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R. Silva" , Justin Stitt , linux-hardening@vger.kernel.org, Andrew Morton , Nathan Chancellor , Nick Desaulniers , Bill Wendling , Mark Rutland , Miguel Ojeda , Marco Elver , Jakub Kicinski , Przemek Kitszel , Masahiro Yamada , linux-kernel@vger.kernel.org, llvm@lists.linux.dev Subject: [PATCH v2 3/5] overflow: Introduce add_would_overflow() Date: Tue, 30 Jan 2024 14:06:08 -0800 Message-Id: <20240130220614.1154497-3-keescook@chromium.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20240130220218.it.154-kees@kernel.org> References: <20240130220218.it.154-kees@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=1484; i=keescook@chromium.org; h=from:subject; bh=WUwqmJoFZQeyqmuC4k6x7kK2L9hMV5zmyghrfRiNqjc=; b=owEBbQKS/ZANAwAKAYly9N/cbcAmAcsmYgBluXLSKrOGOdtE6GxGZsc08FzWIhOaMnOeNq/p8 lHKmLHU8x2JAjMEAAEKAB0WIQSlw/aPIp3WD3I+bhOJcvTf3G3AJgUCZbly0gAKCRCJcvTf3G3A JsybD/9hil900CeIkSDVu7dEhGUU7Eh3jgkpN4uvXxQKhpz1xxwIYnxerdxt4kUhSZ3PU7Wn+a8 y2tMl38HSeHfTMijx0VTRIz766tSzidw/km095DK7xlLqc1C7p0bOe1fXmjDJjZMo/h+B4iYAUP 786UqO4ZLOPpSWWjbEoirC1DSpvbcZbf9v7z1W8wRV1v25gyUBQOvYrUMm1YCOaMm0RQGLfuLPC 9VVUdvY4jETXBTpUlKQ7apR4LH+2R5ioDpI9ZaCEuIoZfny7BG9mJBkmXZuvWSrXUzwoqvhEQOi d/JwwmkQ97OSBCj3vYl/eYqvSADKpwdPKlHA1/LuyVDmqtbvEF5Zpvy/BxkFgcPvwProrebcWtj 4Kc0aWfaId1UDIVNhDIbt2cGolemw66t7obWCVe59lXAAxjT5g1SQpAbVmnvDU0Pq88Ty4chzEN a5B1zUIWzfXejwU/U02FFfpn6jzIxuavta2dAkaqF57YIfzdaiKfCqE6G78qg7/EIUwJ1qsKJlD NtnqoqDMkGYOdmKSvMerFSc6HJuJAPskCMyoatyDAXt3Lors/XN0qMiAFiPxyW1JE7Q/EvtUcer 2tuf3HJSurwaeE4R4tAEbTLHd0N57a495U5UbSpkLEwag6gPdKC/6sH5j119nzxFUVW0AxTv/+S YGphMUzZKOqjzuw== X-Developer-Key: i=keescook@chromium.org; a=openpgp; fpr=A5C3F68F229DD60F723E6E138972F4DFDC6DC026 X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1789554813415501629 X-GMAIL-MSGID: 1789554813415501629 For instances where only the overflow needs to be checked (and the sum isn't used), provide the new helper add_would_overflow(), which is a wrapper for check_add_overflow(). Cc: Rasmus Villemoes Cc: "Gustavo A. R. Silva" Cc: Justin Stitt Cc: linux-hardening@vger.kernel.org Signed-off-by: Kees Cook --- include/linux/overflow.h | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/include/linux/overflow.h b/include/linux/overflow.h index 210e5602e89b..3c46c648d2e8 100644 --- a/include/linux/overflow.h +++ b/include/linux/overflow.h @@ -104,6 +104,22 @@ static inline bool __must_check __must_check_overflow(bool overflow) __builtin_add_overflow(__filter_integral(a), b, \ __filter_ptrint(d)))) +/** + * add_would_overflow() - Check if an addition would overflow + * @var: variable to add to that is checked for overflow + * @offset: value to add + * + * Returns true if the sum would overflow. + * + * To keep a copy of the sum when the addition doesn't overflow, use + * check_add_overflow() instead. + */ +#define add_would_overflow(var, offset) \ + __must_check_overflow(({ \ + typeof(var) __result; \ + check_add_overflow(var, offset, &__result); \ + })) + /** * check_sub_overflow() - Calculate subtraction with overflow checking * @a: minuend; value to subtract from