On Wed, Jan 15, 2025 at 12:20:59PM -0800, Jeff Xu wrote: > Hi Lorenzo > > On Wed, Jan 15, 2025 at 11:46 AM Lorenzo Stoakes > <lorenzo.stoakes@xxxxxxxxxx> wrote: > > > > Jeff, > > > > My name is Lorenzo, not Lorenze. > > > I apologize. No worries, sorry I realise it was probably a typo! But just in case you didn't realise :P > > > I've made it abundantly clear that this (NACKed) series cannot allow the > > kernel to be in a broken state even if a user sets flags to do so. > > > > This is because users might lack context to make this decision and > > incorrectly do so, and now we ship a known-broken kernel. > > > > You are now suggesting disabling the !CRIU requirement. Which violates my > > _requirements_ (not optional features). > > > Sure, I can add CRIU back. > > Are you fine with UML and gViso not working under this CONFIG ? > UML/gViso doesn't use any KCONFIG like CRIU does. Yeah this is a concern, wouldn't we be able to catch UML with a flag? Apologies my fault for maybe not being totally up to date with this, but what exactly was the gViso (is it gVisor actually?) > > > You seem to be saying you're pushing an internal feature on upstream and > > only care about internal use cases, this is not how upstream works, as > > Matthew alludes to. > > > > I have told you that my requirements are: > > > > 1. You cannot allow a user to set config or boot options to have a > > broken kernel configuration. > > > Can you clarify on the definition of "broken kernel configuration": Anything that'd unexpected break userland in a way that would be entirely unexpected. Especially so if there is a real disconnect between the person who is enabling the feature and the program. For instance if a distro wants to be big on security, is (as is entirely reasonable) concerned about an unsealed VDSO/VVAR/etc. being exploited, so turns on the flag, but _doesn't realise_ or doesn't communicate (such a big problem and difficult actually for many distros/vendors) that this will break certain programs - and then users do a kernel update, and *bang* their whole system is broken. It's really this kind of scenario I'm worried about. This is the crux of it really. > > Do you consider "setting mseal kernel cmd line under 32 bit build" as broken ? > If so, this problem is not solvable and I might just not try to solve > it for the next version. Yeah, I really don't like the kernel cmd line thing, because of this risk of disconnect - your justification for it is prima facie reasonable - the distro didn't want to enable the thing by default but you want more security - but then we have this issue with the possible disconnect between 'hey here is security feature X' vs. 'security feature X breaks Y, Z + alpha'. > > If you just refer to a need to detect CRIU, in KCONFIG or/and kernel > cmd line, this is solvable. > > > 2. You must provide evidence that the arches you claim work with this, > > actually do. > > > Sure See my reply to Kees as to what this comprises, sorry if I was not clear previously. > > > You seem to have eliminated that from your summary as if the very thing > > that makes this series NACKed were not pertinent. > > > In my last email, I tried to cover all code-logic related comments, > which is blocking me. > I also mentioned I will address non-code related comments > (threat-model/test etc), later. Ack. I felt that you hadn't hit on my fundamental objections and this was in effect - a final analysis as to how you would be moving forward with v5 - but apologies if you did intend to separately discuss them. > > > if you do not address these correctly, I will simply have to reject your v5 > > too and it'll waste everybody's time. I _genuinely_ don't want to have to > > do this. > > > > Any solution MUST fulfil these requirements. I also want to see v5 as an > > RFC honestly at this stage, since it seems we are VERY MUCH in a discussion > > phase rather than a patch phase at this time. > > > Sure. To be clear - if the series is viable, I want to see it merged. And to further clarify - a simpler, smaller version of this that explicitly disallows breakage in config options suffices (though we must clarify the gVisor + UML things). If I just wanted to reject this outright, I'd tell you :) (I don't). I just need to feel vaguely less anxious about breaking things! :) > > > I really want to help you improve mseal and get things upstream, but I > > can't ignore my duty to ensure that the kernel remains stable and we don't > > hand kernel users (overly huge) footguns. I hate to be negative, but this > > is why I am pushing back so much here. > > > Thanks. You can help me by answering my questions, and clarify your > requirements. I appreciate your time to make this feature useful. Sure, hopefully I have done so, do follow up if anything was unclear. > > Please take note that the security feature often takes away > capabilities. Sometimes it is impossible to meet security, usability > or performance goals simultaneously. I'm trying my best to get all > aspected satisfied. Ack, and I realise it's often a difficult trade-off. I just worry about compounding complexity in consequences of kernel configuration vs. userland stuff + the disconnect between the two. > > -Jeff > > > Thanks! Cheers, Lorenzo
