LXR linux/mm/process_vm

   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
  92        /* Work out address and page range required */
  93        if (len == 0)
  94                return 0;
  95        nr_pages = (addr + len - 1) / PAGE_SIZE - addr / PAGE_SIZE + 1;
  96
  97        while (!rc && nr_pages && iov_iter_count(iter)) {
  98                int pages = min(nr_pages, max_pages_per_loop);
  99                size_t bytes;
 100
 101                /* Get the pages we're interested in */
 102                pages = get_user_pages_unlocked(task, mm, pa, pages,
 103                                                vm_write, 0, process_pages);
 104                if (pages <= 0)
 105                        return -EFAULT;
 106
 107                bytes = pages * PAGE_SIZE - start_offset;
 108                if (bytes > len)
 109                        bytes = len;
 110
 111                rc = process_vm_rw_pages(process_pages,
 112                                         start_offset, bytes, iter,
 113                                         vm_write);
 114                len -= bytes;
 115                start_offset = 0;
 116                nr_pages -= pages;
 117                pa += pages * PAGE_SIZE;
 118                while (pages)
 119                        put_page(process_pages[--pages]);
 120        }
 121
 122        return rc;
 123}
 124
 125/* Maximum number of entries for process pages array
 126   which lives on stack */
 127#define PVM_MAX_PP_ARRAY_COUNT 16
 128
 129/**
 130 * process_vm_rw_core - core of reading/writing pages from task specified
 131 * @pid: PID of process to read/write from/to
 132 * @iter: where to copy to/from locally
 133 * @rvec: iovec array specifying where to copy to/from in the other process
 134 * @riovcnt: size of rvec array
 135 * @flags: currently unused
 136 * @vm_write: 0 if reading from other process, 1 if writing to other process
 137 * Returns the number of bytes read/written or error code. May
 138 *  return less bytes than expected if an error occurs during the copying
 139 *  process.
 140 */
 141static ssize_t process_vm_rw_core(pid_t pid, struct iov_iter *iter,
 142                                  const struct iovec *rvec,
 143                                  unsigned long riovcnt,
 144                                  unsigned long flags, int vm_write)
 145{
 146        struct task_struct *task;
 147        struct page *pp_stack[PVM_MAX_PP_ARRAY_COUNT];
 148        struct page **process_pages = pp_stack;
 149        struct mm_struct *mm;
 150        unsigned long i;
 151        ssize_t rc = 0;
 152        unsigned long nr_pages = 0;
 153        unsigned long nr_pages_iov;
 154        ssize_t iov_len;
 155        size_t total_len = iov_iter_count(iter);
 156
 157        /*
 158         * Work out how many pages of struct pages we're going to need
 159         * when eventually calling get_user_pages
 160         */
 161        for (i = 0; i < riovcnt; i++) {
 162                iov_len = rvec[i].iov_len;
 163                if (iov_len > 0) {
 164                        nr_pages_iov = ((unsigned long)rvec[i].iov_base
 165                                        + iov_len)
 166                                / PAGE_SIZE - (unsigned long)rvec[i].iov_base
 167                                / PAGE_SIZE + 1;
 168                        nr_pages = max(nr_pages, nr_pages_iov);
 169                }
 170        }
 171
 172        if (nr_pages == 0)
 173                return 0;
 174
 175        if (nr_pages > PVM_MAX_PP_ARRAY_COUNT) {
 176                /* For reliability don't try to kmalloc more than
 177                   2 pages worth */
 178                process_pages = kmalloc(min_t(size_t, PVM_MAX_KMALLOC_PAGES,
 179                                              sizeof(struct pages *)*nr_pages),
 180                                        GFP_KERNEL);
 181
 182                if (!process_pages)
 183                        return -ENOMEM;
 184        }
 185
 186        /* Get process information */
 187        rcu_read_lock();
 188        task = find_task_by_vpid(pid);
 189        if (task)
 190                get_task_struct(task);
 191        rcu_read_unlock();
 192        if (!task) {
 193                rc = -ESRCH;
 194                goto free_proc_pages;
 195        }
 196
 197        mm = mm_access(task, PTRACE_MODE_ATTACH);
 198        if (!mm || IS_ERR(mm)) {
 199                rc = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH;
 200                /*
 201                 * Explicitly map EACCES to EPERM as EPERM is a more a
 202                 * appropriate error code for process_vw_readv/writev
 203                 */
 204                if (rc == -EACCES)
 205                        rc = -EPERM;
 206                goto put_task_struct;
 207        }
 208
 209        for (i = 0; i < riovcnt && iov_iter_count(iter) && !rc; i++)
 210                rc = process_vm_rw_single_vec(
 211                        (unsigned long)rvec[i].iov_base, rvec[i].iov_len,
 212                        iter, process_pages, mm, task, vm_write);
 213
 214        /* copied = space before - space after */
 215        total_len -= iov_iter_count(iter);
 216
 217        /* If we have managed to copy any data at all then
 218           we return the number of bytes copied. Otherwise
 219           we return the error code */
 220        if (total_len)
 221                rc = total_len;
 222
 223        mmput(mm);
 224
 225put_task_struct:
 226        put_task_struct(task);
 227
 228free_proc_pages:
 229        if (process_pages != pp_stack)
 230                kfree(process_pages);
 231        return rc;
 232}
 233
 234/**
 235 * process_vm_rw - check iovecs before calling core routine
 236 * @pid: PID of process to read/write from/to
 237 * @lvec: iovec array specifying where to copy to/from locally
 238 * @liovcnt: size of lvec array
 239 * @rvec: iovec array specifying where to copy to/from in the other process
 240 * @riovcnt: size of rvec array
 241 * @flags: currently unused
 242 * @vm_write: 0 if reading from other process, 1 if writing to other process
 243 * Returns the number of bytes read/written or error code. May
 244 *  return less bytes than expected if an error occurs during the copying
 245 *  process.
 246 */
 247static ssize_t process_vm_rw(pid_t pid,
 248                             const struct iovec __user *lvec,
 249                             unsigned long liovcnt,
 250                             const struct iovec __user *rvec,
 251                             unsigned long riovcnt,
 252                             unsigned long flags, int vm_write)
 253{
 254        struct iovec iovstack_l[UIO_FASTIOV];
 255        struct iovec iovstack_r[UIO_FASTIOV];
 256        struct iovec *iov_l = iovstack_l;
 257        struct iovec *iov_r = iovstack_r;
 258        struct iov_iter iter;
 259        ssize_t rc;
 260        int dir = vm_write ? WRITE : READ;
 261
 262        if (flags != 0)
 263                return -EINVAL;
 264
 265        /* Check iovecs */
 266        rc = import_iovec(dir, lvec, liovcnt, UIO_FASTIOV, &iov_l, &iter);
 267        if (rc < 0)
 268                return rc;
 269        if (!iov_iter_count(&iter))
 270                goto free_iovecs;
 271
 272        rc = rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt, UIO_FASTIOV,
 273                                   iovstack_r, &iov_r);
 274        if (rc <= 0)
 275                goto free_iovecs;
 276
 277        rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write);
 278
 279free_iovecs:
 280        if (iov_r != iovstack_r)
 281                kfree(iov_r);
 282        kfree(iov_l);
 283
 284        return rc;
 285}
 286
 287SYSCALL_DEFINE6(process_vm_readv, pid_t, pid, const struct iovec __user *, lvec,
 288                unsigned long, liovcnt, const struct iovec __user *, rvec,
 289                unsigned long, riovcnt, unsigned long, flags)
 290{
 291        return process_vm_rw(pid, lvec, liovcnt, rvec, riovcnt, flags, 0);
 292}
 293
 294SYSCALL_DEFINE6(process_vm_writev, pid_t, pid,
 295                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, 1);
 300}
 301
 302#ifdef CONFIG_COMPAT
 303
 304static ssize_t
 305compat_process_vm_rw(compat_pid_t pid,
 306                     const struct compat_iovec __user *lvec,
 307                     unsigned long liovcnt,
 308                     const struct compat_iovec __user *rvec,
 309                     unsigned long riovcnt,
 310                     unsigned long flags, int vm_write)
 311{
 312        struct iovec iovstack_l[UIO_FASTIOV];
 313        struct iovec iovstack_r[UIO_FASTIOV];
 314        struct iovec *iov_l = iovstack_l;
 315        struct iovec *iov_r = iovstack_r;
 316        struct iov_iter iter;
 317        ssize_t rc = -EFAULT;
 318        int dir = vm_write ? WRITE : READ;
 319
 320        if (flags != 0)
 321                return -EINVAL;
 322
 323        rc = compat_import_iovec(dir, lvec, liovcnt, UIO_FASTIOV, &iov_l, &iter);
 324        if (rc < 0)
 325                return rc;
 326        if (!iov_iter_count(&iter))
 327                goto free_iovecs;
 328        rc = compat_rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt,
 329                                          UIO_FASTIOV, iovstack_r,
 330                                          &iov_r);
 331        if (rc <= 0)
 332                goto free_iovecs;
 333
 334        rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write);
 335
 336free_iovecs:
 337        if (iov_r != iovstack_r)
 338                kfree(iov_r);
 339        kfree(iov_l);
 340        return rc;
 341}
 342
 343COMPAT_SYSCALL_DEFINE6(process_vm_readv, compat_pid_t, pid,
 344                       const struct compat_iovec __user *, lvec,
 345                       compat_ulong_t, liovcnt,
 346                       const struct compat_iovec __user *, rvec,
 347                       compat_ulong_t, riovcnt,
 348                       compat_ulong_t, flags)
 349{
 350        return compat_process_vm_rw(pid, lvec, liovcnt, rvec,
 351                                    riovcnt, flags, 0);
 352}
 353
 354COMPAT_SYSCALL_DEFINE6(process_vm_writev, 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, 1);
 363}
 364
 365#endif
 366