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Date: Tue, 30 Aug 2022 21:34:06 +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 v3] overflow: Allow mixed type arguments
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@...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>
Reviewed-by: Andrzej Hajda <andrzej.hajda@...el.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),
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