[PATCH] kasan: fix unit tests with CONFIG_UBSAN_LOCAL_BOUNDS enabled

[Peter Collingbourne <pcc@google.com>]

These tests deliberately access these arrays out of bounds,
which will cause the dynamic local bounds checks inserted by
CONFIG_UBSAN_LOCAL_BOUNDS to fail and panic the kernel. To avoid this
problem, access the arrays via volatile pointers, which will prevent
the compiler from being able to determine the array bounds.

Signed-off-by: Peter Collingbourne <pcc@google.com>
Cc: stable@vger.kernel.org
Link: https://linux-review.googlesource.com/id/I90b1713fbfa1bf68ff895aef099ea77b98a7c3b9
---
 lib/test_kasan.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index dc05cfc2d12f..2a078e8e7b8e 100644
--- a/lib/test_kasan.c
+++ b/lib/test_kasan.c
@@ -654,8 +654,8 @@ static char global_array[10];
 
 static void kasan_global_oob(struct kunit *test)
 {
-	volatile int i = 3;
-	char *p = &global_array[ARRAY_SIZE(global_array) + i];
+	char *volatile array = global_array;
+	char *p = &array[ARRAY_SIZE(global_array) + 3];
 
 	/* Only generic mode instruments globals. */
 	KASAN_TEST_NEEDS_CONFIG_ON(test, CONFIG_KASAN_GENERIC);
@@ -703,8 +703,8 @@ static void ksize_uaf(struct kunit *test)
 static void kasan_stack_oob(struct kunit *test)
 {
 	char stack_array[10];
-	volatile int i = OOB_TAG_OFF;
-	char *p = &stack_array[ARRAY_SIZE(stack_array) + i];
+	char *volatile array = stack_array;
+	char *p = &array[ARRAY_SIZE(stack_array) + OOB_TAG_OFF];
 
 	KASAN_TEST_NEEDS_CONFIG_ON(test, CONFIG_KASAN_STACK);
 
@@ -715,7 +715,8 @@ static void kasan_alloca_oob_left(struct kunit *test)
 {
 	volatile int i = 10;
 	char alloca_array[i];
-	char *p = alloca_array - 1;
+	char *volatile array = alloca_array;
+	char *p = array - 1;
 
 	/* Only generic mode instruments dynamic allocas. */
 	KASAN_TEST_NEEDS_CONFIG_ON(test, CONFIG_KASAN_GENERIC);
@@ -728,7 +729,8 @@ static void kasan_alloca_oob_right(struct kunit *test)
 {
 	volatile int i = 10;
 	char alloca_array[i];
-	char *p = alloca_array + i;
+	char *volatile array = alloca_array;
+	char *p = array + i;
 
 	/* Only generic mode instruments dynamic allocas. */
 	KASAN_TEST_NEEDS_CONFIG_ON(test, CONFIG_KASAN_GENERIC);
-- 
2.31.1.607.g51e8a6a459-goog