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([2600:1700:e321:62f0:da43:aeff:fecc:bfd5]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-314bc3e1255sm66792348eec.4.2026.07.28.08.02.29 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 28 Jul 2026 08:02:30 -0700 (PDT) Sender: Guenter Roeck Message-ID: <0fbf7f69-bb90-4209-b9d5-258759711496@roeck-us.net> Date: Tue, 28 Jul 2026 08:02:28 -0700 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] hwmon: (cros_ec) Handle temperature conversion overflows To: =?UTF-8?Q?Thomas_Wei=C3=9Fschuh?= , Benson Leung Cc: Guenter Roeck , chrome-platform@lists.linux.dev, linux-hwmon@vger.kernel.org, linux-kernel@vger.kernel.org References: <20260728-cros_ec-hwmon-overflow-v2-1-d24e24d0792b@weissschuh.net> Content-Language: en-US From: Guenter Roeck Autocrypt: addr=linux@roeck-us.net; keydata= xsFNBE6H1WcBEACu6jIcw5kZ5dGeJ7E7B2uweQR/4FGxH10/H1O1+ApmcQ9i87XdZQiB9cpN RYHA7RCEK2dh6dDccykQk3bC90xXMPg+O3R+C/SkwcnUak1UZaeK/SwQbq/t0tkMzYDRxfJ7 nyFiKxUehbNF3r9qlJgPqONwX5vJy4/GvDHdddSCxV41P/ejsZ8PykxyJs98UWhF54tGRWFl 7i1xvaDB9lN5WTLRKSO7wICuLiSz5WZHXMkyF4d+/O5ll7yz/o/JxK5vO/sduYDIlFTvBZDh gzaEtNf5tQjsjG4io8E0Yq0ViobLkS2RTNZT8ICq/Jmvl0SpbHRvYwa2DhNsK0YjHFQBB0FX IdhdUEzNefcNcYvqigJpdICoP2e4yJSyflHFO4dr0OrdnGLe1Zi/8Xo/2+M1dSSEt196rXaC kwu2KgIgmkRBb3cp2vIBBIIowU8W3qC1+w+RdMUrZxKGWJ3juwcgveJlzMpMZNyM1jobSXZ0 VHGMNJ3MwXlrEFPXaYJgibcg6brM6wGfX/LBvc/haWw4yO24lT5eitm4UBdIy9pKkKmHHh7s jfZJkB5fWKVdoCv/omy6UyH6ykLOPFugl+hVL2Prf8xrXuZe1CMS7ID9Lc8FaL1ROIN/W8Vk BIsJMaWOhks//7d92Uf3EArDlDShwR2+D+AMon8NULuLBHiEUQARAQABzTJHdWVudGVyIFJv ZWNrIChMaW51eCBhY2NvdW50KSA8bGludXhAcm9lY2stdXMubmV0PsLBgQQTAQIAKwIbAwYL CQgHAwIGFQgCCQoLBBYCAwECHgECF4ACGQEFAmgrMyQFCSbODQkACgkQyx8mb86fmYGcWRAA oRwrk7V8fULqnGGpBIjp7pvR187Yzx+lhMGUHuM5H56TFEqeVwCMLWB2x1YRolYbY4MEFlQg VUFcfeW0OknSr1s6wtrtQm0gdkolM8OcCL9ptTHOg1mmXa4YpW8QJiL0AVtbpE9BroeWGl9v 2TGILPm9mVp+GmMQgkNeCS7Jonq5f5pDUGumAMguWzMFEg+Imt9wr2YA7aGen7KPSqJeQPpj onPKhu7O/KJKkuC50ylxizHzmGx+IUSmOZxN950pZUFvVZH9CwhAAl+NYUtcF5ry/uSYG2U7 DCvpzqOryJRemKN63qt1bjF6cltsXwxjKOw6CvdjJYA3n6xCWLuJ6yk6CAy1Ukh545NhgBAs rGGVkl6TUBi0ixL3EF3RWLa9IMDcHN32r7OBhw6vbul8HqyTFZWY2ksTvlTl+qG3zV6AJuzT WdXmbcKN+TdhO5XlxVlbZoCm7ViBj1+PvIFQZCnLAhqSd/DJlhaq8fFXx1dCUPgQDcD+wo65 qulV/NijfU8bzFfEPgYP/3LP+BSAyFs33y/mdP8kbMxSCjnLEhimQMrSSo/To1Gxp5C97fw5 3m1CaMILGKCmfI1B8iA8zd8ib7t1Rg0qCwcAnvsM36SkrID32GfFbv873bNskJCHAISK3Xkz qo7IYZmjk/IJGbsiGzxUhvicwkgKE9r7a1rOwU0ETofVZwEQALlLbQeBDTDbwQYrj0gbx3bq 7kpKABxN2MqeuqGr02DpS9883d/t7ontxasXoEz2GTioevvRmllJlPQERVxM8gQoNg22twF7 pB/zsrIjxkE9heE4wYfN1AyzT+AxgYN6f8hVQ7Nrc9XgZZe+8IkuW/Nf64KzNJXnSH4u6nJM J2+Dt274YoFcXR1nG76Q259mKwzbCukKbd6piL+VsT/qBrLhZe9Ivbjq5WMdkQKnP7gYKCAi pNVJC4enWfivZsYupMd9qn7Uv/oCZDYoBTdMSBUblaLMwlcjnPpOYK5rfHvC4opxl+P/Vzyz 6WC2TLkPtKvYvXmdsI6rnEI4Uucg0Au/Ulg7aqqKhzGPIbVaL+U0Wk82nz6hz+WP2ggTrY1w ZlPlRt8WM9w6WfLf2j+PuGklj37m+KvaOEfLsF1v464dSpy1tQVHhhp8LFTxh/6RWkRIR2uF I4v3Xu/k5D0LhaZHpQ4C+xKsQxpTGuYh2tnRaRL14YMW1dlI3HfeB2gj7Yc8XdHh9vkpPyuT nY/ZsFbnvBtiw7GchKKri2gDhRb2QNNDyBnQn5mRFw7CyuFclAksOdV/sdpQnYlYcRQWOUGY HhQ5eqTRZjm9z+qQe/T0HQpmiPTqQcIaG/edgKVTUjITfA7AJMKLQHgp04Vylb+G6jocnQQX JqvvP09whbqrABEBAAHCwWUEGAECAA8CGwwFAmgrMyQFCSbODQkACgkQyx8mb86fmYHlgg/9 H5JeDmB4jsreE9Bn621wZk7NMzxy9STxiVKSh8Mq4pb+IDu1RU2iLyetCY1TiJlcxnE362kj njrfAdqyPteHM+LU59NtEbGwrfcXdQoh4XdMuPA5ADetPLma3YiRa3VsVkLwpnR7ilgwQw6u dycEaOxQ7LUXCs0JaGVVP25Z2hMkHBwx6BlW6EZLNgzGI2rswSZ7SKcsBd1IRHVf0miwIFYy j/UEfAFNW+tbtKPNn3xZTLs3quQN7GdYLh+J0XxITpBZaFOpwEKV+VS36pSLnNl0T5wm0E/y scPJ0OVY7ly5Vm1nnoH4licaU5Y1nSkFR/j2douI5P7Cj687WuNMC6CcFd6j72kRfxklOqXw zvy+2NEcXyziiLXp84130yxAKXfluax9sZhhrhKT6VrD45S6N3HxJpXQ/RY/EX35neH2/F7B RgSloce2+zWfpELyS1qRkCUTt1tlGV2p+y2BPfXzrHn2vxvbhEn1QpQ6t+85FKN8YEhJEygJ F0WaMvQMNrk9UAUziVcUkLU52NS9SXqpVg8vgrO0JKx97IXFPcNh0DWsSj/0Y8HO/RDkGXYn FDMj7fZSPKyPQPmEHg+W/KzxSSfdgWIHF2QaQ0b2q1wOSec4Rti52ohmNSY+KNIW/zODhugJ np3900V20aS7eD9K8GTU0TGC1pyz6IVJwIE= In-Reply-To: <20260728-cros_ec-hwmon-overflow-v2-1-d24e24d0792b@weissschuh.net> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 7/28/26 03:17, Thomas Weißschuh wrote: > The calculations converting between the different temperature units can > overflow on 32-bit systems, resulting in incorrect data. > > Detect these overflows and handle them. > > The code is written in a way that there is a single conversion function > and the compiler can recognize when overflows are impossible (on 64-bit > and in cros_ec_hwmon_temp_to_millicelsius()). If the compiler detects > this, it will optimize away the overflow checks. > > Signed-off-by: Thomas Weißschuh > --- > Changes in v2: > - Drop already applied patch 1. > - Also handle overflow of u32 -> long. > - Clarify commit message wrt compiler optimizations. > - Use __always_inline over __flatten to allow the compiler to optimize > away more unnecessary overflow checks. > - Link to v1: https://patch.msgid.link/20260630-cros_ec-hwmon-overflow-v1-0-3d2ecd3eb0f2@weissschuh.net > --- > drivers/hwmon/cros_ec_hwmon.c | 31 ++++++++++++++++++++++++++----- > 1 file changed, 26 insertions(+), 5 deletions(-) > > diff --git a/drivers/hwmon/cros_ec_hwmon.c b/drivers/hwmon/cros_ec_hwmon.c > index 1337b646e022..004a8180b665 100644 > --- a/drivers/hwmon/cros_ec_hwmon.c > +++ b/drivers/hwmon/cros_ec_hwmon.c > @@ -5,11 +5,13 @@ > * Copyright (C) 2024 Thomas Weißschuh > */ > > +#include > #include > #include > #include > #include > #include > +#include > #include > #include > #include > @@ -151,14 +153,28 @@ static bool cros_ec_hwmon_is_error_temp(u8 temp) > /* This differs slightly from the variant in units.h to avoid rounding inconsistencies. */ > #define CROS_EC_HWMON_ABSOLUTE_ZERO_MILLICELSIUS (-273000) > > -static long cros_ec_hwmon_kelvin_to_millicelsius(long t) > +static __always_inline bool cros_ec_hwmon_kelvin_to_millicelsius_overflow(long t, long *ret) > { > - return t * MILLIDEGREE_PER_DEGREE + CROS_EC_HWMON_ABSOLUTE_ZERO_MILLICELSIUS; > + if (check_mul_overflow(t, MILLIDEGREE_PER_DEGREE, ret)) > + return true; > + > + if (check_add_overflow(*ret, CROS_EC_HWMON_ABSOLUTE_ZERO_MILLICELSIUS, ret)) > + return true; > + > + return false; return check_add_overflow(*ret, CROS_EC_HWMON_ABSOLUTE_ZERO_MILLICELSIUS, ret); > } > > static long cros_ec_hwmon_temp_to_millicelsius(u8 temp) The maximum value of "temp" is 255. > { > - return cros_ec_hwmon_kelvin_to_millicelsius((((long)temp) + EC_TEMP_SENSOR_OFFSET)); 255 + 200 = 455. 455 * 1000 = 455000 (not even counting the conversion from kelvin to C). How could this ever overflow ? > + long ret; > + > + if (check_add_overflow(temp, EC_TEMP_SENSOR_OFFSET, &ret)) > + BUILD_BUG(); > + > + if (cros_ec_hwmon_kelvin_to_millicelsius_overflow(ret, &ret)) > + BUILD_BUG(); > + > + return ret; > } > > static bool cros_ec_hwmon_attr_is_temp_threshold(u32 attr) > @@ -236,8 +252,13 @@ static int cros_ec_hwmon_read(struct device *dev, enum hwmon_sensor_types type, > ret = cros_ec_hwmon_read_temp_threshold(priv->cros_ec, channel, > cros_ec_hwmon_attr_to_thres(attr), > &threshold); > - if (ret == 0) > - *val = cros_ec_hwmon_kelvin_to_millicelsius(threshold); > + if (ret == 0) { > + if (overflows_type(threshold, long)) > + *val = LONG_MAX; > + > + if (cros_ec_hwmon_kelvin_to_millicelsius_overflow(threshold, val)) > + *val = LONG_MAX; > + } I agree with Sashiko - it does not make sense to call cros_ec_hwmon_kelvin_to_millicelsius_overflow() if it is already known that threshold overflowed. Personally I think this is way too complicated. An overflowing temperature above 255 degrees C does not make any sense, and returning LONG_MAX as temperature seems a bit odd. I would just have checked for some reasonable limit, such as if (threshold > 255 + 273) *val = 255000; else *val = cros_ec_hwmon_kelvin_to_millicelsius(threshold); If it does make sense to return LONG_MAX as temperature for some reason, that should be explained. Thanks, Guenter