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overflow: Introduce wrapping_add(), wrapping_sub(), and wrapping_mul()
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. Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org> Reviewed-by: Marco Elver <elver@google.com> Acked-by: Mark Rutland <mark.rutland@arm.com> Signed-off-by: Kees Cook <keescook@chromium.org>
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2 changed files with 68 additions and 4 deletions
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@ -65,6 +65,22 @@ static inline bool __must_check __must_check_overflow(bool overflow)
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#define check_add_overflow(a, b, d) \
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#define check_add_overflow(a, b, d) \
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__must_check_overflow(__builtin_add_overflow(a, b, d))
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__must_check_overflow(__builtin_add_overflow(a, b, d))
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/**
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* wrapping_add() - Intentionally perform a wrapping addition
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* @type: type for result of calculation
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* @a: first addend
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* @b: second addend
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*
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* Return the potentially wrapped-around addition without
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* tripping any wrap-around sanitizers that may be enabled.
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*/
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#define wrapping_add(type, a, b) \
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({ \
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type __val; \
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__builtin_add_overflow(a, b, &__val); \
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__val; \
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})
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/**
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/**
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* check_sub_overflow() - Calculate subtraction with overflow checking
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* check_sub_overflow() - Calculate subtraction with overflow checking
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* @a: minuend; value to subtract from
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* @a: minuend; value to subtract from
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@ -79,6 +95,22 @@ static inline bool __must_check __must_check_overflow(bool overflow)
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#define check_sub_overflow(a, b, d) \
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#define check_sub_overflow(a, b, d) \
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__must_check_overflow(__builtin_sub_overflow(a, b, d))
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__must_check_overflow(__builtin_sub_overflow(a, b, d))
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/**
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* wrapping_sub() - Intentionally perform a wrapping subtraction
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* @type: type for result of calculation
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* @a: minuend; value to subtract from
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* @b: subtrahend; value to subtract from @a
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*
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* Return the potentially wrapped-around subtraction without
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* tripping any wrap-around sanitizers that may be enabled.
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*/
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#define wrapping_sub(type, a, b) \
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({ \
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type __val; \
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__builtin_sub_overflow(a, b, &__val); \
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__val; \
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})
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/**
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/**
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* check_mul_overflow() - Calculate multiplication with overflow checking
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* check_mul_overflow() - Calculate multiplication with overflow checking
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* @a: first factor
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* @a: first factor
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@ -93,6 +125,22 @@ static inline bool __must_check __must_check_overflow(bool overflow)
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#define check_mul_overflow(a, b, d) \
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#define check_mul_overflow(a, b, d) \
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__must_check_overflow(__builtin_mul_overflow(a, b, d))
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__must_check_overflow(__builtin_mul_overflow(a, b, d))
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/**
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* wrapping_mul() - Intentionally perform a wrapping multiplication
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* @type: type for result of calculation
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* @a: first factor
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* @b: second factor
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*
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* Return the potentially wrapped-around multiplication without
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* tripping any wrap-around sanitizers that may be enabled.
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*/
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#define wrapping_mul(type, a, b) \
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({ \
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type __val; \
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__builtin_mul_overflow(a, b, &__val); \
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__val; \
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})
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/**
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/**
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* check_shl_overflow() - Calculate a left-shifted value and check overflow
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* check_shl_overflow() - Calculate a left-shifted value and check overflow
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* @a: Value to be shifted
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* @a: Value to be shifted
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@ -258,20 +258,36 @@ DEFINE_TEST_ARRAY(s64) = {
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\
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\
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_of = check_ ## op ## _overflow(a, b, &_r); \
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_of = check_ ## op ## _overflow(a, b, &_r); \
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KUNIT_EXPECT_EQ_MSG(test, _of, of, \
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KUNIT_EXPECT_EQ_MSG(test, _of, of, \
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"expected "fmt" "sym" "fmt" to%s overflow (type %s)\n", \
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"expected check "fmt" "sym" "fmt" to%s overflow (type %s)\n", \
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a, b, of ? "" : " not", #t); \
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a, b, of ? "" : " not", #t); \
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KUNIT_EXPECT_EQ_MSG(test, _r, r, \
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KUNIT_EXPECT_EQ_MSG(test, _r, r, \
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"expected "fmt" "sym" "fmt" == "fmt", got "fmt" (type %s)\n", \
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"expected check "fmt" "sym" "fmt" == "fmt", got "fmt" (type %s)\n", \
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a, b, r, _r, #t); \
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a, b, r, _r, #t); \
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/* Check for internal macro side-effects. */ \
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/* Check for internal macro side-effects. */ \
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_of = check_ ## op ## _overflow(_a_orig++, _b_orig++, &_r); \
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_of = check_ ## op ## _overflow(_a_orig++, _b_orig++, &_r); \
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KUNIT_EXPECT_EQ_MSG(test, _a_orig, _a_bump, "Unexpected " #op " macro side-effect!\n"); \
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KUNIT_EXPECT_EQ_MSG(test, _a_orig, _a_bump, \
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KUNIT_EXPECT_EQ_MSG(test, _b_orig, _b_bump, "Unexpected " #op " macro side-effect!\n"); \
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"Unexpected check " #op " macro side-effect!\n"); \
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KUNIT_EXPECT_EQ_MSG(test, _b_orig, _b_bump, \
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"Unexpected check " #op " macro side-effect!\n"); \
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\
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_r = wrapping_ ## op(t, a, b); \
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KUNIT_EXPECT_TRUE_MSG(test, _r == r, \
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"expected wrap "fmt" "sym" "fmt" == "fmt", got "fmt" (type %s)\n", \
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a, b, r, _r, #t); \
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/* Check for internal macro side-effects. */ \
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_a_orig = a; \
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_b_orig = b; \
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_r = wrapping_ ## op(t, _a_orig++, _b_orig++); \
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KUNIT_EXPECT_EQ_MSG(test, _a_orig, _a_bump, \
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"Unexpected wrap " #op " macro side-effect!\n"); \
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KUNIT_EXPECT_EQ_MSG(test, _b_orig, _b_bump, \
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"Unexpected wrap " #op " macro side-effect!\n"); \
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} while (0)
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} while (0)
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#define DEFINE_TEST_FUNC_TYPED(n, t, fmt) \
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#define DEFINE_TEST_FUNC_TYPED(n, t, fmt) \
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static void do_test_ ## n(struct kunit *test, const struct test_ ## n *p) \
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static void do_test_ ## n(struct kunit *test, const struct test_ ## n *p) \
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{ \
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{ \
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/* check_{add,sub,mul}_overflow() and wrapping_{add,sub,mul} */ \
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check_one_op(t, fmt, add, "+", p->a, p->b, p->sum, p->s_of); \
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check_one_op(t, fmt, add, "+", p->a, p->b, p->sum, p->s_of); \
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check_one_op(t, fmt, add, "+", p->b, p->a, p->sum, p->s_of); \
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check_one_op(t, fmt, add, "+", p->b, p->a, p->sum, p->s_of); \
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check_one_op(t, fmt, sub, "-", p->a, p->b, p->diff, p->d_of); \
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check_one_op(t, fmt, sub, "-", p->a, p->b, p->diff, p->d_of); \
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