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TOMOYO Linux Cross Reference
Linux/kernel/kcov.c

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  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 /* Number of 64-bit words written per one comparison: */
 26 #define KCOV_WORDS_PER_CMP 4
 27 
 28 /*
 29  * kcov descriptor (one per opened debugfs file).
 30  * State transitions of the descriptor:
 31  *  - initial state after open()
 32  *  - then there must be a single ioctl(KCOV_INIT_TRACE) call
 33  *  - then, mmap() call (several calls are allowed but not useful)
 34  *  - then, ioctl(KCOV_ENABLE, arg), where arg is
 35  *      KCOV_TRACE_PC - to trace only the PCs
 36  *      or
 37  *      KCOV_TRACE_CMP - to trace only the comparison operands
 38  *  - then, ioctl(KCOV_DISABLE) to disable the task.
 39  * Enabling/disabling ioctls can be repeated (only one task a time allowed).
 40  */
 41 struct kcov {
 42         /*
 43          * Reference counter. We keep one for:
 44          *  - opened file descriptor
 45          *  - task with enabled coverage (we can't unwire it from another task)
 46          */
 47         atomic_t                refcount;
 48         /* The lock protects mode, size, area and t. */
 49         spinlock_t              lock;
 50         enum kcov_mode          mode;
 51         /* Size of arena (in long's for KCOV_MODE_TRACE). */
 52         unsigned                size;
 53         /* Coverage buffer shared with user space. */
 54         void                    *area;
 55         /* Task for which we collect coverage, or NULL. */
 56         struct task_struct      *t;
 57 };
 58 
 59 static notrace bool check_kcov_mode(enum kcov_mode needed_mode, struct task_struct *t)
 60 {
 61         unsigned int mode;
 62 
 63         /*
 64          * We are interested in code coverage as a function of a syscall inputs,
 65          * so we ignore code executed in interrupts.
 66          */
 67         if (!in_task())
 68                 return false;
 69         mode = READ_ONCE(t->kcov_mode);
 70         /*
 71          * There is some code that runs in interrupts but for which
 72          * in_interrupt() returns false (e.g. preempt_schedule_irq()).
 73          * READ_ONCE()/barrier() effectively provides load-acquire wrt
 74          * interrupts, there are paired barrier()/WRITE_ONCE() in
 75          * kcov_ioctl_locked().
 76          */
 77         barrier();
 78         return mode == needed_mode;
 79 }
 80 
 81 static notrace unsigned long canonicalize_ip(unsigned long ip)
 82 {
 83 #ifdef CONFIG_RANDOMIZE_BASE
 84         ip -= kaslr_offset();
 85 #endif
 86         return ip;
 87 }
 88 
 89 /*
 90  * Entry point from instrumented code.
 91  * This is called once per basic-block/edge.
 92  */
 93 void notrace __sanitizer_cov_trace_pc(void)
 94 {
 95         struct task_struct *t;
 96         unsigned long *area;
 97         unsigned long ip = canonicalize_ip(_RET_IP_);
 98         unsigned long pos;
 99 
100         t = current;
101         if (!check_kcov_mode(KCOV_MODE_TRACE_PC, t))
102                 return;
103 
104         area = t->kcov_area;
105         /* The first 64-bit word is the number of subsequent PCs. */
106         pos = READ_ONCE(area[0]) + 1;
107         if (likely(pos < t->kcov_size)) {
108                 area[pos] = ip;
109                 WRITE_ONCE(area[0], pos);
110         }
111 }
112 EXPORT_SYMBOL(__sanitizer_cov_trace_pc);
113 
114 #ifdef CONFIG_KCOV_ENABLE_COMPARISONS
115 static void notrace write_comp_data(u64 type, u64 arg1, u64 arg2, u64 ip)
116 {
117         struct task_struct *t;
118         u64 *area;
119         u64 count, start_index, end_pos, max_pos;
120 
121         t = current;
122         if (!check_kcov_mode(KCOV_MODE_TRACE_CMP, t))
123                 return;
124 
125         ip = canonicalize_ip(ip);
126 
127         /*
128          * We write all comparison arguments and types as u64.
129          * The buffer was allocated for t->kcov_size unsigned longs.
130          */
131         area = (u64 *)t->kcov_area;
132         max_pos = t->kcov_size * sizeof(unsigned long);
133 
134         count = READ_ONCE(area[0]);
135 
136         /* Every record is KCOV_WORDS_PER_CMP 64-bit words. */
137         start_index = 1 + count * KCOV_WORDS_PER_CMP;
138         end_pos = (start_index + KCOV_WORDS_PER_CMP) * sizeof(u64);
139         if (likely(end_pos <= max_pos)) {
140                 area[start_index] = type;
141                 area[start_index + 1] = arg1;
142                 area[start_index + 2] = arg2;
143                 area[start_index + 3] = ip;
144                 WRITE_ONCE(area[0], count + 1);
145         }
146 }
147 
148 void notrace __sanitizer_cov_trace_cmp1(u8 arg1, u8 arg2)
149 {
150         write_comp_data(KCOV_CMP_SIZE(0), arg1, arg2, _RET_IP_);
151 }
152 EXPORT_SYMBOL(__sanitizer_cov_trace_cmp1);
153 
154 void notrace __sanitizer_cov_trace_cmp2(u16 arg1, u16 arg2)
155 {
156         write_comp_data(KCOV_CMP_SIZE(1), arg1, arg2, _RET_IP_);
157 }
158 EXPORT_SYMBOL(__sanitizer_cov_trace_cmp2);
159 
160 void notrace __sanitizer_cov_trace_cmp4(u32 arg1, u32 arg2)
161 {
162         write_comp_data(KCOV_CMP_SIZE(2), arg1, arg2, _RET_IP_);
163 }
164 EXPORT_SYMBOL(__sanitizer_cov_trace_cmp4);
165 
166 void notrace __sanitizer_cov_trace_cmp8(u64 arg1, u64 arg2)
167 {
168         write_comp_data(KCOV_CMP_SIZE(3), arg1, arg2, _RET_IP_);
169 }
170 EXPORT_SYMBOL(__sanitizer_cov_trace_cmp8);
171 
172 void notrace __sanitizer_cov_trace_const_cmp1(u8 arg1, u8 arg2)
173 {
174         write_comp_data(KCOV_CMP_SIZE(0) | KCOV_CMP_CONST, arg1, arg2,
175                         _RET_IP_);
176 }
177 EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp1);
178 
179 void notrace __sanitizer_cov_trace_const_cmp2(u16 arg1, u16 arg2)
180 {
181         write_comp_data(KCOV_CMP_SIZE(1) | KCOV_CMP_CONST, arg1, arg2,
182                         _RET_IP_);
183 }
184 EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp2);
185 
186 void notrace __sanitizer_cov_trace_const_cmp4(u32 arg1, u32 arg2)
187 {
188         write_comp_data(KCOV_CMP_SIZE(2) | KCOV_CMP_CONST, arg1, arg2,
189                         _RET_IP_);
190 }
191 EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp4);
192 
193 void notrace __sanitizer_cov_trace_const_cmp8(u64 arg1, u64 arg2)
194 {
195         write_comp_data(KCOV_CMP_SIZE(3) | KCOV_CMP_CONST, arg1, arg2,
196                         _RET_IP_);
197 }
198 EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp8);
199 
200 void notrace __sanitizer_cov_trace_switch(u64 val, u64 *cases)
201 {
202         u64 i;
203         u64 count = cases[0];
204         u64 size = cases[1];
205         u64 type = KCOV_CMP_CONST;
206 
207         switch (size) {
208         case 8:
209                 type |= KCOV_CMP_SIZE(0);
210                 break;
211         case 16:
212                 type |= KCOV_CMP_SIZE(1);
213                 break;
214         case 32:
215                 type |= KCOV_CMP_SIZE(2);
216                 break;
217         case 64:
218                 type |= KCOV_CMP_SIZE(3);
219                 break;
220         default:
221                 return;
222         }
223         for (i = 0; i < count; i++)
224                 write_comp_data(type, cases[i + 2], val, _RET_IP_);
225 }
226 EXPORT_SYMBOL(__sanitizer_cov_trace_switch);
227 #endif /* ifdef CONFIG_KCOV_ENABLE_COMPARISONS */
228 
229 static void kcov_get(struct kcov *kcov)
230 {
231         atomic_inc(&kcov->refcount);
232 }
233 
234 static void kcov_put(struct kcov *kcov)
235 {
236         if (atomic_dec_and_test(&kcov->refcount)) {
237                 vfree(kcov->area);
238                 kfree(kcov);
239         }
240 }
241 
242 void kcov_task_init(struct task_struct *t)
243 {
244         WRITE_ONCE(t->kcov_mode, KCOV_MODE_DISABLED);
245         barrier();
246         t->kcov_size = 0;
247         t->kcov_area = NULL;
248         t->kcov = NULL;
249 }
250 
251 void kcov_task_exit(struct task_struct *t)
252 {
253         struct kcov *kcov;
254 
255         kcov = t->kcov;
256         if (kcov == NULL)
257                 return;
258         spin_lock(&kcov->lock);
259         if (WARN_ON(kcov->t != t)) {
260                 spin_unlock(&kcov->lock);
261                 return;
262         }
263         /* Just to not leave dangling references behind. */
264         kcov_task_init(t);
265         kcov->t = NULL;
266         kcov->mode = KCOV_MODE_INIT;
267         spin_unlock(&kcov->lock);
268         kcov_put(kcov);
269 }
270 
271 static int kcov_mmap(struct file *filep, struct vm_area_struct *vma)
272 {
273         int res = 0;
274         void *area;
275         struct kcov *kcov = vma->vm_file->private_data;
276         unsigned long size, off;
277         struct page *page;
278 
279         area = vmalloc_user(vma->vm_end - vma->vm_start);
280         if (!area)
281                 return -ENOMEM;
282 
283         spin_lock(&kcov->lock);
284         size = kcov->size * sizeof(unsigned long);
285         if (kcov->mode != KCOV_MODE_INIT || vma->vm_pgoff != 0 ||
286             vma->vm_end - vma->vm_start != size) {
287                 res = -EINVAL;
288                 goto exit;
289         }
290         if (!kcov->area) {
291                 kcov->area = area;
292                 vma->vm_flags |= VM_DONTEXPAND;
293                 spin_unlock(&kcov->lock);
294                 for (off = 0; off < size; off += PAGE_SIZE) {
295                         page = vmalloc_to_page(kcov->area + off);
296                         if (vm_insert_page(vma, vma->vm_start + off, page))
297                                 WARN_ONCE(1, "vm_insert_page() failed");
298                 }
299                 return 0;
300         }
301 exit:
302         spin_unlock(&kcov->lock);
303         vfree(area);
304         return res;
305 }
306 
307 static int kcov_open(struct inode *inode, struct file *filep)
308 {
309         struct kcov *kcov;
310 
311         kcov = kzalloc(sizeof(*kcov), GFP_KERNEL);
312         if (!kcov)
313                 return -ENOMEM;
314         kcov->mode = KCOV_MODE_DISABLED;
315         atomic_set(&kcov->refcount, 1);
316         spin_lock_init(&kcov->lock);
317         filep->private_data = kcov;
318         return nonseekable_open(inode, filep);
319 }
320 
321 static int kcov_close(struct inode *inode, struct file *filep)
322 {
323         kcov_put(filep->private_data);
324         return 0;
325 }
326 
327 /*
328  * Fault in a lazily-faulted vmalloc area before it can be used by
329  * __santizer_cov_trace_pc(), to avoid recursion issues if any code on the
330  * vmalloc fault handling path is instrumented.
331  */
332 static void kcov_fault_in_area(struct kcov *kcov)
333 {
334         unsigned long stride = PAGE_SIZE / sizeof(unsigned long);
335         unsigned long *area = kcov->area;
336         unsigned long offset;
337 
338         for (offset = 0; offset < kcov->size; offset += stride)
339                 READ_ONCE(area[offset]);
340 }
341 
342 static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,
343                              unsigned long arg)
344 {
345         struct task_struct *t;
346         unsigned long size, unused;
347 
348         switch (cmd) {
349         case KCOV_INIT_TRACE:
350                 /*
351                  * Enable kcov in trace mode and setup buffer size.
352                  * Must happen before anything else.
353                  */
354                 if (kcov->mode != KCOV_MODE_DISABLED)
355                         return -EBUSY;
356                 /*
357                  * Size must be at least 2 to hold current position and one PC.
358                  * Later we allocate size * sizeof(unsigned long) memory,
359                  * that must not overflow.
360                  */
361                 size = arg;
362                 if (size < 2 || size > INT_MAX / sizeof(unsigned long))
363                         return -EINVAL;
364                 kcov->size = size;
365                 kcov->mode = KCOV_MODE_INIT;
366                 return 0;
367         case KCOV_ENABLE:
368                 /*
369                  * Enable coverage for the current task.
370                  * At this point user must have been enabled trace mode,
371                  * and mmapped the file. Coverage collection is disabled only
372                  * at task exit or voluntary by KCOV_DISABLE. After that it can
373                  * be enabled for another task.
374                  */
375                 if (kcov->mode != KCOV_MODE_INIT || !kcov->area)
376                         return -EINVAL;
377                 t = current;
378                 if (kcov->t != NULL || t->kcov != NULL)
379                         return -EBUSY;
380                 if (arg == KCOV_TRACE_PC)
381                         kcov->mode = KCOV_MODE_TRACE_PC;
382                 else if (arg == KCOV_TRACE_CMP)
383 #ifdef CONFIG_KCOV_ENABLE_COMPARISONS
384                         kcov->mode = KCOV_MODE_TRACE_CMP;
385 #else
386                 return -ENOTSUPP;
387 #endif
388                 else
389                         return -EINVAL;
390                 kcov_fault_in_area(kcov);
391                 /* Cache in task struct for performance. */
392                 t->kcov_size = kcov->size;
393                 t->kcov_area = kcov->area;
394                 /* See comment in check_kcov_mode(). */
395                 barrier();
396                 WRITE_ONCE(t->kcov_mode, kcov->mode);
397                 t->kcov = kcov;
398                 kcov->t = t;
399                 /* This is put either in kcov_task_exit() or in KCOV_DISABLE. */
400                 kcov_get(kcov);
401                 return 0;
402         case KCOV_DISABLE:
403                 /* Disable coverage for the current task. */
404                 unused = arg;
405                 if (unused != 0 || current->kcov != kcov)
406                         return -EINVAL;
407                 t = current;
408                 if (WARN_ON(kcov->t != t))
409                         return -EINVAL;
410                 kcov_task_init(t);
411                 kcov->t = NULL;
412                 kcov->mode = KCOV_MODE_INIT;
413                 kcov_put(kcov);
414                 return 0;
415         default:
416                 return -ENOTTY;
417         }
418 }
419 
420 static long kcov_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
421 {
422         struct kcov *kcov;
423         int res;
424 
425         kcov = filep->private_data;
426         spin_lock(&kcov->lock);
427         res = kcov_ioctl_locked(kcov, cmd, arg);
428         spin_unlock(&kcov->lock);
429         return res;
430 }
431 
432 static const struct file_operations kcov_fops = {
433         .open           = kcov_open,
434         .unlocked_ioctl = kcov_ioctl,
435         .compat_ioctl   = kcov_ioctl,
436         .mmap           = kcov_mmap,
437         .release        = kcov_close,
438 };
439 
440 static int __init kcov_init(void)
441 {
442         /*
443          * The kcov debugfs file won't ever get removed and thus,
444          * there is no need to protect it against removal races. The
445          * use of debugfs_create_file_unsafe() is actually safe here.
446          */
447         if (!debugfs_create_file_unsafe("kcov", 0600, NULL, NULL, &kcov_fops)) {
448                 pr_err("failed to create kcov in debugfs\n");
449                 return -ENOMEM;
450         }
451         return 0;
452 }
453 
454 device_initcall(kcov_init);
455 

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