bpf: export crash_kexec() as destructive kfunc

Allow properly marked bpf programs to call crash_kexec().
Signed-off-by: NArtem Savkov <asavkov@redhat.com>
Link: https://lore.kernel.org/r/20220810065905.475418-3-asavkov@redhat.comSigned-off-by: NAlexei Starovoitov <ast@kernel.org>

kernel/bpf/helpers.c

@@ -1725,3 +1725,21 @@ bpf_base_func_proto(enum bpf_func_id func_id)
 		return NULL;
 	}
 }
+
+BTF_SET8_START(tracing_btf_ids)
+#ifdef CONFIG_KEXEC_CORE
+BTF_ID_FLAGS(func, crash_kexec, KF_DESTRUCTIVE)
+#endif
+BTF_SET8_END(tracing_btf_ids)
+
+static const struct btf_kfunc_id_set tracing_kfunc_set = {
+	.owner = THIS_MODULE,
+	.set   = &tracing_btf_ids,
+};
+
+static int __init kfunc_init(void)
+{
+	return register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING, &tracing_kfunc_set);
+}
+
+late_initcall(kfunc_init);