linux-kernel - Re: [PATCH] pwm: mtk_disp: fix disp

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <152b6912-ce2f-5580-1e2a-550a6fd7e6ed@collabora.com>
Date:   Thu, 6 Jul 2023 14:45:16 +0200
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Alexandre Mergnat <amergnat@...libre.com>,
        Shuijing Li <shuijing.li@...iatek.com>,
        thierry.reding@...il.com, u.kleine-koenig@...gutronix.de,
        matthias.bgg@...il.com
Cc:     devicetree@...r.kernel.org, linux-pwm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org,
        Project_Global_Chrome_Upstream_Group@...iatek.com,
        jitao.shi@...iatek.com
Subject: Re: [PATCH] pwm: mtk_disp: fix disp_pwm coverity issue

Il 06/07/23 14:29, Alexandre Mergnat ha scritto:
> 
> 
> On 06/07/2023 12:04, Shuijing Li wrote:
>> There is a coverity issue in the original mtk_disp_pwm_get_state()
>> function. In function call DIV64_U64_ROUND_UP, division by expression
>> Which may be zero has undefined behavior.
>> Fix this accordingly.
>>
>> Signed-off-by: Shuijing Li <shuijing.li@...iatek.com>
>> ---
>>   drivers/pwm/pwm-mtk-disp.c | 9 ++++++++-
>>   1 file changed, 8 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/pwm/pwm-mtk-disp.c b/drivers/pwm/pwm-mtk-disp.c
>> index 79e321e96f56..ca00058a6ef4 100644
>> --- a/drivers/pwm/pwm-mtk-disp.c
>> +++ b/drivers/pwm/pwm-mtk-disp.c
>> @@ -196,6 +196,14 @@ static int mtk_disp_pwm_get_state(struct pwm_chip *chip,
>>           return err;
>>       }
>> +    rate = clk_get_rate(mdp->clk_main);
>> +    if (rate <= 0) {
>> +        dev_err(chip->dev, "Can't get rate: %pe\n", ERR_PTR(rate));
>> +        clk_disable_unprepare(mdp->clk_mm);
>> +        clk_disable_unprepare(mdp->clk_main);
>> +        return err;
>> +    }
>> +
>>       /*
>>        * Apply DISP_PWM_DEBUG settings to choose whether to enable or disable
>>        * registers double buffer and manual commit to working register before
>> @@ -206,7 +214,6 @@ static int mtk_disp_pwm_get_state(struct pwm_chip *chip,
>>                        mdp->data->bls_debug_mask,
>>                        mdp->data->bls_debug_mask);
>> -    rate = clk_get_rate(mdp->clk_main);
>>       con0 = readl(mdp->base + mdp->data->con0);
>>       con1 = readl(mdp->base + mdp->data->con1);
>>       pwm_en = readl(mdp->base + DISP_PWM_EN);
> 
> IMHO, it should be done int the function `mtk_disp_pwm_apply` too.
> Do you agree ?
> 

I think that realistically this will never happen.

We're getting the clk_main clock's handle at probe time (or fail and get out),
then the PWM clock never has the CLK_GET_RATE_NOCACHE flag, as there wouldn't
be any reason to not cache the rates for this clock.
But even if we had the CLK_GET_RATE_NOCACHE flag, it wouldn't change much, as
our validation actually happens at probe time...

This means that our call to clk_get_rate is guaranteed to have a not NULL
pointer to this clock's `struct clk_core` and, unless the declaration of
this clock in the clock controller driver was wrong, for it, or for its
parent, the branch...

	if (!core->num_parents || core->parent)
		return core->rate;

...is always satisfied, so, in the end, this instance of clk_get_rate() can't
really return zero.
If you got such an issue, I suggest to check what the problem is, as it is
likely to be outside of this driver.


...that, besides the fact that the proposed code is incorrect, as clk_get_rate()
returns an `unsigned long`, so `rate` can never be less than zero, anyway.


Cheers,
Angelo