[PATCH 01/12] Security: Add CAP_COMPROMISE_KERNEL

[Serge E. Hallyn]

Quoting Vivek Goyal (vgoyal at redhat.com):
...
> Giving CAP_MODIFY_KERNEL to processess upon signature verification
> will simplify things a bit.
> 
> Only thing is that signature verification alone is not sufficient. We
> also need to make sure after signature verification executable can
> not be modified in memory in any way. So that means atleast couple of
> things.

Also what about context?  If I construct a mounts namespace a certain
way, can I trick this executable into loading an old singed bzImage that
I had laying around?

ISTM the only sane thing to do, if you're going down this road,
is to have CAP_MODIFIY_KERNEL pulled from bounding set for everyone
except a getty started by init on ttyS0.  Then log in on serial
to update.  Or run a damon with CAP_MODIFIY_KERNEL which listens
to a init_net_ns netlink socket for very basic instructions, like
"find and install latest signed bzImage in /boot".  Then you can
at least trust that /boot for that daemon is not faked.