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/sched/mm.h>
  16 #include <linux/highmem.h>
  17 #include <linux/ptrace.h>
  18 #include <linux/slab.h>
  19 #include <linux/syscalls.h>
  20
  21 #ifdef CONFIG_COMPAT
  22 #include <linux/compat.h>
  23 #endif
  24
  25 /**
  26  * process_vm_rw_pages - read/write pages from task specified
  27  * @pages: array of pointers to pages we want to copy
  28  * @start_offset: offset in page to start copying from/to
  29  * @len: number of bytes to copy
  30  * @iter: where to copy to/from locally
  31  * @vm_write: 0 means copy from, 1 means copy to
  32  * Returns 0 on success, error code otherwise
  33  */
  34 static int process_vm_rw_pages(struct page **pages,
  35                                unsigned offset,
  36                                size_t len,
  37                                struct iov_iter *iter,
  38                                int vm_write)
  39 {
  40         /* Do the copy for each page */
  41         while (len && iov_iter_count(iter)) {
  42                 struct page *page = *pages++;
  43                 size_t copy = PAGE_SIZE - offset;
  44                 size_t copied;
  45
  46                 if (copy > len)
  47                         copy = len;
  48
  49                 if (vm_write) {
  50                         copied = copy_page_from_iter(page, offset, copy, iter);
  51                         set_page_dirty_lock(page);
  52                 } else {
  53                         copied = copy_page_to_iter(page, offset, copy, iter);
  54                 }
  55                 len -= copied;
  56                 if (copied < copy && iov_iter_count(iter))
  57                         return -EFAULT;
  58                 offset = 0;
  59         }
  60         return 0;
  61 }
  62
  63 /* Maximum number of pages kmalloc'd to hold struct page's during copy */
  64 #define PVM_MAX_KMALLOC_PAGES (PAGE_SIZE * 2)
  65
  66 /**
  67  * process_vm_rw_single_vec - read/write pages from task specified
  68  * @addr: start memory address of target process
  69  * @len: size of area to copy to/from
  70  * @iter: where to copy to/from locally
  71  * @process_pages: struct pages area that can store at least
  72  *  nr_pages_to_copy struct page pointers
  73  * @mm: mm for task
  74  * @task: task to read/write from
  75  * @vm_write: 0 means copy from, 1 means copy to
  76  * Returns 0 on success or on failure error code
  77  */
  78 static int process_vm_rw_single_vec(unsigned long addr,
  79                                     unsigned long len,
  80                                     struct iov_iter *iter,
  81                                     struct page **process_pages,
  82                                     struct mm_struct *mm,
  83                                     struct task_struct *task,
  84                                     int vm_write)
  85 {
  86         unsigned long pa = addr & PAGE_MASK;
  87         unsigned long start_offset = addr - pa;
  88         unsigned long nr_pages;
  89         ssize_t rc = 0;
  90         unsigned long max_pages_per_loop = PVM_MAX_KMALLOC_PAGES
  91                 / sizeof(struct pages *);
  92         unsigned int flags = 0;
  93
  94         /* Work out address and page range required */
  95         if (len == 0)
  96                 return 0;
  97         nr_pages = (addr + len - 1) / PAGE_SIZE - addr / PAGE_SIZE + 1;
  98
  99         if (vm_write)
 100                 flags |= FOLL_WRITE;
 101
 102         while (!rc && nr_pages && iov_iter_count(iter)) {
 103                 int pages = min(nr_pages, max_pages_per_loop);
 104                 int locked = 1;
 105                 size_t bytes;
 106
 107                 /*
 108                  * Get the pages we're interested in.  We must
 109                  * access remotely because task/mm might not
 110                  * current/current->mm
 111                  */
 112                 down_read(&mm->mmap_sem);
 113                 pages = get_user_pages_remote(task, mm, pa, pages, flags,
 114                                               process_pages, NULL, &locked);
 115                 if (locked)
 116                         up_read(&mm->mmap_sem);
 117                 if (pages <= 0)
 118                         return -EFAULT;
 119
 120                 bytes = pages * PAGE_SIZE - start_offset;
 121                 if (bytes > len)
 122                         bytes = len;
 123
 124                 rc = process_vm_rw_pages(process_pages,
 125                                          start_offset, bytes, iter,
 126                                          vm_write);
 127                 len -= bytes;
 128                 start_offset = 0;
 129                 nr_pages -= pages;
 130                 pa += pages * PAGE_SIZE;
 131                 while (pages)
 132                         put_page(process_pages[--pages]);
 133         }
 134
 135         return rc;
 136 }
 137
 138 /* Maximum number of entries for process pages array
 139    which lives on stack */
 140 #define PVM_MAX_PP_ARRAY_COUNT 16
 141
 142 /**
 143  * process_vm_rw_core - core of reading/writing pages from task specified
 144  * @pid: PID of process to read/write from/to
 145  * @iter: where to copy to/from locally
 146  * @rvec: iovec array specifying where to copy to/from in the other process
 147  * @riovcnt: size of rvec array
 148  * @flags: currently unused
 149  * @vm_write: 0 if reading from other process, 1 if writing to other process
 150  * Returns the number of bytes read/written or error code. May
 151  *  return less bytes than expected if an error occurs during the copying
 152  *  process.
 153  */
 154 static ssize_t process_vm_rw_core(pid_t pid, struct iov_iter *iter,
 155                                   const struct iovec *rvec,
 156                                   unsigned long riovcnt,
 157                                   unsigned long flags, int vm_write)
 158 {
 159         struct task_struct *task;
 160         struct page *pp_stack[PVM_MAX_PP_ARRAY_COUNT];
 161         struct page **process_pages = pp_stack;
 162         struct mm_struct *mm;
 163         unsigned long i;
 164         ssize_t rc = 0;
 165         unsigned long nr_pages = 0;
 166         unsigned long nr_pages_iov;
 167         ssize_t iov_len;
 168         size_t total_len = iov_iter_count(iter);
 169
 170         /*
 171          * Work out how many pages of struct pages we're going to need
 172          * when eventually calling get_user_pages
 173          */
 174         for (i = 0; i < riovcnt; i++) {
 175                 iov_len = rvec[i].iov_len;
 176                 if (iov_len > 0) {
 177                         nr_pages_iov = ((unsigned long)rvec[i].iov_base
 178                                         + iov_len)
 179                                 / PAGE_SIZE - (unsigned long)rvec[i].iov_base
 180                                 / PAGE_SIZE + 1;
 181                         nr_pages = max(nr_pages, nr_pages_iov);
 182                 }
 183         }
 184
 185         if (nr_pages == 0)
 186                 return 0;
 187
 188         if (nr_pages > PVM_MAX_PP_ARRAY_COUNT) {
 189                 /* For reliability don't try to kmalloc more than
 190                    2 pages worth */
 191                 process_pages = kmalloc(min_t(size_t, PVM_MAX_KMALLOC_PAGES,
 192                                               sizeof(struct pages *)*nr_pages),
 193                                         GFP_KERNEL);
 194
 195                 if (!process_pages)
 196                         return -ENOMEM;
 197         }
 198
 199         /* Get process information */
 200         rcu_read_lock();
 201         task = find_task_by_vpid(pid);
 202         if (task)
 203                 get_task_struct(task);
 204         rcu_read_unlock();
 205         if (!task) {
 206                 rc = -ESRCH;
 207                 goto free_proc_pages;
 208         }
 209
 210         mm = mm_access(task, PTRACE_MODE_ATTACH_REALCREDS);
 211         if (!mm || IS_ERR(mm)) {
 212                 rc = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH;
 213                 /*
 214                  * Explicitly map EACCES to EPERM as EPERM is a more a
 215                  * appropriate error code for process_vw_readv/writev
 216                  */
 217                 if (rc == -EACCES)
 218                         rc = -EPERM;
 219                 goto put_task_struct;
 220         }
 221
 222         for (i = 0; i < riovcnt && iov_iter_count(iter) && !rc; i++)
 223                 rc = process_vm_rw_single_vec(
 224                         (unsigned long)rvec[i].iov_base, rvec[i].iov_len,
 225                         iter, process_pages, mm, task, vm_write);
 226
 227         /* copied = space before - space after */
 228         total_len -= iov_iter_count(iter);
 229
 230         /* If we have managed to copy any data at all then
 231            we return the number of bytes copied. Otherwise
 232            we return the error code */
 233         if (total_len)
 234                 rc = total_len;
 235
 236         mmput(mm);
 237
 238 put_task_struct:
 239         put_task_struct(task);
 240
 241 free_proc_pages:
 242         if (process_pages != pp_stack)
 243                 kfree(process_pages);
 244         return rc;
 245 }
 246
 247 /**
 248  * process_vm_rw - check iovecs before calling core routine
 249  * @pid: PID of process to read/write from/to
 250  * @lvec: iovec array specifying where to copy to/from locally
 251  * @liovcnt: size of lvec array
 252  * @rvec: iovec array specifying where to copy to/from in the other process
 253  * @riovcnt: size of rvec array
 254  * @flags: currently unused
 255  * @vm_write: 0 if reading from other process, 1 if writing to other process
 256  * Returns the number of bytes read/written or error code. May
 257  *  return less bytes than expected if an error occurs during the copying
 258  *  process.
 259  */
 260 static ssize_t process_vm_rw(pid_t pid,
 261                              const struct iovec __user *lvec,
 262                              unsigned long liovcnt,
 263                              const struct iovec __user *rvec,
 264                              unsigned long riovcnt,
 265                              unsigned long flags, int vm_write)
 266 {
 267         struct iovec iovstack_l[UIO_FASTIOV];
 268         struct iovec iovstack_r[UIO_FASTIOV];
 269         struct iovec *iov_l = iovstack_l;
 270         struct iovec *iov_r = iovstack_r;
 271         struct iov_iter iter;
 272         ssize_t rc;
 273         int dir = vm_write ? WRITE : READ;
 274
 275         if (flags != 0)
 276                 return -EINVAL;
 277
 278         /* Check iovecs */
 279         rc = import_iovec(dir, lvec, liovcnt, UIO_FASTIOV, &iov_l, &iter);
 280         if (rc < 0)
 281                 return rc;
 282         if (!iov_iter_count(&iter))
 283                 goto free_iovecs;
 284
 285         rc = rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt, UIO_FASTIOV,
 286                                    iovstack_r, &iov_r);
 287         if (rc <= 0)
 288                 goto free_iovecs;
 289
 290         rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write);
 291
 292 free_iovecs:
 293         if (iov_r != iovstack_r)
 294                 kfree(iov_r);
 295         kfree(iov_l);
 296
 297         return rc;
 298 }
 299
 300 SYSCALL_DEFINE6(process_vm_readv, pid_t, pid, const struct iovec __user *, lvec,
 301                 unsigned long, liovcnt, const struct iovec __user *, rvec,
 302                 unsigned long, riovcnt, unsigned long, flags)
 303 {
 304         return process_vm_rw(pid, lvec, liovcnt, rvec, riovcnt, flags, 0);
 305 }
 306
 307 SYSCALL_DEFINE6(process_vm_writev, pid_t, pid,
 308                 const struct iovec __user *, lvec,
 309                 unsigned long, liovcnt, const struct iovec __user *, rvec,
 310                 unsigned long, riovcnt, unsigned long, flags)
 311 {
 312         return process_vm_rw(pid, lvec, liovcnt, rvec, riovcnt, flags, 1);
 313 }
 314
 315 #ifdef CONFIG_COMPAT
 316
 317 static ssize_t
 318 compat_process_vm_rw(compat_pid_t pid,
 319                      const struct compat_iovec __user *lvec,
 320                      unsigned long liovcnt,
 321                      const struct compat_iovec __user *rvec,
 322                      unsigned long riovcnt,
 323                      unsigned long flags, int vm_write)
 324 {
 325         struct iovec iovstack_l[UIO_FASTIOV];
 326         struct iovec iovstack_r[UIO_FASTIOV];
 327         struct iovec *iov_l = iovstack_l;
 328         struct iovec *iov_r = iovstack_r;
 329         struct iov_iter iter;
 330         ssize_t rc = -EFAULT;
 331         int dir = vm_write ? WRITE : READ;
 332
 333         if (flags != 0)
 334                 return -EINVAL;
 335
 336         rc = compat_import_iovec(dir, lvec, liovcnt, UIO_FASTIOV, &iov_l, &iter);
 337         if (rc < 0)
 338                 return rc;
 339         if (!iov_iter_count(&iter))
 340                 goto free_iovecs;
 341         rc = compat_rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt,
 342                                           UIO_FASTIOV, iovstack_r,
 343                                           &iov_r);
 344         if (rc <= 0)
 345                 goto free_iovecs;
 346
 347         rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write);
 348
 349 free_iovecs:
 350         if (iov_r != iovstack_r)
 351                 kfree(iov_r);
 352         kfree(iov_l);
 353         return rc;
 354 }
 355
 356 COMPAT_SYSCALL_DEFINE6(process_vm_readv, compat_pid_t, pid,
 357                        const struct compat_iovec __user *, lvec,
 358                        compat_ulong_t, liovcnt,
 359                        const struct compat_iovec __user *, rvec,
 360                        compat_ulong_t, riovcnt,
 361                        compat_ulong_t, flags)
 362 {
 363         return compat_process_vm_rw(pid, lvec, liovcnt, rvec,
 364                                     riovcnt, flags, 0);
 365 }
 366
 367 COMPAT_SYSCALL_DEFINE6(process_vm_writev, compat_pid_t, pid,
 368                        const struct compat_iovec __user *, lvec,
 369                        compat_ulong_t, liovcnt,
 370                        const struct compat_iovec __user *, rvec,
 371                        compat_ulong_t, riovcnt,
 372                        compat_ulong_t, flags)
 373 {
 374         return compat_process_vm_rw(pid, lvec, liovcnt, rvec,
 375                                     riovcnt, flags, 1);
 376 }
 377
 378 #endif