[linux.git] / kernel / kcov.c

#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>

/*
 * 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;
		unsigned long ip = _RET_IP_;

#ifdef CONFIG_RANDOMIZE_BASE
		ip -= kaslr_offset();
#endif

		/*
		 * 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] = 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
db862358	4	#include <linux/atomic.h>
5c9a8750	5	#include <linux/compiler.h>
db862358 KW	6	#include <linux/errno.h>
db862358 KW	7	#include <linux/export.h>
5c9a8750 DV	8	#include <linux/types.h>
	9	#include <linux/file.h>
	10	#include <linux/fs.h>
db862358	11	#include <linux/init.h>
5c9a8750	12	#include <linux/mm.h>
db862358	13	#include <linux/preempt.h>
5c9a8750	14	#include <linux/printk.h>
166ad0e1	15	#include <linux/sched.h>
5c9a8750 DV	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>
4983f0ab	22	#include <asm/setup.h>
5c9a8750 DV	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	*/
bdab42df	54	void notrace __sanitizer_cov_trace_pc(void)
5c9a8750 DV	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.
b274c0bb AK	63	* The checks for whether we are in an interrupt are open-coded, because
	64	* 1. We can't use in_interrupt() here, since it also returns true
	65	* when we are inside local_bh_disable() section.
	66	* 2. We don't want to use (in_irq() \| in_serving_softirq() \| in_nmi()),
	67	* since that leads to slower generated code (three separate tests,
	68	* one for each of the flags).
5c9a8750	69	*/
b274c0bb AK	70	if (!t \|\| (preempt_count() & (HARDIRQ_MASK \| SOFTIRQ_OFFSET
b274c0bb AK	71	\| NMI_MASK)))
5c9a8750 DV	72	return;
	73	mode = READ_ONCE(t->kcov_mode);
	74	if (mode == KCOV_MODE_TRACE) {
	75	unsigned long *area;
	76	unsigned long pos;
4983f0ab AP	77	unsigned long ip = _RET_IP_;
	78
	79	#ifdef CONFIG_RANDOMIZE_BASE
	80	ip -= kaslr_offset();
	81	#endif
5c9a8750 DV	82
	83	/*
	84	* There is some code that runs in interrupts but for which
	85	* in_interrupt() returns false (e.g. preempt_schedule_irq()).
	86	* READ_ONCE()/barrier() effectively provides load-acquire wrt
	87	* interrupts, there are paired barrier()/WRITE_ONCE() in
	88	* kcov_ioctl_locked().
	89	*/
	90	barrier();
	91	area = t->kcov_area;
	92	/* The first word is number of subsequent PCs. */
	93	pos = READ_ONCE(area[0]) + 1;
	94	if (likely(pos < t->kcov_size)) {
4983f0ab	95	area[pos] = ip;
5c9a8750 DV	96	WRITE_ONCE(area[0], pos);
	97	}
	98	}
	99	}
	100	EXPORT_SYMBOL(__sanitizer_cov_trace_pc);
	101
	102	static void kcov_get(struct kcov *kcov)
	103	{
	104	atomic_inc(&kcov->refcount);
	105	}
	106
	107	static void kcov_put(struct kcov *kcov)
	108	{
	109	if (atomic_dec_and_test(&kcov->refcount)) {
	110	vfree(kcov->area);
	111	kfree(kcov);
	112	}
	113	}
	114
	115	void kcov_task_init(struct task_struct *t)
	116	{
	117	t->kcov_mode = KCOV_MODE_DISABLED;
	118	t->kcov_size = 0;
	119	t->kcov_area = NULL;
	120	t->kcov = NULL;
	121	}
	122
	123	void kcov_task_exit(struct task_struct *t)
	124	{
	125	struct kcov *kcov;
	126
	127	kcov = t->kcov;
	128	if (kcov == NULL)
	129	return;
	130	spin_lock(&kcov->lock);
	131	if (WARN_ON(kcov->t != t)) {
	132	spin_unlock(&kcov->lock);
	133	return;
	134	}
	135	/* Just to not leave dangling references behind. */
	136	kcov_task_init(t);
	137	kcov->t = NULL;
	138	spin_unlock(&kcov->lock);
	139	kcov_put(kcov);
	140	}
	141
	142	static int kcov_mmap(struct file filep, struct vm_area_struct vma)
	143	{
	144	int res = 0;
	145	void *area;
	146	struct kcov *kcov = vma->vm_file->private_data;
	147	unsigned long size, off;
	148	struct page *page;
	149
	150	area = vmalloc_user(vma->vm_end - vma->vm_start);
	151	if (!area)
	152	return -ENOMEM;
	153
	154	spin_lock(&kcov->lock);
	155	size = kcov->size * sizeof(unsigned long);
	156	if (kcov->mode == KCOV_MODE_DISABLED \|\| vma->vm_pgoff != 0 \|\|
	157	vma->vm_end - vma->vm_start != size) {
	158	res = -EINVAL;
	159	goto exit;
160	}
161	if (!kcov->area) {
162	kcov->area = area;
163	vma->vm_flags \|= VM_DONTEXPAND;
164	spin_unlock(&kcov->lock);
165	for (off = 0; off < size; off += PAGE_SIZE) {
166	page = vmalloc_to_page(kcov->area + off);
167	if (vm_insert_page(vma, vma->vm_start + off, page))
168	WARN_ONCE(1, "vm_insert_page() failed");
169	}
170	return 0;
171	}
172	exit:
173	spin_unlock(&kcov->lock);
174	vfree(area);
175	return res;
176	}
177
178	static int kcov_open(struct inode inode, struct file filep)
179	{
180	struct kcov *kcov;
181
182	kcov = kzalloc(sizeof(*kcov), GFP_KERNEL);
183	if (!kcov)
184	return -ENOMEM;
185	atomic_set(&kcov->refcount, 1);
186	spin_lock_init(&kcov->lock);
187	filep->private_data = kcov;
188	return nonseekable_open(inode, filep);
189	}
190
191	static int kcov_close(struct inode inode, struct file filep)
192	{
193	kcov_put(filep->private_data);
194	return 0;
195	}
196
197	static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,
198	unsigned long arg)
199	{
200	struct task_struct *t;
201	unsigned long size, unused;
202
203	switch (cmd) {
204	case KCOV_INIT_TRACE:
205	/*
206	* Enable kcov in trace mode and setup buffer size.
207	* Must happen before anything else.
208	*/
209	if (kcov->mode != KCOV_MODE_DISABLED)
210	return -EBUSY;
211	/*
212	* Size must be at least 2 to hold current position and one PC.
213	* Later we allocate size * sizeof(unsigned long) memory,
214	* that must not overflow.
215	*/
216	size = arg;
217	if (size < 2 \|\| size > INT_MAX / sizeof(unsigned long))
218	return -EINVAL;
219	kcov->size = size;
220	kcov->mode = KCOV_MODE_TRACE;
221	return 0;
222	case KCOV_ENABLE:
223	/*
224	* Enable coverage for the current task.
225	* At this point user must have been enabled trace mode,
226	* and mmapped the file. Coverage collection is disabled only
227	* at task exit or voluntary by KCOV_DISABLE. After that it can
228	* be enabled for another task.
229	*/
230	unused = arg;
231	if (unused != 0 \|\| kcov->mode == KCOV_MODE_DISABLED \|\|
232	kcov->area == NULL)
233	return -EINVAL;
234	if (kcov->t != NULL)
235	return -EBUSY;
236	t = current;
237	/* Cache in task struct for performance. */
238	t->kcov_size = kcov->size;
239	t->kcov_area = kcov->area;
240	/* See comment in __sanitizer_cov_trace_pc(). */
241	barrier();
242	WRITE_ONCE(t->kcov_mode, kcov->mode);
243	t->kcov = kcov;
244	kcov->t = t;
245	/* This is put either in kcov_task_exit() or in KCOV_DISABLE. */
246	kcov_get(kcov);
247	return 0;
248	case KCOV_DISABLE:
249	/* Disable coverage for the current task. */
250	unused = arg;
251	if (unused != 0 \|\| current->kcov != kcov)
252	return -EINVAL;
253	t = current;
254	if (WARN_ON(kcov->t != t))
255	return -EINVAL;
256	kcov_task_init(t);
257	kcov->t = NULL;
258	kcov_put(kcov);
259	return 0;
260	default:
261	return -ENOTTY;
262	}
263	}
264
265	static long kcov_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
266	{
267	struct kcov *kcov;
268	int res;
269
270	kcov = filep->private_data;
271	spin_lock(&kcov->lock);
272	res = kcov_ioctl_locked(kcov, cmd, arg);
273	spin_unlock(&kcov->lock);
274	return res;
275	}
276
277	static const struct file_operations kcov_fops = {
278	.open = kcov_open,
279	.unlocked_ioctl = kcov_ioctl,
280	.mmap = kcov_mmap,
281	.release = kcov_close,
282	};
283
284	static int __init kcov_init(void)
285	{
df4565f9 NS	286	/*
	287	* The kcov debugfs file won't ever get removed and thus,
	288	* there is no need to protect it against removal races. The
	289	* use of debugfs_create_file_unsafe() is actually safe here.
	290	*/
	291	if (!debugfs_create_file_unsafe("kcov", 0600, NULL, NULL, &kcov_fops)) {
5c9a8750 DV	292	pr_err("failed to create kcov in debugfs\n");
	293	return -ENOMEM;
	294	}
	295	return 0;
	296	}
	297
	298	device_initcall(kcov_init);