On Wed, 31 Jan 2024 at 22:01, Paul Heidekrüger <paul.heidekrueger@xxxxxx> wrote: > > Hi! > > This RFC patch adds tests that detect whether KASan is able to catch > unsafe atomic accesses. > > Since v1, which can be found on Bugzilla (see "Closes:" tag), I've made > the following suggested changes: > > * Adjust size of allocations to make kasan_atomics() work with all KASan modes > * Remove comments and move tests closer to the bitops tests > * For functions taking two addresses as an input, test each address in a separate function call. > * Rename variables for clarity > * Add tests for READ_ONCE(), WRITE_ONCE(), smp_load_acquire() and smp_store_release() > > I'm still uncelar on which kinds of atomic accesses we should be testing > though. The patch below only covers a subset, and I don't know if it > would be feasible to just manually add all atomics of interest. Which > ones would those be exactly? The atomics wrappers are generated by a script. An exhaustive test case would, if generated by hand, be difficult to keep in sync if some variants are removed or renamed (although that's probably a relatively rare occurrence). I would probably just cover some of the most common ones that all architectures (that support KASAN) provide. I think you are already covering some of the most important ones, and I'd just say it's good enough for the test. > As Andrey pointed out on Bugzilla, if we > were to include all of the atomic64_* ones, that would make a lot of > function calls. Just include a few atomic64_ cases, similar to the ones you already include for atomic_. Although beware that the atomic64_t helpers are likely not available on 32-bit architectures, so you need an #ifdef CONFIG_64BIT. Alternatively, there is also atomic_long_t, which (on 64-bit architectures) just wraps atomic64_t helpers, and on 32-bit the atomic_t ones. I'd probably opt for the atomic_long_t variants, just to keep it simpler and get some additional coverage on 32-bit architectures. > Also, the availability of atomics varies between architectures; I did my > testing on arm64. Is something like gen-atomic-instrumented.sh required? I would not touch gen-atomic-instrumented.sh for the test. > Many thanks, > Paul > > CC: Marco Elver <elver@xxxxxxxxxx> > CC: Andrey Konovalov <andreyknvl@xxxxxxxxx> > Closes: https://bugzilla.kernel.org/show_bug.cgi?id=214055 > Signed-off-by: Paul Heidekrüger <paul.heidekrueger@xxxxxx> > --- > mm/kasan/kasan_test.c | 50 +++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 50 insertions(+) > > diff --git a/mm/kasan/kasan_test.c b/mm/kasan/kasan_test.c > index 8281eb42464b..1ab4444fe4a0 100644 > --- a/mm/kasan/kasan_test.c > +++ b/mm/kasan/kasan_test.c > @@ -1150,6 +1150,55 @@ static void kasan_bitops_tags(struct kunit *test) > kfree(bits); > } > > +static void kasan_atomics_helper(struct kunit *test, void *unsafe, void *safe) > +{ > + int *i_safe = (int *)safe; > + int *i_unsafe = (int *)unsafe; > + > + KUNIT_EXPECT_KASAN_FAIL(test, READ_ONCE(*i_unsafe)); > + KUNIT_EXPECT_KASAN_FAIL(test, WRITE_ONCE(*i_unsafe, 42)); > + KUNIT_EXPECT_KASAN_FAIL(test, smp_load_acquire(i_unsafe)); > + KUNIT_EXPECT_KASAN_FAIL(test, smp_store_release(i_unsafe, 42)); > + KUNIT_EXPECT_KASAN_FAIL(test, atomic_read(unsafe)); > + KUNIT_EXPECT_KASAN_FAIL(test, atomic_set(unsafe, 42)); > + KUNIT_EXPECT_KASAN_FAIL(test, atomic_add(42, unsafe)); > + KUNIT_EXPECT_KASAN_FAIL(test, atomic_sub(42, unsafe)); > + KUNIT_EXPECT_KASAN_FAIL(test, atomic_inc(unsafe)); > + KUNIT_EXPECT_KASAN_FAIL(test, atomic_dec(unsafe)); > + KUNIT_EXPECT_KASAN_FAIL(test, atomic_and(42, unsafe)); > + KUNIT_EXPECT_KASAN_FAIL(test, atomic_andnot(42, unsafe)); > + KUNIT_EXPECT_KASAN_FAIL(test, atomic_or(42, unsafe)); > + KUNIT_EXPECT_KASAN_FAIL(test, atomic_xor(42, unsafe)); > + KUNIT_EXPECT_KASAN_FAIL(test, atomic_xchg(unsafe, 42)); > + KUNIT_EXPECT_KASAN_FAIL(test, atomic_cmpxchg(unsafe, 21, 42)); > + KUNIT_EXPECT_KASAN_FAIL(test, atomic_try_cmpxchg(unsafe, safe, 42)); > + KUNIT_EXPECT_KASAN_FAIL(test, atomic_try_cmpxchg(safe, unsafe, 42)); > + KUNIT_EXPECT_KASAN_FAIL(test, atomic_sub_and_test(42, unsafe)); > + KUNIT_EXPECT_KASAN_FAIL(test, atomic_dec_and_test(unsafe)); > + KUNIT_EXPECT_KASAN_FAIL(test, atomic_inc_and_test(unsafe)); > + KUNIT_EXPECT_KASAN_FAIL(test, atomic_add_negative(42, unsafe)); > + KUNIT_EXPECT_KASAN_FAIL(test, atomic_add_unless(unsafe, 21, 42)); > + KUNIT_EXPECT_KASAN_FAIL(test, atomic_inc_not_zero(unsafe)); > + KUNIT_EXPECT_KASAN_FAIL(test, atomic_inc_unless_negative(unsafe)); > + KUNIT_EXPECT_KASAN_FAIL(test, atomic_dec_unless_positive(unsafe)); > + KUNIT_EXPECT_KASAN_FAIL(test, atomic_dec_if_positive(unsafe)); > +} > + > +static void kasan_atomics(struct kunit *test) > +{ > + int *a1, *a2; If you're casting it to void* below and never using as an int* in this function, just make these void* (the sizeof can just be sizeof(int)). > + a1 = kzalloc(48, GFP_KERNEL); > + KUNIT_ASSERT_NOT_ERR_OR_NULL(test, a1); > + a2 = kzalloc(sizeof(*a1), GFP_KERNEL); > + KUNIT_ASSERT_NOT_ERR_OR_NULL(test, a1); > + > + kasan_atomics_helper(test, (void *)a1 + 48, (void *)a2); We try to ensure (where possible) that the KASAN tests are not destructive to the rest of the kernel. I think the size of "48" was chosen to fall into the 64-byte size class, similar to the bitops. I would just copy that comment, so nobody attempts to change it in future. :-) > + kfree(a1); > + kfree(a2); Thanks, -- Marco
