver.com>
+
+commit 1bd54d851f50dea6af30c3e6ff4f3e9aab5558f9 upstream.
+
+kgdboc_option_setup does not check input argument before passing it
+to strlen. The argument would be a NULL pointer if "ekgdboc", without
+its value, is set in command line and thus cause the following panic.
+
+PANIC: early exception 0xe3 IP 10:ffffffff8fbbb620 error 0 cr2 0x0
+[ 0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 4.18-rc8+ #1
+[ 0.000000] RIP: 0010:strlen+0x0/0x20
+...
+[ 0.000000] Call Trace
+[ 0.000000] ? kgdboc_option_setup+0x9/0xa0
+[ 0.000000] ? kgdboc_early_init+0x6/0x1b
+[ 0.000000] ? do_early_param+0x4d/0x82
+[ 0.000000] ? parse_args+0x212/0x330
+[ 0.000000] ? rdinit_setup+0x26/0x26
+[ 0.000000] ? parse_early_options+0x20/0x23
+[ 0.000000] ? rdinit_setup+0x26/0x26
+[ 0.000000] ? parse_early_param+0x2d/0x39
+[ 0.000000] ? setup_arch+0x2f7/0xbf4
+[ 0.000000] ? start_kernel+0x5e/0x4c2
+[ 0.000000] ? load_ucode_bsp+0x113/0x12f
+[ 0.000000] ? secondary_startup_64+0xa5/0xb0
+
+This patch adds a check to prevent the panic.
+
+Cc: stable@vger.kernel.org
+Cc: jason.wessel@windriver.com
+Cc: gregkh@linuxfoundation.org
+Cc: jslaby@suse.com
+Signed-off-by: He Zhe <zhe.he@windriver.com>
+Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+
+---
+ drivers/tty/serial/kgdboc.c | 5 +++++
+ 1 file changed, 5 insertions(+)
+
+--- a/drivers/tty/serial/kgdboc.c
++++ b/drivers/tty/serial/kgdboc.c
+@@ -133,6 +133,11 @@ static void kgdboc_unregister_kbd(void)
+
+ static int kgdboc_option_setup(char *opt)
+ {
++ if (!opt) {
++ pr_err("kgdboc: config string not provided\n");
++ return -EINVAL;
++ }
++
+ if (strlen(opt) >= MAX_CONFIG_LEN) {
+ printk(KERN_ERR "kgdboc: config string too long\n");
+ return -ENOSPC;