Re: Linux guest kernel threat model for Confidential Computing

From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Christophe de Dinechin <dinechin@redhat.com>,
	"Reshetova, Elena" <elena.reshetova@intel.com>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	Theodore Ts'o <tytso@mit.edu>,
	Carlos Bilbao <carlos.bilbao@amd.com>,
	"Shishkin, Alexander" <alexander.shishkin@intel.com>,
	"Shutemov, Kirill" <kirill.shutemov@intel.com>,
	"Kuppuswamy,
	Sathyanarayanan" <sathyanarayanan.kuppuswamy@intel.com>,
	"Kleen, Andi" <andi.kleen@intel.com>,
	"Hansen, Dave" <dave.hansen@intel.com>,
	Peter Zijlstra <peterz@infradead.org>,
	"Wunner, Lukas" <lukas.wunner@intel.com>,
	Mika Westerberg <mika.westerberg@linux.intel.com>,
	Jason Wang <jasowang@redhat.com>,
	"Poimboe, Josh" <jpoimboe@redhat.com>,
	"aarcange@redhat.com" <aarcange@redhat.com>,
	Cfir Cohen <cfir@google.com>, Marc Orr <marcorr@google.com>,
	"jbachmann@google.com" <jbachmann@google.com>,
	"pgonda@google.com" <pgonda@google.com>,
	"keescook@chromium.org" <keescook@chromium.org>,
	James Morris <jmorris@namei.org>,
	Michael Kelley <mikelley@microsoft.com>,
	"Lange, Jon" <jlange@microsoft.com>,
	"linux-coco@lists.linux.dev" <linux-coco@lists.linux.dev>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: Linux guest kernel threat model for Confidential Computing
Date: Thu, 9 Feb 2023 19:48:08 +0000	[thread overview]
Message-ID: <Y+VN+DnL4XQhGKhv@work-vm> (raw)
In-Reply-To: <87bkm42dcs.ffs@tglx>

* Thomas Gleixner (tglx@linutronix.de) wrote:
> On Wed, Feb 08 2023 at 18:02, David Alan Gilbert wrote:
> > * Greg Kroah-Hartman (gregkh@linuxfoundation.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@redhat.com / Manchester, UK