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
