From: Matthew Garrett <mjg59@srcf.ucam.org>
Date: Fri, 9 Mar 2012 13:39:37 +0000 (-0500)
Subject: acpi: Limit access to custom_method if securelevel is set
X-Git-Tag: archive/raspbian/4.9.30-2+deb9u2+rpi1~8^2~64
X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=d95a0dbfd13d7d65ab4988ce26a74d5eed48c07f;p=linux-4.9.git

acpi: Limit access to custom_method if securelevel is set

custom_method effectively allows arbitrary access to system memory, making
it possible for an attacker to modify the kernel at runtime. Prevent this
if securelevel has been set.

Signed-off-by: Matthew Garrett <mjg59@srcf.ucam.org>

Gbp-Pq: Topic features/all/securelevel
Gbp-Pq: Name acpi-limit-access-to-custom_method-if-securelevel-is.patch
---

diff --git a/drivers/acpi/custom_method.c b/drivers/acpi/custom_method.c
index c68e72414a67..359f45d54543 100644
--- a/drivers/acpi/custom_method.c
+++ b/drivers/acpi/custom_method.c
@@ -8,6 +8,7 @@
 #include <linux/uaccess.h>
 #include <linux/debugfs.h>
 #include <linux/acpi.h>
+#include <linux/security.h>
 
 #include "internal.h"
 
@@ -29,6 +30,9 @@ static ssize_t cm_write(struct file *file, const char __user * user_buf,
 	struct acpi_table_header table;
 	acpi_status status;
 
+	if (get_securelevel() > 0)
+		return -EPERM;
+
 	if (!(*ppos)) {
 		/* parse the table header to get the table length */
 		if (count <= sizeof(struct acpi_table_header))