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Subject: Re: [PATCH] thermal: cpufreq_cooling: fix slab OOB issue
To:     Michael Kao <michael.kao@mediatek.com>, fan.chen@mediatek.com,
        Zhang Rui <rui.zhang@intel.com>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        linux-pm@vger.kernel.org, srv_heupstream@mediatek.com
Cc:     Eduardo Valentin <edubezval@gmail.com>,
        Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Matthias Brugger <matthias.bgg@gmail.com>, hsinyi@chromium.org,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        linux-mediatek@lists.infradead.org,
        brian-sy yang <brian-sy.yang@mediatek.com>
References: <20201223074849.1989-1-michael.kao@mediatek.com>
From:   Lukasz Luba <lukasz.luba@arm.com>
Message-ID: <010350df-e094-cf12-1c17-f56aa4b20b9f@arm.com>
Date:   Mon, 28 Dec 2020 10:28:31 +0000
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On 12/23/20 7:48 AM, Michael Kao wrote:
> From: brian-sy yang <brian-sy.yang@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

Thank you for looking at this and sending a fix.

It's worth to add the 'fixes' line:

Fixes: 371a3bc79c11b ("thermal/drivers/cpufreq_cooling: Fix wrong 
frequency converted from power")

IIRC that patch was sent to stable trees. Might be worth to check
and apply this fix.


> 
> Signed-off-by: brian-sy yang <brian-sy.yang@mediatek.com>


Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>


> ---
>   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;
>   	}
>