![Petr Mladek](/assets/img/avatar_default.png)
We might need to do some actions before the shadow variable is freed. For example, we might need to remove it from a list or free some data that it points to. This is already possible now. The user can get the shadow variable by klp_shadow_get(), do the necessary actions, and then call klp_shadow_free(). This patch allows to do it a more elegant way. The user could implement the needed actions in a callback that is passed to klp_shadow_free() as a parameter. The callback usually does reverse operations to the constructor callback that can be called by klp_shadow_*alloc(). It is especially useful for klp_shadow_free_all(). There we need to do these extra actions for each found shadow variable with the given ID. Note that the memory used by the shadow variable itself is still released later by rcu callback. It is needed to protect internal structures that keep all shadow variables. But the destructor is called immediately. The shadow variable must not be access anyway after klp_shadow_free() is called. The user is responsible to protect this any suitable way. Be aware that the destructor is called under klp_shadow_lock. It is the same as for the contructor in klp_shadow_alloc(). Signed-off-by: Petr Mladek <pmladek@suse.com> Acked-by: Josh Poimboeuf <jpoimboe@redhat.com> Acked-by: Miroslav Benes <mbenes@suse.cz> Signed-off-by: Jiri Kosina <jkosina@suse.cz>
157 lines
3.7 KiB
C
157 lines
3.7 KiB
C
/*
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* Copyright (C) 2017 Joe Lawrence <joe.lawrence@redhat.com>
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version 2
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* of the License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, see <http://www.gnu.org/licenses/>.
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*/
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/*
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* livepatch-shadow-fix2.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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* Adds functionality to livepatch-shadow-mod's in-flight data
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* structures through a shadow variable. The livepatch patches a
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* routine that periodically inspects data structures, incrementing a
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* per-data-structure counter, creating the counter if needed.
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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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#define SV_COUNTER 2
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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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bool livepatch_fix2_dummy_check(struct dummy *d, unsigned long jiffies)
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{
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int *shadow_count;
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/*
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* Patch: handle in-flight dummy structures, if they do not
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* already have a SV_COUNTER shadow variable, then attach a
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* new one.
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*/
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shadow_count = klp_shadow_get_or_alloc(d, SV_COUNTER,
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sizeof(*shadow_count), GFP_NOWAIT,
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NULL, NULL);
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if (shadow_count)
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*shadow_count += 1;
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return time_after(jiffies, d->jiffies_expire);
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}
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static void livepatch_fix2_dummy_leak_dtor(void *obj, void *shadow_data)
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{
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void *d = obj;
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void **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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void livepatch_fix2_dummy_free(struct dummy *d)
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{
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void **shadow_leak;
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int *shadow_count;
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/* Patch: copy the memory leak patch from the fix1 module. */
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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_fix2_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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/*
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* Patch: fetch the SV_COUNTER shadow variable and display
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* the final count. Detach the shadow variable.
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*/
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shadow_count = klp_shadow_get(d, SV_COUNTER);
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if (shadow_count) {
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pr_info("%s: dummy @ %p, check counter = %d\n",
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__func__, d, *shadow_count);
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klp_shadow_free(d, SV_COUNTER, NULL);
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}
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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_check",
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.new_func = livepatch_fix2_dummy_check,
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},
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{
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.old_name = "dummy_free",
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.new_func = livepatch_fix2_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_fix2_init(void)
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{
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int ret;
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ret = klp_register_patch(&patch);
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if (ret)
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return ret;
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ret = klp_enable_patch(&patch);
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if (ret) {
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WARN_ON(klp_unregister_patch(&patch));
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return ret;
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}
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return 0;
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}
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static void livepatch_shadow_fix2_exit(void)
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{
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/* Cleanup any existing SV_COUNTER shadow variables */
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klp_shadow_free_all(SV_COUNTER, NULL);
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WARN_ON(klp_unregister_patch(&patch));
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}
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module_init(livepatch_shadow_fix2_init);
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module_exit(livepatch_shadow_fix2_exit);
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MODULE_LICENSE("GPL");
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MODULE_INFO(livepatch, "Y");
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