[linux.git] / kernel / kcov.c

#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.
	 */
	if (!t || in_interrupt())
		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\n");
		return -ENOMEM;
	}
	return 0;
}

device_initcall(kcov_init);
Commit	Line	Data
5c9a8750 DV	1	#define pr_fmt(fmt) "kcov: " fmt
5c9a8750 DV	2
36f05ae8	3	#define DISABLE_BRANCH_PROFILING
5c9a8750 DV	4	#include <linux/compiler.h>
	5	#include <linux/types.h>
	6	#include <linux/file.h>
	7	#include <linux/fs.h>
	8	#include <linux/mm.h>
	9	#include <linux/printk.h>
	10	#include <linux/slab.h>
	11	#include <linux/spinlock.h>
	12	#include <linux/vmalloc.h>
	13	#include <linux/debugfs.h>
	14	#include <linux/uaccess.h>
	15	#include <linux/kcov.h>
	16
	17	/*
	18	* kcov descriptor (one per opened debugfs file).
	19	* State transitions of the descriptor:
	20	* - initial state after open()
	21	* - then there must be a single ioctl(KCOV_INIT_TRACE) call
	22	* - then, mmap() call (several calls are allowed but not useful)
	23	* - then, repeated enable/disable for a task (only one task a time allowed)
	24	*/
	25	struct kcov {
	26	/*
	27	* Reference counter. We keep one for:
	28	* - opened file descriptor
	29	* - task with enabled coverage (we can't unwire it from another task)
	30	*/
	31	atomic_t refcount;
	32	/* The lock protects mode, size, area and t. */
	33	spinlock_t lock;
	34	enum kcov_mode mode;
	35	/* Size of arena (in long's for KCOV_MODE_TRACE). */
	36	unsigned size;
	37	/* Coverage buffer shared with user space. */
	38	void *area;
	39	/* Task for which we collect coverage, or NULL. */
	40	struct task_struct *t;
	41	};
	42
	43	/*
	44	* Entry point from instrumented code.
	45	* This is called once per basic-block/edge.
	46	*/
bdab42df	47	void notrace __sanitizer_cov_trace_pc(void)
5c9a8750 DV	48	{
	49	struct task_struct *t;
	50	enum kcov_mode mode;
	51
	52	t = current;
	53	/*
	54	* We are interested in code coverage as a function of a syscall inputs,
	55	* so we ignore code executed in interrupts.
	56	*/
	57	if (!t \|\| in_interrupt())
	58	return;
	59	mode = READ_ONCE(t->kcov_mode);
	60	if (mode == KCOV_MODE_TRACE) {
	61	unsigned long *area;
	62	unsigned long pos;
	63
	64	/*
	65	* There is some code that runs in interrupts but for which
	66	* in_interrupt() returns false (e.g. preempt_schedule_irq()).
	67	* READ_ONCE()/barrier() effectively provides load-acquire wrt
	68	* interrupts, there are paired barrier()/WRITE_ONCE() in
	69	* kcov_ioctl_locked().
	70	*/
	71	barrier();
	72	area = t->kcov_area;
	73	/* The first word is number of subsequent PCs. */
	74	pos = READ_ONCE(area[0]) + 1;
	75	if (likely(pos < t->kcov_size)) {
	76	area[pos] = _RET_IP_;
	77	WRITE_ONCE(area[0], pos);
	78	}
	79	}
	80	}
	81	EXPORT_SYMBOL(__sanitizer_cov_trace_pc);
	82
	83	static void kcov_get(struct kcov *kcov)
	84	{
	85	atomic_inc(&kcov->refcount);
	86	}
	87
	88	static void kcov_put(struct kcov *kcov)
	89	{
	90	if (atomic_dec_and_test(&kcov->refcount)) {
	91	vfree(kcov->area);
	92	kfree(kcov);
	93	}
	94	}
	95
	96	void kcov_task_init(struct task_struct *t)
	97	{
	98	t->kcov_mode = KCOV_MODE_DISABLED;
	99	t->kcov_size = 0;
	100	t->kcov_area = NULL;
	101	t->kcov = NULL;
	102	}
	103
	104	void kcov_task_exit(struct task_struct *t)
	105	{
	106	struct kcov *kcov;
	107
	108	kcov = t->kcov;
	109	if (kcov == NULL)
	110	return;
	111	spin_lock(&kcov->lock);
112	if (WARN_ON(kcov->t != t)) {
113	spin_unlock(&kcov->lock);
114	return;
115	}
116	/* Just to not leave dangling references behind. */
117	kcov_task_init(t);
118	kcov->t = NULL;
119	spin_unlock(&kcov->lock);
120	kcov_put(kcov);
121	}
122
123	static int kcov_mmap(struct file filep, struct vm_area_struct vma)
124	{
125	int res = 0;
126	void *area;
127	struct kcov *kcov = vma->vm_file->private_data;
128	unsigned long size, off;
129	struct page *page;
130
131	area = vmalloc_user(vma->vm_end - vma->vm_start);
132	if (!area)
133	return -ENOMEM;
134
135	spin_lock(&kcov->lock);
136	size = kcov->size * sizeof(unsigned long);
137	if (kcov->mode == KCOV_MODE_DISABLED \|\| vma->vm_pgoff != 0 \|\|
138	vma->vm_end - vma->vm_start != size) {
139	res = -EINVAL;
140	goto exit;
141	}
142	if (!kcov->area) {
143	kcov->area = area;
144	vma->vm_flags \|= VM_DONTEXPAND;
145	spin_unlock(&kcov->lock);
146	for (off = 0; off < size; off += PAGE_SIZE) {
147	page = vmalloc_to_page(kcov->area + off);
148	if (vm_insert_page(vma, vma->vm_start + off, page))
149	WARN_ONCE(1, "vm_insert_page() failed");
150	}
151	return 0;
152	}
153	exit:
154	spin_unlock(&kcov->lock);
155	vfree(area);
156	return res;
157	}
158
159	static int kcov_open(struct inode inode, struct file filep)
160	{
161	struct kcov *kcov;
162
163	kcov = kzalloc(sizeof(*kcov), GFP_KERNEL);
164	if (!kcov)
165	return -ENOMEM;
166	atomic_set(&kcov->refcount, 1);
167	spin_lock_init(&kcov->lock);
168	filep->private_data = kcov;
169	return nonseekable_open(inode, filep);
170	}
171
172	static int kcov_close(struct inode inode, struct file filep)
173	{
174	kcov_put(filep->private_data);
175	return 0;
176	}
177
178	static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,
179	unsigned long arg)
180	{
181	struct task_struct *t;
182	unsigned long size, unused;
183
184	switch (cmd) {
185	case KCOV_INIT_TRACE:
186	/*
187	* Enable kcov in trace mode and setup buffer size.
188	* Must happen before anything else.
189	*/
190	if (kcov->mode != KCOV_MODE_DISABLED)
191	return -EBUSY;
192	/*
193	* Size must be at least 2 to hold current position and one PC.
194	* Later we allocate size * sizeof(unsigned long) memory,
195	* that must not overflow.
196	*/
197	size = arg;
198	if (size < 2 \|\| size > INT_MAX / sizeof(unsigned long))
199	return -EINVAL;
200	kcov->size = size;
201	kcov->mode = KCOV_MODE_TRACE;
202	return 0;
203	case KCOV_ENABLE:
204	/*
205	* Enable coverage for the current task.
206	* At this point user must have been enabled trace mode,
207	* and mmapped the file. Coverage collection is disabled only
208	* at task exit or voluntary by KCOV_DISABLE. After that it can
209	* be enabled for another task.
210	*/
211	unused = arg;
212	if (unused != 0 \|\| kcov->mode == KCOV_MODE_DISABLED \|\|
213	kcov->area == NULL)
214	return -EINVAL;
215	if (kcov->t != NULL)
216	return -EBUSY;
217	t = current;
218	/* Cache in task struct for performance. */
219	t->kcov_size = kcov->size;
220	t->kcov_area = kcov->area;
221	/* See comment in __sanitizer_cov_trace_pc(). */
222	barrier();
223	WRITE_ONCE(t->kcov_mode, kcov->mode);
224	t->kcov = kcov;
225	kcov->t = t;
226	/* This is put either in kcov_task_exit() or in KCOV_DISABLE. */
227	kcov_get(kcov);
228	return 0;
229	case KCOV_DISABLE:
230	/* Disable coverage for the current task. */
231	unused = arg;
232	if (unused != 0 \|\| current->kcov != kcov)
233	return -EINVAL;
234	t = current;
235	if (WARN_ON(kcov->t != t))
236	return -EINVAL;
237	kcov_task_init(t);
238	kcov->t = NULL;
239	kcov_put(kcov);
240	return 0;
241	default:
242	return -ENOTTY;
243	}
244	}
245
246	static long kcov_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
247	{
248	struct kcov *kcov;
249	int res;
250
251	kcov = filep->private_data;
252	spin_lock(&kcov->lock);
253	res = kcov_ioctl_locked(kcov, cmd, arg);
254	spin_unlock(&kcov->lock);
255	return res;
256	}
257
258	static const struct file_operations kcov_fops = {
259	.open = kcov_open,
260	.unlocked_ioctl = kcov_ioctl,
261	.mmap = kcov_mmap,
262	.release = kcov_close,
263	};
264
265	static int __init kcov_init(void)
266	{
df4565f9 NS	267	/*
	268	* The kcov debugfs file won't ever get removed and thus,
	269	* there is no need to protect it against removal races. The
	270	* use of debugfs_create_file_unsafe() is actually safe here.
	271	*/
	272	if (!debugfs_create_file_unsafe("kcov", 0600, NULL, NULL, &kcov_fops)) {
5c9a8750 DV	273	pr_err("failed to create kcov in debugfs\n");
	274	return -ENOMEM;
	275	}
	276	return 0;
	277	}
	278
	279	device_initcall(kcov_init);