On Tue, Feb 13, 2024 at 02:10:58PM -0800, Kees Cook wrote: > Provide helpers that will perform wrapping addition, subtraction, or > multiplication without tripping the arithmetic wrap-around sanitizers. The > first argument is the type under which the wrap-around should happen > with. In other words, these two calls will get very different results: > > wrapping_mul(int, 50, 50) == 2500 > wrapping_mul(u8, 50, 50) == 196 > > Add to the selftests to validate behavior and lack of side-effects. > > Cc: Rasmus Villemoes <[email protected]> > Cc: Marco Elver <[email protected]> > Cc: Eric Biggers <[email protected]> > Cc: Mark Rutland <[email protected]> > Cc: [email protected] > Reviewed-by: Gustavo A. R. Silva <[email protected]> > Reviewed-by: Marco Elver <[email protected]> > Signed-off-by: Kees Cook <[email protected]>
Acked-by: Mark Rutland <[email protected]> Mark. > --- > include/linux/overflow.h | 48 ++++++++++++++++++++++++++++++++++++++++ > lib/overflow_kunit.c | 24 ++++++++++++++++---- > 2 files changed, 68 insertions(+), 4 deletions(-) > > diff --git a/include/linux/overflow.h b/include/linux/overflow.h > index 4e741ebb8005..849a49fb496e 100644 > --- a/include/linux/overflow.h > +++ b/include/linux/overflow.h > @@ -64,6 +64,22 @@ static inline bool __must_check __must_check_overflow(bool > overflow) > #define check_add_overflow(a, b, d) \ > __must_check_overflow(__builtin_add_overflow(a, b, d)) > > +/** > + * wrapping_add() - Intentionally perform a wrapping addition > + * @type: type for result of calculation > + * @a: first addend > + * @b: second addend > + * > + * Return the potentially wrapped-around addition without > + * tripping any wrap-around sanitizers that may be enabled. > + */ > +#define wrapping_add(type, a, b) \ > + ({ \ > + type __val; \ > + __builtin_add_overflow(a, b, &__val); \ > + __val; \ > + }) > + > /** > * check_sub_overflow() - Calculate subtraction with overflow checking > * @a: minuend; value to subtract from > @@ -77,6 +93,22 @@ static inline bool __must_check __must_check_overflow(bool > overflow) > #define check_sub_overflow(a, b, d) \ > __must_check_overflow(__builtin_sub_overflow(a, b, d)) > > +/** > + * wrapping_sub() - Intentionally perform a wrapping subtraction > + * @type: type for result of calculation > + * @a: minuend; value to subtract from > + * @b: subtrahend; value to subtract from @a > + * > + * Return the potentially wrapped-around subtraction without > + * tripping any wrap-around sanitizers that may be enabled. > + */ > +#define wrapping_sub(type, a, b) \ > + ({ \ > + type __val; \ > + __builtin_sub_overflow(a, b, &__val); \ > + __val; \ > + }) > + > /** > * check_mul_overflow() - Calculate multiplication with overflow checking > * @a: first factor > @@ -90,6 +122,22 @@ static inline bool __must_check > __must_check_overflow(bool overflow) > #define check_mul_overflow(a, b, d) \ > __must_check_overflow(__builtin_mul_overflow(a, b, d)) > > +/** > + * wrapping_mul() - Intentionally perform a wrapping multiplication > + * @type: type for result of calculation > + * @a: first factor > + * @b: second factor > + * > + * Return the potentially wrapped-around multiplication without > + * tripping any wrap-around sanitizers that may be enabled. > + */ > +#define wrapping_mul(type, a, b) \ > + ({ \ > + type __val; \ > + __builtin_mul_overflow(a, b, &__val); \ > + __val; \ > + }) > + > /** > * check_shl_overflow() - Calculate a left-shifted value and check overflow > * @a: Value to be shifted > diff --git a/lib/overflow_kunit.c b/lib/overflow_kunit.c > index c527f6b75789..d3fdb906d3fe 100644 > --- a/lib/overflow_kunit.c > +++ b/lib/overflow_kunit.c > @@ -258,20 +258,36 @@ 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_EQ_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_EQ_MSG(test, _a_orig, _a_bump, "Unexpected " #op " macro > side-effect!\n"); \ > - KUNIT_EXPECT_EQ_MSG(test, _b_orig, _b_bump, "Unexpected " #op " macro > side-effect!\n"); \ > + KUNIT_EXPECT_EQ_MSG(test, _a_orig, _a_bump, \ > + "Unexpected check " #op " macro side-effect!\n"); \ > + KUNIT_EXPECT_EQ_MSG(test, _b_orig, _b_bump, \ > + "Unexpected check " #op " macro side-effect!\n"); \ > + \ > + _r = wrapping_ ## op(t, a, b); \ > + KUNIT_EXPECT_TRUE_MSG(test, _r == r, \ > + "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 = wrapping_ ## op(t, _a_orig++, _b_orig++); \ > + KUNIT_EXPECT_EQ_MSG(test, _a_orig, _a_bump, \ > + "Unexpected wrap " #op " macro side-effect!\n"); \ > + KUNIT_EXPECT_EQ_MSG(test, _b_orig, _b_bump, \ > + "Unexpected wrap " #op " macro side-effect!\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 wrapping_{add,sub,mul} */ \ > 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); \ > -- > 2.34.1 >
