From: "Michael S. Tsirkin" <mst@redhat.com>
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>,
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: Fri, 27 Jan 2023 09:32:49 -0500 [thread overview]
Message-ID: <20230127090526-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <DM8PR11MB57501BD39CC1E88206E6CD5FE7CC9@DM8PR11MB5750.namprd11.prod.outlook.com>
On Fri, Jan 27, 2023 at 12:25:09PM +0000, Reshetova, Elena wrote:
>
> > On Fri, Jan 27, 2023 at 08:52:22AM +0000, Reshetova, Elena wrote:
> > > > On Wed, Jan 25, 2023 at 03:29:07PM +0000, Reshetova, Elena wrote:
> > > > > And this is a very special aspect of 'hardening' since it is about hardening a
> > > > kernel
> > > > > under different threat model/assumptions.
> > > >
> > > > I am not sure it's that special in that hardening IMHO is not a specific
> > > > threat model or a set of assumptions. IIUC it's just something that
> > > > helps reduce severity of vulnerabilities. Similarly, one can use the CC
> > > > hardware in a variety of ways I guess. And one way is just that -
> > > > hardening linux such that ability to corrupt guest memory does not
> > > > automatically escalate into guest code execution.
> > >
> > > I am not sure if I fully follow you on this. I do agree that it is in principle
> > > the same 'hardening' that we have been doing in Linux for decades just
> > > applied to a new attack surface, host <-> guest, vs userspace <->kernel.
> >
> > Sorry about being unclear this is not the type of hardening I meant
> > really. The "hardening" you meant is preventing kernel vulnerabilities,
> > right? This is what we've been doing for decades.
> > But I meant slightly newer things like e.g. KASLR or indeed ASLR generally -
> > we are trying to reduce a chance a vulnerability causes random
> > code execution as opposed to a DOS. To think in these terms you do not
> > need to think about attack surfaces - in the system including
> > a hypervisor, guest supervisor and guest userspace hiding
> > one component from others is helpful even if they share
> > a privelege level.
>
> Do you mean that the fact that CoCo guest has memory encrypted
> can help even in non-CoCo scenarios?
Yes.
> I am sorry, I still seem not to be able
> to grasp your idea fully. When the privilege level is shared, there is no
> incentive to perform privilege escalation attacks across components,
> so why hide them from each other?
Because limiting horisontal movement between components is still valuable.
> Data protection? But I don’t think you
> are talking about this? I do agree that KASLR is stronger when you remove
> the possibility to read the memory (make sure kernel code is execute only)
> you are trying to attack, but again not sure if you mean this.
It's an example. If kernel was 100% secure we won't need KASLR. Nothing
ever is though.
> >
> >
> >
> > > Interfaces have changed, but the types of vulnerabilities, etc are the same.
> > > The attacker model is somewhat different because we have
> > > different expectations on what host/hypervisor should be able to do
> > > to the guest (following business reasons and use-cases), versus what we
> > > expect normal userspace being able to "do" towards kernel. The host and
> > > hypervisor still has a lot of control over the guest (ability to start/stop it,
> > > manage its resources, etc). But the reasons behind this doesn’t come
> > > from the fact that security CoCo HW not being able to support this stricter
> > > security model (it cannot now indeed, but this is a design decision), but
> > > from the fact that it is important for Cloud service providers to retain that
> > > level of control over their infrastructure.
> >
> > Surely they need ability to control resource usage, not ability to execute DOS
> > attacks. Current hardware just does not have ability to allow the former
> > without the later.
>
> I don’t see why it cannot be added to HW if requirement comes. However, I think
> in cloud provider world being able to control resources equals to being able
> to deny these resources when required, so being able to denial of service its clients
> is kind of build-in expectation that everyone just agrees on.
>
> >
> > > >
> > > > If you put it this way, you get to participate in a well understood
> > > > problem space instead of constantly saying "yes but CC is special". And
> > > > further, you will now talk about features as opposed to fixing bugs.
> > > > Which will stop annoying people who currently seem annoyed by the
> > > > implication that their code is buggy simply because it does not cache in
> > > > memory all data read from hardware. Finally, you then don't really need
> > > > to explain why e.g. DoS is not a problem but info leak is a problem - when
> > > > for many users it's actually the reverse - the reason is not that it's
> > > > not part of a threat model - which then makes you work hard to define
> > > > the threat model - but simply that CC hardware does not support this
> > > > kind of hardening.
> > >
> > > But this won't be correct statement, because it is not limitation of HW, but the
> > > threat and business model that Confidential Computing exists in. I am not
> > > aware of a single cloud provider who would be willing to use the HW that
> > > takes the full control of their infrastructure and running confidential guests,
> > > leaving them with no mechanisms to control the load balancing, enforce
> > > resource usage, etc. So, given that nobody needs/willing to use such HW,
> > > such HW simply doesn’t exist.
> > >
> > > So, I would still say that the model we operate in CoCo usecases is somewhat
> > > special, but I do agree that given that we list a couple of these special
> > assumptions
> > > (over which ones we have no control or ability to influence, none of us are
> > business
> > > people), then the rest becomes just careful enumeration of attack surface
> > interfaces
> > > and break up of potential mitigations.
> > >
> > > Best Regards,
> > > Elena.
> > >
> >
> > I'd say each business has a slightly different business model, no?
> > Finding common ground is what helps us share code ...
>
> Fully agree, and a good discussion with everyone willing to listen and cooperate
> can go a long way into defining the best implementation.
>
> Best Regards,
> Elena.
Right. My point was that trying to show how CC usecases are similar to other
existing ones will be more helpful for everyone than just focusing on how they
are different. I hope I was able to show some similarities.
--
MST
next prev parent reply other threads:[~2023-01-27 14:37 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
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 [this message]
2023-01-27 20:51 ` Carlos Bilbao
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