I've been working on integrating filesystem extended attribute support in tmpfs, libarchive, and pkg(8).
Other operating systems tag ELF objects with various flags. We in HardenedBSD prefer not to use such a heavy-handed approach. Making use of filesystem extended attributes enables out-of-band (OOB) management of security flags. HardenedBSD makes use of extended attributes to toggle exploit mitigations on a per-binary basis. Using an OOB method provides flexibility along with an easy avenue for future growth.
I've made changes to libarchive in the base OS and have submitted a patch upstream. The patch takes a best-effort approach to restoring system-level extended attributes. Setting system-level extended attributes is a privileged operation. If an archive entry contains a systeam-level extended attribute and the extraction process is not privileged, setting the extended attribute will fail. The failure will be ignored and the extraction process will continue as normal. (The same holds true today without the patch.)
Extended attribute support in tmpfs is a bare minimum, with the ability to add and list, but not remove extended attributes. Anyone desiring to provide complete extended attribute support is welcome to provide a patch.
Finally, HardenedBSD forked FreeBSD's package manager, aptly named pkg. The package manager must be aware of filesystem extended attributes. pkg can now include any filesystem extended attribute and is not limited to HardenedBSD's use. I will make some attempt at upstreaming the changes to pkg after the changes to libarchive have been upstreamed.
The future is bright for filesystem extended attributes. One could imagine a future in which pkg stores the hash of files as extended attributes, and the kernel checks the hash against the stored attribute. The sky is the limit.
I am now integrating exploit mitigation toggling into the ports tree such that HardenedBSD ships packages with exploit mitigations toggled for those misbehaving applications (like firefox, java, nodejs, etc.)