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
  92         /* Work out address and page range required */
  93         if (len == 0)
  94                 return 0;
  95         nr_pages = (addr + len - 1) / PAGE_SIZE - addr / PAGE_SIZE + 1;
  96
  97         while (!rc && nr_pages && iov_iter_count(iter)) {
  98                 int pages = min(nr_pages, max_pages_per_loop);
  99                 size_t bytes;
 100
 101                 /* Get the pages we're interested in */
 102                 pages = get_user_pages_unlocked(task, mm, pa, pages,
 103                                                 vm_write, 0, process_pages);
 104                 if (pages <= 0)
 105                         return -EFAULT;
 106
 107                 bytes = pages * PAGE_SIZE - start_offset;
 108                 if (bytes > len)
 109                         bytes = len;
 110
 111                 rc = process_vm_rw_pages(process_pages,
 112                                          start_offset, bytes, iter,
 113                                          vm_write);
 114                 len -= bytes;
 115                 start_offset = 0;
 116                 nr_pages -= pages;
 117                 pa += pages * PAGE_SIZE;
 118                 while (pages)
 119                         put_page(process_pages[--pages]);
 120         }
 121
 122         return rc;
 123 }
 124
 125 /* Maximum number of entries for process pages array
 126    which lives on stack */
 127 #define PVM_MAX_PP_ARRAY_COUNT 16
 128
 129 /**
 130  * process_vm_rw_core - core of reading/writing pages from task specified
 131  * @pid: PID of process to read/write from/to
 132  * @iter: where to copy to/from locally
 133  * @rvec: iovec array specifying where to copy to/from in the other process
 134  * @riovcnt: size of rvec array
 135  * @flags: currently unused
 136  * @vm_write: 0 if reading from other process, 1 if writing to other process
 137  * Returns the number of bytes read/written or error code. May
 138  *  return less bytes than expected if an error occurs during the copying
 139  *  process.
 140  */
 141 static ssize_t process_vm_rw_core(pid_t pid, struct iov_iter *iter,
 142                                   const struct iovec *rvec,
 143                                   unsigned long riovcnt,
 144                                   unsigned long flags, int vm_write)
 145 {
 146         struct task_struct *task;
 147         struct page *pp_stack[PVM_MAX_PP_ARRAY_COUNT];
 148         struct page **process_pages = pp_stack;
 149         struct mm_struct *mm;
 150         unsigned long i;
 151         ssize_t rc = 0;
 152         unsigned long nr_pages = 0;
 153         unsigned long nr_pages_iov;
 154         ssize_t iov_len;
 155         size_t total_len = iov_iter_count(iter);
 156
 157         /*
 158          * Work out how many pages of struct pages we're going to need
 159          * when eventually calling get_user_pages
 160          */
 161         for (i = 0; i < riovcnt; i++) {
 162                 iov_len = rvec[i].iov_len;
 163                 if (iov_len > 0) {
 164                         nr_pages_iov = ((unsigned long)rvec[i].iov_base
 165                                         + iov_len)
 166                                 / PAGE_SIZE - (unsigned long)rvec[i].iov_base
 167                                 / PAGE_SIZE + 1;
 168                         nr_pages = max(nr_pages, nr_pages_iov);
 169                 }
 170         }
 171
 172         if (nr_pages == 0)
 173                 return 0;
 174
 175         if (nr_pages > PVM_MAX_PP_ARRAY_COUNT) {
 176                 /* For reliability don't try to kmalloc more than
 177                    2 pages worth */
 178                 process_pages = kmalloc(min_t(size_t, PVM_MAX_KMALLOC_PAGES,
 179                                               sizeof(struct pages *)*nr_pages),
 180                                         GFP_KERNEL);
 181
 182                 if (!process_pages)
 183                         return -ENOMEM;
 184         }
 185
 186         /* Get process information */
 187         rcu_read_lock();
 188         task = find_task_by_vpid(pid);
 189         if (task)
 190                 get_task_struct(task);
 191         rcu_read_unlock();
 192         if (!task) {
 193                 rc = -ESRCH;
 194                 goto free_proc_pages;
 195         }
 196
 197         mm = mm_access(task, PTRACE_MODE_ATTACH_REALCREDS);
 198         if (!mm || IS_ERR(mm)) {
 199                 rc = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH;
 200                 /*
 201                  * Explicitly map EACCES to EPERM as EPERM is a more a
 202                  * appropriate error code for process_vw_readv/writev
 203                  */
 204                 if (rc == -EACCES)
 205                         rc = -EPERM;
 206                 goto put_task_struct;
 207         }
 208
 209         for (i = 0; i < riovcnt && iov_iter_count(iter) && !rc; i++)
 210                 rc = process_vm_rw_single_vec(
 211                         (unsigned long)rvec[i].iov_base, rvec[i].iov_len,
 212                         iter, process_pages, mm, task, vm_write);
 213
 214         /* copied = space before - space after */
 215         total_len -= iov_iter_count(iter);
 216
 217         /* If we have managed to copy any data at all then
 218            we return the number of bytes copied. Otherwise
 219            we return the error code */
 220         if (total_len)
 221                 rc = total_len;
 222
 223         mmput(mm);
 224
 225 put_task_struct:
 226         put_task_struct(task);
 227
 228 free_proc_pages:
 229         if (process_pages != pp_stack)
 230                 kfree(process_pages);
 231         return rc;
 232 }
 233
 234 /**
 235  * process_vm_rw - check iovecs before calling core routine
 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(pid_t pid,
 248                              const struct iovec __user *lvec,
 249                              unsigned long liovcnt,
 250                              const struct iovec __user *rvec,
 251                              unsigned long riovcnt,
 252                              unsigned long flags, int vm_write)
 253 {
 254         struct iovec iovstack_l[UIO_FASTIOV];
 255         struct iovec iovstack_r[UIO_FASTIOV];
 256         struct iovec *iov_l = iovstack_l;
 257         struct iovec *iov_r = iovstack_r;
 258         struct iov_iter iter;
 259         ssize_t rc;
 260         int dir = vm_write ? WRITE : READ;
 261
 262         if (flags != 0)
 263                 return -EINVAL;
 264
 265         /* Check iovecs */
 266         rc = import_iovec(dir, lvec, liovcnt, UIO_FASTIOV, &iov_l, &iter);
 267         if (rc < 0)
 268                 return rc;
 269         if (!iov_iter_count(&iter))
 270                 goto free_iovecs;
 271
 272         rc = rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt, UIO_FASTIOV,
 273                                    iovstack_r, &iov_r);
 274         if (rc <= 0)
 275                 goto free_iovecs;
 276
 277         rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write);
 278
 279 free_iovecs:
 280         if (iov_r != iovstack_r)
 281                 kfree(iov_r);
 282         kfree(iov_l);
 283
 284         return rc;
 285 }
 286
 287 SYSCALL_DEFINE6(process_vm_readv, pid_t, pid, const struct iovec __user *, lvec,
 288                 unsigned long, liovcnt, const struct iovec __user *, rvec,
 289                 unsigned long, riovcnt, unsigned long, flags)
 290 {
 291         return process_vm_rw(pid, lvec, liovcnt, rvec, riovcnt, flags, 0);
 292 }
 293
 294 SYSCALL_DEFINE6(process_vm_writev, pid_t, pid,
 295                 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, 1);
 300 }
 301
 302 #ifdef CONFIG_COMPAT
 303
 304 static ssize_t
 305 compat_process_vm_rw(compat_pid_t pid,
 306                      const struct compat_iovec __user *lvec,
 307                      unsigned long liovcnt,
 308                      const struct compat_iovec __user *rvec,
 309                      unsigned long riovcnt,
 310                      unsigned long flags, int vm_write)
 311 {
 312         struct iovec iovstack_l[UIO_FASTIOV];
 313         struct iovec iovstack_r[UIO_FASTIOV];
 314         struct iovec *iov_l = iovstack_l;
 315         struct iovec *iov_r = iovstack_r;
 316         struct iov_iter iter;
 317         ssize_t rc = -EFAULT;
 318         int dir = vm_write ? WRITE : READ;
 319
 320         if (flags != 0)
 321                 return -EINVAL;
 322
 323         rc = compat_import_iovec(dir, lvec, liovcnt, UIO_FASTIOV, &iov_l, &iter);
 324         if (rc < 0)
 325                 return rc;
 326         if (!iov_iter_count(&iter))
 327                 goto free_iovecs;
 328         rc = compat_rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt,
 329                                           UIO_FASTIOV, iovstack_r,
 330                                           &iov_r);
 331         if (rc <= 0)
 332                 goto free_iovecs;
 333
 334         rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write);
 335
 336 free_iovecs:
 337         if (iov_r != iovstack_r)
 338                 kfree(iov_r);
 339         kfree(iov_l);
 340         return rc;
 341 }
 342
 343 COMPAT_SYSCALL_DEFINE6(process_vm_readv, compat_pid_t, pid,
 344                        const struct compat_iovec __user *, lvec,
 345                        compat_ulong_t, liovcnt,
 346                        const struct compat_iovec __user *, rvec,
 347                        compat_ulong_t, riovcnt,
 348                        compat_ulong_t, flags)
 349 {
 350         return compat_process_vm_rw(pid, lvec, liovcnt, rvec,
 351                                     riovcnt, flags, 0);
 352 }
 353
 354 COMPAT_SYSCALL_DEFINE6(process_vm_writev, compat_pid_t, pid,
 355                        const struct compat_iovec __user *, lvec,
 356                        compat_ulong_t, liovcnt,
 357                        const struct compat_iovec __user *, rvec,
 358                        compat_ulong_t, riovcnt,
 359                        compat_ulong_t, flags)
 360 {
 361         return compat_process_vm_rw(pid, lvec, liovcnt, rvec,
 362                                     riovcnt, flags, 1);
 363 }
 364
 365 #endif