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R. Silva" , linux-hardening@vger.kernel.org, Nathan Chancellor , Bill Wendling , Justin Stitt , Mark Rutland , Miguel Ojeda , Marco Elver , linux-kernel@vger.kernel.org, llvm@lists.linux.dev Subject: [PATCH 3/5] overflow: Introduce add_would_overflow() Date: Mon, 29 Jan 2024 10:34:07 -0800 Message-Id: <20240129183411.3791340-3-keescook@chromium.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20240129182845.work.694-kees@kernel.org> References: <20240129182845.work.694-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=1441; i=keescook@chromium.org; h=from:subject; bh=bPuN//AdVknGbgllRjlIvn/Clq0xqhyiE00zUL59Fq8=; b=owEBbQKS/ZANAwAKAYly9N/cbcAmAcsmYgBlt++h2FKZ64lhvgMVubeJc2zcQ8AiATcuXgzT3 N2+Ojy6lfmJAjMEAAEKAB0WIQSlw/aPIp3WD3I+bhOJcvTf3G3AJgUCZbfvoQAKCRCJcvTf3G3A JsB1EACiRI4ou3Zupww8pxGpDJGKw0Mzmo0sXE1H89oQSQhBTuWnITC0KCLQ0+7gJlrdiPNk/qs trLpEQhdhR4HM3mQzWWlinUrzp/Q9sWMbwGycyA6FYjVmj2rHqjUkxVTWwTZfUP11KhNFzZaDl8 m7EFhbTKe2FXbxWXhIvqjEB3w8H5KIODSEdIZvogFq4zMfOOo95nQNqRKAPDlAWU/Mwp3yIm4WY Rr5MBfXvkqB0GhtP1yudXc1H5Zt+aoNTUxgkVc8H0Gsi1hZtgkqfY92HjqMiBDD4f4+cd+YOz7G ZFlytqR6CA7U+HqGI83MolTXQi5O7MLs6tcRlG+fngeL1XONXC9XBfaB6sivScBLMAcPtN4wE4u rvMHeNcgWDPBZJtAdB19kL2a6YjU5a+yXEuW2hMc3nkgODqT02HJxgPBYjGVwCVMzfbQs5LSrMn X/kFqaAODLc2TysaBWAipvjIEQbD+by3K1EXviNpmeH8j41LmdlDvRa/ps5E5IJxDs6fZUputvS QSu6YOoUvrS3pCl6N/TQ3N6kP+9zrENcBIl7O6kg0+uOjVCK6TerDtMy+rPBBIzfBKDhyEbDBiJ MAaR36vxCNu73DVFISrdoqkhNiU1IyLTm4OExzpjcyFm/ZcdQZGxvf6FWFPRsdpCLYmf8jisLW2 U74ZK2xMeH/Bbdw== X-Developer-Key: i=keescook@chromium.org; a=openpgp; fpr=A5C3F68F229DD60F723E6E138972F4DFDC6DC026 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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: 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)))) =20 +/** + * 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 --=20 2.34.1