Re: [PATCH v2] platform/x86: dell-wmi-sysman: Make init_bios_attributes() ACPI object parsing more robust

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 3/26/21 4:40 PM, Ksr, Prasanth wrote:
> 
> 
> Hi,
> 
> [EXTERNAL EMAIL] 
> 
>> Hi,
>>
>> On 3/21/21 1:16 PM, Hans de Goede wrote:
>>> Make init_bios_attributes() ACPI object parsing more robust:
>>> 1. Always check that the type of the return ACPI object is package, rather
>>>    then only checking this for instance_id == 0 2. Check that the 
>>> package has the minimum amount of elements which will
>>>    be consumed by the populate_foo_data() for the attr_type
>>>
>>> Note/TODO: The populate_foo_data() functions should also be made more 
>>> robust. The should check the type of each of the elements matches the 
>>> type which they expect and in case of populate_enum_data()
>>> obj->package.count should be passed to it as an argument and it should
>>> re-check this itself since it consume a variable number of elements.
>>>
>>> Fixes: e8a60aa7404b ("platform/x86: Introduce support for Systems 
>>> Management Driver over WMI for Dell Systems")
>>> Cc: Divya Bharathi <Divya_Bharathi@dell.com>
>>> Cc: Mario Limonciello <mario.limonciello@dell.com>
>>> Signed-off-by: Hans de Goede <hdegoede@redhat.com>
>>> ---
>>> Changes in v2:
>>> - Restore behavior of returning -ENODEV when the get_wmiobj_pointer() call
>>>   for instance_id == 0 returns NULL. Otherwise
>>>   /sys/class/firmware-attributes/dell-wmi-sysman will get created with an
>>>   empty attributes dir (empty except for pending_reboot and 
>>> reset_bios)
> 
>> So the reason for this change in v2 is that testing on a Dell Latitude E5570:
>> https://bugzilla.redhat.com/show_bug.cgi?id=1936171
>>
>> With v1 of this patch results in an empty attributes dir (empty except for pending_reboot and reset_bios), interestingly enough there are both System and Admin dirs created under Authentication, so the BIOS of this device seems to have the GUIDs for both the attributes and the authentication interfaces; and it >has the 2 standard authentication objects, theoretically allowing changing the BIOS passwords from within Linux, but it does not advertise any attributes which can be changed.
>>
>> With the new v2 patch, the driver will now simply refuse to load (and it should no longer crash during cleanup because of the other patches).
>>
>> But I wonder what is actually the right thing to do here ?  Arguably being able to change the BIOS passwords has some value on its own ?
>>
>> Mario, what is your take on this?
> 
> Ideally we should not be hitting this code path at all. I am working with perry to see the results after applying the patches on the system.
> If this is behavior we consistently see on older system BIOS then we will patch the code to avoid code path and bail out early not loading the driver.

With v2 of my patches (which have been merged) we do bail out as soon as it is clear that there is no enum-type (*) attribute
with instance_id 0. That is pretty-much the earliest that we can bail and that works fine.

What I was wondering is if that is the right thing to do though. On the E5570 there seem to be no enum/int/str attributes at all but what if there are enum + int attributes + no str attributes for example ?

Also maybe the BIOS password interface on its own, without having any attributes at all has some value by itself ?

*) enums are the first type we check for

> Also I was not cc'ed on the mail threads where the bugs were discussed so going further please add me and Divya for reporting any issues on the driver

Yes that was my mistake, sorry about that. I'll make sure to Cc Divya and you on future emails about the dell-wmi-sysman driver.

Regards,

Hans




>>> ---
>>>  .../x86/dell/dell-wmi-sysman/sysman.c         | 32 ++++++++++++++++---
>>>  1 file changed, 28 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/drivers/platform/x86/dell/dell-wmi-sysman/sysman.c 
>>> b/drivers/platform/x86/dell/dell-wmi-sysman/sysman.c
>>> index 7410ccae650c..a90ae6ba4a73 100644
>>> --- a/drivers/platform/x86/dell/dell-wmi-sysman/sysman.c
>>> +++ b/drivers/platform/x86/dell/dell-wmi-sysman/sysman.c
>>> @@ -399,6 +399,7 @@ static int init_bios_attributes(int attr_type, const char *guid)
>>>  	union acpi_object *obj = NULL;
>>>  	union acpi_object *elements;
>>> 	struct kset *tmp_set;
>>> +	int min_elements;
>>>
>>>  	/* instance_id needs to be reset for each type GUID
>>>  	 * also, instance IDs are unique within GUID but not across @@ 
>>> -409,14 +410,38 @@ static int init_bios_attributes(int attr_type, const char *guid)
>>>  	retval = alloc_attributes_data(attr_type);
>>>  	if (retval)
>>>  		return retval;
>>> +
>>> +	switch (attr_type) {
>>> +	case ENUM:	min_elements = 8;	break;
>>> +	case INT:	min_elements = 9;	break;
>>> +	case STR:	min_elements = 8;	break;
>>> +	case PO:	min_elements = 4;	break;
>>> +	default:
>>> +		pr_err("Error: Unknown attr_type: %d\n", attr_type);
>>> +		return -EINVAL;
>>> +	}
>>> +
>>>  	/* need to use specific instance_id and guid combination to get right data */
>>>  	obj = get_wmiobj_pointer(instance_id, guid);
>>> -	if (!obj || obj->type != ACPI_TYPE_PACKAGE)
>>> +	if (!obj)
>>>  		return -ENODEV;
>>> -	elements = obj->package.elements;
>>>  
>>>  	mutex_lock(&wmi_priv.mutex);
>>> -	while (elements) {
>>> +	while (obj) {
>>> +		if (obj->type != ACPI_TYPE_PACKAGE) {
>>> +			pr_err("Error: Expected ACPI-package type, got: %d\n", obj->type);
>>> +			retval = -EIO;
>>> +			goto err_attr_init;
>>> +		}
>>> +
>>> +		if (obj->package.count < min_elements) {
>>> +			pr_err("Error: ACPI-package does not have enough elements: %d < %d\n",
>>> +			       obj->package.count, min_elements);
>>> +			goto nextobj;
>>> +		}
>>> +
>>> +		elements = obj->package.elements;
>>> +
>>>  		/* sanity checking */
>>>  		if (elements[ATTR_NAME].type != ACPI_TYPE_STRING) {
>>>  			pr_debug("incorrect element type\n"); @@ -481,7 +506,6 @@ static 
>>> int init_bios_attributes(int attr_type, const char *guid)
>>> 		kfree(obj);
>>>  		instance_id++;
>>>  		obj = get_wmiobj_pointer(instance_id, guid);
>>> -		elements = obj ? obj->package.elements : NULL;
>>> 	}
>>>  
>>>  	mutex_unlock(&wmi_priv.mutex);
>>>
>