1 // SPDX-License-Identifier: GPL-2.0
2 #define pr_fmt(fmt) "kcov: " fmt
4 #define DISABLE_BRANCH_PROFILING
5 #include <linux/atomic.h>
6 #include <linux/compiler.h>
7 #include <linux/errno.h>
8 #include <linux/export.h>
9 #include <linux/types.h>
10 #include <linux/file.h>
12 #include <linux/init.h>
14 #include <linux/preempt.h>
15 #include <linux/printk.h>
16 #include <linux/sched.h>
17 #include <linux/slab.h>
18 #include <linux/spinlock.h>
19 #include <linux/vmalloc.h>
20 #include <linux/debugfs.h>
21 #include <linux/uaccess.h>
22 #include <linux/kcov.h>
23 #include <asm/setup.h>
26 * kcov descriptor (one per opened debugfs file).
27 * State transitions of the descriptor:
28 * - initial state after open()
29 * - then there must be a single ioctl(KCOV_INIT_TRACE) call
30 * - then, mmap() call (several calls are allowed but not useful)
31 * - then, repeated enable/disable for a task (only one task a time allowed)
35 * Reference counter. We keep one for:
36 * - opened file descriptor
37 * - task with enabled coverage (we can't unwire it from another task)
40 /* The lock protects mode, size, area and t. */
43 /* Size of arena (in long's for KCOV_MODE_TRACE). */
45 /* Coverage buffer shared with user space. */
47 /* Task for which we collect coverage, or NULL. */
48 struct task_struct *t;
52 * Entry point from instrumented code.
53 * This is called once per basic-block/edge.
55 void notrace __sanitizer_cov_trace_pc(void)
57 struct task_struct *t;
62 * We are interested in code coverage as a function of a syscall inputs,
63 * so we ignore code executed in interrupts.
67 mode = READ_ONCE(t->kcov_mode);
68 if (mode == KCOV_MODE_TRACE) {
71 unsigned long ip = _RET_IP_;
73 #ifdef CONFIG_RANDOMIZE_BASE
78 * There is some code that runs in interrupts but for which
79 * in_interrupt() returns false (e.g. preempt_schedule_irq()).
80 * READ_ONCE()/barrier() effectively provides load-acquire wrt
81 * interrupts, there are paired barrier()/WRITE_ONCE() in
82 * kcov_ioctl_locked().
86 /* The first word is number of subsequent PCs. */
87 pos = READ_ONCE(area[0]) + 1;
88 if (likely(pos < t->kcov_size)) {
90 WRITE_ONCE(area[0], pos);
94 EXPORT_SYMBOL(__sanitizer_cov_trace_pc);
96 static void kcov_get(struct kcov *kcov)
98 atomic_inc(&kcov->refcount);
101 static void kcov_put(struct kcov *kcov)
103 if (atomic_dec_and_test(&kcov->refcount)) {
109 void kcov_task_init(struct task_struct *t)
111 WRITE_ONCE(t->kcov_mode, KCOV_MODE_DISABLED);
118 void kcov_task_exit(struct task_struct *t)
125 spin_lock(&kcov->lock);
126 if (WARN_ON(kcov->t != t)) {
127 spin_unlock(&kcov->lock);
130 /* Just to not leave dangling references behind. */
133 spin_unlock(&kcov->lock);
137 static int kcov_mmap(struct file *filep, struct vm_area_struct *vma)
141 struct kcov *kcov = vma->vm_file->private_data;
142 unsigned long size, off;
145 area = vmalloc_user(vma->vm_end - vma->vm_start);
149 spin_lock(&kcov->lock);
150 size = kcov->size * sizeof(unsigned long);
151 if (kcov->mode == KCOV_MODE_DISABLED || vma->vm_pgoff != 0 ||
152 vma->vm_end - vma->vm_start != size) {
158 vma->vm_flags |= VM_DONTEXPAND;
159 spin_unlock(&kcov->lock);
160 for (off = 0; off < size; off += PAGE_SIZE) {
161 page = vmalloc_to_page(kcov->area + off);
162 if (vm_insert_page(vma, vma->vm_start + off, page))
163 WARN_ONCE(1, "vm_insert_page() failed");
168 spin_unlock(&kcov->lock);
173 static int kcov_open(struct inode *inode, struct file *filep)
177 kcov = kzalloc(sizeof(*kcov), GFP_KERNEL);
180 atomic_set(&kcov->refcount, 1);
181 spin_lock_init(&kcov->lock);
182 filep->private_data = kcov;
183 return nonseekable_open(inode, filep);
186 static int kcov_close(struct inode *inode, struct file *filep)
188 kcov_put(filep->private_data);
192 static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,
195 struct task_struct *t;
196 unsigned long size, unused;
199 case KCOV_INIT_TRACE:
201 * Enable kcov in trace mode and setup buffer size.
202 * Must happen before anything else.
204 if (kcov->mode != KCOV_MODE_DISABLED)
207 * Size must be at least 2 to hold current position and one PC.
208 * Later we allocate size * sizeof(unsigned long) memory,
209 * that must not overflow.
212 if (size < 2 || size > INT_MAX / sizeof(unsigned long))
215 kcov->mode = KCOV_MODE_TRACE;
219 * Enable coverage for the current task.
220 * At this point user must have been enabled trace mode,
221 * and mmapped the file. Coverage collection is disabled only
222 * at task exit or voluntary by KCOV_DISABLE. After that it can
223 * be enabled for another task.
226 if (unused != 0 || kcov->mode == KCOV_MODE_DISABLED ||
230 if (kcov->t != NULL || t->kcov != NULL)
232 /* Cache in task struct for performance. */
233 t->kcov_size = kcov->size;
234 t->kcov_area = kcov->area;
235 /* See comment in __sanitizer_cov_trace_pc(). */
237 WRITE_ONCE(t->kcov_mode, kcov->mode);
240 /* This is put either in kcov_task_exit() or in KCOV_DISABLE. */
244 /* Disable coverage for the current task. */
246 if (unused != 0 || current->kcov != kcov)
249 if (WARN_ON(kcov->t != t))
260 static long kcov_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
265 kcov = filep->private_data;
266 spin_lock(&kcov->lock);
267 res = kcov_ioctl_locked(kcov, cmd, arg);
268 spin_unlock(&kcov->lock);
272 static const struct file_operations kcov_fops = {
274 .unlocked_ioctl = kcov_ioctl,
275 .compat_ioctl = kcov_ioctl,
277 .release = kcov_close,
280 static int __init kcov_init(void)
283 * The kcov debugfs file won't ever get removed and thus,
284 * there is no need to protect it against removal races. The
285 * use of debugfs_create_file_unsafe() is actually safe here.
287 if (!debugfs_create_file_unsafe("kcov", 0600, NULL, NULL, &kcov_fops)) {
288 pr_err("failed to create kcov in debugfs\n");
294 device_initcall(kcov_init);