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         unsigned int 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(u32 arg1, u32 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(u32 arg1, u32 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         WRITE_ONCE(t->kcov_mode, KCOV_MODE_DISABLED);
 245         barrier();
 246         t->kcov_size = 0;
 247         t->kcov_area = NULL;
 248         t->kcov = NULL;
 249 }
 250
 251 void kcov_task_exit(struct task_struct *t)
 252 {
 253         struct kcov *kcov;
 254
 255         kcov = t->kcov;
 256         if (kcov == NULL)
 257                 return;
 258         spin_lock(&kcov->lock);
 259         if (WARN_ON(kcov->t != t)) {
 260                 spin_unlock(&kcov->lock);
 261                 return;
 262         }
 263         /* Just to not leave dangling references behind. */
 264         kcov_task_init(t);
 265         kcov->t = NULL;
 266         kcov->mode = KCOV_MODE_INIT;
 267         spin_unlock(&kcov->lock);
 268         kcov_put(kcov);
 269 }
 270
 271 static int kcov_mmap(struct file *filep, struct vm_area_struct *vma)
 272 {
 273         int res = 0;
 274         void *area;
 275         struct kcov *kcov = vma->vm_file->private_data;
 276         unsigned long size, off;
 277         struct page *page;
 278
 279         area = vmalloc_user(vma->vm_end - vma->vm_start);
 280         if (!area)
 281                 return -ENOMEM;
 282
 283         spin_lock(&kcov->lock);
 284         size = kcov->size * sizeof(unsigned long);
 285         if (kcov->mode != KCOV_MODE_INIT || vma->vm_pgoff != 0 ||
 286             vma->vm_end - vma->vm_start != size) {
 287                 res = -EINVAL;
 288                 goto exit;
 289         }
 290         if (!kcov->area) {
 291                 kcov->area = area;
 292                 vma->vm_flags |= VM_DONTEXPAND;
 293                 spin_unlock(&kcov->lock);
 294                 for (off = 0; off < size; off += PAGE_SIZE) {
 295                         page = vmalloc_to_page(kcov->area + off);
 296                         if (vm_insert_page(vma, vma->vm_start + off, page))
 297                                 WARN_ONCE(1, "vm_insert_page() failed");
 298                 }
 299                 return 0;
 300         }
 301 exit:
 302         spin_unlock(&kcov->lock);
 303         vfree(area);
 304         return res;
 305 }
 306
 307 static int kcov_open(struct inode *inode, struct file *filep)
 308 {
 309         struct kcov *kcov;
 310
 311         kcov = kzalloc(sizeof(*kcov), GFP_KERNEL);
 312         if (!kcov)
 313                 return -ENOMEM;
 314         kcov->mode = KCOV_MODE_DISABLED;
 315         atomic_set(&kcov->refcount, 1);
 316         spin_lock_init(&kcov->lock);
 317         filep->private_data = kcov;
 318         return nonseekable_open(inode, filep);
 319 }
 320
 321 static int kcov_close(struct inode *inode, struct file *filep)
 322 {
 323         kcov_put(filep->private_data);
 324         return 0;
 325 }
 326
 327 /*
 328  * Fault in a lazily-faulted vmalloc area before it can be used by
 329  * __santizer_cov_trace_pc(), to avoid recursion issues if any code on the
 330  * vmalloc fault handling path is instrumented.
 331  */
 332 static void kcov_fault_in_area(struct kcov *kcov)
 333 {
 334         unsigned long stride = PAGE_SIZE / sizeof(unsigned long);
 335         unsigned long *area = kcov->area;
 336         unsigned long offset;
 337
 338         for (offset = 0; offset < kcov->size; offset += stride)
 339                 READ_ONCE(area[offset]);
 340 }
 341
 342 static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,
 343                              unsigned long arg)
 344 {
 345         struct task_struct *t;
 346         unsigned long size, unused;
 347
 348         switch (cmd) {
 349         case KCOV_INIT_TRACE:
 350                 /*
 351                  * Enable kcov in trace mode and setup buffer size.
 352                  * Must happen before anything else.
 353                  */
 354                 if (kcov->mode != KCOV_MODE_DISABLED)
 355                         return -EBUSY;
 356                 /*
 357                  * Size must be at least 2 to hold current position and one PC.
 358                  * Later we allocate size * sizeof(unsigned long) memory,
 359                  * that must not overflow.
 360                  */
 361                 size = arg;
 362                 if (size < 2 || size > INT_MAX / sizeof(unsigned long))
 363                         return -EINVAL;
 364                 kcov->size = size;
 365                 kcov->mode = KCOV_MODE_INIT;
 366                 return 0;
 367         case KCOV_ENABLE:
 368                 /*
 369                  * Enable coverage for the current task.
 370                  * At this point user must have been enabled trace mode,
 371                  * and mmapped the file. Coverage collection is disabled only
 372                  * at task exit or voluntary by KCOV_DISABLE. After that it can
 373                  * be enabled for another task.
 374                  */
 375                 if (kcov->mode != KCOV_MODE_INIT || !kcov->area)
 376                         return -EINVAL;
 377                 t = current;
 378                 if (kcov->t != NULL || t->kcov != NULL)
 379                         return -EBUSY;
 380                 if (arg == KCOV_TRACE_PC)
 381                         kcov->mode = KCOV_MODE_TRACE_PC;
 382                 else if (arg == KCOV_TRACE_CMP)
 383 #ifdef CONFIG_KCOV_ENABLE_COMPARISONS
 384                         kcov->mode = KCOV_MODE_TRACE_CMP;
 385 #else
 386                 return -ENOTSUPP;
 387 #endif
 388                 else
 389                         return -EINVAL;
 390                 kcov_fault_in_area(kcov);
 391                 /* Cache in task struct for performance. */
 392                 t->kcov_size = kcov->size;
 393                 t->kcov_area = kcov->area;
 394                 /* See comment in check_kcov_mode(). */
 395                 barrier();
 396                 WRITE_ONCE(t->kcov_mode, kcov->mode);
 397                 t->kcov = kcov;
 398                 kcov->t = t;
 399                 /* This is put either in kcov_task_exit() or in KCOV_DISABLE. */
 400                 kcov_get(kcov);
 401                 return 0;
 402         case KCOV_DISABLE:
 403                 /* Disable coverage for the current task. */
 404                 unused = arg;
 405                 if (unused != 0 || current->kcov != kcov)
 406                         return -EINVAL;
 407                 t = current;
 408                 if (WARN_ON(kcov->t != t))
 409                         return -EINVAL;
 410                 kcov_task_init(t);
 411                 kcov->t = NULL;
 412                 kcov->mode = KCOV_MODE_INIT;
 413                 kcov_put(kcov);
 414                 return 0;
 415         default:
 416                 return -ENOTTY;
 417         }
 418 }
 419
 420 static long kcov_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
 421 {
 422         struct kcov *kcov;
 423         int res;
 424
 425         kcov = filep->private_data;
 426         spin_lock(&kcov->lock);
 427         res = kcov_ioctl_locked(kcov, cmd, arg);
 428         spin_unlock(&kcov->lock);
 429         return res;
 430 }
 431
 432 static const struct file_operations kcov_fops = {
 433         .open           = kcov_open,
 434         .unlocked_ioctl = kcov_ioctl,
 435         .compat_ioctl   = kcov_ioctl,
 436         .mmap           = kcov_mmap,
 437         .release        = kcov_close,
 438 };
 439
 440 static int __init kcov_init(void)
 441 {
 442         /*
 443          * The kcov debugfs file won't ever get removed and thus,
 444          * there is no need to protect it against removal races. The
 445          * use of debugfs_create_file_unsafe() is actually safe here.
 446          */
 447         if (!debugfs_create_file_unsafe("kcov", 0600, NULL, NULL, &kcov_fops)) {
 448                 pr_err("failed to create kcov in debugfs\n");
 449                 return -ENOMEM;
 450         }
 451         return 0;
 452 }
 453
 454 device_initcall(kcov_init);