Re: [PATCH v11 14/15] platform/x86: dell-smbios-wmi: introduce userspace interface

[Edward O'Callaghan]

On Sat, Oct 21, 2017 at 4:40 AM, Mario Limonciello
<mario.limonciello@xxxxxxxx> wrote:
> It's important for the driver to provide a R/W ioctl to ensure that
> two competing userspace processes don't race to provide or read each
> others data.
>
> This userspace character device will be used to perform SMBIOS calls
> from any applications.
>
> It provides an ioctl that will allow passing the WMI calling
> interface buffer between userspace and kernel space.
>
> This character device is intended to deprecate the dcdbas kernel module
> and the interface that it provides to userspace.
>
> To perform an SMBIOS IOCTL call using the character device userspace will
> perform a read() on the the character device.  The WMI bus will provide
> a u64 variable containing the necessary size of the IOCTL buffer.
>
> The API for interacting with this interface is defined in documentation
> as well as the WMI uapi header provides the format of the structures.
>
> Not all userspace requests will be accepted.  The dell-smbios filtering
> functionality will be used to prevent access to certain tokens and calls.
>
> All whitelisted commands and tokens are now shared out to userspace so
> applications don't need to define them in their own headers.
>
> Signed-off-by: Mario Limonciello <mario.limonciello@xxxxxxxx>
> Reviewed-by: Edward O'Callaghan <quasisec@xxxxxxxxxx>
> ---
>  Documentation/ABI/testing/dell-smbios-wmi | 41 ++++++++++++++++++++++++
>  drivers/platform/x86/dell-smbios-wmi.c    | 53 ++++++++++++++++++++++++-------
>  drivers/platform/x86/dell-smbios.h        | 32 ++-----------------
>  include/uapi/linux/wmi.h                  | 47 +++++++++++++++++++++++++++
>  4 files changed, 132 insertions(+), 41 deletions(-)
>  create mode 100644 Documentation/ABI/testing/dell-smbios-wmi
>
> diff --git a/Documentation/ABI/testing/dell-smbios-wmi b/Documentation/ABI/testing/dell-smbios-wmi
> new file mode 100644
> index 000000000000..fc919ce16008
> --- /dev/null
> +++ b/Documentation/ABI/testing/dell-smbios-wmi
> @@ -0,0 +1,41 @@
> +What:          /dev/wmi/dell-smbios
> +Date:          November 2017
> +KernelVersion: 4.15
> +Contact:       "Mario Limonciello" <mario.limonciello@xxxxxxxx>
> +Description:
> +               Perform SMBIOS calls on supported Dell machines.
> +               through the Dell ACPI-WMI interface.
> +
> +               IOCTL's and buffer formats are defined in:
> +               <uapi/linux/wmi.h>
> +
> +               1) To perform an SMBIOS call from userspace, you'll need to
> +               first determine the minimum size of the calling interface
> +               buffer for your machine.
> +               Platforms that contain larger buffers can return larger
> +               objects from the system firmware.
> +               Commonly this size is either 4k or 32k.
> +
> +               To determine the size of the buffer read() a u64 dword from
> +               the WMI character device /dev/wmi/dell-smbios.
> +
> +               2) After you've determined the minimum size of the calling
> +               interface buffer, you can allocate a structure that represents
> +               the structure documented above.
> +
> +               3) In the 'length' object store the size of the buffer you
> +               determined above and allocated.
> +
> +               4) In this buffer object, prepare as necessary for the SMBIOS
> +               call you're interested in.  Typically SMBIOS buffers have
> +               "class", "select", and "input" defined to values that coincide
> +               with the data you are interested in.
> +               Documenting class/select/input values is outside of the scope
> +               of this documentation. Check with the libsmbios project for
> +               further documentation on these values.
> +
> +               6) Run the call by using ioctl() as described in the header.
> +
> +               7) The output will be returned in the buffer object.
> +
> +               8) Be sure to free up your allocated object.
> diff --git a/drivers/platform/x86/dell-smbios-wmi.c b/drivers/platform/x86/dell-smbios-wmi.c
> index d2b8438ea91f..04b0153c9bee 100644
> --- a/drivers/platform/x86/dell-smbios-wmi.c
> +++ b/drivers/platform/x86/dell-smbios-wmi.c
> @@ -30,17 +30,6 @@ struct misc_bios_flags_structure {
>
>  #define DELL_WMI_SMBIOS_GUID "A80593CE-A997-11DA-B012-B622A1EF5492"
>
> -struct dell_wmi_extensions {
> -       __u32 argattrib;
> -       __u32 blength;
> -       __u8 data[];
> -} __packed;
> -
> -struct dell_wmi_smbios_buffer {
> -       struct calling_interface_buffer std;
> -       struct dell_wmi_extensions ext;
> -} __packed;
> -
>  struct wmi_smbios_priv {
>         struct dell_wmi_smbios_buffer *buf;
>         struct list_head list;
> @@ -117,6 +106,41 @@ int dell_smbios_wmi_call(struct calling_interface_buffer *buffer)
>         return ret;
>  }
>
> +static long dell_smbios_wmi_filter(struct wmi_device *wdev, unsigned int cmd,
> +                                  struct wmi_ioctl_buffer *arg)
> +{
> +       struct wmi_smbios_priv *priv;
> +       int ret = 0;
> +
> +       switch (cmd) {
> +       case DELL_WMI_SMBIOS_CMD:
> +               mutex_lock(&call_mutex);
> +               priv = dev_get_drvdata(&wdev->dev);
> +               if (!priv) {
> +                       ret = -ENODEV;
> +                       goto fail_smbios_cmd;
> +               }
> +               memcpy(priv->buf, arg, priv->req_buf_size);
> +               if (dell_smbios_call_filter(&wdev->dev, &priv->buf->std)) {
> +                       dev_err(&wdev->dev, "Invalid call %d/%d:%8x\n",
> +                               priv->buf->std.class, priv->buf->std.select,
> +                               priv->buf->std.input[0]);
> +                       ret = -EFAULT;
> +                       goto fail_smbios_cmd;
> +               }
> +               ret = run_smbios_call(priv->wdev);
> +               if (ret)
> +                       goto fail_smbios_cmd;
> +               memcpy(arg, priv->buf, priv->req_buf_size);
> +fail_smbios_cmd:
> +               mutex_unlock(&call_mutex);
> +               break;
> +       default:
> +               ret = -ENOIOCTLCMD;
> +       }
> +       return ret;
> +}
> +
>  static int dell_smbios_wmi_probe(struct wmi_device *wdev)
>  {
>         struct wmi_smbios_priv *priv;
> @@ -135,6 +159,12 @@ static int dell_smbios_wmi_probe(struct wmi_device *wdev)
>         if (!dell_wmi_get_size(&priv->req_buf_size))
>                 return -EPROBE_DEFER;
>
> +       /* add in the length object we will use internally with ioctl */
> +       priv->req_buf_size += sizeof(u64);
> +       ret = set_required_buffer_size(wdev, priv->req_buf_size);
> +       if (ret)
> +               return ret;
> +
>         count = get_order(priv->req_buf_size);
>         priv->buf = (void *)__get_free_pages(GFP_KERNEL, count);
>         if (!priv->buf)
> @@ -210,6 +240,7 @@ static struct wmi_driver dell_smbios_wmi_driver = {
>         .probe = dell_smbios_wmi_probe,
>         .remove = dell_smbios_wmi_remove,
>         .id_table = dell_smbios_wmi_id_table,
> +       .filter_callback = dell_smbios_wmi_filter,
>  };
>
>  static int __init init_dell_smbios_wmi(void)
> diff --git a/drivers/platform/x86/dell-smbios.h b/drivers/platform/x86/dell-smbios.h
> index 23256f79a4b8..138d478d9adc 100644
> --- a/drivers/platform/x86/dell-smbios.h
> +++ b/drivers/platform/x86/dell-smbios.h
> @@ -17,23 +17,11 @@
>  #define _DELL_SMBIOS_H_
>
>  #include <linux/device.h>
> +#include <uapi/linux/wmi.h>
>
> -/* Classes and selects used in kernel drivers */
> -#define CLASS_TOKEN_READ 0
> -#define CLASS_TOKEN_WRITE 1
> -#define SELECT_TOKEN_STD 0
> -#define SELECT_TOKEN_BAT 1
> -#define SELECT_TOKEN_AC 2
> +/* Classes and selects used only in kernel drivers */
>  #define CLASS_KBD_BACKLIGHT 4
>  #define SELECT_KBD_BACKLIGHT 11
> -#define CLASS_FLASH_INTERFACE 7
> -#define SELECT_FLASH_INTERFACE 3
> -#define CLASS_ADMIN_PROP 10
> -#define SELECT_ADMIN_PROP 3
> -#define CLASS_INFO 17
> -#define SELECT_RFKILL 11
> -#define SELECT_APP_REGISTRATION        3
> -#define SELECT_DOCK 22
>
>  /* Tokens used in kernel drivers, any of these
>   * should be filtered from userspace access
> @@ -50,24 +38,8 @@
>  #define GLOBAL_MIC_MUTE_ENABLE 0x0364
>  #define GLOBAL_MIC_MUTE_DISABLE        0x0365
>
> -/* tokens whitelisted to userspace use */
> -#define CAPSULE_EN_TOKEN       0x0461
> -#define CAPSULE_DIS_TOKEN      0x0462
> -#define WSMT_EN_TOKEN          0x04EC
> -#define WSMT_DIS_TOKEN         0x04ED
> -
>  struct notifier_block;
>
> -/* This structure will be modified by the firmware when we enter
> - * system management mode, hence the volatiles */
> -
> -struct calling_interface_buffer {
> -       u16 class;
> -       u16 select;
> -       volatile u32 input[4];
> -       volatile u32 output[4];
> -} __packed;
> -
>  struct calling_interface_token {
>         u16 tokenID;
>         u16 location;
> diff --git a/include/uapi/linux/wmi.h b/include/uapi/linux/wmi.h
> index 7e52350ac9b3..5ff61f2d37ba 100644
> --- a/include/uapi/linux/wmi.h
> +++ b/include/uapi/linux/wmi.h
> @@ -10,6 +10,7 @@
>  #ifndef _UAPI_LINUX_WMI_H
>  #define _UAPI_LINUX_WMI_H
>
> +#include <linux/ioctl.h>
>  #include <linux/types.h>
>
>  /* WMI bus will filter all WMI vendor driver requests through this IOC */
> @@ -23,4 +24,50 @@ struct wmi_ioctl_buffer {
>         __u8    data[];
>  };
>
> +/* This structure may be modified by the firmware when we enter
> + * system management mode through SMM, hence the volatiles
> + */
> +struct calling_interface_buffer {
> +       __u16 class;

Hey Mario,

I just realized that there is a slight problem calling this identifier
"class" for userspace that happens to be written in C++ that #includes
this header as class is a reversed word.
Perhaps we could rename it to class_ or something otherwise userspace
has to shim with a C object and extern it with new identifiers to the
C++ component, which is awkward.

Kind Regards,
Edward.

> +       __u16 select;
> +       volatile __u32 input[4];
> +       volatile __u32 output[4];
> +} __packed;
> +
> +struct dell_wmi_extensions {
> +       __u32 argattrib;
> +       __u32 blength;
> +       __u8 data[];
> +} __packed;
> +
> +struct dell_wmi_smbios_buffer {
> +       __u64 length;
> +       struct calling_interface_buffer std;
> +       struct dell_wmi_extensions      ext;
> +} __packed;
> +
> +/* Whitelisted smbios class/select commands */
> +#define CLASS_TOKEN_READ       0
> +#define CLASS_TOKEN_WRITE      1
> +#define SELECT_TOKEN_STD       0
> +#define SELECT_TOKEN_BAT       1
> +#define SELECT_TOKEN_AC                2
> +#define CLASS_FLASH_INTERFACE  7
> +#define SELECT_FLASH_INTERFACE 3
> +#define CLASS_ADMIN_PROP       10
> +#define SELECT_ADMIN_PROP      3
> +#define CLASS_INFO             17
> +#define SELECT_RFKILL          11
> +#define SELECT_APP_REGISTRATION        3
> +#define SELECT_DOCK            22
> +
> +/* whitelisted tokens */
> +#define CAPSULE_EN_TOKEN       0x0461
> +#define CAPSULE_DIS_TOKEN      0x0462
> +#define WSMT_EN_TOKEN          0x04EC
> +#define WSMT_DIS_TOKEN         0x04ED
> +
> +/* Dell SMBIOS calling IOCTL command used by dell-smbios-wmi */
> +#define DELL_WMI_SMBIOS_CMD    _IOWR(WMI_IOC, 0, struct dell_wmi_smbios_buffer)
> +
>  #endif
> --
> 2.14.1
>