Re: [PATCH v2] platform/x86: thinkpad_acpi: sysfs interface to auxmac

[Ilpo Järvinen]

On Fri, 15 Sep 2023, Fernando Eckhardt Valle wrote:

> Newer Thinkpads have a feature called Mac Address Passthrough.
> This patch provides a sysfs interface that userspace can use
> to get this auxiliary mac address.
> 
> Changes in v2:
> - Added documentation
> - All handling of the auxmac value is done in the _init function.
> 
> Signed-off-by: Fernando Eckhardt Valle <fevalle@xxxxxx>
> ---
>  .../admin-guide/laptops/thinkpad-acpi.rst     | 20 +++++
>  drivers/platform/x86/thinkpad_acpi.c          | 78 +++++++++++++++++++
>  2 files changed, 98 insertions(+)
> 
> diff --git a/Documentation/admin-guide/laptops/thinkpad-acpi.rst b/Documentation/admin-guide/laptops/thinkpad-acpi.rst
> index e27a1c3f6..6207c363f 100644
> --- a/Documentation/admin-guide/laptops/thinkpad-acpi.rst
> +++ b/Documentation/admin-guide/laptops/thinkpad-acpi.rst
> @@ -53,6 +53,7 @@ detailed description):
>  	- Lap mode sensor
>  	- Setting keyboard language
>  	- WWAN Antenna type
> +	- Auxmac
>  
>  A compatibility table by model and feature is maintained on the web
>  site, http://ibm-acpi.sf.net/. I appreciate any success or failure
> @@ -1511,6 +1512,25 @@ Currently 2 antenna types are supported as mentioned below:
>  The property is read-only. If the platform doesn't have support the sysfs
>  class is not created.
>  
> +Auxmac
> +------
> +
> +sysfs: auxmac
> +
> +Some newer Thinkpads have a feature called MAC Address Passthrough. This
> +feature is implemented by the system firmware to provide a system unique MAC,
> +that can override a dock or USB ethernet dongle MAC, when connected to a
> +network. This property enables user-space to easily determine the MAC address
> +if the feature is enabled.
> +
> +The values of this auxiliary MAC are:
> +
> +        cat /sys/devices/platform/thinkpad_acpi/auxmac
> +
> +If the feature is disabled, the value will be 'disabled'.
> +
> +This property is read-only.
> +
>  Adaptive keyboard
>  -----------------
>  
> diff --git a/drivers/platform/x86/thinkpad_acpi.c b/drivers/platform/x86/thinkpad_acpi.c
> index d70c89d32..05cc3a1e2 100644
> --- a/drivers/platform/x86/thinkpad_acpi.c
> +++ b/drivers/platform/x86/thinkpad_acpi.c
> @@ -10785,6 +10785,79 @@ static struct ibm_struct dprc_driver_data = {
>  	.name = "dprc",
>  };
>  
> +/*
> + * Auxmac
> + *
> + * This auxiliary mac address is enabled in the bios through the
> + * Mac Address Passthrough feature. In most cases, there are three
> + * possibilities: Internal Mac, Second Mac, and disabled.
> + *
> + */
> +
> +#define AUXMAC_LEN 12
> +#define AUXMAC_START 9
> +#define AUXMAC_STRLEN 22
> +static char auxmac[AUXMAC_LEN];
> +
> +static int auxmac_init(struct ibm_init_struct *iibm)
> +{
> +	acpi_status status;
> +	struct acpi_buffer buffer = { ACPI_ALLOCATE_BUFFER, NULL };
> +	union acpi_object *obj;
> +
> +	status = acpi_evaluate_object(NULL, "\\MACA", NULL, &buffer);
> +
> +	if (ACPI_FAILURE(status))
> +		return -ENODEV;
> +
> +	obj = (union acpi_object *)buffer.pointer;
> +
> +	if (obj->type != ACPI_TYPE_STRING || obj->string.length != AUXMAC_STRLEN) {
> +		pr_info("Invalid buffer for mac addr passthrough.\n");

MAC address

> +		goto auxmacinvalid;
> +	}
> +
> +	if (strncmp(obj->string.pointer + 0x8, "#", 1) != 0 ||
> +	    strncmp(obj->string.pointer + 0x15, "#", 1) != 0) {

Why use strncmp with (..., 1)? These offsets should defines above and not 
use literals.

> +		pr_info("Invalid header for mac addr passthrough.\n");

MAC address

> +		goto auxmacinvalid;
> +	}
> +
> +	if (strncmp(obj->string.pointer + 0x9, "XXXXXXXXXXXX", AUXMAC_LEN) == 0)

Why you're not using AUXMAC_START here?

It's also bit confusing that some of the offset are hex and some non-hex 
numbers. 

> +		memcpy(auxmac, "disabled", 9);

Don't use memcpy() for copying a string.

> +	else
> +		memcpy(auxmac, obj->string.pointer + AUXMAC_START, AUXMAC_LEN);

What about the termination of auxmac? It's given 

> +
> +	kfree(obj);
> +	return 0;
> +
> +auxmacinvalid:
> +	kfree(obj);
> +	memcpy(auxmac, "unavailable", 11);

Again, don't use memcpy() to copy a string. You even got it wrong here 
compared with the other case where you copied also the zero terminator.

> +	return 0;
> +}
> +
> +static struct ibm_struct auxmac_data = {
> +	.name = "auxmac",
> +};
> +
> +static ssize_t auxmac_show(struct device *dev,
> +			   struct device_attribute *attr,
> +			   char *buf)
> +{
> +	return sysfs_emit(buf, "%s\n", auxmac);

This requires proper termination for the string but you didn't ensure it 
above.

-- 
 i.

> +}
> +static DEVICE_ATTR_RO(auxmac);
> +
> +static struct attribute *auxmac_attributes[] = {
> +	&dev_attr_auxmac.attr,
> +	NULL
> +};
> +
> +static const struct attribute_group auxmac_attr_group = {
> +	.attrs = auxmac_attributes,
> +};
> +
>  /* --------------------------------------------------------------------- */
>  
>  static struct attribute *tpacpi_driver_attributes[] = {
> @@ -10843,6 +10916,7 @@ static const struct attribute_group *tpacpi_groups[] = {
>  	&proxsensor_attr_group,
>  	&kbdlang_attr_group,
>  	&dprc_attr_group,
> +	&auxmac_attr_group,
>  	NULL,
>  };
>  
> @@ -11414,6 +11488,10 @@ static struct ibm_init_struct ibms_init[] __initdata = {
>  		.init = tpacpi_dprc_init,
>  		.data = &dprc_driver_data,
>  	},
> +	{
> +		.init = auxmac_init,
> +		.data = &auxmac_data,
> +	},
>  };
>  
>  static int __init set_ibm_param(const char *val, const struct kernel_param *kp)
>