On 09/07/20 20:40, Jim Mattson wrote: > On Thu, Jul 9, 2020 at 11:31 AM Paolo Bonzini <pbonzini@xxxxxxxxxx> 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! Paolo
