linux-hardening - [PATCH v7 1/3] overflow: Adjust check_*_overflow() kern-doc to reflect results

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Date: Wed, 14 Feb 2024 11:46:01 -0800
From: Kees Cook <keescook@...omium.org>
To: Andy Shevchenko <andy@...nel.org>
Cc: Kees Cook <keescook@...omium.org>,
	"Gustavo A . R . Silva" <gustavoars@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	linux-hardening@...r.kernel.org,
	Rasmus Villemoes <rasmus.villemoes@...vas.dk>,
	Marco Elver <elver@...gle.com>,
	Eric Biggers <ebiggers@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: [PATCH v7 1/3] overflow: Adjust check_*_overflow() kern-doc to reflect results

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 <gustavoars@...nel.org>
Signed-off-by: Kees Cook <keescook@...omium.org>
---
Cc: Mark Rutland <mark.rutland@....com>
Cc: linux-hardening@...r.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(bool 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(bool 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 considered
- * "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 whether
+ * 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(bool 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 whether
+ * wrap-around occurred.
  */
 #define check_mul_overflow(a, b, d)	\
 	__must_check_overflow(__builtin_mul_overflow(a, b, d))
-- 
2.34.1