On Thu, 2017-01-05 at 15:21 -0700, Jason Gunthorpe wrote: > On Thu, Jan 05, 2017 at 11:55:49AM -0800, James Bottomley wrote: > > > We don't really have that choice: Keys require authorization, so > > you have to have an auth session. > > I know, this is why I suggested a combo op (kernel level atomicity > is clearly DOS safe)..
Transactions are a hard thing to guarantee to be DoS safe and the more complex they get, the more difficult they are to police within the kernel. Plus we have to keep the R/W interface for backwards compatibility now that we have it and I just don't see how we could layer transactions into it without having some sort of in-kernel emulator. > > If you want things like PCR sealed or time limited keys, you don't > > really have a choice on policy sessions either. > > .. and advanced stuff like is what I was talking about giving up for > unpriv if it can't be allowed safely ... > > > I think we've got to the point where arguing about our divergent > > use requirements shows the default should be 0600 and every command > > enabled so that whatever changes the device to 0666 also applies > > the command > > Well, that is what we already have with /dev/tpm0. Except that doesn't have the RM. > I'm very surprised by this level of disagreement, so I'm inclined to > drop the idea that the kernel can directly support a 0666 cdev at > all. Great. We'll keep it at 0600 and let userspace sort it out; that way policy becomes flexible too. > Lets stick with the user space broker process and just introduce > enough kernel RM to enable co-existance with kernel users and clean > -up on crash. This should be enough to make a user space broker much > simpler. I wouldn't go that far. I'm still planning a userspace tss2 without any access broker daemon, but let's see how far I get on top of the RM. I think building in stages is a good way to get actual use experience to guide the next stage. > So Jarkko's uapi is basically fine.. No need for a kernel white > list/etc I suspect we'll eventually get to needing one, but I'm happy to begin without and see what that experience tells us before we try to build it. This is actually a better way of doing stuff because we can add to an API based on what we find in the field; the hard thing is pulling back an API that doesn't work. > I had really hoped we could have a secure default 0666 cdev that > would be able to support the basic use of your user space plugins > without a daemon :( I think we can; I just don't think we can define a single in-kernel use policy that supports everyone's use case, so punting to userspace and letting it sort out the desired policy for the platform will work for everyone. James
