LXR linux/mm/process_vm

   1/*
   2 * linux/mm/process_vm_access.c
   3 *
   4 * Copyright (C) 2010-2011 Christopher Yeoh <cyeoh@au1.ibm.com>, IBM Corp.
   5 *
   6 * This program is free software; you can redistribute it and/or
   7 * modify it under the terms of the GNU General Public License
   8 * as published by the Free Software Foundation; either version
   9 * 2 of the License, or (at your option) any later version.
  10 */
  11
  12#include <linux/mm.h>
  13#include <linux/uio.h>
  14#include <linux/sched.h>
  15#include <linux/highmem.h>
  16#include <linux/ptrace.h>
  17#include <linux/slab.h>
  18#include <linux/syscalls.h>
  19
  20#ifdef CONFIG_COMPAT
  21#include <linux/compat.h>
  22#endif
  23
  24/**
  25 * process_vm_rw_pages - read/write pages from task specified
  26 * @task: task to read/write from
  27 * @mm: mm for task
  28 * @process_pages: struct pages area that can store at least
  29 *  nr_pages_to_copy struct page pointers
  30 * @pa: address of page in task to start copying from/to
  31 * @start_offset: offset in page to start copying from/to
  32 * @len: number of bytes to copy
  33 * @lvec: iovec array specifying where to copy to/from
  34 * @lvec_cnt: number of elements in iovec array
  35 * @lvec_current: index in iovec array we are up to
  36 * @lvec_offset: offset in bytes from current iovec iov_base we are up to
  37 * @vm_write: 0 means copy from, 1 means copy to
  38 * @nr_pages_to_copy: number of pages to copy
  39 * @bytes_copied: returns number of bytes successfully copied
  40 * Returns 0 on success, error code otherwise
  41 */
  42static int process_vm_rw_pages(struct task_struct *task,
  43                               struct mm_struct *mm,
  44                               struct page **process_pages,
  45                               unsigned long pa,
  46                               unsigned long start_offset,
  47                               unsigned long len,
  48                               const struct iovec *lvec,
  49                               unsigned long lvec_cnt,
  50                               unsigned long *lvec_current,
  51                               size_t *lvec_offset,
  52                               int vm_write,
  53                               unsigned int nr_pages_to_copy,
  54                               ssize_t *bytes_copied)
  55{
  56        int pages_pinned;
  57        void *target_kaddr;
  58        int pgs_copied = 0;
  59        int j;
  60        int ret;
  61        ssize_t bytes_to_copy;
  62        ssize_t rc = 0;
  63
  64        *bytes_copied = 0;
  65
  66        /* Get the pages we're interested in */
  67        down_read(&mm->mmap_sem);
  68        pages_pinned = get_user_pages(task, mm, pa,
  69                                      nr_pages_to_copy,
  70                                      vm_write, 0, process_pages, NULL);
  71        up_read(&mm->mmap_sem);
  72
  73        if (pages_pinned != nr_pages_to_copy) {
  74                rc = -EFAULT;
  75                goto end;
  76        }
  77
  78        /* Do the copy for each page */
  79        for (pgs_copied = 0;
  80             (pgs_copied < nr_pages_to_copy) && (*lvec_current < lvec_cnt);
  81             pgs_copied++) {
  82                /* Make sure we have a non zero length iovec */
  83                while (*lvec_current < lvec_cnt
  84                       && lvec[*lvec_current].iov_len == 0)
  85                        (*lvec_current)++;
  86                if (*lvec_current == lvec_cnt)
  87                        break;
  88
  89                /*
  90                 * Will copy smallest of:
  91                 * - bytes remaining in page
  92                 * - bytes remaining in destination iovec
  93                 */
  94                bytes_to_copy = min_t(ssize_t, PAGE_SIZE - start_offset,
  95                                      len - *bytes_copied);
  96                bytes_to_copy = min_t(ssize_t, bytes_to_copy,
  97                                      lvec[*lvec_current].iov_len
  98                                      - *lvec_offset);
  99
 100                target_kaddr = kmap(process_pages[pgs_copied]) + start_offset;
 101
 102                if (vm_write)
 103                        ret = copy_from_user(target_kaddr,
 104                                             lvec[*lvec_current].iov_base
 105                                             + *lvec_offset,
 106                                             bytes_to_copy);
 107                else
 108                        ret = copy_to_user(lvec[*lvec_current].iov_base
 109                                           + *lvec_offset,
 110                                           target_kaddr, bytes_to_copy);
 111                kunmap(process_pages[pgs_copied]);
 112                if (ret) {
 113                        *bytes_copied += bytes_to_copy - ret;
 114                        pgs_copied++;
 115                        rc = -EFAULT;
 116                        goto end;
 117                }
 118                *bytes_copied += bytes_to_copy;
 119                *lvec_offset += bytes_to_copy;
 120                if (*lvec_offset == lvec[*lvec_current].iov_len) {
 121                        /*
 122                         * Need to copy remaining part of page into the
 123                         * next iovec if there are any bytes left in page
 124                         */
 125                        (*lvec_current)++;
 126                        *lvec_offset = 0;
 127                        start_offset = (start_offset + bytes_to_copy)
 128                                % PAGE_SIZE;
 129                        if (start_offset)
 130                                pgs_copied--;
 131                } else {
 132                        start_offset = 0;
 133                }
 134        }
 135
 136end:
 137        if (vm_write) {
 138                for (j = 0; j < pages_pinned; j++) {
 139                        if (j < pgs_copied)
 140                                set_page_dirty_lock(process_pages[j]);
 141                        put_page(process_pages[j]);
 142                }
 143        } else {
 144                for (j = 0; j < pages_pinned; j++)
 145                        put_page(process_pages[j]);
 146        }
 147
 148        return rc;
 149}
 150
 151/* Maximum number of pages kmalloc'd to hold struct page's during copy */
 152#define PVM_MAX_KMALLOC_PAGES (PAGE_SIZE * 2)
 153
 154/**
 155 * process_vm_rw_single_vec - read/write pages from task specified
 156 * @addr: start memory address of target process
 157 * @len: size of area to copy to/from
 158 * @lvec: iovec array specifying where to copy to/from locally
 159 * @lvec_cnt: number of elements in iovec array
 160 * @lvec_current: index in iovec array we are up to
 161 * @lvec_offset: offset in bytes from current iovec iov_base we are up to
 162 * @process_pages: struct pages area that can store at least
 163 *  nr_pages_to_copy struct page pointers
 164 * @mm: mm for task
 165 * @task: task to read/write from
 166 * @vm_write: 0 means copy from, 1 means copy to
 167 * @bytes_copied: returns number of bytes successfully copied
 168 * Returns 0 on success or on failure error code
 169 */
 170static int process_vm_rw_single_vec(unsigned long addr,
 171                                    unsigned long len,
 172                                    const struct iovec *lvec,
 173                                    unsigned long lvec_cnt,
 174                                    unsigned long *lvec_current,
 175                                    size_t *lvec_offset,
 176                                    struct page **process_pages,
 177                                    struct mm_struct *mm,
 178                                    struct task_struct *task,
 179                                    int vm_write,
 180                                    ssize_t *bytes_copied)
 181{
 182        unsigned long pa = addr & PAGE_MASK;
 183        unsigned long start_offset = addr - pa;
 184        unsigned long nr_pages;
 185        ssize_t bytes_copied_loop;
 186        ssize_t rc = 0;
 187        unsigned long nr_pages_copied = 0;
 188        unsigned long nr_pages_to_copy;
 189        unsigned long max_pages_per_loop = PVM_MAX_KMALLOC_PAGES
 190                / sizeof(struct pages *);
 191
 192        *bytes_copied = 0;
 193
 194        /* Work out address and page range required */
 195        if (len == 0)
 196                return 0;
 197        nr_pages = (addr + len - 1) / PAGE_SIZE - addr / PAGE_SIZE + 1;
 198
 199        while ((nr_pages_copied < nr_pages) && (*lvec_current < lvec_cnt)) {
 200                nr_pages_to_copy = min(nr_pages - nr_pages_copied,
 201                                       max_pages_per_loop);
 202
 203                rc = process_vm_rw_pages(task, mm, process_pages, pa,
 204                                         start_offset, len,
 205                                         lvec, lvec_cnt,
 206                                         lvec_current, lvec_offset,
 207                                         vm_write, nr_pages_to_copy,
 208                                         &bytes_copied_loop);
 209                start_offset = 0;
 210                *bytes_copied += bytes_copied_loop;
 211
 212                if (rc < 0) {
 213                        return rc;
 214                } else {
 215                        len -= bytes_copied_loop;
 216                        nr_pages_copied += nr_pages_to_copy;
 217                        pa += nr_pages_to_copy * PAGE_SIZE;
 218                }
 219        }
 220
 221        return rc;
 222}
 223
 224/* Maximum number of entries for process pages array
 225   which lives on stack */
 226#define PVM_MAX_PP_ARRAY_COUNT 16
 227
 228/**
 229 * process_vm_rw_core - core of reading/writing pages from task specified
 230 * @pid: PID of process to read/write from/to
 231 * @lvec: iovec array specifying where to copy to/from locally
 232 * @liovcnt: size of lvec array
 233 * @rvec: iovec array specifying where to copy to/from in the other process
 234 * @riovcnt: size of rvec array
 235 * @flags: currently unused
 236 * @vm_write: 0 if reading from other process, 1 if writing to other process
 237 * Returns the number of bytes read/written or error code. May
 238 *  return less bytes than expected if an error occurs during the copying
 239 *  process.
 240 */
 241static ssize_t process_vm_rw_core(pid_t pid, const struct iovec *lvec,
 242                                  unsigned long liovcnt,
 243                                  const struct iovec *rvec,
 244                                  unsigned long riovcnt,
 245                                  unsigned long flags, int vm_write)
 246{
 247        struct task_struct *task;
 248        struct page *pp_stack[PVM_MAX_PP_ARRAY_COUNT];
 249        struct page **process_pages = pp_stack;
 250        struct mm_struct *mm;
 251        unsigned long i;
 252        ssize_t rc = 0;
 253        ssize_t bytes_copied_loop;
 254        ssize_t bytes_copied = 0;
 255        unsigned long nr_pages = 0;
 256        unsigned long nr_pages_iov;
 257        unsigned long iov_l_curr_idx = 0;
 258        size_t iov_l_curr_offset = 0;
 259        ssize_t iov_len;
 260
 261        /*
 262         * Work out how many pages of struct pages we're going to need
 263         * when eventually calling get_user_pages
 264         */
 265        for (i = 0; i < riovcnt; i++) {
 266                iov_len = rvec[i].iov_len;
 267                if (iov_len > 0) {
 268                        nr_pages_iov = ((unsigned long)rvec[i].iov_base
 269                                        + iov_len)
 270                                / PAGE_SIZE - (unsigned long)rvec[i].iov_base
 271                                / PAGE_SIZE + 1;
 272                        nr_pages = max(nr_pages, nr_pages_iov);
 273                }
 274        }
 275
 276        if (nr_pages == 0)
 277                return 0;
 278
 279        if (nr_pages > PVM_MAX_PP_ARRAY_COUNT) {
 280                /* For reliability don't try to kmalloc more than
 281                   2 pages worth */
 282                process_pages = kmalloc(min_t(size_t, PVM_MAX_KMALLOC_PAGES,
 283                                              sizeof(struct pages *)*nr_pages),
 284                                        GFP_KERNEL);
 285
 286                if (!process_pages)
 287                        return -ENOMEM;
 288        }
 289
 290        /* Get process information */
 291        rcu_read_lock();
 292        task = find_task_by_vpid(pid);
 293        if (task)
 294                get_task_struct(task);
 295        rcu_read_unlock();
 296        if (!task) {
 297                rc = -ESRCH;
 298                goto free_proc_pages;
 299        }
 300
 301        mm = mm_access(task, PTRACE_MODE_ATTACH);
 302        if (!mm || IS_ERR(mm)) {
 303                rc = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH;
 304                /*
 305                 * Explicitly map EACCES to EPERM as EPERM is a more a
 306                 * appropriate error code for process_vw_readv/writev
 307                 */
 308                if (rc == -EACCES)
 309                        rc = -EPERM;
 310                goto put_task_struct;
 311        }
 312
 313        for (i = 0; i < riovcnt && iov_l_curr_idx < liovcnt; i++) {
 314                rc = process_vm_rw_single_vec(
 315                        (unsigned long)rvec[i].iov_base, rvec[i].iov_len,
 316                        lvec, liovcnt, &iov_l_curr_idx, &iov_l_curr_offset,
 317                        process_pages, mm, task, vm_write, &bytes_copied_loop);
 318                bytes_copied += bytes_copied_loop;
 319                if (rc != 0) {
 320                        /* If we have managed to copy any data at all then
 321                           we return the number of bytes copied. Otherwise
 322                           we return the error code */
 323                        if (bytes_copied)
 324                                rc = bytes_copied;
 325                        goto put_mm;
 326                }
 327        }
 328
 329        rc = bytes_copied;
 330put_mm:
 331        mmput(mm);
 332
 333put_task_struct:
 334        put_task_struct(task);
 335
 336free_proc_pages:
 337        if (process_pages != pp_stack)
 338                kfree(process_pages);
 339        return rc;
 340}
 341
 342/**
 343 * process_vm_rw - check iovecs before calling core routine
 344 * @pid: PID of process to read/write from/to
 345 * @lvec: iovec array specifying where to copy to/from locally
 346 * @liovcnt: size of lvec array
 347 * @rvec: iovec array specifying where to copy to/from in the other process
 348 * @riovcnt: size of rvec array
 349 * @flags: currently unused
 350 * @vm_write: 0 if reading from other process, 1 if writing to other process
 351 * Returns the number of bytes read/written or error code. May
 352 *  return less bytes than expected if an error occurs during the copying
 353 *  process.
 354 */
 355static ssize_t process_vm_rw(pid_t pid,
 356                             const struct iovec __user *lvec,
 357                             unsigned long liovcnt,
 358                             const struct iovec __user *rvec,
 359                             unsigned long riovcnt,
 360                             unsigned long flags, int vm_write)
 361{
 362        struct iovec iovstack_l[UIO_FASTIOV];
 363        struct iovec iovstack_r[UIO_FASTIOV];
 364        struct iovec *iov_l = iovstack_l;
 365        struct iovec *iov_r = iovstack_r;
 366        ssize_t rc;
 367
 368        if (flags != 0)
 369                return -EINVAL;
 370
 371        /* Check iovecs */
 372        if (vm_write)
 373                rc = rw_copy_check_uvector(WRITE, lvec, liovcnt, UIO_FASTIOV,
 374                                           iovstack_l, &iov_l);
 375        else
 376                rc = rw_copy_check_uvector(READ, lvec, liovcnt, UIO_FASTIOV,
 377                                           iovstack_l, &iov_l);
 378        if (rc <= 0)
 379                goto free_iovecs;
 380
 381        rc = rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt, UIO_FASTIOV,
 382                                   iovstack_r, &iov_r);
 383        if (rc <= 0)
 384                goto free_iovecs;
 385
 386        rc = process_vm_rw_core(pid, iov_l, liovcnt, iov_r, riovcnt, flags,
 387                                vm_write);
 388
 389free_iovecs:
 390        if (iov_r != iovstack_r)
 391                kfree(iov_r);
 392        if (iov_l != iovstack_l)
 393                kfree(iov_l);
 394
 395        return rc;
 396}
 397
 398SYSCALL_DEFINE6(process_vm_readv, pid_t, pid, const struct iovec __user *, lvec,
 399                unsigned long, liovcnt, const struct iovec __user *, rvec,
 400                unsigned long, riovcnt, unsigned long, flags)
 401{
 402        return process_vm_rw(pid, lvec, liovcnt, rvec, riovcnt, flags, 0);
 403}
 404
 405SYSCALL_DEFINE6(process_vm_writev, pid_t, pid,
 406                const struct iovec __user *, lvec,
 407                unsigned long, liovcnt, const struct iovec __user *, rvec,
 408                unsigned long, riovcnt, unsigned long, flags)
 409{
 410        return process_vm_rw(pid, lvec, liovcnt, rvec, riovcnt, flags, 1);
 411}
 412
 413#ifdef CONFIG_COMPAT
 414
 415asmlinkage ssize_t
 416compat_process_vm_rw(compat_pid_t pid,
 417                     const struct compat_iovec __user *lvec,
 418                     unsigned long liovcnt,
 419                     const struct compat_iovec __user *rvec,
 420                     unsigned long riovcnt,
 421                     unsigned long flags, int vm_write)
 422{
 423        struct iovec iovstack_l[UIO_FASTIOV];
 424        struct iovec iovstack_r[UIO_FASTIOV];
 425        struct iovec *iov_l = iovstack_l;
 426        struct iovec *iov_r = iovstack_r;
 427        ssize_t rc = -EFAULT;
 428
 429        if (flags != 0)
 430                return -EINVAL;
 431
 432        if (vm_write)
 433                rc = compat_rw_copy_check_uvector(WRITE, lvec, liovcnt,
 434                                                  UIO_FASTIOV, iovstack_l,
 435                                                  &iov_l);
 436        else
 437                rc = compat_rw_copy_check_uvector(READ, lvec, liovcnt,
 438                                                  UIO_FASTIOV, iovstack_l,
 439                                                  &iov_l);
 440        if (rc <= 0)
 441                goto free_iovecs;
 442        rc = compat_rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt,
 443                                          UIO_FASTIOV, iovstack_r,
 444                                          &iov_r);
 445        if (rc <= 0)
 446                goto free_iovecs;
 447
 448        rc = process_vm_rw_core(pid, iov_l, liovcnt, iov_r, riovcnt, flags,
 449                           vm_write);
 450
 451free_iovecs:
 452        if (iov_r != iovstack_r)
 453                kfree(iov_r);
 454        if (iov_l != iovstack_l)
 455                kfree(iov_l);
 456        return rc;
 457}
 458
 459asmlinkage ssize_t
 460compat_sys_process_vm_readv(compat_pid_t pid,
 461                            const struct compat_iovec __user *lvec,
 462                            unsigned long liovcnt,
 463                            const struct compat_iovec __user *rvec,
 464                            unsigned long riovcnt,
 465                            unsigned long flags)
 466{
 467        return compat_process_vm_rw(pid, lvec, liovcnt, rvec,
 468                                    riovcnt, flags, 0);
 469}
 470
 471asmlinkage ssize_t
 472compat_sys_process_vm_writev(compat_pid_t pid,
 473                             const struct compat_iovec __user *lvec,
 474                             unsigned long liovcnt,
 475                             const struct compat_iovec __user *rvec,
 476                             unsigned long riovcnt,
 477                             unsigned long flags)
 478{
 479        return compat_process_vm_rw(pid, lvec, liovcnt, rvec,
 480                                    riovcnt, flags, 1);
 481}
 482
 483#endif
 484