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          */
  64         if (!t || !in_task())
  65                 return;
  66         mode = READ_ONCE(t->kcov_mode);
  67         if (mode == KCOV_MODE_TRACE) {
  68                 unsigned long *area;
  69                 unsigned long pos;
  70                 unsigned long ip = _RET_IP_;
  71
  72 #ifdef CONFIG_RANDOMIZE_BASE
  73                 ip -= kaslr_offset();
  74 #endif
  75
  76                 /*
  77                  * There is some code that runs in interrupts but for which
  78                  * in_interrupt() returns false (e.g. preempt_schedule_irq()).
  79                  * READ_ONCE()/barrier() effectively provides load-acquire wrt
  80                  * interrupts, there are paired barrier()/WRITE_ONCE() in
  81                  * kcov_ioctl_locked().
  82                  */
  83                 barrier();
  84                 area = t->kcov_area;
  85                 /* The first word is number of subsequent PCs. */
  86                 pos = READ_ONCE(area[0]) + 1;
  87                 if (likely(pos < t->kcov_size)) {
  88                         area[pos] = ip;
  89                         WRITE_ONCE(area[0], pos);
  90                 }
  91         }
  92 }
  93 EXPORT_SYMBOL(__sanitizer_cov_trace_pc);
  94
  95 static void kcov_get(struct kcov *kcov)
  96 {
  97         atomic_inc(&kcov->refcount);
  98 }
  99
 100 static void kcov_put(struct kcov *kcov)
 101 {
 102         if (atomic_dec_and_test(&kcov->refcount)) {
 103                 vfree(kcov->area);
 104                 kfree(kcov);
 105         }
 106 }
 107
 108 void kcov_task_init(struct task_struct *t)
 109 {
 110         t->kcov_mode = KCOV_MODE_DISABLED;
 111         t->kcov_size = 0;
 112         t->kcov_area = NULL;
 113         t->kcov = NULL;
 114 }
 115
 116 void kcov_task_exit(struct task_struct *t)
 117 {
 118         struct kcov *kcov;
 119
 120         kcov = t->kcov;
 121         if (kcov == NULL)
 122                 return;
 123         spin_lock(&kcov->lock);
 124         if (WARN_ON(kcov->t != t)) {
 125                 spin_unlock(&kcov->lock);
 126                 return;
 127         }
 128         /* Just to not leave dangling references behind. */
 129         kcov_task_init(t);
 130         kcov->t = NULL;
 131         spin_unlock(&kcov->lock);
 132         kcov_put(kcov);
 133 }
 134
 135 static int kcov_mmap(struct file *filep, struct vm_area_struct *vma)
 136 {
 137         int res = 0;
 138         void *area;
 139         struct kcov *kcov = vma->vm_file->private_data;
 140         unsigned long size, off;
 141         struct page *page;
 142
 143         area = vmalloc_user(vma->vm_end - vma->vm_start);
 144         if (!area)
 145                 return -ENOMEM;
 146
 147         spin_lock(&kcov->lock);
 148         size = kcov->size * sizeof(unsigned long);
 149         if (kcov->mode == KCOV_MODE_DISABLED || vma->vm_pgoff != 0 ||
 150             vma->vm_end - vma->vm_start != size) {
 151                 res = -EINVAL;
 152                 goto exit;
 153         }
 154         if (!kcov->area) {
 155                 kcov->area = area;
 156                 vma->vm_flags |= VM_DONTEXPAND;
 157                 spin_unlock(&kcov->lock);
 158                 for (off = 0; off < size; off += PAGE_SIZE) {
 159                         page = vmalloc_to_page(kcov->area + off);
 160                         if (vm_insert_page(vma, vma->vm_start + off, page))
 161                                 WARN_ONCE(1, "vm_insert_page() failed");
 162                 }
 163                 return 0;
 164         }
 165 exit:
 166         spin_unlock(&kcov->lock);
 167         vfree(area);
 168         return res;
 169 }
 170
 171 static int kcov_open(struct inode *inode, struct file *filep)
 172 {
 173         struct kcov *kcov;
 174
 175         kcov = kzalloc(sizeof(*kcov), GFP_KERNEL);
 176         if (!kcov)
 177                 return -ENOMEM;
 178         atomic_set(&kcov->refcount, 1);
 179         spin_lock_init(&kcov->lock);
 180         filep->private_data = kcov;
 181         return nonseekable_open(inode, filep);
 182 }
 183
 184 static int kcov_close(struct inode *inode, struct file *filep)
 185 {
 186         kcov_put(filep->private_data);
 187         return 0;
 188 }
 189
 190 static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,
 191                              unsigned long arg)
 192 {
 193         struct task_struct *t;
 194         unsigned long size, unused;
 195
 196         switch (cmd) {
 197         case KCOV_INIT_TRACE:
 198                 /*
 199                  * Enable kcov in trace mode and setup buffer size.
 200                  * Must happen before anything else.
 201                  */
 202                 if (kcov->mode != KCOV_MODE_DISABLED)
 203                         return -EBUSY;
 204                 /*
 205                  * Size must be at least 2 to hold current position and one PC.
 206                  * Later we allocate size * sizeof(unsigned long) memory,
 207                  * that must not overflow.
 208                  */
 209                 size = arg;
 210                 if (size < 2 || size > INT_MAX / sizeof(unsigned long))
 211                         return -EINVAL;
 212                 kcov->size = size;
 213                 kcov->mode = KCOV_MODE_TRACE;
 214                 return 0;
 215         case KCOV_ENABLE:
 216                 /*
 217                  * Enable coverage for the current task.
 218                  * At this point user must have been enabled trace mode,
 219                  * and mmapped the file. Coverage collection is disabled only
 220                  * at task exit or voluntary by KCOV_DISABLE. After that it can
 221                  * be enabled for another task.
 222                  */
 223                 unused = arg;
 224                 if (unused != 0 || kcov->mode == KCOV_MODE_DISABLED ||
 225                     kcov->area == NULL)
 226                         return -EINVAL;
 227                 if (kcov->t != NULL)
 228                         return -EBUSY;
 229                 t = current;
 230                 /* Cache in task struct for performance. */
 231                 t->kcov_size = kcov->size;
 232                 t->kcov_area = kcov->area;
 233                 /* See comment in __sanitizer_cov_trace_pc(). */
 234                 barrier();
 235                 WRITE_ONCE(t->kcov_mode, kcov->mode);
 236                 t->kcov = kcov;
 237                 kcov->t = t;
 238                 /* This is put either in kcov_task_exit() or in KCOV_DISABLE. */
 239                 kcov_get(kcov);
 240                 return 0;
 241         case KCOV_DISABLE:
 242                 /* Disable coverage for the current task. */
 243                 unused = arg;
 244                 if (unused != 0 || current->kcov != kcov)
 245                         return -EINVAL;
 246                 t = current;
 247                 if (WARN_ON(kcov->t != t))
 248                         return -EINVAL;
 249                 kcov_task_init(t);
 250                 kcov->t = NULL;
 251                 kcov_put(kcov);
 252                 return 0;
 253         default:
 254                 return -ENOTTY;
 255         }
 256 }
 257
 258 static long kcov_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
 259 {
 260         struct kcov *kcov;
 261         int res;
 262
 263         kcov = filep->private_data;
 264         spin_lock(&kcov->lock);
 265         res = kcov_ioctl_locked(kcov, cmd, arg);
 266         spin_unlock(&kcov->lock);
 267         return res;
 268 }
 269
 270 static const struct file_operations kcov_fops = {
 271         .open           = kcov_open,
 272         .unlocked_ioctl = kcov_ioctl,
 273         .compat_ioctl   = kcov_ioctl,
 274         .mmap           = kcov_mmap,
 275         .release        = kcov_close,
 276 };
 277
 278 static int __init kcov_init(void)
 279 {
 280         /*
 281          * The kcov debugfs file won't ever get removed and thus,
 282          * there is no need to protect it against removal races. The
 283          * use of debugfs_create_file_unsafe() is actually safe here.
 284          */
 285         if (!debugfs_create_file_unsafe("kcov", 0600, NULL, NULL, &kcov_fops)) {
 286                 pr_err("failed to create kcov in debugfs\n");
 287                 return -ENOMEM;
 288         }
 289         return 0;
 290 }
 291
 292 device_initcall(kcov_init);