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/sched.h> 11 #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 */ 26 struct 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 */ 48 void notrace __sanitizer_cov_trace_pc(void) 49 { 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. 57 * 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). 63 */ 64 if (!t || (preempt_count() & (HARDIRQ_MASK | SOFTIRQ_OFFSET 65 | NMI_MASK))) 66 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 } 89 EXPORT_SYMBOL(__sanitizer_cov_trace_pc); 90 91 static void kcov_get(struct kcov *kcov) 92 { 93 atomic_inc(&kcov->refcount); 94 } 95 96 static void kcov_put(struct kcov *kcov) 97 { 98 if (atomic_dec_and_test(&kcov->refcount)) { 99 vfree(kcov->area); 100 kfree(kcov); 101 } 102 } 103 104 void 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 } 111 112 void 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 } 130 131 static 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 } 161 exit: 162 spin_unlock(&kcov->lock); 163 vfree(area); 164 return res; 165 } 166 167 static 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 } 179 180 static int kcov_close(struct inode *inode, struct file *filep) 181 { 182 kcov_put(filep->private_data); 183 return 0; 184 } 185 186 static 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 } 253 254 static 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 } 265 266 static const struct file_operations kcov_fops = { 267 .open = kcov_open, 268 .unlocked_ioctl = kcov_ioctl, 269 .mmap = kcov_mmap, 270 .release = kcov_close, 271 }; 272 273 static int __init kcov_init(void) 274 { 275 /* 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)) { 281 pr_err("failed to create kcov in debugfs\n"); 282 return -ENOMEM; 283 } 284 return 0; 285 } 286 287 device_initcall(kcov_init); 288