linux-kernel - Re: Linux guest kernel threat model for Confidential Computing

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Date:   Thu, 9 Feb 2023 19:48:08 +0000
From:   "Dr. David Alan Gilbert" <dgilbert@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Christophe de Dinechin <dinechin@...hat.com>,
        "Reshetova, Elena" <elena.reshetova@...el.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Theodore Ts'o <tytso@....edu>,
        Carlos Bilbao <carlos.bilbao@....com>,
        "Shishkin, Alexander" <alexander.shishkin@...el.com>,
        "Shutemov, Kirill" <kirill.shutemov@...el.com>,
        "Kuppuswamy, Sathyanarayanan" <sathyanarayanan.kuppuswamy@...el.com>,
        "Kleen, Andi" <andi.kleen@...el.com>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Wunner, Lukas" <lukas.wunner@...el.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Jason Wang <jasowang@...hat.com>,
        "Poimboe, Josh" <jpoimboe@...hat.com>,
        "aarcange@...hat.com" <aarcange@...hat.com>,
        Cfir Cohen <cfir@...gle.com>, Marc Orr <marcorr@...gle.com>,
        "jbachmann@...gle.com" <jbachmann@...gle.com>,
        "pgonda@...gle.com" <pgonda@...gle.com>,
        "keescook@...omium.org" <keescook@...omium.org>,
        James Morris <jmorris@...ei.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        "Lange, Jon" <jlange@...rosoft.com>,
        "linux-coco@...ts.linux.dev" <linux-coco@...ts.linux.dev>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Linux guest kernel threat model for Confidential Computing

* Thomas Gleixner (tglx@...utronix.de) wrote:
> On Wed, Feb 08 2023 at 18:02, David Alan Gilbert wrote:
> > * Greg Kroah-Hartman (gregkh@...uxfoundation.org) wrote:
> >> Anyway, you all are just spinning in circles now.  I'll just mute this
> >> thread until I see an actual code change as it seems to be full of
> >> people not actually sending anything we can actually do anything with.
> 
> There have been random patchs posted which finally caused this
> discussion to start. Wrong order obviously :)
> 
> > I think the challenge will be to come up with non-intrusive, minimal
> > changes;  obviously you don't want stuff shutgunned everywhere.
> 
> That has been tried by doing random surgery, e.g. caching some
> particular PCI config value. While that might not look intrusive on the
> first glance, these kind of punctual changes are the begin of a whack a
> mole game and will end up in an uncoordinated maze of tiny mitigations
> which make the code harder to maintain.
> 
> The real challenge is to come up with threat classes and mechanisms
> which squash the whole class. Done right, e.g. caching a range of config
> space values (or all of it) might give a benefit even for the bare metal
> or general virtualization case.

Yeh, reasonable.

> That's quite some work, but its much more palatable than a trickle of
> "fixes" when yet another source of trouble has been detected by a tool
> or human inspection.
> 
> It's also more future proof because with the current approach of
> scratching the itch of the day the probability that the just "mitigated"
> issue comes back due to unrelated changes is very close to 100%.
> 
> It's not any different than any other threat class problem.

I wonder if  trying to group/categorise the output of Intel's
tool would allow common problematic patterns to be found to then
try and come up with more concrete fixes for whole classes of issues.

Dave

> Thanks,
> 
>         tglx
> 
> 
-- 
Dr. David Alan Gilbert / dgilbert@...hat.com / Manchester, UK