mtd: phram: Add the kernel lock down check

The phram MTD driver may map any memory pages no matter whether it's
reserved or whatever used for systems, which basically allows user
bypassing the lock down.

Add the check and abort the probe if the kernel is locked down for
LOCKDOWN_DEV_MEM.

Reported-by: Fabian Vogt <[email protected]>
Suggested-by: Fabian Vogt <[email protected]>
Signed-off-by: Takashi Iwai <[email protected]>
Acked-by: Richard Weinberger <[email protected]>
Signed-off-by: Miquel Raynal <[email protected]>

Author: tiwai

drivers/mtd/devices/phram.c

@@ -30,6 +30,7 @@
 #include <linux/platform_device.h>
 #include <linux/of_address.h>
 #include <linux/of.h>
+#include <linux/security.h>
 
 struct phram_mtd_list {
 	struct mtd_info mtd;
@@ -410,6 +411,10 @@ static int __init init_phram(void)
 {
 	int ret;
 
+	ret = security_locked_down(LOCKDOWN_DEV_MEM);
+	if (ret)
+		return ret;
+
 	ret = platform_driver_register(&phram_driver);
 	if (ret)
 		return ret;