Patchwork [3.5.y.z,extended,stable] Patch "x86/msr: Add capabilities check" has been added to staging queue

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Submitter Herton Ronaldo Krzesinski
Date Jan. 31, 2013, 10:11 p.m.
Message ID <1359670262-17468-1-git-send-email-herton.krzesinski@canonical.com>
Download mbox | patch
Permalink /patch/217279/
State New
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Herton Ronaldo Krzesinski - Jan. 31, 2013, 10:11 p.m.
This is a note to let you know that I have just added a patch titled

    x86/msr: Add capabilities check

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Herton

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From a3548c94186c9384109eb18f8325e1bbaba49232 Mon Sep 17 00:00:00 2001
From: Alan Cox <alan@linux.intel.com>
Date: Thu, 15 Nov 2012 13:06:22 +0000
Subject: [PATCH] x86/msr: Add capabilities check

commit c903f0456bc69176912dee6dd25c6a66ee1aed00 upstream.

At the moment the MSR driver only relies upon file system
checks. This means that anything as root with any capability set
can write to MSRs. Historically that wasn't very interesting but
on modern processors the MSRs are such that writing to them
provides several ways to execute arbitary code in kernel space.
Sample code and documentation on doing this is circulating and
MSR attacks are used on Windows 64bit rootkits already.

In the Linux case you still need to be able to open the device
file so the impact is fairly limited and reduces the security of
some capability and security model based systems down towards
that of a generic "root owns the box" setup.

Therefore they should require CAP_SYS_RAWIO to prevent an
elevation of capabilities. The impact of this is fairly minimal
on most setups because they don't have heavy use of
capabilities. Those using SELinux, SMACK or AppArmor rules might
want to consider if their rulesets on the MSR driver could be
tighter.

Signed-off-by: Alan Cox <alan@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski@canonical.com>
---
 arch/x86/kernel/msr.c |    3 +++
 1 file changed, 3 insertions(+)

--
1.7.9.5

Patch

diff --git a/arch/x86/kernel/msr.c b/arch/x86/kernel/msr.c
index eb11369..8563b64 100644
--- a/arch/x86/kernel/msr.c
+++ b/arch/x86/kernel/msr.c
@@ -174,6 +174,9 @@  static int msr_open(struct inode *inode, struct file *file)
 	unsigned int cpu;
 	struct cpuinfo_x86 *c;

+	if (!capable(CAP_SYS_RAWIO))
+		return -EPERM;
+
 	cpu = iminor(file->f_path.dentry->d_inode);
 	if (cpu >= nr_cpu_ids || !cpu_online(cpu))
 		return -ENXIO;	/* No such CPU */