HID: bpf: add HID-BPF hooks for hid_hw_output_report

Same story than hid_hw_raw_requests:

This allows to intercept and prevent or change the behavior of
hid_hw_output_report() 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_hw_output_report(), 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/[email protected]
Acked-by: Jiri Kosina <[email protected]>
Signed-off-by: Benjamin Tissoires <[email protected]>

Author: Benjamin Tissoires

drivers/hid/bpf/hid_bpf_dispatch.c

@@ -113,6 +113,40 @@ int dispatch_hid_bpf_raw_requests(struct hid_device *hdev,
 }
 EXPORT_SYMBOL_GPL(dispatch_hid_bpf_raw_requests);
 
+int dispatch_hid_bpf_output_report(struct hid_device *hdev,
+				   __u8 *buf, u32 size, __u64 source,
+				   bool from_bpf)
+{
+	struct hid_bpf_ctx_kern ctx_kern = {
+		.ctx = {
+			.hid = hdev,
+			.allocated_size = size,
+			.size = size,
+		},
+		.data = buf,
+		.from_bpf = from_bpf,
+	};
+	struct hid_bpf_ops *e;
+	int ret, idx;
+
+	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_output_report)
+			continue;
+
+		ret = e->hid_hw_output_report(&ctx_kern.ctx, source);
+		if (ret)
+			goto out;
+	}
+	ret = 0;
+
+out:
+	srcu_read_unlock(&hdev->bpf.srcu, idx);
+	return ret;
+}
+EXPORT_SYMBOL_GPL(dispatch_hid_bpf_output_report);
+
 u8 *call_hid_bpf_rdesc_fixup(struct hid_device *hdev, u8 *rdesc, unsigned int *size)
 {
 	int ret;
@@ -443,10 +477,7 @@ hid_bpf_hw_output_report(struct hid_bpf_ctx *ctx, __u8 *buf, size_t buf__sz)
 	if (!dma_data)
 		return -ENOMEM;
 
-	ret = hid_ops->hid_hw_output_report(hdev,
-						dma_data,
-						size,
-						(__u64)ctx);
+	ret = hid_ops->hid_hw_output_report(hdev, dma_data, size, (__u64)ctx, true);
 
 	kfree(dma_data);
 	return ret;

drivers/hid/bpf/hid_bpf_struct_ops.c

@@ -45,6 +45,7 @@ static int hid_bpf_ops_check_member(const struct btf_type *t,
 	switch (moff) {
 	case offsetof(struct hid_bpf_ops, hid_rdesc_fixup):
 	case offsetof(struct hid_bpf_ops, hid_hw_request):
+	case offsetof(struct hid_bpf_ops, hid_hw_output_report):
 		break;
 	default:
 		if (prog->sleepable)

drivers/hid/hid-core.c

@@ -2445,16 +2445,22 @@ int hid_hw_raw_request(struct hid_device *hdev,
 }
 EXPORT_SYMBOL_GPL(hid_hw_raw_request);
 
-int __hid_hw_output_report(struct hid_device *hdev, __u8 *buf, size_t len, __u64 source)
+int __hid_hw_output_report(struct hid_device *hdev, __u8 *buf, size_t len, __u64 source,
+			   bool from_bpf)
 {
 	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_output_report(hdev, buf, len, source, from_bpf);
+	if (ret)
+		return ret;
+
 	if (hdev->ll_driver->output_report)
 		return hdev->ll_driver->output_report(hdev, buf, len);
 
@@ -2472,7 +2478,7 @@ int __hid_hw_output_report(struct hid_device *hdev, __u8 *buf, size_t len, __u64
  */
 int hid_hw_output_report(struct hid_device *hdev, __u8 *buf, size_t len)
 {
-	return __hid_hw_output_report(hdev, buf, len, 0);
+	return __hid_hw_output_report(hdev, buf, len, 0, false);
 }
 EXPORT_SYMBOL_GPL(hid_hw_output_report);
 

drivers/hid/hidraw.c

@@ -140,7 +140,7 @@ static ssize_t hidraw_send_report(struct file *file, const char __user *buffer,
 
 	if ((report_type == HID_OUTPUT_REPORT) &&
 	    !(dev->quirks & HID_QUIRK_NO_OUTPUT_REPORTS_ON_INTR_EP)) {
-		ret = __hid_hw_output_report(dev, buf, count, (__u64)file);
+		ret = __hid_hw_output_report(dev, buf, count, (__u64)file, false);
 		/*
 		 * compatibility with old implementation of USB-HID and I2C-HID:
 		 * if the device does not support receiving output reports,

include/linux/hid.h

@@ -1130,7 +1130,8 @@ int __hid_hw_raw_request(struct hid_device *hdev,
 			 size_t len, enum hid_report_type rtype,
 			 enum hid_class_request reqtype,
 			 __u64 source, bool from_bpf);
-int __hid_hw_output_report(struct hid_device *hdev, __u8 *buf, size_t len, __u64 source);
+int __hid_hw_output_report(struct hid_device *hdev, __u8 *buf, size_t len, __u64 source,
+			   bool from_bpf);
 int hid_hw_raw_request(struct hid_device *hdev,
 		       unsigned char reportnum, __u8 *buf,
 		       size_t len, enum hid_report_type rtype,

include/linux/hid_bpf.h

@@ -70,7 +70,7 @@ struct hid_ops {
 				  enum hid_class_request reqtype,
 				  __u64 source, bool from_bpf);
 	int (*hid_hw_output_report)(struct hid_device *hdev, __u8 *buf, size_t len,
-				    __u64 source);
+				    __u64 source, bool from_bpf);
 	int (*hid_input_report)(struct hid_device *hid, enum hid_report_type type,
 				u8 *data, u32 size, int interrupt, u64 source);
 	struct module *owner;
@@ -154,6 +154,24 @@ struct hid_bpf_ops {
 			       enum hid_report_type rtype, enum hid_class_request reqtype,
 			       __u64 source);
 
+	/**
+	 * @hid_hw_output_report: called whenever a hid_hw_output_report() call is emitted
+	 * on the HID device
+	 *
+	 * It has the following arguments:
+	 *
+	 * ``ctx``: The HID-BPF context as &struct hid_bpf_ctx
+	 * ``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 written to the device; a negative error
+	 * code interrupts the processing of this call.
+	 */
+	int (*hid_hw_output_report)(struct hid_bpf_ctx *ctx, __u64 source);
+
 
 	/* private: do not show up in the docs */
 	struct hid_device *hdev;
@@ -182,6 +200,8 @@ int dispatch_hid_bpf_raw_requests(struct hid_device *hdev,
 				  u32 size, enum hid_report_type rtype,
 				  enum hid_class_request reqtype,
 				  __u64 source, bool from_bpf);
+int dispatch_hid_bpf_output_report(struct hid_device *hdev, __u8 *buf, u32 size,
+				   __u64 source, bool from_bpf);
 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);
@@ -196,6 +216,8 @@ static inline int dispatch_hid_bpf_raw_requests(struct hid_device *hdev,
 						u32 size, enum hid_report_type rtype,
 						enum hid_class_request reqtype,
 						u64 source, bool from_bpf) { return 0; }
+static inline int dispatch_hid_bpf_output_report(struct hid_device *hdev, __u8 *buf, u32 size,
+						 __u64 source, bool from_bpf) { 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) {}