1 // SPDX-License-Identifier: GPL-2.0
2 #define pr_fmt(fmt) "kcov: " fmt
3
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>
11 #include <linux/fs.h>
12 #include <linux/init.h>
13 #include <linux/mm.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>
24
25 /*
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)
32 */
33 struct kcov {
34 /*
35 * Reference counter. We keep one for:
36 * - opened file descriptor
37 * - task with enabled coverage (we can't unwire it from another task)
38 */
39 atomic_t refcount;
40 /* The lock protects mode, size, area and t. */
41 spinlock_t lock;
42 enum kcov_mode mode;
43 /* Size of arena (in long's for KCOV_MODE_TRACE). */
44 unsigned size;
45 /* Coverage buffer shared with user space. */
46 void *area;
47 /* Task for which we collect coverage, or NULL. */
48 struct task_struct *t;
49 };
50
51 /*
52 * Entry point from instrumented code.
53 * This is called once per basic-block/edge.
54 */
__sanitizer_cov_trace_pc(void)55 void notrace __sanitizer_cov_trace_pc(void)
56 {
57 struct task_struct *t;
58 enum kcov_mode mode;
59
60 t = current;
61 /*
62 * We are interested in code coverage as a function of a syscall inputs,
63 * so we ignore code executed in interrupts.
64 */
65 if (!t || !in_task())
66 return;
67 mode = READ_ONCE(t->kcov_mode);
68 if (mode == KCOV_MODE_TRACE) {
69 unsigned long *area;
70 unsigned long pos;
71 unsigned long ip = _RET_IP_;
72
73 #ifdef CONFIG_RANDOMIZE_BASE
74 ip -= kaslr_offset();
75 #endif
76
77 /*
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().
83 */
84 barrier();
85 area = t->kcov_area;
86 /* The first word is number of subsequent PCs. */
87 pos = READ_ONCE(area[0]) + 1;
88 if (likely(pos < t->kcov_size)) {
89 area[pos] = ip;
90 WRITE_ONCE(area[0], pos);
91 }
92 }
93 }
94 EXPORT_SYMBOL(__sanitizer_cov_trace_pc);
95
kcov_get(struct kcov * kcov)96 static void kcov_get(struct kcov *kcov)
97 {
98 atomic_inc(&kcov->refcount);
99 }
100
kcov_put(struct kcov * kcov)101 static void kcov_put(struct kcov *kcov)
102 {
103 if (atomic_dec_and_test(&kcov->refcount)) {
104 vfree(kcov->area);
105 kfree(kcov);
106 }
107 }
108
kcov_task_init(struct task_struct * t)109 void kcov_task_init(struct task_struct *t)
110 {
111 WRITE_ONCE(t->kcov_mode, KCOV_MODE_DISABLED);
112 barrier();
113 t->kcov_size = 0;
114 t->kcov_area = NULL;
115 t->kcov = NULL;
116 }
117
kcov_task_exit(struct task_struct * t)118 void kcov_task_exit(struct task_struct *t)
119 {
120 struct kcov *kcov;
121
122 kcov = t->kcov;
123 if (kcov == NULL)
124 return;
125 spin_lock(&kcov->lock);
126 if (WARN_ON(kcov->t != t)) {
127 spin_unlock(&kcov->lock);
128 return;
129 }
130 /* Just to not leave dangling references behind. */
131 kcov_task_init(t);
132 kcov->t = NULL;
133 spin_unlock(&kcov->lock);
134 kcov_put(kcov);
135 }
136
kcov_mmap(struct file * filep,struct vm_area_struct * vma)137 static int kcov_mmap(struct file *filep, struct vm_area_struct *vma)
138 {
139 int res = 0;
140 void *area;
141 struct kcov *kcov = vma->vm_file->private_data;
142 unsigned long size, off;
143 struct page *page;
144
145 area = vmalloc_user(vma->vm_end - vma->vm_start);
146 if (!area)
147 return -ENOMEM;
148
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) {
153 res = -EINVAL;
154 goto exit;
155 }
156 if (!kcov->area) {
157 kcov->area = area;
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");
164 }
165 return 0;
166 }
167 exit:
168 spin_unlock(&kcov->lock);
169 vfree(area);
170 return res;
171 }
172
kcov_open(struct inode * inode,struct file * filep)173 static int kcov_open(struct inode *inode, struct file *filep)
174 {
175 struct kcov *kcov;
176
177 kcov = kzalloc(sizeof(*kcov), GFP_KERNEL);
178 if (!kcov)
179 return -ENOMEM;
180 atomic_set(&kcov->refcount, 1);
181 spin_lock_init(&kcov->lock);
182 filep->private_data = kcov;
183 return nonseekable_open(inode, filep);
184 }
185
kcov_close(struct inode * inode,struct file * filep)186 static int kcov_close(struct inode *inode, struct file *filep)
187 {
188 kcov_put(filep->private_data);
189 return 0;
190 }
191
kcov_ioctl_locked(struct kcov * kcov,unsigned int cmd,unsigned long arg)192 static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,
193 unsigned long arg)
194 {
195 struct task_struct *t;
196 unsigned long size, unused;
197
198 switch (cmd) {
199 case KCOV_INIT_TRACE:
200 /*
201 * Enable kcov in trace mode and setup buffer size.
202 * Must happen before anything else.
203 */
204 if (kcov->mode != KCOV_MODE_DISABLED)
205 return -EBUSY;
206 /*
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.
210 */
211 size = arg;
212 if (size < 2 || size > INT_MAX / sizeof(unsigned long))
213 return -EINVAL;
214 kcov->size = size;
215 kcov->mode = KCOV_MODE_TRACE;
216 return 0;
217 case KCOV_ENABLE:
218 /*
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.
224 */
225 unused = arg;
226 if (unused != 0 || kcov->mode == KCOV_MODE_DISABLED ||
227 kcov->area == NULL)
228 return -EINVAL;
229 t = current;
230 if (kcov->t != NULL || t->kcov != NULL)
231 return -EBUSY;
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(). */
236 barrier();
237 WRITE_ONCE(t->kcov_mode, kcov->mode);
238 t->kcov = kcov;
239 kcov->t = t;
240 /* This is put either in kcov_task_exit() or in KCOV_DISABLE. */
241 kcov_get(kcov);
242 return 0;
243 case KCOV_DISABLE:
244 /* Disable coverage for the current task. */
245 unused = arg;
246 if (unused != 0 || current->kcov != kcov)
247 return -EINVAL;
248 t = current;
249 if (WARN_ON(kcov->t != t))
250 return -EINVAL;
251 kcov_task_init(t);
252 kcov->t = NULL;
253 kcov_put(kcov);
254 return 0;
255 default:
256 return -ENOTTY;
257 }
258 }
259
kcov_ioctl(struct file * filep,unsigned int cmd,unsigned long arg)260 static long kcov_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
261 {
262 struct kcov *kcov;
263 int res;
264
265 kcov = filep->private_data;
266 spin_lock(&kcov->lock);
267 res = kcov_ioctl_locked(kcov, cmd, arg);
268 spin_unlock(&kcov->lock);
269 return res;
270 }
271
272 static const struct file_operations kcov_fops = {
273 .open = kcov_open,
274 .unlocked_ioctl = kcov_ioctl,
275 .compat_ioctl = kcov_ioctl,
276 .mmap = kcov_mmap,
277 .release = kcov_close,
278 };
279
kcov_init(void)280 static int __init kcov_init(void)
281 {
282 /*
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.
286 */
287 if (!debugfs_create_file_unsafe("kcov", 0600, NULL, NULL, &kcov_fops)) {
288 pr_err("failed to create kcov in debugfs\n");
289 return -ENOMEM;
290 }
291 return 0;
292 }
293
294 device_initcall(kcov_init);
295