From: Guenter Roeck Date: Tue, 4 Aug 2026 03:48:11 +0000 (-0700) Subject: hwmon: (corsair-psu) Fix linear11 calculation X-Git-Url: http://git.ipfire.org/gitweb/?a=commitdiff_plain;h=c6c4234928d2eb4f61fecb61067e612d9bdbd2ff;p=thirdparty%2Fkernel%2Flinux.git hwmon: (corsair-psu) Fix linear11 calculation In corsairpsu_linear11_to_int(), the mantissa is extracted using bitwise operations and cast to s16 before being shifted left: static int corsairpsu_linear11_to_int(const u16 val, const int scale) { ... const int mant = (((s16)(val & 0x7ff)) << 5) >> 5; ... } Due to C integer promotion rules, the masked value (which is always positive) is promoted to a 32-bit integer before the left shift. As a result, the sign bit is never extended to bit 31 of the promoted integer. When the device hardware reports a negative temperature in Linear11 format (such as an ambient temperature probe reporting sub-zero), the negative mantissa is parsed incorrectly as a massive positive value. For example, -1 becomes 2047, which scales to 2047 degrees Celsius. Fix the problem by type casting the result of the left shift operation to s16. Another problem is left-shifting of negative values. In C, the result of left-shifting negative values is undefined. Use a multiplication instead to avoid the problem. Also use a local s64 variable to store temporary results, change the return value type from int to long, and clamp the final value to LONG_MIN and LONG_MAX to avoid under- and overflow issues while retaining as much information as possible. Reported-by: Sashiko Cc: Wilken Gottwalt Signed-off-by: Guenter Roeck Tested-by: Wilken Gottwalt Link: https://lore.kernel.org/r/20260804034811.2385506-1-linux@roeck-us.net Signed-off-by: Guenter Roeck --- diff --git a/drivers/hwmon/corsair-psu.c b/drivers/hwmon/corsair-psu.c index ebcaddf337d8..0cf072f86acb 100644 --- a/drivers/hwmon/corsair-psu.c +++ b/drivers/hwmon/corsair-psu.c @@ -137,13 +137,18 @@ struct corsairpsu_data { }; /* some values are SMBus LINEAR11 data which need a conversion */ -static int corsairpsu_linear11_to_int(const u16 val, const int scale) +static long corsairpsu_linear11_to_long(const u16 val, const int scale) { const int exp = ((s16)val) >> 11; - const int mant = (((s16)(val & 0x7ff)) << 5) >> 5; - const int result = mant * scale; + const int mant = ((s16)((val & 0x7ff) << 5)) >> 5; + s64 result = mant * scale; - return (exp >= 0) ? (result << exp) : (result >> -exp); + if (exp >= 0) + result *= (int)(1UL << exp); + else + result >>= -exp; + + return clamp(result, LONG_MIN, LONG_MAX); } /* the micro-controller uses percentage values to control pwm */ @@ -263,13 +268,13 @@ static int corsairpsu_get_value(struct corsairpsu_data *priv, u8 cmd, u8 rail, l case PSU_CMD_RAIL_AMPS: case PSU_CMD_TEMP0: case PSU_CMD_TEMP1: - *val = corsairpsu_linear11_to_int(tmp & 0xFFFF, 1000); + *val = corsairpsu_linear11_to_long(tmp & 0xFFFF, 1000); break; case PSU_CMD_FAN: - *val = corsairpsu_linear11_to_int(tmp & 0xFFFF, 1); + *val = corsairpsu_linear11_to_long(tmp & 0xFFFF, 1); break; case PSU_CMD_FAN_PWM_ENABLE: - *val = corsairpsu_linear11_to_int(tmp & 0xFFFF, 1); + *val = corsairpsu_linear11_to_long(tmp & 0xFFFF, 1); /* * 0 = automatic mode, means the micro-controller controls the fan using a plan * which can be modified, but changing this plan is not supported by this @@ -283,12 +288,12 @@ static int corsairpsu_get_value(struct corsairpsu_data *priv, u8 cmd, u8 rail, l *val = 2; break; case PSU_CMD_FAN_PWM: - *val = corsairpsu_linear11_to_int(tmp & 0xFFFF, 1); + *val = corsairpsu_linear11_to_long(tmp & 0xFFFF, 1); *val = corsairpsu_dutycycle_to_pwm(*val); break; case PSU_CMD_RAIL_WATTS: case PSU_CMD_TOTAL_WATTS: - *val = corsairpsu_linear11_to_int(tmp & 0xFFFF, 1000000); + *val = corsairpsu_linear11_to_long(tmp & 0xFFFF, 1000000); break; case PSU_CMD_TOTAL_UPTIME: case PSU_CMD_UPTIME: