On Tue, 26 Mar 2019, Andy Lutomirski wrote:

quoted

        kernel_is_locked_down("ioperm")

becomes

        kernel_is_locked_down(LOCKDOWN_IOPERM)

and this function checks e.g.

        if (lockdown_polcy[id]) {
                fail or warn;
        }

Thoughts?

I'm concerned that this gives too much useless flexibility to
administrators and user code in general.  If you can break kernel
integrity, you can break kernel integrity -- it shouldn't really
matter *how* you break it.

OTOH, this seems like a combination of mechanism and policy. The 3 modes 
are a help here, but I wonder if they may be too coarse grained still, 
e.g. if someone wants to allow a specific mechanism according to their own 
threat model and mitigations.

Secure boot gives you some assurance of the static state of the system at 
boot time, and lockdown is certainly useful (with or without secure boot), 
but it's not a complete solution to runtime kernel integrity protection by 
any stretch of the imagination.  I'm concerned about it being perceived as 
such.

I'm not sure how to think about it architecturally and how it fits as such 
in the mainline kernel.


-- 
James Morris
[off-list ref]