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Friday, June 10, 2011

SMEP and KVM – sounds interesting

Recently a patch was dropped into the KVM community – adding support for the Intel SMEP cpu feature (if available on the CPU). I thought to myself, what the hell is SMEP?
According to the Intel Software Developers Manual it is “Supervisor-Mode Execution Prevention” – this sounds like a great thing as the kernel is prevented from executing ‘user data’ in kernel mode – ie. If there is an exploit that delivers a page of data and asks the kernel to execute it then this wont happen and a fault will be triggered. This sounds like a neat piece of work and as it’s all h/w based then there should be little overhead.
Like me, i’m guessing you’re wondering if your system has the SMEP cpu feature then this code will show you. Don’t be disappointed if your cpu doesn’t have it – it’s a very new feature and I can’t even find what cpu’s implement it.
Anyway, it’s a step in the right direction and that future direction will hopefully allow hypervisors to be that little bit more secure from un-trusted VM’s and provide a VM ‘shell’ environment that’s a little more secure for the VM’s. Unfortunately the way things currently stand the usefulness for KVM is unlikely to be immediately realised as intel engineers suggest enabling SMEP without a guest vm’s knowledge is likely to be ‘problematic’.