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c349cdca JP |
1 | /* |
2 | * patch.c - livepatch patching functions | |
3 | * | |
4 | * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com> | |
5 | * Copyright (C) 2014 SUSE | |
6 | * Copyright (C) 2015 Josh Poimboeuf <jpoimboe@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 | #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt | |
23 | ||
24 | #include <linux/livepatch.h> | |
25 | #include <linux/list.h> | |
26 | #include <linux/ftrace.h> | |
27 | #include <linux/rculist.h> | |
28 | #include <linux/slab.h> | |
29 | #include <linux/bug.h> | |
30 | #include <linux/printk.h> | |
93862e38 | 31 | #include "core.h" |
c349cdca | 32 | #include "patch.h" |
d83a7cb3 | 33 | #include "transition.h" |
c349cdca JP |
34 | |
35 | static LIST_HEAD(klp_ops); | |
36 | ||
19514910 | 37 | struct klp_ops *klp_find_ops(void *old_func) |
c349cdca JP |
38 | { |
39 | struct klp_ops *ops; | |
40 | struct klp_func *func; | |
41 | ||
42 | list_for_each_entry(ops, &klp_ops, node) { | |
43 | func = list_first_entry(&ops->func_stack, struct klp_func, | |
44 | stack_node); | |
19514910 | 45 | if (func->old_func == old_func) |
c349cdca JP |
46 | return ops; |
47 | } | |
48 | ||
49 | return NULL; | |
50 | } | |
51 | ||
52 | static void notrace klp_ftrace_handler(unsigned long ip, | |
53 | unsigned long parent_ip, | |
54 | struct ftrace_ops *fops, | |
55 | struct pt_regs *regs) | |
56 | { | |
57 | struct klp_ops *ops; | |
58 | struct klp_func *func; | |
d83a7cb3 | 59 | int patch_state; |
c349cdca JP |
60 | |
61 | ops = container_of(fops, struct klp_ops, fops); | |
62 | ||
842c0884 | 63 | /* |
6932689e | 64 | * A variant of synchronize_rcu() is used to allow patching functions |
842c0884 PM |
65 | * where RCU is not watching, see klp_synchronize_transition(). |
66 | */ | |
67 | preempt_disable_notrace(); | |
d83a7cb3 | 68 | |
c349cdca JP |
69 | func = list_first_or_null_rcu(&ops->func_stack, struct klp_func, |
70 | stack_node); | |
d83a7cb3 JP |
71 | |
72 | /* | |
73 | * func should never be NULL because preemption should be disabled here | |
74 | * and unregister_ftrace_function() does the equivalent of a | |
6932689e | 75 | * synchronize_rcu() before the func_stack removal. |
d83a7cb3 | 76 | */ |
c349cdca JP |
77 | if (WARN_ON_ONCE(!func)) |
78 | goto unlock; | |
79 | ||
d83a7cb3 JP |
80 | /* |
81 | * In the enable path, enforce the order of the ops->func_stack and | |
82 | * func->transition reads. The corresponding write barrier is in | |
83 | * __klp_enable_patch(). | |
84 | * | |
85 | * (Note that this barrier technically isn't needed in the disable | |
86 | * path. In the rare case where klp_update_patch_state() runs before | |
87 | * this handler, its TIF_PATCH_PENDING read and this func->transition | |
88 | * read need to be ordered. But klp_update_patch_state() already | |
89 | * enforces that.) | |
90 | */ | |
91 | smp_rmb(); | |
92 | ||
93 | if (unlikely(func->transition)) { | |
94 | ||
95 | /* | |
96 | * Enforce the order of the func->transition and | |
97 | * current->patch_state reads. Otherwise we could read an | |
98 | * out-of-date task state and pick the wrong function. The | |
99 | * corresponding write barrier is in klp_init_transition(). | |
100 | */ | |
101 | smp_rmb(); | |
102 | ||
103 | patch_state = current->patch_state; | |
104 | ||
105 | WARN_ON_ONCE(patch_state == KLP_UNDEFINED); | |
106 | ||
107 | if (patch_state == KLP_UNPATCHED) { | |
108 | /* | |
109 | * Use the previously patched version of the function. | |
110 | * If no previous patches exist, continue with the | |
111 | * original function. | |
112 | */ | |
113 | func = list_entry_rcu(func->stack_node.next, | |
114 | struct klp_func, stack_node); | |
115 | ||
116 | if (&func->stack_node == &ops->func_stack) | |
117 | goto unlock; | |
118 | } | |
119 | } | |
120 | ||
e1452b60 JB |
121 | /* |
122 | * NOPs are used to replace existing patches with original code. | |
123 | * Do nothing! Setting pc would cause an infinite loop. | |
124 | */ | |
125 | if (func->nop) | |
126 | goto unlock; | |
127 | ||
c349cdca | 128 | klp_arch_set_pc(regs, (unsigned long)func->new_func); |
e1452b60 | 129 | |
c349cdca | 130 | unlock: |
842c0884 | 131 | preempt_enable_notrace(); |
c349cdca JP |
132 | } |
133 | ||
134 | /* | |
135 | * Convert a function address into the appropriate ftrace location. | |
136 | * | |
137 | * Usually this is just the address of the function, but on some architectures | |
138 | * it's more complicated so allow them to provide a custom behaviour. | |
139 | */ | |
140 | #ifndef klp_get_ftrace_location | |
141 | static unsigned long klp_get_ftrace_location(unsigned long faddr) | |
142 | { | |
143 | return faddr; | |
144 | } | |
145 | #endif | |
146 | ||
147 | static void klp_unpatch_func(struct klp_func *func) | |
148 | { | |
149 | struct klp_ops *ops; | |
150 | ||
151 | if (WARN_ON(!func->patched)) | |
152 | return; | |
19514910 | 153 | if (WARN_ON(!func->old_func)) |
c349cdca JP |
154 | return; |
155 | ||
19514910 | 156 | ops = klp_find_ops(func->old_func); |
c349cdca JP |
157 | if (WARN_ON(!ops)) |
158 | return; | |
159 | ||
160 | if (list_is_singular(&ops->func_stack)) { | |
161 | unsigned long ftrace_loc; | |
162 | ||
19514910 PM |
163 | ftrace_loc = |
164 | klp_get_ftrace_location((unsigned long)func->old_func); | |
c349cdca JP |
165 | if (WARN_ON(!ftrace_loc)) |
166 | return; | |
167 | ||
168 | WARN_ON(unregister_ftrace_function(&ops->fops)); | |
169 | WARN_ON(ftrace_set_filter_ip(&ops->fops, ftrace_loc, 1, 0)); | |
170 | ||
171 | list_del_rcu(&func->stack_node); | |
172 | list_del(&ops->node); | |
173 | kfree(ops); | |
174 | } else { | |
175 | list_del_rcu(&func->stack_node); | |
176 | } | |
177 | ||
178 | func->patched = false; | |
179 | } | |
180 | ||
181 | static int klp_patch_func(struct klp_func *func) | |
182 | { | |
183 | struct klp_ops *ops; | |
184 | int ret; | |
185 | ||
19514910 | 186 | if (WARN_ON(!func->old_func)) |
c349cdca JP |
187 | return -EINVAL; |
188 | ||
189 | if (WARN_ON(func->patched)) | |
190 | return -EINVAL; | |
191 | ||
19514910 | 192 | ops = klp_find_ops(func->old_func); |
c349cdca JP |
193 | if (!ops) { |
194 | unsigned long ftrace_loc; | |
195 | ||
19514910 PM |
196 | ftrace_loc = |
197 | klp_get_ftrace_location((unsigned long)func->old_func); | |
c349cdca JP |
198 | if (!ftrace_loc) { |
199 | pr_err("failed to find location for function '%s'\n", | |
200 | func->old_name); | |
201 | return -EINVAL; | |
202 | } | |
203 | ||
204 | ops = kzalloc(sizeof(*ops), GFP_KERNEL); | |
205 | if (!ops) | |
206 | return -ENOMEM; | |
207 | ||
208 | ops->fops.func = klp_ftrace_handler; | |
209 | ops->fops.flags = FTRACE_OPS_FL_SAVE_REGS | | |
210 | FTRACE_OPS_FL_DYNAMIC | | |
211 | FTRACE_OPS_FL_IPMODIFY; | |
212 | ||
213 | list_add(&ops->node, &klp_ops); | |
214 | ||
215 | INIT_LIST_HEAD(&ops->func_stack); | |
216 | list_add_rcu(&func->stack_node, &ops->func_stack); | |
217 | ||
218 | ret = ftrace_set_filter_ip(&ops->fops, ftrace_loc, 0, 0); | |
219 | if (ret) { | |
220 | pr_err("failed to set ftrace filter for function '%s' (%d)\n", | |
221 | func->old_name, ret); | |
222 | goto err; | |
223 | } | |
224 | ||
225 | ret = register_ftrace_function(&ops->fops); | |
226 | if (ret) { | |
227 | pr_err("failed to register ftrace handler for function '%s' (%d)\n", | |
228 | func->old_name, ret); | |
229 | ftrace_set_filter_ip(&ops->fops, ftrace_loc, 1, 0); | |
230 | goto err; | |
231 | } | |
232 | ||
233 | ||
234 | } else { | |
235 | list_add_rcu(&func->stack_node, &ops->func_stack); | |
236 | } | |
237 | ||
238 | func->patched = true; | |
239 | ||
240 | return 0; | |
241 | ||
242 | err: | |
243 | list_del_rcu(&func->stack_node); | |
244 | list_del(&ops->node); | |
245 | kfree(ops); | |
246 | return ret; | |
247 | } | |
248 | ||
d697bad5 | 249 | static void __klp_unpatch_object(struct klp_object *obj, bool nops_only) |
c349cdca JP |
250 | { |
251 | struct klp_func *func; | |
252 | ||
d697bad5 PM |
253 | klp_for_each_func(obj, func) { |
254 | if (nops_only && !func->nop) | |
255 | continue; | |
256 | ||
c349cdca JP |
257 | if (func->patched) |
258 | klp_unpatch_func(func); | |
d697bad5 | 259 | } |
c349cdca | 260 | |
d697bad5 PM |
261 | if (obj->dynamic || !nops_only) |
262 | obj->patched = false; | |
263 | } | |
264 | ||
265 | ||
266 | void klp_unpatch_object(struct klp_object *obj) | |
267 | { | |
268 | __klp_unpatch_object(obj, false); | |
c349cdca JP |
269 | } |
270 | ||
271 | int klp_patch_object(struct klp_object *obj) | |
272 | { | |
273 | struct klp_func *func; | |
274 | int ret; | |
275 | ||
276 | if (WARN_ON(obj->patched)) | |
277 | return -EINVAL; | |
278 | ||
279 | klp_for_each_func(obj, func) { | |
280 | ret = klp_patch_func(func); | |
281 | if (ret) { | |
282 | klp_unpatch_object(obj); | |
283 | return ret; | |
284 | } | |
285 | } | |
286 | obj->patched = true; | |
287 | ||
288 | return 0; | |
289 | } | |
d83a7cb3 | 290 | |
d697bad5 | 291 | static void __klp_unpatch_objects(struct klp_patch *patch, bool nops_only) |
d83a7cb3 JP |
292 | { |
293 | struct klp_object *obj; | |
294 | ||
295 | klp_for_each_object(patch, obj) | |
296 | if (obj->patched) | |
d697bad5 PM |
297 | __klp_unpatch_object(obj, nops_only); |
298 | } | |
299 | ||
300 | void klp_unpatch_objects(struct klp_patch *patch) | |
301 | { | |
302 | __klp_unpatch_objects(patch, false); | |
303 | } | |
304 | ||
305 | void klp_unpatch_objects_dynamic(struct klp_patch *patch) | |
306 | { | |
307 | __klp_unpatch_objects(patch, true); | |
d83a7cb3 | 308 | } |