kernel/kcov.c

   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);