kernel/kcov.c

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