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
15static int fei_kprobe_handler(struct kprobe *kp, struct pt_regs *regs);
16
17static 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
26struct fei_attr {
27	struct list_head list;
28	struct kprobe kp;
29	unsigned long retval;
30};
31static DEFINE_MUTEX(fei_lock);
32static LIST_HEAD(fei_attr_list);
33static DECLARE_FAULT_ATTR(fei_fault_attr);
34static struct dentry *fei_debugfs_dir;
35
36static 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
56static 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
75static void fei_attr_free(struct fei_attr *attr)
76{
77	if (attr) {
78		kfree(attr->kp.symbol_name);
79		kfree(attr);
80	}
81}
82
83static 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
95static 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
107static 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;
131out:
132	mutex_unlock(&fei_lock);
133
134	return err;
135}
136
137static 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}
152DEFINE_DEBUGFS_ATTRIBUTE(fei_retval_ops, fei_retval_get, fei_retval_set,
153			 "%llx\n");
154
155static 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
164static void fei_debugfs_remove_attr(struct fei_attr *attr)
165{
166	debugfs_lookup_and_remove(attr->kp.symbol_name, fei_debugfs_dir);
167}
168
169static 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}
181NOKPROBE_SYMBOL(fei_kprobe_handler)
182
183static 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
189static void fei_seq_stop(struct seq_file *m, void *v)
190{
191	mutex_unlock(&fei_lock);
192}
193
194static 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
199static 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
207static 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
214static int fei_open(struct inode *inode, struct file *file)
215{
216	return seq_open(file, &fei_seq_ops);
217}
218
219static 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
227static 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
236static 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;
301out:
302	mutex_unlock(&fei_lock);
303	kfree(buf);
304	return ret;
305}
306
307static 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
315static 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
334late_initcall(fei_debugfs_init);
335