// SPDX-License-Identifier: GPL-2.0-or-later
/*
* shadow.c - Shadow Variables
*
* Copyright (C) 2014 Josh Poimboeuf <[email protected]>
* Copyright (C) 2014 Seth Jennings <[email protected]>
* Copyright (C) 2017 Joe Lawrence <[email protected]>
*/
/**
* 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);
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