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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 <firstname.lastname@example.org> Cc: Linus Torvalds <email@example.com> Cc: Andrew Morton <firstname.lastname@example.org> Cc: Peter Zijlstra <email@example.com> Cc: Horses <firstname.lastname@example.org> Signed-off-by: Ingo Molnar <email@example.com>
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