powercap: make attributes only readable by root

As power consumption can be used as a side-channel attack to get access to
sensitive data, make access to powercap privileged by default.

CVE-2020-8694
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Marcelo Cerri <marcelo.cerri@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

drivers/powercap/powercap_sys.c

@@ -224,46 +224,46 @@ static int seed_constraint_attributes(void)
 
 	for (i = 0; i < MAX_CONSTRAINTS_PER_ZONE; ++i) {
 		ret = create_constraint_attribute(i, "power_limit_uw",
-					S_IWUSR | S_IRUGO,
+					S_IWUSR | S_IRUSR,
 					&constraint_attrs[i].power_limit_attr,
 					show_constraint_power_limit_uw,
 					store_constraint_power_limit_uw);
 		if (ret)
 			goto err_alloc;
 		ret = create_constraint_attribute(i, "time_window_us",
-					S_IWUSR | S_IRUGO,
+					S_IWUSR | S_IRUSR,
 					&constraint_attrs[i].time_window_attr,
 					show_constraint_time_window_us,
 					store_constraint_time_window_us);
 		if (ret)
 			goto err_alloc;
-		ret = create_constraint_attribute(i, "name", S_IRUGO,
+		ret = create_constraint_attribute(i, "name", S_IRUSR,
 				&constraint_attrs[i].name_attr,
 				show_constraint_name,
 				NULL);
 		if (ret)
 			goto err_alloc;
-		ret = create_constraint_attribute(i, "max_power_uw", S_IRUGO,
+		ret = create_constraint_attribute(i, "max_power_uw", S_IRUSR,
 				&constraint_attrs[i].max_power_attr,
 				show_constraint_max_power_uw,
 				NULL);
 		if (ret)
 			goto err_alloc;
-		ret = create_constraint_attribute(i, "min_power_uw", S_IRUGO,
+		ret = create_constraint_attribute(i, "min_power_uw", S_IRUSR,
 				&constraint_attrs[i].min_power_attr,
 				show_constraint_min_power_uw,
 				NULL);
 		if (ret)
 			goto err_alloc;
 		ret = create_constraint_attribute(i, "max_time_window_us",
-				S_IRUGO,
+				S_IRUSR,
 				&constraint_attrs[i].max_time_window_attr,
 				show_constraint_max_time_window_us,
 				NULL);
 		if (ret)
 			goto err_alloc;
 		ret = create_constraint_attribute(i, "min_time_window_us",
-				S_IRUGO,
+				S_IRUSR,
 				&constraint_attrs[i].min_time_window_attr,
 				show_constraint_min_time_window_us,
 				NULL);
@@ -362,23 +362,29 @@ static void create_power_zone_common_attributes(
 	int count = 0;
 
 	power_zone->zone_dev_attrs[count++] = &dev_attr_name.attr;
-	if (power_zone->ops->get_max_energy_range_uj)
+	if (power_zone->ops->get_max_energy_range_uj) {
+		dev_attr_max_energy_range_uj.attr.mode = S_IRUSR;
 		power_zone->zone_dev_attrs[count++] =
 					&dev_attr_max_energy_range_uj.attr;
+	}
 	if (power_zone->ops->get_energy_uj) {
 		if (power_zone->ops->reset_energy_uj)
-			dev_attr_energy_uj.attr.mode = S_IWUSR | S_IRUGO;
+			dev_attr_energy_uj.attr.mode = S_IWUSR | S_IRUSR;
 		else
-			dev_attr_energy_uj.attr.mode = S_IRUGO;
+			dev_attr_energy_uj.attr.mode = S_IRUSR;
 		power_zone->zone_dev_attrs[count++] =
 					&dev_attr_energy_uj.attr;
 	}
-	if (power_zone->ops->get_power_uw)
+	if (power_zone->ops->get_power_uw) {
+		dev_attr_power_uw.attr.mode = S_IRUSR;
 		power_zone->zone_dev_attrs[count++] =
 					&dev_attr_power_uw.attr;
-	if (power_zone->ops->get_max_power_range_uw)
+	}
+	if (power_zone->ops->get_max_power_range_uw) {
+		dev_attr_max_power_range_uw.attr.mode = S_IRUSR;
 		power_zone->zone_dev_attrs[count++] =
 					&dev_attr_max_power_range_uw.attr;
+	}
 	power_zone->zone_dev_attrs[count] = NULL;
 	power_zone->zone_attr_count = count;
 }