selftests: add tests for the HID-bpf initial implementation

The tests are pretty basic:
- create a virtual uhid device that no userspace will like (to not mess
  up the running system)
- attach a BPF prog to it
- open the matching hidraw node
- inject one event and check:
  * that the BPF program can do something on the event stream
  * can modify the event stream
- add another test where we attach/detach BPF programs to see if we get
  errors

Note: the Makefile is extracted from selftests/bpf so we can rebuild
the libbpf and bpftool components from the current kernel tree without
relying on system installed components.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

2 files changed, 55 insertions, 0 deletions

diff --git a/tools/testing/selftests/hid/progs/hid.c b/tools/testing/selftests/hid/progs/hid.c
new file mode 100644
index 000000000000..b23ae2304346
--- /dev/null
+++ b/tools/testing/selftests/hid/progs/hid.c
@@ -0,0 +1,41 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2022 Red hat */
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+#include "hid_bpf_helpers.h"
+
+char _license[] SEC("license") = "GPL";
+
+struct attach_prog_args {
+	int prog_fd;
+	unsigned int hid;
+	int retval;
+};
+
+__u64 callback_check = 52;
+__u64 callback2_check = 52;
+
+SEC("?fmod_ret/hid_bpf_device_event")
+int BPF_PROG(hid_first_event, struct hid_bpf_ctx *hid_ctx)
+{
+	__u8 *rw_data = hid_bpf_get_data(hid_ctx, 0 /* offset */, 3 /* size */);
+
+	if (!rw_data)
+		return 0; /* EPERM check */
+
+	callback_check = rw_data[1];
+
+	rw_data[2] = rw_data[1] + 5;
+
+	return 0;
+}
+
+SEC("syscall")
+int attach_prog(struct attach_prog_args *ctx)
+{
+	ctx->retval = hid_bpf_attach_prog(ctx->hid,
+					  ctx->prog_fd,
+					  0);
+	return 0;
+}
diff --git a/tools/testing/selftests/hid/progs/hid_bpf_helpers.h b/tools/testing/selftests/hid/progs/hid_bpf_helpers.h
new file mode 100644
index 000000000000..b9fa33f7d580
--- /dev/null
+++ b/tools/testing/selftests/hid/progs/hid_bpf_helpers.h
@@ -0,0 +1,14 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/* Copyright (c) 2022 Benjamin Tissoires
+ */
+
+#ifndef __HID_BPF_HELPERS_H
+#define __HID_BPF_HELPERS_H
+
+/* following are kfuncs exported by HID for HID-BPF */
+extern __u8 *hid_bpf_get_data(struct hid_bpf_ctx *ctx,
+			      unsigned int offset,
+			      const size_t __sz) __ksym;
+extern int hid_bpf_attach_prog(unsigned int hid_id, int prog_fd, u32 flags) __ksym;
+
+#endif /* __HID_BPF_HELPERS_H */