mm/process_vm_access.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /*
   3  * linux/mm/process_vm_access.c
   4  *
   5  * Copyright (C) 2010-2011 Christopher Yeoh <cyeoh@au1.ibm.com>, IBM Corp.
   6  */
   7
   8 #include <linux/mm.h>
   9 #include <linux/uio.h>
  10 #include <linux/sched.h>
  11 #include <linux/sched/mm.h>
  12 #include <linux/highmem.h>
  13 #include <linux/ptrace.h>
  14 #include <linux/slab.h>
  15 #include <linux/syscalls.h>
  16
  17 #ifdef CONFIG_COMPAT
  18 #include <linux/compat.h>
  19 #endif
  20
  21 /**
  22  * process_vm_rw_pages - read/write pages from task specified
  23  * @pages: array of pointers to pages we want to copy
  24  * @offset: offset in page to start copying from/to
  25  * @len: number of bytes to copy
  26  * @iter: where to copy to/from locally
  27  * @vm_write: 0 means copy from, 1 means copy to
  28  * Returns 0 on success, error code otherwise
  29  */
  30 static int process_vm_rw_pages(struct page **pages,
  31                                unsigned offset,
  32                                size_t len,
  33                                struct iov_iter *iter,
  34                                int vm_write)
  35 {
  36         /* Do the copy for each page */
  37         while (len && iov_iter_count(iter)) {
  38                 struct page *page = *pages++;
  39                 size_t copy = PAGE_SIZE - offset;
  40                 size_t copied;
  41
  42                 if (copy > len)
  43                         copy = len;
  44
  45                 if (vm_write)
  46                         copied = copy_page_from_iter(page, offset, copy, iter);
  47                 else
  48                         copied = copy_page_to_iter(page, offset, copy, iter);
  49
  50                 len -= copied;
  51                 if (copied < copy && iov_iter_count(iter))
  52                         return -EFAULT;
  53                 offset = 0;
  54         }
  55         return 0;
  56 }
  57
  58 /* Maximum number of pages kmalloc'd to hold struct page's during copy */
  59 #define PVM_MAX_KMALLOC_PAGES (PAGE_SIZE * 2)
  60
  61 /**
  62  * process_vm_rw_single_vec - read/write pages from task specified
  63  * @addr: start memory address of target process
  64  * @len: size of area to copy to/from
  65  * @iter: where to copy to/from locally
  66  * @process_pages: struct pages area that can store at least
  67  *  nr_pages_to_copy struct page pointers
  68  * @mm: mm for task
  69  * @task: task to read/write from
  70  * @vm_write: 0 means copy from, 1 means copy to
  71  * Returns 0 on success or on failure error code
  72  */
  73 static int process_vm_rw_single_vec(unsigned long addr,
  74                                     unsigned long len,
  75                                     struct iov_iter *iter,
  76                                     struct page **process_pages,
  77                                     struct mm_struct *mm,
  78                                     struct task_struct *task,
  79                                     int vm_write)
  80 {
  81         unsigned long pa = addr & PAGE_MASK;
  82         unsigned long start_offset = addr - pa;
  83         unsigned long nr_pages;
  84         ssize_t rc = 0;
  85         unsigned long max_pages_per_loop = PVM_MAX_KMALLOC_PAGES
  86                 / sizeof(struct pages *);
  87         unsigned int flags = 0;
  88
  89         /* Work out address and page range required */
  90         if (len == 0)
  91                 return 0;
  92         nr_pages = (addr + len - 1) / PAGE_SIZE - addr / PAGE_SIZE + 1;
  93
  94         if (vm_write)
  95                 flags |= FOLL_WRITE;
  96
  97         while (!rc && nr_pages && iov_iter_count(iter)) {
  98                 int pinned_pages = min(nr_pages, max_pages_per_loop);
  99                 int locked = 1;
 100                 size_t bytes;
 101
 102                 /*
 103                  * Get the pages we're interested in.  We must
 104                  * access remotely because task/mm might not
 105                  * current/current->mm
 106                  */
 107                 down_read(&mm->mmap_sem);
 108                 pinned_pages = pin_user_pages_remote(task, mm, pa, pinned_pages,
 109                                                      flags, process_pages,
 110                                                      NULL, &locked);
 111                 if (locked)
 112                         up_read(&mm->mmap_sem);
 113                 if (pinned_pages <= 0)
 114                         return -EFAULT;
 115
 116                 bytes = pinned_pages * PAGE_SIZE - start_offset;
 117                 if (bytes > len)
 118                         bytes = len;
 119
 120                 rc = process_vm_rw_pages(process_pages,
 121                                          start_offset, bytes, iter,
 122                                          vm_write);
 123                 len -= bytes;
 124                 start_offset = 0;
 125                 nr_pages -= pinned_pages;
 126                 pa += pinned_pages * PAGE_SIZE;
 127
 128                 /* If vm_write is set, the pages need to be made dirty: */
 129                 unpin_user_pages_dirty_lock(process_pages, pinned_pages,
 130                                             vm_write);
 131         }
 132
 133         return rc;
 134 }
 135
 136 /* Maximum number of entries for process pages array
 137    which lives on stack */
 138 #define PVM_MAX_PP_ARRAY_COUNT 16
 139
 140 /**
 141  * process_vm_rw_core - core of reading/writing pages from task specified
 142  * @pid: PID of process to read/write from/to
 143  * @iter: where to copy to/from locally
 144  * @rvec: iovec array specifying where to copy to/from in the other process
 145  * @riovcnt: size of rvec array
 146  * @flags: currently unused
 147  * @vm_write: 0 if reading from other process, 1 if writing to other process
 148  *
 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         task = find_get_task_by_vpid(pid);
 200         if (!task) {
 201                 rc = -ESRCH;
 202                 goto free_proc_pages;
 203         }
 204
 205         mm = mm_access(task, PTRACE_MODE_ATTACH_REALCREDS);
 206         if (!mm || IS_ERR(mm)) {
 207                 rc = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH;
 208                 /*
 209                  * Explicitly map EACCES to EPERM as EPERM is a more
 210                  * appropriate error code for process_vw_readv/writev
 211                  */
 212                 if (rc == -EACCES)
 213                         rc = -EPERM;
 214                 goto put_task_struct;
 215         }
 216
 217         for (i = 0; i < riovcnt && iov_iter_count(iter) && !rc; i++)
 218                 rc = process_vm_rw_single_vec(
 219                         (unsigned long)rvec[i].iov_base, rvec[i].iov_len,
 220                         iter, process_pages, mm, task, vm_write);
 221
 222         /* copied = space before - space after */
 223         total_len -= iov_iter_count(iter);
 224
 225         /* If we have managed to copy any data at all then
 226            we return the number of bytes copied. Otherwise
 227            we return the error code */
 228         if (total_len)
 229                 rc = total_len;
 230
 231         mmput(mm);
 232
 233 put_task_struct:
 234         put_task_struct(task);
 235
 236 free_proc_pages:
 237         if (process_pages != pp_stack)
 238                 kfree(process_pages);
 239         return rc;
 240 }
 241
 242 /**
 243  * process_vm_rw - check iovecs before calling core routine
 244  * @pid: PID of process to read/write from/to
 245  * @lvec: iovec array specifying where to copy to/from locally
 246  * @liovcnt: size of lvec array
 247  * @rvec: iovec array specifying where to copy to/from in the other process
 248  * @riovcnt: size of rvec array
 249  * @flags: currently unused
 250  * @vm_write: 0 if reading from other process, 1 if writing to other process
 251  *
 252  * Returns the number of bytes read/written or error code. May
 253  *  return less bytes than expected if an error occurs during the copying
 254  *  process.
 255  */
 256 static ssize_t process_vm_rw(pid_t pid,
 257                              const struct iovec __user *lvec,
 258                              unsigned long liovcnt,
 259                              const struct iovec __user *rvec,
 260                              unsigned long riovcnt,
 261                              unsigned long flags, int vm_write)
 262 {
 263         struct iovec iovstack_l[UIO_FASTIOV];
 264         struct iovec iovstack_r[UIO_FASTIOV];
 265         struct iovec *iov_l = iovstack_l;
 266         struct iovec *iov_r = iovstack_r;
 267         struct iov_iter iter;
 268         ssize_t rc;
 269         int dir = vm_write ? WRITE : READ;
 270
 271         if (flags != 0)
 272                 return -EINVAL;
 273
 274         /* Check iovecs */
 275         rc = import_iovec(dir, lvec, liovcnt, UIO_FASTIOV, &iov_l, &iter);
 276         if (rc < 0)
 277                 return rc;
 278         if (!iov_iter_count(&iter))
 279                 goto free_iovecs;
 280
 281         rc = rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt, UIO_FASTIOV,
 282                                    iovstack_r, &iov_r);
 283         if (rc <= 0)
 284                 goto free_iovecs;
 285
 286         rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write);
 287
 288 free_iovecs:
 289         if (iov_r != iovstack_r)
 290                 kfree(iov_r);
 291         kfree(iov_l);
 292
 293         return rc;
 294 }
 295
 296 SYSCALL_DEFINE6(process_vm_readv, pid_t, pid, const struct iovec __user *, lvec,
 297                 unsigned long, liovcnt, const struct iovec __user *, rvec,
 298                 unsigned long, riovcnt, unsigned long, flags)
 299 {
 300         return process_vm_rw(pid, lvec, liovcnt, rvec, riovcnt, flags, 0);
 301 }
 302
 303 SYSCALL_DEFINE6(process_vm_writev, pid_t, pid,
 304                 const struct iovec __user *, lvec,
 305                 unsigned long, liovcnt, const struct iovec __user *, rvec,
 306                 unsigned long, riovcnt, unsigned long, flags)
 307 {
 308         return process_vm_rw(pid, lvec, liovcnt, rvec, riovcnt, flags, 1);
 309 }
 310
 311 #ifdef CONFIG_COMPAT
 312
 313 static ssize_t
 314 compat_process_vm_rw(compat_pid_t pid,
 315                      const struct compat_iovec __user *lvec,
 316                      unsigned long liovcnt,
 317                      const struct compat_iovec __user *rvec,
 318                      unsigned long riovcnt,
 319                      unsigned long flags, int vm_write)
 320 {
 321         struct iovec iovstack_l[UIO_FASTIOV];
 322         struct iovec iovstack_r[UIO_FASTIOV];
 323         struct iovec *iov_l = iovstack_l;
 324         struct iovec *iov_r = iovstack_r;
 325         struct iov_iter iter;
 326         ssize_t rc = -EFAULT;
 327         int dir = vm_write ? WRITE : READ;
 328
 329         if (flags != 0)
 330                 return -EINVAL;
 331
 332         rc = compat_import_iovec(dir, lvec, liovcnt, UIO_FASTIOV, &iov_l, &iter);
 333         if (rc < 0)
 334                 return rc;
 335         if (!iov_iter_count(&iter))
 336                 goto free_iovecs;
 337         rc = compat_rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt,
 338                                           UIO_FASTIOV, iovstack_r,
 339                                           &iov_r);
 340         if (rc <= 0)
 341                 goto free_iovecs;
 342
 343         rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write);
 344
 345 free_iovecs:
 346         if (iov_r != iovstack_r)
 347                 kfree(iov_r);
 348         kfree(iov_l);
 349         return rc;
 350 }
 351
 352 COMPAT_SYSCALL_DEFINE6(process_vm_readv, compat_pid_t, pid,
 353                        const struct compat_iovec __user *, lvec,
 354                        compat_ulong_t, liovcnt,
 355                        const struct compat_iovec __user *, rvec,
 356                        compat_ulong_t, riovcnt,
 357                        compat_ulong_t, flags)
 358 {
 359         return compat_process_vm_rw(pid, lvec, liovcnt, rvec,
 360                                     riovcnt, flags, 0);
 361 }
 362
 363 COMPAT_SYSCALL_DEFINE6(process_vm_writev, compat_pid_t, pid,
 364                        const struct compat_iovec __user *, lvec,
 365                        compat_ulong_t, liovcnt,
 366                        const struct compat_iovec __user *, rvec,
 367                        compat_ulong_t, riovcnt,
 368                        compat_ulong_t, flags)
 369 {
 370         return compat_process_vm_rw(pid, lvec, liovcnt, rvec,
 371                                     riovcnt, flags, 1);
 372 }
 373
 374 #endif