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                 int locked = 1;
 104                 size_t bytes;
 105
 106                 /*
 107                  * Get the pages we're interested in.  We must
 108                  * access remotely because task/mm might not
 109                  * current/current->mm
 110                  */
 111                 down_read(&mm->mmap_sem);
 112                 pages = get_user_pages_remote(task, mm, pa, pages, flags,
 113                                               process_pages, NULL, &locked);
 114                 if (locked)
 115                         up_read(&mm->mmap_sem);
 116                 if (pages <= 0)
 117                         return -EFAULT;
 118
 119                 bytes = pages * PAGE_SIZE - start_offset;
 120                 if (bytes > len)
 121                         bytes = len;
 122
 123                 rc = process_vm_rw_pages(process_pages,
 124                                          start_offset, bytes, iter,
 125                                          vm_write);
 126                 len -= bytes;
 127                 start_offset = 0;
 128                 nr_pages -= pages;
 129                 pa += pages * PAGE_SIZE;
 130                 while (pages)
 131                         put_page(process_pages[--pages]);
 132         }
 133
 134         return rc;
 135 }
 136
 137 /* Maximum number of entries for process pages array
 138    which lives on stack */
 139 #define PVM_MAX_PP_ARRAY_COUNT 16
 140
 141 /**
 142  * process_vm_rw_core - core of reading/writing pages from task specified
 143  * @pid: PID of process to read/write from/to
 144  * @iter: where to copy to/from locally
 145  * @rvec: iovec array specifying where to copy to/from in the other process
 146  * @riovcnt: size of rvec array
 147  * @flags: currently unused
 148  * @vm_write: 0 if reading from other process, 1 if writing to other process
 149  * Returns the number of bytes read/written or error code. May
 150  *  return less bytes than expected if an error occurs during the copying
 151  *  process.
 152  */
 153 static ssize_t process_vm_rw_core(pid_t pid, struct iov_iter *iter,
 154                                   const struct iovec *rvec,
 155                                   unsigned long riovcnt,
 156                                   unsigned long flags, int vm_write)
 157 {
 158         struct task_struct *task;
 159         struct page *pp_stack[PVM_MAX_PP_ARRAY_COUNT];
 160         struct page **process_pages = pp_stack;
 161         struct mm_struct *mm;
 162         unsigned long i;
 163         ssize_t rc = 0;
 164         unsigned long nr_pages = 0;
 165         unsigned long nr_pages_iov;
 166         ssize_t iov_len;
 167         size_t total_len = iov_iter_count(iter);
 168
 169         /*
 170          * Work out how many pages of struct pages we're going to need
 171          * when eventually calling get_user_pages
 172          */
 173         for (i = 0; i < riovcnt; i++) {
 174                 iov_len = rvec[i].iov_len;
 175                 if (iov_len > 0) {
 176                         nr_pages_iov = ((unsigned long)rvec[i].iov_base
 177                                         + iov_len)
 178                                 / PAGE_SIZE - (unsigned long)rvec[i].iov_base
 179                                 / PAGE_SIZE + 1;
 180                         nr_pages = max(nr_pages, nr_pages_iov);
 181                 }
 182         }
 183
 184         if (nr_pages == 0)
 185                 return 0;
 186
 187         if (nr_pages > PVM_MAX_PP_ARRAY_COUNT) {
 188                 /* For reliability don't try to kmalloc more than
 189                    2 pages worth */
 190                 process_pages = kmalloc(min_t(size_t, PVM_MAX_KMALLOC_PAGES,
 191                                               sizeof(struct pages *)*nr_pages),
 192                                         GFP_KERNEL);
 193
 194                 if (!process_pages)
 195                         return -ENOMEM;
 196         }
 197
 198         /* Get process information */
 199         rcu_read_lock();
 200         task = find_task_by_vpid(pid);
 201         if (task)
 202                 get_task_struct(task);
 203         rcu_read_unlock();
 204         if (!task) {
 205                 rc = -ESRCH;
 206                 goto free_proc_pages;
 207         }
 208
 209         mm = mm_access(task, PTRACE_MODE_ATTACH_REALCREDS);
 210         if (!mm || IS_ERR(mm)) {
 211                 rc = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH;
 212                 /*
 213                  * Explicitly map EACCES to EPERM as EPERM is a more a
 214                  * appropriate error code for process_vw_readv/writev
 215                  */
 216                 if (rc == -EACCES)
 217                         rc = -EPERM;
 218                 goto put_task_struct;
 219         }
 220
 221         for (i = 0; i < riovcnt && iov_iter_count(iter) && !rc; i++)
 222                 rc = process_vm_rw_single_vec(
 223                         (unsigned long)rvec[i].iov_base, rvec[i].iov_len,
 224                         iter, process_pages, mm, task, vm_write);
 225
 226         /* copied = space before - space after */
 227         total_len -= iov_iter_count(iter);
 228
 229         /* If we have managed to copy any data at all then
 230            we return the number of bytes copied. Otherwise
 231            we return the error code */
 232         if (total_len)
 233                 rc = total_len;
 234
 235         mmput(mm);
 236
 237 put_task_struct:
 238         put_task_struct(task);
 239
 240 free_proc_pages:
 241         if (process_pages != pp_stack)
 242                 kfree(process_pages);
 243         return rc;
 244 }
 245
 246 /**
 247  * process_vm_rw - check iovecs before calling core routine
 248  * @pid: PID of process to read/write from/to
 249  * @lvec: iovec array specifying where to copy to/from locally
 250  * @liovcnt: size of lvec array
 251  * @rvec: iovec array specifying where to copy to/from in the other process
 252  * @riovcnt: size of rvec array
 253  * @flags: currently unused
 254  * @vm_write: 0 if reading from other process, 1 if writing to other process
 255  * Returns the number of bytes read/written or error code. May
 256  *  return less bytes than expected if an error occurs during the copying
 257  *  process.
 258  */
 259 static ssize_t process_vm_rw(pid_t pid,
 260                              const struct iovec __user *lvec,
 261                              unsigned long liovcnt,
 262                              const struct iovec __user *rvec,
 263                              unsigned long riovcnt,
 264                              unsigned long flags, int vm_write)
 265 {
 266         struct iovec iovstack_l[UIO_FASTIOV];
 267         struct iovec iovstack_r[UIO_FASTIOV];
 268         struct iovec *iov_l = iovstack_l;
 269         struct iovec *iov_r = iovstack_r;
 270         struct iov_iter iter;
 271         ssize_t rc;
 272         int dir = vm_write ? WRITE : READ;
 273
 274         if (flags != 0)
 275                 return -EINVAL;
 276
 277         /* Check iovecs */
 278         rc = import_iovec(dir, lvec, liovcnt, UIO_FASTIOV, &iov_l, &iter);
 279         if (rc < 0)
 280                 return rc;
 281         if (!iov_iter_count(&iter))
 282                 goto free_iovecs;
 283
 284         rc = rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt, UIO_FASTIOV,
 285                                    iovstack_r, &iov_r);
 286         if (rc <= 0)
 287                 goto free_iovecs;
 288
 289         rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write);
 290
 291 free_iovecs:
 292         if (iov_r != iovstack_r)
 293                 kfree(iov_r);
 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         int dir = vm_write ? WRITE : READ;
 331
 332         if (flags != 0)
 333                 return -EINVAL;
 334
 335         rc = compat_import_iovec(dir, lvec, liovcnt, UIO_FASTIOV, &iov_l, &iter);
 336         if (rc < 0)
 337                 return rc;
 338         if (!iov_iter_count(&iter))
 339                 goto free_iovecs;
 340         rc = compat_rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt,
 341                                           UIO_FASTIOV, iovstack_r,
 342                                           &iov_r);
 343         if (rc <= 0)
 344                 goto free_iovecs;
 345
 346         rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write);
 347
 348 free_iovecs:
 349         if (iov_r != iovstack_r)
 350                 kfree(iov_r);
 351         kfree(iov_l);
 352         return rc;
 353 }
 354
 355 COMPAT_SYSCALL_DEFINE6(process_vm_readv, compat_pid_t, pid,
 356                        const struct compat_iovec __user *, lvec,
 357                        compat_ulong_t, liovcnt,
 358                        const struct compat_iovec __user *, rvec,
 359                        compat_ulong_t, riovcnt,
 360                        compat_ulong_t, flags)
 361 {
 362         return compat_process_vm_rw(pid, lvec, liovcnt, rvec,
 363                                     riovcnt, flags, 0);
 364 }
 365
 366 COMPAT_SYSCALL_DEFINE6(process_vm_writev, compat_pid_t, pid,
 367                        const struct compat_iovec __user *, lvec,
 368                        compat_ulong_t, liovcnt,
 369                        const struct compat_iovec __user *, rvec,
 370                        compat_ulong_t, riovcnt,
 371                        compat_ulong_t, flags)
 372 {
 373         return compat_process_vm_rw(pid, lvec, liovcnt, rvec,
 374                                     riovcnt, flags, 1);
 375 }
 376
 377 #endif