kernel/kcov.c - third_party/linux - Git at Google

 // 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 bool check_kcov_mode(enum kcov_mode needed_mode, struct task_struct *t)
 {
 	enum kcov_mode 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 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 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)
 {
 	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;
 	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;
 }

 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;
 		/* 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\n");
 		return -ENOMEM;
 	}
 	return 0;
 }

 device_initcall(kcov_init);
	// 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 bool check_kcov_mode(enum kcov_mode needed_mode, struct task_struct *t)
	{
	enum kcov_mode 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 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 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)
	{
	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;
	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;
	}

	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;
	/* 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\n");
	return -ENOMEM;
	}
	return 0;
	}

	device_initcall(kcov_init);