From: Marco Elver <elver@xxxxxxxxxx> Subject: kasan: test: add globals left-out-of-bounds test Add a test checking that KASAN generic can also detect out-of-bounds accesses to the left of globals. Unfortunately it seems that GCC doesn't catch this (tested GCC 10, 11). The main difference between GCC's globals redzoning and Clang's is that GCC relies on using increased alignment to producing padding, where Clang's redzoning implementation actually adds real data after the global and doesn't rely on alignment to produce padding. I believe this is the main reason why GCC can't reliably catch globals out-of-bounds in this case. Given this is now a known issue, to avoid failing the whole test suite, skip this test case with GCC. Link: https://lkml.kernel.org/r/20211117130714.135656-1-elver@xxxxxxxxxx Signed-off-by: Marco Elver <elver@xxxxxxxxxx> Reported-by: Kaiwan N Billimoria <kaiwan.billimoria@xxxxxxxxx> Reviewed-by: Andrey Konovalov <andreyknvl@xxxxxxxxx> Cc: Alexander Potapenko <glider@xxxxxxxxxx> Cc: Andrey Ryabinin <ryabinin.a.a@xxxxxxxxx> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx> Cc: Kaiwan N Billimoria <kaiwan.billimoria@xxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- lib/test_kasan.c | 19 +++++++++++++++++-- 1 file changed, 17 insertions(+), 2 deletions(-) --- a/lib/test_kasan.c~kasan-test-add-globals-left-out-of-bounds-test +++ a/lib/test_kasan.c @@ -700,7 +700,7 @@ static void kmem_cache_bulk(struct kunit static char global_array[10]; -static void kasan_global_oob(struct kunit *test) +static void kasan_global_oob_right(struct kunit *test) { /* * Deliberate out-of-bounds access. To prevent CONFIG_UBSAN_LOCAL_BOUNDS @@ -723,6 +723,20 @@ static void kasan_global_oob(struct kuni KUNIT_EXPECT_KASAN_FAIL(test, *(volatile char *)p); } +static void kasan_global_oob_left(struct kunit *test) +{ + char *volatile array = global_array; + char *p = array - 3; + + /* + * GCC is known to fail this test, skip it. + * See https://bugzilla.kernel.org/show_bug.cgi?id=215051. + */ + KASAN_TEST_NEEDS_CONFIG_ON(test, CONFIG_CC_IS_CLANG); + KASAN_TEST_NEEDS_CONFIG_ON(test, CONFIG_KASAN_GENERIC); + KUNIT_EXPECT_KASAN_FAIL(test, *(volatile char *)p); +} + /* Check that ksize() makes the whole object accessible. */ static void ksize_unpoisons_memory(struct kunit *test) { @@ -1162,7 +1176,8 @@ static struct kunit_case kasan_kunit_tes KUNIT_CASE(kmem_cache_oob), KUNIT_CASE(kmem_cache_accounted), KUNIT_CASE(kmem_cache_bulk), - KUNIT_CASE(kasan_global_oob), + KUNIT_CASE(kasan_global_oob_right), + KUNIT_CASE(kasan_global_oob_left), KUNIT_CASE(kasan_stack_oob), KUNIT_CASE(kasan_alloca_oob_left), KUNIT_CASE(kasan_alloca_oob_right), _
