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Wed, 14 Feb 2024 11:46:05 -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 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 X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1790904904936472625 X-GMAIL-MSGID: 1790904904936472625 This allows replacements of the idioms "var += offset" and "var -= 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 Reviewed-by: Marco Elver Acked-by: Mark Rutland --- 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(bool overflow) __val; \ }) +/** + * wrapping_assign_add() - Intentionally perform a wrapping increment assignment + * @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 = &(var); \ + *__ptr = 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; \ }) +/** + * wrapping_assign_sub() - Intentionally perform a wrapping decrement assign + * @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 = &(var); \ + *__ptr = 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) = { "Unexpected wrap " #op " macro side-effect!\n"); \ } while (0) +static int global_counter; +static void bump_counter(void) +{ + global_counter++; +} + +static int get_index(void) +{ + volatile int index = 0; + bump_counter(); + return index; +} + +#define check_self_op(fmt, op, sym, a, b) do { \ + typeof(a + 0) _a = a; \ + typeof(b + 0) _b = b; \ + typeof(a + 0) _a_sym = a; \ + typeof(a + 0) _a_orig[1] = { a }; \ + typeof(b + 0) _b_orig = b; \ + typeof(b + 0) _b_bump = b + 1; \ + typeof(a + 0) _r; \ + \ + _a_sym sym _b; \ + _r = wrapping_ ## op(_a, _b); \ + KUNIT_EXPECT_TRUE_MSG(test, _r == _a_sym, \ + "expected "fmt" "#op" "fmt" == "fmt", got "fmt"\n", \ + a, b, _a_sym, _r); \ + KUNIT_EXPECT_TRUE_MSG(test, _a == _a_sym, \ + "expected "fmt" "#op" "fmt" == "fmt", got "fmt"\n", \ + a, b, _a_sym, _a); \ + /* Check for internal macro side-effects. */ \ + global_counter = 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 struct 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, +=, p->a, p->b); \ + check_self_op(fmt, assign_add, +=, p->b, p->a); \ + check_self_op(fmt, assign_sub, -=, p->a, p->b); \ } \ \ static void n ## _overflow_test(struct kunit *test) { \