On Thu, Jan 26, 2023 at 04:01:55PM -0600, William Roberts wrote: > On Thu, Jan 26, 2023 at 3:30 PM Jarkko Sakkinen <jarkko@xxxxxxxxxx> wrote: > > > > On Thu, Jan 26, 2023 at 11:32:22AM -0600, William Roberts wrote: > > > On Thu, Jan 26, 2023 at 11:21 AM Jarkko Sakkinen <jarkko@xxxxxxxxxx> wrote: > > > > > > > > On Tue, Jan 24, 2023 at 07:38:04AM -0500, James Bottomley wrote: > > > > > On Mon, 2023-01-23 at 11:48 -0600, William Roberts wrote: > > > > > > On Fri, Jan 20, 2023 at 9:29 PM Jarkko Sakkinen <jarkko@xxxxxxxxxx> > > > > > > wrote: > > > > > > > > > > > > > > On Sat, Jan 14, 2023 at 09:55:37AM -0500, James Bottomley wrote: > > > > > > > > On Tue, 2023-01-03 at 13:10 -0800, Matthew Garrett wrote: > > > > > > > > > On Tue, Jan 3, 2023 at 1:05 PM William Roberts > > > > > > > > > <bill.c.roberts@xxxxxxxxx> wrote: > > > > > > > > > > > > > > > > > > > What's the use case of using the creation data and ticket in > > > > > > > > > > this context? Who gets the creationData and the ticket? > > > > > > > > > > Could a user supplied outsideInfo work? IIRC I saw some > > > > > > > > > > patches flying around where the sessions will get encrypted > > > > > > > > > > and presumably correctly as well. This would allow the > > > > > > > > > > transfer of that outsideInfo, like the NV Index PCR value to > > > > > > > > > > be included and integrity protected by the session HMAC. > > > > > > > > > > > > > > > > > > The goal is to ensure that the key was generated by the kernel. > > > > > > > > > In the absence of the creation data, an attacker could generate > > > > > > > > > a hibernation image using their own key and trick the kernel > > > > > > > > > into resuming arbitrary code. We don't have any way to pass > > > > > > > > > secret data from the hibernate kernel to the resume kernel, so > > > > > > > > > I don't think there's any easy way to do it with outsideinfo. > > > > > > > > > > > > > > > > Can we go back again to why you can't use locality? It's exactly > > > > > > > > designed for this since locality is part of creation data. > > > > > > > > Currently everything only uses locality 0, so it's impossible for > > > > > > > > anyone on Linux to produce a key with anything other than 0 in > > > > > > > > the creation data for locality. However, the dynamic launch > > > > > > > > people are proposing that the Kernel should use Locality 2 for > > > > > > > > all its operations, which would allow you to distinguish a key > > > > > > > > created by the kernel from one created by a user by locality. > > > > > > > > > > > > > > > > I think the previous objection was that not all TPMs implement > > > > > > > > locality, but then not all laptops have TPMs either, so if you > > > > > > > > ever come across one which has a TPM but no locality, it's in a > > > > > > > > very similar security boat to one which has no TPM. > > > > > > > > > > > > > > Kernel could try to use locality 2 and use locality 0 as fallback. > > > > > > > > > > > > I don't think that would work for Matthew, they need something > > > > > > reliable to indicate key provenance. > > > > > > > > > > No, I think it would be good enough: locality 0 means anyone (including > > > > > the kernel on a machine which doesn't function correctly) could have > > > > > created this key. Locality 2 would mean only the kernel could have > > > > > created this key. > > > > > > > > > > By the time the kernel boots and before it loads the hibernation image > > > > > it will know the answer to the question "does my TPM support locality > > > > > 2", so it can use that in its security assessment: if the kernel > > > > > supports locality 2 and the key wasn't created in locality 2 then > > > > > assume an attack. Obviously, if the kernel doesn't support locality 2 > > > > > then the hibernation resume has to accept any old key, but that's the > > > > > same as the situation today. > > > > > > > > This sounds otherwise great to me but why bother even allowing a > > > > machine with no-locality TPM to be involved with hibernate? Simply > > > > detect locality support during driver initialization and disallow > > > > sealed hibernation (or whatever the feature was called) if localities > > > > were not detected. > > > > > > > > I get supporting old hardware with old features but it does not make > > > > sense to maintain new features with hardware, which clearly does not > > > > scale, right? > > > > > > > > BR, Jarkko > > > > > > Here's a thought, what if we had a static/cmd line configurable > > > no-auth NV Index and writelocked it with the expected key information, > > > name or something. I guess the problem is atomicity with write/lock, > > > but can't the kernel lock out all other users? > > > > > > An attacker would need to issue tpm2_startup, which in this case would DOS > > > the kernel in both scenarios. If an attacker already wrote and locked the NV > > > index, that would also be a DOS. If they already wrote it, the kernel simply > > > writes whatever they want. Is there an attack I am missing? > > > > > > I guess the issue here would be setup, since creating the NV index requires > > > hierarchy auth, does the kernel have platform auth or is that already shut down > > > by firmware (I can't recall)? A null hierarchy volatile lockable index would be > > > nice for this, too bad that doesn't exist. > > > > How do you see this would better when compared to finding a way to use > > locality, which could potentially be made to somewhat simple to setup > > (practically zero config)? > > > > I never said it was better, I said here is a thought for discussion. > If we had to support older hardware (I could care less about things > that don't support localities, but some might not), this could be an > avenue to support them without walling off a PCR. I pointed out the > downsides, and argument could be made that when localities is not > supported then walling off PCR23 is the better approach if older > hardware is an issue. This all hinges on do we care about things > that don't support multiple localities. I don't, im for if you have locality > support you get the feature else you don't. Probably does not make much sense to care for this feature. BR, Jarkko
