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 */ 25 struct 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 */ 47 void 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 } 81 EXPORT_SYMBOL(__sanitizer_cov_trace_pc); 82 83 static void kcov_get(struct kcov *kcov) 84 { 85 atomic_inc(&kcov->refcount); 86 } 87 88 static 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 96 void 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 } 103 104 void 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 } 122 123 static 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 } 153 exit: 154 spin_unlock(&kcov->lock); 155 vfree(area); 156 return res; 157 } 158 159 static 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 } 171 172 static int kcov_close(struct inode *inode, struct file *filep) 173 { 174 kcov_put(filep->private_data); 175 return 0; 176 } 177 178 static 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 } 245 246 static 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 } 257 258 static const struct file_operations kcov_fops = { 259 .open = kcov_open, 260 .unlocked_ioctl = kcov_ioctl, 261 .mmap = kcov_mmap, 262 .release = kcov_close, 263 }; 264 265 static 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 } 278 279 device_initcall(kcov_init); 280