overflow: Introduce wrapping_assign_add() and wrapping_assign_sub()
This allows replacements of the idioms "var += offset" and "var -=
offset" with the wrapping_assign_add() and wrapping_assign_sub() helpers
respectively. They will avoid wrap-around sanitizer instrumentation.
Add to the selftests to validate behavior and lack of side-effects.
Reviewed-by: Marco Elver <elver@google.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
diff --git a/lib/overflow_kunit.c b/lib/overflow_kunit.c
index d3fdb90..65e8a72 100644
--- a/lib/overflow_kunit.c
+++ b/lib/overflow_kunit.c
@@ -284,6 +284,45 @@ DEFINE_TEST_ARRAY(s64) = {
"Unexpected wrap " #op " macro side-effect!\n"); \
} while (0)
+static int global_counter;
+static void bump_counter(void)
+{
+ global_counter++;
+}
+
+static int get_index(void)
+{
+ volatile int index = 0;
+ bump_counter();
+ return index;
+}
+
+#define check_self_op(fmt, op, sym, a, b) do { \
+ typeof(a + 0) _a = a; \
+ typeof(b + 0) _b = b; \
+ typeof(a + 0) _a_sym = a; \
+ typeof(a + 0) _a_orig[1] = { a }; \
+ typeof(b + 0) _b_orig = b; \
+ typeof(b + 0) _b_bump = b + 1; \
+ typeof(a + 0) _r; \
+ \
+ _a_sym sym _b; \
+ _r = wrapping_ ## op(_a, _b); \
+ KUNIT_EXPECT_TRUE_MSG(test, _r == _a_sym, \
+ "expected "fmt" "#op" "fmt" == "fmt", got "fmt"\n", \
+ a, b, _a_sym, _r); \
+ KUNIT_EXPECT_TRUE_MSG(test, _a == _a_sym, \
+ "expected "fmt" "#op" "fmt" == "fmt", got "fmt"\n", \
+ a, b, _a_sym, _a); \
+ /* Check for internal macro side-effects. */ \
+ global_counter = 0; \
+ wrapping_ ## op(_a_orig[get_index()], _b_orig++); \
+ KUNIT_EXPECT_EQ_MSG(test, global_counter, 1, \
+ "Unexpected wrapping_" #op " macro side-effect on arg1!\n"); \
+ KUNIT_EXPECT_EQ_MSG(test, _b_orig, _b_bump, \
+ "Unexpected wrapping_" #op " macro side-effect on arg2!\n"); \
+} while (0)
+
#define DEFINE_TEST_FUNC_TYPED(n, t, fmt) \
static void do_test_ ## n(struct kunit *test, const struct test_ ## n *p) \
{ \
@@ -293,6 +332,10 @@ static void do_test_ ## n(struct kunit *test, const struct test_ ## n *p) \
check_one_op(t, fmt, sub, "-", p->a, p->b, p->diff, p->d_of); \
check_one_op(t, fmt, mul, "*", p->a, p->b, p->prod, p->p_of); \
check_one_op(t, fmt, mul, "*", p->b, p->a, p->prod, p->p_of); \
+ /* wrapping_assign_{add,sub}() */ \
+ check_self_op(fmt, assign_add, +=, p->a, p->b); \
+ check_self_op(fmt, assign_add, +=, p->b, p->a); \
+ check_self_op(fmt, assign_sub, -=, p->a, p->b); \
} \
\
static void n ## _overflow_test(struct kunit *test) { \
