From: Ben Hutchings <ben@decadent.org.uk>
Date: Fri, 30 Aug 2019 15:54:24 +0100
Subject: mtd: phram,slram: Disable when the kernel is locked down
Forwarded: https://lore.kernel.org/linux-security-module/20190830154720.eekfjt6c4jzvlbfz@decadent.org.uk/

These drivers allow mapping arbitrary memory ranges as MTD devices.
This should be disabled to preserve the kernel's integrity when it is
locked down.

* Add the HWPARAM flag to the module parameters
* When slram is built-in, it uses __setup() to read kernel parameters,
  so add an explicit check security_locked_down() check

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Cc: Matthew Garrett <mjg59@google.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Joern Engel <joern@lazybastard.org>
Cc: linux-mtd@lists.infradead.org
---
 drivers/mtd/devices/phram.c | 6 +++++-
 drivers/mtd/devices/slram.c | 9 ++++++++-
 2 files changed, 13 insertions(+), 2 deletions(-)

--- a/drivers/mtd/devices/phram.c
+++ b/drivers/mtd/devices/phram.c
@@ -364,7 +364,11 @@ static int phram_param_call(const char *
 #endif
 }
 
-module_param_call(phram, phram_param_call, NULL, NULL, 0200);
+static const struct kernel_param_ops phram_param_ops = {
+	.set = phram_param_call
+};
+__module_param_call(MODULE_PARAM_PREFIX, phram, &phram_param_ops, NULL,
+		    0200, -1, KERNEL_PARAM_FL_HWPARAM | hwparam_iomem);
 MODULE_PARM_DESC(phram, "Memory region to map. \"phram=<name>,<start>,<length>[,<erasesize>]\"");
 
 #ifdef CONFIG_OF
--- a/drivers/mtd/devices/slram.c
+++ b/drivers/mtd/devices/slram.c
@@ -43,6 +43,7 @@
 #include <linux/ioctl.h>
 #include <linux/init.h>
 #include <linux/io.h>
+#include <linux/security.h>
 
 #include <linux/mtd/mtd.h>
 
@@ -65,7 +66,7 @@ typedef struct slram_mtd_list {
 #ifdef MODULE
 static char *map[SLRAM_MAX_DEVICES_PARAMS];
 
-module_param_array(map, charp, NULL, 0);
+module_param_hw_array(map, charp, iomem, NULL, 0);
 MODULE_PARM_DESC(map, "List of memory regions to map. \"map=<name>, <start>, <length / end>\"");
 #else
 static char *map;
@@ -281,11 +282,17 @@ static int __init init_slram(void)
 #ifndef MODULE
 	char *devstart;
 	char *devlength;
+	int ret;
 
 	if (!map) {
 		E("slram: not enough parameters.\n");
 		return(-EINVAL);
 	}
+
+	ret = security_locked_down(LOCKDOWN_MODULE_PARAMETERS);
+	if (ret)
+		return ret;
+
 	while (map) {
 		devname = devstart = devlength = NULL;
 
