On Fri, Nov 18, 2022 at 6:06 AM Kees Cook <keescook@xxxxxxxxxxxx> wrote: > > 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@xxxxxxxxxxxx> 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/kunit/usercopy > > > > > > 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@xxxxxxxxxxx/ > > > > 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 > > -- > Kees Cook FWIW, I had another quick look at this yesterday, and I suspect that (at least one of) the problem(s) is that function pointers like mm->get_unmapped_area are only setup as part of exec(), so a newly-created mm isn't actually useful. Looking at, e.g., arch_pick_mm_layout(), there's a whole bunch of architecture-dependent stuff here to handle, e.g., 32-bit compat. Cheers, -- David
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