> As Peter Zijlstra pointed out, there is another, perhaps surprising advantage to removing the unneeded endbr instructions. The kernel limits the functions that are available to loadable modules, and proprietary modules are limited even further. It is a common technique for proprietary modules to look up the non-exported functions they need in the kernel's symbol table, then call them via an indirect branch, thus bypassing the kernel's limitations. But, with IBT enabled, any function lacking an endbr instruction will no longer be callable in this way.

This is an amusing consequence but of course code that is deliberately trying to violate the GPL an running in the kernel address space is usually more than willing to work around such trivialities, e.g. by patching the kernel's text at runtime to remove the instructions. But maybe now we can call them out for reducing kernel security in addition to being jerks in general :)