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

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Message-ID: <58788f05-04c3-e71c-12c3-0123be55012c@amazon.com>
Date:   Mon, 17 Jun 2019 09:38:00 +0200
From:   Alexander Graf <graf@...zon.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...capital.net>
CC:     Dave Hansen <dave.hansen@...el.com>,
        Marius Hillenbrand <mhillenb@...zon.de>, <kvm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <kernel-hardening@...ts.openwall.com>, <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 14.06.19 16:21, Thomas Gleixner 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.


Would that mean that with Meltdown affected CPUs we open speculation 
attacks against the mmlocal memory from KVM user space?


Alex