HID: bpf: add HID-BPF hooks for hid_hw_raw_requests

This allows to intercept and prevent or change the behavior of
hid_hw_raw_request() from a bpf program.

The intent is to solve a couple of use case:
- firewalling a HID device: a firewall can monitor who opens the hidraw
nodes and then prevent or allow access to write operations on that
hidraw node.
- change the behavior of a device and emulate a new HID feature request

The hook is allowed to be run as sleepable so it can itself call
hid_bpf_hw_request(), which allows to "convert" one feature request into
another or even call the feature request on a different HID device on the
same physical device.

Link: https://patch.msgid.link/[e-mail]
Acked-by: Jiri Kosina <[e-mail]>
Signed-off-by: Benjamin Tissoires <[e-mail]>

drivers/hid/bpf/hid_bpf_dispatch.c

···
 }
 EXPORT_SYMBOL_GPL(dispatch_hid_bpf_device_event);
 
+int dispatch_hid_bpf_raw_requests(struct hid_device *hdev,
+				  unsigned char reportnum, u8 *buf,
+				  u32 size, enum hid_report_type rtype,
+				  enum hid_class_request reqtype,
+				  u64 source)
+{
+	struct hid_bpf_ctx_kern ctx_kern = {
+		.ctx = {
+			.hid = hdev,
+			.allocated_size = size,
+			.size = size,
+		},
+		.data = buf,
+	};
+	struct hid_bpf_ops *e;
+	int ret, idx;
+
+	if (rtype >= HID_REPORT_TYPES)
+		return -EINVAL;
+
+	idx = srcu_read_lock(&hdev->bpf.srcu);
+	list_for_each_entry_srcu(e, &hdev->bpf.prog_list, list,
+				 srcu_read_lock_held(&hdev->bpf.srcu)) {
+		if (!e->hid_hw_request)
+			continue;
+
+		ret = e->hid_hw_request(&ctx_kern.ctx, reportnum, rtype, reqtype, source);
+		if (ret)
+			goto out;
+	}
+	ret = 0;
+
+out:
+	srcu_read_unlock(&hdev->bpf.srcu, idx);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(dispatch_hid_bpf_raw_requests);
+
 u8 *call_hid_bpf_rdesc_fixup(struct hid_device *hdev, u8 *rdesc, unsigned int *size)
 {
 	int ret;

drivers/hid/bpf/hid_bpf_struct_ops.c

···
 
 	switch (moff) {
 	case offsetof(struct hid_bpf_ops, hid_rdesc_fixup):
+	case offsetof(struct hid_bpf_ops, hid_hw_request):
 		break;
 	default:
 		if (prog->sleepable)

drivers/hid/hid-core.c

···
 			 __u64 source)
 {
 	unsigned int max_buffer_size = HID_MAX_BUFFER_SIZE;
+	int ret;
 
 	if (hdev->ll_driver->max_buffer_size)
 		max_buffer_size = hdev->ll_driver->max_buffer_size;
 
 	if (len < 1 || len > max_buffer_size || !buf)
 		return -EINVAL;
+
+	ret = dispatch_hid_bpf_raw_requests(hdev, reportnum, buf, len, rtype,
+					    reqtype, source);
+	if (ret)
+		return ret;
 
 	return hdev->ll_driver->raw_request(hdev, reportnum, buf, len,
 					    rtype, reqtype);

include/linux/hid_bpf.h

···
 	 */
 	int (*hid_rdesc_fixup)(struct hid_bpf_ctx *ctx);
 
+	/**
+	 * @hid_hw_request: called whenever a hid_hw_raw_request() call is emitted
+	 * on the HID device
+	 *
+	 * It has the following arguments:
+	 *
+	 * ``ctx``: The HID-BPF context as &struct hid_bpf_ctx
+	 * ``reportnum``: the report number, as in hid_hw_raw_request()
+	 * ``rtype``: the report type (``HID_INPUT_REPORT``, ``HID_FEATURE_REPORT``,
+	 *            ``HID_OUTPUT_REPORT``)
+	 * ``reqtype``: the request
+	 * ``source``: a u64 referring to a uniq but identifiable source. If %0, the
+	 *             kernel itself emitted that call. For hidraw, ``source`` is set
+	 *             to the associated ``struct file *``.
+	 *
+	 * Return: %0 to keep processing the request by hid-core; any other value
+	 * stops hid-core from processing that event. A positive value should be
+	 * returned with the number of bytes returned in the incoming buffer; a
+	 * negative error code interrupts the processing of this call.
+	 */
+	int (*hid_hw_request)(struct hid_bpf_ctx *ctx, unsigned char reportnum,
+			       enum hid_report_type rtype, enum hid_class_request reqtype,
+			       __u64 source);
+
+
 	/* private: do not show up in the docs */
 	struct hid_device *hdev;
 };
···
 #ifdef CONFIG_HID_BPF
 u8 *dispatch_hid_bpf_device_event(struct hid_device *hid, enum hid_report_type type, u8 *data,
 				  u32 *size, int interrupt, u64 source);
+int dispatch_hid_bpf_raw_requests(struct hid_device *hdev,
+				  unsigned char reportnum, __u8 *buf,
+				  u32 size, enum hid_report_type rtype,
+				  enum hid_class_request reqtype,
+				  __u64 source);
 int hid_bpf_connect_device(struct hid_device *hdev);
 void hid_bpf_disconnect_device(struct hid_device *hdev);
 void hid_bpf_destroy_device(struct hid_device *hid);
···
 static inline u8 *dispatch_hid_bpf_device_event(struct hid_device *hid, enum hid_report_type type,
 						u8 *data, u32 *size, int interrupt,
 						u64 source) { return data; }
+static inline int dispatch_hid_bpf_raw_requests(struct hid_device *hdev,
+						unsigned char reportnum, u8 *buf,
+						u32 size, enum hid_report_type rtype,
+						enum hid_class_request reqtype,
+						u64 source) { return 0; }
 static inline int hid_bpf_connect_device(struct hid_device *hdev) { return 0; }
 static inline void hid_bpf_disconnect_device(struct hid_device *hdev) {}
 static inline void hid_bpf_destroy_device(struct hid_device *hid) {}