linux-kernel - Re: [PATCH v2 1/2] hwmon: (lm90) Prevent integer overflow of temperature calculations

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Message-ID: <ffedf276-245b-1be6-4182-5d7a117eedd4@gmail.com>
Date:   Mon, 21 Jun 2021 18:35:10 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Zhang Rui <rui.zhang@...el.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Amit Kucheria <amitk@...nel.org>,
        Jean Delvare <jdelvare@...e.com>, linux-hwmon@...r.kernel.org,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-tegra@...r.kernel.org
Subject: Re: [PATCH v2 1/2] hwmon: (lm90) Prevent integer overflow of
 temperature calculations

21.06.2021 17:24, Guenter Roeck пишет:
> On Mon, Jun 21, 2021 at 03:14:40PM +0300, Dmitry Osipenko wrote:
>> 21.06.2021 15:12, Guenter Roeck пишет:
>>> On Mon, Jun 21, 2021 at 12:14:07AM +0300, Dmitry Osipenko wrote:
>>>> The minimum temperature value that is passed to the driver is unlimited
>>>> and value that is close to INT_MIN results in integer overflow of
>>>> temperature calculations made by the driver. Limit the value in order
>>>> to prevent the overflow. For now the overflow condition is harmless,
>>>> but thermal framework won't work properly once we will support the
>>>> set_trips() callback because it will pass INT_MIN value to the driver.
>>>>
>>> AFAICS that should only happen for lm99 because all other values
>>> are bound in the temp_to_xxx functions. Where else do you see an
>>> overflow (or underflow) ?
>>
>> You're correct that the overflow affects only lm99. But why we should
>> ignore it?
> 
> That isn't the point. The point is that you claimed there would be a
> generic underflow, which is not the case. That means we'll only need
> to apply the fix to the lm99 specific code (which unconditionally
> subtracts an offset from the provided value, causing the underflow).
> 
> Anyway, thanks for alerting me to the issue. As it turns out, there are
> other underflow issues in the driver. With improved module test scripts,
> I get:
> 
> Testing lm90 ...
> temp1_crit_hyst: Suspected underflow: [min=54000, read 85000, written -9223372036854775808]
> Testing lm99 ...
> temp1_crit_hyst: Suspected underflow: [min=96000, read 127000, written -9223372036854775808]
> temp2_crit: Suspected underflow: [min=-112000, read 143000, written -9223372036854775808]
> temp2_min: Suspected underflow: [min=-112000, read 143875, written -9223372036854775808]
> temp2_max: Suspected underflow: [min=-112000, read 143875, written -9223372036854775808]
> 
> So we'll need fixes for lm99 temp2_{min/max/crit} and for temp1_crit_hyst
> (the latter affects all chips supported by the driver).

I'll prepare v3 with the updated commit message and fixed
temp1_crit_hyst, thank you.