// SPDX-License-Identifier: GPL-2.0-or-later /* * 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> */ /** * 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);
