From 7095a8f0fb4f45709394254f598b77b6500b38ff Mon Sep 17 00:00:00 2001
From: Andrey Konovalov <andreyknvl@google.com>
Date: Wed, 3 Feb 2021 15:35:03 +1100
Subject: [PATCH] FROMGIT: kasan: add compiler barriers to
 KUNIT_EXPECT_KASAN_FAIL

It might not be obvious to the compiler that the expression must be
executed between writing and reading to fail_data. In this case, the
compiler might reorder or optimize away some of the accesses, and
the tests will fail.

Add compiler barriers around the expression in KUNIT_EXPECT_KASAN_FAIL
and use READ/WRITE_ONCE() for accessing fail_data fields.

Link: https://linux-review.googlesource.com/id/I046079f48641a1d36fe627fc8827a9249102fd50
Link: https://lkml.kernel.org/r/6f11596f367d8ae8f71d800351e9a5d91eda19f6.1610733117.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: Stephen Rothwell <sfr@canb.auug.org.au>
(cherry picked from commit 5d475f65379312f435e323c64e76563963e360d5
 https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git akpm)
Bug: 172318110
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Change-Id: I2c062c0e63edbc928804b0c70ea4e370673b1d92
---
 lib/test_kasan.c  | 17 ++++++++++++-----
 mm/kasan/report.c |  2 +-
 2 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index ef663bcf83e5..2419e36e117b 100644
--- a/lib/test_kasan.c
+++ b/lib/test_kasan.c
@@ -68,23 +68,30 @@ static void kasan_test_exit(struct kunit *test)
  * 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).
+ *
+ * Since the compiler doesn't see that the expression can change the fail_data
+ * fields, it can reorder or optimize away the accesses to those fields.
+ * Use READ/WRITE_ONCE() for the accesses and compiler barriers around the
+ * expression to prevent that.
  */
 #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;				\
+	WRITE_ONCE(fail_data.report_expected, true);		\
+	WRITE_ONCE(fail_data.report_found, false);		\
 	kunit_add_named_resource(test,				\
 				NULL,				\
 				NULL,				\
 				&resource,			\
 				"kasan_data", &fail_data);	\
+	barrier();						\
 	expression;						\
+	barrier();						\
 	KUNIT_EXPECT_EQ(test,					\
-			fail_data.report_expected,		\
-			fail_data.report_found);		\
+			READ_ONCE(fail_data.report_expected),	\
+			READ_ONCE(fail_data.report_found));	\
 	if (IS_ENABLED(CONFIG_KASAN_HW_TAGS)) {			\
-		if (fail_data.report_found)			\
+		if (READ_ONCE(fail_data.report_found))		\
 			hw_enable_tagging();			\
 		migrate_enable();				\
 	}							\
diff --git a/mm/kasan/report.c b/mm/kasan/report.c
index 53b4ceded1be..87b271206163 100644
--- a/mm/kasan/report.c
+++ b/mm/kasan/report.c
@@ -333,7 +333,7 @@ static void kasan_update_kunit_status(struct kunit *cur_test)
 	}
 
 	kasan_data = (struct kunit_kasan_expectation *)resource->data;
-	kasan_data->report_found = true;
+	WRITE_ONCE(kasan_data->report_found, true);
 	kunit_put_resource(resource);
 }
 #endif /* IS_ENABLED(CONFIG_KUNIT) */