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overflow: Introduce wrapping_add(), wrapping_sub(), and wrapping_mul()

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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>
This commit is contained in:
Kees Cook
2024-01-18 16:05:52 -08:00
parent 3e19086fb5
commit d70de8054c
2 changed files with 68 additions and 4 deletions
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48
include/linux/overflow.h
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@@ -65,6 +65,22 @@ static inline bool __must_check __must_check_overflow(bool overflow)
#define check_add_overflow(a, b, d) \
__must_check_overflow(__builtin_add_overflow(a, b, d))
/**
* wrapping_add() - Intentionally perform a wrapping addition
* @type: type for result of calculation
* @a: first addend
* @b: second addend
*
* Return the potentially wrapped-around addition without
* tripping any wrap-around sanitizers that may be enabled.
*/
#define wrapping_add(type, a, b) \
({ \
type __val; \
__builtin_add_overflow(a, b, &__val); \
__val; \
})
/**
* check_sub_overflow() - Calculate subtraction with overflow checking
* @a: minuend; value to subtract from
@@ -79,6 +95,22 @@ static inline bool __must_check __must_check_overflow(bool overflow)
#define check_sub_overflow(a, b, d) \
__must_check_overflow(__builtin_sub_overflow(a, b, d))
/**
* wrapping_sub() - Intentionally perform a wrapping subtraction
* @type: type for result of calculation
* @a: minuend; value to subtract from
* @b: subtrahend; value to subtract from @a
*
* Return the potentially wrapped-around subtraction without
* tripping any wrap-around sanitizers that may be enabled.
*/
#define wrapping_sub(type, a, b) \
({ \
type __val; \
__builtin_sub_overflow(a, b, &__val); \
__val; \
})
/**
* check_mul_overflow() - Calculate multiplication with overflow checking
* @a: first factor
@@ -93,6 +125,22 @@ static inline bool __must_check __must_check_overflow(bool overflow)
#define check_mul_overflow(a, b, d) \
__must_check_overflow(__builtin_mul_overflow(a, b, d))
/**
* wrapping_mul() - Intentionally perform a wrapping multiplication
* @type: type for result of calculation
* @a: first factor
* @b: second factor
*
* Return the potentially wrapped-around multiplication without
* tripping any wrap-around sanitizers that may be enabled.
*/
#define wrapping_mul(type, a, b) \
({ \
type __val; \
__builtin_mul_overflow(a, b, &__val); \
__val; \
})
/**
* check_shl_overflow() - Calculate a left-shifted value and check overflow
* @a: Value to be shifted