On Mon, 2019-06-17 at 18:50 -0700, Andy Lutomirski wrote: > On Mon, Jun 17, 2019 at 5:48 PM Kai Huang <kai.huang@xxxxxxxxxxxxxxx> wrote: > > > > > > > > > > > And another silly argument: if we had /dev/mktme, then we could > > > > possibly get away with avoiding all the keyring stuff entirely. > > > > Instead, you open /dev/mktme and you get your own key under the hook. > > > > If you want two keys, you open /dev/mktme twice. If you want some > > > > other program to be able to see your memory, you pass it the fd. > > > > > > We still like the keyring because it's one-stop-shopping as the place > > > that *owns* the hardware KeyID slots. Those are global resources and > > > scream for a single global place to allocate and manage them. The > > > hardware slots also need to be shared between any anonymous and > > > file-based users, no matter what the APIs for the anonymous side. > > > > MKTME driver (who creates /dev/mktme) can also be the one-stop-shopping. I think whether to > > choose > > keyring to manage MKTME key should be based on whether we need/should take advantage of existing > > key > > retention service functionalities. For example, with key retention service we can > > revoke/invalidate/set expiry for a key (not sure whether MKTME needs those although), and we > > have > > several keyrings -- thread specific keyring, process specific keyring, user specific keyring, > > etc, > > thus we can control who can/cannot find the key, etc. I think managing MKTME key in MKTME driver > > doesn't have those advantages. > > > > Trying to evaluate this with the current proposed code is a bit odd, I > think. Suppose you create a thread-specific key and then fork(). The > child can presumably still use the key regardless of whether the child > can nominally access the key in the keyring because the PTEs are still > there. Right. This is a little bit odd, although virtualization (Qemu, which is the main use case of MKTME at least so far) doesn't use fork(). > > More fundamentally, in some sense, the current code has no semantics. > Associating a key with memory and "encrypting" it doesn't actually do > anything unless you are attacking the memory bus but you haven't > compromised the kernel. There's no protection against a guest that > can corrupt its EPT tables, there's no protection against kernel bugs > (*especially* if the duplicate direct map design stays), and there > isn't even any fd or other object around by which you can only access > the data if you can see the key. I am not saying managing MKTME key/keyID in key retention service is definitely better, but it seems all those you mentioned are not related to whether to choose key retention service to manage MKTME key/keyID? Or you are saying it doesn't matter we manage key/keyID in key retention service or in MKTME driver, since MKTME barely have any security benefits (besides physical attack)? > > I'm also wondering whether the kernel will always be able to be a > one-stop shop for key allocation -- if the MKTME hardware gains > interesting new uses down the road, who knows how key allocation will > work? I by now don't have any use case which requires to manage key/keyID specifically for its own use, rather than letting kernel to manage keyID allocation. Please inspire us if you have any potential. Thanks, -Kai
