312 lines
9.3 KiB
C
312 lines
9.3 KiB
C
|
/*
|
||
|
|
* shadow.c - Shadow Variables
|
||
|
|
*
|
||
|
|
* Copyright (C) 2014 Josh Poimboeuf <jpoimboe@redhat.com>
|
||
|
|
* Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
|
||
|
|
* Copyright (C) 2017 Joe Lawrence <joe.lawrence@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/>.
|
||
|
|
*/
|
||
|
|
|
||
|
|
/**
|
||
|
|
* DOC: Shadow variable API concurrency notes:
|
||
|
|
*
|
||
|
|
* The shadow variable API provides a simple relationship between an
|
||
|
|
* <obj, id> pair and a pointer value. It is the responsibility of the
|
||
|
|
* caller to provide any mutual exclusion required of the shadow data.
|
||
|
|
*
|
||
|
|
* Once a shadow variable is attached to its parent object via the
|
||
|
|
* klp_shadow_*alloc() API calls, it is considered live: any subsequent
|
||
|
|
* call to klp_shadow_get() may then return the shadow variable's data
|
||
|
|
* pointer. Callers of klp_shadow_*alloc() should prepare shadow data
|
||
|
|
* accordingly.
|
||
|
|
*
|
||
|
|
* The klp_shadow_*alloc() API calls may allocate memory for new shadow
|
||
|
|
* variable structures. Their implementation does not call kmalloc
|
||
|
|
* inside any spinlocks, but API callers should pass GFP flags according
|
||
|
|
* to their specific needs.
|
||
|
|
*
|
||
|
|
* The klp_shadow_hash is an RCU-enabled hashtable and is safe against
|
||
|
|
* concurrent klp_shadow_free() and klp_shadow_get() operations.
|
||
|
|
*/
|
||
|
|
|
||
|
|
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
|
||
|
|
|
||
|
|
#include <linux/hashtable.h>
|
||
|
|
#include <linux/slab.h>
|
||
|
|
#include <linux/livepatch.h>
|
||
|
|
|
||
|
|
static DEFINE_HASHTABLE(klp_shadow_hash, 12);
|
||
|
|
|
||
|
|
/*
|
||
|
|
* klp_shadow_lock provides exclusive access to the klp_shadow_hash and
|
||
|
|
* the shadow variables it references.
|
||
|
|
*/
|
||
|
|
static DEFINE_SPINLOCK(klp_shadow_lock);
|
||
|
|
|
||
|
|
/**
|
||
|
|
* struct klp_shadow - shadow variable structure
|
||
|
|
* @node: klp_shadow_hash hash table node
|
||
|
|
* @rcu_head: RCU is used to safely free this structure
|
||
|
|
* @obj: pointer to parent object
|
||
|
|
* @id: data identifier
|
||
|
|
* @data: data area
|
||
|
|
*/
|
||
|
|
struct klp_shadow {
|
||
|
|
struct hlist_node node;
|
||
|
|
struct rcu_head rcu_head;
|
||
|
|
void *obj;
|
||
|
|
unsigned long id;
|
||
|
|
char data[];
|
||
|
|
};
|
||
|
|
|
||
|
|
/**
|
||
|
|
* klp_shadow_match() - verify a shadow variable matches given <obj, id>
|
||
|
|
* @shadow: shadow variable to match
|
||
|
|
* @obj: pointer to parent object
|
||
|
|
* @id: data identifier
|
||
|
|
*
|
||
|
|
* Return: true if the shadow variable matches.
|
||
|
|
*/
|
||
|
|
static inline bool klp_shadow_match(struct klp_shadow *shadow, void *obj,
|
||
|
|
unsigned long id)
|
||
|
|
{
|
||
|
|
return shadow->obj == obj && shadow->id == id;
|
||
|
|
}
|
||
|
|
|
||
|
|
/**
|
||
|
|
* klp_shadow_get() - retrieve a shadow variable data pointer
|
||
|
|
* @obj: pointer to parent object
|
||
|
|
* @id: data identifier
|
||
|
|
*
|
||
|
|
* Return: the shadow variable data element, NULL on failure.
|
||
|
|
*/
|
||
|
|
void *klp_shadow_get(void *obj, unsigned long id)
|
||
|
|
{
|
||
|
|
struct klp_shadow *shadow;
|
||
|
|
|
||
|
|
rcu_read_lock();
|
||
|
|
|
||
|
|
hash_for_each_possible_rcu(klp_shadow_hash, shadow, node,
|
||
|
|
(unsigned long)obj) {
|
||
|
|
|
||
|
|
if (klp_shadow_match(shadow, obj, id)) {
|
||
|
|
rcu_read_unlock();
|
||
|
|
return shadow->data;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
rcu_read_unlock();
|
||
|
|
|
||
|
|
return NULL;
|
||
|
|
}
|
||
|
|
EXPORT_SYMBOL_GPL(klp_shadow_get);
|
||
|
|
|
||
|
|
static void *__klp_shadow_get_or_alloc(void *obj, unsigned long id,
|
||
|
|
size_t size, gfp_t gfp_flags,
|
||
|
|
klp_shadow_ctor_t ctor, void *ctor_data,
|
||
|
|
bool warn_on_exist)
|
||
|
|
{
|
||
|
|
struct klp_shadow *new_shadow;
|
||
|
|
void *shadow_data;
|
||
|
|
unsigned long flags;
|
||
|
|
|
||
|
|
/* Check if the shadow variable already exists */
|
||
|
|
shadow_data = klp_shadow_get(obj, id);
|
||
|
|
if (shadow_data)
|
||
|
|
goto exists;
|
||
|
|
|
||
|
|
/*
|
||
|
|
* Allocate a new shadow variable. Fill it with zeroes by default.
|
||
|
|
* More complex setting can be done by @ctor function. But it is
|
||
|
|
* called only when the buffer is really used (under klp_shadow_lock).
|
||
|
|
*/
|
||
|
|
new_shadow = kzalloc(size + sizeof(*new_shadow), gfp_flags);
|
||
|
|
if (!new_shadow)
|
||
|
|
return NULL;
|
||
|
|
|
||
|
|
/* Look for <obj, id> again under the lock */
|
||
|
|
spin_lock_irqsave(&klp_shadow_lock, flags);
|
||
|
|
shadow_data = klp_shadow_get(obj, id);
|
||
|
|
if (unlikely(shadow_data)) {
|
||
|
|
/*
|
||
|
|
* Shadow variable was found, throw away speculative
|
||
|
|
* allocation.
|
||
|
|
*/
|
||
|
|
spin_unlock_irqrestore(&klp_shadow_lock, flags);
|
||
|
|
kfree(new_shadow);
|
||
|
|
goto exists;
|
||
|
|
}
|
||
|
|
|
||
|
|
new_shadow->obj = obj;
|
||
|
|
new_shadow->id = id;
|
||
|
|
|
||
|
|
if (ctor) {
|
||
|
|
int err;
|
||
|
|
|
||
|
|
err = ctor(obj, new_shadow->data, ctor_data);
|
||
|
|
if (err) {
|
||
|
|
spin_unlock_irqrestore(&klp_shadow_lock, flags);
|
||
|
|
kfree(new_shadow);
|
||
|
|
pr_err("Failed to construct shadow variable <%p, %lx> (%d)\n",
|
||
|
|
obj, id, err);
|
||
|
|
return NULL;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
/* No <obj, id> found, so attach the newly allocated one */
|
||
|
|
hash_add_rcu(klp_shadow_hash, &new_shadow->node,
|
||
|
|
(unsigned long)new_shadow->obj);
|
||
|
|
spin_unlock_irqrestore(&klp_shadow_lock, flags);
|
||
|
|
|
||
|
|
return new_shadow->data;
|
||
|
|
|
||
|
|
exists:
|
||
|
|
if (warn_on_exist) {
|
||
|
|
WARN(1, "Duplicate shadow variable <%p, %lx>\n", obj, id);
|
||
|
|
return NULL;
|
||
|
|
}
|
||
|
|
|
||
|
|
return shadow_data;
|
||
|
|
}
|
||
|
|
|
||
|
|
/**
|
||
|
|
* klp_shadow_alloc() - allocate and add a new shadow variable
|
||
|
|
* @obj: pointer to parent object
|
||
|
|
* @id: data identifier
|
||
|
|
* @size: size of attached data
|
||
|
|
* @gfp_flags: GFP mask for allocation
|
||
|
|
* @ctor: custom constructor to initialize the shadow data (optional)
|
||
|
|
* @ctor_data: pointer to any data needed by @ctor (optional)
|
||
|
|
*
|
||
|
|
* Allocates @size bytes for new shadow variable data using @gfp_flags.
|
||
|
|
* The data are zeroed by default. They are further initialized by @ctor
|
||
|
|
* function if it is not NULL. The new shadow variable is then added
|
||
|
|
* to the global hashtable.
|
||
|
|
*
|
||
|
|
* If an existing <obj, id> shadow variable can be found, this routine will
|
||
|
|
* issue a WARN, exit early and return NULL.
|
||
|
|
*
|
||
|
|
* This function guarantees that the constructor function is called only when
|
||
|
|
* the variable did not exist before. The cost is that @ctor is called
|
||
|
|
* in atomic context under a spin lock.
|
||
|
|
*
|
||
|
|
* Return: the shadow variable data element, NULL on duplicate or
|
||
|
|
* failure.
|
||
|
|
*/
|
||
|
|
void *klp_shadow_alloc(void *obj, unsigned long id,
|
||
|
|
size_t size, gfp_t gfp_flags,
|
||
|
|
klp_shadow_ctor_t ctor, void *ctor_data)
|
||
|
|
{
|
||
|
|
return __klp_shadow_get_or_alloc(obj, id, size, gfp_flags,
|
||
|
|
ctor, ctor_data, true);
|
||
|
|
}
|
||
|
|
EXPORT_SYMBOL_GPL(klp_shadow_alloc);
|
||
|
|
|
||
|
|
/**
|
||
|
|
* klp_shadow_get_or_alloc() - get existing or allocate a new shadow variable
|
||
|
|
* @obj: pointer to parent object
|
||
|
|
* @id: data identifier
|
||
|
|
* @size: size of attached data
|
||
|
|
* @gfp_flags: GFP mask for allocation
|
||
|
|
* @ctor: custom constructor to initialize the shadow data (optional)
|
||
|
|
* @ctor_data: pointer to any data needed by @ctor (optional)
|
||
|
|
*
|
||
|
|
* Returns a pointer to existing shadow data if an <obj, id> shadow
|
||
|
|
* variable is already present. Otherwise, it creates a new shadow
|
||
|
|
* variable like klp_shadow_alloc().
|
||
|
|
*
|
||
|
|
* This function guarantees that only one shadow variable exists with the given
|
||
|
|
* @id for the given @obj. It also guarantees that the constructor function
|
||
|
|
* will be called only when the variable did not exist before. The cost is
|
||
|
|
* that @ctor is called in atomic context under a spin lock.
|
||
|
|
*
|
||
|
|
* Return: the shadow variable data element, NULL on failure.
|
||
|
|
*/
|
||
|
|
void *klp_shadow_get_or_alloc(void *obj, unsigned long id,
|
||
|
|
size_t size, gfp_t gfp_flags,
|
||
|
|
klp_shadow_ctor_t ctor, void *ctor_data)
|
||
|
|
{
|
||
|
|
return __klp_shadow_get_or_alloc(obj, id, size, gfp_flags,
|
||
|
|
ctor, ctor_data, false);
|
||
|
|
}
|
||
|
|
EXPORT_SYMBOL_GPL(klp_shadow_get_or_alloc);
|
||
|
|
|
||
|
|
static void klp_shadow_free_struct(struct klp_shadow *shadow,
|
||
|
|
klp_shadow_dtor_t dtor)
|
||
|
|
{
|
||
|
|
hash_del_rcu(&shadow->node);
|
||
|
|
if (dtor)
|
||
|
|
dtor(shadow->obj, shadow->data);
|
||
|
|
kfree_rcu(shadow, rcu_head);
|
||
|
|
}
|
||
|
|
|
||
|
|
/**
|
||
|
|
* klp_shadow_free() - detach and free a <obj, id> shadow variable
|
||
|
|
* @obj: pointer to parent object
|
||
|
|
* @id: data identifier
|
||
|
|
* @dtor: custom callback that can be used to unregister the variable
|
||
|
|
* and/or free data that the shadow variable points to (optional)
|
||
|
|
*
|
||
|
|
* This function releases the memory for this <obj, id> shadow variable
|
||
|
|
* instance, callers should stop referencing it accordingly.
|
||
|
|
*/
|
||
|
|
void klp_shadow_free(void *obj, unsigned long id, klp_shadow_dtor_t dtor)
|
||
|
|
{
|
||
|
|
struct klp_shadow *shadow;
|
||
|
|
unsigned long flags;
|
||
|
|
|
||
|
|
spin_lock_irqsave(&klp_shadow_lock, flags);
|
||
|
|
|
||
|
|
/* Delete <obj, id> from hash */
|
||
|
|
hash_for_each_possible(klp_shadow_hash, shadow, node,
|
||
|
|
(unsigned long)obj) {
|
||
|
|
|
||
|
|
if (klp_shadow_match(shadow, obj, id)) {
|
||
|
|
klp_shadow_free_struct(shadow, dtor);
|
||
|
|
break;
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
spin_unlock_irqrestore(&klp_shadow_lock, flags);
|
||
|
|
}
|
||
|
|
EXPORT_SYMBOL_GPL(klp_shadow_free);
|
||
|
|
|
||
|
|
/**
|
||
|
|
* klp_shadow_free_all() - detach and free all <*, id> shadow variables
|
||
|
|
* @id: data identifier
|
||
|
|
* @dtor: custom callback that can be used to unregister the variable
|
||
|
|
* and/or free data that the shadow variable points to (optional)
|
||
|
|
*
|
||
|
|
* This function releases the memory for all <*, id> shadow variable
|
||
|
|
* instances, callers should stop referencing them accordingly.
|
||
|
|
*/
|
||
|
|
void klp_shadow_free_all(unsigned long id, klp_shadow_dtor_t dtor)
|
||
|
|
{
|
||
|
|
struct klp_shadow *shadow;
|
||
|
|
unsigned long flags;
|
||
|
|
int i;
|
||
|
|
|
||
|
|
spin_lock_irqsave(&klp_shadow_lock, flags);
|
||
|
|
|
||
|
|
/* Delete all <*, id> from hash */
|
||
|
|
hash_for_each(klp_shadow_hash, i, shadow, node) {
|
||
|
|
if (klp_shadow_match(shadow, shadow->obj, id))
|
||
|
|
klp_shadow_free_struct(shadow, dtor);
|
||
|
|
}
|
||
|
|
|
||
|
|
spin_unlock_irqrestore(&klp_shadow_lock, flags);
|
||
|
|
}
|
||
|
|
EXPORT_SYMBOL_GPL(klp_shadow_free_all);
|