linux/samples/livepatch/livepatch-shadow-mod.c at multikernel-arm · multikernel/linux · GitHub

History

212 lines (177 loc) · 5.28 KB

Raw

100

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

127

128

129

130

131

132

133

134

135

136

137

138

139

140

141

142

143

144

145

146

147

148

149

150

151

152

153

154

155

156

157

158

159

160

161

162

163

164

165

166

167

168

169

170

171

172

173

174

175

176

177

178

179

180

181

182

183

184

185

186

187

188

189

190

191

192

193

194

195

196

197

198

199

200

201

202

203

204

205

206

207

208

209

210

211

212

// SPDX-License-Identifier: GPL-2.0-or-later

* livepatch-shadow-mod.c - Shadow variables, buggy module demo

* Purpose

* -------

* As a demonstration of livepatch shadow variable API, this module

* introduces memory leak behavior that livepatch modules

* livepatch-shadow-fix1.ko and livepatch-shadow-fix2.ko correct and

* enhance.

* WARNING - even though the livepatch-shadow-fix modules patch the

* memory leak, please load these modules at your own risk -- some

* amount of memory may leaked before the bug is patched.

* Usage

* -----

* Step 1 - Load the buggy demonstration module:

* insmod samples/livepatch/livepatch-shadow-mod.ko

* Watch dmesg output for a few moments to see new dummy being allocated

* and a periodic cleanup check. (Note: a small amount of memory is

* being leaked.)

* Step 2 - Load livepatch fix1:

* insmod samples/livepatch/livepatch-shadow-fix1.ko

* Continue watching dmesg and note that now livepatch_fix1_dummy_free()

* and livepatch_fix1_dummy_alloc() are logging messages about leaked

* memory and eventually leaks prevented.

* Step 3 - Load livepatch fix2 (on top of fix1):

* insmod samples/livepatch/livepatch-shadow-fix2.ko

* This module extends functionality through shadow variables, as a new

* "check" counter is added to the dummy structure. Periodic dmesg

* messages will log these as dummies are cleaned up.

* Step 4 - Cleanup

* Unwind the demonstration by disabling the livepatch fix modules, then

* removing them and the demo module:

* echo 0 > /sys/kernel/livepatch/livepatch_shadow_fix2/enabled

* echo 0 > /sys/kernel/livepatch/livepatch_shadow_fix1/enabled

* rmmod livepatch-shadow-fix2

* rmmod livepatch-shadow-fix1

* rmmod livepatch-shadow-mod

#include <linux/kernel.h>

#include <linux/module.h>

#include <linux/sched.h>

#include <linux/slab.h>

#include <linux/stat.h>

#include <linux/workqueue.h>

MODULE_LICENSE("GPL");

MODULE_AUTHOR("Joe Lawrence <joe.lawrence@redhat.com>");

MODULE_DESCRIPTION("Buggy module for shadow variable demo");

/* Allocate new dummies every second */

#define ALLOC_PERIOD 1

/* Check for expired dummies after a few new ones have been allocated */

#define CLEANUP_PERIOD (3 * ALLOC_PERIOD)

/* Dummies expire after a few cleanup instances */

#define EXPIRE_PERIOD (4 * CLEANUP_PERIOD)

* Keep a list of all the dummies so we can clean up any residual ones

* on module exit

static LIST_HEAD(dummy_list);

static DEFINE_MUTEX(dummy_list_mutex);

struct dummy {

struct list_head list;

unsigned long jiffies_expire;

};

static __used noinline struct dummy *dummy_alloc(void)

{

struct dummy *d;

int *leak;

d = kzalloc(sizeof(*d), GFP_KERNEL);

if (!d)

return NULL;

d->jiffies_expire = jiffies + secs_to_jiffies(EXPIRE_PERIOD);

/* Oops, forgot to save leak! */

leak = kzalloc(sizeof(*leak), GFP_KERNEL);

if (!leak) {

kfree(d);

return NULL;

}

pr_info("%s: dummy @ %p, expires @ %lx\n",

__func__, d, d->jiffies_expire);

return d;

}

static __used noinline void dummy_free(struct dummy *d)

{

pr_info("%s: dummy @ %p, expired = %lx\n",

__func__, d, d->jiffies_expire);

kfree(d);

}

static __used noinline bool dummy_check(struct dummy *d,

unsigned long jiffies)

{

return time_after(jiffies, d->jiffies_expire);

}

* alloc_work_func: allocates new dummy structures, allocates additional

* memory, aptly named "leak", but doesn't keep

* permanent record of it.

static void alloc_work_func(struct work_struct *work);

static DECLARE_DELAYED_WORK(alloc_dwork, alloc_work_func);

static void alloc_work_func(struct work_struct *work)

{

struct dummy *d;

d = dummy_alloc();

if (!d)

return;

mutex_lock(&dummy_list_mutex);

list_add(&d->list, &dummy_list);

mutex_unlock(&dummy_list_mutex);

schedule_delayed_work(&alloc_dwork, secs_to_jiffies(ALLOC_PERIOD));

}

* cleanup_work_func: frees dummy structures. Without knownledge of

* "leak", it leaks the additional memory that

* alloc_work_func created.

static void cleanup_work_func(struct work_struct *work);

static DECLARE_DELAYED_WORK(cleanup_dwork, cleanup_work_func);

static void cleanup_work_func(struct work_struct *work)

{

struct dummy *d, *tmp;

unsigned long j;

j = jiffies;

pr_info("%s: jiffies = %lx\n", __func__, j);

mutex_lock(&dummy_list_mutex);

list_for_each_entry_safe(d, tmp, &dummy_list, list) {

/* Kick out and free any expired dummies */

if (dummy_check(d, j)) {

list_del(&d->list);

dummy_free(d);

}

mutex_unlock(&dummy_list_mutex);

schedule_delayed_work(&cleanup_dwork, secs_to_jiffies(CLEANUP_PERIOD));

}

static int livepatch_shadow_mod_init(void)

{

schedule_delayed_work(&alloc_dwork, secs_to_jiffies(ALLOC_PERIOD));

schedule_delayed_work(&cleanup_dwork, secs_to_jiffies(CLEANUP_PERIOD));

return 0;

}

static void livepatch_shadow_mod_exit(void)

{

struct dummy *d, *tmp;

/* Wait for any dummies at work */

cancel_delayed_work_sync(&alloc_dwork);

cancel_delayed_work_sync(&cleanup_dwork);

/* Cleanup residual dummies */

list_for_each_entry_safe(d, tmp, &dummy_list, list) {

list_del(&d->list);

dummy_free(d);

}

module_init(livepatch_shadow_mod_init);

module_exit(livepatch_shadow_mod_exit);

linux/samples/livepatch/livepatch-shadow-mod.c at multikernel-arm · multikernel/linux · GitHub

Expand file tree

Breadcrumbs

livepatch-shadow-mod.c

Latest commit

History

Breadcrumbs

livepatch-shadow-mod.c

File metadata and controls