Re: [PATCH v4] platform/x86: thinkpad_acpi: sysfs interface to auxmac

[Fernando Eckhardt Valle (FIPT)]

Hi Ilpo,
Thanks for the feedback again!

> Okay, I wasn't expecting this change as this relies on the nul termination
> by strscpy() since the original buffer does not have one but the #
> character there. But I guess it isn't harmful either.
Yes, precisely because strscpy() put the 'nul terminator' I thought it would be ok. In the tests I did, everything always worked fine too.

>  AUXMAC_START is an offset ??? It should be AUXMAC_LEN.
I thought that since the string 'disabled' has length 8, then I would use AUXMAC_START which is defined as 9 , because that way strscpy would copy the 8 characters of 'disabled' + the nul terminator. Wouldn't that be correct? Or would it be better to use AUXMAC_LEN which is defined to 12?

> I only now realized there are two gotos to auxmacinvalid. Therefore, I'd
> do this instead:
2 'goto'... I agree.

Fernando

________________________________________
From: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx>
Sent: Friday, September 22, 2023 5:51 AM
To: Fernando Eckhardt Valle (FIPT)
Cc: Hans de Goede; Mark Pearson; corbet@xxxxxxx; hmh@xxxxxxxxxx; markgross@xxxxxxxxxx; linux-doc@xxxxxxxxxxxxxxx; LKML; ibm-acpi-devel@xxxxxxxxxxxxxxxxxxxxx; platform-driver-x86@xxxxxxxxxxxxxxx
Subject: Re: [PATCH v4] platform/x86: thinkpad_acpi: sysfs interface to auxmac

On Thu, 21 Sep 2023, Fernando Eckhardt Valle wrote:

> Newer Thinkpads have a feature called MAC Address Pass-through.
> This patch provides a sysfs interface that userspace can use
> to get this auxiliary mac address.
>
> Signed-off-by: Fernando Eckhardt Valle <fevalle@xxxxxx>
> ---
> Changes in v4:
> - strscpy() in all string copies.
> Changes in v3:
> - Added null terminator to auxmac string when copying auxiliary
> mac address value.
> Changes in v2:
> - Added documentation.
> - All handling of the auxmac value is done in the _init function.
> ---
>  .../admin-guide/laptops/thinkpad-acpi.rst     | 20 +++++
>  drivers/platform/x86/thinkpad_acpi.c          | 79 +++++++++++++++++++
>  2 files changed, 99 insertions(+)
>
> diff --git a/Documentation/admin-guide/laptops/thinkpad-acpi.rst b/Documentation/admin-guide/laptops/thinkpad-acpi.rst
> index e27a1c3f6..98d304010 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 Pass-through. 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..f430cc9ed 100644
> --- a/drivers/platform/x86/thinkpad_acpi.c
> +++ b/drivers/platform/x86/thinkpad_acpi.c
> @@ -10785,6 +10785,80 @@ static struct ibm_struct dprc_driver_data = {
>       .name = "dprc",
>  };
>
> +/*
> + * Auxmac
> + *
> + * This auxiliary mac address is enabled in the bios through the
> + * MAC Address Pass-through 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
> +#define AUXMAC_BEGIN_MARKER 8
> +#define AUXMAC_END_MARKER 21
> +
> +static char auxmac[AUXMAC_LEN + 1];
> +
> +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 = buffer.pointer;
> +
> +     if (obj->type != ACPI_TYPE_STRING || obj->string.length != AUXMAC_STRLEN) {
> +             pr_info("Invalid buffer for MAC address pass-through.\n");
> +             strscpy(auxmac, "unavailable", AUXMAC_LEN);
> +             goto auxmacinvalid;
> +     }
> +
> +     if (obj->string.pointer[AUXMAC_BEGIN_MARKER] != '#' ||
> +         obj->string.pointer[AUXMAC_END_MARKER] != '#') {
> +             pr_info("Invalid header for MAC address pass-through.\n");
> +             strscpy(auxmac, "unavailable", AUXMAC_LEN);
> +             goto auxmacinvalid;
> +     }
> +
> +     if (strncmp(obj->string.pointer + AUXMAC_START, "XXXXXXXXXXXX", AUXMAC_LEN) != 0)
> +             strscpy(auxmac, obj->string.pointer + AUXMAC_START, AUXMAC_LEN + 1);

Okay, I wasn't expecting this change as this relies on the nul termination
by strscpy() since the original buffer does not have one but the #
character there. But I guess it isn't harmful either.

> +     else
> +             strscpy(auxmac, "disabled", AUXMAC_START);

AUXMAC_START is an offset ??? It should be AUXMAC_LEN.

> +
> +auxmacinvalid:
> +     kfree(obj);
> +     return 0;

I only now realized there are two gotos to auxmacinvalid. Therefore, I'd
do this instead:

free:
        kfree(obj);
        return 0;
auxmacinvalid:
        strscpy(auxmac, "unavailable", AUXMAC_LEN);
        goto free;

I'm sorry about my incorrect suggestion the last time.

> +}
> +
> +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);
> +}
> +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 +10917,7 @@ static const struct attribute_group *tpacpi_groups[] = {
>       &proxsensor_attr_group,
>       &kbdlang_attr_group,
>       &dprc_attr_group,
> +     &auxmac_attr_group,
>       NULL,
>  };
>
> @@ -11414,6 +11489,10 @@ 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)
>

--
 i.