linux-kernel - Re: [RFC 00/16] KVM protected memory extension

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Date:   Thu, 4 Jun 2020 14:03:12 -0700
From:   Jim Mattson <jmattson@...gle.com>
To:     "Nakajima, Jun" <jun.nakajima@...el.com>
Cc:     Will Deacon <will@...nel.org>,
        "Christopherson, Sean J" <sean.j.christopherson@...el.com>,
        Marc Zyngier <maz@...nel.org>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>,
        David Rientjes <rientjes@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Will Drewry <wad@...omium.org>,
        "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
        "Kleen, Andi" <andi.kleen@...el.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        "kernel-team@...roid.com" <kernel-team@...roid.com>
Subject: Re: [RFC 00/16] KVM protected memory extension

On Thu, Jun 4, 2020 at 12:09 PM Nakajima, Jun <jun.nakajima@...el.com> wrote:

> We (Intel virtualization team) are also working on a similar thing, prototyping to meet such requirements, i..e "some level of confidentiality to guests”. Linux/KVM is the host, and the Kirill’s patches are helpful when removing the mappings from the host to achieve memory isolation of a guest. But, it’s not easy to prove there are no other mappings.
>
> To raise the level of security, our idea is to de-privilege the host kernel just to enforce memory isolation using EPT (Extended Page Table) that virtualizes guest (the host kernel in this case) physical memory; almost everything is passthrough. And the EPT for the host kernel excludes the memory for the guest(s) that has confidential info. So, the host kernel shouldn’t cause VM exits as long as it’s behaving well (CPUID still causes a VM exit, though).

You're Intel. Can't you just change the CPUID intercept from required
to optional? It seems like this should be in the realm of a small
microcode patch.