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/compat.h>
   9 #include <linux/mm.h>
  10 #include <linux/uio.h>
  11 #include <linux/sched.h>
  12 #include <linux/sched/mm.h>
  13 #include <linux/highmem.h>
  14 #include <linux/ptrace.h>
  15 #include <linux/slab.h>
  16 #include <linux/syscalls.h>
  17
  18 /**
  19  * process_vm_rw_pages - read/write pages from task specified
  20  * @pages: array of pointers to pages we want to copy
  21  * @offset: offset in page to start copying from/to
  22  * @len: number of bytes to copy
  23  * @iter: where to copy to/from locally
  24  * @vm_write: 0 means copy from, 1 means copy to
  25  * Returns 0 on success, error code otherwise
  26  */
  27 static int process_vm_rw_pages(struct page **pages,
  28                                unsigned offset,
  29                                size_t len,
  30                                struct iov_iter *iter,
  31                                int vm_write)
  32 {
  33         /* Do the copy for each page */
  34         while (len && iov_iter_count(iter)) {
  35                 struct page *page = *pages++;
  36                 size_t copy = PAGE_SIZE - offset;
  37                 size_t copied;
  38
  39                 if (copy > len)
  40                         copy = len;
  41
  42                 if (vm_write)
  43                         copied = copy_page_from_iter(page, offset, copy, iter);
  44                 else
  45                         copied = copy_page_to_iter(page, offset, copy, iter);
  46
  47                 len -= copied;
  48                 if (copied < copy && iov_iter_count(iter))
  49                         return -EFAULT;
  50                 offset = 0;
  51         }
  52         return 0;
  53 }
  54
  55 /* Maximum number of pages kmalloc'd to hold struct page's during copy */
  56 #define PVM_MAX_KMALLOC_PAGES 2
  57
  58 /* Maximum number of pages that can be stored at a time */
  59 #define PVM_MAX_USER_PAGES (PVM_MAX_KMALLOC_PAGES * PAGE_SIZE / sizeof(struct page *))
  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 int flags = 0;
  86
  87         /* Work out address and page range required */
  88         if (len == 0)
  89                 return 0;
  90         nr_pages = (addr + len - 1) / PAGE_SIZE - addr / PAGE_SIZE + 1;
  91
  92         if (vm_write)
  93                 flags |= FOLL_WRITE;
  94
  95         while (!rc && nr_pages && iov_iter_count(iter)) {
  96                 int pinned_pages = min_t(unsigned long, nr_pages, PVM_MAX_USER_PAGES);
  97                 int locked = 1;
  98                 size_t bytes;
  99
 100                 /*
 101                  * Get the pages we're interested in.  We must
 102                  * access remotely because task/mm might not
 103                  * current/current->mm
 104                  */
 105                 mmap_read_lock(mm);
 106                 pinned_pages = pin_user_pages_remote(mm, pa, pinned_pages,
 107                                                      flags, process_pages,
 108                                                      &locked);
 109                 if (locked)
 110                         mmap_read_unlock(mm);
 111                 if (pinned_pages <= 0)
 112                         return -EFAULT;
 113
 114                 bytes = pinned_pages * PAGE_SIZE - start_offset;
 115                 if (bytes > len)
 116                         bytes = len;
 117
 118                 rc = process_vm_rw_pages(process_pages,
 119                                          start_offset, bytes, iter,
 120                                          vm_write);
 121                 len -= bytes;
 122                 start_offset = 0;
 123                 nr_pages -= pinned_pages;
 124                 pa += pinned_pages * PAGE_SIZE;
 125
 126                 /* If vm_write is set, the pages need to be made dirty: */
 127                 unpin_user_pages_dirty_lock(process_pages, pinned_pages,
 128                                             vm_write);
 129         }
 130
 131         return rc;
 132 }
 133
 134 /* Maximum number of entries for process pages array
 135    which lives on stack */
 136 #define PVM_MAX_PP_ARRAY_COUNT 16
 137
 138 /**
 139  * process_vm_rw_core - core of reading/writing pages from task specified
 140  * @pid: PID of process to read/write from/to
 141  * @iter: where to copy to/from locally
 142  * @rvec: iovec array specifying where to copy to/from in the other process
 143  * @riovcnt: size of rvec array
 144  * @flags: currently unused
 145  * @vm_write: 0 if reading from other process, 1 if writing to other process
 146  *
 147  * Returns the number of bytes read/written or error code. May
 148  *  return less bytes than expected if an error occurs during the copying
 149  *  process.
 150  */
 151 static ssize_t process_vm_rw_core(pid_t pid, struct iov_iter *iter,
 152                                   const struct iovec *rvec,
 153                                   unsigned long riovcnt,
 154                                   unsigned long flags, int vm_write)
 155 {
 156         struct task_struct *task;
 157         struct page *pp_stack[PVM_MAX_PP_ARRAY_COUNT];
 158         struct page **process_pages = pp_stack;
 159         struct mm_struct *mm;
 160         unsigned long i;
 161         ssize_t rc = 0;
 162         unsigned long nr_pages = 0;
 163         unsigned long nr_pages_iov;
 164         ssize_t iov_len;
 165         size_t total_len = iov_iter_count(iter);
 166
 167         /*
 168          * Work out how many pages of struct pages we're going to need
 169          * when eventually calling get_user_pages
 170          */
 171         for (i = 0; i < riovcnt; i++) {
 172                 iov_len = rvec[i].iov_len;
 173                 if (iov_len > 0) {
 174                         nr_pages_iov = ((unsigned long)rvec[i].iov_base
 175                                         + iov_len - 1)
 176                                 / PAGE_SIZE - (unsigned long)rvec[i].iov_base
 177                                 / PAGE_SIZE + 1;
 178                         nr_pages = max(nr_pages, nr_pages_iov);
 179                 }
 180         }
 181
 182         if (nr_pages == 0)
 183                 return 0;
 184
 185         if (nr_pages > PVM_MAX_PP_ARRAY_COUNT) {
 186                 /* For reliability don't try to kmalloc more than
 187                    2 pages worth */
 188                 process_pages = kmalloc(min_t(size_t, PVM_MAX_KMALLOC_PAGES * PAGE_SIZE,
 189                                               sizeof(struct page *)*nr_pages),
 190                                         GFP_KERNEL);
 191
 192                 if (!process_pages)
 193                         return -ENOMEM;
 194         }
 195
 196         /* Get process information */
 197         task = find_get_task_by_vpid(pid);
 198         if (!task) {
 199                 rc = -ESRCH;
 200                 goto free_proc_pages;
 201         }
 202
 203         mm = mm_access(task, PTRACE_MODE_ATTACH_REALCREDS);
 204         if (IS_ERR(mm)) {
 205                 rc = PTR_ERR(mm);
 206                 /*
 207                  * Explicitly map EACCES to EPERM as EPERM is a more
 208                  * appropriate error code for process_vw_readv/writev
 209                  */
 210                 if (rc == -EACCES)
 211                         rc = -EPERM;
 212                 goto put_task_struct;
 213         }
 214
 215         for (i = 0; i < riovcnt && iov_iter_count(iter) && !rc; i++)
 216                 rc = process_vm_rw_single_vec(
 217                         (unsigned long)rvec[i].iov_base, rvec[i].iov_len,
 218                         iter, process_pages, mm, task, vm_write);
 219
 220         /* copied = space before - space after */
 221         total_len -= iov_iter_count(iter);
 222
 223         /* If we have managed to copy any data at all then
 224            we return the number of bytes copied. Otherwise
 225            we return the error code */
 226         if (total_len)
 227                 rc = total_len;
 228
 229         mmput(mm);
 230
 231 put_task_struct:
 232         put_task_struct(task);
 233
 234 free_proc_pages:
 235         if (process_pages != pp_stack)
 236                 kfree(process_pages);
 237         return rc;
 238 }
 239
 240 /**
 241  * process_vm_rw - check iovecs before calling core routine
 242  * @pid: PID of process to read/write from/to
 243  * @lvec: iovec array specifying where to copy to/from locally
 244  * @liovcnt: size of lvec array
 245  * @rvec: iovec array specifying where to copy to/from in the other process
 246  * @riovcnt: size of rvec array
 247  * @flags: currently unused
 248  * @vm_write: 0 if reading from other process, 1 if writing to other process
 249  *
 250  * Returns the number of bytes read/written or error code. May
 251  *  return less bytes than expected if an error occurs during the copying
 252  *  process.
 253  */
 254 static ssize_t process_vm_rw(pid_t pid,
 255                              const struct iovec __user *lvec,
 256                              unsigned long liovcnt,
 257                              const struct iovec __user *rvec,
 258                              unsigned long riovcnt,
 259                              unsigned long flags, int vm_write)
 260 {
 261         struct iovec iovstack_l[UIO_FASTIOV];
 262         struct iovec iovstack_r[UIO_FASTIOV];
 263         struct iovec *iov_l = iovstack_l;
 264         struct iovec *iov_r;
 265         struct iov_iter iter;
 266         ssize_t rc;
 267         int dir = vm_write ? ITER_SOURCE : ITER_DEST;
 268
 269         if (flags != 0)
 270                 return -EINVAL;
 271
 272         /* Check iovecs */
 273         rc = import_iovec(dir, lvec, liovcnt, UIO_FASTIOV, &iov_l, &iter);
 274         if (rc < 0)
 275                 return rc;
 276         if (!iov_iter_count(&iter))
 277                 goto free_iov_l;
 278         iov_r = iovec_from_user(rvec, riovcnt, UIO_FASTIOV, iovstack_r,
 279                                 in_compat_syscall());
 280         if (IS_ERR(iov_r)) {
 281                 rc = PTR_ERR(iov_r);
 282                 goto free_iov_l;
 283         }
 284         rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write);
 285         if (iov_r != iovstack_r)
 286                 kfree(iov_r);
 287 free_iov_l:
 288         kfree(iov_l);
 289         return rc;
 290 }
 291
 292 SYSCALL_DEFINE6(process_vm_readv, pid_t, pid, const struct iovec __user *, lvec,
 293                 unsigned long, liovcnt, const struct iovec __user *, rvec,
 294                 unsigned long, riovcnt, unsigned long, flags)
 295 {
 296         return process_vm_rw(pid, lvec, liovcnt, rvec, riovcnt, flags, 0);
 297 }
 298
 299 SYSCALL_DEFINE6(process_vm_writev, pid_t, pid,
 300                 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, 1);
 305 }