1// SPDX-License-Identifier: GPL-2.0-or-later
  2/*
  3 * Copyright (C) 2017 Joe Lawrence <joe.lawrence@redhat.com>
  4 */
  5
  6/*
  7 * livepatch-shadow-fix2.c - Shadow variables, livepatch demo
  8 *
  9 * Purpose
 10 * -------
 11 *
 12 * Adds functionality to livepatch-shadow-mod's in-flight data
 13 * structures through a shadow variable.  The livepatch patches a
 14 * routine that periodically inspects data structures, incrementing a
 15 * per-data-structure counter, creating the counter if needed.
 16 *
 17 *
 18 * Usage
 19 * -----
 20 *
 21 * This module is not intended to be standalone.  See the "Usage"
 22 * section of livepatch-shadow-mod.c.
 23 */
 24
 25#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 26
 27#include <linux/module.h>
 28#include <linux/kernel.h>
 29#include <linux/livepatch.h>
 30#include <linux/slab.h>
 31
 32/* Shadow variable enums */
 33#define SV_LEAK		1
 34#define SV_COUNTER	2
 35
 36struct dummy {
 37	struct list_head list;
 38	unsigned long jiffies_expire;
 39};
 40
 41static bool livepatch_fix2_dummy_check(struct dummy *d, unsigned long jiffies)
 42{
 43	int *shadow_count;
 44
 45	/*
 46	 * Patch: handle in-flight dummy structures, if they do not
 47	 * already have a SV_COUNTER shadow variable, then attach a
 48	 * new one.
 49	 */
 50	shadow_count = klp_shadow_get_or_alloc(d, SV_COUNTER,
 51				sizeof(*shadow_count), GFP_NOWAIT,
 52				NULL, NULL);
 53	if (shadow_count)
 54		*shadow_count += 1;
 55
 56	return time_after(jiffies, d->jiffies_expire);
 57}
 58
 59static void livepatch_fix2_dummy_leak_dtor(void *obj, void *shadow_data)
 60{
 61	void *d = obj;
 62	void **shadow_leak = shadow_data;
 63
 64	kfree(*shadow_leak);
 65	pr_info("%s: dummy @ %p, prevented leak @ %p\n",
 66			 __func__, d, *shadow_leak);
 67}
 68
 69static void livepatch_fix2_dummy_free(struct dummy *d)
 70{
 71	void **shadow_leak;
 72	int *shadow_count;
 73
 74	/* Patch: copy the memory leak patch from the fix1 module. */
 75	shadow_leak = klp_shadow_get(d, SV_LEAK);
 76	if (shadow_leak)
 77		klp_shadow_free(d, SV_LEAK, livepatch_fix2_dummy_leak_dtor);
 78	else
 79		pr_info("%s: dummy @ %p leaked!\n", __func__, d);
 80
 81	/*
 82	 * Patch: fetch the SV_COUNTER shadow variable and display
 83	 * the final count.  Detach the shadow variable.
 84	 */
 85	shadow_count = klp_shadow_get(d, SV_COUNTER);
 86	if (shadow_count) {
 87		pr_info("%s: dummy @ %p, check counter = %d\n",
 88			__func__, d, *shadow_count);
 89		klp_shadow_free(d, SV_COUNTER, NULL);
 90	}
 91
 92	kfree(d);
 93}
 94
 95static struct klp_func funcs[] = {
 96	{
 97		.old_name = "dummy_check",
 98		.new_func = livepatch_fix2_dummy_check,
 99	},
100	{
101		.old_name = "dummy_free",
102		.new_func = livepatch_fix2_dummy_free,
103	}, { }
104};
105
106static struct klp_object objs[] = {
107	{
108		.name = "livepatch_shadow_mod",
109		.funcs = funcs,
110	}, { }
111};
112
113static struct klp_patch patch = {
114	.mod = THIS_MODULE,
115	.objs = objs,
116};
117
118static int livepatch_shadow_fix2_init(void)
119{
120	return klp_enable_patch(&patch);
121}
122
123static void livepatch_shadow_fix2_exit(void)
124{
125	/* Cleanup any existing SV_COUNTER shadow variables */
126	klp_shadow_free_all(SV_COUNTER, NULL);
127}
128
129module_init(livepatch_shadow_fix2_init);
130module_exit(livepatch_shadow_fix2_exit);
131MODULE_LICENSE("GPL");
132MODULE_INFO(livepatch, "Y");