projects/linux·blob v5.8 · refs

349 lines · 10.0 KiB

1// SPDX-License-Identifier: GPL-2.0
2
3#include <linux/atomic.h>
4#include <linux/bsearch.h>
5#include <linux/bug.h>
6#include <linux/debugfs.h>
7#include <linux/init.h>
8#include <linux/kallsyms.h>
9#include <linux/sched.h>
10#include <linux/seq_file.h>
11#include <linux/slab.h>
12#include <linux/sort.h>
13#include <linux/string.h>
14#include <linux/uaccess.h>
15
16#include "kcsan.h"
17
18/*
19 * Statistics counters.
20 */
21static atomic_long_t counters[KCSAN_COUNTER_COUNT];
22
23/*
24 * Addresses for filtering functions from reporting. This list can be used as a
25 * whitelist or blacklist.
26 */
27static struct {
28 unsigned long *addrs; /* array of addresses */
29 size_t size; /* current size */
30 int used; /* number of elements used */
31 bool sorted; /* if elements are sorted */
32 bool whitelist; /* if list is a blacklist or whitelist */
33} report_filterlist = {
34 .addrs = NULL,
35 .size = 8, /* small initial size */
36 .used = 0,
37 .sorted = false,
38 .whitelist = false, /* default is blacklist */
39};
40static DEFINE_SPINLOCK(report_filterlist_lock);
41
42static const char *counter_to_name(enum kcsan_counter_id id)
43{
44 switch (id) {
45 case KCSAN_COUNTER_USED_WATCHPOINTS: return "used_watchpoints";
46 case KCSAN_COUNTER_SETUP_WATCHPOINTS: return "setup_watchpoints";
47 case KCSAN_COUNTER_DATA_RACES: return "data_races";
48 case KCSAN_COUNTER_ASSERT_FAILURES: return "assert_failures";
49 case KCSAN_COUNTER_NO_CAPACITY: return "no_capacity";
50 case KCSAN_COUNTER_REPORT_RACES: return "report_races";
51 case KCSAN_COUNTER_RACES_UNKNOWN_ORIGIN: return "races_unknown_origin";
52 case KCSAN_COUNTER_UNENCODABLE_ACCESSES: return "unencodable_accesses";
53 case KCSAN_COUNTER_ENCODING_FALSE_POSITIVES: return "encoding_false_positives";
54 case KCSAN_COUNTER_COUNT:
55 BUG();
56 }
57 return NULL;
58}
59
60void kcsan_counter_inc(enum kcsan_counter_id id)
61{
62 atomic_long_inc(&counters[id]);
63}
64
65void kcsan_counter_dec(enum kcsan_counter_id id)
66{
67 atomic_long_dec(&counters[id]);
68}
69
70/*
71 * The microbenchmark allows benchmarking KCSAN core runtime only. To run
72 * multiple threads, pipe 'microbench=<iters>' from multiple tasks into the
73 * debugfs file. This will not generate any conflicts, and tests fast-path only.
74 */
75static noinline void microbenchmark(unsigned long iters)
76{
77 const struct kcsan_ctx ctx_save = current->kcsan_ctx;
78 const bool was_enabled = READ_ONCE(kcsan_enabled);
79 cycles_t cycles;
80
81 /* We may have been called from an atomic region; reset context. */
82 memset(&current->kcsan_ctx, 0, sizeof(current->kcsan_ctx));
83 /*
84 * Disable to benchmark fast-path for all accesses, and (expected
85 * negligible) call into slow-path, but never set up watchpoints.
86 */
87 WRITE_ONCE(kcsan_enabled, false);
88
89 pr_info("KCSAN: %s begin | iters: %lu\n", __func__, iters);
90
91 cycles = get_cycles();
92 while (iters--) {
93 unsigned long addr = iters & ((PAGE_SIZE << 8) - 1);
94 int type = !(iters & 0x7f) ? KCSAN_ACCESS_ATOMIC :
95 (!(iters & 0xf) ? KCSAN_ACCESS_WRITE : 0);
96 __kcsan_check_access((void *)addr, sizeof(long), type);
97 }
98 cycles = get_cycles() - cycles;
99
100 pr_info("KCSAN: %s end | cycles: %llu\n", __func__, cycles);
101
102 WRITE_ONCE(kcsan_enabled, was_enabled);
103 /* restore context */
104 current->kcsan_ctx = ctx_save;
105}
106
107/*
108 * Simple test to create conflicting accesses. Write 'test=<iters>' to KCSAN's
109 * debugfs file from multiple tasks to generate real conflicts and show reports.
110 */
111static long test_dummy;
112static long test_flags;
113static long test_scoped;
114static noinline void test_thread(unsigned long iters)
115{
116 const long CHANGE_BITS = 0xff00ff00ff00ff00L;
117 const struct kcsan_ctx ctx_save = current->kcsan_ctx;
118 cycles_t cycles;
119
120 /* We may have been called from an atomic region; reset context. */
121 memset(&current->kcsan_ctx, 0, sizeof(current->kcsan_ctx));
122
123 pr_info("KCSAN: %s begin | iters: %lu\n", __func__, iters);
124 pr_info("test_dummy@%px, test_flags@%px, test_scoped@%px,\n",
125 &test_dummy, &test_flags, &test_scoped);
126
127 cycles = get_cycles();
128 while (iters--) {
129 /* These all should generate reports. */
130 __kcsan_check_read(&test_dummy, sizeof(test_dummy));
131 ASSERT_EXCLUSIVE_WRITER(test_dummy);
132 ASSERT_EXCLUSIVE_ACCESS(test_dummy);
133
134 ASSERT_EXCLUSIVE_BITS(test_flags, ~CHANGE_BITS); /* no report */
135 __kcsan_check_read(&test_flags, sizeof(test_flags)); /* no report */
136
137 ASSERT_EXCLUSIVE_BITS(test_flags, CHANGE_BITS); /* report */
138 __kcsan_check_read(&test_flags, sizeof(test_flags)); /* no report */
139
140 /* not actually instrumented */
141 WRITE_ONCE(test_dummy, iters); /* to observe value-change */
142 __kcsan_check_write(&test_dummy, sizeof(test_dummy));
143
144 test_flags ^= CHANGE_BITS; /* generate value-change */
145 __kcsan_check_write(&test_flags, sizeof(test_flags));
146
147 BUG_ON(current->kcsan_ctx.scoped_accesses.prev);
148 {
149 /* Should generate reports anywhere in this block. */
150 ASSERT_EXCLUSIVE_WRITER_SCOPED(test_scoped);
151 ASSERT_EXCLUSIVE_ACCESS_SCOPED(test_scoped);
152 BUG_ON(!current->kcsan_ctx.scoped_accesses.prev);
153 /* Unrelated accesses. */
154 __kcsan_check_access(&cycles, sizeof(cycles), 0);
155 __kcsan_check_access(&cycles, sizeof(cycles), KCSAN_ACCESS_ATOMIC);
156 }
157 BUG_ON(current->kcsan_ctx.scoped_accesses.prev);
158 }
159 cycles = get_cycles() - cycles;
160
161 pr_info("KCSAN: %s end | cycles: %llu\n", __func__, cycles);
162
163 /* restore context */
164 current->kcsan_ctx = ctx_save;
165}
166
167static int cmp_filterlist_addrs(const void *rhs, const void *lhs)
168{
169 const unsigned long a = *(const unsigned long *)rhs;
170 const unsigned long b = *(const unsigned long *)lhs;
171
172 return a < b ? -1 : a == b ? 0 : 1;
173}
174
175bool kcsan_skip_report_debugfs(unsigned long func_addr)
176{
177 unsigned long symbolsize, offset;
178 unsigned long flags;
179 bool ret = false;
180
181 if (!kallsyms_lookup_size_offset(func_addr, &symbolsize, &offset))
182 return false;
183 func_addr -= offset; /* Get function start */
184
185 spin_lock_irqsave(&report_filterlist_lock, flags);
186 if (report_filterlist.used == 0)
187 goto out;
188
189 /* Sort array if it is unsorted, and then do a binary search. */
190 if (!report_filterlist.sorted) {
191 sort(report_filterlist.addrs, report_filterlist.used,
192 sizeof(unsigned long), cmp_filterlist_addrs, NULL);
193 report_filterlist.sorted = true;
194 }
195 ret = !!bsearch(&func_addr, report_filterlist.addrs,
196 report_filterlist.used, sizeof(unsigned long),
197 cmp_filterlist_addrs);
198 if (report_filterlist.whitelist)
199 ret = !ret;
200
201out:
202 spin_unlock_irqrestore(&report_filterlist_lock, flags);
203 return ret;
204}
205
206static void set_report_filterlist_whitelist(bool whitelist)
207{
208 unsigned long flags;
209
210 spin_lock_irqsave(&report_filterlist_lock, flags);
211 report_filterlist.whitelist = whitelist;
212 spin_unlock_irqrestore(&report_filterlist_lock, flags);
213}
214
215/* Returns 0 on success, error-code otherwise. */
216static ssize_t insert_report_filterlist(const char *func)
217{
218 unsigned long flags;
219 unsigned long addr = kallsyms_lookup_name(func);
220 ssize_t ret = 0;
221
222 if (!addr) {
223 pr_err("KCSAN: could not find function: '%s'\n", func);
224 return -ENOENT;
225 }
226
227 spin_lock_irqsave(&report_filterlist_lock, flags);
228
229 if (report_filterlist.addrs == NULL) {
230 /* initial allocation */
231 report_filterlist.addrs =
232 kmalloc_array(report_filterlist.size,
233 sizeof(unsigned long), GFP_ATOMIC);
234 if (report_filterlist.addrs == NULL) {
235 ret = -ENOMEM;
236 goto out;
237 }
238 } else if (report_filterlist.used == report_filterlist.size) {
239 /* resize filterlist */
240 size_t new_size = report_filterlist.size * 2;
241 unsigned long *new_addrs =
242 krealloc(report_filterlist.addrs,
243 new_size * sizeof(unsigned long), GFP_ATOMIC);
244
245 if (new_addrs == NULL) {
246 /* leave filterlist itself untouched */
247 ret = -ENOMEM;
248 goto out;
249 }
250
251 report_filterlist.size = new_size;
252 report_filterlist.addrs = new_addrs;
253 }
254
255 /* Note: deduplicating should be done in userspace. */
256 report_filterlist.addrs[report_filterlist.used++] =
257 kallsyms_lookup_name(func);
258 report_filterlist.sorted = false;
259
260out:
261 spin_unlock_irqrestore(&report_filterlist_lock, flags);
262
263 return ret;
264}
265
266static int show_info(struct seq_file *file, void *v)
267{
268 int i;
269 unsigned long flags;
270
271 /* show stats */
272 seq_printf(file, "enabled: %i\n", READ_ONCE(kcsan_enabled));
273 for (i = 0; i < KCSAN_COUNTER_COUNT; ++i)
274 seq_printf(file, "%s: %ld\n", counter_to_name(i),
275 atomic_long_read(&counters[i]));
276
277 /* show filter functions, and filter type */
278 spin_lock_irqsave(&report_filterlist_lock, flags);
279 seq_printf(file, "\n%s functions: %s\n",
280 report_filterlist.whitelist ? "whitelisted" : "blacklisted",
281 report_filterlist.used == 0 ? "none" : "");
282 for (i = 0; i < report_filterlist.used; ++i)
283 seq_printf(file, " %ps\n", (void *)report_filterlist.addrs[i]);
284 spin_unlock_irqrestore(&report_filterlist_lock, flags);
285
286 return 0;
287}
288
289static int debugfs_open(struct inode *inode, struct file *file)
290{
291 return single_open(file, show_info, NULL);
292}
293
294static ssize_t
295debugfs_write(struct file *file, const char __user *buf, size_t count, loff_t *off)
296{
297 char kbuf[KSYM_NAME_LEN];
298 char *arg;
299 int read_len = count < (sizeof(kbuf) - 1) ? count : (sizeof(kbuf) - 1);
300
301 if (copy_from_user(kbuf, buf, read_len))
302 return -EFAULT;
303 kbuf[read_len] = '\0';
304 arg = strstrip(kbuf);
305
306 if (!strcmp(arg, "on")) {
307 WRITE_ONCE(kcsan_enabled, true);
308 } else if (!strcmp(arg, "off")) {
309 WRITE_ONCE(kcsan_enabled, false);
310 } else if (!strncmp(arg, "microbench=", sizeof("microbench=") - 1)) {
311 unsigned long iters;
312
313 if (kstrtoul(&arg[sizeof("microbench=") - 1], 0, &iters))
314 return -EINVAL;
315 microbenchmark(iters);
316 } else if (!strncmp(arg, "test=", sizeof("test=") - 1)) {
317 unsigned long iters;
318
319 if (kstrtoul(&arg[sizeof("test=") - 1], 0, &iters))
320 return -EINVAL;
321 test_thread(iters);
322 } else if (!strcmp(arg, "whitelist")) {
323 set_report_filterlist_whitelist(true);
324 } else if (!strcmp(arg, "blacklist")) {
325 set_report_filterlist_whitelist(false);
326 } else if (arg[0] == '!') {
327 ssize_t ret = insert_report_filterlist(&arg[1]);
328
329 if (ret < 0)
330 return ret;
331 } else {
332 return -EINVAL;
333 }
334
335 return count;
336}
337
338static const struct file_operations debugfs_ops =
339{
340 .read = seq_read,
341 .open = debugfs_open,
342 .write = debugfs_write,
343 .release = single_release
344};
345
346void __init kcsan_debugfs_init(void)
347{
348 debugfs_create_file("kcsan", 0644, NULL, NULL, &debugfs_ops);
349}