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 (PAGE_SIZE * 2)
  57
  58 /**
  59  * process_vm_rw_single_vec - read/write pages from task specified
  60  * @addr: start memory address of target process
  61  * @len: size of area to copy to/from
  62  * @iter: where to copy to/from locally
  63  * @process_pages: struct pages area that can store at least
  64  *  nr_pages_to_copy struct page pointers
  65  * @mm: mm for task
  66  * @task: task to read/write from
  67  * @vm_write: 0 means copy from, 1 means copy to
  68  * Returns 0 on success or on failure error code
  69  */
  70 static int process_vm_rw_single_vec(unsigned long addr,
  71                                     unsigned long len,
  72                                     struct iov_iter *iter,
  73                                     struct page **process_pages,
  74                                     struct mm_struct *mm,
  75                                     struct task_struct *task,
  76                                     int vm_write)
  77 {
  78         unsigned long pa = addr & PAGE_MASK;
  79         unsigned long start_offset = addr - pa;
  80         unsigned long nr_pages;
  81         ssize_t rc = 0;
  82         unsigned long max_pages_per_loop = PVM_MAX_KMALLOC_PAGES
  83                 / sizeof(struct pages *);
  84         unsigned int flags = 0;
  85
  86         /* Work out address and page range required */
  87         if (len == 0)
  88                 return 0;
  89         nr_pages = (addr + len - 1) / PAGE_SIZE - addr / PAGE_SIZE + 1;
  90
  91         if (vm_write)
  92                 flags |= FOLL_WRITE;
  93
  94         while (!rc && nr_pages && iov_iter_count(iter)) {
  95                 int pinned_pages = min(nr_pages, max_pages_per_loop);
  96                 int locked = 1;
  97                 size_t bytes;
  98
  99                 /*
 100                  * Get the pages we're interested in.  We must
 101                  * access remotely because task/mm might not
 102                  * current/current->mm
 103                  */
 104                 mmap_read_lock(mm);
 105                 pinned_pages = pin_user_pages_remote(mm, pa, pinned_pages,
 106                                                      flags, process_pages,
 107                                                      NULL, &locked);
 108                 if (locked)
 109                         mmap_read_unlock(mm);
 110                 if (pinned_pages <= 0)
 111                         return -EFAULT;
 112
 113                 bytes = pinned_pages * PAGE_SIZE - start_offset;
 114                 if (bytes > len)
 115                         bytes = len;
 116
 117                 rc = process_vm_rw_pages(process_pages,
 118                                          start_offset, bytes, iter,
 119                                          vm_write);
 120                 len -= bytes;
 121                 start_offset = 0;
 122                 nr_pages -= pinned_pages;
 123                 pa += pinned_pages * PAGE_SIZE;
 124
 125                 /* If vm_write is set, the pages need to be made dirty: */
 126                 unpin_user_pages_dirty_lock(process_pages, pinned_pages,
 127                                             vm_write);
 128         }
 129
 130         return rc;
 131 }
 132
 133 /* Maximum number of entries for process pages array
 134    which lives on stack */
 135 #define PVM_MAX_PP_ARRAY_COUNT 16
 136
 137 /**
 138  * process_vm_rw_core - core of reading/writing pages from task specified
 139  * @pid: PID of process to read/write from/to
 140  * @iter: where to copy to/from locally
 141  * @rvec: iovec array specifying where to copy to/from in the other process
 142  * @riovcnt: size of rvec array
 143  * @flags: currently unused
 144  * @vm_write: 0 if reading from other process, 1 if writing to other process
 145  *
 146  * Returns the number of bytes read/written or error code. May
 147  *  return less bytes than expected if an error occurs during the copying
 148  *  process.
 149  */
 150 static ssize_t process_vm_rw_core(pid_t pid, struct iov_iter *iter,
 151                                   const struct iovec *rvec,
 152                                   unsigned long riovcnt,
 153                                   unsigned long flags, int vm_write)
 154 {
 155         struct task_struct *task;
 156         struct page *pp_stack[PVM_MAX_PP_ARRAY_COUNT];
 157         struct page **process_pages = pp_stack;
 158         struct mm_struct *mm;
 159         unsigned long i;
 160         ssize_t rc = 0;
 161         unsigned long nr_pages = 0;
 162         unsigned long nr_pages_iov;
 163         ssize_t iov_len;
 164         size_t total_len = iov_iter_count(iter);
 165
 166         /*
 167          * Work out how many pages of struct pages we're going to need
 168          * when eventually calling get_user_pages
 169          */
 170         for (i = 0; i < riovcnt; i++) {
 171                 iov_len = rvec[i].iov_len;
 172                 if (iov_len > 0) {
 173                         nr_pages_iov = ((unsigned long)rvec[i].iov_base
 174                                         + iov_len)
 175                                 / PAGE_SIZE - (unsigned long)rvec[i].iov_base
 176                                 / PAGE_SIZE + 1;
 177                         nr_pages = max(nr_pages, nr_pages_iov);
 178                 }
 179         }
 180
 181         if (nr_pages == 0)
 182                 return 0;
 183
 184         if (nr_pages > PVM_MAX_PP_ARRAY_COUNT) {
 185                 /* For reliability don't try to kmalloc more than
 186                    2 pages worth */
 187                 process_pages = kmalloc(min_t(size_t, PVM_MAX_KMALLOC_PAGES,
 188                                               sizeof(struct pages *)*nr_pages),
 189                                         GFP_KERNEL);
 190
 191                 if (!process_pages)
 192                         return -ENOMEM;
 193         }
 194
 195         /* Get process information */
 196         task = find_get_task_by_vpid(pid);
 197         if (!task) {
 198                 rc = -ESRCH;
 199                 goto free_proc_pages;
 200         }
 201
 202         mm = mm_access(task, PTRACE_MODE_ATTACH_REALCREDS);
 203         if (!mm || IS_ERR(mm)) {
 204                 rc = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH;
 205                 /*
 206                  * Explicitly map EACCES to EPERM as EPERM is a more
 207                  * appropriate error code for process_vw_readv/writev
 208                  */
 209                 if (rc == -EACCES)
 210                         rc = -EPERM;
 211                 goto put_task_struct;
 212         }
 213
 214         for (i = 0; i < riovcnt && iov_iter_count(iter) && !rc; i++)
 215                 rc = process_vm_rw_single_vec(
 216                         (unsigned long)rvec[i].iov_base, rvec[i].iov_len,
 217                         iter, process_pages, mm, task, vm_write);
 218
 219         /* copied = space before - space after */
 220         total_len -= iov_iter_count(iter);
 221
 222         /* If we have managed to copy any data at all then
 223            we return the number of bytes copied. Otherwise
 224            we return the error code */
 225         if (total_len)
 226                 rc = total_len;
 227
 228         mmput(mm);
 229
 230 put_task_struct:
 231         put_task_struct(task);
 232
 233 free_proc_pages:
 234         if (process_pages != pp_stack)
 235                 kfree(process_pages);
 236         return rc;
 237 }
 238
 239 /**
 240  * process_vm_rw - check iovecs before calling core routine
 241  * @pid: PID of process to read/write from/to
 242  * @lvec: iovec array specifying where to copy to/from locally
 243  * @liovcnt: size of lvec array
 244  * @rvec: iovec array specifying where to copy to/from in the other process
 245  * @riovcnt: size of rvec array
 246  * @flags: currently unused
 247  * @vm_write: 0 if reading from other process, 1 if writing to other process
 248  *
 249  * Returns the number of bytes read/written or error code. May
 250  *  return less bytes than expected if an error occurs during the copying
 251  *  process.
 252  */
 253 static ssize_t process_vm_rw(pid_t pid,
 254                              const struct iovec __user *lvec,
 255                              unsigned long liovcnt,
 256                              const struct iovec __user *rvec,
 257                              unsigned long riovcnt,
 258                              unsigned long flags, int vm_write)
 259 {
 260         struct iovec iovstack_l[UIO_FASTIOV];
 261         struct iovec iovstack_r[UIO_FASTIOV];
 262         struct iovec *iov_l = iovstack_l;
 263         struct iovec *iov_r;
 264         struct iov_iter iter;
 265         ssize_t rc;
 266         int dir = vm_write ? WRITE : READ;
 267
 268         if (flags != 0)
 269                 return -EINVAL;
 270
 271         /* Check iovecs */
 272         rc = import_iovec(dir, lvec, liovcnt, UIO_FASTIOV, &iov_l, &iter);
 273         if (rc < 0)
 274                 return rc;
 275         if (!iov_iter_count(&iter))
 276                 goto free_iov_l;
 277         iov_r = iovec_from_user(rvec, riovcnt, UIO_FASTIOV, iovstack_r,
 278                                 in_compat_syscall());
 279         if (IS_ERR(iov_r)) {
 280                 rc = PTR_ERR(iov_r);
 281                 goto free_iov_l;
 282         }
 283         rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write);
 284         if (iov_r != iovstack_r)
 285                 kfree(iov_r);
 286 free_iov_l:
 287         kfree(iov_l);
 288         return rc;
 289 }
 290
 291 SYSCALL_DEFINE6(process_vm_readv, pid_t, pid, const struct iovec __user *, lvec,
 292                 unsigned long, liovcnt, const struct iovec __user *, rvec,
 293                 unsigned long, riovcnt, unsigned long, flags)
 294 {
 295         return process_vm_rw(pid, lvec, liovcnt, rvec, riovcnt, flags, 0);
 296 }
 297
 298 SYSCALL_DEFINE6(process_vm_writev, pid_t, pid,
 299                 const struct iovec __user *, lvec,
 300                 unsigned long, liovcnt, const struct iovec __user *, rvec,
 301                 unsigned long, riovcnt, unsigned long, flags)
 302 {
 303         return process_vm_rw(pid, lvec, liovcnt, rvec, riovcnt, flags, 1);
 304 }