From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pj1-f43.google.com (mail-pj1-f43.google.com [209.85.216.43]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6B335411A00 for ; Wed, 29 Jul 2026 16:26:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.216.43 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785342377; cv=none; b=iOPs2cLzh6Uz9+QWNAX7eeGplFeNUl+qPhU6PcZiPVBVQXQF+h+sD0mzCAK3u5/Z5ZDh1ejVQYBcRMQpg0GpHW+lO3kmBBnfG4ZQxZVzbC5XX/+zro4vjc3qFgB0v6J22+wFaUSCiOta6BXYZr5FgWk1Gwmarux3T5teMxZ8Gjg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785342377; c=relaxed/simple; bh=95g2Up5/imKiObVCxkbw85lGqHoF9oj1780LHUtvc2k=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Rk3b2EAhym3qkZRxYIrpSrc4RPV2m5pmBtnO9uXUD18Z8Jk8wd7LgSxze4LblR3NRDdxJoK7JbWlGqlt5kE7wDqLSrXGw0qD92O7YuUK2+SO0tz2AHm0jWP/vV+0bkl7uhQnhq70vLVyF8L57Bsj39P6EfC6W2PBVAlbILaubV8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=roeck-us.net; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=ff2brwF+; arc=none smtp.client-ip=209.85.216.43 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=roeck-us.net Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="ff2brwF+" Received: by mail-pj1-f43.google.com with SMTP id 98e67ed59e1d1-38125cebfdaso1535715a91.1 for ; Wed, 29 Jul 2026 09:26:14 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1785342373; x=1785947173; darn=vger.kernel.org; h=content-transfer-encoding:content-type:in-reply-to:autocrypt:from :content-language:references:cc:to:subject:user-agent:mime-version :date:message-id:sender:from:to:cc:subject:date:message-id:reply-to :content-type; bh=w0QKfFF6SybzHh4NHRd13vYkPnBaPdyFedjE+mfxuW0=; b=ff2brwF+d3jIUJ1NLcrXa1vnRnngUmV3jtCBcGLidqBqEJk6jpstSFXusYxdspr++r S1PAUnRad1i7TFkkhDnZEEHdoKfi89QQ9WXYWaUoNyc/GrswTrDqVBRiFQVY1n0RX/Zt o9UAKTwQVSeV5SIhz3IcS2wmHQDJ4BgOWl/2Yn7musb01bpiZOk39RwzOwNVHO2Fk3uH CrNC0roUnXaronrvYBUqS/MD8wAJwP3s99lIxIHrfqGEHmWDWszgQS0S7N6o7snT+NlL /SkbmuzEVDNMLkiPB9+/GF1ChAQeP0Te1c2HxCrCQwFrxQgvNL3nOUPpxHR/HlemdoIO bnqg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1785342373; x=1785947173; h=content-transfer-encoding:content-type:in-reply-to:autocrypt:from :content-language:references:cc:to:subject:user-agent:mime-version :date:message-id:sender:x-gm-gg:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to:content-type; bh=w0QKfFF6SybzHh4NHRd13vYkPnBaPdyFedjE+mfxuW0=; b=jqnyAmps9Fi2WRYD4S/ztuNB9B1aPrSg/RJWZJkPlM387i0pIgKMLDqy+pGicgXIye Lxg/4XP21LbwQ3U1IIzcNY6Q/qmLGjJwMJqCG+TgCnQZLN1I1e9SZq9UINnMNt5B6hrZ Hl0a5OABjFFiS5qEmNkc19Pc60d/OBfad0VcCwa7UpsTblXIAx60+ItuPPwyA+qXcq7c QJswldNQayJFfmEsUaC1YWOXqLySDZ5VkFjC3Z506C/VsH36XCj78r5QKD4BZpLoUDW/ bRBQfEWNpZMxrWZ+GwKWkDZxO0f2RC0Pw+owbusZYEh/mfPO/y9UWbfSbQOcZkrBdh4i v4NQ== X-Forwarded-Encrypted: i=1; AHgh+RpMtPxnuVhOS7+fYo8GbM0pXMzc6j8mK7B+m3jGv8P2qmOzCK0G46ek0jGCu0AITv9tujalGOg+rXZ2vRo=@vger.kernel.org X-Gm-Message-State: AOJu0YwFw2Dbti/vQcquaHWhXQAKn4znxTSWAwKHFRRvwPhzcMLPX4eN /GD5pqn1IkTQLpOFXPDHyzlsC7HwAdjkox3JKfrLd0JJ1PTW4rgJb+MwHasDZw== X-Gm-Gg: AR+sD11Onjy/9gUZotbBQcFbt7vGSAR13b0BGfW/gMPjYymlfM7V/irORZ1r58Ny6Yl sJpnKYtALqTqFqawQbq+9dWbvsvt2oXuJcXomNdhD0OLHWUTUKrHTsFkwhFciWK0aV4jrOFhRCh jCD/Cxc5dWpm93V61QseTLJVbAyoBc6+/SR0jHEWYMx/kk6jsi0NsgTu0OksWOuJmWDtVDDXkl2 jImB0of3KYkLLoIF+wpgpZpY2KE7K2TMNjaJKXIIk41UwavnL0uTeQsvpW8971tcKelEhmkw8TL pk2+sZnCJP6nIg3l8D8OZ5WXEP7FDyN97Sj60MobAL/7ATuxcXXQaz93RJkmExc4zh07scYGyq2 2lTnnN2T/xQtlNIMo38u9fHN4N04qArSU5h7IME/zYiaw/3bFSxNUlAUJ9mC5h310AcoLt9fJKG 1yYUoS2HD5mjFW1NNHsiDnhWbvdaqIFPB9tmXKD4K5eBKfQimIrQtlFljk5/474v7FEvtCnX8Vh Q6MS/SMaDKKNB+4aRMmYX+y7oPCUfaGm0/hmw== X-Received: by 2002:a17:90b:5205:b0:38e:6f90:eabd with SMTP id 98e67ed59e1d1-38f6a3d599fmr8698559a91.5.1785342372800; Wed, 29 Jul 2026 09:26:12 -0700 (PDT) Received: from ?IPV6:2600:1700:e321:62f0:da43:aeff:fecc:bfd5? ([2600:1700:e321:62f0:da43:aeff:fecc:bfd5]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-13e72735084sm10770491c88.12.2026.07.29.09.26.11 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 29 Jul 2026 09:26:12 -0700 (PDT) Sender: Guenter Roeck Message-ID: <8cccd303-1af3-4bc6-afda-2ebf33c41958@roeck-us.net> Date: Wed, 29 Jul 2026 09:26:11 -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?= Cc: Benson Leung , 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> <0fbf7f69-bb90-4209-b9d5-258759711496@roeck-us.net> <63f9c782-3e4e-468e-a31f-901d1e2ff40b@t-8ch.de> 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: <63f9c782-3e4e-468e-a31f-901d1e2ff40b@t-8ch.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 7/29/26 08:40, Thomas Weißschuh wrote: > On 2026-07-28 08:02:28-0700, Guenter Roeck wrote: >> 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 ? > > It will never overflow. And the compiler knows this and optimizes away > all the overflow checks. Otherwise the build would straight up fail to > the BUILD_BUG()s below. > > The idea was that not everyone reading this code needs to do the > calculations and double-check. > No, sorry. You accomplished the opposite: You made me re-check the calculations because it was obvious to me that there can be no overflow. So you wasted my time. I am absolutely opposed to unnecessary checks, even if they are compiled away. Guenter