On Mon, 25 Mar 2019, Andy Lutomirski wrote:

A while back, I suggested an approach to actually make this stuff
mergeable: submit a patch series that adds lockdown mode, enables it
by command line option (and maybe sysctl) *only* and has either no
effect or only a token effect.  Then we can add actual features to
lockdown mode one at a time and review them separately.

This makes sense to me.

And I'm going to complain loudly unless two things change about this
whole thing:

1. Lockdown mode becomes three states, not a boolean.  The states are:
no lockdown, best-effort-to-protect-kernel-integrity, and
best-effort-to-protect-kernel-secrecy-and-integrity.  And this BPF
mess illustrates why: most users will really strongly object to
turning off BPF when they actually just want to protect kernel
integrity.  And as far as I know, things like Secure Boot policy will
mostly care about integrity, not secrecy, and tracing and such should
work on a normal locked-down kernel.  So I think we need this knob.

Another approach would be to make this entirely policy based:

- Assign an ID to each lockdown point
- Implement a policy mechanism where each ID is mapped to 0 or 1
- Allow this policy to be specified statically or dynamically

So, 

	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?

2. All the proponents of this series, and the documentation, needs to
document that it's best effort.  There will always be security bugs,
and there will always be things we miss.

Right.  Maintaining this feature will be an ongoing effort, and if its not 
actively maintained, it will bitrot and become useless.


-- 
James Morris
[off-list ref]