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Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189190191192193194195196197198199200201202203204205206207208209210211212213214215216217218219220221222223224225226227228229230231232233234235236237238239240241242243244245246247248249250251252253254255256257258259260261262263264265266267268269270271272273274275276277278279280281282283284285286287288289290291292293294295296297298299300// 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);