Message-ID: <84f0c52f-38ec-a2f3-cf1d-09f412f9542c@gmx.de>
Date:   Tue, 15 Feb 2022 22:00:33 +0100
From:   Armin Wolf <W_Armin@....de>
To:     Pali Rohár <pali@...nel.org>
Cc:     jdelvare@...e.com, linux@...ck-us.net, linux-hwmon@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/7] hwmon: (dell-smm) Allow for specifying fan control
 method as module parameter


Am 15.02.2022 um 21:31 schrieb Pali Rohár:
> On Tuesday 15 February 2022 21:19:17 Armin Wolf wrote:
>> Am 15.02.22 um 20:49 schrieb Pali Rohár:
>>> On Tuesday 15 February 2022 20:44:20 Armin Wolf wrote:
>>>> Am 15.02.22 um 20:19 schrieb Pali Rohár:
>>>>> On Tuesday 15 February 2022 20:11:07 Armin Wolf wrote:
>>>>>> Right now, the only way to test if setting manual/auto fan control works
>>>>>> is to edit and recompile the module, which may be too cumbersome for
>>>>>> the average user.
>>>>> There is also another way suitable for testing purposes which do not
>>>>> requires any kernel patch. Call iopl(3) syscall which changes I/O
>>>>> privilege level to 3 and which allows to poke I/O registers.
>>>>>
>>>> This is not possible under kernel lockdown/Secure Boot.
>>> Under Secure Boot it should be still possible.
>> Afaik, access to iopl() and ioperm() is blocked in this mode too.
>> This for example causes dell-bios-fan-control to fail when
>> the machine is booted in Secure Boot mode.
> Well, then it is the cost of the usage of Secure Boot. If you need
> additional functionality then disable it.
>
>>> With kernel lockdown, no kernel testing/debugging at HW level is
>>> acceptable due to security reasons, as it is against what kernel
>>> lockdown should achieve.
>>>
>> That is the reason i limited the number of selectable code pairs to
>> two which are known to work on a wide range of machines.
>> So users are unable to specify SMM commands, which are controlled by
>> the driver. If this still is to much, then we may drop this patch.
> This kernel driver dell-smm-hwmon should use same security model as
> other parts in kernel. So if kernel disallow user to specify custom
> parameters for io ports (those which are not provided by platform data)
> then it should be disabled also in this driver.
>
> It is really _bad_ practice to trying invent a security hole to the
> existing security model.

Understandable, i will drop this patch(es) then.

>>>>>> Allow for specifying the desired fan mode control method when loading
>>>>>> the module, but taint the kernel if so since there is the possibility
>>>>>> for strange side effects on non-whitelisted models.
>>>>>> Also update docs and kernel-parameters.txt accordingly.
>>>>>>
>>>>>> Tested on a Dell Inspiron 3505.
>>>>>>
>>>>>> Signed-off-by: Armin Wolf <W_Armin@....de>
>>>>>> ---
>>>>>>     .../admin-guide/kernel-parameters.txt         |  3 +++
>>>>>>     Documentation/hwmon/dell-smm-hwmon.rst        | 21 ++++++++++------
>>>>>>     drivers/hwmon/dell-smm-hwmon.c                | 25 +++++++++++++------
>>>>>>     3 files changed, 35 insertions(+), 14 deletions(-)
>>>>>>
>>>>>> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
>>>>>> index d68053db21cc..4f1b6c2b7ed1 100644
>>>>>> --- a/Documentation/admin-guide/kernel-parameters.txt
>>>>>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>>>>>> @@ -968,6 +968,9 @@
>>>>>>     	dell_smm_hwmon.fan_max=
>>>>>>     			[HW] Maximum configurable fan speed.
>>>>>>
>>>>>> +	dell_smm_hwmon.fan_mode_method=
>>>>>> +			[HW] Method to use for changing fan mode.
>>>>>> +
>>>>>>     	dfltcc=		[HW,S390]
>>>>>>     			Format: { on | off | def_only | inf_only | always }
>>>>>>     			on:       s390 zlib hardware support for compression on
>>>>>> diff --git a/Documentation/hwmon/dell-smm-hwmon.rst b/Documentation/hwmon/dell-smm-hwmon.rst
>>>>>> index beec88491171..564d99cda869 100644
>>>>>> --- a/Documentation/hwmon/dell-smm-hwmon.rst
>>>>>> +++ b/Documentation/hwmon/dell-smm-hwmon.rst
>>>>>> @@ -67,13 +67,16 @@ for your hardware. It is possible that codes that work for other
>>>>>>     laptops actually work for yours as well, or that you have to discover
>>>>>>     new codes.
>>>>>>
>>>>>> -Check the list ``i8k_whitelist_fan_control`` in file
>>>>>> -``drivers/hwmon/dell-smm-hwmon.c`` in the kernel tree: as a first
>>>>>> -attempt you can try to add your machine and use an already-known code
>>>>>> -pair. If, after recompiling the kernel, you see that ``pwm1_enable``
>>>>>> -is present and works (i.e., you can manually control the fan speed),
>>>>>> -then please submit your finding as a kernel patch, so that other users
>>>>>> -can benefit from it. Please see
>>>>>> +As a first step, you can load the module with the module parameter
>>>>>> +``fan_mode_method`` set to 1 to test if your hardware works with
>>>>>> +an already know method for disabling automatic BIOS fan control.
>>>>>> +If ``pwm1_enable`` is now present and works (i.e., you can
>>>>>> +manually control the fan speed), then please submit your finding
>>>>>> +as a kernel patch, so that other users can benefit from it.
>>>>>> +Just add your model to the list ``i8k_whitelist_fan_control`` in
>>>>>> +file ``drivers/hwmon/dell-smm-hwmon.c`` in the kernel tree and use
>>>>>> +the already known code pair.
>>>>>> +Please read
>>>>>>     :ref:`Documentation/process/submitting-patches.rst <submittingpatches>`
>>>>>>     for information on submitting patches.
>>>>>>
>>>>>> @@ -120,6 +123,10 @@ Module parameters
>>>>>>                        Maximum configurable fan speed. (default:
>>>>>>                        autodetect)
>>>>>>
>>>>>> +* fan_mode_method:uint
>>>>>> +                   Method to use for changing fan mode (default:
>>>>>> +                   from whitelist)
>>>>>> +
>>>>>>     Legacy ``/proc`` interface
>>>>>>     --------------------------
>>>>>>
>>>>>> diff --git a/drivers/hwmon/dell-smm-hwmon.c b/drivers/hwmon/dell-smm-hwmon.c
>>>>>> index 9949eeb79378..1c4cc516c8b2 100644
>>>>>> --- a/drivers/hwmon/dell-smm-hwmon.c
>>>>>> +++ b/drivers/hwmon/dell-smm-hwmon.c
>>>>>> @@ -111,6 +111,10 @@ static uint fan_max;
>>>>>>     module_param(fan_max, uint, 0);
>>>>>>     MODULE_PARM_DESC(fan_max, "Maximum configurable fan speed (default: autodetect)");
>>>>>>
>>>>>> +static uint fan_mode_method;
>>>>>> +module_param_unsafe(fan_mode_method, uint, 0);
>>>>>> +MODULE_PARM_DESC(fan_mode_method, "Method to use for changing fan mode (default: from whitelist)");
>>>>> No, please really do not introduce another kernel parameter for this
>>>>> driver. There are already many and we do not need to extend this list.
>> Since there are two code pairs, i could not reuse the force param for that.
>> Since the newly added pair is unused, should i remove it and reuse the
>> force param?
> For such things like this there is debugfs, if you really need to
> specify / provide custom values.
>
>>>>>> +
>>>>>>     struct smm_regs {
>>>>>>     	unsigned int eax;
>>>>>>     	unsigned int ebx;
>>>>>> @@ -677,7 +681,7 @@ static umode_t dell_smm_is_visible(const void *drvdata, enum hwmon_sensor_types
>>>>>>
>>>>>>     			break;
>>>>>>     		case hwmon_pwm_enable:
>>>>>> -			if (data->auto_fan)
>>>>>> +			if (data->auto_fan && data->manual_fan)
>>>>>>     				/*
>>>>>>     				 * There is no command for retrieve the current status
>>>>>>     				 * from BIOS, and userspace/firmware itself can change
>>>>>> @@ -1282,14 +1286,21 @@ static int __init dell_smm_probe(struct platform_device *pdev)
>>>>>>     	data->i8k_fan_max = fan_max ? : I8K_FAN_HIGH;	/* Must not be 0 */
>>>>>>     	data->i8k_pwm_mult = DIV_ROUND_UP(255, data->i8k_fan_max);
>>>>>>
>>>>>> -	fan_control = dmi_first_match(i8k_whitelist_fan_control);
>>>>>> -	if (fan_control && fan_control->driver_data) {
>>>>>> -		const struct i8k_fan_control_data *control = fan_control->driver_data;
>>>>>> +	/* value specified via module param overrides whitelist */
>>>>>> +	if (fan_mode_method > 0 && fan_mode_method <= ARRAY_SIZE(i8k_fan_control_data)) {
>>>>>> +		data->manual_fan = i8k_fan_control_data[fan_mode_method - 1].manual_fan;
>>>>>> +		data->auto_fan = i8k_fan_control_data[fan_mode_method - 1].auto_fan;
>>>>>> +	} else {
>>>>>> +		fan_control = dmi_first_match(i8k_whitelist_fan_control);
>>>>>> +		if (fan_control && fan_control->driver_data) {
>>>>>> +			const struct i8k_fan_control_data *control = fan_control->driver_data;
>>>>>>
>>>>>> -		data->manual_fan = control->manual_fan;
>>>>>> -		data->auto_fan = control->auto_fan;
>>>>>> -		dev_info(&pdev->dev, "enabling support for setting automatic/manual fan control\n");
>>>>>> +			data->manual_fan = control->manual_fan;
>>>>>> +			data->auto_fan = control->auto_fan;
>>>>>> +		}
>>>>>>     	}
>>>>>> +	if (data->manual_fan && data->auto_fan)
>>>>>> +		dev_info(&pdev->dev, "enabling support for setting automatic/manual fan control\n");
>>>>>>
>>>>>>     	if (!fan_mult) {
>>>>>>     		/*
>>>>>> --
>>>>>> 2.30.2
>>>>>>

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