174 lines
3.9 KiB
C
174 lines
3.9 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* Copyright (C) 2017 Joe Lawrence <joe.lawrence@redhat.com>
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*/
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/*
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* livepatch-shadow-fix1.c - Shadow variables, livepatch demo
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*
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* Purpose
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* -------
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*
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* Fixes the memory leak introduced in livepatch-shadow-mod through the
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* use of a shadow variable. This fix demonstrates the "extending" of
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* short-lived data structures by patching its allocation and release
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* functions.
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*
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*
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* Usage
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* -----
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*
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* This module is not intended to be standalone. See the "Usage"
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* section of livepatch-shadow-mod.c.
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*/
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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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#include <linux/module.h>
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#include <linux/kernel.h>
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#include <linux/livepatch.h>
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#include <linux/slab.h>
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/* Shadow variable enums */
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#define SV_LEAK 1
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/* Allocate new dummies every second */
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#define ALLOC_PERIOD 1
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/* Check for expired dummies after a few new ones have been allocated */
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#define CLEANUP_PERIOD (3 * ALLOC_PERIOD)
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/* Dummies expire after a few cleanup instances */
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#define EXPIRE_PERIOD (4 * CLEANUP_PERIOD)
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struct dummy {
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struct list_head list;
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unsigned long jiffies_expire;
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};
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/*
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* The constructor makes more sense together with klp_shadow_get_or_alloc().
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* In this example, it would be safe to assign the pointer also to the shadow
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* variable returned by klp_shadow_alloc(). But we wanted to show the more
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* complicated use of the API.
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*/
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static int shadow_leak_ctor(void *obj, void *shadow_data, void *ctor_data)
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{
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int **shadow_leak = shadow_data;
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int **leak = ctor_data;
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if (!ctor_data)
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return -EINVAL;
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*shadow_leak = *leak;
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return 0;
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}
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static struct dummy *livepatch_fix1_dummy_alloc(void)
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{
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struct dummy *d;
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int *leak;
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int **shadow_leak;
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d = kzalloc(sizeof(*d), GFP_KERNEL);
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if (!d)
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return NULL;
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d->jiffies_expire = jiffies +
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msecs_to_jiffies(1000 * EXPIRE_PERIOD);
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/*
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* Patch: save the extra memory location into a SV_LEAK shadow
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* variable. A patched dummy_free routine can later fetch this
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* pointer to handle resource release.
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*/
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leak = kzalloc(sizeof(*leak), GFP_KERNEL);
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if (!leak)
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goto err_leak;
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shadow_leak = klp_shadow_alloc(d, SV_LEAK, sizeof(leak), GFP_KERNEL,
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shadow_leak_ctor, &leak);
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if (!shadow_leak) {
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pr_err("%s: failed to allocate shadow variable for the leaking pointer: dummy @ %p, leak @ %p\n",
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__func__, d, leak);
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goto err_shadow;
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}
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pr_info("%s: dummy @ %p, expires @ %lx\n",
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__func__, d, d->jiffies_expire);
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return d;
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err_shadow:
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kfree(leak);
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err_leak:
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kfree(d);
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return NULL;
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}
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static void livepatch_fix1_dummy_leak_dtor(void *obj, void *shadow_data)
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{
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void *d = obj;
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int **shadow_leak = shadow_data;
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kfree(*shadow_leak);
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pr_info("%s: dummy @ %p, prevented leak @ %p\n",
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__func__, d, *shadow_leak);
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}
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static void livepatch_fix1_dummy_free(struct dummy *d)
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{
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int **shadow_leak;
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/*
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* Patch: fetch the saved SV_LEAK shadow variable, detach and
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* free it. Note: handle cases where this shadow variable does
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* not exist (ie, dummy structures allocated before this livepatch
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* was loaded.)
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*/
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shadow_leak = klp_shadow_get(d, SV_LEAK);
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if (shadow_leak)
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klp_shadow_free(d, SV_LEAK, livepatch_fix1_dummy_leak_dtor);
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else
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pr_info("%s: dummy @ %p leaked!\n", __func__, d);
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kfree(d);
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}
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static struct klp_func funcs[] = {
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{
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.old_name = "dummy_alloc",
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.new_func = livepatch_fix1_dummy_alloc,
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},
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{
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.old_name = "dummy_free",
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.new_func = livepatch_fix1_dummy_free,
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}, { }
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};
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static struct klp_object objs[] = {
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{
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.name = "livepatch_shadow_mod",
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.funcs = funcs,
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}, { }
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};
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static struct klp_patch patch = {
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.mod = THIS_MODULE,
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.objs = objs,
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};
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static int livepatch_shadow_fix1_init(void)
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{
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return klp_enable_patch(&patch);
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}
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static void livepatch_shadow_fix1_exit(void)
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{
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/* Cleanup any existing SV_LEAK shadow variables */
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klp_shadow_free_all(SV_LEAK, livepatch_fix1_dummy_leak_dtor);
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}
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module_init(livepatch_shadow_fix1_init);
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module_exit(livepatch_shadow_fix1_exit);
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MODULE_LICENSE("GPL");
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MODULE_INFO(livepatch, "Y");
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