kernel/kcov.c

   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 /*
  26  * kcov descriptor (one per opened debugfs file).
  27  * State transitions of the descriptor:
  28  *  - initial state after open()
  29  *  - then there must be a single ioctl(KCOV_INIT_TRACE) call
  30  *  - then, mmap() call (several calls are allowed but not useful)
  31  *  - then, repeated enable/disable for a task (only one task a time allowed)
  32  */
  33 struct kcov {
  34         /*
  35          * Reference counter. We keep one for:
  36          *  - opened file descriptor
  37          *  - task with enabled coverage (we can't unwire it from another task)
  38          */
  39         atomic_t                refcount;
  40         /* The lock protects mode, size, area and t. */
  41         spinlock_t              lock;
  42         enum kcov_mode          mode;
  43         /* Size of arena (in long's for KCOV_MODE_TRACE). */
  44         unsigned                size;
  45         /* Coverage buffer shared with user space. */
  46         void                    *area;
  47         /* Task for which we collect coverage, or NULL. */
  48         struct task_struct      *t;
  49 };
  50
  51 /*
  52  * Entry point from instrumented code.
  53  * This is called once per basic-block/edge.
  54  */
  55 void notrace __sanitizer_cov_trace_pc(void)
  56 {
  57         struct task_struct *t;
  58         enum kcov_mode mode;
  59
  60         t = current;
  61         /*
  62          * We are interested in code coverage as a function of a syscall inputs,
  63          * so we ignore code executed in interrupts.
  64          */
  65         if (!t || !in_task())
  66                 return;
  67         mode = READ_ONCE(t->kcov_mode);
  68         if (mode == KCOV_MODE_TRACE) {
  69                 unsigned long *area;
  70                 unsigned long pos;
  71                 unsigned long ip = _RET_IP_;
  72
  73 #ifdef CONFIG_RANDOMIZE_BASE
  74                 ip -= kaslr_offset();
  75 #endif
  76
  77                 /*
  78                  * There is some code that runs in interrupts but for which
  79                  * in_interrupt() returns false (e.g. preempt_schedule_irq()).
  80                  * READ_ONCE()/barrier() effectively provides load-acquire wrt
  81                  * interrupts, there are paired barrier()/WRITE_ONCE() in
  82                  * kcov_ioctl_locked().
  83                  */
  84                 barrier();
  85                 area = t->kcov_area;
  86                 /* The first word is number of subsequent PCs. */
  87                 pos = READ_ONCE(area[0]) + 1;
  88                 if (likely(pos < t->kcov_size)) {
  89                         area[pos] = ip;
  90                         WRITE_ONCE(area[0], pos);
  91                 }
  92         }
  93 }
  94 EXPORT_SYMBOL(__sanitizer_cov_trace_pc);
  95
  96 static void kcov_get(struct kcov *kcov)
  97 {
  98         atomic_inc(&kcov->refcount);
  99 }
 100
 101 static void kcov_put(struct kcov *kcov)
 102 {
 103         if (atomic_dec_and_test(&kcov->refcount)) {
 104                 vfree(kcov->area);
 105                 kfree(kcov);
 106         }
 107 }
 108
 109 void kcov_task_init(struct task_struct *t)
 110 {
 111         t->kcov_mode = KCOV_MODE_DISABLED;
 112         t->kcov_size = 0;
 113         t->kcov_area = NULL;
 114         t->kcov = NULL;
 115 }
 116
 117 void kcov_task_exit(struct task_struct *t)
 118 {
 119         struct kcov *kcov;
 120
 121         kcov = t->kcov;
 122         if (kcov == NULL)
 123                 return;
 124         spin_lock(&kcov->lock);
 125         if (WARN_ON(kcov->t != t)) {
 126                 spin_unlock(&kcov->lock);
 127                 return;
 128         }
 129         /* Just to not leave dangling references behind. */
 130         kcov_task_init(t);
 131         kcov->t = NULL;
 132         spin_unlock(&kcov->lock);
 133         kcov_put(kcov);
 134 }
 135
 136 static int kcov_mmap(struct file *filep, struct vm_area_struct *vma)
 137 {
 138         int res = 0;
 139         void *area;
 140         struct kcov *kcov = vma->vm_file->private_data;
 141         unsigned long size, off;
 142         struct page *page;
 143
 144         area = vmalloc_user(vma->vm_end - vma->vm_start);
 145         if (!area)
 146                 return -ENOMEM;
 147
 148         spin_lock(&kcov->lock);
 149         size = kcov->size * sizeof(unsigned long);
 150         if (kcov->mode == KCOV_MODE_DISABLED || vma->vm_pgoff != 0 ||
 151             vma->vm_end - vma->vm_start != size) {
 152                 res = -EINVAL;
 153                 goto exit;
 154         }
 155         if (!kcov->area) {
 156                 kcov->area = area;
 157                 vma->vm_flags |= VM_DONTEXPAND;
 158                 spin_unlock(&kcov->lock);
 159                 for (off = 0; off < size; off += PAGE_SIZE) {
 160                         page = vmalloc_to_page(kcov->area + off);
 161                         if (vm_insert_page(vma, vma->vm_start + off, page))
 162                                 WARN_ONCE(1, "vm_insert_page() failed");
 163                 }
 164                 return 0;
 165         }
 166 exit:
 167         spin_unlock(&kcov->lock);
 168         vfree(area);
 169         return res;
 170 }
 171
 172 static int kcov_open(struct inode *inode, struct file *filep)
 173 {
 174         struct kcov *kcov;
 175
 176         kcov = kzalloc(sizeof(*kcov), GFP_KERNEL);
 177         if (!kcov)
 178                 return -ENOMEM;
 179         atomic_set(&kcov->refcount, 1);
 180         spin_lock_init(&kcov->lock);
 181         filep->private_data = kcov;
 182         return nonseekable_open(inode, filep);
 183 }
 184
 185 static int kcov_close(struct inode *inode, struct file *filep)
 186 {
 187         kcov_put(filep->private_data);
 188         return 0;
 189 }
 190
 191 static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,
 192                              unsigned long arg)
 193 {
 194         struct task_struct *t;
 195         unsigned long size, unused;
 196
 197         switch (cmd) {
 198         case KCOV_INIT_TRACE:
 199                 /*
 200                  * Enable kcov in trace mode and setup buffer size.
 201                  * Must happen before anything else.
 202                  */
 203                 if (kcov->mode != KCOV_MODE_DISABLED)
 204                         return -EBUSY;
 205                 /*
 206                  * Size must be at least 2 to hold current position and one PC.
 207                  * Later we allocate size * sizeof(unsigned long) memory,
 208                  * that must not overflow.
 209                  */
 210                 size = arg;
 211                 if (size < 2 || size > INT_MAX / sizeof(unsigned long))
 212                         return -EINVAL;
 213                 kcov->size = size;
 214                 kcov->mode = KCOV_MODE_TRACE;
 215                 return 0;
 216         case KCOV_ENABLE:
 217                 /*
 218                  * Enable coverage for the current task.
 219                  * At this point user must have been enabled trace mode,
 220                  * and mmapped the file. Coverage collection is disabled only
 221                  * at task exit or voluntary by KCOV_DISABLE. After that it can
 222                  * be enabled for another task.
 223                  */
 224                 unused = arg;
 225                 if (unused != 0 || kcov->mode == KCOV_MODE_DISABLED ||
 226                     kcov->area == NULL)
 227                         return -EINVAL;
 228                 if (kcov->t != NULL)
 229                         return -EBUSY;
 230                 t = current;
 231                 /* Cache in task struct for performance. */
 232                 t->kcov_size = kcov->size;
 233                 t->kcov_area = kcov->area;
 234                 /* See comment in __sanitizer_cov_trace_pc(). */
 235                 barrier();
 236                 WRITE_ONCE(t->kcov_mode, kcov->mode);
 237                 t->kcov = kcov;
 238                 kcov->t = t;
 239                 /* This is put either in kcov_task_exit() or in KCOV_DISABLE. */
 240                 kcov_get(kcov);
 241                 return 0;
 242         case KCOV_DISABLE:
 243                 /* Disable coverage for the current task. */
 244                 unused = arg;
 245                 if (unused != 0 || current->kcov != kcov)
 246                         return -EINVAL;
 247                 t = current;
 248                 if (WARN_ON(kcov->t != t))
 249                         return -EINVAL;
 250                 kcov_task_init(t);
 251                 kcov->t = NULL;
 252                 kcov_put(kcov);
 253                 return 0;
 254         default:
 255                 return -ENOTTY;
 256         }
 257 }
 258
 259 static long kcov_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
 260 {
 261         struct kcov *kcov;
 262         int res;
 263
 264         kcov = filep->private_data;
 265         spin_lock(&kcov->lock);
 266         res = kcov_ioctl_locked(kcov, cmd, arg);
 267         spin_unlock(&kcov->lock);
 268         return res;
 269 }
 270
 271 static const struct file_operations kcov_fops = {
 272         .open           = kcov_open,
 273         .unlocked_ioctl = kcov_ioctl,
 274         .compat_ioctl   = kcov_ioctl,
 275         .mmap           = kcov_mmap,
 276         .release        = kcov_close,
 277 };
 278
 279 static int __init kcov_init(void)
 280 {
 281         /*
 282          * The kcov debugfs file won't ever get removed and thus,
 283          * there is no need to protect it against removal races. The
 284          * use of debugfs_create_file_unsafe() is actually safe here.
 285          */
 286         if (!debugfs_create_file_unsafe("kcov", 0600, NULL, NULL, &kcov_fops)) {
 287                 pr_err("failed to create kcov in debugfs\n");
 288                 return -ENOMEM;
 289         }
 290         return 0;
 291 }
 292
 293 device_initcall(kcov_init);