kernel/kcsan/debugfs.c

   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 static DEFINE_RAW_SPINLOCK(report_filterlist_lock);
  51
  52 /*
  53  * The microbenchmark allows benchmarking KCSAN core runtime only. To run
  54  * multiple threads, pipe 'microbench=<iters>' from multiple tasks into the
  55  * debugfs file. This will not generate any conflicts, and tests fast-path only.
  56  */
  57 static noinline void microbenchmark(unsigned long iters)
  58 {
  59         const struct kcsan_ctx ctx_save = current->kcsan_ctx;
  60         const bool was_enabled = READ_ONCE(kcsan_enabled);
  61         u64 cycles;
  62
  63         /* We may have been called from an atomic region; reset context. */
  64         memset(&current->kcsan_ctx, 0, sizeof(current->kcsan_ctx));
  65         /*
  66          * Disable to benchmark fast-path for all accesses, and (expected
  67          * negligible) call into slow-path, but never set up watchpoints.
  68          */
  69         WRITE_ONCE(kcsan_enabled, false);
  70
  71         pr_info("%s begin | iters: %lu\n", __func__, iters);
  72
  73         cycles = get_cycles();
  74         while (iters--) {
  75                 unsigned long addr = iters & ((PAGE_SIZE << 8) - 1);
  76                 int type = !(iters & 0x7f) ? KCSAN_ACCESS_ATOMIC :
  77                                 (!(iters & 0xf) ? KCSAN_ACCESS_WRITE : 0);
  78                 __kcsan_check_access((void *)addr, sizeof(long), type);
  79         }
  80         cycles = get_cycles() - cycles;
  81
  82         pr_info("%s end   | cycles: %llu\n", __func__, cycles);
  83
  84         WRITE_ONCE(kcsan_enabled, was_enabled);
  85         /* restore context */
  86         current->kcsan_ctx = ctx_save;
  87 }
  88
  89 static int cmp_filterlist_addrs(const void *rhs, const void *lhs)
  90 {
  91         const unsigned long a = *(const unsigned long *)rhs;
  92         const unsigned long b = *(const unsigned long *)lhs;
  93
  94         return a < b ? -1 : a == b ? 0 : 1;
  95 }
  96
  97 bool kcsan_skip_report_debugfs(unsigned long func_addr)
  98 {
  99         unsigned long symbolsize, offset;
 100         unsigned long flags;
 101         bool ret = false;
 102
 103         if (!kallsyms_lookup_size_offset(func_addr, &symbolsize, &offset))
 104                 return false;
 105         func_addr -= offset; /* Get function start */
 106
 107         raw_spin_lock_irqsave(&report_filterlist_lock, flags);
 108         if (report_filterlist.used == 0)
 109                 goto out;
 110
 111         /* Sort array if it is unsorted, and then do a binary search. */
 112         if (!report_filterlist.sorted) {
 113                 sort(report_filterlist.addrs, report_filterlist.used,
 114                      sizeof(unsigned long), cmp_filterlist_addrs, NULL);
 115                 report_filterlist.sorted = true;
 116         }
 117         ret = !!bsearch(&func_addr, report_filterlist.addrs,
 118                         report_filterlist.used, sizeof(unsigned long),
 119                         cmp_filterlist_addrs);
 120         if (report_filterlist.whitelist)
 121                 ret = !ret;
 122
 123 out:
 124         raw_spin_unlock_irqrestore(&report_filterlist_lock, flags);
 125         return ret;
 126 }
 127
 128 static void set_report_filterlist_whitelist(bool whitelist)
 129 {
 130         unsigned long flags;
 131
 132         raw_spin_lock_irqsave(&report_filterlist_lock, flags);
 133         report_filterlist.whitelist = whitelist;
 134         raw_spin_unlock_irqrestore(&report_filterlist_lock, flags);
 135 }
 136
 137 /* Returns 0 on success, error-code otherwise. */
 138 static ssize_t insert_report_filterlist(const char *func)
 139 {
 140         unsigned long flags;
 141         unsigned long addr = kallsyms_lookup_name(func);
 142         unsigned long *delay_free = NULL;
 143         unsigned long *new_addrs = NULL;
 144         size_t new_size = 0;
 145         ssize_t ret = 0;
 146
 147         if (!addr) {
 148                 pr_err("could not find function: '%s'\n", func);
 149                 return -ENOENT;
 150         }
 151
 152 retry_alloc:
 153         /*
 154          * Check if we need an allocation, and re-validate under the lock. Since
 155          * the report_filterlist_lock is a raw, cannot allocate under the lock.
 156          */
 157         if (data_race(report_filterlist.used == report_filterlist.size)) {
 158                 new_size = (report_filterlist.size ?: 4) * 2;
 159                 delay_free = new_addrs = kmalloc_array(new_size, sizeof(unsigned long), GFP_KERNEL);
 160                 if (!new_addrs)
 161                         return -ENOMEM;
 162         }
 163
 164         raw_spin_lock_irqsave(&report_filterlist_lock, flags);
 165         if (report_filterlist.used == report_filterlist.size) {
 166                 /* Check we pre-allocated enough, and retry if not. */
 167                 if (report_filterlist.used >= new_size) {
 168                         raw_spin_unlock_irqrestore(&report_filterlist_lock, flags);
 169                         kfree(new_addrs); /* kfree(NULL) is safe */
 170                         delay_free = new_addrs = NULL;
 171                         goto retry_alloc;
 172                 }
 173
 174                 if (report_filterlist.used)
 175                         memcpy(new_addrs, report_filterlist.addrs, report_filterlist.used * sizeof(unsigned long));
 176                 delay_free = report_filterlist.addrs; /* free the old list */
 177                 report_filterlist.addrs = new_addrs;  /* switch to the new list */
 178                 report_filterlist.size = new_size;
 179         }
 180
 181         /* Note: deduplicating should be done in userspace. */
 182         report_filterlist.addrs[report_filterlist.used++] = addr;
 183         report_filterlist.sorted = false;
 184
 185         raw_spin_unlock_irqrestore(&report_filterlist_lock, flags);
 186
 187         kfree(delay_free);
 188         return ret;
 189 }
 190
 191 static int show_info(struct seq_file *file, void *v)
 192 {
 193         int i;
 194         unsigned long flags;
 195
 196         /* show stats */
 197         seq_printf(file, "enabled: %i\n", READ_ONCE(kcsan_enabled));
 198         for (i = 0; i < KCSAN_COUNTER_COUNT; ++i) {
 199                 seq_printf(file, "%s: %ld\n", counter_names[i],
 200                            atomic_long_read(&kcsan_counters[i]));
 201         }
 202
 203         /* show filter functions, and filter type */
 204         raw_spin_lock_irqsave(&report_filterlist_lock, flags);
 205         seq_printf(file, "\n%s functions: %s\n",
 206                    report_filterlist.whitelist ? "whitelisted" : "blacklisted",
 207                    report_filterlist.used == 0 ? "none" : "");
 208         for (i = 0; i < report_filterlist.used; ++i)
 209                 seq_printf(file, " %ps\n", (void *)report_filterlist.addrs[i]);
 210         raw_spin_unlock_irqrestore(&report_filterlist_lock, flags);
 211
 212         return 0;
 213 }
 214
 215 static int debugfs_open(struct inode *inode, struct file *file)
 216 {
 217         return single_open(file, show_info, NULL);
 218 }
 219
 220 static ssize_t
 221 debugfs_write(struct file *file, const char __user *buf, size_t count, loff_t *off)
 222 {
 223         char kbuf[KSYM_NAME_LEN];
 224         char *arg;
 225         const size_t read_len = min(count, sizeof(kbuf) - 1);
 226
 227         if (copy_from_user(kbuf, buf, read_len))
 228                 return -EFAULT;
 229         kbuf[read_len] = '\0';
 230         arg = strstrip(kbuf);
 231
 232         if (!strcmp(arg, "on")) {
 233                 WRITE_ONCE(kcsan_enabled, true);
 234         } else if (!strcmp(arg, "off")) {
 235                 WRITE_ONCE(kcsan_enabled, false);
 236         } else if (str_has_prefix(arg, "microbench=")) {
 237                 unsigned long iters;
 238
 239                 if (kstrtoul(&arg[strlen("microbench=")], 0, &iters))
 240                         return -EINVAL;
 241                 microbenchmark(iters);
 242         } else if (!strcmp(arg, "whitelist")) {
 243                 set_report_filterlist_whitelist(true);
 244         } else if (!strcmp(arg, "blacklist")) {
 245                 set_report_filterlist_whitelist(false);
 246         } else if (arg[0] == '!') {
 247                 ssize_t ret = insert_report_filterlist(&arg[1]);
 248
 249                 if (ret < 0)
 250                         return ret;
 251         } else {
 252                 return -EINVAL;
 253         }
 254
 255         return count;
 256 }
 257
 258 static const struct file_operations debugfs_ops =
 259 {
 260         .read    = seq_read,
 261         .open    = debugfs_open,
 262         .write   = debugfs_write,
 263         .release = single_release
 264 };
 265
 266 static int __init kcsan_debugfs_init(void)
 267 {
 268         debugfs_create_file("kcsan", 0644, NULL, NULL, &debugfs_ops);
 269         return 0;
 270 }
 271
 272 late_initcall(kcsan_debugfs_init);