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 **iovp,
  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         const struct iovec *iov = *iovp;
  64
  65         *bytes_copied = 0;
  66
  67         /* Get the pages we're interested in */
  68         down_read(&mm->mmap_sem);
  69         pages_pinned = get_user_pages(task, mm, pa,
  70                                       nr_pages_to_copy,
  71                                       vm_write, 0, process_pages, NULL);
  72         up_read(&mm->mmap_sem);
  73
  74         if (pages_pinned != nr_pages_to_copy) {
  75                 rc = -EFAULT;
  76                 goto end;
  77         }
  78
  79         /* Do the copy for each page */
  80         for (pgs_copied = 0;
  81              (pgs_copied < nr_pages_to_copy) && (*lvec_current < lvec_cnt);
  82              pgs_copied++) {
  83                 /* Make sure we have a non zero length iovec */
  84                 while (*lvec_current < lvec_cnt
  85                        && iov->iov_len == 0) {
  86                         iov++;
  87                         (*lvec_current)++;
  88                 }
  89                 if (*lvec_current == lvec_cnt)
  90                         break;
  91
  92                 /*
  93                  * Will copy smallest of:
  94                  * - bytes remaining in page
  95                  * - bytes remaining in destination iovec
  96                  */
  97                 bytes_to_copy = min_t(ssize_t, PAGE_SIZE - start_offset,
  98                                       len - *bytes_copied);
  99                 bytes_to_copy = min_t(ssize_t, bytes_to_copy,
 100                                       iov->iov_len
 101                                       - *lvec_offset);
 102
 103                 target_kaddr = kmap(process_pages[pgs_copied]) + start_offset;
 104
 105                 if (vm_write)
 106                         ret = copy_from_user(target_kaddr,
 107                                              iov->iov_base
 108                                              + *lvec_offset,
 109                                              bytes_to_copy);
 110                 else
 111                         ret = copy_to_user(iov->iov_base
 112                                            + *lvec_offset,
 113                                            target_kaddr, bytes_to_copy);
 114                 kunmap(process_pages[pgs_copied]);
 115                 if (ret) {
 116                         *bytes_copied += bytes_to_copy - ret;
 117                         pgs_copied++;
 118                         rc = -EFAULT;
 119                         goto end;
 120                 }
 121                 *bytes_copied += bytes_to_copy;
 122                 *lvec_offset += bytes_to_copy;
 123                 if (*lvec_offset == iov->iov_len) {
 124                         /*
 125                          * Need to copy remaining part of page into the
 126                          * next iovec if there are any bytes left in page
 127                          */
 128                         (*lvec_current)++;
 129                         iov++;
 130                         *lvec_offset = 0;
 131                         start_offset = (start_offset + bytes_to_copy)
 132                                 % PAGE_SIZE;
 133                         if (start_offset)
 134                                 pgs_copied--;
 135                 } else {
 136                         start_offset = 0;
 137                 }
 138         }
 139
 140 end:
 141         if (vm_write) {
 142                 for (j = 0; j < pages_pinned; j++) {
 143                         if (j < pgs_copied)
 144                                 set_page_dirty_lock(process_pages[j]);
 145                         put_page(process_pages[j]);
 146                 }
 147         } else {
 148                 for (j = 0; j < pages_pinned; j++)
 149                         put_page(process_pages[j]);
 150         }
 151
 152         *iovp = iov;
 153         return rc;
 154 }
 155
 156 /* Maximum number of pages kmalloc'd to hold struct page's during copy */
 157 #define PVM_MAX_KMALLOC_PAGES (PAGE_SIZE * 2)
 158
 159 /**
 160  * process_vm_rw_single_vec - read/write pages from task specified
 161  * @addr: start memory address of target process
 162  * @len: size of area to copy to/from
 163  * @lvec: iovec array specifying where to copy to/from locally
 164  * @lvec_cnt: number of elements in iovec array
 165  * @lvec_current: index in iovec array we are up to
 166  * @lvec_offset: offset in bytes from current iovec iov_base we are up to
 167  * @process_pages: struct pages area that can store at least
 168  *  nr_pages_to_copy struct page pointers
 169  * @mm: mm for task
 170  * @task: task to read/write from
 171  * @vm_write: 0 means copy from, 1 means copy to
 172  * @bytes_copied: returns number of bytes successfully copied
 173  * Returns 0 on success or on failure error code
 174  */
 175 static int process_vm_rw_single_vec(unsigned long addr,
 176                                     unsigned long len,
 177                                     const struct iovec *lvec,
 178                                     unsigned long lvec_cnt,
 179                                     unsigned long *lvec_current,
 180                                     size_t *lvec_offset,
 181                                     struct page **process_pages,
 182                                     struct mm_struct *mm,
 183                                     struct task_struct *task,
 184                                     int vm_write,
 185                                     ssize_t *bytes_copied)
 186 {
 187         unsigned long pa = addr & PAGE_MASK;
 188         unsigned long start_offset = addr - pa;
 189         unsigned long nr_pages;
 190         ssize_t bytes_copied_loop;
 191         ssize_t rc = 0;
 192         unsigned long nr_pages_copied = 0;
 193         unsigned long nr_pages_to_copy;
 194         unsigned long max_pages_per_loop = PVM_MAX_KMALLOC_PAGES
 195                 / sizeof(struct pages *);
 196         const struct iovec *iov = lvec + *lvec_current;
 197
 198         *bytes_copied = 0;
 199
 200         /* Work out address and page range required */
 201         if (len == 0)
 202                 return 0;
 203         nr_pages = (addr + len - 1) / PAGE_SIZE - addr / PAGE_SIZE + 1;
 204
 205         while ((nr_pages_copied < nr_pages) && (*lvec_current < lvec_cnt)) {
 206                 nr_pages_to_copy = min(nr_pages - nr_pages_copied,
 207                                        max_pages_per_loop);
 208
 209                 rc = process_vm_rw_pages(task, mm, process_pages, pa,
 210                                          start_offset, len,
 211                                          &iov, lvec_cnt,
 212                                          lvec_current, lvec_offset,
 213                                          vm_write, nr_pages_to_copy,
 214                                          &bytes_copied_loop);
 215                 start_offset = 0;
 216                 *bytes_copied += bytes_copied_loop;
 217
 218                 if (rc < 0) {
 219                         return rc;
 220                 } else {
 221                         len -= bytes_copied_loop;
 222                         nr_pages_copied += nr_pages_to_copy;
 223                         pa += nr_pages_to_copy * PAGE_SIZE;
 224                 }
 225         }
 226
 227         return rc;
 228 }
 229
 230 /* Maximum number of entries for process pages array
 231    which lives on stack */
 232 #define PVM_MAX_PP_ARRAY_COUNT 16
 233
 234 /**
 235  * process_vm_rw_core - core of reading/writing pages from task specified
 236  * @pid: PID of process to read/write from/to
 237  * @lvec: iovec array specifying where to copy to/from locally
 238  * @liovcnt: size of lvec array
 239  * @rvec: iovec array specifying where to copy to/from in the other process
 240  * @riovcnt: size of rvec array
 241  * @flags: currently unused
 242  * @vm_write: 0 if reading from other process, 1 if writing to other process
 243  * Returns the number of bytes read/written or error code. May
 244  *  return less bytes than expected if an error occurs during the copying
 245  *  process.
 246  */
 247 static ssize_t process_vm_rw_core(pid_t pid, const struct iovec *lvec,
 248                                   unsigned long liovcnt,
 249                                   const struct iovec *rvec,
 250                                   unsigned long riovcnt,
 251                                   unsigned long flags, int vm_write)
 252 {
 253         struct task_struct *task;
 254         struct page *pp_stack[PVM_MAX_PP_ARRAY_COUNT];
 255         struct page **process_pages = pp_stack;
 256         struct mm_struct *mm;
 257         unsigned long i;
 258         ssize_t rc = 0;
 259         ssize_t bytes_copied_loop;
 260         ssize_t bytes_copied = 0;
 261         unsigned long nr_pages = 0;
 262         unsigned long nr_pages_iov;
 263         unsigned long iov_l_curr_idx = 0;
 264         size_t iov_l_curr_offset = 0;
 265         ssize_t iov_len;
 266
 267         /*
 268          * Work out how many pages of struct pages we're going to need
 269          * when eventually calling get_user_pages
 270          */
 271         for (i = 0; i < riovcnt; i++) {
 272                 iov_len = rvec[i].iov_len;
 273                 if (iov_len > 0) {
 274                         nr_pages_iov = ((unsigned long)rvec[i].iov_base
 275                                         + iov_len)
 276                                 / PAGE_SIZE - (unsigned long)rvec[i].iov_base
 277                                 / PAGE_SIZE + 1;
 278                         nr_pages = max(nr_pages, nr_pages_iov);
 279                 }
 280         }
 281
 282         if (nr_pages == 0)
 283                 return 0;
 284
 285         if (nr_pages > PVM_MAX_PP_ARRAY_COUNT) {
 286                 /* For reliability don't try to kmalloc more than
 287                    2 pages worth */
 288                 process_pages = kmalloc(min_t(size_t, PVM_MAX_KMALLOC_PAGES,
 289                                               sizeof(struct pages *)*nr_pages),
 290                                         GFP_KERNEL);
 291
 292                 if (!process_pages)
 293                         return -ENOMEM;
 294         }
 295
 296         /* Get process information */
 297         rcu_read_lock();
 298         task = find_task_by_vpid(pid);
 299         if (task)
 300                 get_task_struct(task);
 301         rcu_read_unlock();
 302         if (!task) {
 303                 rc = -ESRCH;
 304                 goto free_proc_pages;
 305         }
 306
 307         mm = mm_access(task, PTRACE_MODE_ATTACH);
 308         if (!mm || IS_ERR(mm)) {
 309                 rc = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH;
 310                 /*
 311                  * Explicitly map EACCES to EPERM as EPERM is a more a
 312                  * appropriate error code for process_vw_readv/writev
 313                  */
 314                 if (rc == -EACCES)
 315                         rc = -EPERM;
 316                 goto put_task_struct;
 317         }
 318
 319         for (i = 0; i < riovcnt && iov_l_curr_idx < liovcnt; i++) {
 320                 rc = process_vm_rw_single_vec(
 321                         (unsigned long)rvec[i].iov_base, rvec[i].iov_len,
 322                         lvec, liovcnt, &iov_l_curr_idx, &iov_l_curr_offset,
 323                         process_pages, mm, task, vm_write, &bytes_copied_loop);
 324                 bytes_copied += bytes_copied_loop;
 325                 if (rc != 0) {
 326                         /* If we have managed to copy any data at all then
 327                            we return the number of bytes copied. Otherwise
 328                            we return the error code */
 329                         if (bytes_copied)
 330                                 rc = bytes_copied;
 331                         goto put_mm;
 332                 }
 333         }
 334
 335         rc = bytes_copied;
 336 put_mm:
 337         mmput(mm);
 338
 339 put_task_struct:
 340         put_task_struct(task);
 341
 342 free_proc_pages:
 343         if (process_pages != pp_stack)
 344                 kfree(process_pages);
 345         return rc;
 346 }
 347
 348 /**
 349  * process_vm_rw - check iovecs before calling core routine
 350  * @pid: PID of process to read/write from/to
 351  * @lvec: iovec array specifying where to copy to/from locally
 352  * @liovcnt: size of lvec array
 353  * @rvec: iovec array specifying where to copy to/from in the other process
 354  * @riovcnt: size of rvec array
 355  * @flags: currently unused
 356  * @vm_write: 0 if reading from other process, 1 if writing to other process
 357  * Returns the number of bytes read/written or error code. May
 358  *  return less bytes than expected if an error occurs during the copying
 359  *  process.
 360  */
 361 static ssize_t process_vm_rw(pid_t pid,
 362                              const struct iovec __user *lvec,
 363                              unsigned long liovcnt,
 364                              const struct iovec __user *rvec,
 365                              unsigned long riovcnt,
 366                              unsigned long flags, int vm_write)
 367 {
 368         struct iovec iovstack_l[UIO_FASTIOV];
 369         struct iovec iovstack_r[UIO_FASTIOV];
 370         struct iovec *iov_l = iovstack_l;
 371         struct iovec *iov_r = iovstack_r;
 372         ssize_t rc;
 373
 374         if (flags != 0)
 375                 return -EINVAL;
 376
 377         /* Check iovecs */
 378         if (vm_write)
 379                 rc = rw_copy_check_uvector(WRITE, lvec, liovcnt, UIO_FASTIOV,
 380                                            iovstack_l, &iov_l);
 381         else
 382                 rc = rw_copy_check_uvector(READ, lvec, liovcnt, UIO_FASTIOV,
 383                                            iovstack_l, &iov_l);
 384         if (rc <= 0)
 385                 goto free_iovecs;
 386
 387         rc = rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt, UIO_FASTIOV,
 388                                    iovstack_r, &iov_r);
 389         if (rc <= 0)
 390                 goto free_iovecs;
 391
 392         rc = process_vm_rw_core(pid, iov_l, liovcnt, iov_r, riovcnt, flags,
 393                                 vm_write);
 394
 395 free_iovecs:
 396         if (iov_r != iovstack_r)
 397                 kfree(iov_r);
 398         if (iov_l != iovstack_l)
 399                 kfree(iov_l);
 400
 401         return rc;
 402 }
 403
 404 SYSCALL_DEFINE6(process_vm_readv, pid_t, pid, const struct iovec __user *, lvec,
 405                 unsigned long, liovcnt, const struct iovec __user *, rvec,
 406                 unsigned long, riovcnt, unsigned long, flags)
 407 {
 408         return process_vm_rw(pid, lvec, liovcnt, rvec, riovcnt, flags, 0);
 409 }
 410
 411 SYSCALL_DEFINE6(process_vm_writev, pid_t, pid,
 412                 const struct iovec __user *, lvec,
 413                 unsigned long, liovcnt, const struct iovec __user *, rvec,
 414                 unsigned long, riovcnt, unsigned long, flags)
 415 {
 416         return process_vm_rw(pid, lvec, liovcnt, rvec, riovcnt, flags, 1);
 417 }
 418
 419 #ifdef CONFIG_COMPAT
 420
 421 asmlinkage ssize_t
 422 compat_process_vm_rw(compat_pid_t pid,
 423                      const struct compat_iovec __user *lvec,
 424                      unsigned long liovcnt,
 425                      const struct compat_iovec __user *rvec,
 426                      unsigned long riovcnt,
 427                      unsigned long flags, int vm_write)
 428 {
 429         struct iovec iovstack_l[UIO_FASTIOV];
 430         struct iovec iovstack_r[UIO_FASTIOV];
 431         struct iovec *iov_l = iovstack_l;
 432         struct iovec *iov_r = iovstack_r;
 433         ssize_t rc = -EFAULT;
 434
 435         if (flags != 0)
 436                 return -EINVAL;
 437
 438         if (vm_write)
 439                 rc = compat_rw_copy_check_uvector(WRITE, lvec, liovcnt,
 440                                                   UIO_FASTIOV, iovstack_l,
 441                                                   &iov_l);
 442         else
 443                 rc = compat_rw_copy_check_uvector(READ, lvec, liovcnt,
 444                                                   UIO_FASTIOV, iovstack_l,
 445                                                   &iov_l);
 446         if (rc <= 0)
 447                 goto free_iovecs;
 448         rc = compat_rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt,
 449                                           UIO_FASTIOV, iovstack_r,
 450                                           &iov_r);
 451         if (rc <= 0)
 452                 goto free_iovecs;
 453
 454         rc = process_vm_rw_core(pid, iov_l, liovcnt, iov_r, riovcnt, flags,
 455                            vm_write);
 456
 457 free_iovecs:
 458         if (iov_r != iovstack_r)
 459                 kfree(iov_r);
 460         if (iov_l != iovstack_l)
 461                 kfree(iov_l);
 462         return rc;
 463 }
 464
 465 asmlinkage ssize_t
 466 compat_sys_process_vm_readv(compat_pid_t pid,
 467                             const struct compat_iovec __user *lvec,
 468                             unsigned long liovcnt,
 469                             const struct compat_iovec __user *rvec,
 470                             unsigned long riovcnt,
 471                             unsigned long flags)
 472 {
 473         return compat_process_vm_rw(pid, lvec, liovcnt, rvec,
 474                                     riovcnt, flags, 0);
 475 }
 476
 477 asmlinkage ssize_t
 478 compat_sys_process_vm_writev(compat_pid_t pid,
 479                              const struct compat_iovec __user *lvec,
 480                              unsigned long liovcnt,
 481                              const struct compat_iovec __user *rvec,
 482                              unsigned long riovcnt,
 483                              unsigned long flags)
 484 {
 485         return compat_process_vm_rw(pid, lvec, liovcnt, rvec,
 486                                     riovcnt, flags, 1);
 487 }
 488
 489 #endif