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@google.com
Signed-off-by: Marco Elver <elver@google.com>
Reported-by: Kaiwan N Billimoria <kaiwan.billimoria@gmail.com>
Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Kaiwan N Billimoria <kaiwan.billimoria@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index 0643573f86862b04d5e67bf088aeb17a59da5020..818e763b5b87bc29add3232fa6aab9a3eb09e399 100644 (file)
--- a/lib/test_kasan.c
+++ b/lib/test_kasan.c
@@ -700,7 +700,7 @@ static void kmem_cache_bulk(struct kunit *test)
 
 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 kunit *test)
        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_test_cases[] = {
        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),