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Message-ID: <0272e34e-1660-1c55-29c5-4234e8d7d0fc@intel.com>
Date:   Tue, 30 Aug 2022 21:34:06 +0200
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Subject: Re: [PATCH v3] overflow: Allow mixed type arguments
Content-Language: en-US
To:     Kees Cook <keescook@chromium.org>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc:     Gwan-gyeong Mun <gwan-gyeong.mun@intel.com>,
        "Gustavo A. R. Silva" <gustavoars@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        linux-hardening@vger.kernel.org,
        Daniel Latypov <dlatypov@google.com>,
        Vitor Massaru Iha <vitor@massaru.org>,
        linux-kernel@vger.kernel.org
References: <20220830192147.47069-1-keescook@chromium.org>
From:   Andrzej Hajda <andrzej.hajda@intel.com>
Organization: Intel Technology Poland sp. z o.o. - ul. Slowackiego 173, 80-298
 Gdansk - KRS 101882 - NIP 957-07-52-316
In-Reply-To: <20220830192147.47069-1-keescook@chromium.org>
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On 30.08.2022 21:21, 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,
> now that the fallback macros have been 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, and double-check for accidental macro
> side-effects.
>
> [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>

Reviewed-by: Andrzej Hajda <andrzej.hajda@intel.com>

Regards
Andrzej


> ---
> v3: drop needless local variables (Andrzej)
> v2: https://lore.kernel.org/lkml/20220829214550.3443472-1-keescook@chromium.org
> v1: https://lore.kernel.org/lkml/20220829204729.3409270-1-keescook@chromium.org
> ---
>   include/linux/overflow.h |  72 ++++++++++++++++------------
>   lib/overflow_kunit.c     | 101 ++++++++++++++++++++++++++++-----------
>   2 files changed, 113 insertions(+), 60 deletions(-)
>
> diff --git a/include/linux/overflow.h b/include/linux/overflow.h
> index 0eb3b192f07a..19dfdd74835e 100644
> --- a/include/linux/overflow.h
> +++ b/include/linux/overflow.h
> @@ -51,40 +51,50 @@ static inline bool __must_check __must_check_overflow(bool overflow)
>   	return unlikely(overflow);
>   }
>   
> -/*
> - * For simplicity and code hygiene, the fallback code below insists on
> - * a, b and *d having the same type (similar to the min() and max()
> - * macros), whereas gcc's type-generic overflow checkers accept
> - * different types. Hence we don't just make check_add_overflow an
> - * alias for __builtin_add_overflow, but add type checks similar to
> - * below.
> +/** check_add_overflow() - Calculate addition with overflow checking
> + *
> + * @a: first addend
> + * @b: second addend
> + * @d: pointer to store sum
> + *
> + * Returns 0 on success.
> + *
> + * *@d holds the results of the attempted addition, but is not considered
> + * "safe for use" on a non-zero return value, which indicates that the
> + * sum has overflowed or been truncated.
>    */
> -#define check_add_overflow(a, b, d) __must_check_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);	\
> -}))
> +#define check_add_overflow(a, b, d)	\
> +	__must_check_overflow(__builtin_add_overflow(a, b, d))
>   
> -#define check_sub_overflow(a, b, d) __must_check_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);	\
> -}))
> +/** check_sub_overflow() - Calculate subtraction with overflow checking
> + *
> + * @a: minuend; value to subtract from
> + * @b: subtrahend; value to subtract from @a
> + * @d: pointer to store difference
> + *
> + * Returns 0 on success.
> + *
> + * *@d holds the results of the attempted subtraction, but is not considered
> + * "safe for use" on a non-zero return value, which indicates that the
> + * difference has underflowed or been truncated.
> + */
> +#define check_sub_overflow(a, b, d)	\
> +	__must_check_overflow(__builtin_sub_overflow(a, b, d))
>   
> -#define check_mul_overflow(a, b, d) __must_check_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);	\
> -}))
> +/** check_mul_overflow() - Calculate multiplication with overflow checking
> + *
> + * @a: first factor
> + * @b: second factor
> + * @d: pointer to store product
> + *
> + * Returns 0 on success.
> + *
> + * *@d holds the results of the attempted multiplication, but is not
> + * considered "safe for use" on a non-zero return value, which indicates
> + * that the product has overflowed or been truncated.
> + */
> +#define check_mul_overflow(a, b, d)	\
> +	__must_check_overflow(__builtin_mul_overflow(a, b, d))
>   
>   /** check_shl_overflow() - Calculate a left-shifted value and check overflow
>    *
> diff --git a/lib/overflow_kunit.c b/lib/overflow_kunit.c
> index 7e3e43679b73..0d98c9bc75da 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},
> @@ -222,21 +225,27 @@ DEFINE_TEST_ARRAY(s64) = {
>   };
>   #endif
>   
> -#define check_one_op(t, fmt, op, sym, a, b, r, of) do {		\
> -	t _r;							\
> -	bool _of;						\
> -								\
> -	_of = check_ ## op ## _overflow(a, b, &_r);		\
> -	KUNIT_EXPECT_EQ_MSG(test, _of, of,			\
> +#define check_one_op(t, fmt, op, sym, a, b, r, of) do {			\
> +	int _a_orig = a, _a_bump = a + 1;				\
> +	int _b_orig = b, _b_bump = b + 1;				\
> +	bool _of;							\
> +	t _r;								\
> +									\
> +	_of = check_ ## op ## _overflow(a, b, &_r);			\
> +	KUNIT_EXPECT_EQ_MSG(test, _of, of,				\
>   		"expected "fmt" "sym" "fmt" to%s overflow (type %s)\n",	\
> -		a, b, of ? "" : " not", #t);			\
> -	KUNIT_EXPECT_EQ_MSG(test, _r, r,			\
> +		a, b, of ? "" : " not", #t);				\
> +	KUNIT_EXPECT_EQ_MSG(test, _r, r,				\
>   		"expected "fmt" "sym" "fmt" == "fmt", got "fmt" (type %s)\n", \
> -		a, b, r, _r, #t);				\
> +		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"); \
>   } 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 +254,18 @@ 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 +277,33 @@ 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 +688,21 @@ 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),