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R . Silva" , Mark Rutland , linux-hardening@vger.kernel.org, Rasmus Villemoes , Marco Elver , Eric Biggers , Andrew Morton , linux-kernel@vger.kernel.org Subject: [PATCH v7 1/3] overflow: Adjust check_*_overflow() kern-doc to reflect results Date: Wed, 14 Feb 2024 11:46:01 -0800 Message-Id: <20240214194605.602505-1-keescook@chromium.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20240214194432.makes.837-kees@kernel.org> References: <20240214194432.makes.837-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=2828; i=keescook@chromium.org; h=from:subject; bh=XRea/mEhcbAGWa9Y4NibhO2kDjISXokmQWKcnCxCkCA=; b=owEBbQKS/ZANAwAKAYly9N/cbcAmAcsmYgBlzRh7r+ya4r7uEt9x8g08cu6WVWLE7l1GWFkDZ 9tMyyEzBZiJAjMEAAEKAB0WIQSlw/aPIp3WD3I+bhOJcvTf3G3AJgUCZc0YewAKCRCJcvTf3G3A JokeD/4syUq1+l4y9hFWnYnriJZrkny078pHVb3PIOY5XYIudZ7ZTv5wuMAwVzHjGujXsmINAAO pvn3kJa2F6Fu75yGUOsdFeG+YwFY6VARtUIQDEgUtoGl9ulfw/jzOViuCCPRtZ8VE+6yAsrz34V cI4G7wA8IuprJ7z7dYaOGt6npq+U390i9v9w19QuSX6Q61KrNl2Oj4Sd8WAuCWs6xnUj2fGa9fy No3EaO924o3xaALxo8oKz8difZ+2TlvzxarU3j+wXtuwKLtE8xtUYcJRQoRYcWtZPH189hLRZZ/ OSs3HhcGiJyzihAAVr7oRL9Q323ECK+cbgVhHgVUNE1qrQbI8kEbKqWmqqdaEeLO1CjQVfeCbwN tlSPBwgtAkSvDTFssmMwHj+PI2dg8R6nNULk/ZYzsgBjABA/VYd6gNSmGE71Clc7t6OoJ1716iR ccUkN/TTWttr2MhLMa9f5sEsqFKd49BxDylTAqgO6NvD7qAbqb8V69oJ22k9+67QhFLnxAKNNxp kAsCJkher0VmBPGWFR7dK9KbrTYa5hPVrdKrjzTOphv+FKiWzPs5+dS4UfNQF0Ani7da/rQsisj LgY3RieGWc9W3kAP7vFeEf9JkLj7p2aAp9dVUDMObMj5wbTzD6+sK3QbS5kqou0OuVJTG3LO+6T H3GIukbfitb4mnA== 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 Signed-off-by: Kees Cook Acked-by: Mark Rutland --- Cc: Mark Rutland Cc: linux-hardening@vger.kernel.org --- include/linux/overflow.h | 21 +++++++++------------ 1 file changed, 9 insertions(+), 12 deletions(-) diff --git a/include/linux/overflow.h b/include/linux/overflow.h index 7b5cf4a5cd19..ad64d810c8aa 100644 --- a/include/linux/overflow.h +++ b/include/linux/overflow.h @@ -57,11 +57,10 @@ static inline bool __must_check __must_check_overflow(b= ool overflow) * @b: second addend * @d: pointer to store sum * - * Returns 0 on success. + * Returns true on wrap-around, false otherwise. * - * *@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, regardless of whether + * wrap-around occurred. */ #define check_add_overflow(a, b, d) \ __must_check_overflow(__builtin_add_overflow(a, b, d)) @@ -72,11 +71,10 @@ static inline bool __must_check __must_check_overflow(b= ool overflow) * @b: subtrahend; value to subtract from @a * @d: pointer to store difference * - * Returns 0 on success. + * Returns true on wrap-around, false otherwise. * - * *@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, regardless of wheth= er + * wrap-around occurred. */ #define check_sub_overflow(a, b, d) \ __must_check_overflow(__builtin_sub_overflow(a, b, d)) @@ -87,11 +85,10 @@ static inline bool __must_check __must_check_overflow(b= ool overflow) * @b: second factor * @d: pointer to store product * - * Returns 0 on success. + * Returns true on wrap-around, false otherwise. * - * *@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, regardless of wh= ether + * wrap-around occurred. */ #define check_mul_overflow(a, b, d) \ __must_check_overflow(__builtin_mul_overflow(a, b, d)) --=20 2.34.1 From nobody Tue Dec 23 22:07:52 2025 Received: from mail-pg1-f177.google.com (mail-pg1-f177.google.com [209.85.215.177]) (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 AB6F113B7A8 for ; 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R . Silva" , Marco Elver , Mark Rutland , Rasmus Villemoes , Eric Biggers , linux-hardening@vger.kernel.org, Andrew Morton , linux-kernel@vger.kernel.org Subject: [PATCH v7 2/3] overflow: Introduce wrapping_add(), wrapping_sub(), and wrapping_mul() Date: Wed, 14 Feb 2024 11:46:02 -0800 Message-Id: <20240214194605.602505-2-keescook@chromium.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20240214194432.makes.837-kees@kernel.org> References: <20240214194432.makes.837-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=5699; i=keescook@chromium.org; h=from:subject; bh=YgOkKOXlR0ASzxusUpx89CgykDXZ1IYPis0fKK7VnqI=; b=owEBbQKS/ZANAwAKAYly9N/cbcAmAcsmYgBlzRh75R0GQGPPZ3V/orJDK5K3S77Rr4Gn5Trr5 BIOzQyMkSqJAjMEAAEKAB0WIQSlw/aPIp3WD3I+bhOJcvTf3G3AJgUCZc0YewAKCRCJcvTf3G3A JmR6D/47QsZE4N+Np5gKhL0eBIwumGpqxvTd6vDXmG0nJVHUr6MjBIsXaVPK8xgyC/CBJkqHnu4 /3CHWgIQetK5nnziOHmusOYYYjzqjJ7xOwoZkv88oXIiHRBhoAJd4YGLeA4q2Xcr5R7cNm57+nI g7r7mIiy6m9H5c8409RHq8KglRXp1Fl/+DxfSSvPBmXPOciQvunRQLX7hTDqWYdoBtf7yMVic8r w3pVGGvmp1kXhNrzadU8VmDX/kI8nXu+oIuIklW6NhWUYUszF/AYva+k1jXU55cDxlpXBcWa/lP +prkhaCEwcTFYk8GubRxedPFKOf9Kh/LVKoQAJCLe7wForOeNv4FGhfj6bHQHrT1BslZK69u3H4 dTDMEbvct38Yf0Y4jhHoec64KVzGJ0dW1YMmneNkMWoEh5N6a1d6vuQRdJ3FDiDQAtzY+jMf1yE 9ICNjGGU2xplXOsF/qa52hktVd2fCKxQtOZWY697Pv8tzEnkzl6rIqdk/zl7UtNitVg7NJFp1dQ VNTe5XOaY30gijj3BGqF94elswFSPP01/Uqw1hSUVJCGoo8krNGAWp4ek1+MN0Xr4NvOwvGrFB4 TGJr+ZryV3TfTElN0qb4RVawAVOSy7Jflpogzin+/kO4/HTiDnZyBkO1Xh17AYFrH7v/d42jBrl 8juwtUGbB4vwKdQ== 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. Reviewed-by: Gustavo A. R. Silva Reviewed-by: Marco Elver Acked-by: Mark Rutland Signed-off-by: Kees Cook --- Cc: Rasmus Villemoes Cc: Marco Elver Cc: Eric Biggers Cc: Mark Rutland Cc: linux-hardening@vger.kernel.org --- 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 ad64d810c8aa..d3ff8e2bec29 100644 --- a/include/linux/overflow.h +++ b/include/linux/overflow.h @@ -65,6 +65,22 @@ 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 @@ -79,6 +95,22 @@ 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 @@ -93,6 +125,22 @@ 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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R. Silva" , linux-hardening@vger.kernel.org, Andrew Morton , linux-kernel@vger.kernel.org Subject: [PATCH v7 3/3] overflow: Introduce wrapping_assign_add() and wrapping_assign_sub() Date: Wed, 14 Feb 2024 11:46:03 -0800 Message-Id: <20240214194605.602505-3-keescook@chromium.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20240214194432.makes.837-kees@kernel.org> References: <20240214194432.makes.837-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=4684; i=keescook@chromium.org; h=from:subject; bh=WpCfOJKQI2tEPzWqXq2AwhFgSH1gItVpb6dbVuRrWwo=; b=owEBbQKS/ZANAwAKAYly9N/cbcAmAcsmYgBlzRh7+CaMXERKbG/TjLkrLLxvw47pmVByFgyp2 54s77/hIuKJAjMEAAEKAB0WIQSlw/aPIp3WD3I+bhOJcvTf3G3AJgUCZc0YewAKCRCJcvTf3G3A JsTHD/9V5W7uSsNqclqE+WRbQgUNPUGr2Z0aTYhid2E0NBqKt6TgpdzgEwYnkz9QuNi5PtqbfeT 3KTzVu2TztVAD4MhsWpK2R/8I/5oxcFJ4EmlZyWwT9dBWDK+zSRK/cEYDvgORPHFFUkL+6JLKmx IFd5SgbuvI+F9E0kHGN2iReicG9HHlGEfZSaEKLx2kyFfpupG9h+M+7kTxuH1X5ir78pyd9W6Tt J2UBp+xPAMuTNMBLRLJWuZHq+TvGU1Kz/JK5zEx0fbqz8cALwhRivwYPFrDN0Y2iEzqLgV/MpjC SHjYSsrc5iWCXjP0EemrzTB5cIGSeLBraofYV92DRO/p2mDB9MMmb7qPEfhVmUr+8f3th+vMAAc pAA0F9PgA6bqNHULJ2zElabbp5GuOulS5jBINn/wKJzioxU4878geM1q2k8PTPSUepBcZFd3UPY fbKEUR6FYlggQ/7iP6jF3xBAO1vq7KoNWQNYFjHeK54ugrWSJSFJUdV9YPPw4hQsdv9mub8VJqy Hft7QxCQWfSYhP67h/+sl5pFlyz55GXeBD61nGAQgwb+rS8SWO+zDWbxGGjYToUvmBu/lRs/TDS k1/esybUWsrTq1oqfi/k8Cy6C08yc9t8PKr+FCbSmcTCPhLiMe4Z/UIEQxMPB+w0u4eS812ZPDy k7VJ5j6GMhaPMJw== 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 offset" with the wrapping_assign_add() and wrapping_assign_sub() helpers respectively. They will avoid wrap-around sanitizer instrumentation. Add to the selftests to validate behavior and lack of side-effects. Signed-off-by: Kees Cook Acked-by: Mark Rutland Reviewed-by: Marco Elver --- Cc: Rasmus Villemoes Cc: Marco Elver Cc: Eric Biggers Cc: Mark Rutland Cc: "Gustavo A. R. Silva" Cc: linux-hardening@vger.kernel.org --- 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 d3ff8e2bec29..dede374832c9 100644 --- a/include/linux/overflow.h +++ b/include/linux/overflow.h @@ -81,6 +81,22 @@ static inline bool __must_check __must_check_overflow(bo= ol overflow) __val; \ }) =20 +/** + * wrapping_assign_add() - Intentionally perform a wrapping increment assi= gnment + * @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_assign_add(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 @@ -111,6 +127,22 @@ static inline bool __must_check __must_check_overflow(= bool overflow) __val; \ }) =20 +/** + * wrapping_assign_sub() - Intentionally perform a wrapping decrement assi= gn + * @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_assign_sub(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..65e8a72a83bf 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_assign_{add,sub}() */ \ + check_self_op(fmt, assign_add, +=3D, p->a, p->b); \ + check_self_op(fmt, assign_add, +=3D, p->b, p->a); \ + check_self_op(fmt, assign_sub, -=3D, p->a, p->b); \ } \ \ static void n ## _overflow_test(struct kunit *test) { \ --=20 2.34.1