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SubjectRe: [PATCH] KVM: nSVM: vmentry ignores EFER.LMA and possibly RFLAGS.VM
On 09/07/20 20:40, Jim Mattson wrote:
> On Thu, Jul 9, 2020 at 11:31 AM Paolo Bonzini <> wrote:
>> On 09/07/20 20:28, Jim Mattson wrote:
>>>> That said, the VMCB here is guest memory and it can change under our
>>>> feet between nested_vmcb_checks and nested_prepare_vmcb_save. Copying
>>>> the whole save area is overkill, but we probably should copy at least
>>>> EFER/CR0/CR3/CR4 in a struct at the beginning of nested_svm_vmrun; this
>>>> way there'd be no TOC/TOU issues between nested_vmcb_checks and
>>>> nested_svm_vmrun. This would also make it easier to reuse the checks in
>>>> svm_set_nested_state. Maybe Maxim can look at it while I'm on vacation,
>>>> as he's eager to do more nSVM stuff. :D
>>> I fear that nested SVM is rife with TOCTTOU issues.
>> I am pretty sure about that, actually. :)
>> Another possibility to stomp them in a more efficient manner could be to
>> rely on the dirty flags, and use them to set up an in-memory copy of the
>> VMCB.
> That sounds like a great idea! Is Maxim going to look into that?

Now he is!


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