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
 25atomic_long_t kcsan_counters[KCSAN_COUNTER_COUNT];
 26static 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};
 37static_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 */
 43static 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};
 56static 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 */
 63static 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(&current->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
 95static 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
103bool 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
129out:
130	spin_unlock_irqrestore(&report_filterlist_lock, flags);
131	return ret;
132}
133
134static 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. */
144static 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
188out:
189	spin_unlock_irqrestore(&report_filterlist_lock, flags);
190
191	return ret;
192}
193
194static 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
218static int debugfs_open(struct inode *inode, struct file *file)
219{
220	return single_open(file, show_info, NULL);
221}
222
223static ssize_t
224debugfs_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
261static 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
269static int __init kcsan_debugfs_init(void)
270{
271	debugfs_create_file("kcsan", 0644, NULL, NULL, &debugfs_ops);
272	return 0;
273}
274
275late_initcall(kcsan_debugfs_init);