This allows replacements of the idioms "var += offset" and "var -= offset" with the inc_wrap() and dec_wrap() helpers respectively. They will avoid wrap-around sanitizer instrumentation.
Add to the selftests to validate behavior and lack of side-effects. Cc: Rasmus Villemoes <[email protected]> Cc: Mark Rutland <[email protected]> Cc: "Gustavo A. R. Silva" <[email protected]> Cc: Justin Stitt <[email protected]> Cc: [email protected] Signed-off-by: Kees Cook <[email protected]> --- include/linux/overflow.h | 28 +++++++++++++++++++++ lib/overflow_kunit.c | 54 ++++++++++++++++++++++++++++++++++------ 2 files changed, 75 insertions(+), 7 deletions(-) diff --git a/include/linux/overflow.h b/include/linux/overflow.h index c9139f88578b..075c30218145 100644 --- a/include/linux/overflow.h +++ b/include/linux/overflow.h @@ -138,6 +138,20 @@ static inline bool __must_check __must_check_overflow(bool overflow) __val; \ }) +/** + * inc_wrap() - Intentionally perform a wrapping increment + * @a: variable to be incremented + * @b: amount to add + * + * Increments @a by @b with wrap-around. Returns the resulting + * value of @a. Will not trip any wrap-around sanitizers. + */ +#define inc_wrap(var, offset) \ + ({ \ + typeof(var) *__ptr = &(var); \ + *__ptr = add_wrap(typeof(var), *__ptr, offset); \ + }) + /** * check_sub_overflow() - Calculate subtraction with overflow checking * @a: minuend; value to subtract from @@ -169,6 +183,20 @@ static inline bool __must_check __must_check_overflow(bool overflow) __val; \ }) +/** + * dec_wrap() - Intentionally perform a wrapping decrement + * @a: variable to be decremented + * @b: amount to subtract + * + * Decrements @a by @b with wrap-around. Returns the resulting + * value of @a. Will not trip any wrap-around sanitizers. + */ +#define dec_wrap(var, offset) \ + ({ \ + typeof(var) *__ptr = &(var); \ + *__ptr = sub_wrap(typeof(var), *__ptr, offset); \ + }) + /** * check_mul_overflow() - Calculate multiplication with overflow checking * @a: first factor diff --git a/lib/overflow_kunit.c b/lib/overflow_kunit.c index 319f950872bd..46af7ccde0c6 100644 --- a/lib/overflow_kunit.c +++ b/lib/overflow_kunit.c @@ -265,36 +265,76 @@ DEFINE_TEST_ARRAY(s64) = { \ _of = check_ ## op ## _overflow(a, b, &_r); \ KUNIT_EXPECT_EQ_MSG(test, _of, of, \ - "expected "fmt" "sym" "fmt" to%s overflow (type %s)\n", \ + "expected check "fmt" "sym" "fmt" to%s overflow (type %s)\n", \ a, b, of ? "" : " not", #t); \ KUNIT_EXPECT_TRUE_MSG(test, _r == r, \ - "expected "fmt" "sym" "fmt" == "fmt", got "fmt" (type %s)\n", \ + "expected check "fmt" "sym" "fmt" == "fmt", got "fmt" (type %s)\n", \ a, b, r, _r, #t); \ /* Check for internal macro side-effects. */ \ _of = check_ ## op ## _overflow(_a_orig++, _b_orig++, &_r); \ - KUNIT_EXPECT_TRUE_MSG(test, _a_orig == _a_bump, "Unexpected " #op " macro side-effect!\n"); \ - KUNIT_EXPECT_TRUE_MSG(test, _b_orig == _b_bump, "Unexpected " #op " macro side-effect!\n"); \ + KUNIT_EXPECT_TRUE_MSG(test, _a_orig == _a_bump, "Unexpected check " #op " macro side-effect!\n"); \ + KUNIT_EXPECT_TRUE_MSG(test, _b_orig == _b_bump, "Unexpected check " #op " macro side-effect!\n"); \ \ _r = op ## _wrap(t, a, b); \ KUNIT_EXPECT_TRUE_MSG(test, _r == r, \ - "expected "fmt" "sym" "fmt" == "fmt", got "fmt" (type %s)\n", \ + "expected wrap "fmt" "sym" "fmt" == "fmt", got "fmt" (type %s)\n", \ a, b, r, _r, #t); \ /* Check for internal macro side-effects. */ \ _a_orig = a; \ _b_orig = b; \ _r = op ## _wrap(t, _a_orig++, _b_orig++); \ - KUNIT_EXPECT_TRUE_MSG(test, _a_orig == _a_bump, "Unexpected " #op " macro side-effect!\n"); \ - KUNIT_EXPECT_TRUE_MSG(test, _b_orig == _b_bump, "Unexpected " #op " macro side-effect!\n"); \ + KUNIT_EXPECT_TRUE_MSG(test, _a_orig == _a_bump, "Unexpected wrap " #op " macro side-effect!\n"); \ + KUNIT_EXPECT_TRUE_MSG(test, _b_orig == _b_bump, "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 = op ## _wrap(_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; \ + op ## _wrap(_a_orig[get_index()], _b_orig++); \ + KUNIT_EXPECT_EQ_MSG(test, global_counter, 1, "Unexpected " #op "_wrap() macro side-effect on arg1!\n"); \ + KUNIT_EXPECT_TRUE_MSG(test, _b_orig == _b_bump, "Unexpected " #op "_wrap() 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) \ { \ + /* check_{add,sub,mul}_overflow() and {add,sub,mul}_wrap() */ \ check_one_op(t, fmt, add, "+", p->a, p->b, p->sum, p->s_of); \ check_one_op(t, fmt, add, "+", p->b, p->a, p->sum, p->s_of); \ 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); \ + /* {inc,dec}_wrap() */ \ + check_self_op(fmt, inc, +=, p->a, p->b); \ + check_self_op(fmt, inc, +=, p->b, p->a); \ + check_self_op(fmt, dec, -=, p->a, p->b); \ } \ \ static void n ## _overflow_test(struct kunit *test) { \ -- 2.34.1
