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

[Avi Kivity <avi@qumranet.com>]

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.


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