cachepc-linux

Fork of AMDESE/linux with modifications for CachePC side-channel attack
git clone https://git.sinitax.com/sinitax/cachepc-linux
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livepatch-shadow-fix1.c (4014B)

      1// SPDX-License-Identifier: GPL-2.0-or-later
      2/*
      3 * Copyright (C) 2017 Joe Lawrence <joe.lawrence@redhat.com>
      4 */
      5
      6/*
      7 * livepatch-shadow-fix1.c - Shadow variables, livepatch demo
      8 *
      9 * Purpose
     10 * -------
     11 *
     12 * Fixes the memory leak introduced in livepatch-shadow-mod through the
     13 * use of a shadow variable.  This fix demonstrates the "extending" of
     14 * short-lived data structures by patching its allocation and release
     15 * functions.
     16 *
     17 *
     18 * Usage
     19 * -----
     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 ": " fmt
     26
     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		1
     34
     35/* Allocate new dummies every second */
     36#define ALLOC_PERIOD	1
     37/* 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 shadow
     50 * variable returned by klp_shadow_alloc().  But we wanted to show the more
     51 * 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 shadow
     80	 * variable.  A patched dummy_free routine can later fetch this
     81	 * 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 and
    123	 * free it.  Note: handle cases where this shadow variable does
    124	 * not exist (ie, dummy structures allocated before this livepatch
    125	 * 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	else
    131		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");