projects/linux·blob v5.2 · refs

296 lines · 6.5 KiB

1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * patch.c - livepatch patching functions
4 *
5 * Copyright (C) 2014 Seth Jennings <[email protected]>
6 * Copyright (C) 2014 SUSE
7 * Copyright (C) 2015 Josh Poimboeuf <[email protected]>
8 */
9
10#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
11
12#include <linux/livepatch.h>
13#include <linux/list.h>
14#include <linux/ftrace.h>
15#include <linux/rculist.h>
16#include <linux/slab.h>
17#include <linux/bug.h>
18#include <linux/printk.h>
19#include "core.h"
20#include "patch.h"
21#include "transition.h"
22
23static LIST_HEAD(klp_ops);
24
25struct klp_ops *klp_find_ops(void *old_func)
26{
27 struct klp_ops *ops;
28 struct klp_func *func;
29
30 list_for_each_entry(ops, &klp_ops, node) {
31 func = list_first_entry(&ops->func_stack, struct klp_func,
32 stack_node);
33 if (func->old_func == old_func)
34 return ops;
35 }
36
37 return NULL;
38}
39
40static void notrace klp_ftrace_handler(unsigned long ip,
41 unsigned long parent_ip,
42 struct ftrace_ops *fops,
43 struct pt_regs *regs)
44{
45 struct klp_ops *ops;
46 struct klp_func *func;
47 int patch_state;
48
49 ops = container_of(fops, struct klp_ops, fops);
50
51 /*
52 * A variant of synchronize_rcu() is used to allow patching functions
53 * where RCU is not watching, see klp_synchronize_transition().
54 */
55 preempt_disable_notrace();
56
57 func = list_first_or_null_rcu(&ops->func_stack, struct klp_func,
58 stack_node);
59
60 /*
61 * func should never be NULL because preemption should be disabled here
62 * and unregister_ftrace_function() does the equivalent of a
63 * synchronize_rcu() before the func_stack removal.
64 */
65 if (WARN_ON_ONCE(!func))
66 goto unlock;
67
68 /*
69 * In the enable path, enforce the order of the ops->func_stack and
70 * func->transition reads. The corresponding write barrier is in
71 * __klp_enable_patch().
72 *
73 * (Note that this barrier technically isn't needed in the disable
74 * path. In the rare case where klp_update_patch_state() runs before
75 * this handler, its TIF_PATCH_PENDING read and this func->transition
76 * read need to be ordered. But klp_update_patch_state() already
77 * enforces that.)
78 */
79 smp_rmb();
80
81 if (unlikely(func->transition)) {
82
83 /*
84 * Enforce the order of the func->transition and
85 * current->patch_state reads. Otherwise we could read an
86 * out-of-date task state and pick the wrong function. The
87 * corresponding write barrier is in klp_init_transition().
88 */
89 smp_rmb();
90
91 patch_state = current->patch_state;
92
93 WARN_ON_ONCE(patch_state == KLP_UNDEFINED);
94
95 if (patch_state == KLP_UNPATCHED) {
96 /*
97 * Use the previously patched version of the function.
98 * If no previous patches exist, continue with the
99 * original function.
100 */
101 func = list_entry_rcu(func->stack_node.next,
102 struct klp_func, stack_node);
103
104 if (&func->stack_node == &ops->func_stack)
105 goto unlock;
106 }
107 }
108
109 /*
110 * NOPs are used to replace existing patches with original code.
111 * Do nothing! Setting pc would cause an infinite loop.
112 */
113 if (func->nop)
114 goto unlock;
115
116 klp_arch_set_pc(regs, (unsigned long)func->new_func);
117
118unlock:
119 preempt_enable_notrace();
120}
121
122/*
123 * Convert a function address into the appropriate ftrace location.
124 *
125 * Usually this is just the address of the function, but on some architectures
126 * it's more complicated so allow them to provide a custom behaviour.
127 */
128#ifndef klp_get_ftrace_location
129static unsigned long klp_get_ftrace_location(unsigned long faddr)
130{
131 return faddr;
132}
133#endif
134
135static void klp_unpatch_func(struct klp_func *func)
136{
137 struct klp_ops *ops;
138
139 if (WARN_ON(!func->patched))
140 return;
141 if (WARN_ON(!func->old_func))
142 return;
143
144 ops = klp_find_ops(func->old_func);
145 if (WARN_ON(!ops))
146 return;
147
148 if (list_is_singular(&ops->func_stack)) {
149 unsigned long ftrace_loc;
150
151 ftrace_loc =
152 klp_get_ftrace_location((unsigned long)func->old_func);
153 if (WARN_ON(!ftrace_loc))
154 return;
155
156 WARN_ON(unregister_ftrace_function(&ops->fops));
157 WARN_ON(ftrace_set_filter_ip(&ops->fops, ftrace_loc, 1, 0));
158
159 list_del_rcu(&func->stack_node);
160 list_del(&ops->node);
161 kfree(ops);
162 } else {
163 list_del_rcu(&func->stack_node);
164 }
165
166 func->patched = false;
167}
168
169static int klp_patch_func(struct klp_func *func)
170{
171 struct klp_ops *ops;
172 int ret;
173
174 if (WARN_ON(!func->old_func))
175 return -EINVAL;
176
177 if (WARN_ON(func->patched))
178 return -EINVAL;
179
180 ops = klp_find_ops(func->old_func);
181 if (!ops) {
182 unsigned long ftrace_loc;
183
184 ftrace_loc =
185 klp_get_ftrace_location((unsigned long)func->old_func);
186 if (!ftrace_loc) {
187 pr_err("failed to find location for function '%s'\n",
188 func->old_name);
189 return -EINVAL;
190 }
191
192 ops = kzalloc(sizeof(*ops), GFP_KERNEL);
193 if (!ops)
194 return -ENOMEM;
195
196 ops->fops.func = klp_ftrace_handler;
197 ops->fops.flags = FTRACE_OPS_FL_SAVE_REGS |
198 FTRACE_OPS_FL_DYNAMIC |
199 FTRACE_OPS_FL_IPMODIFY;
200
201 list_add(&ops->node, &klp_ops);
202
203 INIT_LIST_HEAD(&ops->func_stack);
204 list_add_rcu(&func->stack_node, &ops->func_stack);
205
206 ret = ftrace_set_filter_ip(&ops->fops, ftrace_loc, 0, 0);
207 if (ret) {
208 pr_err("failed to set ftrace filter for function '%s' (%d)\n",
209 func->old_name, ret);
210 goto err;
211 }
212
213 ret = register_ftrace_function(&ops->fops);
214 if (ret) {
215 pr_err("failed to register ftrace handler for function '%s' (%d)\n",
216 func->old_name, ret);
217 ftrace_set_filter_ip(&ops->fops, ftrace_loc, 1, 0);
218 goto err;
219 }
220
221
222 } else {
223 list_add_rcu(&func->stack_node, &ops->func_stack);
224 }
225
226 func->patched = true;
227
228 return 0;
229
230err:
231 list_del_rcu(&func->stack_node);
232 list_del(&ops->node);
233 kfree(ops);
234 return ret;
235}
236
237static void __klp_unpatch_object(struct klp_object *obj, bool nops_only)
238{
239 struct klp_func *func;
240
241 klp_for_each_func(obj, func) {
242 if (nops_only && !func->nop)
243 continue;
244
245 if (func->patched)
246 klp_unpatch_func(func);
247 }
248
249 if (obj->dynamic || !nops_only)
250 obj->patched = false;
251}
252
253
254void klp_unpatch_object(struct klp_object *obj)
255{
256 __klp_unpatch_object(obj, false);
257}
258
259int klp_patch_object(struct klp_object *obj)
260{
261 struct klp_func *func;
262 int ret;
263
264 if (WARN_ON(obj->patched))
265 return -EINVAL;
266
267 klp_for_each_func(obj, func) {
268 ret = klp_patch_func(func);
269 if (ret) {
270 klp_unpatch_object(obj);
271 return ret;
272 }
273 }
274 obj->patched = true;
275
276 return 0;
277}
278
279static void __klp_unpatch_objects(struct klp_patch *patch, bool nops_only)
280{
281 struct klp_object *obj;
282
283 klp_for_each_object(patch, obj)
284 if (obj->patched)
285 __klp_unpatch_object(obj, nops_only);
286}
287
288void klp_unpatch_objects(struct klp_patch *patch)
289{
290 __klp_unpatch_objects(patch, false);
291}
292
293void klp_unpatch_objects_dynamic(struct klp_patch *patch)
294{
295 __klp_unpatch_objects(patch, true);
296}