platform/x86: dell-smbios-wmi: introduce userspace interface

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@dell.com>
Reviewed-by: Edward O'Callaghan <quasisec@google.com>
Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>

Documentation/ABI/testing/dell-smbios-wmi

+What:		/dev/wmi/dell-smbios
+Date:		November 2017
+KernelVersion:	4.15
+Contact:	"Mario Limonciello" <mario.limonciello@dell.com>
+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.

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 +106,42 @@ 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.cmd_class,
+				priv->buf->std.cmd_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 +160,12 @@ 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 +241,7 @@ 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)

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 cmd_class;
-	u16 cmd_select;
-	volatile u32 input[4];
-	volatile u32 output[4];
-} __packed;
-
 struct calling_interface_token {
 	u16 tokenID;
 	u16 location;

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 cmd_class;
+	__u16 cmd_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