1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * KCSAN debugfs interface.
4 *
5 * Copyright (C) 2019, Google LLC.
6 */
7
8 #define pr_fmt(fmt) "kcsan: " fmt
9
10 #include <linux/atomic.h>
11 #include <linux/bsearch.h>
12 #include <linux/bug.h>
13 #include <linux/debugfs.h>
14 #include <linux/init.h>
15 #include <linux/kallsyms.h>
16 #include <linux/sched.h>
17 #include <linux/seq_file.h>
18 #include <linux/slab.h>
19 #include <linux/sort.h>
20 #include <linux/string.h>
21 #include <linux/uaccess.h>
22
23 #include "kcsan.h"
24
25 atomic_long_t kcsan_counters[KCSAN_COUNTER_COUNT];
26 static const char *const counter_names[] = {
27 [KCSAN_COUNTER_USED_WATCHPOINTS] = "used_watchpoints",
28 [KCSAN_COUNTER_SETUP_WATCHPOINTS] = "setup_watchpoints",
29 [KCSAN_COUNTER_DATA_RACES] = "data_races",
30 [KCSAN_COUNTER_ASSERT_FAILURES] = "assert_failures",
31 [KCSAN_COUNTER_NO_CAPACITY] = "no_capacity",
32 [KCSAN_COUNTER_REPORT_RACES] = "report_races",
33 [KCSAN_COUNTER_RACES_UNKNOWN_ORIGIN] = "races_unknown_origin",
34 [KCSAN_COUNTER_UNENCODABLE_ACCESSES] = "unencodable_accesses",
35 [KCSAN_COUNTER_ENCODING_FALSE_POSITIVES] = "encoding_false_positives",
36 };
37 static_assert(ARRAY_SIZE(counter_names) == KCSAN_COUNTER_COUNT);
38
39 /*
40 * Addresses for filtering functions from reporting. This list can be used as a
41 * whitelist or blacklist.
42 */
43 static struct {
44 unsigned long *addrs; /* array of addresses */
45 size_t size; /* current size */
46 int used; /* number of elements used */
47 bool sorted; /* if elements are sorted */
48 bool whitelist; /* if list is a blacklist or whitelist */
49 } report_filterlist = {
50 .addrs = NULL,
51 .size = 8, /* small initial size */
52 .used = 0,
53 .sorted = false,
54 .whitelist = false, /* default is blacklist */
55 };
56 static DEFINE_SPINLOCK(report_filterlist_lock);
57
58 /*
59 * The microbenchmark allows benchmarking KCSAN core runtime only. To run
60 * multiple threads, pipe 'microbench=<iters>' from multiple tasks into the
61 * debugfs file. This will not generate any conflicts, and tests fast-path only.
62 */
microbenchmark(unsigned long iters)63 static noinline void microbenchmark(unsigned long iters)
64 {
65 const struct kcsan_ctx ctx_save = current->kcsan_ctx;
66 const bool was_enabled = READ_ONCE(kcsan_enabled);
67 cycles_t cycles;
68
69 /* We may have been called from an atomic region; reset context. */
70 memset(¤t->kcsan_ctx, 0, sizeof(current->kcsan_ctx));
71 /*
72 * Disable to benchmark fast-path for all accesses, and (expected
73 * negligible) call into slow-path, but never set up watchpoints.
74 */
75 WRITE_ONCE(kcsan_enabled, false);
76
77 pr_info("%s begin | iters: %lu\n", __func__, iters);
78
79 cycles = get_cycles();
80 while (iters--) {
81 unsigned long addr = iters & ((PAGE_SIZE << 8) - 1);
82 int type = !(iters & 0x7f) ? KCSAN_ACCESS_ATOMIC :
83 (!(iters & 0xf) ? KCSAN_ACCESS_WRITE : 0);
84 __kcsan_check_access((void *)addr, sizeof(long), type);
85 }
86 cycles = get_cycles() - cycles;
87
88 pr_info("%s end | cycles: %llu\n", __func__, cycles);
89
90 WRITE_ONCE(kcsan_enabled, was_enabled);
91 /* restore context */
92 current->kcsan_ctx = ctx_save;
93 }
94
cmp_filterlist_addrs(const void * rhs,const void * lhs)95 static int cmp_filterlist_addrs(const void *rhs, const void *lhs)
96 {
97 const unsigned long a = *(const unsigned long *)rhs;
98 const unsigned long b = *(const unsigned long *)lhs;
99
100 return a < b ? -1 : a == b ? 0 : 1;
101 }
102
kcsan_skip_report_debugfs(unsigned long func_addr)103 bool kcsan_skip_report_debugfs(unsigned long func_addr)
104 {
105 unsigned long symbolsize, offset;
106 unsigned long flags;
107 bool ret = false;
108
109 if (!kallsyms_lookup_size_offset(func_addr, &symbolsize, &offset))
110 return false;
111 func_addr -= offset; /* Get function start */
112
113 spin_lock_irqsave(&report_filterlist_lock, flags);
114 if (report_filterlist.used == 0)
115 goto out;
116
117 /* Sort array if it is unsorted, and then do a binary search. */
118 if (!report_filterlist.sorted) {
119 sort(report_filterlist.addrs, report_filterlist.used,
120 sizeof(unsigned long), cmp_filterlist_addrs, NULL);
121 report_filterlist.sorted = true;
122 }
123 ret = !!bsearch(&func_addr, report_filterlist.addrs,
124 report_filterlist.used, sizeof(unsigned long),
125 cmp_filterlist_addrs);
126 if (report_filterlist.whitelist)
127 ret = !ret;
128
129 out:
130 spin_unlock_irqrestore(&report_filterlist_lock, flags);
131 return ret;
132 }
133
set_report_filterlist_whitelist(bool whitelist)134 static void set_report_filterlist_whitelist(bool whitelist)
135 {
136 unsigned long flags;
137
138 spin_lock_irqsave(&report_filterlist_lock, flags);
139 report_filterlist.whitelist = whitelist;
140 spin_unlock_irqrestore(&report_filterlist_lock, flags);
141 }
142
143 /* Returns 0 on success, error-code otherwise. */
insert_report_filterlist(const char * func)144 static ssize_t insert_report_filterlist(const char *func)
145 {
146 unsigned long flags;
147 unsigned long addr = kallsyms_lookup_name(func);
148 ssize_t ret = 0;
149
150 if (!addr) {
151 pr_err("could not find function: '%s'\n", func);
152 return -ENOENT;
153 }
154
155 spin_lock_irqsave(&report_filterlist_lock, flags);
156
157 if (report_filterlist.addrs == NULL) {
158 /* initial allocation */
159 report_filterlist.addrs =
160 kmalloc_array(report_filterlist.size,
161 sizeof(unsigned long), GFP_ATOMIC);
162 if (report_filterlist.addrs == NULL) {
163 ret = -ENOMEM;
164 goto out;
165 }
166 } else if (report_filterlist.used == report_filterlist.size) {
167 /* resize filterlist */
168 size_t new_size = report_filterlist.size * 2;
169 unsigned long *new_addrs =
170 krealloc(report_filterlist.addrs,
171 new_size * sizeof(unsigned long), GFP_ATOMIC);
172
173 if (new_addrs == NULL) {
174 /* leave filterlist itself untouched */
175 ret = -ENOMEM;
176 goto out;
177 }
178
179 report_filterlist.size = new_size;
180 report_filterlist.addrs = new_addrs;
181 }
182
183 /* Note: deduplicating should be done in userspace. */
184 report_filterlist.addrs[report_filterlist.used++] =
185 kallsyms_lookup_name(func);
186 report_filterlist.sorted = false;
187
188 out:
189 spin_unlock_irqrestore(&report_filterlist_lock, flags);
190
191 return ret;
192 }
193
show_info(struct seq_file * file,void * v)194 static int show_info(struct seq_file *file, void *v)
195 {
196 int i;
197 unsigned long flags;
198
199 /* show stats */
200 seq_printf(file, "enabled: %i\n", READ_ONCE(kcsan_enabled));
201 for (i = 0; i < KCSAN_COUNTER_COUNT; ++i) {
202 seq_printf(file, "%s: %ld\n", counter_names[i],
203 atomic_long_read(&kcsan_counters[i]));
204 }
205
206 /* show filter functions, and filter type */
207 spin_lock_irqsave(&report_filterlist_lock, flags);
208 seq_printf(file, "\n%s functions: %s\n",
209 report_filterlist.whitelist ? "whitelisted" : "blacklisted",
210 report_filterlist.used == 0 ? "none" : "");
211 for (i = 0; i < report_filterlist.used; ++i)
212 seq_printf(file, " %ps\n", (void *)report_filterlist.addrs[i]);
213 spin_unlock_irqrestore(&report_filterlist_lock, flags);
214
215 return 0;
216 }
217
debugfs_open(struct inode * inode,struct file * file)218 static int debugfs_open(struct inode *inode, struct file *file)
219 {
220 return single_open(file, show_info, NULL);
221 }
222
223 static ssize_t
debugfs_write(struct file * file,const char __user * buf,size_t count,loff_t * off)224 debugfs_write(struct file *file, const char __user *buf, size_t count, loff_t *off)
225 {
226 char kbuf[KSYM_NAME_LEN];
227 char *arg;
228 int read_len = count < (sizeof(kbuf) - 1) ? count : (sizeof(kbuf) - 1);
229
230 if (copy_from_user(kbuf, buf, read_len))
231 return -EFAULT;
232 kbuf[read_len] = '\0';
233 arg = strstrip(kbuf);
234
235 if (!strcmp(arg, "on")) {
236 WRITE_ONCE(kcsan_enabled, true);
237 } else if (!strcmp(arg, "off")) {
238 WRITE_ONCE(kcsan_enabled, false);
239 } else if (str_has_prefix(arg, "microbench=")) {
240 unsigned long iters;
241
242 if (kstrtoul(&arg[strlen("microbench=")], 0, &iters))
243 return -EINVAL;
244 microbenchmark(iters);
245 } else if (!strcmp(arg, "whitelist")) {
246 set_report_filterlist_whitelist(true);
247 } else if (!strcmp(arg, "blacklist")) {
248 set_report_filterlist_whitelist(false);
249 } else if (arg[0] == '!') {
250 ssize_t ret = insert_report_filterlist(&arg[1]);
251
252 if (ret < 0)
253 return ret;
254 } else {
255 return -EINVAL;
256 }
257
258 return count;
259 }
260
261 static const struct file_operations debugfs_ops =
262 {
263 .read = seq_read,
264 .open = debugfs_open,
265 .write = debugfs_write,
266 .release = single_release
267 };
268
kcsan_debugfs_init(void)269 static void __init kcsan_debugfs_init(void)
270 {
271 debugfs_create_file("kcsan", 0644, NULL, NULL, &debugfs_ops);
272 }
273
274 late_initcall(kcsan_debugfs_init);
275