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Diffstat (limited to 'samples/livepatch/livepatch-shadow-fix1.c')
| -rw-r--r-- | samples/livepatch/livepatch-shadow-fix1.c | 173 |
1 files changed, 173 insertions, 0 deletions
diff --git a/samples/livepatch/livepatch-shadow-fix1.c b/samples/livepatch/livepatch-shadow-fix1.c new file mode 100644 index 000000000..6701641bf --- /dev/null +++ b/samples/livepatch/livepatch-shadow-fix1.c @@ -0,0 +1,173 @@ +// 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) +{ + int **shadow_leak = shadow_data; + int **leak = ctor_data; + + if (!ctor_data) + return -EINVAL; + + *shadow_leak = *leak; + return 0; +} + +static struct dummy *livepatch_fix1_dummy_alloc(void) +{ + struct dummy *d; + int *leak; + int **shadow_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(*leak), GFP_KERNEL); + if (!leak) + goto err_leak; + + shadow_leak = klp_shadow_alloc(d, SV_LEAK, sizeof(leak), GFP_KERNEL, + shadow_leak_ctor, &leak); + if (!shadow_leak) { + pr_err("%s: failed to allocate shadow variable for the leaking pointer: dummy @ %p, leak @ %p\n", + __func__, d, leak); + goto err_shadow; + } + + pr_info("%s: dummy @ %p, expires @ %lx\n", + __func__, d, d->jiffies_expire); + + return d; + +err_shadow: + kfree(leak); +err_leak: + kfree(d); + return NULL; +} + +static void livepatch_fix1_dummy_leak_dtor(void *obj, void *shadow_data) +{ + void *d = obj; + int **shadow_leak = shadow_data; + + pr_info("%s: dummy @ %p, prevented leak @ %p\n", + __func__, d, *shadow_leak); + kfree(*shadow_leak); +} + +static void livepatch_fix1_dummy_free(struct dummy *d) +{ + int **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"); |