diff options
author | Kees Cook <keescook@chromium.org> | 2024-01-18 16:05:52 -0800 |
---|---|---|
committer | Kees Cook <keescook@chromium.org> | 2024-02-29 13:38:01 -0800 |
commit | d70de8054c58d7bd9a4654c9f4797d29fa46d545 (patch) | |
tree | bcc66c9026a9407845dca2827111bf619c092626 /include/linux/overflow.h | |
parent | 3e19086fb5a9079611de426e8cb2f4503e28757e (diff) | |
download | lwn-d70de8054c58d7bd9a4654c9f4797d29fa46d545.tar.gz lwn-d70de8054c58d7bd9a4654c9f4797d29fa46d545.zip |
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>
Diffstat (limited to 'include/linux/overflow.h')
-rw-r--r-- | include/linux/overflow.h | 48 |
1 files changed, 48 insertions, 0 deletions
diff --git a/include/linux/overflow.h b/include/linux/overflow.h index ad64d810c8aa..d3ff8e2bec29 100644 --- a/include/linux/overflow.h +++ b/include/linux/overflow.h @@ -66,6 +66,22 @@ static inline bool __must_check __must_check_overflow(bool overflow) __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 * @b: subtrahend; value to subtract from @a @@ -80,6 +96,22 @@ static inline bool __must_check __must_check_overflow(bool overflow) __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 * @b: second factor @@ -94,6 +126,22 @@ static inline bool __must_check __must_check_overflow(bool overflow) __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 * @s: How many bits left to shift |