linux-kernel - Re: [PATCH v1 1/4] hwmon: (acpi_power_meter) Fix using uninitialized variables

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

Message-ID: <f9fc4989-f416-4d88-bc3e-ab7b9fddb4d9@roeck-us.net>
Date: Mon, 25 Nov 2024 20:04:14 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: "lihuisong (C)" <lihuisong@...wei.com>, linux-hwmon@...r.kernel.org,
 linux-kernel@...r.kernel.org
Cc: jdelvare@...e.com, liuyonglong@...wei.com, zhanjie9@...ilicon.com,
 zhenglifeng1@...wei.com
Subject: Re: [PATCH v1 1/4] hwmon: (acpi_power_meter) Fix using uninitialized
 variables

On 11/25/24 17:56, lihuisong (C) wrote:
> Hi Guente,
> 
> Thanks for your timely review.
> 
> 在 2024/11/26 0:03, Guenter Roeck 写道:
>> On 11/25/24 01:34, Huisong Li wrote:
>>> The 'power1_alarm' attribute uses the 'power' and 'cap' in the
>>> acpi_power_meter_resource structure. However, these two fields are just
>>> updated when user query 'power' and 'cap' attribute, or hardware enforced
>>> limit. If user directly query the 'power1_alarm' attribute without queryng
>>> above two attributes, driver will use the uninitialized variables to judge.
>>> In addition, the 'power1_alarm' attribute needs to update power and cap to
>>> show the real state.
>>>
>>> Signed-off-by: Huisong Li <lihuisong@...wei.com>
>>> ---
>>>   drivers/hwmon/acpi_power_meter.c | 10 ++++++++++
>>>   1 file changed, 10 insertions(+)
>>>
>>> diff --git a/drivers/hwmon/acpi_power_meter.c b/drivers/hwmon/acpi_power_meter.c
>>> index 2f1c9d97ad21..4c3314e35d30 100644
>>> --- a/drivers/hwmon/acpi_power_meter.c
>>> +++ b/drivers/hwmon/acpi_power_meter.c
>>> @@ -396,6 +396,9 @@ static ssize_t show_val(struct device *dev,
>>>       struct acpi_device *acpi_dev = to_acpi_device(dev);
>>>       struct acpi_power_meter_resource *resource = acpi_dev->driver_data;
>>>       u64 val = 0;
>>> +    int ret;
>>> +
>>> +    guard(mutex)(&resource->lock);
>>>         switch (attr->index) {
>>>       case 0:
>>> @@ -423,6 +426,13 @@ static ssize_t show_val(struct device *dev,
>>>               val = 0;
>>>           break;
>>>       case 6:
>>> +        ret = update_meter(resource);
>>> +        if (ret)
>>> +            return ret;
>>> +        ret = update_cap(resource);
>>> +        if (ret)
>>> +            return ret;
>>> +
>>>           if (resource->power > resource->cap)
>>>               val = 1;
>>>           else
>>
>>
>> While technically correct, the implementation of this attribute defeats its
>> purpose. It is supposed to reflect the current status as reported by the
>> hardware. A real fix would be to use the associated notification to set or
>> reset a status flag, and to report the current value of that flag as reported
>> by the hardware.
> I know what you mean.
> The Notify(power_meter, 0x83) is supposed to meet your proposal IIUC.
> It's good, but it depands on hardware support notification.
>>
>> If there is no notification support, the attribute should not even exist,
>> unless there is a means to retrieve its value from ACPI (the status itself,
>> not by comparing temperature values).
> Currently, the 'power1_alarm' attribute is created just when platform support the power meter meassurement(bit0 of the supported capabilities in _PMC).
> And it doesn't see if the platform support notifications.
>  From the current implementation of this driver, this sysfs can also reflect the status by comparing power and cap,
> which is good to the platform that support hardware limit from some out-of-band mechanism but doesn't support any notification.
> 

The point is that this can also be done from userspace. Hardware monitoring drivers
are supposed to provide hardware attributes, not software attributes derived from it.

Guenter