Hi,
This has diverged from the original topic a bit, so I've changed the Subject to hopefully gain visibility. :)
For KUnit, it would be REALLY nice to have a way to attach a userspace VM to a kernel thread so we can do userspace memory mapping manipulation, etc. Neither David nor I have been able to figure out the right set of steps to make this happen. What are we missing?
Details below...
On Wed, Nov 16, 2022 at 12:34:40PM +0800, David Gow wrote:
On Mon, Nov 7, 2022 at 11:59 AM Kees Cook keescook@chromium.org wrote:
On Sun, Nov 06, 2022 at 02:16:57AM +0000, Pedro Falcato wrote: David, has there been any work on adding a way to instantiate userspace VMAs in a KUnit test? I tried to write this myself, but I couldn't figure out how to make the userspace memory mappings appear. Here's my fumbling attempt: https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git/log/?h=devel/...
I really wish KUnit had userspace mapping support -- I have a bunch of unit tests that need to get built up around checking for regressions here, etc.
Hi Kees,
Sorry the the delayed response!
Alas, my attempts to get this to work haven't been much more successful than yours. It's definitely something we'd like to support, but I confess to not knowing enough about the mm code to know exactly what would be involved.
The workaround is to load tests as modules, and use something like Vitor's original patch here: https://lore.kernel.org/all/20200721174036.71072-1-vitor@massaru.org/
Basically, using the existing mm of the module loader. Adapting those changes to your branch (and fixing a couple of back-to-front KUnit assertions) does work for me when built as a module, in an x86_64 vm:
root@slicestar:~# modprobe usercopy_kunit [ 52.986290] # Subtest: usercopy [ 52.986701] 1..1 [ 53.246058] ok 1 - usercopy_test [ 53.246628] ok 1 - usercopy
But getting it to work with built-in tests hasn't been successful so far. I wondered if we could just piggy-back on init_mm or similar, but that doesn't seem to work either.
So, in the short-term, this is only possible for modules. If that's useful enough, we can get Vitor's support patch (or something similar) in, and just mark any tests module-only (or have them skip if there's no mm). Because kunit.py only runs built-in tests, though, it's definitely less convenient.
Thanks for any pointers! :)
-Kees