linux/kernel/kcov.c
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   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/* Number of 64-bit words written per one comparison: */
  26#define KCOV_WORDS_PER_CMP 4
  27
  28/*
  29 * kcov descriptor (one per opened debugfs file).
  30 * State transitions of the descriptor:
  31 *  - initial state after open()
  32 *  - then there must be a single ioctl(KCOV_INIT_TRACE) call
  33 *  - then, mmap() call (several calls are allowed but not useful)
  34 *  - then, ioctl(KCOV_ENABLE, arg), where arg is
  35 *      KCOV_TRACE_PC - to trace only the PCs
  36 *      or
  37 *      KCOV_TRACE_CMP - to trace only the comparison operands
  38 *  - then, ioctl(KCOV_DISABLE) to disable the task.
  39 * Enabling/disabling ioctls can be repeated (only one task a time allowed).
  40 */
  41struct kcov {
  42        /*
  43         * Reference counter. We keep one for:
  44         *  - opened file descriptor
  45         *  - task with enabled coverage (we can't unwire it from another task)
  46         */
  47        atomic_t                refcount;
  48        /* The lock protects mode, size, area and t. */
  49        spinlock_t              lock;
  50        enum kcov_mode          mode;
  51        /* Size of arena (in long's for KCOV_MODE_TRACE). */
  52        unsigned                size;
  53        /* Coverage buffer shared with user space. */
  54        void                    *area;
  55        /* Task for which we collect coverage, or NULL. */
  56        struct task_struct      *t;
  57};
  58
  59static notrace bool check_kcov_mode(enum kcov_mode needed_mode, struct task_struct *t)
  60{
  61        unsigned int mode;
  62
  63        /*
  64         * We are interested in code coverage as a function of a syscall inputs,
  65         * so we ignore code executed in interrupts.
  66         */
  67        if (!in_task())
  68                return false;
  69        mode = READ_ONCE(t->kcov_mode);
  70        /*
  71         * There is some code that runs in interrupts but for which
  72         * in_interrupt() returns false (e.g. preempt_schedule_irq()).
  73         * READ_ONCE()/barrier() effectively provides load-acquire wrt
  74         * interrupts, there are paired barrier()/WRITE_ONCE() in
  75         * kcov_ioctl_locked().
  76         */
  77        barrier();
  78        return mode == needed_mode;
  79}
  80
  81static notrace unsigned long canonicalize_ip(unsigned long ip)
  82{
  83#ifdef CONFIG_RANDOMIZE_BASE
  84        ip -= kaslr_offset();
  85#endif
  86        return ip;
  87}
  88
  89/*
  90 * Entry point from instrumented code.
  91 * This is called once per basic-block/edge.
  92 */
  93void notrace __sanitizer_cov_trace_pc(void)
  94{
  95        struct task_struct *t;
  96        unsigned long *area;
  97        unsigned long ip = canonicalize_ip(_RET_IP_);
  98        unsigned long pos;
  99
 100        t = current;
 101        if (!check_kcov_mode(KCOV_MODE_TRACE_PC, t))
 102                return;
 103
 104        area = t->kcov_area;
 105        /* The first 64-bit word is the number of subsequent PCs. */
 106        pos = READ_ONCE(area[0]) + 1;
 107        if (likely(pos < t->kcov_size)) {
 108                area[pos] = ip;
 109                WRITE_ONCE(area[0], pos);
 110        }
 111}
 112EXPORT_SYMBOL(__sanitizer_cov_trace_pc);
 113
 114#ifdef CONFIG_KCOV_ENABLE_COMPARISONS
 115static void write_comp_data(u64 type, u64 arg1, u64 arg2, u64 ip)
 116{
 117        struct task_struct *t;
 118        u64 *area;
 119        u64 count, start_index, end_pos, max_pos;
 120
 121        t = current;
 122        if (!check_kcov_mode(KCOV_MODE_TRACE_CMP, t))
 123                return;
 124
 125        ip = canonicalize_ip(ip);
 126
 127        /*
 128         * We write all comparison arguments and types as u64.
 129         * The buffer was allocated for t->kcov_size unsigned longs.
 130         */
 131        area = (u64 *)t->kcov_area;
 132        max_pos = t->kcov_size * sizeof(unsigned long);
 133
 134        count = READ_ONCE(area[0]);
 135
 136        /* Every record is KCOV_WORDS_PER_CMP 64-bit words. */
 137        start_index = 1 + count * KCOV_WORDS_PER_CMP;
 138        end_pos = (start_index + KCOV_WORDS_PER_CMP) * sizeof(u64);
 139        if (likely(end_pos <= max_pos)) {
 140                area[start_index] = type;
 141                area[start_index + 1] = arg1;
 142                area[start_index + 2] = arg2;
 143                area[start_index + 3] = ip;
 144                WRITE_ONCE(area[0], count + 1);
 145        }
 146}
 147
 148void notrace __sanitizer_cov_trace_cmp1(u8 arg1, u8 arg2)
 149{
 150        write_comp_data(KCOV_CMP_SIZE(0), arg1, arg2, _RET_IP_);
 151}
 152EXPORT_SYMBOL(__sanitizer_cov_trace_cmp1);
 153
 154void notrace __sanitizer_cov_trace_cmp2(u16 arg1, u16 arg2)
 155{
 156        write_comp_data(KCOV_CMP_SIZE(1), arg1, arg2, _RET_IP_);
 157}
 158EXPORT_SYMBOL(__sanitizer_cov_trace_cmp2);
 159
 160void notrace __sanitizer_cov_trace_cmp4(u32 arg1, u32 arg2)
 161{
 162        write_comp_data(KCOV_CMP_SIZE(2), arg1, arg2, _RET_IP_);
 163}
 164EXPORT_SYMBOL(__sanitizer_cov_trace_cmp4);
 165
 166void notrace __sanitizer_cov_trace_cmp8(u64 arg1, u64 arg2)
 167{
 168        write_comp_data(KCOV_CMP_SIZE(3), arg1, arg2, _RET_IP_);
 169}
 170EXPORT_SYMBOL(__sanitizer_cov_trace_cmp8);
 171
 172void notrace __sanitizer_cov_trace_const_cmp1(u8 arg1, u8 arg2)
 173{
 174        write_comp_data(KCOV_CMP_SIZE(0) | KCOV_CMP_CONST, arg1, arg2,
 175                        _RET_IP_);
 176}
 177EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp1);
 178
 179void notrace __sanitizer_cov_trace_const_cmp2(u16 arg1, u16 arg2)
 180{
 181        write_comp_data(KCOV_CMP_SIZE(1) | KCOV_CMP_CONST, arg1, arg2,
 182                        _RET_IP_);
 183}
 184EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp2);
 185
 186void notrace __sanitizer_cov_trace_const_cmp4(u32 arg1, u32 arg2)
 187{
 188        write_comp_data(KCOV_CMP_SIZE(2) | KCOV_CMP_CONST, arg1, arg2,
 189                        _RET_IP_);
 190}
 191EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp4);
 192
 193void notrace __sanitizer_cov_trace_const_cmp8(u64 arg1, u64 arg2)
 194{
 195        write_comp_data(KCOV_CMP_SIZE(3) | KCOV_CMP_CONST, arg1, arg2,
 196                        _RET_IP_);
 197}
 198EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp8);
 199
 200void notrace __sanitizer_cov_trace_switch(u64 val, u64 *cases)
 201{
 202        u64 i;
 203        u64 count = cases[0];
 204        u64 size = cases[1];
 205        u64 type = KCOV_CMP_CONST;
 206
 207        switch (size) {
 208        case 8:
 209                type |= KCOV_CMP_SIZE(0);
 210                break;
 211        case 16:
 212                type |= KCOV_CMP_SIZE(1);
 213                break;
 214        case 32:
 215                type |= KCOV_CMP_SIZE(2);
 216                break;
 217        case 64:
 218                type |= KCOV_CMP_SIZE(3);
 219                break;
 220        default:
 221                return;
 222        }
 223        for (i = 0; i < count; i++)
 224                write_comp_data(type, cases[i + 2], val, _RET_IP_);
 225}
 226EXPORT_SYMBOL(__sanitizer_cov_trace_switch);
 227#endif /* ifdef CONFIG_KCOV_ENABLE_COMPARISONS */
 228
 229static void kcov_get(struct kcov *kcov)
 230{
 231        atomic_inc(&kcov->refcount);
 232}
 233
 234static void kcov_put(struct kcov *kcov)
 235{
 236        if (atomic_dec_and_test(&kcov->refcount)) {
 237                vfree(kcov->area);
 238                kfree(kcov);
 239        }
 240}
 241
 242void kcov_task_init(struct task_struct *t)
 243{
 244        WRITE_ONCE(t->kcov_mode, KCOV_MODE_DISABLED);
 245        barrier();
 246        t->kcov_size = 0;
 247        t->kcov_area = NULL;
 248        t->kcov = NULL;
 249}
 250
 251void kcov_task_exit(struct task_struct *t)
 252{
 253        struct kcov *kcov;
 254
 255        kcov = t->kcov;
 256        if (kcov == NULL)
 257                return;
 258        spin_lock(&kcov->lock);
 259        if (WARN_ON(kcov->t != t)) {
 260                spin_unlock(&kcov->lock);
 261                return;
 262        }
 263        /* Just to not leave dangling references behind. */
 264        kcov_task_init(t);
 265        kcov->t = NULL;
 266        kcov->mode = KCOV_MODE_INIT;
 267        spin_unlock(&kcov->lock);
 268        kcov_put(kcov);
 269}
 270
 271static int kcov_mmap(struct file *filep, struct vm_area_struct *vma)
 272{
 273        int res = 0;
 274        void *area;
 275        struct kcov *kcov = vma->vm_file->private_data;
 276        unsigned long size, off;
 277        struct page *page;
 278
 279        area = vmalloc_user(vma->vm_end - vma->vm_start);
 280        if (!area)
 281                return -ENOMEM;
 282
 283        spin_lock(&kcov->lock);
 284        size = kcov->size * sizeof(unsigned long);
 285        if (kcov->mode != KCOV_MODE_INIT || vma->vm_pgoff != 0 ||
 286            vma->vm_end - vma->vm_start != size) {
 287                res = -EINVAL;
 288                goto exit;
 289        }
 290        if (!kcov->area) {
 291                kcov->area = area;
 292                vma->vm_flags |= VM_DONTEXPAND;
 293                spin_unlock(&kcov->lock);
 294                for (off = 0; off < size; off += PAGE_SIZE) {
 295                        page = vmalloc_to_page(kcov->area + off);
 296                        if (vm_insert_page(vma, vma->vm_start + off, page))
 297                                WARN_ONCE(1, "vm_insert_page() failed");
 298                }
 299                return 0;
 300        }
 301exit:
 302        spin_unlock(&kcov->lock);
 303        vfree(area);
 304        return res;
 305}
 306
 307static int kcov_open(struct inode *inode, struct file *filep)
 308{
 309        struct kcov *kcov;
 310
 311        kcov = kzalloc(sizeof(*kcov), GFP_KERNEL);
 312        if (!kcov)
 313                return -ENOMEM;
 314        kcov->mode = KCOV_MODE_DISABLED;
 315        atomic_set(&kcov->refcount, 1);
 316        spin_lock_init(&kcov->lock);
 317        filep->private_data = kcov;
 318        return nonseekable_open(inode, filep);
 319}
 320
 321static int kcov_close(struct inode *inode, struct file *filep)
 322{
 323        kcov_put(filep->private_data);
 324        return 0;
 325}
 326
 327/*
 328 * Fault in a lazily-faulted vmalloc area before it can be used by
 329 * __santizer_cov_trace_pc(), to avoid recursion issues if any code on the
 330 * vmalloc fault handling path is instrumented.
 331 */
 332static void kcov_fault_in_area(struct kcov *kcov)
 333{
 334        unsigned long stride = PAGE_SIZE / sizeof(unsigned long);
 335        unsigned long *area = kcov->area;
 336        unsigned long offset;
 337
 338        for (offset = 0; offset < kcov->size; offset += stride)
 339                READ_ONCE(area[offset]);
 340}
 341
 342static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,
 343                             unsigned long arg)
 344{
 345        struct task_struct *t;
 346        unsigned long size, unused;
 347
 348        switch (cmd) {
 349        case KCOV_INIT_TRACE:
 350                /*
 351                 * Enable kcov in trace mode and setup buffer size.
 352                 * Must happen before anything else.
 353                 */
 354                if (kcov->mode != KCOV_MODE_DISABLED)
 355                        return -EBUSY;
 356                /*
 357                 * Size must be at least 2 to hold current position and one PC.
 358                 * Later we allocate size * sizeof(unsigned long) memory,
 359                 * that must not overflow.
 360                 */
 361                size = arg;
 362                if (size < 2 || size > INT_MAX / sizeof(unsigned long))
 363                        return -EINVAL;
 364                kcov->size = size;
 365                kcov->mode = KCOV_MODE_INIT;
 366                return 0;
 367        case KCOV_ENABLE:
 368                /*
 369                 * Enable coverage for the current task.
 370                 * At this point user must have been enabled trace mode,
 371                 * and mmapped the file. Coverage collection is disabled only
 372                 * at task exit or voluntary by KCOV_DISABLE. After that it can
 373                 * be enabled for another task.
 374                 */
 375                if (kcov->mode != KCOV_MODE_INIT || !kcov->area)
 376                        return -EINVAL;
 377                t = current;
 378                if (kcov->t != NULL || t->kcov != NULL)
 379                        return -EBUSY;
 380                if (arg == KCOV_TRACE_PC)
 381                        kcov->mode = KCOV_MODE_TRACE_PC;
 382                else if (arg == KCOV_TRACE_CMP)
 383#ifdef CONFIG_KCOV_ENABLE_COMPARISONS
 384                        kcov->mode = KCOV_MODE_TRACE_CMP;
 385#else
 386                return -ENOTSUPP;
 387#endif
 388                else
 389                        return -EINVAL;
 390                kcov_fault_in_area(kcov);
 391                /* Cache in task struct for performance. */
 392                t->kcov_size = kcov->size;
 393                t->kcov_area = kcov->area;
 394                /* See comment in check_kcov_mode(). */
 395                barrier();
 396                WRITE_ONCE(t->kcov_mode, kcov->mode);
 397                t->kcov = kcov;
 398                kcov->t = t;
 399                /* This is put either in kcov_task_exit() or in KCOV_DISABLE. */
 400                kcov_get(kcov);
 401                return 0;
 402        case KCOV_DISABLE:
 403                /* Disable coverage for the current task. */
 404                unused = arg;
 405                if (unused != 0 || current->kcov != kcov)
 406                        return -EINVAL;
 407                t = current;
 408                if (WARN_ON(kcov->t != t))
 409                        return -EINVAL;
 410                kcov_task_init(t);
 411                kcov->t = NULL;
 412                kcov->mode = KCOV_MODE_INIT;
 413                kcov_put(kcov);
 414                return 0;
 415        default:
 416                return -ENOTTY;
 417        }
 418}
 419
 420static long kcov_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
 421{
 422        struct kcov *kcov;
 423        int res;
 424
 425        kcov = filep->private_data;
 426        spin_lock(&kcov->lock);
 427        res = kcov_ioctl_locked(kcov, cmd, arg);
 428        spin_unlock(&kcov->lock);
 429        return res;
 430}
 431
 432static const struct file_operations kcov_fops = {
 433        .open           = kcov_open,
 434        .unlocked_ioctl = kcov_ioctl,
 435        .compat_ioctl   = kcov_ioctl,
 436        .mmap           = kcov_mmap,
 437        .release        = kcov_close,
 438};
 439
 440static int __init kcov_init(void)
 441{
 442        /*
 443         * The kcov debugfs file won't ever get removed and thus,
 444         * there is no need to protect it against removal races. The
 445         * use of debugfs_create_file_unsafe() is actually safe here.
 446         */
 447        if (!debugfs_create_file_unsafe("kcov", 0600, NULL, NULL, &kcov_fops)) {
 448                pr_err("failed to create kcov in debugfs\n");
 449                return -ENOMEM;
 450        }
 451        return 0;
 452}
 453
 454device_initcall(kcov_init);
 455