I have been playing with Linux IMA/EVM on a Gentoo Hardened (with SELinux) system for a while and have been documenting what I think is interesting/necessary for Gentoo Linux users when they want to use IMA/EVM as well. Note that the documentation of the Linux IMA/EVM project itself is very decent. It's all on a single wiki page, but it's decent and I learned a lot from it.

That being said, I do have the impression that the method they suggest for generating IMA hashes for the entire system is not always working properly. It might be because of SELinux on my system, but for now I'm searching for another method that does seem to work well (I'm currently trying my luck with a find ... -exec evmctl based command). But once the hashes are registered, it works pretty well (well, there's a probably small SELinux problem where loading a new policy or updating the existing policies seems to generate stale rules and I have to reboot my system, but I'll find the culprit of that soon ;-)

The IMA Guide has been updated to reflect recent findings - including how to load a custom policy, and I have also started on the EVM Guide. I think it'll take me a day or three to finish off the rough edges and then I'll start creating a new SELinux node (KVM) image that users can use with various Gentoo Hardened-supported technologies enabled (PaX, grSecurity, SELinux, IMA and EVM).

So if you're curious about IMA/EVM and willing to try it out on Gentoo Linux, please have a look at those documents and see if they assist you (or confuse you even more).