blob: 3cbb0c879705f7a29f1d5bfad58551c098e69432 [file] [log] [blame]
Dmitry Vyukov5c9a8752016-03-22 14:27:30 -07001#define pr_fmt(fmt) "kcov: " fmt
2
Andrey Ryabinin36f05ae2016-04-28 16:18:55 -07003#define DISABLE_BRANCH_PROFILING
Dmitry Vyukov5c9a8752016-03-22 14:27:30 -07004#include <linux/compiler.h>
5#include <linux/types.h>
6#include <linux/file.h>
7#include <linux/fs.h>
8#include <linux/mm.h>
9#include <linux/printk.h>
Kefeng Wang166ad0e2016-12-07 14:44:36 -080010#include <linux/sched.h>
Dmitry Vyukov5c9a8752016-03-22 14:27:30 -070011#include <linux/slab.h>
12#include <linux/spinlock.h>
13#include <linux/vmalloc.h>
14#include <linux/debugfs.h>
15#include <linux/uaccess.h>
16#include <linux/kcov.h>
17
18/*
19 * kcov descriptor (one per opened debugfs file).
20 * State transitions of the descriptor:
21 * - initial state after open()
22 * - then there must be a single ioctl(KCOV_INIT_TRACE) call
23 * - then, mmap() call (several calls are allowed but not useful)
24 * - then, repeated enable/disable for a task (only one task a time allowed)
25 */
26struct kcov {
27 /*
28 * Reference counter. We keep one for:
29 * - opened file descriptor
30 * - task with enabled coverage (we can't unwire it from another task)
31 */
32 atomic_t refcount;
33 /* The lock protects mode, size, area and t. */
34 spinlock_t lock;
35 enum kcov_mode mode;
36 /* Size of arena (in long's for KCOV_MODE_TRACE). */
37 unsigned size;
38 /* Coverage buffer shared with user space. */
39 void *area;
40 /* Task for which we collect coverage, or NULL. */
41 struct task_struct *t;
42};
43
44/*
45 * Entry point from instrumented code.
46 * This is called once per basic-block/edge.
47 */
James Morsebdab42d2016-04-28 16:18:52 -070048void notrace __sanitizer_cov_trace_pc(void)
Dmitry Vyukov5c9a8752016-03-22 14:27:30 -070049{
50 struct task_struct *t;
51 enum kcov_mode mode;
52
53 t = current;
54 /*
55 * We are interested in code coverage as a function of a syscall inputs,
56 * so we ignore code executed in interrupts.
Andrey Konovalovb274c0b2016-10-27 17:46:21 -070057 * The checks for whether we are in an interrupt are open-coded, because
58 * 1. We can't use in_interrupt() here, since it also returns true
59 * when we are inside local_bh_disable() section.
60 * 2. We don't want to use (in_irq() | in_serving_softirq() | in_nmi()),
61 * since that leads to slower generated code (three separate tests,
62 * one for each of the flags).
Dmitry Vyukov5c9a8752016-03-22 14:27:30 -070063 */
Andrey Konovalovb274c0b2016-10-27 17:46:21 -070064 if (!t || (preempt_count() & (HARDIRQ_MASK | SOFTIRQ_OFFSET
65 | NMI_MASK)))
Dmitry Vyukov5c9a8752016-03-22 14:27:30 -070066 return;
67 mode = READ_ONCE(t->kcov_mode);
68 if (mode == KCOV_MODE_TRACE) {
69 unsigned long *area;
70 unsigned long pos;
71
72 /*
73 * There is some code that runs in interrupts but for which
74 * in_interrupt() returns false (e.g. preempt_schedule_irq()).
75 * READ_ONCE()/barrier() effectively provides load-acquire wrt
76 * interrupts, there are paired barrier()/WRITE_ONCE() in
77 * kcov_ioctl_locked().
78 */
79 barrier();
80 area = t->kcov_area;
81 /* The first word is number of subsequent PCs. */
82 pos = READ_ONCE(area[0]) + 1;
83 if (likely(pos < t->kcov_size)) {
84 area[pos] = _RET_IP_;
85 WRITE_ONCE(area[0], pos);
86 }
87 }
88}
89EXPORT_SYMBOL(__sanitizer_cov_trace_pc);
90
91static void kcov_get(struct kcov *kcov)
92{
93 atomic_inc(&kcov->refcount);
94}
95
96static void kcov_put(struct kcov *kcov)
97{
98 if (atomic_dec_and_test(&kcov->refcount)) {
99 vfree(kcov->area);
100 kfree(kcov);
101 }
102}
103
104void kcov_task_init(struct task_struct *t)
105{
106 t->kcov_mode = KCOV_MODE_DISABLED;
107 t->kcov_size = 0;
108 t->kcov_area = NULL;
109 t->kcov = NULL;
110}
111
112void kcov_task_exit(struct task_struct *t)
113{
114 struct kcov *kcov;
115
116 kcov = t->kcov;
117 if (kcov == NULL)
118 return;
119 spin_lock(&kcov->lock);
120 if (WARN_ON(kcov->t != t)) {
121 spin_unlock(&kcov->lock);
122 return;
123 }
124 /* Just to not leave dangling references behind. */
125 kcov_task_init(t);
126 kcov->t = NULL;
127 spin_unlock(&kcov->lock);
128 kcov_put(kcov);
129}
130
131static int kcov_mmap(struct file *filep, struct vm_area_struct *vma)
132{
133 int res = 0;
134 void *area;
135 struct kcov *kcov = vma->vm_file->private_data;
136 unsigned long size, off;
137 struct page *page;
138
139 area = vmalloc_user(vma->vm_end - vma->vm_start);
140 if (!area)
141 return -ENOMEM;
142
143 spin_lock(&kcov->lock);
144 size = kcov->size * sizeof(unsigned long);
145 if (kcov->mode == KCOV_MODE_DISABLED || vma->vm_pgoff != 0 ||
146 vma->vm_end - vma->vm_start != size) {
147 res = -EINVAL;
148 goto exit;
149 }
150 if (!kcov->area) {
151 kcov->area = area;
152 vma->vm_flags |= VM_DONTEXPAND;
153 spin_unlock(&kcov->lock);
154 for (off = 0; off < size; off += PAGE_SIZE) {
155 page = vmalloc_to_page(kcov->area + off);
156 if (vm_insert_page(vma, vma->vm_start + off, page))
157 WARN_ONCE(1, "vm_insert_page() failed");
158 }
159 return 0;
160 }
161exit:
162 spin_unlock(&kcov->lock);
163 vfree(area);
164 return res;
165}
166
167static int kcov_open(struct inode *inode, struct file *filep)
168{
169 struct kcov *kcov;
170
171 kcov = kzalloc(sizeof(*kcov), GFP_KERNEL);
172 if (!kcov)
173 return -ENOMEM;
174 atomic_set(&kcov->refcount, 1);
175 spin_lock_init(&kcov->lock);
176 filep->private_data = kcov;
177 return nonseekable_open(inode, filep);
178}
179
180static int kcov_close(struct inode *inode, struct file *filep)
181{
182 kcov_put(filep->private_data);
183 return 0;
184}
185
186static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,
187 unsigned long arg)
188{
189 struct task_struct *t;
190 unsigned long size, unused;
191
192 switch (cmd) {
193 case KCOV_INIT_TRACE:
194 /*
195 * Enable kcov in trace mode and setup buffer size.
196 * Must happen before anything else.
197 */
198 if (kcov->mode != KCOV_MODE_DISABLED)
199 return -EBUSY;
200 /*
201 * Size must be at least 2 to hold current position and one PC.
202 * Later we allocate size * sizeof(unsigned long) memory,
203 * that must not overflow.
204 */
205 size = arg;
206 if (size < 2 || size > INT_MAX / sizeof(unsigned long))
207 return -EINVAL;
208 kcov->size = size;
209 kcov->mode = KCOV_MODE_TRACE;
210 return 0;
211 case KCOV_ENABLE:
212 /*
213 * Enable coverage for the current task.
214 * At this point user must have been enabled trace mode,
215 * and mmapped the file. Coverage collection is disabled only
216 * at task exit or voluntary by KCOV_DISABLE. After that it can
217 * be enabled for another task.
218 */
219 unused = arg;
220 if (unused != 0 || kcov->mode == KCOV_MODE_DISABLED ||
221 kcov->area == NULL)
222 return -EINVAL;
223 if (kcov->t != NULL)
224 return -EBUSY;
225 t = current;
226 /* Cache in task struct for performance. */
227 t->kcov_size = kcov->size;
228 t->kcov_area = kcov->area;
229 /* See comment in __sanitizer_cov_trace_pc(). */
230 barrier();
231 WRITE_ONCE(t->kcov_mode, kcov->mode);
232 t->kcov = kcov;
233 kcov->t = t;
234 /* This is put either in kcov_task_exit() or in KCOV_DISABLE. */
235 kcov_get(kcov);
236 return 0;
237 case KCOV_DISABLE:
238 /* Disable coverage for the current task. */
239 unused = arg;
240 if (unused != 0 || current->kcov != kcov)
241 return -EINVAL;
242 t = current;
243 if (WARN_ON(kcov->t != t))
244 return -EINVAL;
245 kcov_task_init(t);
246 kcov->t = NULL;
247 kcov_put(kcov);
248 return 0;
249 default:
250 return -ENOTTY;
251 }
252}
253
254static long kcov_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
255{
256 struct kcov *kcov;
257 int res;
258
259 kcov = filep->private_data;
260 spin_lock(&kcov->lock);
261 res = kcov_ioctl_locked(kcov, cmd, arg);
262 spin_unlock(&kcov->lock);
263 return res;
264}
265
266static const struct file_operations kcov_fops = {
267 .open = kcov_open,
268 .unlocked_ioctl = kcov_ioctl,
269 .mmap = kcov_mmap,
270 .release = kcov_close,
271};
272
273static int __init kcov_init(void)
274{
Nicolai Stangedf4565f2016-05-24 14:05:05 +0200275 /*
276 * The kcov debugfs file won't ever get removed and thus,
277 * there is no need to protect it against removal races. The
278 * use of debugfs_create_file_unsafe() is actually safe here.
279 */
280 if (!debugfs_create_file_unsafe("kcov", 0600, NULL, NULL, &kcov_fops)) {
Dmitry Vyukov5c9a8752016-03-22 14:27:30 -0700281 pr_err("failed to create kcov in debugfs\n");
282 return -ENOMEM;
283 }
284 return 0;
285}
286
287device_initcall(kcov_init);