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