kasan: don't run tests when KASAN is not enabled

Don't run KASAN tests when it's disabled with kasan.mode=off to avoid
corrupting kernel memory.

Link: https://linux-review.googlesource.com/id/I6447af436a69a94bfc35477f6bf4e2122948355e
Link: https://lkml.kernel.org/r/25bd4fb5cae7b421d806a1f33fb633edd313f0c7.1610733117.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Marco Elver <elver@google.com>
Reviewed-by: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Branislav Rankov <Branislav.Rankov@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Kevin Brodsky <kevin.brodsky@arm.com>
Cc: Peter Collingbourne <pcc@google.com>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/test_kasan.c

@@ -47,6 +47,11 @@ static bool multishot;
  */
 static int kasan_test_init(struct kunit *test)
 {
+	if (!kasan_enabled()) {
+		kunit_err(test, "can't run KASAN tests with KASAN disabled");
+		return -1;
+	}
+
 	multishot = kasan_save_enable_multi_shot();
 	kasan_set_tagging_report_once(false);
 	return 0;