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/*
* Copyright (C) 2014 Josh Poimboeuf <jpoimboe@redhat.com>
* Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, see <http://www.gnu.org/licenses/>.
*/
/*
* kpatch shadow variables
*
* These functions can be used to add new "shadow" fields to existing data
* structures. For example, to allocate a "newpid" variable associated with an
* instance of task_struct, and assign it a value of 1000:
*
* struct task_struct *tsk = current;
* int *newpid;
* newpid = kpatch_shadow_alloc(tsk, "newpid", sizeof(int), GFP_KERNEL);
* if (newpid)
* *newpid = 1000;
*
* To retrieve a pointer to the variable:
*
* struct task_struct *tsk = current;
* int *newpid;
* newpid = kpatch_shadow_get(tsk, "newpid");
* if (newpid)
* printk("task newpid = %d\n", *newpid); // prints "task newpid = 1000"
*
* To free it:
*
* kpatch_shadow_free(tsk, "newpid");
*/
#include <linux/hashtable.h>
#include <linux/slab.h>
#include "kpatch.h"
static DEFINE_HASHTABLE(kpatch_shadow_hash, 12);
static DEFINE_SPINLOCK(kpatch_shadow_lock);
struct kpatch_shadow {
struct hlist_node node;
struct rcu_head rcu_head;
void *obj;
union {
char *var; /* assumed to be 4-byte aligned */
unsigned long flags;
};
void *data;
};
#define SHADOW_FLAG_INPLACE 0x1
#define SHADOW_FLAG_RESERVED0 0x2 /* reserved for future use */
#define SHADOW_FLAG_MASK 0x3
#define SHADOW_PTR_MASK (~(SHADOW_FLAG_MASK))
static inline void shadow_set_inplace(struct kpatch_shadow *shadow)
{
shadow->flags |= SHADOW_FLAG_INPLACE;
}
static inline int shadow_is_inplace(struct kpatch_shadow *shadow)
{
return shadow->flags & SHADOW_FLAG_INPLACE;
}
static inline char *shadow_var(struct kpatch_shadow *shadow)
{
return (char *)((unsigned long)shadow->var & SHADOW_PTR_MASK);
}
void *kpatch_shadow_alloc(void *obj, char *var, size_t size, gfp_t gfp)
{
unsigned long flags;
struct kpatch_shadow *shadow;
shadow = kmalloc(sizeof(*shadow), gfp);
if (!shadow)
return NULL;
shadow->obj = obj;
shadow->var = kstrdup(var, gfp);
if (!shadow->var) {
kfree(shadow);
return NULL;
}
if (size <= sizeof(shadow->data)) {
shadow->data = &shadow->data;
shadow_set_inplace(shadow);
} else {
shadow->data = kmalloc(size, gfp);
if (!shadow->data) {
kfree(shadow->var);
kfree(shadow);
return NULL;
}
}
spin_lock_irqsave(&kpatch_shadow_lock, flags);
hash_add_rcu(kpatch_shadow_hash, &shadow->node, (unsigned long)obj);
spin_unlock_irqrestore(&kpatch_shadow_lock, flags);
return shadow->data;
}
EXPORT_SYMBOL_GPL(kpatch_shadow_alloc);
static void kpatch_shadow_rcu_free(struct rcu_head *head)
{
struct kpatch_shadow *shadow;
shadow = container_of(head, struct kpatch_shadow, rcu_head);
if (!shadow_is_inplace(shadow))
kfree(shadow->data);
kfree(shadow_var(shadow));
kfree(shadow);
}
void kpatch_shadow_free(void *obj, char *var)
{
unsigned long flags;
struct kpatch_shadow *shadow;
spin_lock_irqsave(&kpatch_shadow_lock, flags);
hash_for_each_possible(kpatch_shadow_hash, shadow, node,
(unsigned long)obj) {
if (shadow->obj == obj && !strcmp(shadow_var(shadow), var)) {
hash_del_rcu(&shadow->node);
spin_unlock_irqrestore(&kpatch_shadow_lock, flags);
call_rcu(&shadow->rcu_head, kpatch_shadow_rcu_free);
return;
}
}
spin_unlock_irqrestore(&kpatch_shadow_lock, flags);
}
EXPORT_SYMBOL_GPL(kpatch_shadow_free);
void *kpatch_shadow_get(void *obj, char *var)
{
struct kpatch_shadow *shadow;
rcu_read_lock();
hash_for_each_possible_rcu(kpatch_shadow_hash, shadow, node,
(unsigned long)obj) {
if (shadow->obj == obj && !strcmp(shadow_var(shadow), var)) {
rcu_read_unlock();
if (shadow_is_inplace(shadow))
return &(shadow->data);
return shadow->data;
}
}
rcu_read_unlock();
return NULL;
}
EXPORT_SYMBOL_GPL(kpatch_shadow_get);
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