Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/livepatching

Pull livepatching fix from Jiri Kosina:
 "Shadow variable API list_head initialization fix from Petr Mladek"

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/livepatching:
  livepatch: Allow to call a custom callback when freeing shadow variables
  livepatch: Initialize shadow variables safely by a custom callback

Documentation/livepatch/shadow-vars.txt

@@ -34,9 +34,13 @@ meta-data and shadow-data:
   - data[] - storage for shadow data
 
 It is important to note that the klp_shadow_alloc() and
-klp_shadow_get_or_alloc() calls, described below, store a *copy* of the
-data that the functions are provided.  Callers should provide whatever
-mutual exclusion is required of the shadow data.
+klp_shadow_get_or_alloc() are zeroing the variable by default.
+They also allow to call a custom constructor function when a non-zero
+value is needed. Callers should provide whatever mutual exclusion
+is required.
+
+Note that the constructor is called under klp_shadow_lock spinlock. It allows
+to do actions that can be done only once when a new variable is allocated.
 
 * klp_shadow_get() - retrieve a shadow variable data pointer
   - search hashtable for <obj, id> pair
@@ -47,7 +51,7 @@ mutual exclusion is required of the shadow data.
     - WARN and return NULL
   - if <obj, id> doesn't already exist
     - allocate a new shadow variable
-    - copy data into the new shadow variable
+    - initialize the variable using a custom constructor and data when provided
     - add <obj, id> to the global hashtable
 
 * klp_shadow_get_or_alloc() - get existing or alloc a new shadow variable
@@ -56,16 +60,20 @@ mutual exclusion is required of the shadow data.
     - return existing shadow variable
   - if <obj, id> doesn't already exist
     - allocate a new shadow variable
-    - copy data into the new shadow variable
+    - initialize the variable using a custom constructor and data when provided
     - add <obj, id> pair to the global hashtable
 
 * klp_shadow_free() - detach and free a <obj, id> shadow variable
   - find and remove a <obj, id> reference from global hashtable
-    - if found, free shadow variable
+    - if found
+      - call destructor function if defined
+      - free shadow variable
 
 * klp_shadow_free_all() - detach and free all <*, id> shadow variables
   - find and remove any <*, id> references from global hashtable
-    - if found, free shadow variable
+    - if found
+      - call destructor function if defined
+      - free shadow variable
 
 
 2. Use cases
@@ -107,7 +115,8 @@ struct sta_info *sta_info_alloc(struct ieee80211_sub_if_data *sdata,
 	sta = kzalloc(sizeof(*sta) + hw->sta_data_size, gfp);
 
 	/* Attach a corresponding shadow variable, then initialize it */
-	ps_lock = klp_shadow_alloc(sta, PS_LOCK, NULL, sizeof(*ps_lock), gfp);
+	ps_lock = klp_shadow_alloc(sta, PS_LOCK, sizeof(*ps_lock), gfp,
+				   NULL, NULL);
 	if (!ps_lock)
 		goto shadow_fail;
 	spin_lock_init(ps_lock);
@@ -131,7 +140,7 @@ variable:
 
 void sta_info_free(struct ieee80211_local *local, struct sta_info *sta)
 {
-	klp_shadow_free(sta, PS_LOCK);
+	klp_shadow_free(sta, PS_LOCK, NULL);
 	kfree(sta);
 	...
 
@@ -148,16 +157,24 @@ shadow variables to parents already in-flight.
 For commit 1d147bfa6429, a good spot to allocate a shadow spinlock is
 inside ieee80211_sta_ps_deliver_wakeup():
 
+int ps_lock_shadow_ctor(void *obj, void *shadow_data, void *ctor_data)
+{
+	spinlock_t *lock = shadow_data;
+
+	spin_lock_init(lock);
+	return 0;
+}
+
 #define PS_LOCK 1
 void ieee80211_sta_ps_deliver_wakeup(struct sta_info *sta)
 {
-	DEFINE_SPINLOCK(ps_lock_fallback);
 	spinlock_t *ps_lock;
 
 	/* sync with ieee80211_tx_h_unicast_ps_buf */
 	ps_lock = klp_shadow_get_or_alloc(sta, PS_LOCK,
-			&ps_lock_fallback, sizeof(ps_lock_fallback),
-			GFP_ATOMIC);
+			sizeof(*ps_lock), GFP_ATOMIC,
+			ps_lock_shadow_ctor, NULL);
+
 	if (ps_lock)
 		spin_lock(ps_lock);
 	...

include/linux/livepatch.h

@@ -186,13 +186,20 @@ static inline bool klp_have_reliable_stack(void)
 	       IS_ENABLED(CONFIG_HAVE_RELIABLE_STACKTRACE);
 }
 
+typedef int (*klp_shadow_ctor_t)(void *obj,
+				 void *shadow_data,
+				 void *ctor_data);
+typedef void (*klp_shadow_dtor_t)(void *obj, void *shadow_data);
+
 void *klp_shadow_get(void *obj, unsigned long id);
-void *klp_shadow_alloc(void *obj, unsigned long id, void *data,
-		       size_t size, gfp_t gfp_flags);
-void *klp_shadow_get_or_alloc(void *obj, unsigned long id, void *data,
-			      size_t size, gfp_t gfp_flags);
-void klp_shadow_free(void *obj, unsigned long id);
-void klp_shadow_free_all(unsigned long id);
+void *klp_shadow_alloc(void *obj, unsigned long id,
+		       size_t size, gfp_t gfp_flags,
+		       klp_shadow_ctor_t ctor, void *ctor_data);
+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);
+void klp_shadow_free(void *obj, unsigned long id, klp_shadow_dtor_t dtor);
+void klp_shadow_free_all(unsigned long id, klp_shadow_dtor_t dtor);
 
 #else /* !CONFIG_LIVEPATCH */
 

kernel/livepatch/shadow.c

@@ -113,8 +113,10 @@ void *klp_shadow_get(void *obj, unsigned long id)
 }
 EXPORT_SYMBOL_GPL(klp_shadow_get);
 
-static void *__klp_shadow_get_or_alloc(void *obj, unsigned long id, void *data,
-		       size_t size, gfp_t gfp_flags, bool warn_on_exist)
+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;
@@ -125,18 +127,15 @@ static void *__klp_shadow_get_or_alloc(void *obj, unsigned long id, void *data,
 	if (shadow_data)
 		goto exists;
 
-	/* Allocate a new shadow variable for use inside the lock below */
+	/*
+	 * 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;
 
-	new_shadow->obj = obj;
-	new_shadow->id = id;
-
-	/* Initialize the shadow variable if data provided */
-	if (data)
-		memcpy(new_shadow->data, data, size);
-
 	/* Look for <obj, id> again under the lock */
 	spin_lock_irqsave(&klp_shadow_lock, flags);
 	shadow_data = klp_shadow_get(obj, id);
@@ -150,6 +149,22 @@ static void *__klp_shadow_get_or_alloc(void *obj, unsigned long id, void *data,
 		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);
@@ -170,26 +185,32 @@ static void *__klp_shadow_get_or_alloc(void *obj, unsigned long id, void *data,
  * klp_shadow_alloc() - allocate and add a new shadow variable
  * @obj:	pointer to parent object
  * @id:		data identifier
- * @data:	pointer to data to attach to parent
  * @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.
  *
- * Allocates @size bytes for new shadow variable data using @gfp_flags
- * and copies @size bytes from @data into the new shadow variable's own
- * data space.  If @data is NULL, @size bytes are still allocated, but
- * no copy is performed.  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.
  *
- * 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, void *data,
-		       size_t size, gfp_t gfp_flags)
+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, data, size, gfp_flags, true);
+	return __klp_shadow_get_or_alloc(obj, id, size, gfp_flags,
+					 ctor, ctor_data, true);
 }
 EXPORT_SYMBOL_GPL(klp_shadow_alloc);
 
@@ -197,37 +218,51 @@ 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
- * @data:	pointer to data to attach to parent
  * @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 shadow
- * variable will be initialized by the given @data only when it did not
- * exist before.
+ * 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, void *data,
-			       size_t size, gfp_t gfp_flags)
+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, data, size, gfp_flags, false);
+	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)
+void klp_shadow_free(void *obj, unsigned long id, klp_shadow_dtor_t dtor)
 {
 	struct klp_shadow *shadow;
 	unsigned long flags;
@@ -239,8 +274,7 @@ void klp_shadow_free(void *obj, unsigned long id)
 			       (unsigned long)obj) {
 
 		if (klp_shadow_match(shadow, obj, id)) {
-			hash_del_rcu(&shadow->node);
-			kfree_rcu(shadow, rcu_head);
+			klp_shadow_free_struct(shadow, dtor);
 			break;
 		}
 	}
@@ -252,11 +286,13 @@ 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)
+void klp_shadow_free_all(unsigned long id, klp_shadow_dtor_t dtor)
 {
 	struct klp_shadow *shadow;
 	unsigned long flags;
@@ -266,10 +302,8 @@ void klp_shadow_free_all(unsigned long id)
 
 	/* Delete all <*, id> from hash */
 	hash_for_each(klp_shadow_hash, i, shadow, node) {
-		if (klp_shadow_match(shadow, shadow->obj, id)) {
-			hash_del_rcu(&shadow->node);
-			kfree_rcu(shadow, rcu_head);
-		}
+		if (klp_shadow_match(shadow, shadow->obj, id))
+			klp_shadow_free_struct(shadow, dtor);
 	}
 
 	spin_unlock_irqrestore(&klp_shadow_lock, flags);

samples/livepatch/livepatch-shadow-fix1.c

@@ -56,6 +56,21 @@ struct dummy {
 	unsigned long jiffies_expire;
 };
 
+/*
+ * The constructor makes more sense together with klp_shadow_get_or_alloc().
+ * In this example, it would be safe to assign the pointer also to the shadow
+ * variable returned by klp_shadow_alloc().  But we wanted to show the more
+ * complicated use of the API.
+ */
+static int shadow_leak_ctor(void *obj, void *shadow_data, void *ctor_data)
+{
+	void **shadow_leak = shadow_data;
+	void *leak = ctor_data;
+
+	*shadow_leak = leak;
+	return 0;
+}
+
 struct dummy *livepatch_fix1_dummy_alloc(void)
 {
 	struct dummy *d;
@@ -74,7 +89,8 @@ struct dummy *livepatch_fix1_dummy_alloc(void)
 	 * pointer to handle resource release.
 	 */
 	leak = kzalloc(sizeof(int), GFP_KERNEL);
-	klp_shadow_alloc(d, SV_LEAK, &leak, sizeof(leak), GFP_KERNEL);
+	klp_shadow_alloc(d, SV_LEAK, sizeof(leak), GFP_KERNEL,
+			 shadow_leak_ctor, leak);
 
 	pr_info("%s: dummy @ %p, expires @ %lx\n",
 		__func__, d, d->jiffies_expire);
@@ -82,9 +98,19 @@ struct dummy *livepatch_fix1_dummy_alloc(void)
 	return d;
 }
 
+static void livepatch_fix1_dummy_leak_dtor(void *obj, void *shadow_data)
+{
+	void *d = obj;
+	void **shadow_leak = shadow_data;
+
+	kfree(*shadow_leak);
+	pr_info("%s: dummy @ %p, prevented leak @ %p\n",
+			 __func__, d, *shadow_leak);
+}
+
 void livepatch_fix1_dummy_free(struct dummy *d)
 {
-	void **shadow_leak, *leak;
+	void **shadow_leak;
 
 	/*
 	 * Patch: fetch the saved SV_LEAK shadow variable, detach and
@@ -93,15 +119,10 @@ void livepatch_fix1_dummy_free(struct dummy *d)
 	 * was loaded.)
 	 */
 	shadow_leak = klp_shadow_get(d, SV_LEAK);
-	if (shadow_leak) {
-		leak = *shadow_leak;
-		klp_shadow_free(d, SV_LEAK);
-		kfree(leak);
-		pr_info("%s: dummy @ %p, prevented leak @ %p\n",
-			 __func__, d, leak);
-	} else {
+	if (shadow_leak)
+		klp_shadow_free(d, SV_LEAK, livepatch_fix1_dummy_leak_dtor);
+	else
 		pr_info("%s: dummy @ %p leaked!\n", __func__, d);
-	}
 
 	kfree(d);
 }
@@ -147,7 +168,7 @@ static int livepatch_shadow_fix1_init(void)
 static void livepatch_shadow_fix1_exit(void)
 {
 	/* Cleanup any existing SV_LEAK shadow variables */
-	klp_shadow_free_all(SV_LEAK);
+	klp_shadow_free_all(SV_LEAK, livepatch_fix1_dummy_leak_dtor);
 
 	WARN_ON(klp_unregister_patch(&patch));
 }

samples/livepatch/livepatch-shadow-fix2.c

@@ -53,39 +53,42 @@ struct dummy {
 bool livepatch_fix2_dummy_check(struct dummy *d, unsigned long jiffies)
 {
 	int *shadow_count;
-	int count;
 
 	/*
 	 * Patch: handle in-flight dummy structures, if they do not
 	 * already have a SV_COUNTER shadow variable, then attach a
 	 * new one.
 	 */
-	count = 0;
 	shadow_count = klp_shadow_get_or_alloc(d, SV_COUNTER,
-					       &count, sizeof(count),
-					       GFP_NOWAIT);
+				sizeof(*shadow_count), GFP_NOWAIT,
+				NULL, NULL);
 	if (shadow_count)
 		*shadow_count += 1;
 
 	return time_after(jiffies, d->jiffies_expire);
 }
 
+static void livepatch_fix2_dummy_leak_dtor(void *obj, void *shadow_data)
+{
+	void *d = obj;
+	void **shadow_leak = shadow_data;
+
+	kfree(*shadow_leak);
+	pr_info("%s: dummy @ %p, prevented leak @ %p\n",
+			 __func__, d, *shadow_leak);
+}
+
 void livepatch_fix2_dummy_free(struct dummy *d)
 {
-	void **shadow_leak, *leak;
+	void **shadow_leak;
 	int *shadow_count;
 
 	/* Patch: copy the memory leak patch from the fix1 module. */
 	shadow_leak = klp_shadow_get(d, SV_LEAK);
-	if (shadow_leak) {
-		leak = *shadow_leak;
-		klp_shadow_free(d, SV_LEAK);
-		kfree(leak);
-		pr_info("%s: dummy @ %p, prevented leak @ %p\n",
-			 __func__, d, leak);
-	} else {
+	if (shadow_leak)
+		klp_shadow_free(d, SV_LEAK, livepatch_fix2_dummy_leak_dtor);
+	else
 		pr_info("%s: dummy @ %p leaked!\n", __func__, d);
-	}
 
 	/*
 	 * Patch: fetch the SV_COUNTER shadow variable and display
@@ -95,7 +98,7 @@ void livepatch_fix2_dummy_free(struct dummy *d)
 	if (shadow_count) {
 		pr_info("%s: dummy @ %p, check counter = %d\n",
 			__func__, d, *shadow_count);
-		klp_shadow_free(d, SV_COUNTER);
+		klp_shadow_free(d, SV_COUNTER, NULL);
 	}
 
 	kfree(d);
@@ -142,7 +145,7 @@ static int livepatch_shadow_fix2_init(void)
 static void livepatch_shadow_fix2_exit(void)
 {
 	/* Cleanup any existing SV_COUNTER shadow variables */
-	klp_shadow_free_all(SV_COUNTER);
+	klp_shadow_free_all(SV_COUNTER, NULL);
 
 	WARN_ON(klp_unregister_patch(&patch));
 }