From: Kees Cook <keescook@chromium.org>
To: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Cc: Kees Cook <keescook@chromium.org>,
Mark Rutland <mark.rutland@arm.com>,
linux-hardening@vger.kernel.org,
"Gustavo A. R. Silva" <gustavoars@kernel.org>,
Nathan Chancellor <nathan@kernel.org>,
Bill Wendling <morbo@google.com>,
Justin Stitt <justinstitt@google.com>,
Miguel Ojeda <ojeda@kernel.org>, Marco Elver <elver@google.com>,
linux-kernel@vger.kernel.org, llvm@lists.linux.dev
Subject: [PATCH 4/5] overflow: Introduce add_wrap(), sub_wrap(), and mul_wrap()
Date: Mon, 29 Jan 2024 10:34:08 -0800 [thread overview]
Message-ID: <20240129183411.3791340-4-keescook@chromium.org> (raw)
In-Reply-To: <20240129182845.work.694-kees@kernel.org>
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:
add_wrap(int, 50, 50) == 2500
add_wrap(u8, 50, 50) == 196
Cc: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: linux-hardening@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
include/linux/overflow.h | 54 ++++++++++++++++++++++++++++++++++++++++
1 file changed, 54 insertions(+)
diff --git a/include/linux/overflow.h b/include/linux/overflow.h
index 3c46c648d2e8..4f945e9e7881 100644
--- a/include/linux/overflow.h
+++ b/include/linux/overflow.h
@@ -120,6 +120,24 @@ static inline bool __must_check __must_check_overflow(bool overflow)
check_add_overflow(var, offset, &__result); \
}))
+/**
+ * add_wrap() - Intentionally perform a wrapping addition
+ * @type: type to check overflow against
+ * @a: first addend
+ * @b: second addend
+ *
+ * Return the potentially wrapped-around addition without
+ * tripping any overflow sanitizers that may be enabled.
+ */
+#define add_wrap(type, a, b) \
+ ({ \
+ type __sum; \
+ if (check_add_overflow(a, b, &__sum)) { \
+ /* do nothing */ \
+ } \
+ __sum; \
+ })
+
/**
* check_sub_overflow() - Calculate subtraction with overflow checking
* @a: minuend; value to subtract from
@@ -133,6 +151,24 @@ 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 to check underflow against
+ * @a: minuend; value to subtract from
+ * @b: subtrahend; value to subtract from @a
+ *
+ * Return the potentially wrapped-around subtraction without
+ * tripping any overflow 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
@@ -146,6 +182,24 @@ 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 to check underflow against
+ * @a: first factor
+ * @b: second factor
+ *
+ * Return the potentially wrapped-around multiplication without
+ * tripping any overflow 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
--
2.34.1
next prev parent reply other threads:[~2024-01-29 18:34 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-29 18:34 [PATCH 0/5] overflow: Introduce wrapping helpers Kees Cook
2024-01-29 18:34 ` [PATCH 1/5] overflow: Adjust check_*_overflow() kern-doc to reflect results Kees Cook
2024-01-29 18:34 ` [PATCH 2/5] overflow: Expand check_add_overflow() for pointer addition Kees Cook
2024-01-29 18:34 ` [PATCH 3/5] overflow: Introduce add_would_overflow() Kees Cook
2024-01-29 18:34 ` Kees Cook [this message]
2024-01-29 20:08 ` [PATCH 4/5] overflow: Introduce add_wrap(), sub_wrap(), and mul_wrap() Rasmus Villemoes
2024-01-29 20:26 ` Kees Cook
2024-01-29 18:34 ` [PATCH 5/5] overflow: Introduce inc_wrap() and dec_wrap() Kees Cook
2024-01-29 20:16 ` Rasmus Villemoes
2024-01-29 21:56 ` Kees Cook
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