The Windkey and the Lamplighter

Sitting at the SELinux symposium this week, I’ve heard some of the
smartest people in the room compare SELinux’ current state to assembly
language—and they want better languages. But I just heard a
different speaker suggest that an administrator faced with difficult
SELinux policy authoring "make the computer do the hard work for you."

But this is a special sort of work. This work is a kind of thinking.
Historically, computers have only rarely been good at thinking work.
In fact, they’re only good at one very special sort of thinking work:
those where we can express a simple algorithm that can be reliably
applied. For example, computers are good at playing Chess, but not so
good at solving or writing chess problems interesting to humans.
Computers are not generally good at creative thinking. It’s
troublesome to need to restate this.

Given this constraint, obvious as it should be, how did we get past
assembly language? We built compilers. We built interpreters. We
built libraries, particularly sophisticated runtime libraries,
bringing the flexibility of interpreters to compiled languages.
What’s the biggest advantage of modern languages over assembly
languages? I don’t expect much contradiction when I celebrate the
Garbage Collector.

A simple GC can be written in assembly language, then used by other
assembled programs. A simple compiler can be written in assembly
language, then used to produce new programs. The first LISP
interpreters were written in an assembly language 50 years ago using
just this strategy. The core idea here is abstraction: building tools
with simpler interfaces than contents. And the SELinux community
have provided some abstractions. But they haven’t provided them using
SELinux. They’ve provided them using components outside the system.
This is more like a card-punch than a compiler.

There is no ability to use SELinux itself to build new SELinux
capability. In that critical way, it is not like assembly language.
We should not expect to see self-reinforcing, exponential growth in
SELinux capability: SELinux, as a constraining rather than enabling
system, is not the right shape for that.