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/*
* 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/>.
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#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/livepatch_sample/enabled
* $ cat /proc/cmdline
* <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;
if (!klp_have_reliable_stack() && !patch.immediate) {
/*
* WARNING: Be very careful when using 'patch.immediate' in
* your patches. It's ok to use it for simple patches like
* this, but for more complex patches which change function
* semantics, locking semantics, or data structures, it may not
* be safe. Use of this option will also prevent removal of
* the patch.
*
* See Documentation/livepatch/livepatch.txt for more details.
*/
patch.immediate = true;
pr_notice("The consistency model isn't supported for your architecture. Bypassing safety mechanisms and applying the patch immediately.\n");
}
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_unregister_patch(&patch));
}
module_init(livepatch_init);
module_exit(livepatch_exit);
MODULE_LICENSE("GPL");
MODULE_INFO(livepatch, "Y");
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