selftests/hid: add tests for hid_hw_output_report HID-BPF hooks

We add 3 new tests:
- first, we make sure we can prevent the output_report to happen
- second, we make sure that we can detect that a given hidraw client
  was actually doing the request, and for that client only, call ourself
  hid_bpf_hw_output_report(), returning a custom value
- last, we ensure that we can not loop between hooks for
  hid_hw_output_report() and manual calls to hid_bpf_hw_output_report()
  from that same hook

Link: https://patch.msgid.link/20240626-hid_hw_req_bpf-v2-8-cfd60fb6c79f@kernel.org
Acked-by: Jiri Kosina <jkosina@suse.com>
Signed-off-by: Benjamin Tissoires <bentiss@kernel.org>

drivers/hid/bpf/hid_bpf_dispatch.c

@@ -461,11 +461,16 @@ hid_bpf_hw_request(struct hid_bpf_ctx *ctx, __u8 *buf, size_t buf__sz,
 __bpf_kfunc int
 hid_bpf_hw_output_report(struct hid_bpf_ctx *ctx, __u8 *buf, size_t buf__sz)
 {
+	struct hid_bpf_ctx_kern *ctx_kern;
 	struct hid_device *hdev;
 	size_t size = buf__sz;
 	u8 *dma_data;
 	int ret;
 
+	ctx_kern = container_of(ctx, struct hid_bpf_ctx_kern, ctx);
+	if (ctx_kern->from_bpf)
+		return -EDEADLOCK;
+
 	/* check arguments */
 	ret = __hid_bpf_hw_check_params(ctx, buf, &size, HID_OUTPUT_REPORT);
 	if (ret)

tools/testing/selftests/hid/hid_bpf.c

@@ -1028,6 +1028,108 @@ TEST_F(hid_bpf, test_hid_infinite_loop_raw_request_call)
 	ASSERT_EQ(err, 3) TH_LOG("unexpected returned size while reading HIDIOCGFEATURE: %d", err);
 }
 
+/*
+ * Call hid_hw_output_report against the given uhid device,
+ * check that the program is called and prevents the
+ * call to uhid.
+ */
+TEST_F(hid_bpf, test_hid_filter_output_report_call)
+{
+	const struct test_program progs[] = {
+		{ .name = "hid_test_filter_output_report" },
+	};
+	__u8 buf[10] = {0};
+	int err;
+
+	LOAD_PROGRAMS(progs);
+
+	/* first check that we did not attach to device_event */
+
+	/* inject one event */
+	buf[0] = 1;
+	buf[1] = 42;
+	uhid_send_event(_metadata, self->uhid_fd, buf, 6);
+
+	/* read the data from hidraw */
+	memset(buf, 0, sizeof(buf));
+	err = read(self->hidraw_fd, buf, sizeof(buf));
+	ASSERT_EQ(err, 6) TH_LOG("read_hidraw");
+	ASSERT_EQ(buf[0], 1);
+	ASSERT_EQ(buf[1], 42);
+	ASSERT_EQ(buf[2], 0) TH_LOG("leftovers_from_previous_test");
+
+	/* now check that our program is preventing hid_hw_output_report() */
+
+	buf[0] = 1; /* report ID */
+	buf[1] = 2;
+	buf[2] = 42;
+
+	err = write(self->hidraw_fd, buf, 3);
+	ASSERT_LT(err, 0) TH_LOG("unexpected success while sending hid_hw_output_report: %d", err);
+	ASSERT_EQ(errno, 25) TH_LOG("unexpected error code while sending hid_hw_output_report: %d",
+				    errno);
+
+	/* remove our bpf program and check that we can now emit commands */
+
+	/* detach the program */
+	detach_bpf(self);
+
+	self->hidraw_fd = open_hidraw(self->dev_id);
+	ASSERT_GE(self->hidraw_fd, 0) TH_LOG("open_hidraw");
+
+	err = write(self->hidraw_fd, buf, 3);
+	ASSERT_GE(err, 0) TH_LOG("error while sending hid_hw_output_report: %d", err);
+}
+
+/*
+ * Call hid_hw_output_report against the given uhid device,
+ * check that the program is called and can issue the call
+ * to uhid and transform the answer.
+ */
+TEST_F(hid_bpf, test_hid_change_output_report_call)
+{
+	const struct test_program progs[] = {
+		{ .name = "hid_test_hidraw_output_report" },
+	};
+	__u8 buf[10] = {0};
+	int err;
+
+	LOAD_PROGRAMS(progs);
+
+	/* emit hid_hw_output_report from hidraw */
+	buf[0] = 1; /* report ID */
+	buf[1] = 2;
+	buf[2] = 42;
+
+	err = write(self->hidraw_fd, buf, 10);
+	ASSERT_EQ(err, 2) TH_LOG("unexpected returned size while sending hid_hw_output_report: %d",
+				 err);
+}
+
+/*
+ * Call hid_hw_output_report against the given uhid device,
+ * check that the program is not making infinite loops.
+ */
+TEST_F(hid_bpf, test_hid_infinite_loop_output_report_call)
+{
+	const struct test_program progs[] = {
+		{ .name = "hid_test_infinite_loop_output_report" },
+	};
+	__u8 buf[10] = {0};
+	int err;
+
+	LOAD_PROGRAMS(progs);
+
+	/* emit hid_hw_output_report from hidraw */
+	buf[0] = 1; /* report ID */
+	buf[1] = 2;
+	buf[2] = 42;
+
+	err = write(self->hidraw_fd, buf, 8);
+	ASSERT_EQ(err, 2) TH_LOG("unexpected returned size while sending hid_hw_output_report: %d",
+				 err);
+}
+
 /*
  * Attach hid_insert{0,1,2} to the given uhid device,
  * retrieve and open the matching hidraw node,

tools/testing/selftests/hid/progs/hid.c

@@ -385,3 +385,61 @@ SEC(".struct_ops.link")
 struct hid_bpf_ops test_infinite_loop_raw_request = {
 	.hid_hw_request = (void *)hid_test_infinite_loop_raw_request,
 };
+
+SEC("?struct_ops/hid_hw_output_report")
+int BPF_PROG(hid_test_filter_output_report, struct hid_bpf_ctx *hctx, unsigned char reportnum,
+	     enum hid_report_type rtype, enum hid_class_request reqtype, __u64 source)
+{
+	return -25;
+}
+
+SEC(".struct_ops.link")
+struct hid_bpf_ops test_filter_output_report = {
+	.hid_hw_output_report = (void *)hid_test_filter_output_report,
+};
+
+SEC("?struct_ops.s/hid_hw_output_report")
+int BPF_PROG(hid_test_hidraw_output_report, struct hid_bpf_ctx *hctx, __u64 source)
+{
+	__u8 *data = hid_bpf_get_data(hctx, 0 /* offset */, 3 /* size */);
+	int ret;
+
+	if (!data)
+		return 0; /* EPERM check */
+
+	/* check if the incoming request comes from our hidraw operation */
+	if (source == (__u64)current_file)
+		return hid_bpf_hw_output_report(hctx, data, 2);
+
+	return 0;
+}
+
+SEC(".struct_ops.link")
+struct hid_bpf_ops test_hidraw_output_report = {
+	.hid_hw_output_report = (void *)hid_test_hidraw_output_report,
+};
+
+SEC("?struct_ops.s/hid_hw_output_report")
+int BPF_PROG(hid_test_infinite_loop_output_report, struct hid_bpf_ctx *hctx, __u64 source)
+{
+	__u8 *data = hid_bpf_get_data(hctx, 0 /* offset */, 3 /* size */);
+	int ret;
+
+	if (!data)
+		return 0; /* EPERM check */
+
+	/* always forward the request as-is to the device, hid-bpf should prevent
+	 * infinite loops.
+	 */
+
+	ret = hid_bpf_hw_output_report(hctx, data, 2);
+	if (ret == 2)
+		return 2;
+
+	return 0;
+}
+
+SEC(".struct_ops.link")
+struct hid_bpf_ops test_infinite_loop_output_report = {
+	.hid_hw_output_report = (void *)hid_test_infinite_loop_output_report,
+};