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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 | ||
37 | struct klp_ops *klp_find_ops(unsigned long old_addr) | |
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); | |
45 | if (func->old_addr == old_addr) | |
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 PM |
63 | /* |
64 | * A variant of synchronize_sched() is used to allow patching functions | |
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 | |
75 | * synchronize_sched() before the func_stack removal. | |
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 | ||
c349cdca JP |
121 | klp_arch_set_pc(regs, (unsigned long)func->new_func); |
122 | unlock: | |
842c0884 | 123 | preempt_enable_notrace(); |
c349cdca JP |
124 | } |
125 | ||
126 | /* | |
127 | * Convert a function address into the appropriate ftrace location. | |
128 | * | |
129 | * Usually this is just the address of the function, but on some architectures | |
130 | * it's more complicated so allow them to provide a custom behaviour. | |
131 | */ | |
132 | #ifndef klp_get_ftrace_location | |
133 | static unsigned long klp_get_ftrace_location(unsigned long faddr) | |
134 | { | |
135 | return faddr; | |
136 | } | |
137 | #endif | |
138 | ||
139 | static void klp_unpatch_func(struct klp_func *func) | |
140 | { | |
141 | struct klp_ops *ops; | |
142 | ||
143 | if (WARN_ON(!func->patched)) | |
144 | return; | |
145 | if (WARN_ON(!func->old_addr)) | |
146 | return; | |
147 | ||
148 | ops = klp_find_ops(func->old_addr); | |
149 | if (WARN_ON(!ops)) | |
150 | return; | |
151 | ||
152 | if (list_is_singular(&ops->func_stack)) { | |
153 | unsigned long ftrace_loc; | |
154 | ||
155 | ftrace_loc = klp_get_ftrace_location(func->old_addr); | |
156 | if (WARN_ON(!ftrace_loc)) | |
157 | return; | |
158 | ||
159 | WARN_ON(unregister_ftrace_function(&ops->fops)); | |
160 | WARN_ON(ftrace_set_filter_ip(&ops->fops, ftrace_loc, 1, 0)); | |
161 | ||
162 | list_del_rcu(&func->stack_node); | |
163 | list_del(&ops->node); | |
164 | kfree(ops); | |
165 | } else { | |
166 | list_del_rcu(&func->stack_node); | |
167 | } | |
168 | ||
169 | func->patched = false; | |
170 | } | |
171 | ||
172 | static int klp_patch_func(struct klp_func *func) | |
173 | { | |
174 | struct klp_ops *ops; | |
175 | int ret; | |
176 | ||
177 | if (WARN_ON(!func->old_addr)) | |
178 | return -EINVAL; | |
179 | ||
180 | if (WARN_ON(func->patched)) | |
181 | return -EINVAL; | |
182 | ||
183 | ops = klp_find_ops(func->old_addr); | |
184 | if (!ops) { | |
185 | unsigned long ftrace_loc; | |
186 | ||
187 | ftrace_loc = klp_get_ftrace_location(func->old_addr); | |
188 | if (!ftrace_loc) { | |
189 | pr_err("failed to find location for function '%s'\n", | |
190 | func->old_name); | |
191 | return -EINVAL; | |
192 | } | |
193 | ||
194 | ops = kzalloc(sizeof(*ops), GFP_KERNEL); | |
195 | if (!ops) | |
196 | return -ENOMEM; | |
197 | ||
198 | ops->fops.func = klp_ftrace_handler; | |
199 | ops->fops.flags = FTRACE_OPS_FL_SAVE_REGS | | |
200 | FTRACE_OPS_FL_DYNAMIC | | |
201 | FTRACE_OPS_FL_IPMODIFY; | |
202 | ||
203 | list_add(&ops->node, &klp_ops); | |
204 | ||
205 | INIT_LIST_HEAD(&ops->func_stack); | |
206 | list_add_rcu(&func->stack_node, &ops->func_stack); | |
207 | ||
208 | ret = ftrace_set_filter_ip(&ops->fops, ftrace_loc, 0, 0); | |
209 | if (ret) { | |
210 | pr_err("failed to set ftrace filter for function '%s' (%d)\n", | |
211 | func->old_name, ret); | |
212 | goto err; | |
213 | } | |
214 | ||
215 | ret = register_ftrace_function(&ops->fops); | |
216 | if (ret) { | |
217 | pr_err("failed to register ftrace handler for function '%s' (%d)\n", | |
218 | func->old_name, ret); | |
219 | ftrace_set_filter_ip(&ops->fops, ftrace_loc, 1, 0); | |
220 | goto err; | |
221 | } | |
222 | ||
223 | ||
224 | } else { | |
225 | list_add_rcu(&func->stack_node, &ops->func_stack); | |
226 | } | |
227 | ||
228 | func->patched = true; | |
229 | ||
230 | return 0; | |
231 | ||
232 | err: | |
233 | list_del_rcu(&func->stack_node); | |
234 | list_del(&ops->node); | |
235 | kfree(ops); | |
236 | return ret; | |
237 | } | |
238 | ||
239 | void klp_unpatch_object(struct klp_object *obj) | |
240 | { | |
241 | struct klp_func *func; | |
242 | ||
243 | klp_for_each_func(obj, func) | |
244 | if (func->patched) | |
245 | klp_unpatch_func(func); | |
246 | ||
247 | obj->patched = false; | |
248 | } | |
249 | ||
250 | int klp_patch_object(struct klp_object *obj) | |
251 | { | |
252 | struct klp_func *func; | |
253 | int ret; | |
254 | ||
255 | if (WARN_ON(obj->patched)) | |
256 | return -EINVAL; | |
257 | ||
258 | klp_for_each_func(obj, func) { | |
259 | ret = klp_patch_func(func); | |
260 | if (ret) { | |
261 | klp_unpatch_object(obj); | |
262 | return ret; | |
263 | } | |
264 | } | |
265 | obj->patched = true; | |
266 | ||
267 | return 0; | |
268 | } | |
d83a7cb3 JP |
269 | |
270 | void klp_unpatch_objects(struct klp_patch *patch) | |
271 | { | |
272 | struct klp_object *obj; | |
273 | ||
274 | klp_for_each_object(patch, obj) | |
275 | if (obj->patched) | |
276 | klp_unpatch_object(obj); | |
277 | } |