From: Serge E. Hallyn
Date: Thu Mar 21 2013 - 11:36:44 EST

Quoting Vivek Goyal (vgoyal@xxxxxxxxxx):
> 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.
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