#define pr_fmt(fmt) "kcov: " fmt

  #define DISABLE_BRANCH_PROFILING

  #include <linux/compiler.h>
  #include <linux/types.h>
  #include <linux/file.h>
  #include <linux/fs.h>
  #include <linux/mm.h>
  #include <linux/printk.h>
  #include <linux/slab.h>
  #include <linux/spinlock.h>
  #include <linux/vmalloc.h>
  #include <linux/debugfs.h>
  #include <linux/uaccess.h>
  #include <linux/kcov.h>
  
  /*
   * kcov descriptor (one per opened debugfs file).
   * State transitions of the descriptor:
   *  - initial state after open()
   *  - then there must be a single ioctl(KCOV_INIT_TRACE) call
   *  - then, mmap() call (several calls are allowed but not useful)
   *  - then, repeated enable/disable for a task (only one task a time allowed)
   */
  struct kcov {
  	/*
  	 * Reference counter. We keep one for:
  	 *  - opened file descriptor
  	 *  - task with enabled coverage (we can't unwire it from another task)
  	 */
  	atomic_t		refcount;
  	/* The lock protects mode, size, area and t. */
  	spinlock_t		lock;
  	enum kcov_mode		mode;
  	/* Size of arena (in long's for KCOV_MODE_TRACE). */
  	unsigned		size;
  	/* Coverage buffer shared with user space. */
  	void			*area;
  	/* Task for which we collect coverage, or NULL. */
  	struct task_struct	*t;
  };
  
  /*
   * Entry point from instrumented code.
   * This is called once per basic-block/edge.
   */

  void notrace __sanitizer_cov_trace_pc(void)

  {
  	struct task_struct *t;
  	enum kcov_mode mode;
  
  	t = current;
  	/*
  	 * We are interested in code coverage as a function of a syscall inputs,
  	 * so we ignore code executed in interrupts.

  	 * The checks for whether we are in an interrupt are open-coded, because
  	 * 1. We can't use in_interrupt() here, since it also returns true
  	 *    when we are inside local_bh_disable() section.
  	 * 2. We don't want to use (in_irq() | in_serving_softirq() | in_nmi()),
  	 *    since that leads to slower generated code (three separate tests,
  	 *    one for each of the flags).

  	 */

  	if (!t || (preempt_count() & (HARDIRQ_MASK | SOFTIRQ_OFFSET
  							| NMI_MASK)))

  		return;
  	mode = READ_ONCE(t->kcov_mode);
  	if (mode == KCOV_MODE_TRACE) {
  		unsigned long *area;
  		unsigned long pos;
  
  		/*
  		 * There is some code that runs in interrupts but for which
  		 * in_interrupt() returns false (e.g. preempt_schedule_irq()).
  		 * READ_ONCE()/barrier() effectively provides load-acquire wrt
  		 * interrupts, there are paired barrier()/WRITE_ONCE() in
  		 * kcov_ioctl_locked().
  		 */
  		barrier();
  		area = t->kcov_area;
  		/* The first word is number of subsequent PCs. */
  		pos = READ_ONCE(area[0]) + 1;
  		if (likely(pos < t->kcov_size)) {
  			area[pos] = _RET_IP_;
  			WRITE_ONCE(area[0], pos);
  		}
  	}
  }
  EXPORT_SYMBOL(__sanitizer_cov_trace_pc);
  
  static void kcov_get(struct kcov *kcov)
  {
  	atomic_inc(&kcov->refcount);
  }
  
  static void kcov_put(struct kcov *kcov)
  {
  	if (atomic_dec_and_test(&kcov->refcount)) {
  		vfree(kcov->area);
  		kfree(kcov);
  	}
  }
  
  void kcov_task_init(struct task_struct *t)
  {
  	t->kcov_mode = KCOV_MODE_DISABLED;
  	t->kcov_size = 0;
  	t->kcov_area = NULL;
  	t->kcov = NULL;
  }
  
  void kcov_task_exit(struct task_struct *t)
  {
  	struct kcov *kcov;
  
  	kcov = t->kcov;
  	if (kcov == NULL)
  		return;
  	spin_lock(&kcov->lock);
  	if (WARN_ON(kcov->t != t)) {
  		spin_unlock(&kcov->lock);
  		return;
  	}
  	/* Just to not leave dangling references behind. */
  	kcov_task_init(t);
  	kcov->t = NULL;
  	spin_unlock(&kcov->lock);
  	kcov_put(kcov);
  }
  
  static int kcov_mmap(struct file *filep, struct vm_area_struct *vma)
  {
  	int res = 0;
  	void *area;
  	struct kcov *kcov = vma->vm_file->private_data;
  	unsigned long size, off;
  	struct page *page;
  
  	area = vmalloc_user(vma->vm_end - vma->vm_start);
  	if (!area)
  		return -ENOMEM;
  
  	spin_lock(&kcov->lock);
  	size = kcov->size * sizeof(unsigned long);
  	if (kcov->mode == KCOV_MODE_DISABLED || vma->vm_pgoff != 0 ||
  	    vma->vm_end - vma->vm_start != size) {
  		res = -EINVAL;
  		goto exit;
  	}
  	if (!kcov->area) {
  		kcov->area = area;
  		vma->vm_flags |= VM_DONTEXPAND;
  		spin_unlock(&kcov->lock);
  		for (off = 0; off < size; off += PAGE_SIZE) {
  			page = vmalloc_to_page(kcov->area + off);
  			if (vm_insert_page(vma, vma->vm_start + off, page))
  				WARN_ONCE(1, "vm_insert_page() failed");
  		}
  		return 0;
  	}
  exit:
  	spin_unlock(&kcov->lock);
  	vfree(area);
  	return res;
  }
  
  static int kcov_open(struct inode *inode, struct file *filep)
  {
  	struct kcov *kcov;
  
  	kcov = kzalloc(sizeof(*kcov), GFP_KERNEL);
  	if (!kcov)
  		return -ENOMEM;
  	atomic_set(&kcov->refcount, 1);
  	spin_lock_init(&kcov->lock);
  	filep->private_data = kcov;
  	return nonseekable_open(inode, filep);
  }
  
  static int kcov_close(struct inode *inode, struct file *filep)
  {
  	kcov_put(filep->private_data);
  	return 0;
  }
  
  static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,
  			     unsigned long arg)
  {
  	struct task_struct *t;
  	unsigned long size, unused;
  
  	switch (cmd) {
  	case KCOV_INIT_TRACE:
  		/*
  		 * Enable kcov in trace mode and setup buffer size.
  		 * Must happen before anything else.
  		 */
  		if (kcov->mode != KCOV_MODE_DISABLED)
  			return -EBUSY;
  		/*
  		 * Size must be at least 2 to hold current position and one PC.
  		 * Later we allocate size * sizeof(unsigned long) memory,
  		 * that must not overflow.
  		 */
  		size = arg;
  		if (size < 2 || size > INT_MAX / sizeof(unsigned long))
  			return -EINVAL;
  		kcov->size = size;
  		kcov->mode = KCOV_MODE_TRACE;
  		return 0;
  	case KCOV_ENABLE:
  		/*
  		 * Enable coverage for the current task.
  		 * At this point user must have been enabled trace mode,
  		 * and mmapped the file. Coverage collection is disabled only
  		 * at task exit or voluntary by KCOV_DISABLE. After that it can
  		 * be enabled for another task.
  		 */
  		unused = arg;
  		if (unused != 0 || kcov->mode == KCOV_MODE_DISABLED ||
  		    kcov->area == NULL)
  			return -EINVAL;
  		if (kcov->t != NULL)
  			return -EBUSY;
  		t = current;
  		/* Cache in task struct for performance. */
  		t->kcov_size = kcov->size;
  		t->kcov_area = kcov->area;
  		/* See comment in __sanitizer_cov_trace_pc(). */
  		barrier();
  		WRITE_ONCE(t->kcov_mode, kcov->mode);
  		t->kcov = kcov;
  		kcov->t = t;
  		/* This is put either in kcov_task_exit() or in KCOV_DISABLE. */
  		kcov_get(kcov);
  		return 0;
  	case KCOV_DISABLE:
  		/* Disable coverage for the current task. */
  		unused = arg;
  		if (unused != 0 || current->kcov != kcov)
  			return -EINVAL;
  		t = current;
  		if (WARN_ON(kcov->t != t))
  			return -EINVAL;
  		kcov_task_init(t);
  		kcov->t = NULL;
  		kcov_put(kcov);
  		return 0;
  	default:
  		return -ENOTTY;
  	}
  }
  
  static long kcov_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
  {
  	struct kcov *kcov;
  	int res;
  
  	kcov = filep->private_data;
  	spin_lock(&kcov->lock);
  	res = kcov_ioctl_locked(kcov, cmd, arg);
  	spin_unlock(&kcov->lock);
  	return res;
  }
  
  static const struct file_operations kcov_fops = {
  	.open		= kcov_open,
  	.unlocked_ioctl	= kcov_ioctl,
  	.mmap		= kcov_mmap,
  	.release        = kcov_close,
  };
  
  static int __init kcov_init(void)
  {

  	/*
  	 * The kcov debugfs file won't ever get removed and thus,
  	 * there is no need to protect it against removal races. The
  	 * use of debugfs_create_file_unsafe() is actually safe here.
  	 */
  	if (!debugfs_create_file_unsafe("kcov", 0600, NULL, NULL, &kcov_fops)) {

  		pr_err("failed to create kcov in debugfs
  ");
  		return -ENOMEM;
  	}
  	return 0;
  }
  
  device_initcall(kcov_init);