linux-kernel - [PATCH 05/12] Restrict /dev/mem and /dev/kmem when trusted

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Date:	Fri, 13 Mar 2015 11:38:21 -1000
From:	Matthew Garrett <matthew.garrett@...ula.com>
To:	linux-security-module@...r.kernel.org
Cc:	james.l.morris@...cle.com, serge@...lyn.com,
	linux-kernel@...r.kernel.org, keescook@...omium.org, hpa@...or.com,
	gnomes@...rguk.ukuu.org.uk,
	Matthew Garrett <matthew.garrett@...ula.com>
Subject: [PATCH 05/12] Restrict /dev/mem and /dev/kmem when trusted_kernel is true

Allowing users to write to address space provides mechanisms that may permit
modification of the kernel at runtime. Prevent this if trusted_kernel is
true.

Signed-off-by: Matthew Garrett <matthew.garrett@...ula.com>
---
 drivers/char/mem.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index 74227cd..91e7409 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -164,6 +164,9 @@ static ssize_t write_mem(struct file *file, const char __user *buf,
 	unsigned long copied;
 	void *ptr;
 
+	if (get_trusted_kernel())
+		return -EPERM;
+
 	if (p != *ppos)
 		return -EFBIG;
 
@@ -513,6 +516,9 @@ static ssize_t write_kmem(struct file *file, const char __user *buf,
 	char *kbuf; /* k-addr because vwrite() takes vmlist_lock rwlock */
 	int err = 0;
 
+	if (get_trusted_kernel())
+		return -EPERM;
+
 	if (p < (unsigned long) high_memory) {
 		unsigned long to_write = min_t(unsigned long, count,
 					       (unsigned long)high_memory - p);
-- 
2.1.0

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