kernel/kcov.c

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