1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * fail_function.c: Function-based error injection
4 */
5 #include <linux/error-injection.h>
6 #include <linux/debugfs.h>
7 #include <linux/fault-inject.h>
8 #include <linux/kallsyms.h>
9 #include <linux/kprobes.h>
10 #include <linux/module.h>
11 #include <linux/mutex.h>
12 #include <linux/slab.h>
13 #include <linux/uaccess.h>
14
15 static int fei_kprobe_handler(struct kprobe *kp, struct pt_regs *regs);
16
17 static void fei_post_handler(struct kprobe *kp, struct pt_regs *regs,
18 unsigned long flags)
19 {
20 /*
21 * A dummy post handler is required to prohibit optimizing, because
22 * jump optimization does not support execution path overriding.
23 */
24 }
25
26 struct fei_attr {
27 struct list_head list;
28 struct kprobe kp;
29 unsigned long retval;
30 };
31 static DEFINE_MUTEX(fei_lock);
32 static LIST_HEAD(fei_attr_list);
33 static DECLARE_FAULT_ATTR(fei_fault_attr);
34 static struct dentry *fei_debugfs_dir;
35
36 static unsigned long adjust_error_retval(unsigned long addr, unsigned long retv)
37 {
38 switch (get_injectable_error_type(addr)) {
39 case EI_ETYPE_NULL:
40 return 0;
41 case EI_ETYPE_ERRNO:
42 if (retv < (unsigned long)-MAX_ERRNO)
43 return (unsigned long)-EINVAL;
44 break;
45 case EI_ETYPE_ERRNO_NULL:
46 if (retv != 0 && retv < (unsigned long)-MAX_ERRNO)
47 return (unsigned long)-EINVAL;
48 break;
49 case EI_ETYPE_TRUE:
50 return 1;
51 }
52
53 return retv;
54 }
55
56 static struct fei_attr *fei_attr_new(const char *sym, unsigned long addr)
57 {
58 struct fei_attr *attr;
59
60 attr = kzalloc(sizeof(*attr), GFP_KERNEL);
61 if (attr) {
62 attr->kp.symbol_name = kstrdup(sym, GFP_KERNEL);
63 if (!attr->kp.symbol_name) {
64 kfree(attr);
65 return NULL;
66 }
67 attr->kp.pre_handler = fei_kprobe_handler;
68 attr->kp.post_handler = fei_post_handler;
69 attr->retval = adjust_error_retval(addr, 0);
70 INIT_LIST_HEAD(&attr->list);
71 }
72 return attr;
73 }
74
75 static void fei_attr_free(struct fei_attr *attr)
76 {
77 if (attr) {
78 kfree(attr->kp.symbol_name);
79 kfree(attr);
80 }
81 }
82
83 static struct fei_attr *fei_attr_lookup(const char *sym)
84 {
85 struct fei_attr *attr;
86
87 list_for_each_entry(attr, &fei_attr_list, list) {
88 if (!strcmp(attr->kp.symbol_name, sym))
89 return attr;
90 }
91
92 return NULL;
93 }
94
95 static bool fei_attr_is_valid(struct fei_attr *_attr)
96 {
97 struct fei_attr *attr;
98
99 list_for_each_entry(attr, &fei_attr_list, list) {
100 if (attr == _attr)
101 return true;
102 }
103
104 return false;
105 }
106
107 static int fei_retval_set(void *data, u64 val)
108 {
109 struct fei_attr *attr = data;
110 unsigned long retv = (unsigned long)val;
111 int err = 0;
112
113 mutex_lock(&fei_lock);
114 /*
115 * Since this operation can be done after retval file is removed,
116 * It is safer to check the attr is still valid before accessing
117 * its member.
118 */
119 if (!fei_attr_is_valid(attr)) {
120 err = -ENOENT;
121 goto out;
122 }
123
124 if (attr->kp.addr) {
125 if (adjust_error_retval((unsigned long)attr->kp.addr,
126 val) != retv)
127 err = -EINVAL;
128 }
129 if (!err)
130 attr->retval = val;
131 out:
132 mutex_unlock(&fei_lock);
133
134 return err;
135 }
136
137 static int fei_retval_get(void *data, u64 *val)
138 {
139 struct fei_attr *attr = data;
140 int err = 0;
141
142 mutex_lock(&fei_lock);
143 /* Here we also validate @attr to ensure it still exists. */
144 if (!fei_attr_is_valid(attr))
145 err = -ENOENT;
146 else
147 *val = attr->retval;
148 mutex_unlock(&fei_lock);
149
150 return err;
151 }
152 DEFINE_DEBUGFS_ATTRIBUTE(fei_retval_ops, fei_retval_get, fei_retval_set,
153 "%llx\n");
154
155 static void fei_debugfs_add_attr(struct fei_attr *attr)
156 {
157 struct dentry *dir;
158
159 dir = debugfs_create_dir(attr->kp.symbol_name, fei_debugfs_dir);
160
161 debugfs_create_file("retval", 0600, dir, attr, &fei_retval_ops);
162 }
163
164 static void fei_debugfs_remove_attr(struct fei_attr *attr)
165 {
166 debugfs_lookup_and_remove(attr->kp.symbol_name, fei_debugfs_dir);
167 }
168
169 static int fei_kprobe_handler(struct kprobe *kp, struct pt_regs *regs)
170 {
171 struct fei_attr *attr = container_of(kp, struct fei_attr, kp);
172
173 if (should_fail(&fei_fault_attr, 1)) {
174 regs_set_return_value(regs, attr->retval);
175 override_function_with_return(regs);
176 return 1;
177 }
178
179 return 0;
180 }
181 NOKPROBE_SYMBOL(fei_kprobe_handler)
182
183 static void *fei_seq_start(struct seq_file *m, loff_t *pos)
184 {
185 mutex_lock(&fei_lock);
186 return seq_list_start(&fei_attr_list, *pos);
187 }
188
189 static void fei_seq_stop(struct seq_file *m, void *v)
190 {
191 mutex_unlock(&fei_lock);
192 }
193
194 static void *fei_seq_next(struct seq_file *m, void *v, loff_t *pos)
195 {
196 return seq_list_next(v, &fei_attr_list, pos);
197 }
198
199 static int fei_seq_show(struct seq_file *m, void *v)
200 {
201 struct fei_attr *attr = list_entry(v, struct fei_attr, list);
202
203 seq_printf(m, "%ps\n", attr->kp.addr);
204 return 0;
205 }
206
207 static const struct seq_operations fei_seq_ops = {
208 .start = fei_seq_start,
209 .next = fei_seq_next,
210 .stop = fei_seq_stop,
211 .show = fei_seq_show,
212 };
213
214 static int fei_open(struct inode *inode, struct file *file)
215 {
216 return seq_open(file, &fei_seq_ops);
217 }
218
219 static void fei_attr_remove(struct fei_attr *attr)
220 {
221 fei_debugfs_remove_attr(attr);
222 unregister_kprobe(&attr->kp);
223 list_del(&attr->list);
224 fei_attr_free(attr);
225 }
226
227 static void fei_attr_remove_all(void)
228 {
229 struct fei_attr *attr, *n;
230
231 list_for_each_entry_safe(attr, n, &fei_attr_list, list) {
232 fei_attr_remove(attr);
233 }
234 }
235
236 static ssize_t fei_write(struct file *file, const char __user *buffer,
237 size_t count, loff_t *ppos)
238 {
239 struct fei_attr *attr;
240 unsigned long addr;
241 char *buf, *sym;
242 int ret;
243
244 /* cut off if it is too long */
245 if (count > KSYM_NAME_LEN)
246 count = KSYM_NAME_LEN;
247
248 buf = memdup_user_nul(buffer, count);
249 if (IS_ERR(buf))
250 return PTR_ERR(buf);
251
252 sym = strstrip(buf);
253
254 mutex_lock(&fei_lock);
255
256 /* Writing just spaces will remove all injection points */
257 if (sym[0] == '\0') {
258 fei_attr_remove_all();
259 ret = count;
260 goto out;
261 }
262 /* Writing !function will remove one injection point */
263 if (sym[0] == '!') {
264 attr = fei_attr_lookup(sym + 1);
265 if (!attr) {
266 ret = -ENOENT;
267 goto out;
268 }
269 fei_attr_remove(attr);
270 ret = count;
271 goto out;
272 }
273
274 addr = kallsyms_lookup_name(sym);
275 if (!addr) {
276 ret = -EINVAL;
277 goto out;
278 }
279 if (!within_error_injection_list(addr)) {
280 ret = -ERANGE;
281 goto out;
282 }
283 if (fei_attr_lookup(sym)) {
284 ret = -EBUSY;
285 goto out;
286 }
287 attr = fei_attr_new(sym, addr);
288 if (!attr) {
289 ret = -ENOMEM;
290 goto out;
291 }
292
293 ret = register_kprobe(&attr->kp);
294 if (ret) {
295 fei_attr_free(attr);
296 goto out;
297 }
298 fei_debugfs_add_attr(attr);
299 list_add_tail(&attr->list, &fei_attr_list);
300 ret = count;
301 out:
302 mutex_unlock(&fei_lock);
303 kfree(buf);
304 return ret;
305 }
306
307 static const struct file_operations fei_ops = {
308 .open = fei_open,
309 .read = seq_read,
310 .write = fei_write,
311 .llseek = seq_lseek,
312 .release = seq_release,
313 };
314
315 static int __init fei_debugfs_init(void)
316 {
317 struct dentry *dir;
318
319 dir = fault_create_debugfs_attr("fail_function", NULL,
320 &fei_fault_attr);
321 if (IS_ERR(dir))
322 return PTR_ERR(dir);
323
324 /* injectable attribute is just a symlink of error_inject/list */
325 debugfs_create_symlink("injectable", dir, "../error_injection/list");
326
327 debugfs_create_file("inject", 0600, dir, NULL, &fei_ops);
328
329 fei_debugfs_dir = dir;
330
331 return 0;
332 }
333
334 late_initcall(fei_debugfs_init);
335
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