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R . Silva" , linux-hardening@vger.kernel.org, Rasmus Villemoes , Marco Elver , Eric Biggers , Mark Rutland , Andrew Morton , linux-kernel@vger.kernel.org Subject: [PATCH v5 1/3] overflow: Adjust check_*_overflow() kern-doc to reflect results Date: Wed, 7 Feb 2024 07:24:18 -0800 Message-Id: <20240207152422.3855315-1-keescook@chromium.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20240207152317.do.560-kees@kernel.org> References: <20240207152317.do.560-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=2680; i=keescook@chromium.org; h=from:subject; bh=ixNr6X1gB7VeIiW3pk9Za3U1z37zW3zrQNIbl69tCT0=; b=owEBbQKS/ZANAwAKAYly9N/cbcAmAcsmYgBlw6Cj2+8A/TrJjsBiIAx2op9/6wn1k5bn1wnZL w9hYjTQS5WJAjMEAAEKAB0WIQSlw/aPIp3WD3I+bhOJcvTf3G3AJgUCZcOgowAKCRCJcvTf3G3A JrVrEACqhj3zhpOpirlHTgyqw2dv77Afdp4NYgHxwiKF2RhojJQXRmWssRiy/b+PrmQwg8y4Oo+ VVOBsTYIav/X9fxfiqyn7YYrDEibUC0l/4veXMRu0fxl1urJ2J2teom17HOCbGYk17Jnw2lp5VQ 8MYH0cLCa2s4jLHyuxr/hjmpdj2HFIxa5pJZA1aEhK1T2n6kHC4FieG5j/dO26APViY1DRpi5UD /YCsSn++Ad84Z/hCdqVT2mwggO+veFL06gp0NWOH8akV63+sK0OpG027YsZCM31avb6vY+xkOab l6a0Oowld4rRVYya4KKZE0zlL6RcvUwqlc++CEnV7bvUGcU+pUEWUUtnh/i+kml3n+II7Mrjiy8 N9aPF+VMMHp6Ush0kqVm114qsRP/f5ZbrQewIpmkjS5H/YR0PxOjXA1643SF5NQQ/Ngf9UydMth gq/MJhPXhugN/iR4my4tjhJeiL+5CPw0t3jucp+Ur6Tv4dLH08hA7Q3+unglr0v7hF6QdViKD61 cc62FrhC1LGh/lDH+/JMoCWl5KLlGyRBNCLdR+KifoBrc6Rh04AAMBz4HjtUH83D47X5GobBCyu 62sTrx6BawTTwuONlAPvuSU2nA5UyfOGXc0S1IRAuSl0iGiF1OhPqplky0t0VO4D3QMBxeGb45l HKXRtpdvtCn5Yvw== X-Developer-Key: i=keescook@chromium.org; a=openpgp; fpr=A5C3F68F229DD60F723E6E138972F4DFDC6DC026 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" The check_*_overflow() helpers will return results with potentially wrapped-around values. These values have always been checked by the selftests, so avoid the confusing language in the kern-doc. The idea of "safe for use" was relative to the expectation of whether or not the caller wants a wrapped value -- the calculation itself will always follow arithmetic wrapping rules. Reviewed-by: Gustavo A. R. Silva Cc: linux-hardening@vger.kernel.org Signed-off-by: Kees Cook --- include/linux/overflow.h | 18 ++++++------------ 1 file changed, 6 insertions(+), 12 deletions(-) diff --git a/include/linux/overflow.h b/include/linux/overflow.h index 7b5cf4a5cd19..4e741ebb8005 100644 --- a/include/linux/overflow.h +++ b/include/linux/overflow.h @@ -57,11 +57,9 @@ static inline bool __must_check __must_check_overflow(bo= ol overflow) * @b: second addend * @d: pointer to store sum * - * Returns 0 on success. + * Returns 0 on success, 1 on wrap-around. * - * *@d holds the results of the attempted addition, but is not considered - * "safe for use" on a non-zero return value, which indicates that the - * sum has overflowed or been truncated. + * *@d holds the results of the attempted addition, which may wrap-around. */ #define check_add_overflow(a, b, d) \ __must_check_overflow(__builtin_add_overflow(a, b, d)) @@ -72,11 +70,9 @@ static inline bool __must_check __must_check_overflow(bo= ol overflow) * @b: subtrahend; value to subtract from @a * @d: pointer to store difference * - * Returns 0 on success. + * Returns 0 on success, 1 on wrap-around. * - * *@d holds the results of the attempted subtraction, but is not consider= ed - * "safe for use" on a non-zero return value, which indicates that the - * difference has underflowed or been truncated. + * *@d holds the results of the attempted subtraction, which may wrap-arou= nd. */ #define check_sub_overflow(a, b, d) \ __must_check_overflow(__builtin_sub_overflow(a, b, d)) @@ -87,11 +83,9 @@ static inline bool __must_check __must_check_overflow(bo= ol overflow) * @b: second factor * @d: pointer to store product * - * Returns 0 on success. + * Returns 0 on success, 1 on wrap-around. * - * *@d holds the results of the attempted multiplication, but is not - * considered "safe for use" on a non-zero return value, which indicates - * that the product has overflowed or been truncated. + * *@d holds the results of the attempted multiplication, which may wrap-a= round. */ #define check_mul_overflow(a, b, d) \ __must_check_overflow(__builtin_mul_overflow(a, b, d)) --=20 2.34.1 From nobody Mon Feb 9 04:29:34 2026 Received: from mail-pf1-f181.google.com (mail-pf1-f181.google.com [209.85.210.181]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 03AA87F49D for ; 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Silva" , Andrew Morton , linux-kernel@vger.kernel.org Subject: [PATCH v5 2/3] overflow: Introduce wrapping_add(), wrapping_sub(), and wrapping_mul() Date: Wed, 7 Feb 2024 07:24:19 -0800 Message-Id: <20240207152422.3855315-2-keescook@chromium.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20240207152317.do.560-kees@kernel.org> References: <20240207152317.do.560-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=5602; i=keescook@chromium.org; h=from:subject; bh=b+f38qUkFmR/TObhuk4Sc9oAIjIVix3f9cue4x2E+Fo=; b=owEBbQKS/ZANAwAKAYly9N/cbcAmAcsmYgBlw6Cj3wFGEbnwDxyh6eIuINKUEK64qoLls8qiq SfHBN0h+Y6JAjMEAAEKAB0WIQSlw/aPIp3WD3I+bhOJcvTf3G3AJgUCZcOgowAKCRCJcvTf3G3A Jv6xD/0XhE55ZAZLm9uMEhycDNqaeAR5W6+/KhWbDn/Fk6wA4T2KzKrV/PJHcl/ZDfJm533RMVj zZa0cP44ZXsejZND+BZzJ7dYJo1Pq5Et5DRjQRd63Af6SIACjAIDJvG/LWKHQjexVvZJP+ykAGA 7SbXzpne4OjrZRbKXRt2lJxcpX8zT4Q1Yn7OYX0GWkH5Z2gtw6Qe3SqAFud1knCAZrwXI4de+bX mfucHuDRhytInGLFdYr/Nz48LdqGJQnxfCKmNhpVANcNPo3eR3j7ewlieG6aNl+b90hfVp8nobx Y4Idi/+T9KgnAXzSlujsb3yrLQbvnuRD96Y3ZnUfhZ71XB8q2APa29ZUZ7d0Gzc99/7S5aVBBcE d6gjh5HU2kg5lvRhlC/sM2oHaXaDabBqF0Xr02kmjxhkEFwSDRvcnUPWtR2v0G4glcdyKNrHqOV ArLh8Gdm2sTR7g4XhC+vChZJgdYcsUlNvFX6eUWa8hOkNyrwtuxQN6+ZxiwWJZa8RTLMFhEg+Qh aA9I0WyCdp6VadzwkgEeG8uiB4RvFRRN4eW5P6DpvHSP0suL2BvDAO7h0m1b/Dg7OyCyVWr6BS9 s5eY5y5+Q7w6lzkWhBCEQM31XmSxe8oNASCpnUbQWnKZUVQVoq4QBDiiKqOSfjANccJdqNiElA1 0q9RcTfa1raCYew== X-Developer-Key: i=keescook@chromium.org; a=openpgp; fpr=A5C3F68F229DD60F723E6E138972F4DFDC6DC026 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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) =3D=3D 2500 wrapping_mul(u8, 50, 50) =3D=3D 196 Add to the selftests to validate behavior and lack of side-effects. Cc: Rasmus Villemoes Cc: Marco Elver Cc: Eric Biggers Cc: Mark Rutland Cc: linux-hardening@vger.kernel.org Reviewed-by: Gustavo A. R. Silva Signed-off-by: Kees Cook Reviewed-by: Marco Elver --- include/linux/overflow.h | 48 ++++++++++++++++++++++++++++++++++++++++ lib/overflow_kunit.c | 24 ++++++++++++++++---- 2 files changed, 68 insertions(+), 4 deletions(-) diff --git a/include/linux/overflow.h b/include/linux/overflow.h index 4e741ebb8005..849a49fb496e 100644 --- a/include/linux/overflow.h +++ b/include/linux/overflow.h @@ -64,6 +64,22 @@ static inline bool __must_check __must_check_overflow(bo= ol overflow) #define check_add_overflow(a, b, d) \ __must_check_overflow(__builtin_add_overflow(a, b, d)) =20 +/** + * 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 @@ -77,6 +93,22 @@ static inline bool __must_check __must_check_overflow(bo= ol overflow) #define check_sub_overflow(a, b, d) \ __must_check_overflow(__builtin_sub_overflow(a, b, d)) =20 +/** + * 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 @@ -90,6 +122,22 @@ static inline bool __must_check __must_check_overflow(b= ool overflow) #define check_mul_overflow(a, b, d) \ __must_check_overflow(__builtin_mul_overflow(a, b, d)) =20 +/** + * 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 diff --git a/lib/overflow_kunit.c b/lib/overflow_kunit.c index c527f6b75789..d3fdb906d3fe 100644 --- a/lib/overflow_kunit.c +++ b/lib/overflow_kunit.c @@ -258,20 +258,36 @@ DEFINE_TEST_ARRAY(s64) =3D { \ _of =3D 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" =3D=3D "fmt", got "fmt" (type %s)\n", \ + "expected check "fmt" "sym" "fmt" =3D=3D "fmt", got "fmt" (type %s)\n", \ a, b, r, _r, #t); \ /* Check for internal macro side-effects. */ \ _of =3D check_ ## op ## _overflow(_a_orig++, _b_orig++, &_r); \ - KUNIT_EXPECT_EQ_MSG(test, _a_orig, _a_bump, "Unexpected " #op " macro sid= e-effect!\n"); \ - KUNIT_EXPECT_EQ_MSG(test, _b_orig, _b_bump, "Unexpected " #op " macro sid= e-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 =3D wrapping_ ## op(t, a, b); \ + KUNIT_EXPECT_TRUE_MSG(test, _r =3D=3D r, \ + "expected wrap "fmt" "sym" "fmt" =3D=3D "fmt", got "fmt" (type %s)\n", \ + a, b, r, _r, #t); \ + /* Check for internal macro side-effects. */ \ + _a_orig =3D a; \ + _b_orig =3D b; \ + _r =3D wrapping_ ## op(t, _a_orig++, _b_orig++); 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Wed, 07 Feb 2024 07:24:24 -0800 (PST) From: Kees Cook To: Andy Shevchenko Cc: Kees Cook , Rasmus Villemoes , Marco Elver , Eric Biggers , Mark Rutland , "Gustavo A. R. Silva" , linux-hardening@vger.kernel.org, Andrew Morton , linux-kernel@vger.kernel.org Subject: [PATCH v5 3/3] overflow: Introduce wrapping_inc() and wrapping_dec() Date: Wed, 7 Feb 2024 07:24:20 -0800 Message-Id: <20240207152422.3855315-3-keescook@chromium.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20240207152317.do.560-kees@kernel.org> References: <20240207152317.do.560-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=4594; i=keescook@chromium.org; h=from:subject; bh=UF4ZOJtI7adR1ITE12VYKN2eWkYypBgjoqWUYT5HRLA=; b=owEBbQKS/ZANAwAKAYly9N/cbcAmAcsmYgBlw6Ck4Knv0CZm8IYel3Z4RJZj9vYED+A+0Ru26 cX6qKGKwNmJAjMEAAEKAB0WIQSlw/aPIp3WD3I+bhOJcvTf3G3AJgUCZcOgpAAKCRCJcvTf3G3A JoQzD/wI+8Lf+6AaeGFKfxalG4dQxHYlwN0aqDm8Alb9xyyctuWdjfXnTerEf7Zbl0mQKHHonps M8lLZGpLU8sHrOb5ycfRTBw09he+nj3AF9xKEuGKkZ9O8ycxUVz2HqcRyF+lqTKV063RfCkqujw zEGzjrVLjgVd0x1FxNUztDEgZV73ow9l+Cfgp8ERi+ikCTsGdUoho3AorJsW8Y0qvR3JXMM97jQ xFbGLZ0PCLojIvcxjdrKESl63H9hPevoJIB0FG/Sn6WVxyN7kot9WPDJfgQ2WIUqtwMGrXBPDjz OR4YrvEdTDY0TkalsfmYhzoanRrSbRXil3oygyW9YDJKtGsa/+yNubbxSCzacaSqIQRs1oeJmnZ 6IcVxM6bLXJWil6fIa6eUCvhAImjxYs1wh5jG9ZzqnjWfugekmyuEBd/0tHmJ+grIqjRmpVJBrb omBgutZBtt0zqBiK9fTx0LQWQmSCtFnzFvDKPYhIIY0IAYoi3Nml87y7pXmeBcuWEW7n6uUNpKx sJZqMfGtB3ozLCe+nRdTGn39Dq7lh/XJNaYN9FHtqFdo9Hi7R7iHMrW4xnR/Xt8vV4E2jesuwhs X0RHoojimonoJ4txcOJ1P4/8GMLM7KbV4havukwMIjKe34cKjTWZBEkWR09W6VfbAhNC0O9sc30 hB55mBv3p5236Ng== X-Developer-Key: i=keescook@chromium.org; a=openpgp; fpr=A5C3F68F229DD60F723E6E138972F4DFDC6DC026 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" This allows replacements of the idioms "var +=3D offset" and "var -=3D offs= et" with the wrapping_inc() and wrapping_dec() helpers respectively. They will avoid wrap-around sanitizer instrumentation. Add to the selftests to validate behavior and lack of side-effects. Cc: Rasmus Villemoes Cc: Marco Elver Cc: Eric Biggers Cc: Mark Rutland Cc: "Gustavo A. R. Silva" Cc: linux-hardening@vger.kernel.org Signed-off-by: Kees Cook --- include/linux/overflow.h | 32 ++++++++++++++++++++++++++++++ lib/overflow_kunit.c | 43 ++++++++++++++++++++++++++++++++++++++++ 2 files changed, 75 insertions(+) diff --git a/include/linux/overflow.h b/include/linux/overflow.h index 849a49fb496e..f4b18007fd2b 100644 --- a/include/linux/overflow.h +++ b/include/linux/overflow.h @@ -80,6 +80,22 @@ static inline bool __must_check __must_check_overflow(bo= ol overflow) __val; \ }) =20 +/** + * wrapping_inc() - Intentionally perform a wrapping increment + * @var: variable to be incremented + * @offset: amount to add + * + * Increments @var by @offset with wrap-around. Returns the resulting + * value of @var. Will not trip any wrap-around sanitizers. + * + * Returns the new value of @var. + */ +#define wrapping_inc(var, offset) \ + ({ \ + typeof(var) *__ptr =3D &(var); \ + *__ptr =3D wrapping_add(typeof(var), *__ptr, offset); \ + }) + /** * check_sub_overflow() - Calculate subtraction with overflow checking * @a: minuend; value to subtract from @@ -109,6 +125,22 @@ static inline bool __must_check __must_check_overflow(= bool overflow) __val; \ }) =20 +/** + * wrapping_dec() - Intentionally perform a wrapping decrement + * @var: variable to be decremented + * @offset: amount to subtract + * + * Decrements @var by @offset with wrap-around. Returns the resulting + * value of @var. Will not trip any wrap-around sanitizers. + * + * Returns the new value of @var. + */ +#define wrapping_dec(var, offset) \ + ({ \ + typeof(var) *__ptr =3D &(var); \ + *__ptr =3D wrapping_sub(typeof(var), *__ptr, offset); \ + }) + /** * check_mul_overflow() - Calculate multiplication with overflow checking * @a: first factor diff --git a/lib/overflow_kunit.c b/lib/overflow_kunit.c index d3fdb906d3fe..6cadce8f8a47 100644 --- a/lib/overflow_kunit.c +++ b/lib/overflow_kunit.c @@ -284,6 +284,45 @@ DEFINE_TEST_ARRAY(s64) =3D { "Unexpected wrap " #op " macro side-effect!\n"); \ } while (0) =20 +static int global_counter; +static void bump_counter(void) +{ + global_counter++; +} + +static int get_index(void) +{ + volatile int index =3D 0; + bump_counter(); + return index; +} + +#define check_self_op(fmt, op, sym, a, b) do { \ + typeof(a + 0) _a =3D a; \ + typeof(b + 0) _b =3D b; \ + typeof(a + 0) _a_sym =3D a; \ + typeof(a + 0) _a_orig[1] =3D { a }; \ + typeof(b + 0) _b_orig =3D b; \ + typeof(b + 0) _b_bump =3D b + 1; \ + typeof(a + 0) _r; \ + \ + _a_sym sym _b; \ + _r =3D wrapping_ ## op(_a, _b); \ + KUNIT_EXPECT_TRUE_MSG(test, _r =3D=3D _a_sym, \ + "expected "fmt" "#op" "fmt" =3D=3D "fmt", got "fmt"\n", \ + a, b, _a_sym, _r); \ + KUNIT_EXPECT_TRUE_MSG(test, _a =3D=3D _a_sym, \ + "expected "fmt" "#op" "fmt" =3D=3D "fmt", got "fmt"\n", \ + a, b, _a_sym, _a); \ + /* Check for internal macro side-effects. */ \ + global_counter =3D 0; \ + wrapping_ ## op(_a_orig[get_index()], _b_orig++); \ + KUNIT_EXPECT_EQ_MSG(test, global_counter, 1, \ + "Unexpected wrapping_" #op " macro side-effect on arg1!\n"); \ + KUNIT_EXPECT_EQ_MSG(test, _b_orig, _b_bump, \ + "Unexpected wrapping_" #op " macro side-effect on arg2!\n"); \ +} while (0) + #define DEFINE_TEST_FUNC_TYPED(n, t, fmt) \ static void do_test_ ## n(struct kunit *test, const struct test_ ## n *p) \ { \ @@ -293,6 +332,10 @@ static void do_test_ ## n(struct kunit *test, const st= ruct test_ ## n *p) \ check_one_op(t, fmt, sub, "-", p->a, p->b, p->diff, p->d_of); \ check_one_op(t, fmt, mul, "*", p->a, p->b, p->prod, p->p_of); \ check_one_op(t, fmt, mul, "*", p->b, p->a, p->prod, p->p_of); \ + /* wrapping_{inc,dec}() */ \ + check_self_op(fmt, inc, +=3D, p->a, p->b); \ + check_self_op(fmt, inc, +=3D, p->b, p->a); \ + check_self_op(fmt, dec, -=3D, p->a, p->b); \ } \ \ static void n ## _overflow_test(struct kunit *test) { \ --=20 2.34.1