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1// SPDX-License-Identifier: GPL-2.0-or-later2/*3 * Copyright (C) 2017 Joe Lawrence <joe.lawrence@redhat.com>4 */5 6/*7 * livepatch-shadow-fix1.c - Shadow variables, livepatch demo8 *9 * Purpose10 * -------11 *12 * Fixes the memory leak introduced in livepatch-shadow-mod through the13 * use of a shadow variable. This fix demonstrates the "extending" of14 * short-lived data structures by patching its allocation and release15 * functions.16 *17 *18 * Usage19 * -----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 ": " fmt26 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 134 35/* Allocate new dummies every second */36#define ALLOC_PERIOD 137/* Check for expired dummies after a few new ones have been allocated */38#define CLEANUP_PERIOD (3 * ALLOC_PERIOD)39/* Dummies expire after a few cleanup instances */40#define EXPIRE_PERIOD (4 * CLEANUP_PERIOD)41 42struct dummy {43 struct list_head list;44 unsigned long jiffies_expire;45};46 47/*48 * The constructor makes more sense together with klp_shadow_get_or_alloc().49 * In this example, it would be safe to assign the pointer also to the shadow50 * variable returned by klp_shadow_alloc(). But we wanted to show the more51 * complicated use of the API.52 */53static int shadow_leak_ctor(void *obj, void *shadow_data, void *ctor_data)54{55 int **shadow_leak = shadow_data;56 int **leak = ctor_data;57 58 if (!ctor_data)59 return -EINVAL;60 61 *shadow_leak = *leak;62 return 0;63}64 65static struct dummy *livepatch_fix1_dummy_alloc(void)66{67 struct dummy *d;68 int *leak;69 int **shadow_leak;70 71 d = kzalloc(sizeof(*d), GFP_KERNEL);72 if (!d)73 return NULL;74 75 d->jiffies_expire = jiffies +76 msecs_to_jiffies(1000 * EXPIRE_PERIOD);77 78 /*79 * Patch: save the extra memory location into a SV_LEAK shadow80 * variable. A patched dummy_free routine can later fetch this81 * pointer to handle resource release.82 */83 leak = kzalloc(sizeof(*leak), GFP_KERNEL);84 if (!leak)85 goto err_leak;86 87 shadow_leak = klp_shadow_alloc(d, SV_LEAK, sizeof(leak), GFP_KERNEL,88 shadow_leak_ctor, &leak);89 if (!shadow_leak) {90 pr_err("%s: failed to allocate shadow variable for the leaking pointer: dummy @ %p, leak @ %p\n",91 __func__, d, leak);92 goto err_shadow;93 }94 95 pr_info("%s: dummy @ %p, expires @ %lx\n",96 __func__, d, d->jiffies_expire);97 98 return d;99 100err_shadow:101 kfree(leak);102err_leak:103 kfree(d);104 return NULL;105}106 107static void livepatch_fix1_dummy_leak_dtor(void *obj, void *shadow_data)108{109 void *d = obj;110 int **shadow_leak = shadow_data;111 112 pr_info("%s: dummy @ %p, prevented leak @ %p\n",113 __func__, d, *shadow_leak);114 kfree(*shadow_leak);115}116 117static void livepatch_fix1_dummy_free(struct dummy *d)118{119 int **shadow_leak;120 121 /*122 * Patch: fetch the saved SV_LEAK shadow variable, detach and123 * free it. Note: handle cases where this shadow variable does124 * not exist (ie, dummy structures allocated before this livepatch125 * was loaded.)126 */127 shadow_leak = klp_shadow_get(d, SV_LEAK);128 if (shadow_leak)129 klp_shadow_free(d, SV_LEAK, livepatch_fix1_dummy_leak_dtor);130 else131 pr_info("%s: dummy @ %p leaked!\n", __func__, d);132 133 kfree(d);134}135 136static struct klp_func funcs[] = {137 {138 .old_name = "dummy_alloc",139 .new_func = livepatch_fix1_dummy_alloc,140 },141 {142 .old_name = "dummy_free",143 .new_func = livepatch_fix1_dummy_free,144 }, { }145};146 147static struct klp_object objs[] = {148 {149 .name = "livepatch_shadow_mod",150 .funcs = funcs,151 }, { }152};153 154static struct klp_patch patch = {155 .mod = THIS_MODULE,156 .objs = objs,157};158 159static int livepatch_shadow_fix1_init(void)160{161 return klp_enable_patch(&patch);162}163 164static void livepatch_shadow_fix1_exit(void)165{166 /* Cleanup any existing SV_LEAK shadow variables */167 klp_shadow_free_all(SV_LEAK, livepatch_fix1_dummy_leak_dtor);168}169 170module_init(livepatch_shadow_fix1_init);171module_exit(livepatch_shadow_fix1_exit);172MODULE_LICENSE("GPL");173MODULE_INFO(livepatch, "Y");174