Received-SPF: pass (google.com: domain of linux-kernel+bounces-53882-linux.lists.archive=gmail.com@vger.kernel.org designates 139.178.88.99 as permitted sender) client-ip=139.178.88.99;
Message-ID: <992f0e89-3d24-4bc1-8850-e1314f031413@embeddedor.com>
Date: Mon, 5 Feb 2024 14:00:53 -0600
Precedence: bulk
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH v3 1/3] overflow: Adjust check_*_overflow() kern-doc to
 reflect results
Content-Language: en-US
To: Kees Cook <keescook@chromium.org>, linux-hardening@vger.kernel.org
Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>,
 Rasmus Villemoes <rasmus.villemoes@prevas.dk>,
 Mark Rutland <mark.rutland@arm.com>, Marco Elver <elver@google.com>,
 linux-kernel@vger.kernel.org
References: <20240205090854.make.507-kees@kernel.org>
 <20240205091233.1357377-1-keescook@chromium.org>
From: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
In-Reply-To: <20240205091233.1357377-1-keescook@chromium.org>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit


On 2/5/24 03:12, Kees Cook wrote:
> 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.
> 
> Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>
> Cc: linux-hardening@vger.kernel.org
> Signed-off-by: Kees Cook <keescook@chromium.org>

Better to be concise and direct. :)

Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>

Thanks!
-- 
Gustavo

> ---
>   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(bool 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(bool 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 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, which may wrap-around.
>    */
>   #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(bool 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-around.
>    */
>   #define check_mul_overflow(a, b, d)	\
>   	__must_check_overflow(__builtin_mul_overflow(a, b, d))