mm/process_vm_access.c

   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  */
  42 static 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
 136 end:
 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  */
 170 static 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  */
 241 static 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;
 330 put_mm:
 331         mmput(mm);
 332
 333 put_task_struct:
 334         put_task_struct(task);
 335
 336 free_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  */
 355 static 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
 389 free_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
 398 SYSCALL_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
 405 SYSCALL_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
 415 asmlinkage ssize_t
 416 compat_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
 451 free_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
 459 asmlinkage ssize_t
 460 compat_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
 471 asmlinkage ssize_t
 472 compat_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