kernel/kcov.c

   1 #define pr_fmt(fmt) "kcov: " fmt
   2
   3 #define DISABLE_BRANCH_PROFILING
   4 #include <linux/atomic.h>
   5 #include <linux/compiler.h>
   6 #include <linux/errno.h>
   7 #include <linux/export.h>
   8 #include <linux/types.h>
   9 #include <linux/file.h>
  10 #include <linux/fs.h>
  11 #include <linux/init.h>
  12 #include <linux/mm.h>
  13 #include <linux/preempt.h>
  14 #include <linux/printk.h>
  15 #include <linux/sched.h>
  16 #include <linux/slab.h>
  17 #include <linux/spinlock.h>
  18 #include <linux/vmalloc.h>
  19 #include <linux/debugfs.h>
  20 #include <linux/uaccess.h>
  21 #include <linux/kcov.h>
  22 #include <asm/setup.h>
  23
  24 /*
  25  * kcov descriptor (one per opened debugfs file).
  26  * State transitions of the descriptor:
  27  *  - initial state after open()
  28  *  - then there must be a single ioctl(KCOV_INIT_TRACE) call
  29  *  - then, mmap() call (several calls are allowed but not useful)
  30  *  - then, repeated enable/disable for a task (only one task a time allowed)
  31  */
  32 struct kcov {
  33         /*
  34          * Reference counter. We keep one for:
  35          *  - opened file descriptor
  36          *  - task with enabled coverage (we can't unwire it from another task)
  37          */
  38         atomic_t                refcount;
  39         /* The lock protects mode, size, area and t. */
  40         spinlock_t              lock;
  41         enum kcov_mode          mode;
  42         /* Size of arena (in long's for KCOV_MODE_TRACE). */
  43         unsigned                size;
  44         /* Coverage buffer shared with user space. */
  45         void                    *area;
  46         /* Task for which we collect coverage, or NULL. */
  47         struct task_struct      *t;
  48 };
  49
  50 /*
  51  * Entry point from instrumented code.
  52  * This is called once per basic-block/edge.
  53  */
  54 void notrace __sanitizer_cov_trace_pc(void)
  55 {
  56         struct task_struct *t;
  57         enum kcov_mode mode;
  58
  59         t = current;
  60         /*
  61          * We are interested in code coverage as a function of a syscall inputs,
  62          * so we ignore code executed in interrupts.
  63          * The checks for whether we are in an interrupt are open-coded, because
  64          * 1. We can't use in_interrupt() here, since it also returns true
  65          *    when we are inside local_bh_disable() section.
  66          * 2. We don't want to use (in_irq() | in_serving_softirq() | in_nmi()),
  67          *    since that leads to slower generated code (three separate tests,
  68          *    one for each of the flags).
  69          */
  70         if (!t || (preempt_count() & (HARDIRQ_MASK | SOFTIRQ_OFFSET
  71                                                         | NMI_MASK)))
  72                 return;
  73         mode = READ_ONCE(t->kcov_mode);
  74         if (mode == KCOV_MODE_TRACE) {
  75                 unsigned long *area;
  76                 unsigned long pos;
  77                 unsigned long ip = _RET_IP_;
  78
  79 #ifdef CONFIG_RANDOMIZE_BASE
  80                 ip -= kaslr_offset();
  81 #endif
  82
  83                 /*
  84                  * There is some code that runs in interrupts but for which
  85                  * in_interrupt() returns false (e.g. preempt_schedule_irq()).
  86                  * READ_ONCE()/barrier() effectively provides load-acquire wrt
  87                  * interrupts, there are paired barrier()/WRITE_ONCE() in
  88                  * kcov_ioctl_locked().
  89                  */
  90                 barrier();
  91                 area = t->kcov_area;
  92                 /* The first word is number of subsequent PCs. */
  93                 pos = READ_ONCE(area[0]) + 1;
  94                 if (likely(pos < t->kcov_size)) {
  95                         area[pos] = ip;
  96                         WRITE_ONCE(area[0], pos);
  97                 }
  98         }
  99 }
 100 EXPORT_SYMBOL(__sanitizer_cov_trace_pc);
 101
 102 static void kcov_get(struct kcov *kcov)
 103 {
 104         atomic_inc(&kcov->refcount);
 105 }
 106
 107 static void kcov_put(struct kcov *kcov)
 108 {
 109         if (atomic_dec_and_test(&kcov->refcount)) {
 110                 vfree(kcov->area);
 111                 kfree(kcov);
 112         }
 113 }
 114
 115 void kcov_task_init(struct task_struct *t)
 116 {
 117         t->kcov_mode = KCOV_MODE_DISABLED;
 118         t->kcov_size = 0;
 119         t->kcov_area = NULL;
 120         t->kcov = NULL;
 121 }
 122
 123 void kcov_task_exit(struct task_struct *t)
 124 {
 125         struct kcov *kcov;
 126
 127         kcov = t->kcov;
 128         if (kcov == NULL)
 129                 return;
 130         spin_lock(&kcov->lock);
 131         if (WARN_ON(kcov->t != t)) {
 132                 spin_unlock(&kcov->lock);
 133                 return;
 134         }
 135         /* Just to not leave dangling references behind. */
 136         kcov_task_init(t);
 137         kcov->t = NULL;
 138         spin_unlock(&kcov->lock);
 139         kcov_put(kcov);
 140 }
 141
 142 static int kcov_mmap(struct file *filep, struct vm_area_struct *vma)
 143 {
 144         int res = 0;
 145         void *area;
 146         struct kcov *kcov = vma->vm_file->private_data;
 147         unsigned long size, off;
 148         struct page *page;
 149
 150         area = vmalloc_user(vma->vm_end - vma->vm_start);
 151         if (!area)
 152                 return -ENOMEM;
 153
 154         spin_lock(&kcov->lock);
 155         size = kcov->size * sizeof(unsigned long);
 156         if (kcov->mode == KCOV_MODE_DISABLED || vma->vm_pgoff != 0 ||
 157             vma->vm_end - vma->vm_start != size) {
 158                 res = -EINVAL;
 159                 goto exit;
 160         }
 161         if (!kcov->area) {
 162                 kcov->area = area;
 163                 vma->vm_flags |= VM_DONTEXPAND;
 164                 spin_unlock(&kcov->lock);
 165                 for (off = 0; off < size; off += PAGE_SIZE) {
 166                         page = vmalloc_to_page(kcov->area + off);
 167                         if (vm_insert_page(vma, vma->vm_start + off, page))
 168                                 WARN_ONCE(1, "vm_insert_page() failed");
 169                 }
 170                 return 0;
 171         }
 172 exit:
 173         spin_unlock(&kcov->lock);
 174         vfree(area);
 175         return res;
 176 }
 177
 178 static int kcov_open(struct inode *inode, struct file *filep)
 179 {
 180         struct kcov *kcov;
 181
 182         kcov = kzalloc(sizeof(*kcov), GFP_KERNEL);
 183         if (!kcov)
 184                 return -ENOMEM;
 185         atomic_set(&kcov->refcount, 1);
 186         spin_lock_init(&kcov->lock);
 187         filep->private_data = kcov;
 188         return nonseekable_open(inode, filep);
 189 }
 190
 191 static int kcov_close(struct inode *inode, struct file *filep)
 192 {
 193         kcov_put(filep->private_data);
 194         return 0;
 195 }
 196
 197 static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,
 198                              unsigned long arg)
 199 {
 200         struct task_struct *t;
 201         unsigned long size, unused;
 202
 203         switch (cmd) {
 204         case KCOV_INIT_TRACE:
 205                 /*
 206                  * Enable kcov in trace mode and setup buffer size.
 207                  * Must happen before anything else.
 208                  */
 209                 if (kcov->mode != KCOV_MODE_DISABLED)
 210                         return -EBUSY;
 211                 /*
 212                  * Size must be at least 2 to hold current position and one PC.
 213                  * Later we allocate size * sizeof(unsigned long) memory,
 214                  * that must not overflow.
 215                  */
 216                 size = arg;
 217                 if (size < 2 || size > INT_MAX / sizeof(unsigned long))
 218                         return -EINVAL;
 219                 kcov->size = size;
 220                 kcov->mode = KCOV_MODE_TRACE;
 221                 return 0;
 222         case KCOV_ENABLE:
 223                 /*
 224                  * Enable coverage for the current task.
 225                  * At this point user must have been enabled trace mode,
 226                  * and mmapped the file. Coverage collection is disabled only
 227                  * at task exit or voluntary by KCOV_DISABLE. After that it can
 228                  * be enabled for another task.
 229                  */
 230                 unused = arg;
 231                 if (unused != 0 || kcov->mode == KCOV_MODE_DISABLED ||
 232                     kcov->area == NULL)
 233                         return -EINVAL;
 234                 if (kcov->t != NULL)
 235                         return -EBUSY;
 236                 t = current;
 237                 /* Cache in task struct for performance. */
 238                 t->kcov_size = kcov->size;
 239                 t->kcov_area = kcov->area;
 240                 /* See comment in __sanitizer_cov_trace_pc(). */
 241                 barrier();
 242                 WRITE_ONCE(t->kcov_mode, kcov->mode);
 243                 t->kcov = kcov;
 244                 kcov->t = t;
 245                 /* This is put either in kcov_task_exit() or in KCOV_DISABLE. */
 246                 kcov_get(kcov);
 247                 return 0;
 248         case KCOV_DISABLE:
 249                 /* Disable coverage for the current task. */
 250                 unused = arg;
 251                 if (unused != 0 || current->kcov != kcov)
 252                         return -EINVAL;
 253                 t = current;
 254                 if (WARN_ON(kcov->t != t))
 255                         return -EINVAL;
 256                 kcov_task_init(t);
 257                 kcov->t = NULL;
 258                 kcov_put(kcov);
 259                 return 0;
 260         default:
 261                 return -ENOTTY;
 262         }
 263 }
 264
 265 static long kcov_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
 266 {
 267         struct kcov *kcov;
 268         int res;
 269
 270         kcov = filep->private_data;
 271         spin_lock(&kcov->lock);
 272         res = kcov_ioctl_locked(kcov, cmd, arg);
 273         spin_unlock(&kcov->lock);
 274         return res;
 275 }
 276
 277 static const struct file_operations kcov_fops = {
 278         .open           = kcov_open,
 279         .unlocked_ioctl = kcov_ioctl,
 280         .mmap           = kcov_mmap,
 281         .release        = kcov_close,
 282 };
 283
 284 static int __init kcov_init(void)
 285 {
 286         /*
 287          * The kcov debugfs file won't ever get removed and thus,
 288          * there is no need to protect it against removal races. The
 289          * use of debugfs_create_file_unsafe() is actually safe here.
 290          */
 291         if (!debugfs_create_file_unsafe("kcov", 0600, NULL, NULL, &kcov_fops)) {
 292                 pr_err("failed to create kcov in debugfs\n");
 293                 return -ENOMEM;
 294         }
 295         return 0;
 296 }
 297
 298 device_initcall(kcov_init);