kernel/kcsan/debugfs.c

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