Re: [PATCH v2] overflow: Allow mixed type arguments

[Andrzej Hajda <andrzej.hajda@intel.com>]

On 29.08.2022 23:45, Kees Cook wrote:
> When the check_[op]_overflow() helpers were introduced, all arguments were
> required to be the same type to make the fallback macros simpler. However,
> once the fallback macros were removed[1], it is fine to allow mixed
> types, which makes using the helpers much more useful, as they can be
> used to test for type-based overflows (e.g. adding two large ints but
> storing into a u8), as would be handy in the drm core[2].
>
> Remove the restriction, and add additional self-tests that exercise some
> of the mixed-type overflow cases.
>
> [1] https://git.kernel.org/linus/4eb6bd55cfb22ffc20652732340c4962f3ac9a91
> [2] https://lore.kernel.org/lkml/20220824084514.2261614-2-gwan-gyeong.mun@intel.com
>
> Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> Cc: Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>
> Cc: Andrzej Hajda <andrzej.hajda@intel.com>
> Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>
> Cc: Nick Desaulniers <ndesaulniers@google.com>
> Cc: linux-hardening@vger.kernel.org
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
> v2: change names to "type1_type2__output-type" for better readability (Rasmus)
> v1: https://lore.kernel.org/lkml/20220829204729.3409270-1-keescook@chromium.org
> ---
>   include/linux/overflow.h |  6 ----
>   lib/overflow_kunit.c     | 77 +++++++++++++++++++++++++++++-----------
>   2 files changed, 57 insertions(+), 26 deletions(-)
>
> diff --git a/include/linux/overflow.h b/include/linux/overflow.h
> index 0eb3b192f07a..ad692fb11bf3 100644
> --- a/include/linux/overflow.h
> +++ b/include/linux/overflow.h
> @@ -63,8 +63,6 @@ static inline bool __must_check __must_check_overflow(bool overflow)
>   	typeof(a) __a = (a);			\
>   	typeof(b) __b = (b);			\
>   	typeof(d) __d = (d);			\
> -	(void) (&__a == &__b);			\
> -	(void) (&__a == __d);			\
>   	__builtin_add_overflow(__a, __b, __d);	\
>   }))

Is there a reason to keep all local vars?
Why not:
#define check_add_overflow(a, b, d) 
__must_check_overflow(__builtin_add_overflow((a), (b), (d)))

Similar for other macros.

Regards
Andrzej

>   
> @@ -72,8 +70,6 @@ static inline bool __must_check __must_check_overflow(bool overflow)
>   	typeof(a) __a = (a);			\
>   	typeof(b) __b = (b);			\
>   	typeof(d) __d = (d);			\
> -	(void) (&__a == &__b);			\
> -	(void) (&__a == __d);			\
>   	__builtin_sub_overflow(__a, __b, __d);	\
>   }))
>   
> @@ -81,8 +77,6 @@ static inline bool __must_check __must_check_overflow(bool overflow)
>   	typeof(a) __a = (a);			\
>   	typeof(b) __b = (b);			\
>   	typeof(d) __d = (d);			\
> -	(void) (&__a == &__b);			\
> -	(void) (&__a == __d);			\
>   	__builtin_mul_overflow(__a, __b, __d);	\
>   }))
>   
> diff --git a/lib/overflow_kunit.c b/lib/overflow_kunit.c
> index 7e3e43679b73..5e1b51d42e93 100644
> --- a/lib/overflow_kunit.c
> +++ b/lib/overflow_kunit.c
> @@ -16,12 +16,15 @@
>   #include <linux/types.h>
>   #include <linux/vmalloc.h>
>   
> -#define DEFINE_TEST_ARRAY(t)			\
> -	static const struct test_ ## t {	\
> -		t a, b;				\
> -		t sum, diff, prod;		\
> -		bool s_of, d_of, p_of;		\
> -	} t ## _tests[]
> +#define DEFINE_TEST_ARRAY_TYPED(t1, t2, t)			\
> +	static const struct test_ ## t1 ## _ ## t2 ## __ ## t {	\
> +		t1 a;						\
> +		t2 b;						\
> +		t sum, diff, prod;				\
> +		bool s_of, d_of, p_of;				\
> +	} t1 ## _ ## t2 ## __ ## t ## _tests[]
> +
> +#define DEFINE_TEST_ARRAY(t)	DEFINE_TEST_ARRAY_TYPED(t, t, t)
>   
>   DEFINE_TEST_ARRAY(u8) = {
>   	{0, 0, 0, 0, 0, false, false, false},
> @@ -235,8 +238,8 @@ DEFINE_TEST_ARRAY(s64) = {
>   		a, b, r, _r, #t);				\
>   } while (0)
>   
> -#define DEFINE_TEST_FUNC(t, fmt)					\
> -static void do_test_ ## t(struct kunit *test, const struct test_ ## t *p) \
> +#define DEFINE_TEST_FUNC_TYPED(n, t, fmt)				\
> +static void do_test_ ## n(struct kunit *test, const struct test_ ## n *p) \
>   {							   		\
>   	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);	\
> @@ -245,15 +248,18 @@ static void do_test_ ## t(struct kunit *test, const struct test_ ## t *p) \
>   	check_one_op(t, fmt, mul, "*", p->b, p->a, p->prod, p->p_of);	\
>   }									\
>   									\
> -static void t ## _overflow_test(struct kunit *test) {			\
> +static void n ## _overflow_test(struct kunit *test) {			\
>   	unsigned i;							\
>   									\
> -	for (i = 0; i < ARRAY_SIZE(t ## _tests); ++i)			\
> -		do_test_ ## t(test, &t ## _tests[i]);			\
> +	for (i = 0; i < ARRAY_SIZE(n ## _tests); ++i)			\
> +		do_test_ ## n(test, &n ## _tests[i]);			\
>   	kunit_info(test, "%zu %s arithmetic tests finished\n",		\
> -		ARRAY_SIZE(t ## _tests), #t);				\
> +		ARRAY_SIZE(n ## _tests), #n);				\
>   }
>   
> +#define DEFINE_TEST_FUNC(t, fmt)					\
> +	DEFINE_TEST_FUNC_TYPED(t ## _ ## t ## __ ## t, t, fmt)
> +
>   DEFINE_TEST_FUNC(u8, "%d");
>   DEFINE_TEST_FUNC(s8, "%d");
>   DEFINE_TEST_FUNC(u16, "%d");
> @@ -265,6 +271,33 @@ DEFINE_TEST_FUNC(u64, "%llu");
>   DEFINE_TEST_FUNC(s64, "%lld");
>   #endif
>   
> +DEFINE_TEST_ARRAY_TYPED(u32, u32, u8) = {
> +	{0, 0, 0, 0, 0, false, false, false},
> +	{U8_MAX, 2, 1, U8_MAX - 2, U8_MAX - 1, true, false, true},
> +	{U8_MAX + 1, 0, 0, 0, 0, true, true, false},
> +};
> +DEFINE_TEST_FUNC_TYPED(u32_u32__u8, u8, "%d");
> +
> +DEFINE_TEST_ARRAY_TYPED(u32, u32, int) = {
> +	{0, 0, 0, 0, 0, false, false, false},
> +	{U32_MAX, 0, -1, -1, 0, true, true, false},
> +};
> +DEFINE_TEST_FUNC_TYPED(u32_u32__int, int, "%d");
> +
> +DEFINE_TEST_ARRAY_TYPED(u8, u8, int) = {
> +	{0, 0, 0, 0, 0, false, false, false},
> +	{U8_MAX, U8_MAX, 2 * U8_MAX, 0, U8_MAX * U8_MAX, false, false, false},
> +	{1, 2, 3, -1, 2, false, false, false},
> +};
> +DEFINE_TEST_FUNC_TYPED(u8_u8__int, int, "%d");
> +
> +DEFINE_TEST_ARRAY_TYPED(int, int, u8) = {
> +	{0, 0, 0, 0, 0, false, false, false},
> +	{1, 2, 3, U8_MAX, 2, false, true, false},
> +	{-1, 0, U8_MAX, U8_MAX, 0, true, true, false},
> +};
> +DEFINE_TEST_FUNC_TYPED(int_int__u8, u8, "%d");
> +
>   static void overflow_shift_test(struct kunit *test)
>   {
>   	int count = 0;
> @@ -649,17 +682,21 @@ static void overflow_size_helpers_test(struct kunit *test)
>   }
>   
>   static struct kunit_case overflow_test_cases[] = {
> -	KUNIT_CASE(u8_overflow_test),
> -	KUNIT_CASE(s8_overflow_test),
> -	KUNIT_CASE(u16_overflow_test),
> -	KUNIT_CASE(s16_overflow_test),
> -	KUNIT_CASE(u32_overflow_test),
> -	KUNIT_CASE(s32_overflow_test),
> +	KUNIT_CASE(u8_u8__u8_overflow_test),
> +	KUNIT_CASE(s8_s8__s8_overflow_test),
> +	KUNIT_CASE(u16_u16__u16_overflow_test),
> +	KUNIT_CASE(s16_s16__s16_overflow_test),
> +	KUNIT_CASE(u32_u32__u32_overflow_test),
> +	KUNIT_CASE(s32_s32__s32_overflow_test),
>   /* Clang 13 and earlier generate unwanted libcalls on 32-bit. */
>   #if BITS_PER_LONG == 64
> -	KUNIT_CASE(u64_overflow_test),
> -	KUNIT_CASE(s64_overflow_test),
> +	KUNIT_CASE(u64_u64__u64_overflow_test),
> +	KUNIT_CASE(s64_s64__s64_overflow_test),
>   #endif
> +	KUNIT_CASE(u32_u32__u8_overflow_test),
> +	KUNIT_CASE(u32_u32__int_overflow_test),
> +	KUNIT_CASE(u8_u8__int_overflow_test),
> +	KUNIT_CASE(int_int__u8_overflow_test),
>   	KUNIT_CASE(overflow_shift_test),
>   	KUNIT_CASE(overflow_allocation_test),
>   	KUNIT_CASE(overflow_size_helpers_test),