1#define pr_fmt(fmt) "kcov: " fmt
  2
  3#define DISABLE_BRANCH_PROFILING
  4#include <linux/atomic.h>
  5#include <linux/compiler.h>
  6#include <linux/errno.h>
  7#include <linux/export.h>
  8#include <linux/types.h>
  9#include <linux/file.h>
 10#include <linux/fs.h>
 11#include <linux/init.h>
 12#include <linux/mm.h>
 13#include <linux/preempt.h>
 14#include <linux/printk.h>
 15#include <linux/sched.h>
 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>
 22#include <asm/setup.h>
 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 */
 32struct 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 */
 54void notrace __sanitizer_cov_trace_pc(void)
 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.
 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).
 69	 */
 70	if (!t || (preempt_count() & (HARDIRQ_MASK | SOFTIRQ_OFFSET
 71							| NMI_MASK)))
 72		return;
 73	mode = READ_ONCE(t->kcov_mode);
 74	if (mode == KCOV_MODE_TRACE) {
 75		unsigned long *area;
 76		unsigned long pos;
 77		unsigned long ip = _RET_IP_;
 78
 79#ifdef CONFIG_RANDOMIZE_BASE
 80		ip -= kaslr_offset();
 81#endif
 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)) {
 95			area[pos] = ip;
 96			WRITE_ONCE(area[0], pos);
 97		}
 98	}
 99}
100EXPORT_SYMBOL(__sanitizer_cov_trace_pc);
101
102static void kcov_get(struct kcov *kcov)
103{
104	atomic_inc(&kcov->refcount);
105}
106
107static 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
115void 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
123void 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
142static 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	}
172exit:
173	spin_unlock(&kcov->lock);
174	vfree(area);
175	return res;
176}
177
178static 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
191static int kcov_close(struct inode *inode, struct file *filep)
192{
193	kcov_put(filep->private_data);
194	return 0;
195}
196
197static 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
265static 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
277static 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
284static int __init kcov_init(void)
285{
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)) {
292		pr_err("failed to create kcov in debugfs\n");
293		return -ENOMEM;
294	}
295	return 0;
296}
297
298device_initcall(kcov_init);