1 #define pr_fmt(fmt) "kcov: " fmt
3 #define DISABLE_BRANCH_PROFILING
4 #include <linux/compiler.h>
5 #include <linux/types.h>
6 #include <linux/file.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>
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)
27 * Reference counter. We keep one for:
28 * - opened file descriptor
29 * - task with enabled coverage (we can't unwire it from another task)
32 /* The lock protects mode, size, area and t. */
35 /* Size of arena (in long's for KCOV_MODE_TRACE). */
37 /* Coverage buffer shared with user space. */
39 /* Task for which we collect coverage, or NULL. */
40 struct task_struct *t;
44 * Entry point from instrumented code.
45 * This is called once per basic-block/edge.
47 void notrace __sanitizer_cov_trace_pc(void)
49 struct task_struct *t;
54 * We are interested in code coverage as a function of a syscall inputs,
55 * so we ignore code executed in interrupts.
56 * The checks for whether we are in an interrupt are open-coded, because
57 * 1. We can't use in_interrupt() here, since it also returns true
58 * when we are inside local_bh_disable() section.
59 * 2. We don't want to use (in_irq() | in_serving_softirq() | in_nmi()),
60 * since that leads to slower generated code (three separate tests,
61 * one for each of the flags).
63 if (!t || (preempt_count() & (HARDIRQ_MASK | SOFTIRQ_OFFSET
66 mode = READ_ONCE(t->kcov_mode);
67 if (mode == KCOV_MODE_TRACE) {
72 * There is some code that runs in interrupts but for which
73 * in_interrupt() returns false (e.g. preempt_schedule_irq()).
74 * READ_ONCE()/barrier() effectively provides load-acquire wrt
75 * interrupts, there are paired barrier()/WRITE_ONCE() in
76 * kcov_ioctl_locked().
80 /* The first word is number of subsequent PCs. */
81 pos = READ_ONCE(area[0]) + 1;
82 if (likely(pos < t->kcov_size)) {
84 WRITE_ONCE(area[0], pos);
88 EXPORT_SYMBOL(__sanitizer_cov_trace_pc);
90 static void kcov_get(struct kcov *kcov)
92 atomic_inc(&kcov->refcount);
95 static void kcov_put(struct kcov *kcov)
97 if (atomic_dec_and_test(&kcov->refcount)) {
103 void kcov_task_init(struct task_struct *t)
105 t->kcov_mode = KCOV_MODE_DISABLED;
111 void kcov_task_exit(struct task_struct *t)
118 spin_lock(&kcov->lock);
119 if (WARN_ON(kcov->t != t)) {
120 spin_unlock(&kcov->lock);
123 /* Just to not leave dangling references behind. */
126 spin_unlock(&kcov->lock);
130 static int kcov_mmap(struct file *filep, struct vm_area_struct *vma)
134 struct kcov *kcov = vma->vm_file->private_data;
135 unsigned long size, off;
138 area = vmalloc_user(vma->vm_end - vma->vm_start);
142 spin_lock(&kcov->lock);
143 size = kcov->size * sizeof(unsigned long);
144 if (kcov->mode == KCOV_MODE_DISABLED || vma->vm_pgoff != 0 ||
145 vma->vm_end - vma->vm_start != size) {
151 vma->vm_flags |= VM_DONTEXPAND;
152 spin_unlock(&kcov->lock);
153 for (off = 0; off < size; off += PAGE_SIZE) {
154 page = vmalloc_to_page(kcov->area + off);
155 if (vm_insert_page(vma, vma->vm_start + off, page))
156 WARN_ONCE(1, "vm_insert_page() failed");
161 spin_unlock(&kcov->lock);
166 static int kcov_open(struct inode *inode, struct file *filep)
170 kcov = kzalloc(sizeof(*kcov), GFP_KERNEL);
173 atomic_set(&kcov->refcount, 1);
174 spin_lock_init(&kcov->lock);
175 filep->private_data = kcov;
176 return nonseekable_open(inode, filep);
179 static int kcov_close(struct inode *inode, struct file *filep)
181 kcov_put(filep->private_data);
185 static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,
188 struct task_struct *t;
189 unsigned long size, unused;
192 case KCOV_INIT_TRACE:
194 * Enable kcov in trace mode and setup buffer size.
195 * Must happen before anything else.
197 if (kcov->mode != KCOV_MODE_DISABLED)
200 * Size must be at least 2 to hold current position and one PC.
201 * Later we allocate size * sizeof(unsigned long) memory,
202 * that must not overflow.
205 if (size < 2 || size > INT_MAX / sizeof(unsigned long))
208 kcov->mode = KCOV_MODE_TRACE;
212 * Enable coverage for the current task.
213 * At this point user must have been enabled trace mode,
214 * and mmapped the file. Coverage collection is disabled only
215 * at task exit or voluntary by KCOV_DISABLE. After that it can
216 * be enabled for another task.
219 if (unused != 0 || kcov->mode == KCOV_MODE_DISABLED ||
225 /* Cache in task struct for performance. */
226 t->kcov_size = kcov->size;
227 t->kcov_area = kcov->area;
228 /* See comment in __sanitizer_cov_trace_pc(). */
230 WRITE_ONCE(t->kcov_mode, kcov->mode);
233 /* This is put either in kcov_task_exit() or in KCOV_DISABLE. */
237 /* Disable coverage for the current task. */
239 if (unused != 0 || current->kcov != kcov)
242 if (WARN_ON(kcov->t != t))
253 static long kcov_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
258 kcov = filep->private_data;
259 spin_lock(&kcov->lock);
260 res = kcov_ioctl_locked(kcov, cmd, arg);
261 spin_unlock(&kcov->lock);
265 static const struct file_operations kcov_fops = {
267 .unlocked_ioctl = kcov_ioctl,
269 .release = kcov_close,
272 static int __init kcov_init(void)
275 * The kcov debugfs file won't ever get removed and thus,
276 * there is no need to protect it against removal races. The
277 * use of debugfs_create_file_unsafe() is actually safe here.
279 if (!debugfs_create_file_unsafe("kcov", 0600, NULL, NULL, &kcov_fops)) {
280 pr_err("failed to create kcov in debugfs\n");
286 device_initcall(kcov_init);