From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754898Ab3BCO6D (ORCPT ); Sun, 3 Feb 2013 09:58:03 -0500 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:34523 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752099Ab3BCO5z (ORCPT ); Sun, 3 Feb 2013 09:57:55 -0500 Message-Id: <20130203144652.451455680@decadent.org.uk> User-Agent: quilt/0.60-1 Date: Sun, 03 Feb 2013 15:48:19 +0100 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: akpm@linux-foundation.org, Alan Cox , Linus Torvalds , Peter Zijlstra , Ingo Molnar Subject: [ 095/128] x86/msr: Add capabilities check In-Reply-To: <20130203144644.035172954@decadent.org.uk> X-SA-Exim-Connect-IP: 151.216.67.5 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.2-stable review patch. If anyone has any objections, please let me know. ------------------ From: Alan Cox 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 Cc: Linus Torvalds Cc: Andrew Morton Cc: Peter Zijlstra Signed-off-by: Ingo Molnar Signed-off-by: Ben Hutchings --- arch/x86/kernel/msr.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/arch/x86/kernel/msr.c b/arch/x86/kernel/msr.c index a7c5661..4929502 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 */