kernel/kcov.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 #define pr_fmt(fmt) "kcov: " fmt
   3
   4 #define DISABLE_BRANCH_PROFILING
   5 #include <linux/atomic.h>
   6 #include <linux/compiler.h>
   7 #include <linux/errno.h>
   8 #include <linux/export.h>
   9 #include <linux/types.h>
  10 #include <linux/file.h>
  11 #include <linux/fs.h>
  12 #include <linux/init.h>
  13 #include <linux/mm.h>
  14 #include <linux/preempt.h>
  15 #include <linux/printk.h>
  16 #include <linux/sched.h>
  17 #include <linux/slab.h>
  18 #include <linux/spinlock.h>
  19 #include <linux/vmalloc.h>
  20 #include <linux/debugfs.h>
  21 #include <linux/uaccess.h>
  22 #include <linux/kcov.h>
  23 #include <asm/setup.h>
  24
  25 /* Number of 64-bit words written per one comparison: */
  26 #define KCOV_WORDS_PER_CMP 4
  27
  28 /*
  29  * kcov descriptor (one per opened debugfs file).
  30  * State transitions of the descriptor:
  31  *  - initial state after open()
  32  *  - then there must be a single ioctl(KCOV_INIT_TRACE) call
  33  *  - then, mmap() call (several calls are allowed but not useful)
  34  *  - then, ioctl(KCOV_ENABLE, arg), where arg is
  35  *      KCOV_TRACE_PC - to trace only the PCs
  36  *      or
  37  *      KCOV_TRACE_CMP - to trace only the comparison operands
  38  *  - then, ioctl(KCOV_DISABLE) to disable the task.
  39  * Enabling/disabling ioctls can be repeated (only one task a time allowed).
  40  */
  41 struct kcov {
  42         /*
  43          * Reference counter. We keep one for:
  44          *  - opened file descriptor
  45          *  - task with enabled coverage (we can't unwire it from another task)
  46          */
  47         atomic_t                refcount;
  48         /* The lock protects mode, size, area and t. */
  49         spinlock_t              lock;
  50         enum kcov_mode          mode;
  51         /* Size of arena (in long's for KCOV_MODE_TRACE). */
  52         unsigned                size;
  53         /* Coverage buffer shared with user space. */
  54         void                    *area;
  55         /* Task for which we collect coverage, or NULL. */
  56         struct task_struct      *t;
  57 };
  58
  59 static bool check_kcov_mode(enum kcov_mode needed_mode, struct task_struct *t)
  60 {
  61         enum kcov_mode mode;
  62
  63         /*
  64          * We are interested in code coverage as a function of a syscall inputs,
  65          * so we ignore code executed in interrupts.
  66          */
  67         if (!in_task())
  68                 return false;
  69         mode = READ_ONCE(t->kcov_mode);
  70         /*
  71          * There is some code that runs in interrupts but for which
  72          * in_interrupt() returns false (e.g. preempt_schedule_irq()).
  73          * READ_ONCE()/barrier() effectively provides load-acquire wrt
  74          * interrupts, there are paired barrier()/WRITE_ONCE() in
  75          * kcov_ioctl_locked().
  76          */
  77         barrier();
  78         return mode == needed_mode;
  79 }
  80
  81 static unsigned long canonicalize_ip(unsigned long ip)
  82 {
  83 #ifdef CONFIG_RANDOMIZE_BASE
  84         ip -= kaslr_offset();
  85 #endif
  86         return ip;
  87 }
  88
  89 /*
  90  * Entry point from instrumented code.
  91  * This is called once per basic-block/edge.
  92  */
  93 void notrace __sanitizer_cov_trace_pc(void)
  94 {
  95         struct task_struct *t;
  96         unsigned long *area;
  97         unsigned long ip = canonicalize_ip(_RET_IP_);
  98         unsigned long pos;
  99
 100         t = current;
 101         if (!check_kcov_mode(KCOV_MODE_TRACE_PC, t))
 102                 return;
 103
 104         area = t->kcov_area;
 105         /* The first 64-bit word is the number of subsequent PCs. */
 106         pos = READ_ONCE(area[0]) + 1;
 107         if (likely(pos < t->kcov_size)) {
 108                 area[pos] = ip;
 109                 WRITE_ONCE(area[0], pos);
 110         }
 111 }
 112 EXPORT_SYMBOL(__sanitizer_cov_trace_pc);
 113
 114 #ifdef CONFIG_KCOV_ENABLE_COMPARISONS
 115 static void write_comp_data(u64 type, u64 arg1, u64 arg2, u64 ip)
 116 {
 117         struct task_struct *t;
 118         u64 *area;
 119         u64 count, start_index, end_pos, max_pos;
 120
 121         t = current;
 122         if (!check_kcov_mode(KCOV_MODE_TRACE_CMP, t))
 123                 return;
 124
 125         ip = canonicalize_ip(ip);
 126
 127         /*
 128          * We write all comparison arguments and types as u64.
 129          * The buffer was allocated for t->kcov_size unsigned longs.
 130          */
 131         area = (u64 *)t->kcov_area;
 132         max_pos = t->kcov_size * sizeof(unsigned long);
 133
 134         count = READ_ONCE(area[0]);
 135
 136         /* Every record is KCOV_WORDS_PER_CMP 64-bit words. */
 137         start_index = 1 + count * KCOV_WORDS_PER_CMP;
 138         end_pos = (start_index + KCOV_WORDS_PER_CMP) * sizeof(u64);
 139         if (likely(end_pos <= max_pos)) {
 140                 area[start_index] = type;
 141                 area[start_index + 1] = arg1;
 142                 area[start_index + 2] = arg2;
 143                 area[start_index + 3] = ip;
 144                 WRITE_ONCE(area[0], count + 1);
 145         }
 146 }
 147
 148 void notrace __sanitizer_cov_trace_cmp1(u8 arg1, u8 arg2)
 149 {
 150         write_comp_data(KCOV_CMP_SIZE(0), arg1, arg2, _RET_IP_);
 151 }
 152 EXPORT_SYMBOL(__sanitizer_cov_trace_cmp1);
 153
 154 void notrace __sanitizer_cov_trace_cmp2(u16 arg1, u16 arg2)
 155 {
 156         write_comp_data(KCOV_CMP_SIZE(1), arg1, arg2, _RET_IP_);
 157 }
 158 EXPORT_SYMBOL(__sanitizer_cov_trace_cmp2);
 159
 160 void notrace __sanitizer_cov_trace_cmp4(u16 arg1, u16 arg2)
 161 {
 162         write_comp_data(KCOV_CMP_SIZE(2), arg1, arg2, _RET_IP_);
 163 }
 164 EXPORT_SYMBOL(__sanitizer_cov_trace_cmp4);
 165
 166 void notrace __sanitizer_cov_trace_cmp8(u64 arg1, u64 arg2)
 167 {
 168         write_comp_data(KCOV_CMP_SIZE(3), arg1, arg2, _RET_IP_);
 169 }
 170 EXPORT_SYMBOL(__sanitizer_cov_trace_cmp8);
 171
 172 void notrace __sanitizer_cov_trace_const_cmp1(u8 arg1, u8 arg2)
 173 {
 174         write_comp_data(KCOV_CMP_SIZE(0) | KCOV_CMP_CONST, arg1, arg2,
 175                         _RET_IP_);
 176 }
 177 EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp1);
 178
 179 void notrace __sanitizer_cov_trace_const_cmp2(u16 arg1, u16 arg2)
 180 {
 181         write_comp_data(KCOV_CMP_SIZE(1) | KCOV_CMP_CONST, arg1, arg2,
 182                         _RET_IP_);
 183 }
 184 EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp2);
 185
 186 void notrace __sanitizer_cov_trace_const_cmp4(u16 arg1, u16 arg2)
 187 {
 188         write_comp_data(KCOV_CMP_SIZE(2) | KCOV_CMP_CONST, arg1, arg2,
 189                         _RET_IP_);
 190 }
 191 EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp4);
 192
 193 void notrace __sanitizer_cov_trace_const_cmp8(u64 arg1, u64 arg2)
 194 {
 195         write_comp_data(KCOV_CMP_SIZE(3) | KCOV_CMP_CONST, arg1, arg2,
 196                         _RET_IP_);
 197 }
 198 EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp8);
 199
 200 void notrace __sanitizer_cov_trace_switch(u64 val, u64 *cases)
 201 {
 202         u64 i;
 203         u64 count = cases[0];
 204         u64 size = cases[1];
 205         u64 type = KCOV_CMP_CONST;
 206
 207         switch (size) {
 208         case 8:
 209                 type |= KCOV_CMP_SIZE(0);
 210                 break;
 211         case 16:
 212                 type |= KCOV_CMP_SIZE(1);
 213                 break;
 214         case 32:
 215                 type |= KCOV_CMP_SIZE(2);
 216                 break;
 217         case 64:
 218                 type |= KCOV_CMP_SIZE(3);
 219                 break;
 220         default:
 221                 return;
 222         }
 223         for (i = 0; i < count; i++)
 224                 write_comp_data(type, cases[i + 2], val, _RET_IP_);
 225 }
 226 EXPORT_SYMBOL(__sanitizer_cov_trace_switch);
 227 #endif /* ifdef CONFIG_KCOV_ENABLE_COMPARISONS */
 228
 229 static void kcov_get(struct kcov *kcov)
 230 {
 231         atomic_inc(&kcov->refcount);
 232 }
 233
 234 static void kcov_put(struct kcov *kcov)
 235 {
 236         if (atomic_dec_and_test(&kcov->refcount)) {
 237                 vfree(kcov->area);
 238                 kfree(kcov);
 239         }
 240 }
 241
 242 void kcov_task_init(struct task_struct *t)
 243 {
 244         t->kcov_mode = KCOV_MODE_DISABLED;
 245         t->kcov_size = 0;
 246         t->kcov_area = NULL;
 247         t->kcov = NULL;
 248 }
 249
 250 void kcov_task_exit(struct task_struct *t)
 251 {
 252         struct kcov *kcov;
 253
 254         kcov = t->kcov;
 255         if (kcov == NULL)
 256                 return;
 257         spin_lock(&kcov->lock);
 258         if (WARN_ON(kcov->t != t)) {
 259                 spin_unlock(&kcov->lock);
 260                 return;
 261         }
 262         /* Just to not leave dangling references behind. */
 263         kcov_task_init(t);
 264         kcov->t = NULL;
 265         kcov->mode = KCOV_MODE_INIT;
 266         spin_unlock(&kcov->lock);
 267         kcov_put(kcov);
 268 }
 269
 270 static int kcov_mmap(struct file *filep, struct vm_area_struct *vma)
 271 {
 272         int res = 0;
 273         void *area;
 274         struct kcov *kcov = vma->vm_file->private_data;
 275         unsigned long size, off;
 276         struct page *page;
 277
 278         area = vmalloc_user(vma->vm_end - vma->vm_start);
 279         if (!area)
 280                 return -ENOMEM;
 281
 282         spin_lock(&kcov->lock);
 283         size = kcov->size * sizeof(unsigned long);
 284         if (kcov->mode != KCOV_MODE_INIT || vma->vm_pgoff != 0 ||
 285             vma->vm_end - vma->vm_start != size) {
 286                 res = -EINVAL;
 287                 goto exit;
 288         }
 289         if (!kcov->area) {
 290                 kcov->area = area;
 291                 vma->vm_flags |= VM_DONTEXPAND;
 292                 spin_unlock(&kcov->lock);
 293                 for (off = 0; off < size; off += PAGE_SIZE) {
 294                         page = vmalloc_to_page(kcov->area + off);
 295                         if (vm_insert_page(vma, vma->vm_start + off, page))
 296                                 WARN_ONCE(1, "vm_insert_page() failed");
 297                 }
 298                 return 0;
 299         }
 300 exit:
 301         spin_unlock(&kcov->lock);
 302         vfree(area);
 303         return res;
 304 }
 305
 306 static int kcov_open(struct inode *inode, struct file *filep)
 307 {
 308         struct kcov *kcov;
 309
 310         kcov = kzalloc(sizeof(*kcov), GFP_KERNEL);
 311         if (!kcov)
 312                 return -ENOMEM;
 313         kcov->mode = KCOV_MODE_DISABLED;
 314         atomic_set(&kcov->refcount, 1);
 315         spin_lock_init(&kcov->lock);
 316         filep->private_data = kcov;
 317         return nonseekable_open(inode, filep);
 318 }
 319
 320 static int kcov_close(struct inode *inode, struct file *filep)
 321 {
 322         kcov_put(filep->private_data);
 323         return 0;
 324 }
 325
 326 static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,
 327                              unsigned long arg)
 328 {
 329         struct task_struct *t;
 330         unsigned long size, unused;
 331
 332         switch (cmd) {
 333         case KCOV_INIT_TRACE:
 334                 /*
 335                  * Enable kcov in trace mode and setup buffer size.
 336                  * Must happen before anything else.
 337                  */
 338                 if (kcov->mode != KCOV_MODE_DISABLED)
 339                         return -EBUSY;
 340                 /*
 341                  * Size must be at least 2 to hold current position and one PC.
 342                  * Later we allocate size * sizeof(unsigned long) memory,
 343                  * that must not overflow.
 344                  */
 345                 size = arg;
 346                 if (size < 2 || size > INT_MAX / sizeof(unsigned long))
 347                         return -EINVAL;
 348                 kcov->size = size;
 349                 kcov->mode = KCOV_MODE_INIT;
 350                 return 0;
 351         case KCOV_ENABLE:
 352                 /*
 353                  * Enable coverage for the current task.
 354                  * At this point user must have been enabled trace mode,
 355                  * and mmapped the file. Coverage collection is disabled only
 356                  * at task exit or voluntary by KCOV_DISABLE. After that it can
 357                  * be enabled for another task.
 358                  */
 359                 if (kcov->mode != KCOV_MODE_INIT || !kcov->area)
 360                         return -EINVAL;
 361                 if (kcov->t != NULL)
 362                         return -EBUSY;
 363                 if (arg == KCOV_TRACE_PC)
 364                         kcov->mode = KCOV_MODE_TRACE_PC;
 365                 else if (arg == KCOV_TRACE_CMP)
 366 #ifdef CONFIG_KCOV_ENABLE_COMPARISONS
 367                         kcov->mode = KCOV_MODE_TRACE_CMP;
 368 #else
 369                 return -ENOTSUPP;
 370 #endif
 371                 else
 372                         return -EINVAL;
 373                 t = current;
 374                 /* Cache in task struct for performance. */
 375                 t->kcov_size = kcov->size;
 376                 t->kcov_area = kcov->area;
 377                 /* See comment in check_kcov_mode(). */
 378                 barrier();
 379                 WRITE_ONCE(t->kcov_mode, kcov->mode);
 380                 t->kcov = kcov;
 381                 kcov->t = t;
 382                 /* This is put either in kcov_task_exit() or in KCOV_DISABLE. */
 383                 kcov_get(kcov);
 384                 return 0;
 385         case KCOV_DISABLE:
 386                 /* Disable coverage for the current task. */
 387                 unused = arg;
 388                 if (unused != 0 || current->kcov != kcov)
 389                         return -EINVAL;
 390                 t = current;
 391                 if (WARN_ON(kcov->t != t))
 392                         return -EINVAL;
 393                 kcov_task_init(t);
 394                 kcov->t = NULL;
 395                 kcov->mode = KCOV_MODE_INIT;
 396                 kcov_put(kcov);
 397                 return 0;
 398         default:
 399                 return -ENOTTY;
 400         }
 401 }
 402
 403 static long kcov_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
 404 {
 405         struct kcov *kcov;
 406         int res;
 407
 408         kcov = filep->private_data;
 409         spin_lock(&kcov->lock);
 410         res = kcov_ioctl_locked(kcov, cmd, arg);
 411         spin_unlock(&kcov->lock);
 412         return res;
 413 }
 414
 415 static const struct file_operations kcov_fops = {
 416         .open           = kcov_open,
 417         .unlocked_ioctl = kcov_ioctl,
 418         .compat_ioctl   = kcov_ioctl,
 419         .mmap           = kcov_mmap,
 420         .release        = kcov_close,
 421 };
 422
 423 static int __init kcov_init(void)
 424 {
 425         /*
 426          * The kcov debugfs file won't ever get removed and thus,
 427          * there is no need to protect it against removal races. The
 428          * use of debugfs_create_file_unsafe() is actually safe here.
 429          */
 430         if (!debugfs_create_file_unsafe("kcov", 0600, NULL, NULL, &kcov_fops)) {
 431                 pr_err("failed to create kcov in debugfs\n");
 432                 return -ENOMEM;
 433         }
 434         return 0;
 435 }
 436
 437 device_initcall(kcov_init);