HID: bpf: export hid_hw_output_report as a BPF kfunc

We currently only export hid_hw_raw_request() as a BPF kfunc.
However, some devices require an explicit write on the Output Report
instead of the use of the control channel.

So also export hid_hw_output_report to BPF

Link: https://lore.kernel.org/r/20240315-b4-hid-bpf-new-funcs-v4-2-079c282469d3@kernel.org
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>

Documentation/hid/hid-bpf.rst

@@ -179,7 +179,7 @@ Available API that can be used in syscall HID-BPF programs:
 -----------------------------------------------------------
 
 .. kernel-doc:: drivers/hid/bpf/hid_bpf_dispatch.c
-   :functions: hid_bpf_attach_prog hid_bpf_hw_request hid_bpf_allocate_context hid_bpf_release_context
+   :functions: hid_bpf_attach_prog hid_bpf_hw_request hid_bpf_hw_output_report hid_bpf_allocate_context hid_bpf_release_context
 
 General overview of a HID-BPF program
 =====================================

drivers/hid/bpf/hid_bpf_dispatch.c

@@ -376,6 +376,46 @@ hid_bpf_release_context(struct hid_bpf_ctx *ctx)
 	put_device(&hid->dev);
 }
 
+static int
+__hid_bpf_hw_check_params(struct hid_bpf_ctx *ctx, __u8 *buf, size_t *buf__sz,
+			  enum hid_report_type rtype)
+{
+	struct hid_report_enum *report_enum;
+	struct hid_report *report;
+	struct hid_device *hdev;
+	u32 report_len;
+
+	/* check arguments */
+	if (!ctx || !hid_bpf_ops || !buf)
+		return -EINVAL;
+
+	switch (rtype) {
+	case HID_INPUT_REPORT:
+	case HID_OUTPUT_REPORT:
+	case HID_FEATURE_REPORT:
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	if (*buf__sz < 1)
+		return -EINVAL;
+
+	hdev = (struct hid_device *)ctx->hid; /* discard const */
+
+	report_enum = hdev->report_enum + rtype;
+	report = hid_bpf_ops->hid_get_report(report_enum, buf);
+	if (!report)
+		return -EINVAL;
+
+	report_len = hid_report_len(report);
+
+	if (*buf__sz > report_len)
+		*buf__sz = report_len;
+
+	return 0;
+}
+
 /**
  * hid_bpf_hw_request - Communicate with a HID device
  *
@@ -392,24 +432,14 @@ hid_bpf_hw_request(struct hid_bpf_ctx *ctx, __u8 *buf, size_t buf__sz,
 		   enum hid_report_type rtype, enum hid_class_request reqtype)
 {
 	struct hid_device *hdev;
-	struct hid_report *report;
-	struct hid_report_enum *report_enum;
+	size_t size = buf__sz;
 	u8 *dma_data;
-	u32 report_len;
 	int ret;
 
 	/* check arguments */
-	if (!ctx || !hid_bpf_ops || !buf)
-		return -EINVAL;
-
-	switch (rtype) {
-	case HID_INPUT_REPORT:
-	case HID_OUTPUT_REPORT:
-	case HID_FEATURE_REPORT:
-		break;
-	default:
-		return -EINVAL;
-	}
+	ret = __hid_bpf_hw_check_params(ctx, buf, &size, rtype);
+	if (ret)
+		return ret;
 
 	switch (reqtype) {
 	case HID_REQ_GET_REPORT:
@@ -423,29 +453,16 @@ hid_bpf_hw_request(struct hid_bpf_ctx *ctx, __u8 *buf, size_t buf__sz,
 		return -EINVAL;
 	}
 
-	if (buf__sz < 1)
-		return -EINVAL;
-
 	hdev = (struct hid_device *)ctx->hid; /* discard const */
 
-	report_enum = hdev->report_enum + rtype;
-	report = hid_bpf_ops->hid_get_report(report_enum, buf);
-	if (!report)
-		return -EINVAL;
-
-	report_len = hid_report_len(report);
-
-	if (buf__sz > report_len)
-		buf__sz = report_len;
-
-	dma_data = kmemdup(buf, buf__sz, GFP_KERNEL);
+	dma_data = kmemdup(buf, size, GFP_KERNEL);
 	if (!dma_data)
 		return -ENOMEM;
 
 	ret = hid_bpf_ops->hid_hw_raw_request(hdev,
 					      dma_data[0],
 					      dma_data,
-					      buf__sz,
+					      size,
 					      rtype,
 					      reqtype);
 
@@ -455,6 +472,42 @@ hid_bpf_hw_request(struct hid_bpf_ctx *ctx, __u8 *buf, size_t buf__sz,
 	kfree(dma_data);
 	return ret;
 }
+
+/**
+ * hid_bpf_hw_output_report - Send an output report to a HID device
+ *
+ * @ctx: the HID-BPF context previously allocated in hid_bpf_allocate_context()
+ * @buf: a %PTR_TO_MEM buffer
+ * @buf__sz: the size of the data to transfer
+ *
+ * Returns the number of bytes transferred on success, a negative error code otherwise.
+ */
+__bpf_kfunc int
+hid_bpf_hw_output_report(struct hid_bpf_ctx *ctx, __u8 *buf, size_t buf__sz)
+{
+	struct hid_device *hdev;
+	size_t size = buf__sz;
+	u8 *dma_data;
+	int ret;
+
+	/* check arguments */
+	ret = __hid_bpf_hw_check_params(ctx, buf, &size, HID_OUTPUT_REPORT);
+	if (ret)
+		return ret;
+
+	hdev = (struct hid_device *)ctx->hid; /* discard const */
+
+	dma_data = kmemdup(buf, size, GFP_KERNEL);
+	if (!dma_data)
+		return -ENOMEM;
+
+	ret = hid_bpf_ops->hid_hw_output_report(hdev,
+						dma_data,
+						size);
+
+	kfree(dma_data);
+	return ret;
+}
 __bpf_kfunc_end_defs();
 
 /*
@@ -488,6 +541,7 @@ BTF_ID_FLAGS(func, hid_bpf_attach_prog)
 BTF_ID_FLAGS(func, hid_bpf_allocate_context, KF_ACQUIRE | KF_RET_NULL)
 BTF_ID_FLAGS(func, hid_bpf_release_context, KF_RELEASE)
 BTF_ID_FLAGS(func, hid_bpf_hw_request)
+BTF_ID_FLAGS(func, hid_bpf_hw_output_report)
 BTF_KFUNCS_END(hid_bpf_syscall_kfunc_ids)
 
 static const struct btf_kfunc_id_set hid_bpf_syscall_kfunc_set = {

drivers/hid/hid-core.c

@@ -2974,6 +2974,7 @@ EXPORT_SYMBOL_GPL(hid_check_keys_pressed);
 static struct hid_bpf_ops hid_ops = {
 	.hid_get_report = hid_get_report,
 	.hid_hw_raw_request = hid_hw_raw_request,
+	.hid_hw_output_report = hid_hw_output_report,
 	.owner = THIS_MODULE,
 	.bus_type = &hid_bus_type,
 };

include/linux/hid_bpf.h

@@ -103,6 +103,7 @@ struct hid_bpf_ops {
 				  unsigned char reportnum, __u8 *buf,
 				  size_t len, enum hid_report_type rtype,
 				  enum hid_class_request reqtype);
+	int (*hid_hw_output_report)(struct hid_device *hdev, __u8 *buf, size_t len);
 	struct module *owner;
 	const struct bus_type *bus_type;
 };