mlxsw: thermal: Fix out-of-bounds memory accesses

Currently, mlxsw allows cooling states to be set above the maximum
cooling state supported by the driver:

 # cat /sys/class/thermal/thermal_zone2/cdev0/type
 mlxsw_fan
 # cat /sys/class/thermal/thermal_zone2/cdev0/max_state
 10
 # echo 18 > /sys/class/thermal/thermal_zone2/cdev0/cur_state
 # echo $?
 0

This results in out-of-bounds memory accesses when thermal state
transition statistics are enabled (CONFIG_THERMAL_STATISTICS=y), as the
transition table is accessed with a too large index (state) [1].

According to the thermal maintainer, it is the responsibility of the
driver to reject such operations [2].

Therefore, return an error when the state to be set exceeds the maximum
cooling state supported by the driver.

To avoid dead code, as suggested by the thermal maintainer [3],
partially revert commit a421ce08 ("mlxsw: core: Extend cooling
device with cooling levels") that tried to interpret these invalid
cooling states (above the maximum) in a special way. The cooling levels
array is not removed in order to prevent the fans going below 20% PWM,
which would cause them to get stuck at 0% PWM.

[1]
BUG: KASAN: slab-out-of-bounds in thermal_cooling_device_stats_update+0x271/0x290
Read of size 4 at addr ffff8881052f7bf8 by task kworker/0:0/5

CPU: 0 PID: 5 Comm: kworker/0:0 Not tainted 5.15.0-rc3-custom-45935-gce1adf704b14 #122
Hardware name: Mellanox Technologies Ltd. "MSN2410-CB2FO"/"SA000874", BIOS 4.6.5 03/08/2016
Workqueue: events_freezable_power_ thermal_zone_device_check
Call Trace:
 dump_stack_lvl+0x8b/0xb3
 print_address_description.constprop.0+0x1f/0x140
 kasan_report.cold+0x7f/0x11b
 thermal_cooling_device_stats_update+0x271/0x290
 __thermal_cdev_update+0x15e/0x4e0
 thermal_cdev_update+0x9f/0xe0
 step_wise_throttle+0x770/0xee0
 thermal_zone_device_update+0x3f6/0xdf0
 process_one_work+0xa42/0x1770
 worker_thread+0x62f/0x13e0
 kthread+0x3ee/0x4e0
 ret_from_fork+0x1f/0x30

Allocated by task 1:
 kasan_save_stack+0x1b/0x40
 __kasan_kmalloc+0x7c/0x90
 thermal_cooling_device_setup_sysfs+0x153/0x2c0
 __thermal_cooling_device_register.part.0+0x25b/0x9c0
 thermal_cooling_device_register+0xb3/0x100
 mlxsw_thermal_init+0x5c5/0x7e0
 __mlxsw_core_bus_device_register+0xcb3/0x19c0
 mlxsw_core_bus_device_register+0x56/0xb0
 mlxsw_pci_probe+0x54f/0x710
 local_pci_probe+0xc6/0x170
 pci_device_probe+0x2b2/0x4d0
 really_probe+0x293/0xd10
 __driver_probe_device+0x2af/0x440
 driver_probe_device+0x51/0x1e0
 __driver_attach+0x21b/0x530
 bus_for_each_dev+0x14c/0x1d0
 bus_add_driver+0x3ac/0x650
 driver_register+0x241/0x3d0
 mlxsw_sp_module_init+0xa2/0x174
 do_one_initcall+0xee/0x5f0
 kernel_init_freeable+0x45a/0x4de
 kernel_init+0x1f/0x210
 ret_from_fork+0x1f/0x30

The buggy address belongs to the object at ffff8881052f7800
 which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 1016 bytes inside of
 1024-byte region [ffff8881052f7800, ffff8881052f7c00)
The buggy address belongs to the page:
page:0000000052355272 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1052f0
head:0000000052355272 order:3 compound_mapcount:0 compound_pincount:0
flags: 0x200000000010200(slab|head|node=0|zone=2)
raw: 0200000000010200 ffffea0005034800 0000000300000003 ffff888100041dc0
raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8881052f7a80: 00 00 00 00 00 00 04 fc fc fc fc fc fc fc fc fc
 ffff8881052f7b00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8881052f7b80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
                                                                ^
 ffff8881052f7c00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8881052f7c80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc

[2] https://lore.kernel.org/linux-pm/9aca37cb-1629-5c67-1895-1fdc45c0244e@linaro.org/
[3] https://lore.kernel.org/linux-pm/af9857f2-578e-de3a-e62b-6baff7e69fd4@linaro.org/

CC: Daniel Lezcano <daniel.lezcano@linaro.org>
Fixes: a50c1e35 ("mlxsw: core: Implement thermal zone")
Fixes: a421ce08 ("mlxsw: core: Extend cooling device with cooling levels")
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Tested-by: Vadim Pasternak <vadimp@nvidia.com>
Link: https://lore.kernel.org/r/20211012174955.472928-1-idosch@idosch.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/mellanox/mlxsw/core_thermal.c

@@ -24,16 +24,8 @@
 #define MLXSW_THERMAL_ZONE_MAX_NAME	16
 #define MLXSW_THERMAL_TEMP_SCORE_MAX	GENMASK(31, 0)
 #define MLXSW_THERMAL_MAX_STATE	10
+#define MLXSW_THERMAL_MIN_STATE	2
 #define MLXSW_THERMAL_MAX_DUTY	255
-/* Minimum and maximum fan allowed speed in percent: from 20% to 100%. Values
- * MLXSW_THERMAL_MAX_STATE + x, where x is between 2 and 10 are used for
- * setting fan speed dynamic minimum. For example, if value is set to 14 (40%)
- * cooling levels vector will be set to 4, 4, 4, 4, 4, 5, 6, 7, 8, 9, 10 to
- * introduce PWM speed in percent: 40, 40, 40, 40, 40, 50, 60. 70, 80, 90, 100.
- */
-#define MLXSW_THERMAL_SPEED_MIN		(MLXSW_THERMAL_MAX_STATE + 2)
-#define MLXSW_THERMAL_SPEED_MAX		(MLXSW_THERMAL_MAX_STATE * 2)
-#define MLXSW_THERMAL_SPEED_MIN_LEVEL	2		/* 20% */
 
 /* External cooling devices, allowed for binding to mlxsw thermal zones. */
 static char * const mlxsw_thermal_external_allowed_cdev[] = {
@@ -646,49 +638,16 @@ static int mlxsw_thermal_set_cur_state(struct thermal_cooling_device *cdev,
 	struct mlxsw_thermal *thermal = cdev->devdata;
 	struct device *dev = thermal->bus_info->dev;
 	char mfsc_pl[MLXSW_REG_MFSC_LEN];
-	unsigned long cur_state, i;
 	int idx;
-	u8 duty;
 	int err;
 
+	if (state > MLXSW_THERMAL_MAX_STATE)
+		return -EINVAL;
+
 	idx = mlxsw_get_cooling_device_idx(thermal, cdev);
 	if (idx < 0)
 		return idx;
 
-	/* Verify if this request is for changing allowed fan dynamical
-	 * minimum. If it is - update cooling levels accordingly and update
-	 * state, if current state is below the newly requested minimum state.
-	 * For example, if current state is 5, and minimal state is to be
-	 * changed from 4 to 6, thermal->cooling_levels[0 to 5] will be changed
-	 * all from 4 to 6. And state 5 (thermal->cooling_levels[4]) should be
-	 * overwritten.
-	 */
-	if (state >= MLXSW_THERMAL_SPEED_MIN &&
-	    state <= MLXSW_THERMAL_SPEED_MAX) {
-		state -= MLXSW_THERMAL_MAX_STATE;
-		for (i = 0; i <= MLXSW_THERMAL_MAX_STATE; i++)
-			thermal->cooling_levels[i] = max(state, i);
-
-		mlxsw_reg_mfsc_pack(mfsc_pl, idx, 0);
-		err = mlxsw_reg_query(thermal->core, MLXSW_REG(mfsc), mfsc_pl);
-		if (err)
-			return err;
-
-		duty = mlxsw_reg_mfsc_pwm_duty_cycle_get(mfsc_pl);
-		cur_state = mlxsw_duty_to_state(duty);
-
-		/* If current fan state is lower than requested dynamical
-		 * minimum, increase fan speed up to dynamical minimum.
-		 */
-		if (state < cur_state)
-			return 0;
-
-		state = cur_state;
-	}
-
-	if (state > MLXSW_THERMAL_MAX_STATE)
-		return -EINVAL;
-
 	/* Normalize the state to the valid speed range. */
 	state = thermal->cooling_levels[state];
 	mlxsw_reg_mfsc_pack(mfsc_pl, idx, mlxsw_state_to_duty(state));
@@ -998,8 +957,7 @@ int mlxsw_thermal_init(struct mlxsw_core *core,
 
 	/* Initialize cooling levels per PWM state. */
 	for (i = 0; i < MLXSW_THERMAL_MAX_STATE; i++)
-		thermal->cooling_levels[i] = max(MLXSW_THERMAL_SPEED_MIN_LEVEL,
-						 i);
+		thermal->cooling_levels[i] = max(MLXSW_THERMAL_MIN_STATE, i);
 
 	thermal->polling_delay = bus_info->low_frequency ?
 				 MLXSW_THERMAL_SLOW_POLL_INT :