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R. Silva" , Marco Elver , linux-kernel@vger.kernel.org Subject: [PATCH v3 2/3] overflow: Introduce add_wrap(), sub_wrap(), and mul_wrap() Date: Mon, 5 Feb 2024 01:12:30 -0800 Message-Id: <20240205091233.1357377-2-keescook@chromium.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20240205090854.make.507-kees@kernel.org> References: <20240205090854.make.507-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=5170; i=keescook@chromium.org; h=from:subject; bh=Uu4zdTW2mKt9ckOwQpBzTQVr+FjHnYW3s+ZeUJaV4TY=; b=owEBbQKS/ZANAwAKAYly9N/cbcAmAcsmYgBlwKZ/Nm0pF6SN4QjXTBZaM3aZSgGNoHvNCa5I8 5tIXu1d1suJAjMEAAEKAB0WIQSlw/aPIp3WD3I+bhOJcvTf3G3AJgUCZcCmfwAKCRCJcvTf3G3A JvkEEACy5IItnvaa4LrGBcbUWROutsPTmPl0aCSUlLm7QkszAaPgk12TTvyYNnF9DbNyDanPqm8 1f2bs5RMLQvTkBhPHSjm6nUkym0GqENgSZ/NPbOcM1NOFNUd3BmBgfO44IKPNwl+NAvmMvoCMff cGHQrE+L0gH0SIyzX0Fdcv1kOzIna7iczsENiqouV4jeCND8tDeAv9pFkZVz8Qu1EKXTDsKL4t/ YirmrsPi2zi2SveRKigdtLK3ODOodfT8qrzbAmnpVuYGNAtkblnKs+Tto188hCfV20DPglSgpqJ X91CCRbvL1zOW64YOvD/YfyQIc+Vvn6at78f3gFodIiryXasur+E17rejaN8uTRdECFuoeBH5Rt IfechYFxFtFanjMUdqS61scoRcsqMbUqr+1i87bUgFIgfRnO1rHgeiJVUd4gtPGkUlYeREzXlQS d1tjFFfxaiNz4/qMRSHqvawfXO4dcximqzeHZdh12jTEr+cIN0kfp48Lut5ryzSWNcijIYnqIkE R7Xnz5CPiewWtuw9bx2cLxv7WzaT4fAG8jAR3zV86WOJUt02F1p862j88YFvLVjQnbCq4+dEKlT e+9hhhb/CgLsXMqvsC2dHflQ5ueI3nwpIhT0hbTkVXhRgBR4Gae4H6aPPMOtwe/XvnKPtEAabxR 887o1pblbUVWiUQ== X-Developer-Key: i=keescook@chromium.org; a=openpgp; fpr=A5C3F68F229DD60F723E6E138972F4DFDC6DC026 X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1790049685093246753 X-GMAIL-MSGID: 1790049685093246753 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: mul_wrap(int, 50, 50) == 2500 mul_wrap(u8, 50, 50) == 196 Add to the selftests to validate behavior and lack of side-effects. Cc: Rasmus Villemoes Cc: Mark Rutland Cc: linux-hardening@vger.kernel.org Signed-off-by: Kees Cook Reviewed-by: Gustavo A. R. Silva --- include/linux/overflow.h | 54 ++++++++++++++++++++++++++++++++++++++++ lib/overflow_kunit.c | 23 ++++++++++++++--- 2 files changed, 73 insertions(+), 4 deletions(-) diff --git a/include/linux/overflow.h b/include/linux/overflow.h index 4e741ebb8005..9b8c05bdb788 100644 --- a/include/linux/overflow.h +++ b/include/linux/overflow.h @@ -64,6 +64,24 @@ 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)) +/** + * add_wrap() - 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 add_wrap(type, a, b) \ + ({ \ + type __val; \ + if (check_add_overflow(a, b, &__val)) { \ + /* do nothing */ \ + } \ + __val; \ + }) + /** * check_sub_overflow() - Calculate subtraction with overflow checking * @a: minuend; value to subtract from @@ -77,6 +95,24 @@ 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)) +/** + * sub_wrap() - 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 sub_wrap(type, a, b) \ + ({ \ + type __val; \ + if (check_sub_overflow(a, b, &__val)) { \ + /* do nothing */ \ + } \ + __val; \ + }) + /** * check_mul_overflow() - Calculate multiplication with overflow checking * @a: first factor @@ -90,6 +126,24 @@ 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)) +/** + * mul_wrap() - 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 mul_wrap(type, a, b) \ + ({ \ + type __val; \ + if (check_mul_overflow(a, b, &__val)) { \ + /* do nothing */ \ + } \ + __val; \ + }) + /** * check_shl_overflow() - Calculate a left-shifted value and check overflow * @a: Value to be shifted diff --git a/lib/overflow_kunit.c b/lib/overflow_kunit.c index c527f6b75789..064dccd973ad 100644 --- a/lib/overflow_kunit.c +++ b/lib/overflow_kunit.c @@ -258,15 +258,30 @@ DEFINE_TEST_ARRAY(s64) = { \ _of = check_ ## op ## _overflow(a, b, &_r); \ KUNIT_EXPECT_EQ_MSG(test, _of, of, \ - "expected "fmt" "sym" "fmt" to%s overflow (type %s)\n", \ + "expected check "fmt" "sym" "fmt" to%s overflow (type %s)\n", \ a, b, of ? "" : " not", #t); \ KUNIT_EXPECT_EQ_MSG(test, _r, r, \ - "expected "fmt" "sym" "fmt" == "fmt", got "fmt" (type %s)\n", \ + "expected check "fmt" "sym" "fmt" == "fmt", got "fmt" (type %s)\n", \ a, b, r, _r, #t); \ /* Check for internal macro side-effects. */ \ _of = check_ ## op ## _overflow(_a_orig++, _b_orig++, &_r); \ - KUNIT_EXPECT_EQ_MSG(test, _a_orig, _a_bump, "Unexpected " #op " macro side-effect!\n"); \ - KUNIT_EXPECT_EQ_MSG(test, _b_orig, _b_bump, "Unexpected " #op " macro side-effect!\n"); \ + KUNIT_EXPECT_EQ_MSG(test, _a_orig, _a_bump, \ + "Unexpected check " #op " macro side-effect!\n"); \ + KUNIT_EXPECT_EQ_MSG(test, _b_orig, _b_bump, \ + "Unexpected check " #op " macro side-effect!\n"); \ + \ + _r = op ## _wrap(t, a, b); \ + KUNIT_EXPECT_TRUE_MSG(test, _r == r, \ + "expected wrap "fmt" "sym" "fmt" == "fmt", got "fmt" (type %s)\n", \ + a, b, r, _r, #t); \ + /* Check for internal macro side-effects. */ \ + _a_orig = a; \ + _b_orig = b; \ + _r = op ## _wrap(t, _a_orig++, _b_orig++); \ + KUNIT_EXPECT_EQ_MSG(test, _a_orig, _a_bump, \ + "Unexpected wrap " #op " macro side-effect!\n"); \ + KUNIT_EXPECT_EQ_MSG(test, _b_orig, _b_bump, \ + "Unexpected wrap " #op " macro side-effect!\n"); \ } while (0) #define DEFINE_TEST_FUNC_TYPED(n, t, fmt) \