// SPDX-License-Identifier: GPL-2.0

  #define pr_fmt(fmt) "kcov: " fmt

  #define DISABLE_BRANCH_PROFILING

  #include <linux/atomic.h>

  #include <linux/compiler.h>

  #include <linux/errno.h>
  #include <linux/export.h>

  #include <linux/types.h>
  #include <linux/file.h>
  #include <linux/fs.h>

  #include <linux/init.h>

  #include <linux/mm.h>

  #include <linux/preempt.h>

  #include <linux/printk.h>

  #include <linux/sched.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>

  #include <asm/setup.h>

  /* Number of 64-bit words written per one comparison: */
  #define KCOV_WORDS_PER_CMP 4

  /*
   * 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, ioctl(KCOV_ENABLE, arg), where arg is
   *	KCOV_TRACE_PC - to trace only the PCs
   *	or
   *	KCOV_TRACE_CMP - to trace only the comparison operands
   *  - then, ioctl(KCOV_DISABLE) to disable the task.
   * Enabling/disabling ioctls can be repeated (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;
  };

  static notrace bool check_kcov_mode(enum kcov_mode needed_mode, struct task_struct *t)

  {

  	unsigned int mode;

  	/*
  	 * We are interested in code coverage as a function of a syscall inputs,
  	 * so we ignore code executed in interrupts.
  	 */

  	if (!in_task())

  		return false;

  	mode = READ_ONCE(t->kcov_mode);

  	/*
  	 * 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();
  	return mode == needed_mode;
  }

  static notrace unsigned long canonicalize_ip(unsigned long ip)

  {

  #ifdef CONFIG_RANDOMIZE_BASE

  	ip -= kaslr_offset();

  #endif

  	return ip;
  }

  /*
   * Entry point from instrumented code.
   * This is called once per basic-block/edge.
   */
  void notrace __sanitizer_cov_trace_pc(void)
  {
  	struct task_struct *t;
  	unsigned long *area;
  	unsigned long ip = canonicalize_ip(_RET_IP_);
  	unsigned long pos;
  
  	t = current;
  	if (!check_kcov_mode(KCOV_MODE_TRACE_PC, t))
  		return;
  
  	area = t->kcov_area;
  	/* The first 64-bit word is the number of subsequent PCs. */
  	pos = READ_ONCE(area[0]) + 1;
  	if (likely(pos < t->kcov_size)) {
  		area[pos] = ip;
  		WRITE_ONCE(area[0], pos);

  	}
  }
  EXPORT_SYMBOL(__sanitizer_cov_trace_pc);

  #ifdef CONFIG_KCOV_ENABLE_COMPARISONS

  static void notrace write_comp_data(u64 type, u64 arg1, u64 arg2, u64 ip)

  {
  	struct task_struct *t;
  	u64 *area;
  	u64 count, start_index, end_pos, max_pos;
  
  	t = current;
  	if (!check_kcov_mode(KCOV_MODE_TRACE_CMP, t))
  		return;
  
  	ip = canonicalize_ip(ip);
  
  	/*
  	 * We write all comparison arguments and types as u64.
  	 * The buffer was allocated for t->kcov_size unsigned longs.
  	 */
  	area = (u64 *)t->kcov_area;
  	max_pos = t->kcov_size * sizeof(unsigned long);
  
  	count = READ_ONCE(area[0]);
  
  	/* Every record is KCOV_WORDS_PER_CMP 64-bit words. */
  	start_index = 1 + count * KCOV_WORDS_PER_CMP;
  	end_pos = (start_index + KCOV_WORDS_PER_CMP) * sizeof(u64);
  	if (likely(end_pos <= max_pos)) {
  		area[start_index] = type;
  		area[start_index + 1] = arg1;
  		area[start_index + 2] = arg2;
  		area[start_index + 3] = ip;
  		WRITE_ONCE(area[0], count + 1);
  	}
  }
  
  void notrace __sanitizer_cov_trace_cmp1(u8 arg1, u8 arg2)
  {
  	write_comp_data(KCOV_CMP_SIZE(0), arg1, arg2, _RET_IP_);
  }
  EXPORT_SYMBOL(__sanitizer_cov_trace_cmp1);
  
  void notrace __sanitizer_cov_trace_cmp2(u16 arg1, u16 arg2)
  {
  	write_comp_data(KCOV_CMP_SIZE(1), arg1, arg2, _RET_IP_);
  }
  EXPORT_SYMBOL(__sanitizer_cov_trace_cmp2);

  void notrace __sanitizer_cov_trace_cmp4(u32 arg1, u32 arg2)

  {
  	write_comp_data(KCOV_CMP_SIZE(2), arg1, arg2, _RET_IP_);
  }
  EXPORT_SYMBOL(__sanitizer_cov_trace_cmp4);
  
  void notrace __sanitizer_cov_trace_cmp8(u64 arg1, u64 arg2)
  {
  	write_comp_data(KCOV_CMP_SIZE(3), arg1, arg2, _RET_IP_);
  }
  EXPORT_SYMBOL(__sanitizer_cov_trace_cmp8);
  
  void notrace __sanitizer_cov_trace_const_cmp1(u8 arg1, u8 arg2)
  {
  	write_comp_data(KCOV_CMP_SIZE(0) | KCOV_CMP_CONST, arg1, arg2,
  			_RET_IP_);
  }
  EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp1);
  
  void notrace __sanitizer_cov_trace_const_cmp2(u16 arg1, u16 arg2)
  {
  	write_comp_data(KCOV_CMP_SIZE(1) | KCOV_CMP_CONST, arg1, arg2,
  			_RET_IP_);
  }
  EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp2);

  void notrace __sanitizer_cov_trace_const_cmp4(u32 arg1, u32 arg2)

  {
  	write_comp_data(KCOV_CMP_SIZE(2) | KCOV_CMP_CONST, arg1, arg2,
  			_RET_IP_);
  }
  EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp4);
  
  void notrace __sanitizer_cov_trace_const_cmp8(u64 arg1, u64 arg2)
  {
  	write_comp_data(KCOV_CMP_SIZE(3) | KCOV_CMP_CONST, arg1, arg2,
  			_RET_IP_);
  }
  EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp8);
  
  void notrace __sanitizer_cov_trace_switch(u64 val, u64 *cases)
  {
  	u64 i;
  	u64 count = cases[0];
  	u64 size = cases[1];
  	u64 type = KCOV_CMP_CONST;
  
  	switch (size) {
  	case 8:
  		type |= KCOV_CMP_SIZE(0);
  		break;
  	case 16:
  		type |= KCOV_CMP_SIZE(1);
  		break;
  	case 32:
  		type |= KCOV_CMP_SIZE(2);
  		break;
  	case 64:
  		type |= KCOV_CMP_SIZE(3);
  		break;
  	default:
  		return;
  	}
  	for (i = 0; i < count; i++)
  		write_comp_data(type, cases[i + 2], val, _RET_IP_);
  }
  EXPORT_SYMBOL(__sanitizer_cov_trace_switch);
  #endif /* ifdef CONFIG_KCOV_ENABLE_COMPARISONS */

  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)
  {

  	WRITE_ONCE(t->kcov_mode, KCOV_MODE_DISABLED);
  	barrier();

  	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;

  	kcov->mode = KCOV_MODE_INIT;

  	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_INIT || 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;

  	kcov->mode = KCOV_MODE_DISABLED;

  	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;
  }

  /*
   * Fault in a lazily-faulted vmalloc area before it can be used by
   * __santizer_cov_trace_pc(), to avoid recursion issues if any code on the
   * vmalloc fault handling path is instrumented.
   */
  static void kcov_fault_in_area(struct kcov *kcov)
  {
  	unsigned long stride = PAGE_SIZE / sizeof(unsigned long);
  	unsigned long *area = kcov->area;
  	unsigned long offset;
  
  	for (offset = 0; offset < kcov->size; offset += stride)
  		READ_ONCE(area[offset]);
  }

  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_INIT;

  		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.
  		 */

  		if (kcov->mode != KCOV_MODE_INIT || !kcov->area)

  			return -EINVAL;

  		t = current;
  		if (kcov->t != NULL || t->kcov != NULL)

  			return -EBUSY;

  		if (arg == KCOV_TRACE_PC)
  			kcov->mode = KCOV_MODE_TRACE_PC;
  		else if (arg == KCOV_TRACE_CMP)
  #ifdef CONFIG_KCOV_ENABLE_COMPARISONS
  			kcov->mode = KCOV_MODE_TRACE_CMP;
  #else
  		return -ENOTSUPP;
  #endif
  		else
  			return -EINVAL;

  		kcov_fault_in_area(kcov);

  		/* Cache in task struct for performance. */
  		t->kcov_size = kcov->size;
  		t->kcov_area = kcov->area;

  		/* See comment in check_kcov_mode(). */

  		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->mode = KCOV_MODE_INIT;

  		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,

  	.compat_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);