[PATCH v2] thermal: cpufreq_cooling: fix slab OOB issue

[Michael Kao]

From: brian-sy yang <brian-sy.yang at mediatek.com>

Slab OOB issue is scanned by KASAN in cpu_power_to_freq().
If power is limited below the power of OPP0 in EM table,
it will cause slab out-of-bound issue with negative array
index.

Return the lowest frequency if limited power cannot found
a suitable OPP in EM table to fix this issue.

Backtrace:
[<ffffffd02d2a37f0>] die+0x104/0x5ac
[<ffffffd02d2a5630>] bug_handler+0x64/0xd0
[<ffffffd02d288ce4>] brk_handler+0x160/0x258
[<ffffffd02d281e5c>] do_debug_exception+0x248/0x3f0
[<ffffffd02d284488>] el1_dbg+0x14/0xbc
[<ffffffd02d75d1d4>] __kasan_report+0x1dc/0x1e0
[<ffffffd02d75c2e0>] kasan_report+0x10/0x20
[<ffffffd02d75def8>] __asan_report_load8_noabort+0x18/0x28
[<ffffffd02e6fce5c>] cpufreq_power2state+0x180/0x43c
[<ffffffd02e6ead80>] power_actor_set_power+0x114/0x1d4
[<ffffffd02e6fac24>] allocate_power+0xaec/0xde0
[<ffffffd02e6f9f80>] power_allocator_throttle+0x3ec/0x5a4
[<ffffffd02e6ea888>] handle_thermal_trip+0x160/0x294
[<ffffffd02e6edd08>] thermal_zone_device_check+0xe4/0x154
[<ffffffd02d351cb4>] process_one_work+0x5e4/0xe28
[<ffffffd02d352f44>] worker_thread+0xa4c/0xfac
[<ffffffd02d360124>] kthread+0x33c/0x358
[<ffffffd02d289940>] ret_from_fork+0xc/0x18

Fixes: 371a3bc79c11b ("thermal/drivers/cpufreq_cooling: Fix wrong frequency converted from power")
Signed-off-by: brian-sy yang <brian-sy.yang at mediatek.com>
Signed-off-by: Michael Kao <michael.kao at mediatek.com>
Reviewed-by: Lukasz Luba <lukasz.luba at arm.com>
---

Changes from v1:
- add fixes tag
- add reviewed-by

 drivers/thermal/cpufreq_cooling.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/thermal/cpufreq_cooling.c b/drivers/thermal/cpufreq_cooling.c
index cc2959f22f01..fb33b3480a8f 100644
--- a/drivers/thermal/cpufreq_cooling.c
+++ b/drivers/thermal/cpufreq_cooling.c
@@ -123,7 +123,7 @@ static u32 cpu_power_to_freq(struct cpufreq_cooling_device *cpufreq_cdev,
 {
 	int i;
 
-	for (i = cpufreq_cdev->max_level; i >= 0; i--) {
+	for (i = cpufreq_cdev->max_level; i > 0; i--) {
 		if (power >= cpufreq_cdev->em->table[i].power)
 			break;
 	}
-- 
2.18.0