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Message-ID: <8d880425-72f5-6ba6-933f-b8b016da88cd@intel.com>
Date: Tue, 30 Aug 2022 08:40:25 +0200
From: Andrzej Hajda <andrzej.hajda@...el.com>
To: Kees Cook <keescook@...omium.org>,
Rasmus Villemoes <linux@...musvillemoes.dk>
Cc: Gwan-gyeong Mun <gwan-gyeong.mun@...el.com>,
"Gustavo A. R. Silva" <gustavoars@...nel.org>,
Nick Desaulniers <ndesaulniers@...gle.com>,
linux-hardening@...r.kernel.org,
Daniel Latypov <dlatypov@...gle.com>,
Vitor Massaru Iha <vitor@...saru.org>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] overflow: Allow mixed type arguments
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@...musvillemoes.dk>
> Cc: Gwan-gyeong Mun <gwan-gyeong.mun@...el.com>
> Cc: Andrzej Hajda <andrzej.hajda@...el.com>
> Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>
> Cc: Nick Desaulniers <ndesaulniers@...gle.com>
> Cc: linux-hardening@...r.kernel.org
> Signed-off-by: Kees Cook <keescook@...omium.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),
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