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                         if (copy > iov_iter_count(iter))
  50                                 copy = iov_iter_count(iter);
  51                         copied = iov_iter_copy_from_user(page, iter,
  52                                         offset, copy);
  53                         iov_iter_advance(iter, copied);
  54                         set_page_dirty_lock(page);
  55                 } else {
  56                         copied = copy_page_to_iter(page, offset, copy, iter);
  57                 }
  58                 len -= copied;
  59                 if (copied < copy && iov_iter_count(iter))
  60                         return -EFAULT;
  61                 offset = 0;
  62         }
  63         return 0;
  64 }
  65
  66 /* Maximum number of pages kmalloc'd to hold struct page's during copy */
  67 #define PVM_MAX_KMALLOC_PAGES (PAGE_SIZE * 2)
  68
  69 /**
  70  * process_vm_rw_single_vec - read/write pages from task specified
  71  * @addr: start memory address of target process
  72  * @len: size of area to copy to/from
  73  * @iter: where to copy to/from locally
  74  * @process_pages: struct pages area that can store at least
  75  *  nr_pages_to_copy struct page pointers
  76  * @mm: mm for task
  77  * @task: task to read/write from
  78  * @vm_write: 0 means copy from, 1 means copy to
  79  * Returns 0 on success or on failure error code
  80  */
  81 static int process_vm_rw_single_vec(unsigned long addr,
  82                                     unsigned long len,
  83                                     struct iov_iter *iter,
  84                                     struct page **process_pages,
  85                                     struct mm_struct *mm,
  86                                     struct task_struct *task,
  87                                     int vm_write)
  88 {
  89         unsigned long pa = addr & PAGE_MASK;
  90         unsigned long start_offset = addr - pa;
  91         unsigned long nr_pages;
  92         ssize_t rc = 0;
  93         unsigned long max_pages_per_loop = PVM_MAX_KMALLOC_PAGES
  94                 / sizeof(struct pages *);
  95
  96         /* Work out address and page range required */
  97         if (len == 0)
  98                 return 0;
  99         nr_pages = (addr + len - 1) / PAGE_SIZE - addr / PAGE_SIZE + 1;
 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                 down_read(&mm->mmap_sem);
 107                 pages = get_user_pages(task, mm, pa, pages,
 108                                       vm_write, 0, process_pages, NULL);
 109                 up_read(&mm->mmap_sem);
 110
 111                 if (pages <= 0)
 112                         return -EFAULT;
 113
 114                 bytes = pages * PAGE_SIZE - start_offset;
 115                 if (bytes > len)
 116                         bytes = len;
 117
 118                 rc = process_vm_rw_pages(process_pages,
 119                                          start_offset, bytes, iter,
 120                                          vm_write);
 121                 len -= bytes;
 122                 start_offset = 0;
 123                 nr_pages -= pages;
 124                 pa += pages * PAGE_SIZE;
 125                 while (pages)
 126                         put_page(process_pages[--pages]);
 127         }
 128
 129         return rc;
 130 }
 131
 132 /* Maximum number of entries for process pages array
 133    which lives on stack */
 134 #define PVM_MAX_PP_ARRAY_COUNT 16
 135
 136 /**
 137  * process_vm_rw_core - core of reading/writing pages from task specified
 138  * @pid: PID of process to read/write from/to
 139  * @iter: where to copy to/from locally
 140  * @rvec: iovec array specifying where to copy to/from in the other process
 141  * @riovcnt: size of rvec array
 142  * @flags: currently unused
 143  * @vm_write: 0 if reading from other process, 1 if writing to other process
 144  * Returns the number of bytes read/written or error code. May
 145  *  return less bytes than expected if an error occurs during the copying
 146  *  process.
 147  */
 148 static ssize_t process_vm_rw_core(pid_t pid, struct iov_iter *iter,
 149                                   const struct iovec *rvec,
 150                                   unsigned long riovcnt,
 151                                   unsigned long flags, int vm_write)
 152 {
 153         struct task_struct *task;
 154         struct page *pp_stack[PVM_MAX_PP_ARRAY_COUNT];
 155         struct page **process_pages = pp_stack;
 156         struct mm_struct *mm;
 157         unsigned long i;
 158         ssize_t rc = 0;
 159         unsigned long nr_pages = 0;
 160         unsigned long nr_pages_iov;
 161         ssize_t iov_len;
 162         size_t total_len = iov_iter_count(iter);
 163
 164         /*
 165          * Work out how many pages of struct pages we're going to need
 166          * when eventually calling get_user_pages
 167          */
 168         for (i = 0; i < riovcnt; i++) {
 169                 iov_len = rvec[i].iov_len;
 170                 if (iov_len > 0) {
 171                         nr_pages_iov = ((unsigned long)rvec[i].iov_base
 172                                         + iov_len)
 173                                 / PAGE_SIZE - (unsigned long)rvec[i].iov_base
 174                                 / PAGE_SIZE + 1;
 175                         nr_pages = max(nr_pages, nr_pages_iov);
 176                 }
 177         }
 178
 179         if (nr_pages == 0)
 180                 return 0;
 181
 182         if (nr_pages > PVM_MAX_PP_ARRAY_COUNT) {
 183                 /* For reliability don't try to kmalloc more than
 184                    2 pages worth */
 185                 process_pages = kmalloc(min_t(size_t, PVM_MAX_KMALLOC_PAGES,
 186                                               sizeof(struct pages *)*nr_pages),
 187                                         GFP_KERNEL);
 188
 189                 if (!process_pages)
 190                         return -ENOMEM;
 191         }
 192
 193         /* Get process information */
 194         rcu_read_lock();
 195         task = find_task_by_vpid(pid);
 196         if (task)
 197                 get_task_struct(task);
 198         rcu_read_unlock();
 199         if (!task) {
 200                 rc = -ESRCH;
 201                 goto free_proc_pages;
 202         }
 203
 204         mm = mm_access(task, PTRACE_MODE_ATTACH);
 205         if (!mm || IS_ERR(mm)) {
 206                 rc = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH;
 207                 /*
 208                  * Explicitly map EACCES to EPERM as EPERM is a more a
 209                  * appropriate error code for process_vw_readv/writev
 210                  */
 211                 if (rc == -EACCES)
 212                         rc = -EPERM;
 213                 goto put_task_struct;
 214         }
 215
 216         for (i = 0; i < riovcnt && iov_iter_count(iter) && !rc; i++)
 217                 rc = process_vm_rw_single_vec(
 218                         (unsigned long)rvec[i].iov_base, rvec[i].iov_len,
 219                         iter, process_pages, mm, task, vm_write);
 220
 221         /* copied = space before - space after */
 222         total_len -= iov_iter_count(iter);
 223
 224         /* If we have managed to copy any data at all then
 225            we return the number of bytes copied. Otherwise
 226            we return the error code */
 227         if (total_len)
 228                 rc = total_len;
 229
 230         mmput(mm);
 231
 232 put_task_struct:
 233         put_task_struct(task);
 234
 235 free_proc_pages:
 236         if (process_pages != pp_stack)
 237                 kfree(process_pages);
 238         return rc;
 239 }
 240
 241 /**
 242  * process_vm_rw - check iovecs before calling core routine
 243  * @pid: PID of process to read/write from/to
 244  * @lvec: iovec array specifying where to copy to/from locally
 245  * @liovcnt: size of lvec array
 246  * @rvec: iovec array specifying where to copy to/from in the other process
 247  * @riovcnt: size of rvec array
 248  * @flags: currently unused
 249  * @vm_write: 0 if reading from other process, 1 if writing to other process
 250  * Returns the number of bytes read/written or error code. May
 251  *  return less bytes than expected if an error occurs during the copying
 252  *  process.
 253  */
 254 static ssize_t process_vm_rw(pid_t pid,
 255                              const struct iovec __user *lvec,
 256                              unsigned long liovcnt,
 257                              const struct iovec __user *rvec,
 258                              unsigned long riovcnt,
 259                              unsigned long flags, int vm_write)
 260 {
 261         struct iovec iovstack_l[UIO_FASTIOV];
 262         struct iovec iovstack_r[UIO_FASTIOV];
 263         struct iovec *iov_l = iovstack_l;
 264         struct iovec *iov_r = iovstack_r;
 265         struct iov_iter iter;
 266         ssize_t rc;
 267
 268         if (flags != 0)
 269                 return -EINVAL;
 270
 271         /* Check iovecs */
 272         if (vm_write)
 273                 rc = rw_copy_check_uvector(WRITE, lvec, liovcnt, UIO_FASTIOV,
 274                                            iovstack_l, &iov_l);
 275         else
 276                 rc = rw_copy_check_uvector(READ, lvec, liovcnt, UIO_FASTIOV,
 277                                            iovstack_l, &iov_l);
 278         if (rc <= 0)
 279                 goto free_iovecs;
 280
 281         iov_iter_init(&iter, iov_l, liovcnt, rc, 0);
 282
 283         rc = rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt, UIO_FASTIOV,
 284                                    iovstack_r, &iov_r);
 285         if (rc <= 0)
 286                 goto free_iovecs;
 287
 288         rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write);
 289
 290 free_iovecs:
 291         if (iov_r != iovstack_r)
 292                 kfree(iov_r);
 293         if (iov_l != iovstack_l)
 294                 kfree(iov_l);
 295
 296         return rc;
 297 }
 298
 299 SYSCALL_DEFINE6(process_vm_readv, pid_t, pid, 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, 0);
 304 }
 305
 306 SYSCALL_DEFINE6(process_vm_writev, pid_t, pid,
 307                 const struct iovec __user *, lvec,
 308                 unsigned long, liovcnt, const struct iovec __user *, rvec,
 309                 unsigned long, riovcnt, unsigned long, flags)
 310 {
 311         return process_vm_rw(pid, lvec, liovcnt, rvec, riovcnt, flags, 1);
 312 }
 313
 314 #ifdef CONFIG_COMPAT
 315
 316 static ssize_t
 317 compat_process_vm_rw(compat_pid_t pid,
 318                      const struct compat_iovec __user *lvec,
 319                      unsigned long liovcnt,
 320                      const struct compat_iovec __user *rvec,
 321                      unsigned long riovcnt,
 322                      unsigned long flags, int vm_write)
 323 {
 324         struct iovec iovstack_l[UIO_FASTIOV];
 325         struct iovec iovstack_r[UIO_FASTIOV];
 326         struct iovec *iov_l = iovstack_l;
 327         struct iovec *iov_r = iovstack_r;
 328         struct iov_iter iter;
 329         ssize_t rc = -EFAULT;
 330
 331         if (flags != 0)
 332                 return -EINVAL;
 333
 334         if (vm_write)
 335                 rc = compat_rw_copy_check_uvector(WRITE, lvec, liovcnt,
 336                                                   UIO_FASTIOV, iovstack_l,
 337                                                   &iov_l);
 338         else
 339                 rc = compat_rw_copy_check_uvector(READ, lvec, liovcnt,
 340                                                   UIO_FASTIOV, iovstack_l,
 341                                                   &iov_l);
 342         if (rc <= 0)
 343                 goto free_iovecs;
 344         iov_iter_init(&iter, iov_l, liovcnt, rc, 0);
 345         rc = compat_rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt,
 346                                           UIO_FASTIOV, iovstack_r,
 347                                           &iov_r);
 348         if (rc <= 0)
 349                 goto free_iovecs;
 350
 351         rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write);
 352
 353 free_iovecs:
 354         if (iov_r != iovstack_r)
 355                 kfree(iov_r);
 356         if (iov_l != iovstack_l)
 357                 kfree(iov_l);
 358         return rc;
 359 }
 360
 361 COMPAT_SYSCALL_DEFINE6(process_vm_readv, compat_pid_t, pid,
 362                        const struct compat_iovec __user *, lvec,
 363                        compat_ulong_t, liovcnt,
 364                        const struct compat_iovec __user *, rvec,
 365                        compat_ulong_t, riovcnt,
 366                        compat_ulong_t, flags)
 367 {
 368         return compat_process_vm_rw(pid, lvec, liovcnt, rvec,
 369                                     riovcnt, flags, 0);
 370 }
 371
 372 COMPAT_SYSCALL_DEFINE6(process_vm_writev, compat_pid_t, pid,
 373                        const struct compat_iovec __user *, lvec,
 374                        compat_ulong_t, liovcnt,
 375                        const struct compat_iovec __user *, rvec,
 376                        compat_ulong_t, riovcnt,
 377                        compat_ulong_t, flags)
 378 {
 379         return compat_process_vm_rw(pid, lvec, liovcnt, rvec,
 380                                     riovcnt, flags, 1);
 381 }
 382
 383 #endif