livepatch: samples: add sample live patching module

Add a sample live patching module.

Signed-off-by: Seth Jennings <sjenning@redhat.com>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Reviewed-by: Petr Mladek <pmladek@suse.cz>
Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

1 files changed, 87 insertions, 0 deletions

diff --git a/samples/livepatch/livepatch-sample.c b/samples/livepatch/livepatch-sample.c
new file mode 100644
index 000000000000..21f159d51074
--- /dev/null
+++ b/samples/livepatch/livepatch-sample.c
@@ -0,0 +1,87 @@
+/*
+ * livepatch-sample.c - Kernel Live Patching Sample Module
+ *
+ * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/livepatch.h>
+
+/*
+ * This (dumb) live patch overrides the function that prints the
+ * kernel boot cmdline when /proc/cmdline is read.
+ *
+ * Example:
+ * $ cat /proc/cmdline
+ * <your cmdline>
+ * $ insmod livepatch-sample.ko
+ * $ cat /proc/cmdline
+ * this has been live patched
+ * $ echo 0 > /sys/kernel/livepatch/klp_sample/enabled
+ * <your cmdline>
+ */
+
+#include <linux/seq_file.h>
+static int livepatch_cmdline_proc_show(struct seq_file *m, void *v)
+{
+        seq_printf(m, "%s\n", "this has been live patched");
+        return 0;
+}
+
+static struct klp_func funcs[] = {
+        {
+                .old_name = "cmdline_proc_show",
+                .new_func = livepatch_cmdline_proc_show,
+        }, { }
+};
+
+static struct klp_object objs[] = {
+        {
+                /* name being NULL means vmlinux */
+                .funcs = funcs,
+        }, { }
+};
+
+static struct klp_patch patch = {
+        .mod = THIS_MODULE,
+        .objs = objs,
+};
+
+static int livepatch_init(void)
+{
+        int ret;
+
+        ret = klp_register_patch(&patch);
+        if (ret)
+                return ret;
+        ret = klp_enable_patch(&patch);
+        if (ret) {
+                WARN_ON(klp_unregister_patch(&patch));
+                return ret;
+        }
+        return 0;
+}
+
+static void livepatch_exit(void)
+{
+        WARN_ON(klp_disable_patch(&patch));
+        WARN_ON(klp_unregister_patch(&patch));
+}
+
+module_init(livepatch_init);
+module_exit(livepatch_exit);
+MODULE_LICENSE("GPL");