kasan, arm64: allow using KUnit tests with HW_TAGS mode

On a high level, this patch allows running KUnit KASAN tests with the
hardware tag-based KASAN mode.

Internally, this change reenables tag checking at the end of each KASAN
test that triggers a tag fault and leads to tag checking being disabled.

Also simplify is_write calculation in report_tag_fault.

With this patch KASAN tests are still failing for the hardware tag-based
mode; fixes come in the next few patches.

[andreyknvl@google.com: export HW_TAGS symbols for KUnit tests]
  Link: https://lkml.kernel.org/r/e7eeb252da408b08f0c81b950a55fb852f92000b.1613155970.git.andreyknvl@google.com

Link: https://linux-review.googlesource.com/id/Id94dc9eccd33b23cda4950be408c27f879e474c8
Link: https://lkml.kernel.org/r/51b23112cf3fd62b8f8e9df81026fa2b15870501.1610733117.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Branislav Rankov <Branislav.Rankov@arm.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Kevin Brodsky <kevin.brodsky@arm.com>
Cc: Marco Elver <elver@google.com>
Cc: Peter Collingbourne <pcc@google.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>

2 files changed, 31 insertions, 15 deletions

diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
index f5fa4ba126bf..3091432acb0a 100644
--- a/lib/Kconfig.kasan
+++ b/lib/Kconfig.kasan
@@ -190,11 +190,11 @@ config KASAN_KUNIT_TEST
 	  kernel debugging features like KASAN.
 
 	  For more information on KUnit and unit tests in general, please refer
-	  to the KUnit documentation in Documentation/dev-tools/kunit
+	  to the KUnit documentation in Documentation/dev-tools/kunit.
 
 config TEST_KASAN_MODULE
 	tristate "KUnit-incompatible tests of KASAN bug detection capabilities"
-	depends on m && KASAN
+	depends on m && KASAN && !KASAN_HW_TAGS
 	help
 	  This is a part of the KASAN test suite that is incompatible with
 	  KUnit. Currently includes tests that do bad copy_from/to_user
diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index c344fe506ffc..502709db41c0 100644
--- a/lib/test_kasan.c
+++ b/lib/test_kasan.c
@@ -41,16 +41,20 @@ static bool multishot;
 
 /*
  * Temporarily enable multi-shot mode. Otherwise, KASAN would only report the
- * first detected bug and panic the kernel if panic_on_warn is enabled.
+ * first detected bug and panic the kernel if panic_on_warn is enabled. For
+ * hardware tag-based KASAN also allow tag checking to be reenabled for each
+ * test, see the comment for KUNIT_EXPECT_KASAN_FAIL().
  */
 static int kasan_test_init(struct kunit *test)
 {
 	multishot = kasan_save_enable_multi_shot();
+	kasan_set_tagging_report_once(false);
 	return 0;
 }
 
 static void kasan_test_exit(struct kunit *test)
 {
+	kasan_set_tagging_report_once(true);
 	kasan_restore_multi_shot(multishot);
 }
 
@@ -59,19 +63,31 @@ static void kasan_test_exit(struct kunit *test)
  * KASAN report; causes a test failure otherwise. This relies on a KUnit
  * resource named "kasan_data". Do not use this name for KUnit resources
  * outside of KASAN tests.
+ *
+ * For hardware tag-based KASAN, when a tag fault happens, tag checking is
+ * normally auto-disabled. When this happens, this test handler reenables
+ * tag checking. As tag checking can be only disabled or enabled per CPU, this
+ * handler disables migration (preemption).
  */
-#define KUNIT_EXPECT_KASAN_FAIL(test, expression) do { \
-	fail_data.report_expected = true; \
-	fail_data.report_found = false; \
-	kunit_add_named_resource(test, \
-				NULL, \
-				NULL, \
-				&resource, \
-				"kasan_data", &fail_data); \
-	expression; \
-	KUNIT_EXPECT_EQ(test, \
-			fail_data.report_expected, \
-			fail_data.report_found); \
+#define KUNIT_EXPECT_KASAN_FAIL(test, expression) do {		\
+	if (IS_ENABLED(CONFIG_KASAN_HW_TAGS))			\
+		migrate_disable();				\
+	fail_data.report_expected = true;			\
+	fail_data.report_found = false;				\
+	kunit_add_named_resource(test,				\
+				NULL,				\
+				NULL,				\
+				&resource,			\
+				"kasan_data", &fail_data);	\
+	expression;						\
+	KUNIT_EXPECT_EQ(test,					\
+			fail_data.report_expected,		\
+			fail_data.report_found);		\
+	if (IS_ENABLED(CONFIG_KASAN_HW_TAGS)) {			\
+		if (fail_data.report_found)			\
+			kasan_enable_tagging();			\
+		migrate_enable();				\
+	}							\
 } while (0)
 
 #define KASAN_TEST_NEEDS_CONFIG_ON(test, config) do {			\