From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
To: Leon Romanovsky <leon@kernel.org>
Cc: "Reshetova, Elena" <elena.reshetova@intel.com>,
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 18:14:28 +0000 [thread overview]
Message-ID: <Y9LDBKXMwoGrACLZ@work-vm> (raw)
In-Reply-To: <Y9LBInM4uBNCSMDT@unreal>
* Leon Romanovsky (leon@kernel.org) wrote:
> On Thu, Jan 26, 2023 at 05:48:33PM +0000, Reshetova, Elena wrote:
> >
> > > * Reshetova, Elena (elena.reshetova@intel.com) 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? What about an error in
> > > two
> > > > consequent pci reads? What about just some failure that results in erroneous
> > > input?
> > >
> > > I'm not sure you'll get general agreement on those answers for all
> > > devices and situations; I think for most devices for non-CoCo
> > > situations, then people are generally OK with a misbehaving PCI device
> > > causing a kernel crash, since most people are running without IOMMU
> > > anyway, a misbehaving device can cause otherwise undetectable chaos.
> >
> > Ok, if this is a consensus within the kernel community, then we can consider
> > the fixes strictly from the CoCo threat model point of view.
> >
> > >
> > > I'd say:
> > > a) For CoCo, a guest (guaranteed) crash isn't a problem - CoCo doesn't
> > > guarantee forward progress or stop the hypervisor doing something
> > > truly stupid.
> >
> > Yes, denial of service is out of scope but I would not pile all crashes as
> > 'safe' automatically. Depending on the crash, it can be used as a
> > primitive to launch further attacks: privilege escalation, information
> > disclosure and corruption. It is especially true for memory corruption
> > issues.
> >
> > > b) For CoCo, information disclosure, or corruption IS a problem
> >
> > Agreed, but the path to this can incorporate a number of attack
> > primitives, as well as bug chaining. So, if the bug is detected, and
> > fix is easy, instead of thinking about possible implications and its
> > potential usage in exploit writing, safer to fix it.
> >
> > >
> > > c) For non-CoCo some people might care about robustness of the kernel
> > > against a failing PCI device, but generally I think they worry about
> > > a fairly clean failure, even in the unexpected-hot unplug case.
> >
> > Ok.
>
> With my other hat as a representative of hardware vendor (at least for
> NIC part), who cares about quality of our devices, we don't want to hide
> ANY crash related to our devices, especially if it is related to misbehaving
> PCI HW logic. Any uncontrolled "robustness" hides real issues and makes
> QA/customer support much harder.
Yeh if you're adding new code to be more careful, you want the code to
fail/log the problem, not hide it.
(Although heck, I suspect there are a million apparently working PCI
cards out there that break some spec somewhere).
Dave
> Thanks
>
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
next prev parent reply other threads:[~2023-01-26 21:04 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <DM8PR11MB57505481B2FE79C3D56C9201E7CE9@DM8PR11MB5750.namprd11.prod.outlook.com>
[not found] ` <Y9EkCvAfNXnJ+ATo@kroah.com>
2023-01-25 15:29 ` Linux guest kernel threat model for Confidential Computing Reshetova, Elena
2023-01-25 16:40 ` Theodore Ts'o
2023-01-26 8:08 ` Reshetova, Elena
2023-01-26 11:19 ` Leon Romanovsky
2023-01-26 11:29 ` Reshetova, Elena
2023-01-26 12:30 ` Leon Romanovsky
2023-01-26 13:28 ` Reshetova, Elena
2023-01-26 13:50 ` Leon Romanovsky
2023-01-26 20:54 ` Theodore Ts'o
2023-01-27 19:24 ` James Bottomley
2023-01-30 7:42 ` Reshetova, Elena
2023-01-30 12:40 ` James Bottomley
2023-01-31 11:31 ` Reshetova, Elena
2023-01-31 13:28 ` James Bottomley
2023-01-31 15:14 ` Christophe de Dinechin
2023-01-31 17:39 ` Michael S. Tsirkin
2023-02-01 10:52 ` Christophe de Dinechin Dupont de Dinechin
2023-02-01 11:01 ` Michael S. Tsirkin
2023-02-01 13:15 ` Christophe de Dinechin Dupont de Dinechin
2023-02-01 16:02 ` Michael S. Tsirkin
2023-02-01 17:13 ` Christophe de Dinechin
2023-02-06 18:58 ` Dr. David Alan Gilbert
2023-02-02 3:24 ` Jason Wang
2023-02-01 10:24 ` Christophe de Dinechin
2023-01-31 16:34 ` Reshetova, Elena
2023-01-31 17:49 ` James Bottomley
2023-02-02 14:51 ` Jeremi Piotrowski
2023-02-03 14:05 ` Reshetova, Elena
2023-01-27 9:32 ` Jörg Rödel
2023-01-26 13:58 ` Dr. David Alan Gilbert
2023-01-26 17:48 ` Reshetova, Elena
2023-01-26 18:06 ` Leon Romanovsky
2023-01-26 18:14 ` Dr. David Alan Gilbert [this message]
2023-01-26 16:29 ` Michael S. Tsirkin
2023-01-27 8:52 ` Reshetova, Elena
2023-01-27 10:04 ` Michael S. Tsirkin
2023-01-27 12:25 ` Reshetova, Elena
2023-01-27 14:32 ` Michael S. Tsirkin
2023-01-27 20:51 ` Carlos Bilbao
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