linux-kernel - [PATCH 09/15] Restrict /dev/mem and /dev/kmem in secure boot setups

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Date:	Mon, 28 Jan 2013 11:42:33 -0500
From:	Matthew Garrett <matthew.garrett@...ula.com>
To:	linux-kernel@...r.kernel.org
Cc:	linux-efi@...r.kernel.org, linux-security-module@...r.kernel.org,
	Matthew Garrett <matthew.garrett@...ula.com>
Subject: [PATCH 09/15] Restrict /dev/mem and /dev/kmem in secure boot setups

Allowing users to write to address space makes it possible for the kernel
to be subverted. Restrict this when we need to protect the kernel.

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 fc28099..b5df7a8 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -158,6 +158,9 @@ static ssize_t write_mem(struct file *file, const char __user *buf,
 	unsigned long copied;
 	void *ptr;
 
+	if (!capable(CAP_COMPROMISE_KERNEL))
+		return -EPERM;
+
 	if (!valid_phys_addr_range(p, count))
 		return -EFAULT;
 
@@ -530,6 +533,9 @@ 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 (!capable(CAP_COMPROMISE_KERNEL))
+		return -EPERM;
+
 	if (p < (unsigned long) high_memory) {
 		unsigned long to_write = min_t(unsigned long, count,
 					       (unsigned long)high_memory - p);
-- 
1.8.0.2

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