| // SPDX-License-Identifier: GPL-2.0-or-later |
| /* |
| * Copyright (C) 2017 Joe Lawrence <joe.lawrence@redhat.com> |
| */ |
| |
| /* |
| * livepatch-shadow-fix1.c - Shadow variables, livepatch demo |
| * |
| * Purpose |
| * ------- |
| * |
| * Fixes the memory leak introduced in livepatch-shadow-mod through the |
| * use of a shadow variable. This fix demonstrates the "extending" of |
| * short-lived data structures by patching its allocation and release |
| * functions. |
| * |
| * |
| * Usage |
| * ----- |
| * |
| * This module is not intended to be standalone. See the "Usage" |
| * section of livepatch-shadow-mod.c. |
| */ |
| |
| #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt |
| |
| #include <linux/module.h> |
| #include <linux/kernel.h> |
| #include <linux/livepatch.h> |
| #include <linux/slab.h> |
| |
| /* Shadow variable enums */ |
| #define SV_LEAK 1 |
| |
| /* 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) |
| |
| struct dummy { |
| struct list_head list; |
| unsigned long jiffies_expire; |
| }; |
| |
| /* |
| * The constructor makes more sense together with klp_shadow_get_or_alloc(). |
| * In this example, it would be safe to assign the pointer also to the shadow |
| * variable returned by klp_shadow_alloc(). But we wanted to show the more |
| * complicated use of the API. |
| */ |
| static int shadow_leak_ctor(void *obj, void *shadow_data, void *ctor_data) |
| { |
| void **shadow_leak = shadow_data; |
| void *leak = ctor_data; |
| |
| *shadow_leak = leak; |
| return 0; |
| } |
| |
| static struct dummy *livepatch_fix1_dummy_alloc(void) |
| { |
| struct dummy *d; |
| void *leak; |
| |
| d = kzalloc(sizeof(*d), GFP_KERNEL); |
| if (!d) |
| return NULL; |
| |
| d->jiffies_expire = jiffies + |
| msecs_to_jiffies(1000 * EXPIRE_PERIOD); |
| |
| /* |
| * Patch: save the extra memory location into a SV_LEAK shadow |
| * variable. A patched dummy_free routine can later fetch this |
| * pointer to handle resource release. |
| */ |
| leak = kzalloc(sizeof(int), GFP_KERNEL); |
| if (!leak) { |
| kfree(d); |
| return NULL; |
| } |
| |
| klp_shadow_alloc(d, SV_LEAK, sizeof(leak), GFP_KERNEL, |
| shadow_leak_ctor, leak); |
| |
| pr_info("%s: dummy @ %p, expires @ %lx\n", |
| __func__, d, d->jiffies_expire); |
| |
| return d; |
| } |
| |
| static void livepatch_fix1_dummy_leak_dtor(void *obj, void *shadow_data) |
| { |
| void *d = obj; |
| void **shadow_leak = shadow_data; |
| |
| kfree(*shadow_leak); |
| pr_info("%s: dummy @ %p, prevented leak @ %p\n", |
| __func__, d, *shadow_leak); |
| } |
| |
| static void livepatch_fix1_dummy_free(struct dummy *d) |
| { |
| void **shadow_leak; |
| |
| /* |
| * Patch: fetch the saved SV_LEAK shadow variable, detach and |
| * free it. Note: handle cases where this shadow variable does |
| * not exist (ie, dummy structures allocated before this livepatch |
| * was loaded.) |
| */ |
| shadow_leak = klp_shadow_get(d, SV_LEAK); |
| if (shadow_leak) |
| klp_shadow_free(d, SV_LEAK, livepatch_fix1_dummy_leak_dtor); |
| else |
| pr_info("%s: dummy @ %p leaked!\n", __func__, d); |
| |
| kfree(d); |
| } |
| |
| static struct klp_func funcs[] = { |
| { |
| .old_name = "dummy_alloc", |
| .new_func = livepatch_fix1_dummy_alloc, |
| }, |
| { |
| .old_name = "dummy_free", |
| .new_func = livepatch_fix1_dummy_free, |
| }, { } |
| }; |
| |
| static struct klp_object objs[] = { |
| { |
| .name = "livepatch_shadow_mod", |
| .funcs = funcs, |
| }, { } |
| }; |
| |
| static struct klp_patch patch = { |
| .mod = THIS_MODULE, |
| .objs = objs, |
| }; |
| |
| static int livepatch_shadow_fix1_init(void) |
| { |
| return klp_enable_patch(&patch); |
| } |
| |
| static void livepatch_shadow_fix1_exit(void) |
| { |
| /* Cleanup any existing SV_LEAK shadow variables */ |
| klp_shadow_free_all(SV_LEAK, livepatch_fix1_dummy_leak_dtor); |
| } |
| |
| module_init(livepatch_shadow_fix1_init); |
| module_exit(livepatch_shadow_fix1_exit); |
| MODULE_LICENSE("GPL"); |
| MODULE_INFO(livepatch, "Y"); |