1 files changed, 277 insertions, 0 deletions

diff --git a/kernel/livepatch/shadow.c b/kernel/livepatch/shadow.c
new file mode 100644
index 000000000000..fdac27588d60
--- /dev/null
+++ b/kernel/livepatch/shadow.c
@@ -0,0 +1,277 @@
+/*
+ * 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>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, see <http://www.gnu.org/licenses/>.
+ */
+
+/**
+ * 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, void *data,
+                       size_t size, gfp_t gfp_flags, 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 for use inside the lock below */
+        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);
+        if (unlikely(shadow_data)) {
+                /*
+                 * Shadow variable was found, throw away speculative
+                 * allocation.
+                 */
+                spin_unlock_irqrestore(&klp_shadow_lock, flags);
+                kfree(new_shadow);
+                goto exists;
+        }
+
+        /* 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
+ * @data:       pointer to data to attach to parent
+ * @size:       size of attached data
+ * @gfp_flags:  GFP mask for allocation
+ *
+ * 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.
+ *
+ * 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)
+{
+        return __klp_shadow_get_or_alloc(obj, id, data, size, gfp_flags, 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
+ * @data:       pointer to data to attach to parent
+ * @size:       size of attached data
+ * @gfp_flags:  GFP mask for allocation
+ *
+ * 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.
+ *
+ * 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)
+{
+        return __klp_shadow_get_or_alloc(obj, id, data, size, gfp_flags, false);
+}
+EXPORT_SYMBOL_GPL(klp_shadow_get_or_alloc);
+
+/**
+ * klp_shadow_free() - detach and free a <obj, id> shadow variable
+ * @obj:        pointer to parent object
+ * @id:         data identifier
+ *
+ * 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)
+{
+        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)) {
+                        hash_del_rcu(&shadow->node);
+                        kfree_rcu(shadow, rcu_head);
+                        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
+ *
+ * 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)
+{
+        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)) {
+                        hash_del_rcu(&shadow->node);
+                        kfree_rcu(shadow, rcu_head);
+                }
+        }
+
+        spin_unlock_irqrestore(&klp_shadow_lock, flags);
+}
+EXPORT_SYMBOL_GPL(klp_shadow_free_all);