From c903f0456bc69176912dee6dd25c6a66ee1aed00 Mon Sep 17 00:00:00 2001 From: Alan Cox Date: Thu, 15 Nov 2012 13:06:22 +0000 Subject: [PATCH] x86/msr: Add capabilities check 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 Cc: Horses Signed-off-by: Ingo Molnar --- 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 a7c5661f849..4929502c137 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 */