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 = 0;
  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                 /* Get the pages we're interested in */
 106                 pages = get_user_pages_unlocked(task, mm, pa, pages,
 107                                                 process_pages, flags);
 108                 if (pages <= 0)
 109                         return -EFAULT;
 110
 111                 bytes = pages * PAGE_SIZE - start_offset;
 112                 if (bytes > len)
 113                         bytes = len;
 114
 115                 rc = process_vm_rw_pages(process_pages,
 116                                          start_offset, bytes, iter,
 117                                          vm_write);
 118                 len -= bytes;
 119                 start_offset = 0;
 120                 nr_pages -= pages;
 121                 pa += pages * PAGE_SIZE;
 122                 while (pages)
 123                         put_page(process_pages[--pages]);
 124         }
 125
 126         return rc;
 127 }
 128
 129 /* Maximum number of entries for process pages array
 130    which lives on stack */
 131 #define PVM_MAX_PP_ARRAY_COUNT 16
 132
 133 /**
 134  * process_vm_rw_core - core of reading/writing pages from task specified
 135  * @pid: PID of process to read/write from/to
 136  * @iter: where to copy to/from locally
 137  * @rvec: iovec array specifying where to copy to/from in the other process
 138  * @riovcnt: size of rvec array
 139  * @flags: currently unused
 140  * @vm_write: 0 if reading from other process, 1 if writing to other process
 141  * Returns the number of bytes read/written or error code. May
 142  *  return less bytes than expected if an error occurs during the copying
 143  *  process.
 144  */
 145 static ssize_t process_vm_rw_core(pid_t pid, struct iov_iter *iter,
 146                                   const struct iovec *rvec,
 147                                   unsigned long riovcnt,
 148                                   unsigned long flags, int vm_write)
 149 {
 150         struct task_struct *task;
 151         struct page *pp_stack[PVM_MAX_PP_ARRAY_COUNT];
 152         struct page **process_pages = pp_stack;
 153         struct mm_struct *mm;
 154         unsigned long i;
 155         ssize_t rc = 0;
 156         unsigned long nr_pages = 0;
 157         unsigned long nr_pages_iov;
 158         ssize_t iov_len;
 159         size_t total_len = iov_iter_count(iter);
 160
 161         /*
 162          * Work out how many pages of struct pages we're going to need
 163          * when eventually calling get_user_pages
 164          */
 165         for (i = 0; i < riovcnt; i++) {
 166                 iov_len = rvec[i].iov_len;
 167                 if (iov_len > 0) {
 168                         nr_pages_iov = ((unsigned long)rvec[i].iov_base
 169                                         + iov_len)
 170                                 / PAGE_SIZE - (unsigned long)rvec[i].iov_base
 171                                 / PAGE_SIZE + 1;
 172                         nr_pages = max(nr_pages, nr_pages_iov);
 173                 }
 174         }
 175
 176         if (nr_pages == 0)
 177                 return 0;
 178
 179         if (nr_pages > PVM_MAX_PP_ARRAY_COUNT) {
 180                 /* For reliability don't try to kmalloc more than
 181                    2 pages worth */
 182                 process_pages = kmalloc(min_t(size_t, PVM_MAX_KMALLOC_PAGES,
 183                                               sizeof(struct pages *)*nr_pages),
 184                                         GFP_KERNEL);
 185
 186                 if (!process_pages)
 187                         return -ENOMEM;
 188         }
 189
 190         /* Get process information */
 191         rcu_read_lock();
 192         task = find_task_by_vpid(pid);
 193         if (task)
 194                 get_task_struct(task);
 195         rcu_read_unlock();
 196         if (!task) {
 197                 rc = -ESRCH;
 198                 goto free_proc_pages;
 199         }
 200
 201         mm = mm_access(task, PTRACE_MODE_ATTACH_REALCREDS);
 202         if (!mm || IS_ERR(mm)) {
 203                 rc = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH;
 204                 /*
 205                  * Explicitly map EACCES to EPERM as EPERM is a more a
 206                  * appropriate error code for process_vw_readv/writev
 207                  */
 208                 if (rc == -EACCES)
 209                         rc = -EPERM;
 210                 goto put_task_struct;
 211         }
 212
 213         for (i = 0; i < riovcnt && iov_iter_count(iter) && !rc; i++)
 214                 rc = process_vm_rw_single_vec(
 215                         (unsigned long)rvec[i].iov_base, rvec[i].iov_len,
 216                         iter, process_pages, mm, task, vm_write);
 217
 218         /* copied = space before - space after */
 219         total_len -= iov_iter_count(iter);
 220
 221         /* If we have managed to copy any data at all then
 222            we return the number of bytes copied. Otherwise
 223            we return the error code */
 224         if (total_len)
 225                 rc = total_len;
 226
 227         mmput(mm);
 228
 229 put_task_struct:
 230         put_task_struct(task);
 231
 232 free_proc_pages:
 233         if (process_pages != pp_stack)
 234                 kfree(process_pages);
 235         return rc;
 236 }
 237
 238 /**
 239  * process_vm_rw - check iovecs before calling core routine
 240  * @pid: PID of process to read/write from/to
 241  * @lvec: iovec array specifying where to copy to/from locally
 242  * @liovcnt: size of lvec array
 243  * @rvec: iovec array specifying where to copy to/from in the other process
 244  * @riovcnt: size of rvec array
 245  * @flags: currently unused
 246  * @vm_write: 0 if reading from other process, 1 if writing to other process
 247  * Returns the number of bytes read/written or error code. May
 248  *  return less bytes than expected if an error occurs during the copying
 249  *  process.
 250  */
 251 static ssize_t process_vm_rw(pid_t pid,
 252                              const struct iovec __user *lvec,
 253                              unsigned long liovcnt,
 254                              const struct iovec __user *rvec,
 255                              unsigned long riovcnt,
 256                              unsigned long flags, int vm_write)
 257 {
 258         struct iovec iovstack_l[UIO_FASTIOV];
 259         struct iovec iovstack_r[UIO_FASTIOV];
 260         struct iovec *iov_l = iovstack_l;
 261         struct iovec *iov_r = iovstack_r;
 262         struct iov_iter iter;
 263         ssize_t rc;
 264         int dir = vm_write ? WRITE : READ;
 265
 266         if (flags != 0)
 267                 return -EINVAL;
 268
 269         /* Check iovecs */
 270         rc = import_iovec(dir, lvec, liovcnt, UIO_FASTIOV, &iov_l, &iter);
 271         if (rc < 0)
 272                 return rc;
 273         if (!iov_iter_count(&iter))
 274                 goto free_iovecs;
 275
 276         rc = rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt, UIO_FASTIOV,
 277                                    iovstack_r, &iov_r);
 278         if (rc <= 0)
 279                 goto free_iovecs;
 280
 281         rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write);
 282
 283 free_iovecs:
 284         if (iov_r != iovstack_r)
 285                 kfree(iov_r);
 286         kfree(iov_l);
 287
 288         return rc;
 289 }
 290
 291 SYSCALL_DEFINE6(process_vm_readv, pid_t, pid, const struct iovec __user *, lvec,
 292                 unsigned long, liovcnt, const struct iovec __user *, rvec,
 293                 unsigned long, riovcnt, unsigned long, flags)
 294 {
 295         return process_vm_rw(pid, lvec, liovcnt, rvec, riovcnt, flags, 0);
 296 }
 297
 298 SYSCALL_DEFINE6(process_vm_writev, pid_t, pid,
 299                 const struct iovec __user *, lvec,
 300                 unsigned long, liovcnt, const struct iovec __user *, rvec,
 301                 unsigned long, riovcnt, unsigned long, flags)
 302 {
 303         return process_vm_rw(pid, lvec, liovcnt, rvec, riovcnt, flags, 1);
 304 }
 305
 306 #ifdef CONFIG_COMPAT
 307
 308 static ssize_t
 309 compat_process_vm_rw(compat_pid_t pid,
 310                      const struct compat_iovec __user *lvec,
 311                      unsigned long liovcnt,
 312                      const struct compat_iovec __user *rvec,
 313                      unsigned long riovcnt,
 314                      unsigned long flags, int vm_write)
 315 {
 316         struct iovec iovstack_l[UIO_FASTIOV];
 317         struct iovec iovstack_r[UIO_FASTIOV];
 318         struct iovec *iov_l = iovstack_l;
 319         struct iovec *iov_r = iovstack_r;
 320         struct iov_iter iter;
 321         ssize_t rc = -EFAULT;
 322         int dir = vm_write ? WRITE : READ;
 323
 324         if (flags != 0)
 325                 return -EINVAL;
 326
 327         rc = compat_import_iovec(dir, lvec, liovcnt, UIO_FASTIOV, &iov_l, &iter);
 328         if (rc < 0)
 329                 return rc;
 330         if (!iov_iter_count(&iter))
 331                 goto free_iovecs;
 332         rc = compat_rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt,
 333                                           UIO_FASTIOV, iovstack_r,
 334                                           &iov_r);
 335         if (rc <= 0)
 336                 goto free_iovecs;
 337
 338         rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write);
 339
 340 free_iovecs:
 341         if (iov_r != iovstack_r)
 342                 kfree(iov_r);
 343         kfree(iov_l);
 344         return rc;
 345 }
 346
 347 COMPAT_SYSCALL_DEFINE6(process_vm_readv, compat_pid_t, pid,
 348                        const struct compat_iovec __user *, lvec,
 349                        compat_ulong_t, liovcnt,
 350                        const struct compat_iovec __user *, rvec,
 351                        compat_ulong_t, riovcnt,
 352                        compat_ulong_t, flags)
 353 {
 354         return compat_process_vm_rw(pid, lvec, liovcnt, rvec,
 355                                     riovcnt, flags, 0);
 356 }
 357
 358 COMPAT_SYSCALL_DEFINE6(process_vm_writev, compat_pid_t, pid,
 359                        const struct compat_iovec __user *, lvec,
 360                        compat_ulong_t, liovcnt,
 361                        const struct compat_iovec __user *, rvec,
 362                        compat_ulong_t, riovcnt,
 363                        compat_ulong_t, flags)
 364 {
 365         return compat_process_vm_rw(pid, lvec, liovcnt, rvec,
 366                                     riovcnt, flags, 1);
 367 }
 368
 369 #endif