kmsan: another take at fixing memcpy tests

commit 5478afc ("kmsan: fix memcpy tests") uses OPTIMIZER_HIDE_VAR()
to hide the uninitialized var from the compiler optimizations.

However OPTIMIZER_HIDE_VAR(uninit) enforces an immediate check of @uninit,
so memcpy tests did not actually check the behavior of memcpy(), because
they always contained a KMSAN report.

Replace OPTIMIZER_HIDE_VAR() with a file-local macro that just clobbers
the memory with a barrier(), and add a test case for memcpy() that does
not expect an error report.

Also reflow kmsan_test.c with clang-format.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Alexander Potapenko <[email protected]>
Reviewed-by: Marco Elver <[email protected]>
Cc: Daniel Vetter <[email protected]>
Cc: Geert Uytterhoeven <[email protected]>
Cc: Helge Deller <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Tetsuo Handa <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

mm/kmsan/kmsan_test.c

@@ -407,6 +407,37 @@ static void test_printk(struct kunit *test)
  KUNIT_EXPECT_TRUE(test, report_matches(&expect));
 }
 
+/*
+ * Prevent the compiler from optimizing @var away. Without this, Clang may
+ * notice that @var is uninitialized and drop memcpy() calls that use it.
+ *
+ * There is OPTIMIZER_HIDE_VAR() in linux/compier.h that we cannot use here,
+ * because it is implemented as inline assembly receiving @var as a parameter
+ * and will enforce a KMSAN check. Same is true for e.g. barrier_data(var).
+ */
+#define DO_NOT_OPTIMIZE(var) barrier()
+
+/*
+ * Test case: ensure that memcpy() correctly copies initialized values.
+ * Also serves as a regression test to ensure DO_NOT_OPTIMIZE() does not cause
+ * extra checks.
+ */
+static void test_init_memcpy(struct kunit *test)
+{
+ EXPECTATION_NO_REPORT(expect);
+ volatile int src;
+ volatile int dst = 0;
+
+ DO_NOT_OPTIMIZE(src);
+ src = 1;
+ kunit_info(
+ test,
+ "memcpy()ing aligned initialized src to aligned dst (no reports)\n");
+ memcpy((void *)&dst, (void *)&src, sizeof(src));
+ kmsan_check_memory((void *)&dst, sizeof(dst));
+ KUNIT_EXPECT_TRUE(test, report_matches(&expect));
+}
+
 /*
  * Test case: ensure that memcpy() correctly copies uninitialized values between
  * aligned `src` and `dst`.
@@ -420,7 +451,7 @@ static void test_memcpy_aligned_to_aligned(struct kunit *test)
  kunit_info(
  test,
  "memcpy()ing aligned uninit src to aligned dst (UMR report)\n");
- OPTIMIZER_HIDE_VAR(uninit_src);
+ DO_NOT_OPTIMIZE(uninit_src);
  memcpy((void *)&dst, (void *)&uninit_src, sizeof(uninit_src));
  kmsan_check_memory((void *)&dst, sizeof(dst));
  KUNIT_EXPECT_TRUE(test, report_matches(&expect));
@@ -443,7 +474,7 @@ static void test_memcpy_aligned_to_unaligned(struct kunit *test)
  kunit_info(
  test,
  "memcpy()ing aligned uninit src to unaligned dst (UMR report)\n");
- OPTIMIZER_HIDE_VAR(uninit_src);
+ DO_NOT_OPTIMIZE(uninit_src);
  memcpy((void *)&dst[1], (void *)&uninit_src, sizeof(uninit_src));
  kmsan_check_memory((void *)dst, 4);
  KUNIT_EXPECT_TRUE(test, report_matches(&expect));
@@ -467,13 +498,14 @@ static void test_memcpy_aligned_to_unaligned2(struct kunit *test)
  kunit_info(
  test,
  "memcpy()ing aligned uninit src to unaligned dst - part 2 (UMR report)\n");
- OPTIMIZER_HIDE_VAR(uninit_src);
+ DO_NOT_OPTIMIZE(uninit_src);
  memcpy((void *)&dst[1], (void *)&uninit_src, sizeof(uninit_src));
  kmsan_check_memory((void *)&dst[4], sizeof(uninit_src));
  KUNIT_EXPECT_TRUE(test, report_matches(&expect));
 }
 
-static noinline void fibonacci(int *array, int size, int start) {
+static noinline void fibonacci(int *array, int size, int start)
+{
  if (start < 2 || (start == size))
  return;
  array[start] = array[start - 1] + array[start - 2];
@@ -482,8 +514,7 @@ static noinline void fibonacci(int *array, int size, int start) {
 
 static void test_long_origin_chain(struct kunit *test)
 {
- EXPECTATION_UNINIT_VALUE_FN(expect,
- "test_long_origin_chain");
+ EXPECTATION_UNINIT_VALUE_FN(expect, "test_long_origin_chain");
  /* (KMSAN_MAX_ORIGIN_DEPTH * 2) recursive calls to fibonacci(). */
  volatile int accum[KMSAN_MAX_ORIGIN_DEPTH * 2 + 2];
  int last = ARRAY_SIZE(accum) - 1;
@@ -515,6 +546,7 @@ static struct kunit_case kmsan_test_cases[] = {
  KUNIT_CASE(test_uaf),
  KUNIT_CASE(test_percpu_propagate),
  KUNIT_CASE(test_printk),
+ KUNIT_CASE(test_init_memcpy),
  KUNIT_CASE(test_memcpy_aligned_to_aligned),
  KUNIT_CASE(test_memcpy_aligned_to_unaligned),
  KUNIT_CASE(test_memcpy_aligned_to_unaligned2),