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>

2 files changed, 109 insertions, 11 deletions

diff --git a/drivers/hid/bpf/hid_bpf_dispatch.c b/drivers/hid/bpf/hid_bpf_dispatch.c
index 0ef99caf937a..efd4e4b4a615 100644
--- a/drivers/hid/bpf/hid_bpf_dispatch.c
+++ b/drivers/hid/bpf/hid_bpf_dispatch.c
@@ -28,8 +28,9 @@ EXPORT_SYMBOL(hid_bpf_ops);
  *
  * @ctx: The HID-BPF context
  *
- * @return %0 on success and keep processing; a negative error code to interrupt
- * the processing of this event
+ * @return %0 on success and keep processing; a positive value to change the
+ * incoming size buffer; a negative error code to interrupt the processing
+ * of this event
  *
  * Declare an %fmod_ret tracing bpf program to this function and attach this
  * program through hid_bpf_attach_prog() to have this helper called for
@@ -44,23 +45,43 @@ __weak noinline int hid_bpf_device_event(struct hid_bpf_ctx *ctx)
 }
 ALLOW_ERROR_INJECTION(hid_bpf_device_event, ERRNO);
 
-int
+u8 *
 dispatch_hid_bpf_device_event(struct hid_device *hdev, enum hid_report_type type, u8 *data,
-			      u32 size, int interrupt)
+			      u32 *size, int interrupt)
 {
 	struct hid_bpf_ctx_kern ctx_kern = {
 		.ctx = {
 			.hid = hdev,
 			.report_type = type,
-			.size = size,
+			.allocated_size = hdev->bpf.allocated_data,
+			.size = *size,
 		},
-		.data = data,
+		.data = hdev->bpf.device_data,
 	};
+	int ret;
 
 	if (type >= HID_REPORT_TYPES)
-		return -EINVAL;
+		return ERR_PTR(-EINVAL);
+
+	/* no program has been attached yet */
+	if (!hdev->bpf.device_data)
+		return data;
+
+	memset(ctx_kern.data, 0, hdev->bpf.allocated_data);
+	memcpy(ctx_kern.data, data, *size);
+
+	ret = hid_bpf_prog_run(hdev, HID_BPF_PROG_TYPE_DEVICE_EVENT, &ctx_kern);
+	if (ret < 0)
+		return ERR_PTR(ret);
+
+	if (ret) {
+		if (ret > ctx_kern.ctx.allocated_size)
+			return ERR_PTR(-EINVAL);
 
-	return hid_bpf_prog_run(hdev, HID_BPF_PROG_TYPE_DEVICE_EVENT, &ctx_kern);
+		*size = ret;
+	}
+
+	return ctx_kern.data;
 }
 EXPORT_SYMBOL_GPL(dispatch_hid_bpf_device_event);
 
@@ -83,7 +104,7 @@ hid_bpf_get_data(struct hid_bpf_ctx *ctx, unsigned int offset, const size_t rdwr
 
 	ctx_kern = container_of(ctx, struct hid_bpf_ctx_kern, ctx);
 
-	if (rdwr_buf_size + offset > ctx->size)
+	if (rdwr_buf_size + offset > ctx->allocated_size)
 		return NULL;
 
 	return ctx_kern->data + offset;
@@ -110,6 +131,51 @@ static int device_match_id(struct device *dev, const void *id)
 	return hdev->id == *(int *)id;
 }
 
+static int __hid_bpf_allocate_data(struct hid_device *hdev, u8 **data, u32 *size)
+{
+	u8 *alloc_data;
+	unsigned int i, j, max_report_len = 0;
+	size_t alloc_size = 0;
+
+	/* compute the maximum report length for this device */
+	for (i = 0; i < HID_REPORT_TYPES; i++) {
+		struct hid_report_enum *report_enum = hdev->report_enum + i;
+
+		for (j = 0; j < HID_MAX_IDS; j++) {
+			struct hid_report *report = report_enum->report_id_hash[j];
+
+			if (report)
+				max_report_len = max(max_report_len, hid_report_len(report));
+		}
+	}
+
+	/*
+	 * Give us a little bit of extra space and some predictability in the
+	 * buffer length we create. This way, we can tell users that they can
+	 * work on chunks of 64 bytes of memory without having the bpf verifier
+	 * scream at them.
+	 */
+	alloc_size = DIV_ROUND_UP(max_report_len, 64) * 64;
+
+	alloc_data = kzalloc(alloc_size, GFP_KERNEL);
+	if (!alloc_data)
+		return -ENOMEM;
+
+	*data = alloc_data;
+	*size = alloc_size;
+
+	return 0;
+}
+
+static int hid_bpf_allocate_event_data(struct hid_device *hdev)
+{
+	/* hdev->bpf.device_data is already allocated, abort */
+	if (hdev->bpf.device_data)
+		return 0;
+
+	return __hid_bpf_allocate_data(hdev, &hdev->bpf.device_data, &hdev->bpf.allocated_data);
+}
+
 /**
  * hid_bpf_attach_prog - Attach the given @prog_fd to the given HID device
  *
@@ -125,7 +191,7 @@ hid_bpf_attach_prog(unsigned int hid_id, int prog_fd, __u32 flags)
 {
 	struct hid_device *hdev;
 	struct device *dev;
-	int prog_type = hid_bpf_get_prog_attach_type(prog_fd);
+	int err, prog_type = hid_bpf_get_prog_attach_type(prog_fd);
 
 	if (!hid_bpf_ops)
 		return -EINVAL;
@@ -145,6 +211,12 @@ hid_bpf_attach_prog(unsigned int hid_id, int prog_fd, __u32 flags)
 
 	hdev = to_hid_device(dev);
 
+	if (prog_type == HID_BPF_PROG_TYPE_DEVICE_EVENT) {
+		err = hid_bpf_allocate_event_data(hdev);
+		if (err)
+			return err;
+	}
+
 	return __hid_bpf_attach_prog(hdev, prog_type, prog_fd, flags);
 }
 
@@ -158,6 +230,30 @@ static const struct btf_kfunc_id_set hid_bpf_syscall_kfunc_set = {
 	.set   = &hid_bpf_syscall_kfunc_ids,
 };
 
+int hid_bpf_connect_device(struct hid_device *hdev)
+{
+	struct hid_bpf_prog_list *prog_list;
+
+	rcu_read_lock();
+	prog_list = rcu_dereference(hdev->bpf.progs[HID_BPF_PROG_TYPE_DEVICE_EVENT]);
+	rcu_read_unlock();
+
+	/* only allocate BPF data if there are programs attached */
+	if (!prog_list)
+		return 0;
+
+	return hid_bpf_allocate_event_data(hdev);
+}
+EXPORT_SYMBOL_GPL(hid_bpf_connect_device);
+
+void hid_bpf_disconnect_device(struct hid_device *hdev)
+{
+	kfree(hdev->bpf.device_data);
+	hdev->bpf.device_data = NULL;
+	hdev->bpf.allocated_data = 0;
+}
+EXPORT_SYMBOL_GPL(hid_bpf_disconnect_device);
+
 void hid_bpf_destroy_device(struct hid_device *hdev)
 {
 	if (!hdev)
diff --git a/drivers/hid/bpf/hid_bpf_jmp_table.c b/drivers/hid/bpf/hid_bpf_jmp_table.c
index e5f171ab480c..bfcdd7b805a9 100644
--- a/drivers/hid/bpf/hid_bpf_jmp_table.c
+++ b/drivers/hid/bpf/hid_bpf_jmp_table.c
@@ -122,8 +122,10 @@ int hid_bpf_prog_run(struct hid_device *hdev, enum hid_bpf_prog_type type,
 
 		ctx_kern->ctx.index = idx;
 		err = __hid_bpf_tail_call(&ctx_kern->ctx);
-		if (err)
+		if (err < 0)
 			break;
+		if (err)
+			ctx_kern->ctx.retval = err;
 	}
 
  out_unlock: