Re: [patch, try#2] kvm: fix GFP_KERNEL allocation in atomic sectionin kvm_dev_ioctl_create_vcpu()

From: Avi Kivity
Date: Thu Dec 28 2006 - 08:31:08 EST

Ingo Molnar wrote:
I've got a security related question as well: vcpu_load() sets up a physical CPU's VM registers/state, and vcpu_put() drops that. But vcpu_put() only does a put_cpu() call - it does not tear down any VM state that has been loaded into the CPU. Is it guaranteed that (hostile) user-space cannot use that VM state in any unauthorized way? The state is still loaded while arbitrary tasks execute on the CPU. The next vcpu_load() will then override it, but the state lingers around forever.

The new x86 VM instructions: vmclear, vmlaunch, vmresume, vmptrld, vmread, vmwrite, vmxoff, vmxon are all privileged so i guess it should be mostly safe - i'm just wondering whether you thought about this attack angle.

Yes. Userspace cannot snoop on a VM state.

ultimately we want to integrate VM state management into the scheduler and the context-switch lowlevel arch code, but right now CPU state management is done by the KVM 'driver' and there's nothing that isolates other tasks from possible side-effects of a loaded VMX/SVN state.

AFAICS in vmx root mode the vm state only affects vmx instructions; SVM has no architecturally hidden state.

error compiling committee.c: too many arguments to function

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