Commit 007be432 authored by Gui-Dong Han's avatar Gui-Dong Han Committed by Guenter Roeck
Browse files

hwmon: (max16065) Use READ/WRITE_ONCE to avoid compiler optimization induced race 



Simply copying shared data to a local variable cannot prevent data
races. The compiler is allowed to optimize away the local copy and
re-read the shared memory, causing a Time-of-Check Time-of-Use (TOCTOU)
issue if the data changes between the check and the usage.

To enforce the use of the local variable, use READ_ONCE() when reading
the shared data and WRITE_ONCE() when updating it. Apply these macros to
the three identified locations (curr_sense, adc, and fault) where local
variables are used for error validation, ensuring the value remains
consistent.

Reported-by: default avatarBen Hutchings <ben@decadent.org.uk>
Closes: https://lore.kernel.org/all/6fe17868327207e8b850cf9f88b7dc58b2021f73.camel@decadent.org.uk/


Fixes: f5bae264 ("hwmon: Driver for MAX16065 System Manager and compatibles")
Fixes: b8d5acdc ("hwmon: (max16065) Use local variable to avoid TOCTOU")
Cc: stable@vger.kernel.org
Signed-off-by: default avatarGui-Dong Han <hanguidong02@gmail.com>
Link: https://lore.kernel.org/r/20260203121443.5482-1-hanguidong02@gmail.com


Signed-off-by: default avatarGuenter Roeck <linux@roeck-us.net>
parent ddb2325e

drivers/hwmon/max16065.c

+13 −13
Original line number Diff line number Diff line
@@ -151,27 +151,27 @@ static struct max16065_data *max16065_update_device(struct device *dev) 
		int i;



		for (i = 0; i < data->num_adc; i++)

			data->adc[i]

			  = max16065_read_adc(client, MAX16065_ADC(i));

			WRITE_ONCE(data->adc[i],

				   max16065_read_adc(client, MAX16065_ADC(i)));



		if (data->have_current) {

			data->adc[MAX16065_NUM_ADC]

			  = max16065_read_adc(client, MAX16065_CSP_ADC);

			data->curr_sense

			  = i2c_smbus_read_byte_data(client,

						     MAX16065_CURR_SENSE);

			WRITE_ONCE(data->adc[MAX16065_NUM_ADC],

				   max16065_read_adc(client, MAX16065_CSP_ADC));

			WRITE_ONCE(data->curr_sense,

				   i2c_smbus_read_byte_data(client, MAX16065_CURR_SENSE));

		}



		for (i = 0; i < 2; i++)

			data->fault[i]

			  = i2c_smbus_read_byte_data(client, MAX16065_FAULT(i));

			WRITE_ONCE(data->fault[i],

				   i2c_smbus_read_byte_data(client, MAX16065_FAULT(i)));



		/*

		 * MAX16067 and MAX16068 have separate undervoltage and

		 * overvoltage alarm bits. Squash them together.

		 */

		if (data->chip == max16067 || data->chip == max16068)

			data->fault[0] |= data->fault[1];

			WRITE_ONCE(data->fault[0],

				   data->fault[0] | data->fault[1]);



		data->last_updated = jiffies;

		data->valid = true;
@@ -185,7 +185,7 @@ static ssize_t max16065_alarm_show(struct device *dev, 
{

	struct sensor_device_attribute_2 *attr2 = to_sensor_dev_attr_2(da);

	struct max16065_data *data = max16065_update_device(dev);

	int val = data->fault[attr2->nr];

	int val = READ_ONCE(data->fault[attr2->nr]);



	if (val < 0)

		return val;
@@ -203,7 +203,7 @@ static ssize_t max16065_input_show(struct device *dev, 
{

	struct sensor_device_attribute *attr = to_sensor_dev_attr(da);

	struct max16065_data *data = max16065_update_device(dev);

	int adc = data->adc[attr->index];

	int adc = READ_ONCE(data->adc[attr->index]);



	if (unlikely(adc < 0))

		return adc;
@@ -216,7 +216,7 @@ static ssize_t max16065_current_show(struct device *dev, 
				     struct device_attribute *da, char *buf)

{

	struct max16065_data *data = max16065_update_device(dev);

	int curr_sense = data->curr_sense;

	int curr_sense = READ_ONCE(data->curr_sense);



	if (unlikely(curr_sense < 0))

		return curr_sense;