[Ksummit-2013-discuss] [ATTEND] Interface stability guarantees

[H. Peter Anvin]

We all, hopefully, know that the maxim is "don't break userspace".
However, there are clearly some limitations to that.  For example, Linus
recently made the distinction between "userspace" and "kernel support",
when some scripts designed to set up Grub2 groped around the kernel
configuration file left by the build and broke.

However, "broken kernel support" itself is not a killer, obviously; we
already have a whole bunch of workarounds for broken bootloaders (which
gets really gnarly, because different bootloaders are broken in
different ways.)

"Breaking userspace" clearly also doesn't extend to userspace which does
things like "build a kernel module and insert it" (and yes, there are
applications that do that), or a number of similar extremely low level
manipulations.  In the extreme case, fixing a security holes is
"breaking userspace" in the sense that some malware would no longer run
-- but neither might some very bizarre real-life usecase.

We talked a little about this last year, already, but there has been
some interesting corner cases that have reared their heads this past year.

	-hpa