300 lines
8.7 KiB
C
300 lines
8.7 KiB
C
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// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* shadow.c - Shadow Variables
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*
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* Copyright (C) 2014 Josh Poimboeuf <jpoimboe@redhat.com>
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* Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
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* Copyright (C) 2017 Joe Lawrence <joe.lawrence@redhat.com>
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*/
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/**
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* DOC: Shadow variable API concurrency notes:
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*
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* The shadow variable API provides a simple relationship between an
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* <obj, id> pair and a pointer value. It is the responsibility of the
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* caller to provide any mutual exclusion required of the shadow data.
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*
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* Once a shadow variable is attached to its parent object via the
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* klp_shadow_*alloc() API calls, it is considered live: any subsequent
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* call to klp_shadow_get() may then return the shadow variable's data
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* pointer. Callers of klp_shadow_*alloc() should prepare shadow data
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* accordingly.
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*
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* The klp_shadow_*alloc() API calls may allocate memory for new shadow
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* variable structures. Their implementation does not call kmalloc
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* inside any spinlocks, but API callers should pass GFP flags according
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* to their specific needs.
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*
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* The klp_shadow_hash is an RCU-enabled hashtable and is safe against
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* concurrent klp_shadow_free() and klp_shadow_get() operations.
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*/
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#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
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#include <linux/hashtable.h>
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#include <linux/slab.h>
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#include <linux/livepatch.h>
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static DEFINE_HASHTABLE(klp_shadow_hash, 12);
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/*
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* klp_shadow_lock provides exclusive access to the klp_shadow_hash and
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* the shadow variables it references.
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*/
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static DEFINE_SPINLOCK(klp_shadow_lock);
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/**
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* struct klp_shadow - shadow variable structure
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* @node: klp_shadow_hash hash table node
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* @rcu_head: RCU is used to safely free this structure
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* @obj: pointer to parent object
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* @id: data identifier
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* @data: data area
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*/
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struct klp_shadow {
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struct hlist_node node;
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struct rcu_head rcu_head;
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void *obj;
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unsigned long id;
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char data[];
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};
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/**
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* klp_shadow_match() - verify a shadow variable matches given <obj, id>
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* @shadow: shadow variable to match
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* @obj: pointer to parent object
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* @id: data identifier
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*
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* Return: true if the shadow variable matches.
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*/
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static inline bool klp_shadow_match(struct klp_shadow *shadow, void *obj,
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unsigned long id)
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{
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return shadow->obj == obj && shadow->id == id;
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}
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/**
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* klp_shadow_get() - retrieve a shadow variable data pointer
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* @obj: pointer to parent object
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* @id: data identifier
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*
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* Return: the shadow variable data element, NULL on failure.
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*/
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void *klp_shadow_get(void *obj, unsigned long id)
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{
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struct klp_shadow *shadow;
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rcu_read_lock();
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hash_for_each_possible_rcu(klp_shadow_hash, shadow, node,
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(unsigned long)obj) {
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if (klp_shadow_match(shadow, obj, id)) {
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rcu_read_unlock();
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return shadow->data;
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}
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}
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rcu_read_unlock();
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return NULL;
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}
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EXPORT_SYMBOL_GPL(klp_shadow_get);
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static void *__klp_shadow_get_or_alloc(void *obj, unsigned long id,
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size_t size, gfp_t gfp_flags,
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klp_shadow_ctor_t ctor, void *ctor_data,
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bool warn_on_exist)
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{
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struct klp_shadow *new_shadow;
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void *shadow_data;
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unsigned long flags;
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/* Check if the shadow variable already exists */
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shadow_data = klp_shadow_get(obj, id);
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if (shadow_data)
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goto exists;
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/*
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* Allocate a new shadow variable. Fill it with zeroes by default.
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* More complex setting can be done by @ctor function. But it is
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* called only when the buffer is really used (under klp_shadow_lock).
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*/
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new_shadow = kzalloc(size + sizeof(*new_shadow), gfp_flags);
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if (!new_shadow)
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return NULL;
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/* Look for <obj, id> again under the lock */
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spin_lock_irqsave(&klp_shadow_lock, flags);
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shadow_data = klp_shadow_get(obj, id);
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if (unlikely(shadow_data)) {
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/*
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* Shadow variable was found, throw away speculative
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* allocation.
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*/
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spin_unlock_irqrestore(&klp_shadow_lock, flags);
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kfree(new_shadow);
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goto exists;
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}
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new_shadow->obj = obj;
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new_shadow->id = id;
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if (ctor) {
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int err;
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err = ctor(obj, new_shadow->data, ctor_data);
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if (err) {
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spin_unlock_irqrestore(&klp_shadow_lock, flags);
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kfree(new_shadow);
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pr_err("Failed to construct shadow variable <%p, %lx> (%d)\n",
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obj, id, err);
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return NULL;
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}
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}
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/* No <obj, id> found, so attach the newly allocated one */
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hash_add_rcu(klp_shadow_hash, &new_shadow->node,
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(unsigned long)new_shadow->obj);
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spin_unlock_irqrestore(&klp_shadow_lock, flags);
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return new_shadow->data;
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exists:
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if (warn_on_exist) {
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WARN(1, "Duplicate shadow variable <%p, %lx>\n", obj, id);
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return NULL;
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}
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return shadow_data;
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}
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/**
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* klp_shadow_alloc() - allocate and add a new shadow variable
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* @obj: pointer to parent object
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* @id: data identifier
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* @size: size of attached data
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* @gfp_flags: GFP mask for allocation
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* @ctor: custom constructor to initialize the shadow data (optional)
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* @ctor_data: pointer to any data needed by @ctor (optional)
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*
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* Allocates @size bytes for new shadow variable data using @gfp_flags.
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* The data are zeroed by default. They are further initialized by @ctor
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* function if it is not NULL. The new shadow variable is then added
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* to the global hashtable.
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*
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* If an existing <obj, id> shadow variable can be found, this routine will
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* issue a WARN, exit early and return NULL.
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*
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* This function guarantees that the constructor function is called only when
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* the variable did not exist before. The cost is that @ctor is called
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* in atomic context under a spin lock.
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*
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* Return: the shadow variable data element, NULL on duplicate or
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* failure.
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*/
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void *klp_shadow_alloc(void *obj, unsigned long id,
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size_t size, gfp_t gfp_flags,
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klp_shadow_ctor_t ctor, void *ctor_data)
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{
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return __klp_shadow_get_or_alloc(obj, id, size, gfp_flags,
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ctor, ctor_data, true);
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}
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EXPORT_SYMBOL_GPL(klp_shadow_alloc);
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/**
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* klp_shadow_get_or_alloc() - get existing or allocate a new shadow variable
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* @obj: pointer to parent object
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* @id: data identifier
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* @size: size of attached data
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* @gfp_flags: GFP mask for allocation
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* @ctor: custom constructor to initialize the shadow data (optional)
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* @ctor_data: pointer to any data needed by @ctor (optional)
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*
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* Returns a pointer to existing shadow data if an <obj, id> shadow
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* variable is already present. Otherwise, it creates a new shadow
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* variable like klp_shadow_alloc().
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*
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* This function guarantees that only one shadow variable exists with the given
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* @id for the given @obj. It also guarantees that the constructor function
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* will be called only when the variable did not exist before. The cost is
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* that @ctor is called in atomic context under a spin lock.
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*
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* Return: the shadow variable data element, NULL on failure.
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*/
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void *klp_shadow_get_or_alloc(void *obj, unsigned long id,
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size_t size, gfp_t gfp_flags,
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klp_shadow_ctor_t ctor, void *ctor_data)
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{
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return __klp_shadow_get_or_alloc(obj, id, size, gfp_flags,
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ctor, ctor_data, false);
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}
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EXPORT_SYMBOL_GPL(klp_shadow_get_or_alloc);
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static void klp_shadow_free_struct(struct klp_shadow *shadow,
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klp_shadow_dtor_t dtor)
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{
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hash_del_rcu(&shadow->node);
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if (dtor)
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dtor(shadow->obj, shadow->data);
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kfree_rcu(shadow, rcu_head);
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}
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/**
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* klp_shadow_free() - detach and free a <obj, id> shadow variable
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* @obj: pointer to parent object
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* @id: data identifier
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* @dtor: custom callback that can be used to unregister the variable
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* and/or free data that the shadow variable points to (optional)
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*
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* This function releases the memory for this <obj, id> shadow variable
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* instance, callers should stop referencing it accordingly.
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*/
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void klp_shadow_free(void *obj, unsigned long id, klp_shadow_dtor_t dtor)
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{
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struct klp_shadow *shadow;
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unsigned long flags;
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spin_lock_irqsave(&klp_shadow_lock, flags);
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/* Delete <obj, id> from hash */
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hash_for_each_possible(klp_shadow_hash, shadow, node,
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(unsigned long)obj) {
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if (klp_shadow_match(shadow, obj, id)) {
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klp_shadow_free_struct(shadow, dtor);
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break;
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}
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}
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spin_unlock_irqrestore(&klp_shadow_lock, flags);
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}
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EXPORT_SYMBOL_GPL(klp_shadow_free);
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/**
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* klp_shadow_free_all() - detach and free all <*, id> shadow variables
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* @id: data identifier
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* @dtor: custom callback that can be used to unregister the variable
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* and/or free data that the shadow variable points to (optional)
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*
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* This function releases the memory for all <*, id> shadow variable
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* instances, callers should stop referencing them accordingly.
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*/
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void klp_shadow_free_all(unsigned long id, klp_shadow_dtor_t dtor)
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{
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struct klp_shadow *shadow;
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unsigned long flags;
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int i;
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spin_lock_irqsave(&klp_shadow_lock, flags);
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/* Delete all <*, id> from hash */
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hash_for_each(klp_shadow_hash, i, shadow, node) {
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if (klp_shadow_match(shadow, shadow->obj, id))
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klp_shadow_free_struct(shadow, dtor);
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}
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spin_unlock_irqrestore(&klp_shadow_lock, flags);
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}
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EXPORT_SYMBOL_GPL(klp_shadow_free_all);
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