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  * @pages: array of pointers to pages we want to copy
  27  * @start_offset: offset in page to start copying from/to
  28  * @len: number of bytes to copy
  29  * @iter: where to copy to/from locally
  30  * @vm_write: 0 means copy from, 1 means copy to
  31  * Returns 0 on success, error code otherwise
  32  */
  33 static int process_vm_rw_pages(struct page **pages,
  34                                unsigned offset,
  35                                size_t len,
  36                                struct iov_iter *iter,
  37                                int vm_write)
  38 {
  39         /* Do the copy for each page */
  40         while (len && iov_iter_count(iter)) {
  41                 struct page *page = *pages++;
  42                 size_t copy = PAGE_SIZE - offset;
  43                 size_t copied;
  44
  45                 if (copy > len)
  46                         copy = len;
  47
  48                 if (vm_write) {
  49                         copied = copy_page_from_iter(page, offset, copy, iter);
  50                         set_page_dirty_lock(page);
  51                 } else {
  52                         copied = copy_page_to_iter(page, offset, copy, iter);
  53                 }
  54                 len -= copied;
  55                 if (copied < copy && iov_iter_count(iter))
  56                         return -EFAULT;
  57                 offset = 0;
  58         }
  59         return 0;
  60 }
  61
  62 /* Maximum number of pages kmalloc'd to hold struct page's during copy */
  63 #define PVM_MAX_KMALLOC_PAGES (PAGE_SIZE * 2)
  64
  65 /**
  66  * process_vm_rw_single_vec - read/write pages from task specified
  67  * @addr: start memory address of target process
  68  * @len: size of area to copy to/from
  69  * @iter: where to copy to/from locally
  70  * @process_pages: struct pages area that can store at least
  71  *  nr_pages_to_copy struct page pointers
  72  * @mm: mm for task
  73  * @task: task to read/write from
  74  * @vm_write: 0 means copy from, 1 means copy to
  75  * Returns 0 on success or on failure error code
  76  */
  77 static int process_vm_rw_single_vec(unsigned long addr,
  78                                     unsigned long len,
  79                                     struct iov_iter *iter,
  80                                     struct page **process_pages,
  81                                     struct mm_struct *mm,
  82                                     struct task_struct *task,
  83                                     int vm_write)
  84 {
  85         unsigned long pa = addr & PAGE_MASK;
  86         unsigned long start_offset = addr - pa;
  87         unsigned long nr_pages;
  88         ssize_t rc = 0;
  89         unsigned long max_pages_per_loop = PVM_MAX_KMALLOC_PAGES
  90                 / sizeof(struct pages *);
  91         unsigned int flags = FOLL_REMOTE;
  92
  93         /* Work out address and page range required */
  94         if (len == 0)
  95                 return 0;
  96         nr_pages = (addr + len - 1) / PAGE_SIZE - addr / PAGE_SIZE + 1;
  97
  98         if (vm_write)
  99                 flags |= FOLL_WRITE;
 100
 101         while (!rc && nr_pages && iov_iter_count(iter)) {
 102                 int pages = min(nr_pages, max_pages_per_loop);
 103                 size_t bytes;
 104
 105                 /*
 106                  * Get the pages we're interested in.  We must
 107                  * add FOLL_REMOTE because task/mm might not
 108                  * current/current->mm
 109                  */
 110                 pages = __get_user_pages_unlocked(task, mm, pa, pages,
 111                                                   process_pages, flags);
 112                 if (pages <= 0)
 113                         return -EFAULT;
 114
 115                 bytes = pages * PAGE_SIZE - start_offset;
 116                 if (bytes > len)
 117                         bytes = len;
 118
 119                 rc = process_vm_rw_pages(process_pages,
 120                                          start_offset, bytes, iter,
 121                                          vm_write);
 122                 len -= bytes;
 123                 start_offset = 0;
 124                 nr_pages -= pages;
 125                 pa += pages * PAGE_SIZE;
 126                 while (pages)
 127                         put_page(process_pages[--pages]);
 128         }
 129
 130         return rc;
 131 }
 132
 133 /* Maximum number of entries for process pages array
 134    which lives on stack */
 135 #define PVM_MAX_PP_ARRAY_COUNT 16
 136
 137 /**
 138  * process_vm_rw_core - core of reading/writing pages from task specified
 139  * @pid: PID of process to read/write from/to
 140  * @iter: where to copy to/from locally
 141  * @rvec: iovec array specifying where to copy to/from in the other process
 142  * @riovcnt: size of rvec array
 143  * @flags: currently unused
 144  * @vm_write: 0 if reading from other process, 1 if writing to other process
 145  * Returns the number of bytes read/written or error code. May
 146  *  return less bytes than expected if an error occurs during the copying
 147  *  process.
 148  */
 149 static ssize_t process_vm_rw_core(pid_t pid, struct iov_iter *iter,
 150                                   const struct iovec *rvec,
 151                                   unsigned long riovcnt,
 152                                   unsigned long flags, int vm_write)
 153 {
 154         struct task_struct *task;
 155         struct page *pp_stack[PVM_MAX_PP_ARRAY_COUNT];
 156         struct page **process_pages = pp_stack;
 157         struct mm_struct *mm;
 158         unsigned long i;
 159         ssize_t rc = 0;
 160         unsigned long nr_pages = 0;
 161         unsigned long nr_pages_iov;
 162         ssize_t iov_len;
 163         size_t total_len = iov_iter_count(iter);
 164
 165         /*
 166          * Work out how many pages of struct pages we're going to need
 167          * when eventually calling get_user_pages
 168          */
 169         for (i = 0; i < riovcnt; i++) {
 170                 iov_len = rvec[i].iov_len;
 171                 if (iov_len > 0) {
 172                         nr_pages_iov = ((unsigned long)rvec[i].iov_base
 173                                         + iov_len)
 174                                 / PAGE_SIZE - (unsigned long)rvec[i].iov_base
 175                                 / PAGE_SIZE + 1;
 176                         nr_pages = max(nr_pages, nr_pages_iov);
 177                 }
 178         }
 179
 180         if (nr_pages == 0)
 181                 return 0;
 182
 183         if (nr_pages > PVM_MAX_PP_ARRAY_COUNT) {
 184                 /* For reliability don't try to kmalloc more than
 185                    2 pages worth */
 186                 process_pages = kmalloc(min_t(size_t, PVM_MAX_KMALLOC_PAGES,
 187                                               sizeof(struct pages *)*nr_pages),
 188                                         GFP_KERNEL);
 189
 190                 if (!process_pages)
 191                         return -ENOMEM;
 192         }
 193
 194         /* Get process information */
 195         rcu_read_lock();
 196         task = find_task_by_vpid(pid);
 197         if (task)
 198                 get_task_struct(task);
 199         rcu_read_unlock();
 200         if (!task) {
 201                 rc = -ESRCH;
 202                 goto free_proc_pages;
 203         }
 204
 205         mm = mm_access(task, PTRACE_MODE_ATTACH_REALCREDS);
 206         if (!mm || IS_ERR(mm)) {
 207                 rc = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH;
 208                 /*
 209                  * Explicitly map EACCES to EPERM as EPERM is a more a
 210                  * appropriate error code for process_vw_readv/writev
 211                  */
 212                 if (rc == -EACCES)
 213                         rc = -EPERM;
 214                 goto put_task_struct;
 215         }
 216
 217         for (i = 0; i < riovcnt && iov_iter_count(iter) && !rc; i++)
 218                 rc = process_vm_rw_single_vec(
 219                         (unsigned long)rvec[i].iov_base, rvec[i].iov_len,
 220                         iter, process_pages, mm, task, vm_write);
 221
 222         /* copied = space before - space after */
 223         total_len -= iov_iter_count(iter);
 224
 225         /* If we have managed to copy any data at all then
 226            we return the number of bytes copied. Otherwise
 227            we return the error code */
 228         if (total_len)
 229                 rc = total_len;
 230
 231         mmput(mm);
 232
 233 put_task_struct:
 234         put_task_struct(task);
 235
 236 free_proc_pages:
 237         if (process_pages != pp_stack)
 238                 kfree(process_pages);
 239         return rc;
 240 }
 241
 242 /**
 243  * process_vm_rw - check iovecs before calling core routine
 244  * @pid: PID of process to read/write from/to
 245  * @lvec: iovec array specifying where to copy to/from locally
 246  * @liovcnt: size of lvec array
 247  * @rvec: iovec array specifying where to copy to/from in the other process
 248  * @riovcnt: size of rvec array
 249  * @flags: currently unused
 250  * @vm_write: 0 if reading from other process, 1 if writing to other process
 251  * Returns the number of bytes read/written or error code. May
 252  *  return less bytes than expected if an error occurs during the copying
 253  *  process.
 254  */
 255 static ssize_t process_vm_rw(pid_t pid,
 256                              const struct iovec __user *lvec,
 257                              unsigned long liovcnt,
 258                              const struct iovec __user *rvec,
 259                              unsigned long riovcnt,
 260                              unsigned long flags, int vm_write)
 261 {
 262         struct iovec iovstack_l[UIO_FASTIOV];
 263         struct iovec iovstack_r[UIO_FASTIOV];
 264         struct iovec *iov_l = iovstack_l;
 265         struct iovec *iov_r = iovstack_r;
 266         struct iov_iter iter;
 267         ssize_t rc;
 268         int dir = vm_write ? WRITE : READ;
 269
 270         if (flags != 0)
 271                 return -EINVAL;
 272
 273         /* Check iovecs */
 274         rc = import_iovec(dir, lvec, liovcnt, UIO_FASTIOV, &iov_l, &iter);
 275         if (rc < 0)
 276                 return rc;
 277         if (!iov_iter_count(&iter))
 278                 goto free_iovecs;
 279
 280         rc = rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt, UIO_FASTIOV,
 281                                    iovstack_r, &iov_r);
 282         if (rc <= 0)
 283                 goto free_iovecs;
 284
 285         rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write);
 286
 287 free_iovecs:
 288         if (iov_r != iovstack_r)
 289                 kfree(iov_r);
 290         kfree(iov_l);
 291
 292         return rc;
 293 }
 294
 295 SYSCALL_DEFINE6(process_vm_readv, pid_t, pid, const struct iovec __user *, lvec,
 296                 unsigned long, liovcnt, const struct iovec __user *, rvec,
 297                 unsigned long, riovcnt, unsigned long, flags)
 298 {
 299         return process_vm_rw(pid, lvec, liovcnt, rvec, riovcnt, flags, 0);
 300 }
 301
 302 SYSCALL_DEFINE6(process_vm_writev, pid_t, pid,
 303                 const struct iovec __user *, lvec,
 304                 unsigned long, liovcnt, const struct iovec __user *, rvec,
 305                 unsigned long, riovcnt, unsigned long, flags)
 306 {
 307         return process_vm_rw(pid, lvec, liovcnt, rvec, riovcnt, flags, 1);
 308 }
 309
 310 #ifdef CONFIG_COMPAT
 311
 312 static ssize_t
 313 compat_process_vm_rw(compat_pid_t pid,
 314                      const struct compat_iovec __user *lvec,
 315                      unsigned long liovcnt,
 316                      const struct compat_iovec __user *rvec,
 317                      unsigned long riovcnt,
 318                      unsigned long flags, int vm_write)
 319 {
 320         struct iovec iovstack_l[UIO_FASTIOV];
 321         struct iovec iovstack_r[UIO_FASTIOV];
 322         struct iovec *iov_l = iovstack_l;
 323         struct iovec *iov_r = iovstack_r;
 324         struct iov_iter iter;
 325         ssize_t rc = -EFAULT;
 326         int dir = vm_write ? WRITE : READ;
 327
 328         if (flags != 0)
 329                 return -EINVAL;
 330
 331         rc = compat_import_iovec(dir, lvec, liovcnt, UIO_FASTIOV, &iov_l, &iter);
 332         if (rc < 0)
 333                 return rc;
 334         if (!iov_iter_count(&iter))
 335                 goto free_iovecs;
 336         rc = compat_rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt,
 337                                           UIO_FASTIOV, iovstack_r,
 338                                           &iov_r);
 339         if (rc <= 0)
 340                 goto free_iovecs;
 341
 342         rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write);
 343
 344 free_iovecs:
 345         if (iov_r != iovstack_r)
 346                 kfree(iov_r);
 347         kfree(iov_l);
 348         return rc;
 349 }
 350
 351 COMPAT_SYSCALL_DEFINE6(process_vm_readv, compat_pid_t, pid,
 352                        const struct compat_iovec __user *, lvec,
 353                        compat_ulong_t, liovcnt,
 354                        const struct compat_iovec __user *, rvec,
 355                        compat_ulong_t, riovcnt,
 356                        compat_ulong_t, flags)
 357 {
 358         return compat_process_vm_rw(pid, lvec, liovcnt, rvec,
 359                                     riovcnt, flags, 0);
 360 }
 361
 362 COMPAT_SYSCALL_DEFINE6(process_vm_writev, compat_pid_t, pid,
 363                        const struct compat_iovec __user *, lvec,
 364                        compat_ulong_t, liovcnt,
 365                        const struct compat_iovec __user *, rvec,
 366                        compat_ulong_t, riovcnt,
 367                        compat_ulong_t, flags)
 368 {
 369         return compat_process_vm_rw(pid, lvec, liovcnt, rvec,
 370                                     riovcnt, flags, 1);
 371 }
 372
 373 #endif