linux-kernel - Re: [RFC 00/10] Process-local memory allocations for hiding KVM secrets

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Date:   Sun, 16 Jun 2019 15:18:00 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        Marius Hillenbrand <mhillenb@...zon.de>,
        kvm list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Linux-MM <linux-mm@...ck.org>, Alexander Graf <graf@...zon.de>,
        David Woodhouse <dwmw@...zon.co.uk>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [RFC 00/10] Process-local memory allocations for hiding KVM secrets

On Fri, Jun 14, 2019 at 7:21 AM Thomas Gleixner <tglx@...utronix.de> wrote:
>
> On Wed, 12 Jun 2019, Andy Lutomirski wrote:
> > > On Jun 12, 2019, at 12:55 PM, Dave Hansen <dave.hansen@...el.com> wrote:
> > >
> > >> On 6/12/19 10:08 AM, Marius Hillenbrand wrote:
> > >> This patch series proposes to introduce a region for what we call
> > >> process-local memory into the kernel's virtual address space.
> > >
> > > It might be fun to cc some x86 folks on this series.  They might have
> > > some relevant opinions. ;)
> > >
> > > A few high-level questions:
> > >
> > > Why go to all this trouble to hide guest state like registers if all the
> > > guest data itself is still mapped?
> > >
> > > Where's the context-switching code?  Did I just miss it?
> > >
> > > We've discussed having per-cpu page tables where a given PGD is only in
> > > use from one CPU at a time.  I *think* this scheme still works in such a
> > > case, it just adds one more PGD entry that would have to context-switched.
> >
> > Fair warning: Linus is on record as absolutely hating this idea. He might
> > change his mind, but it’s an uphill battle.
>
> Yes I know, but as a benefit we could get rid of all the GSBASE horrors in
> the entry code as we could just put the percpu space into the local PGD.
>

I have personally suggested this to Linus on a couple of occasions,
and he seemed quite skeptical.