HID: bpf: allocate data memory for device_event BPF programs

We need to also be able to change the size of the report.
Reducing it is easy, because we already have the incoming buffer that is
big enough, but extending it is harder.

Pre-allocate a buffer that is big enough to handle all reports of the
device, and use that as the primary buffer for BPF programs.
To be able to change the size of the buffer, we change the device_event
API and request it to return the size of the buffer.

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

1 files changed, 32 insertions, 5 deletions

diff --git a/include/linux/hid_bpf.h b/include/linux/hid_bpf.h
index de3fb1c376d2..b3de462ef3a6 100644
--- a/include/linux/hid_bpf.h
+++ b/include/linux/hid_bpf.h
@@ -28,15 +28,32 @@ struct hid_device;
  *         a bigger index).
  * @hid: the ``struct hid_device`` representing the device itself
  * @report_type: used for ``hid_bpf_device_event()``
+ * @allocated_size: Allocated size of data.
+ *
+ *                  This is how much memory is available and can be requested
+ *                  by the HID program.
+ *                  Note that for ``HID_BPF_RDESC_FIXUP``, that memory is set to
+ *                  ``4096`` (4 KB)
  * @size: Valid data in the data field.
  *
  *        Programs can get the available valid size in data by fetching this field.
+ *        Programs can also change this value by returning a positive number in the
+ *        program.
+ *        To discard the event, return a negative error code.
+ *
+ *        ``size`` must always be less or equal than ``allocated_size`` (it is enforced
+ *        once all BPF programs have been run).
+ * @retval: Return value of the previous program.
  */
 struct hid_bpf_ctx {
 	__u32 index;
 	const struct hid_device *hid;
+	__u32 allocated_size;
 	enum hid_report_type report_type;
-	__s32 size;
+	union {
+		__s32 retval;
+		__s32 size;
+	};
 };
 
 /**
@@ -96,6 +113,12 @@ struct hid_bpf_prog_list {
 
 /* stored in each device */
 struct hid_bpf {
+	u8 *device_data;		/* allocated when a bpf program of type
+					 * SEC(f.../hid_bpf_device_event) has been attached
+					 * to this HID device
+					 */
+	u32 allocated_data;
+
 	struct hid_bpf_prog_list __rcu *progs[HID_BPF_PROG_TYPE_MAX];	/* attached BPF progs */
 	bool destroyed;			/* prevents the assignment of any progs */
 
@@ -103,13 +126,17 @@ struct hid_bpf {
 };
 
 #ifdef CONFIG_HID_BPF
-int dispatch_hid_bpf_device_event(struct hid_device *hid, enum hid_report_type type, u8 *data,
-				  u32 size, int interrupt);
+u8 *dispatch_hid_bpf_device_event(struct hid_device *hid, enum hid_report_type type, u8 *data,
+				  u32 *size, int interrupt);
+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);
 void hid_bpf_device_init(struct hid_device *hid);
 #else /* CONFIG_HID_BPF */
-static inline int dispatch_hid_bpf_device_event(struct hid_device *hid, enum hid_report_type type,
-						u8 *data, u32 size, int interrupt) { return 0; }
+static inline u8 *dispatch_hid_bpf_device_event(struct hid_device *hid, enum hid_report_type type,
+						u8 *data, u32 *size, int interrupt) { return NULL; }
+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) {}
 static inline void hid_bpf_device_init(struct hid_device *hid) {}
 #endif /* CONFIG_HID_BPF */