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livepatch: introduce shadow variable API

Add exported API for livepatch modules: klp_shadow_get() klp_shadow_alloc() klp_shadow_get_or_alloc() klp_shadow_free() klp_shadow_free_all() that implement "shadow" variables, which allow callers to associate new shadow fields to existing data structures. This is intended to be used by livepatch modules seeking to emulate additions to data structure definitions. See Documentation/livepatch/shadow-vars.txt for a summary of the new shadow variable API, including a few common use cases. See samples/livepatch/livepatch-shadow-* for example modules that demonstrate shadow variables. [jkosina@suse.cz: fix __klp_shadow_get_or_alloc() comment as spotted by Josh] Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com> Acked-by: Josh Poimboeuf <jpoimboe@redhat.com> Acked-by: Miroslav Benes <mbenes@suse.cz> Signed-off-by: Jiri Kosina <jkosina@suse.cz>

Joe Lawrence committed 9 years ago

Commit 439e7271 parent dcba7109 files · +1048 −4Browse files

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  1. kernel/livepatch/Makefile +1 −1
  2. kernel/livepatch/shadow.c +277 −0
kernel/livepatch/Makefile+1−1
@@ -1,3 +1,3 @@
11 obj-$(CONFIG_LIVEPATCH) += livepatch.o
22
3−livepatch-objs := core.o patch.o transition.o
3+livepatch-objs := core.o patch.o shadow.o transition.o
kernel/livepatch/shadow.c+277−0
@@ -0,0 +1,277 @@
1+/*
2+ * shadow.c - Shadow Variables
3+ *
4+ * Copyright (C) 2014 Josh Poimboeuf <jpoimboe@redhat.com>
5+ * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
6+ * Copyright (C) 2017 Joe Lawrence <joe.lawrence@redhat.com>
7+ *
8+ * This program is free software; you can redistribute it and/or
9+ * modify it under the terms of the GNU General Public License
10+ * as published by the Free Software Foundation; either version 2
11+ * of the License, or (at your option) any later version.
12+ *
13+ * This program is distributed in the hope that it will be useful,
14+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
15+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
16+ * GNU General Public License for more details.
17+ *
18+ * You should have received a copy of the GNU General Public License
19+ * along with this program; if not, see <http://www.gnu.org/licenses/>.
20+ */
21+
22+/**
23+ * DOC: Shadow variable API concurrency notes:
24+ *
25+ * The shadow variable API provides a simple relationship between an
26+ * <obj, id> pair and a pointer value. It is the responsibility of the
27+ * caller to provide any mutual exclusion required of the shadow data.
28+ *
29+ * Once a shadow variable is attached to its parent object via the
30+ * klp_shadow_*alloc() API calls, it is considered live: any subsequent
31+ * call to klp_shadow_get() may then return the shadow variable's data
32+ * pointer. Callers of klp_shadow_*alloc() should prepare shadow data
33+ * accordingly.
34+ *
35+ * The klp_shadow_*alloc() API calls may allocate memory for new shadow
36+ * variable structures. Their implementation does not call kmalloc
37+ * inside any spinlocks, but API callers should pass GFP flags according
38+ * to their specific needs.
39+ *
40+ * The klp_shadow_hash is an RCU-enabled hashtable and is safe against
41+ * concurrent klp_shadow_free() and klp_shadow_get() operations.
42+ */
43+
44+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
45+
46+#include <linux/hashtable.h>
47+#include <linux/slab.h>
48+#include <linux/livepatch.h>
49+
50+static DEFINE_HASHTABLE(klp_shadow_hash, 12);
51+
52+/*
53+ * klp_shadow_lock provides exclusive access to the klp_shadow_hash and
54+ * the shadow variables it references.
55+ */
56+static DEFINE_SPINLOCK(klp_shadow_lock);
57+
58+/**
59+ * struct klp_shadow - shadow variable structure
60+ * @node: klp_shadow_hash hash table node
61+ * @rcu_head: RCU is used to safely free this structure
62+ * @obj: pointer to parent object
63+ * @id: data identifier
64+ * @data: data area
65+ */
66+struct klp_shadow {
67+ struct hlist_node node;
68+ struct rcu_head rcu_head;
69+ void *obj;
70+ unsigned long id;
71+ char data[];
72+};
73+
74+/**
75+ * klp_shadow_match() - verify a shadow variable matches given <obj, id>
76+ * @shadow: shadow variable to match
77+ * @obj: pointer to parent object
78+ * @id: data identifier
79+ *
80+ * Return: true if the shadow variable matches.
81+ */
82+static inline bool klp_shadow_match(struct klp_shadow *shadow, void *obj,
83+ unsigned long id)
84+{
85+ return shadow->obj == obj && shadow->id == id;
86+}
87+
88+/**
89+ * klp_shadow_get() - retrieve a shadow variable data pointer
90+ * @obj: pointer to parent object
91+ * @id: data identifier
92+ *
93+ * Return: the shadow variable data element, NULL on failure.
94+ */
95+void *klp_shadow_get(void *obj, unsigned long id)
96+{
97+ struct klp_shadow *shadow;
98+
99+ rcu_read_lock();
100+
101+ hash_for_each_possible_rcu(klp_shadow_hash, shadow, node,
102+ (unsigned long)obj) {
103+
104+ if (klp_shadow_match(shadow, obj, id)) {
105+ rcu_read_unlock();
106+ return shadow->data;
107+ }
108+ }
109+
110+ rcu_read_unlock();
111+
112+ return NULL;
113+}
114+EXPORT_SYMBOL_GPL(klp_shadow_get);
115+
116+void *__klp_shadow_get_or_alloc(void *obj, unsigned long id, void *data,
117+ size_t size, gfp_t gfp_flags, bool warn_on_exist)
118+{
119+ struct klp_shadow *new_shadow;
120+ void *shadow_data;
121+ unsigned long flags;
122+
123+ /* Check if the shadow variable already exists */
124+ shadow_data = klp_shadow_get(obj, id);
125+ if (shadow_data)
126+ goto exists;
127+
128+ /* Allocate a new shadow variable for use inside the lock below */
129+ new_shadow = kzalloc(size + sizeof(*new_shadow), gfp_flags);
130+ if (!new_shadow)
131+ return NULL;
132+
133+ new_shadow->obj = obj;
134+ new_shadow->id = id;
135+
136+ /* Initialize the shadow variable if data provided */
137+ if (data)
138+ memcpy(new_shadow->data, data, size);
139+
140+ /* Look for <obj, id> again under the lock */
141+ spin_lock_irqsave(&klp_shadow_lock, flags);
142+ shadow_data = klp_shadow_get(obj, id);
143+ if (unlikely(shadow_data)) {
144+ /*
145+ * Shadow variable was found, throw away speculative
146+ * allocation.
147+ */
148+ spin_unlock_irqrestore(&klp_shadow_lock, flags);
149+ kfree(new_shadow);
150+ goto exists;
151+ }
152+
153+ /* No <obj, id> found, so attach the newly allocated one */
154+ hash_add_rcu(klp_shadow_hash, &new_shadow->node,
155+ (unsigned long)new_shadow->obj);
156+ spin_unlock_irqrestore(&klp_shadow_lock, flags);
157+
158+ return new_shadow->data;
159+
160+exists:
161+ if (warn_on_exist) {
162+ WARN(1, "Duplicate shadow variable <%p, %lx>\n", obj, id);
163+ return NULL;
164+ }
165+
166+ return shadow_data;
167+}
168+
169+/**
170+ * klp_shadow_alloc() - allocate and add a new shadow variable
171+ * @obj: pointer to parent object
172+ * @id: data identifier
173+ * @data: pointer to data to attach to parent
174+ * @size: size of attached data
175+ * @gfp_flags: GFP mask for allocation
176+ *
177+ * Allocates @size bytes for new shadow variable data using @gfp_flags
178+ * and copies @size bytes from @data into the new shadow variable's own
179+ * data space. If @data is NULL, @size bytes are still allocated, but
180+ * no copy is performed. The new shadow variable is then added to the
181+ * global hashtable.
182+ *
183+ * If an existing <obj, id> shadow variable can be found, this routine
184+ * will issue a WARN, exit early and return NULL.
185+ *
186+ * Return: the shadow variable data element, NULL on duplicate or
187+ * failure.
188+ */
189+void *klp_shadow_alloc(void *obj, unsigned long id, void *data,
190+ size_t size, gfp_t gfp_flags)
191+{
192+ return __klp_shadow_get_or_alloc(obj, id, data, size, gfp_flags, true);
193+}
194+EXPORT_SYMBOL_GPL(klp_shadow_alloc);
195+
196+/**
197+ * klp_shadow_get_or_alloc() - get existing or allocate a new shadow variable
198+ * @obj: pointer to parent object
199+ * @id: data identifier
200+ * @data: pointer to data to attach to parent
201+ * @size: size of attached data
202+ * @gfp_flags: GFP mask for allocation
203+ *
204+ * Returns a pointer to existing shadow data if an <obj, id> shadow
205+ * variable is already present. Otherwise, it creates a new shadow
206+ * variable like klp_shadow_alloc().
207+ *
208+ * This function guarantees that only one shadow variable exists with
209+ * the given @id for the given @obj. It also guarantees that the shadow
210+ * variable will be initialized by the given @data only when it did not
211+ * exist before.
212+ *
213+ * Return: the shadow variable data element, NULL on failure.
214+ */
215+void *klp_shadow_get_or_alloc(void *obj, unsigned long id, void *data,
216+ size_t size, gfp_t gfp_flags)
217+{
218+ return __klp_shadow_get_or_alloc(obj, id, data, size, gfp_flags, false);
219+}
220+EXPORT_SYMBOL_GPL(klp_shadow_get_or_alloc);
221+
222+/**
223+ * klp_shadow_free() - detach and free a <obj, id> shadow variable
224+ * @obj: pointer to parent object
225+ * @id: data identifier
226+ *
227+ * This function releases the memory for this <obj, id> shadow variable
228+ * instance, callers should stop referencing it accordingly.
229+ */
230+void klp_shadow_free(void *obj, unsigned long id)
231+{
232+ struct klp_shadow *shadow;
233+ unsigned long flags;
234+
235+ spin_lock_irqsave(&klp_shadow_lock, flags);
236+
237+ /* Delete <obj, id> from hash */
238+ hash_for_each_possible(klp_shadow_hash, shadow, node,
239+ (unsigned long)obj) {
240+
241+ if (klp_shadow_match(shadow, obj, id)) {
242+ hash_del_rcu(&shadow->node);
243+ kfree_rcu(shadow, rcu_head);
244+ break;
245+ }
246+ }
247+
248+ spin_unlock_irqrestore(&klp_shadow_lock, flags);
249+}
250+EXPORT_SYMBOL_GPL(klp_shadow_free);
251+
252+/**
253+ * klp_shadow_free_all() - detach and free all <*, id> shadow variables
254+ * @id: data identifier
255+ *
256+ * This function releases the memory for all <*, id> shadow variable
257+ * instances, callers should stop referencing them accordingly.
258+ */
259+void klp_shadow_free_all(unsigned long id)
260+{
261+ struct klp_shadow *shadow;
262+ unsigned long flags;
263+ int i;
264+
265+ spin_lock_irqsave(&klp_shadow_lock, flags);
266+
267+ /* Delete all <*, id> from hash */
268+ hash_for_each(klp_shadow_hash, i, shadow, node) {
269+ if (klp_shadow_match(shadow, shadow->obj, id)) {
270+ hash_del_rcu(&shadow->node);
271+ kfree_rcu(shadow, rcu_head);
272+ }
273+ }
274+
275+ spin_unlock_irqrestore(&klp_shadow_lock, flags);
276+}
277+EXPORT_SYMBOL_GPL(klp_shadow_free_all);