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From: Paolo Bonzini <pbonzini@redhat.com>
To: Jim Mattson <jmattson@google.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
	kvm list <kvm@vger.kernel.org>,
	Maxim Levitsky <mlevitsk@redhat.com>
Subject: Re: [PATCH] KVM: nSVM: vmentry ignores EFER.LMA and possibly RFLAGS.VM
Date: Thu, 9 Jul 2020 20:31:36 +0200	[thread overview]
Message-ID: <717a1b5d-1bf3-5f72-147a-faccd4611b87@redhat.com> (raw)
In-Reply-To: <CALMp9eRSvdx+UHggLbvFPms3Li2KY-RjZhjGjcQ3=GbSB1YyyA@mail.gmail.com>

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.

Paolo


  reply	other threads:[~2020-07-09 18:31 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-09  9:55 [PATCH] KVM: nSVM: vmentry ignores EFER.LMA and possibly RFLAGS.VM Paolo Bonzini
2020-07-09 17:12 ` Jim Mattson
2020-07-09 17:25   ` Paolo Bonzini
2020-07-09 18:28     ` Jim Mattson
2020-07-09 18:31       ` Paolo Bonzini [this message]
2020-07-09 18:40         ` Jim Mattson
2020-07-09 18:41           ` Paolo Bonzini
2020-07-10  8:37             ` Maxim Levitsky

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