On 4/28/25 17:04, Daniel P. Smith wrote: >> OK, but why do this in Linux as opposed to tboot? Right now, much of the >> TXT magic is done outside of the kernel. Why do it *IN* the kernel? > > There was a patch set submitted to tboot to add AMD support. It was > rejected as tboot is solely focused on Intel TXT implementation. > > This meant I either had to go the route of yet another standalone loader > kernel or do it in the kernel. Doing it as an external loader would have > required a new set of touchpoints, like the one you are highlighting. At > which point, I am sure I would have gotten the question of why I didn't > do it in the kernel. > > But the real motivation for doing it in the kernel is due to Linux's > flexibility, allowing for it to be used in a variety of use-cases. For > instance, Linux is used as a bootloader kernel (see LinuxBoot) allowing > for the starting of the target OS kernel from the hardware D-RTM trust > chain. It can be used in the kexec path to again root the follow-on > kernel in the hardware D-RTM instead of an elongated S-RTM trust chain. > I gave a presentation at LPC 2020[1] covering several use cases if you > are interested. > > [1] https://lpc.events/event/7/contributions/739/
Could we please get a condensed version of that into the cover letter and documentation? But, in the end, this is a change in direction. I don't think what you have here sufficiently justifies the move from an exokernel to the in-kernel approach. I'm open to hearing more, but the justification just isn't here. >> Say we axed tboot support from 6.16, but merged Trenchboot. A user on >> old hardware upgrades their kernel. What happens to them? > > I would not advocate for the remove of tboot support. Humor me, please. What has to happen for Trenchboot to replace tboot if a user is already using tboot? You might not thing it's reasonable and so don't want to answer my question. But I'm not the expert here. I don't know why it's not feasible. >>>> so that Linux support for TXT/tboot can just go away? >> You didn't _really_ answer the question. >> >> Summarizing, I think you're saying that TXT/tboot Linux support can just >> go away, but it will be help if its maintainers help its users >> transition. >> >> Does anybody disagree with that? > > As the lead of the TrenchBoot project, I would not call for the removal > of tboot. We did a lot of collaboration with the previous tboot > maintainer, assisting each other with our solutions. Some may want to > use TXT under the Exo-kernel model that tboot provides. This is one use > case where Linux could work in that fashion but would be extremely less- > than-ideal. Likewise, it would not be ideal to try to add a bunch of > drivers to tboot in order to support the advanced policy-based > environment measurement system that can be achieved with a Linux > configuration. This is a bit hand-wavy for my taste. Can you give one concrete example of something that's hard or impossible with tboot but is easy with Trenchboot? >>> In that perfect world, Intel ACM and tboot developers would review >>> the TrenchBoot Linux series >> >> So, I was looking on the cc list and I didn't see them on there. >> Shouldn't they be cc'd if you want them to review the series? A little >> poking at lore makes me think that they were *NEVER* cc'd. >> >> Is that right, or is my lore-foo weak? > > As I mentioned, we did a significant amount of collaboration with Lukasz > Hawrylko when he was the sole tboot maintainer for Intel. By the time he > moved on, TB was fairly well complete, and at that point the goal was to > get it to an acceptable state for the maintainers. We would be more than > glad to have the current tboot maintainers review it if they would like. Here's the deal: I want *an* ack from the tboot MAINTAINER on at least one patch in this patch set. There's not a chance that we merge duplicate, parallel in-kernel functionality without them saying that this is a reasonable approach. Let me know if I can help facilitate that in any way. I kinda wish that someone would have told me a few years ago that if tboot didn't take your patches that a 5,000-line series was going to plop into my inbox a dozen or more times.
