bpf: lsm: Add selftests for BPF_PROG_TYPE_LSM

* Load/attach a BPF program that hooks to file_mprotect (int)
  and bprm_committed_creds (void).
* Perform an action that triggers the hook.
* Verify if the audit event was received using the shared global
  variables for the process executed.
* Verify if the mprotect returns a -EPERM.

Signed-off-by: KP Singh <kpsingh@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Brendan Jackman <jackmanb@google.com>
Reviewed-by: Florent Revest <revest@google.com>
Reviewed-by: Thomas Garnier <thgarnie@google.com>
Reviewed-by: James Morris <jamorris@linux.microsoft.com>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200329004356.27286-8-kpsingh@chromium.org

tools/testing/selftests/bpf/progs/lsm.c

@@ -0,0 +1,48 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Copyright 2020 Google LLC.
+ */
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+#include  <errno.h>
+
+char _license[] SEC("license") = "GPL";
+
+int monitored_pid = 0;
+int mprotect_count = 0;
+int bprm_count = 0;
+
+SEC("lsm/file_mprotect")
+int BPF_PROG(test_int_hook, struct vm_area_struct *vma,
+	     unsigned long reqprot, unsigned long prot, int ret)
+{
+	if (ret != 0)
+		return ret;
+
+	__u32 pid = bpf_get_current_pid_tgid() >> 32;
+	int is_heap = 0;
+
+	is_heap = (vma->vm_start >= vma->vm_mm->start_brk &&
+		   vma->vm_end <= vma->vm_mm->brk);
+
+	if (is_heap && monitored_pid == pid) {
+		mprotect_count++;
+		ret = -EPERM;
+	}
+
+	return ret;
+}
+
+SEC("lsm/bprm_committed_creds")
+int BPF_PROG(test_void_hook, struct linux_binprm *bprm)
+{
+	__u32 pid = bpf_get_current_pid_tgid() >> 32;
+
+	if (monitored_pid == pid)
+		bprm_count++;
+
+	return 0;
+}