LXR linux/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 */
  25struct 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 */
  47void 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}
  81EXPORT_SYMBOL(__sanitizer_cov_trace_pc);
  82
  83static void kcov_get(struct kcov *kcov)
  84{
  85        atomic_inc(&kcov->refcount);
  86}
  87
  88static 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
  96void 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
 104void 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
 123static 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        }
 153exit:
 154        spin_unlock(&kcov->lock);
 155        vfree(area);
 156        return res;
 157}
 158
 159static 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
 172static int kcov_close(struct inode *inode, struct file *filep)
 173{
 174        kcov_put(filep->private_data);
 175        return 0;
 176}
 177
 178static 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
 246static 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
 258static 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
 265static int __init kcov_init(void)
 266{
 267        if (!debugfs_create_file("kcov", 0600, NULL, NULL, &kcov_fops)) {
 268                pr_err("failed to create kcov in debugfs\n");
 269                return -ENOMEM;
 270        }
 271        return 0;
 272}
 273
 274device_initcall(kcov_init);
 275