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  * @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  *
 151  * Returns the number of bytes read/written or error code. May
 152  *  return less bytes than expected if an error occurs during the copying
 153  *  process.
 154  */
 155 static ssize_t process_vm_rw_core(pid_t pid, struct iov_iter *iter,
 156                                   const struct iovec *rvec,
 157                                   unsigned long riovcnt,
 158                                   unsigned long flags, int vm_write)
 159 {
 160         struct task_struct *task;
 161         struct page *pp_stack[PVM_MAX_PP_ARRAY_COUNT];
 162         struct page **process_pages = pp_stack;
 163         struct mm_struct *mm;
 164         unsigned long i;
 165         ssize_t rc = 0;
 166         unsigned long nr_pages = 0;
 167         unsigned long nr_pages_iov;
 168         ssize_t iov_len;
 169         size_t total_len = iov_iter_count(iter);
 170
 171         /*
 172          * Work out how many pages of struct pages we're going to need
 173          * when eventually calling get_user_pages
 174          */
 175         for (i = 0; i < riovcnt; i++) {
 176                 iov_len = rvec[i].iov_len;
 177                 if (iov_len > 0) {
 178                         nr_pages_iov = ((unsigned long)rvec[i].iov_base
 179                                         + iov_len)
 180                                 / PAGE_SIZE - (unsigned long)rvec[i].iov_base
 181                                 / PAGE_SIZE + 1;
 182                         nr_pages = max(nr_pages, nr_pages_iov);
 183                 }
 184         }
 185
 186         if (nr_pages == 0)
 187                 return 0;
 188
 189         if (nr_pages > PVM_MAX_PP_ARRAY_COUNT) {
 190                 /* For reliability don't try to kmalloc more than
 191                    2 pages worth */
 192                 process_pages = kmalloc(min_t(size_t, PVM_MAX_KMALLOC_PAGES,
 193                                               sizeof(struct pages *)*nr_pages),
 194                                         GFP_KERNEL);
 195
 196                 if (!process_pages)
 197                         return -ENOMEM;
 198         }
 199
 200         /* Get process information */
 201         task = find_get_task_by_vpid(pid);
 202         if (!task) {
 203                 rc = -ESRCH;
 204                 goto free_proc_pages;
 205         }
 206
 207         mm = mm_access(task, PTRACE_MODE_ATTACH_REALCREDS);
 208         if (!mm || IS_ERR(mm)) {
 209                 rc = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH;
 210                 /*
 211                  * Explicitly map EACCES to EPERM as EPERM is a more a
 212                  * appropriate error code for process_vw_readv/writev
 213                  */
 214                 if (rc == -EACCES)
 215                         rc = -EPERM;
 216                 goto put_task_struct;
 217         }
 218
 219         for (i = 0; i < riovcnt && iov_iter_count(iter) && !rc; i++)
 220                 rc = process_vm_rw_single_vec(
 221                         (unsigned long)rvec[i].iov_base, rvec[i].iov_len,
 222                         iter, process_pages, mm, task, vm_write);
 223
 224         /* copied = space before - space after */
 225         total_len -= iov_iter_count(iter);
 226
 227         /* If we have managed to copy any data at all then
 228            we return the number of bytes copied. Otherwise
 229            we return the error code */
 230         if (total_len)
 231                 rc = total_len;
 232
 233         mmput(mm);
 234
 235 put_task_struct:
 236         put_task_struct(task);
 237
 238 free_proc_pages:
 239         if (process_pages != pp_stack)
 240                 kfree(process_pages);
 241         return rc;
 242 }
 243
 244 /**
 245  * process_vm_rw - check iovecs before calling core routine
 246  * @pid: PID of process to read/write from/to
 247  * @lvec: iovec array specifying where to copy to/from locally
 248  * @liovcnt: size of lvec array
 249  * @rvec: iovec array specifying where to copy to/from in the other process
 250  * @riovcnt: size of rvec array
 251  * @flags: currently unused
 252  * @vm_write: 0 if reading from other process, 1 if writing to other process
 253  *
 254  * Returns the number of bytes read/written or error code. May
 255  *  return less bytes than expected if an error occurs during the copying
 256  *  process.
 257  */
 258 static ssize_t process_vm_rw(pid_t pid,
 259                              const struct iovec __user *lvec,
 260                              unsigned long liovcnt,
 261                              const struct iovec __user *rvec,
 262                              unsigned long riovcnt,
 263                              unsigned long flags, int vm_write)
 264 {
 265         struct iovec iovstack_l[UIO_FASTIOV];
 266         struct iovec iovstack_r[UIO_FASTIOV];
 267         struct iovec *iov_l = iovstack_l;
 268         struct iovec *iov_r = iovstack_r;
 269         struct iov_iter iter;
 270         ssize_t rc;
 271         int dir = vm_write ? WRITE : READ;
 272
 273         if (flags != 0)
 274                 return -EINVAL;
 275
 276         /* Check iovecs */
 277         rc = import_iovec(dir, lvec, liovcnt, UIO_FASTIOV, &iov_l, &iter);
 278         if (rc < 0)
 279                 return rc;
 280         if (!iov_iter_count(&iter))
 281                 goto free_iovecs;
 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         kfree(iov_l);
 294
 295         return rc;
 296 }
 297
 298 SYSCALL_DEFINE6(process_vm_readv, pid_t, pid, const struct iovec __user *, lvec,
 299                 unsigned long, liovcnt, const struct iovec __user *, rvec,
 300                 unsigned long, riovcnt, unsigned long, flags)
 301 {
 302         return process_vm_rw(pid, lvec, liovcnt, rvec, riovcnt, flags, 0);
 303 }
 304
 305 SYSCALL_DEFINE6(process_vm_writev, pid_t, pid,
 306                 const struct iovec __user *, lvec,
 307                 unsigned long, liovcnt, const struct iovec __user *, rvec,
 308                 unsigned long, riovcnt, unsigned long, flags)
 309 {
 310         return process_vm_rw(pid, lvec, liovcnt, rvec, riovcnt, flags, 1);
 311 }
 312
 313 #ifdef CONFIG_COMPAT
 314
 315 static ssize_t
 316 compat_process_vm_rw(compat_pid_t pid,
 317                      const struct compat_iovec __user *lvec,
 318                      unsigned long liovcnt,
 319                      const struct compat_iovec __user *rvec,
 320                      unsigned long riovcnt,
 321                      unsigned long flags, int vm_write)
 322 {
 323         struct iovec iovstack_l[UIO_FASTIOV];
 324         struct iovec iovstack_r[UIO_FASTIOV];
 325         struct iovec *iov_l = iovstack_l;
 326         struct iovec *iov_r = iovstack_r;
 327         struct iov_iter iter;
 328         ssize_t rc = -EFAULT;
 329         int dir = vm_write ? WRITE : READ;
 330
 331         if (flags != 0)
 332                 return -EINVAL;
 333
 334         rc = compat_import_iovec(dir, lvec, liovcnt, UIO_FASTIOV, &iov_l, &iter);
 335         if (rc < 0)
 336                 return rc;
 337         if (!iov_iter_count(&iter))
 338                 goto free_iovecs;
 339         rc = compat_rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt,
 340                                           UIO_FASTIOV, iovstack_r,
 341                                           &iov_r);
 342         if (rc <= 0)
 343                 goto free_iovecs;
 344
 345         rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write);
 346
 347 free_iovecs:
 348         if (iov_r != iovstack_r)
 349                 kfree(iov_r);
 350         kfree(iov_l);
 351         return rc;
 352 }
 353
 354 COMPAT_SYSCALL_DEFINE6(process_vm_readv, 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, 0);
 363 }
 364
 365 COMPAT_SYSCALL_DEFINE6(process_vm_writev, compat_pid_t, pid,
 366                        const struct compat_iovec __user *, lvec,
 367                        compat_ulong_t, liovcnt,
 368                        const struct compat_iovec __user *, rvec,
 369                        compat_ulong_t, riovcnt,
 370                        compat_ulong_t, flags)
 371 {
 372         return compat_process_vm_rw(pid, lvec, liovcnt, rvec,
 373                                     riovcnt, flags, 1);
 374 }
 375
 376 #endif