projects/linux·blob v4.8 · refs

279 lines · 6.6 KiB

1#define pr_fmt(fmt) "kcov: " fmt
2
3#define DISABLE_BRANCH_PROFILING
4#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>
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>
16
17/*
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)
24 */
25struct kcov {
26 /*
27 * Reference counter. We keep one for:
28 * - opened file descriptor
29 * - task with enabled coverage (we can't unwire it from another task)
30 */
31 atomic_t refcount;
32 /* The lock protects mode, size, area and t. */
33 spinlock_t lock;
34 enum kcov_mode mode;
35 /* Size of arena (in long's for KCOV_MODE_TRACE). */
36 unsigned size;
37 /* Coverage buffer shared with user space. */
38 void *area;
39 /* Task for which we collect coverage, or NULL. */
40 struct task_struct *t;
41};
42
43/*
44 * Entry point from instrumented code.
45 * This is called once per basic-block/edge.
46 */
47void notrace __sanitizer_cov_trace_pc(void)
48{
49 struct task_struct *t;
50 enum kcov_mode mode;
51
52 t = current;
53 /*
54 * We are interested in code coverage as a function of a syscall inputs,
55 * so we ignore code executed in interrupts.
56 */
57 if (!t || in_interrupt())
58 return;
59 mode = READ_ONCE(t->kcov_mode);
60 if (mode == KCOV_MODE_TRACE) {
61 unsigned long *area;
62 unsigned long pos;
63
64 /*
65 * There is some code that runs in interrupts but for which
66 * in_interrupt() returns false (e.g. preempt_schedule_irq()).
67 * READ_ONCE()/barrier() effectively provides load-acquire wrt
68 * interrupts, there are paired barrier()/WRITE_ONCE() in
69 * kcov_ioctl_locked().
70 */
71 barrier();
72 area = t->kcov_area;
73 /* The first word is number of subsequent PCs. */
74 pos = READ_ONCE(area[0]) + 1;
75 if (likely(pos < t->kcov_size)) {
76 area[pos] = _RET_IP_;
77 WRITE_ONCE(area[0], pos);
78 }
79 }
80}
81EXPORT_SYMBOL(__sanitizer_cov_trace_pc);
82
83static void kcov_get(struct kcov *kcov)
84{
85 atomic_inc(&kcov->refcount);
86}
87
88static void kcov_put(struct kcov *kcov)
89{
90 if (atomic_dec_and_test(&kcov->refcount)) {
91 vfree(kcov->area);
92 kfree(kcov);
93 }
94}
95
96void kcov_task_init(struct task_struct *t)
97{
98 t->kcov_mode = KCOV_MODE_DISABLED;
99 t->kcov_size = 0;
100 t->kcov_area = NULL;
101 t->kcov = NULL;
102}
103
104void kcov_task_exit(struct task_struct *t)
105{
106 struct kcov *kcov;
107
108 kcov = t->kcov;
109 if (kcov == NULL)
110 return;
111 spin_lock(&kcov->lock);
112 if (WARN_ON(kcov->t != t)) {
113 spin_unlock(&kcov->lock);
114 return;
115 }
116 /* Just to not leave dangling references behind. */
117 kcov_task_init(t);
118 kcov->t = NULL;
119 spin_unlock(&kcov->lock);
120 kcov_put(kcov);
121}
122
123static int kcov_mmap(struct file *filep, struct vm_area_struct *vma)
124{
125 int res = 0;
126 void *area;
127 struct kcov *kcov = vma->vm_file->private_data;
128 unsigned long size, off;
129 struct page *page;
130
131 area = vmalloc_user(vma->vm_end - vma->vm_start);
132 if (!area)
133 return -ENOMEM;
134
135 spin_lock(&kcov->lock);
136 size = kcov->size * sizeof(unsigned long);
137 if (kcov->mode == KCOV_MODE_DISABLED || vma->vm_pgoff != 0 ||
138 vma->vm_end - vma->vm_start != size) {
139 res = -EINVAL;
140 goto exit;
141 }
142 if (!kcov->area) {
143 kcov->area = area;
144 vma->vm_flags |= VM_DONTEXPAND;
145 spin_unlock(&kcov->lock);
146 for (off = 0; off < size; off += PAGE_SIZE) {
147 page = vmalloc_to_page(kcov->area + off);
148 if (vm_insert_page(vma, vma->vm_start + off, page))
149 WARN_ONCE(1, "vm_insert_page() failed");
150 }
151 return 0;
152 }
153exit:
154 spin_unlock(&kcov->lock);
155 vfree(area);
156 return res;
157}
158
159static int kcov_open(struct inode *inode, struct file *filep)
160{
161 struct kcov *kcov;
162
163 kcov = kzalloc(sizeof(*kcov), GFP_KERNEL);
164 if (!kcov)
165 return -ENOMEM;
166 atomic_set(&kcov->refcount, 1);
167 spin_lock_init(&kcov->lock);
168 filep->private_data = kcov;
169 return nonseekable_open(inode, filep);
170}
171
172static int kcov_close(struct inode *inode, struct file *filep)
173{
174 kcov_put(filep->private_data);
175 return 0;
176}
177
178static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,
179 unsigned long arg)
180{
181 struct task_struct *t;
182 unsigned long size, unused;
183
184 switch (cmd) {
185 case KCOV_INIT_TRACE:
186 /*
187 * Enable kcov in trace mode and setup buffer size.
188 * Must happen before anything else.
189 */
190 if (kcov->mode != KCOV_MODE_DISABLED)
191 return -EBUSY;
192 /*
193 * Size must be at least 2 to hold current position and one PC.
194 * Later we allocate size * sizeof(unsigned long) memory,
195 * that must not overflow.
196 */
197 size = arg;
198 if (size < 2 || size > INT_MAX / sizeof(unsigned long))
199 return -EINVAL;
200 kcov->size = size;
201 kcov->mode = KCOV_MODE_TRACE;
202 return 0;
203 case KCOV_ENABLE:
204 /*
205 * Enable coverage for the current task.
206 * At this point user must have been enabled trace mode,
207 * and mmapped the file. Coverage collection is disabled only
208 * at task exit or voluntary by KCOV_DISABLE. After that it can
209 * be enabled for another task.
210 */
211 unused = arg;
212 if (unused != 0 || kcov->mode == KCOV_MODE_DISABLED ||
213 kcov->area == NULL)
214 return -EINVAL;
215 if (kcov->t != NULL)
216 return -EBUSY;
217 t = current;
218 /* Cache in task struct for performance. */
219 t->kcov_size = kcov->size;
220 t->kcov_area = kcov->area;
221 /* See comment in __sanitizer_cov_trace_pc(). */
222 barrier();
223 WRITE_ONCE(t->kcov_mode, kcov->mode);
224 t->kcov = kcov;
225 kcov->t = t;
226 /* This is put either in kcov_task_exit() or in KCOV_DISABLE. */
227 kcov_get(kcov);
228 return 0;
229 case KCOV_DISABLE:
230 /* Disable coverage for the current task. */
231 unused = arg;
232 if (unused != 0 || current->kcov != kcov)
233 return -EINVAL;
234 t = current;
235 if (WARN_ON(kcov->t != t))
236 return -EINVAL;
237 kcov_task_init(t);
238 kcov->t = NULL;
239 kcov_put(kcov);
240 return 0;
241 default:
242 return -ENOTTY;
243 }
244}
245
246static long kcov_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
247{
248 struct kcov *kcov;
249 int res;
250
251 kcov = filep->private_data;
252 spin_lock(&kcov->lock);
253 res = kcov_ioctl_locked(kcov, cmd, arg);
254 spin_unlock(&kcov->lock);
255 return res;
256}
257
258static const struct file_operations kcov_fops = {
259 .open = kcov_open,
260 .unlocked_ioctl = kcov_ioctl,
261 .mmap = kcov_mmap,
262 .release = kcov_close,
263};
264
265static int __init kcov_init(void)
266{
267 /*
268 * The kcov debugfs file won't ever get removed and thus,
269 * there is no need to protect it against removal races. The
270 * use of debugfs_create_file_unsafe() is actually safe here.
271 */
272 if (!debugfs_create_file_unsafe("kcov", 0600, NULL, NULL, &kcov_fops)) {
273 pr_err("failed to create kcov in debugfs\n");
274 return -ENOMEM;
275 }
276 return 0;
277}
278
279device_initcall(kcov_init);