Re: Linux guest kernel threat model for Confidential Computing

From: Leon Romanovsky <leon@kernel.org>
To: "Reshetova, Elena" <elena.reshetova@intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"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>,
	Thomas Gleixner <tglx@linutronix.de>,
	Peter Zijlstra <peterz@infradead.org>,
	"Wunner, Lukas" <lukas.wunner@intel.com>,
	Mika Westerberg <mika.westerberg@linux.intel.com>,
	"Michael S. Tsirkin" <mst@redhat.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>,
	Kernel Hardening <kernel-hardening@lists.openwall.com>
Subject: Re: Linux guest kernel threat model for Confidential Computing
Date: Thu, 26 Jan 2023 14:30:19 +0200	[thread overview]
Message-ID: <Y9JyW5bUqV7gWmU8@unreal> (raw)
In-Reply-To: <DM8PR11MB5750414F6638169C7097E365E7CF9@DM8PR11MB5750.namprd11.prod.outlook.com>

On Thu, Jan 26, 2023 at 11:29:20AM +0000, Reshetova, Elena wrote:
> > On Wed, Jan 25, 2023 at 03:29:07PM +0000, Reshetova, Elena wrote:
> > > Replying only to the not-so-far addressed points.
> > >
> > > > On Wed, Jan 25, 2023 at 12:28:13PM +0000, Reshetova, Elena wrote:
> > > > > Hi Greg,
> > 
> > <...>
> > 
> > > > > 3) All the tools are open-source and everyone can start using them right
> > away
> > > > even
> > > > > without any special HW (readme has description of what is needed).
> > > > > Tools and documentation is here:
> > > > > https://github.com/intel/ccc-linux-guest-hardening
> > > >
> > > > Again, as our documentation states, when you submit patches based on
> > > > these tools, you HAVE TO document that.  Otherwise we think you all are
> > > > crazy and will get your patches rejected.  You all know this, why ignore
> > > > it?
> > >
> > > Sorry, I didn’t know that for every bug that is found in linux kernel when
> > > we are submitting a fix that we have to list the way how it has been found.
> > > We will fix this in the future submissions, but some bugs we have are found by
> > > plain code audit, so 'human' is the tool.
> > 
> > My problem with that statement is that by applying different threat
> > model you "invent" bugs which didn't exist in a first place.
> > 
> > For example, in this [1] latest submission, authors labeled correct
> > behaviour as "bug".
> > 
> > [1] https://lore.kernel.org/all/20230119170633.40944-1-
> > alexander.shishkin@linux.intel.com/
> 
> Hm.. Does everyone think that when kernel dies with unhandled page fault 
> (such as in that case) or detection of a KASAN out of bounds violation (as it is in some
> other cases we already have fixes or investigating) it represents a correct behavior even if
> you expect that all your pci HW devices are trusted? 

This is exactly what I said. You presented me the cases which exist in
your invented world. Mentioned unhandled page fault doesn't exist in real
world. If PCI device doesn't work, it needs to be replaced/blocked and not
left to be operable and accessible from the kernel/user.

> What about an error in two consequent pci reads? What about just some
> failure that results in erroneous input?

Yes, some bugs need to be fixed, but they are not related to trust/not-trust
discussion and PCI spec violations.

Thanks

> 
> Best Regards,
> Elena.
> 