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Date:   Mon, 15 Jul 2019 12:33:53 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Andy Lutomirski <luto@kernel.org>
Cc:     Alexandre Chartre <alexandre.chartre@oracle.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Dave Hansen <dave.hansen@intel.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Radim Krcmar <rkrcmar@redhat.com>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        kvm list <kvm@vger.kernel.org>, X86 ML <x86@kernel.org>,
        Linux-MM <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        jan.setjeeilers@oracle.com, Liran Alon <liran.alon@oracle.com>,
        Jonathan Adams <jwadams@google.com>,
        Alexander Graf <graf@amazon.de>,
        Mike Rapoport <rppt@linux.vnet.ibm.com>,
        Paul Turner <pjt@google.com>
Subject: Re: [RFC v2 00/27] Kernel Address Space Isolation
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On Sun, Jul 14, 2019 at 08:06:12AM -0700, Andy Lutomirski wrote:
> On Fri, Jul 12, 2019 at 12:06 PM Peter Zijlstra <peterz@infradead.org> wrote:
> >
> > On Fri, Jul 12, 2019 at 06:37:47PM +0200, Alexandre Chartre wrote:
> > > On 7/12/19 5:16 PM, Thomas Gleixner wrote:
> >
> > > > Right. If we decide to expose more parts of the kernel mappings then that's
> > > > just adding more stuff to the existing user (PTI) map mechanics.
> > >
> > > If we expose more parts of the kernel mapping by adding them to the existing
> > > user (PTI) map, then we only control the mapping of kernel sensitive data but
> > > we don't control user mapping (with ASI, we exclude all user mappings).
> > >
> > > How would you control the mapping of userland sensitive data and exclude them
> > > from the user map? Would you have the application explicitly identify sensitive
> > > data (like Andy suggested with a /dev/xpfo device)?
> >
> > To what purpose do you want to exclude userspace from the kernel
> > mapping; that is, what are you mitigating against with that?
> 
> Mutually distrusting user/guest tenants.  Imagine an attack against a
> VM hosting provider (GCE, for example).  If the overall system is
> well-designed, the host kernel won't possess secrets that are
> important to the overall hosting network.  The interesting secrets are
> in the memory of other tenants running under the same host.  So, if we
> can mostly or completely avoid mapping one tenant's memory in the
> host, we reduce the amount of valuable information that could leak via
> a speculation (or wild read) attack to another tenant.
> 
> The practicality of such a scheme is obviously an open question.

Ah, ok. So it's some virt specific nonsense. I'll go on ignoring it then
;-)