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/sched/mm.h>
  16#include <linux/highmem.h>
  17#include <linux/ptrace.h>
  18#include <linux/slab.h>
  19#include <linux/syscalls.h>
  20
  21#ifdef CONFIG_COMPAT
  22#include <linux/compat.h>
  23#endif
  24
  25/**
  26 * process_vm_rw_pages - read/write pages from task specified
  27 * @pages: array of pointers to pages we want to copy
  28 * @offset: offset in page to start copying from/to
  29 * @len: number of bytes to copy
  30 * @iter: where to copy to/from locally
  31 * @vm_write: 0 means copy from, 1 means copy to
  32 * Returns 0 on success, error code otherwise
  33 */
  34static int process_vm_rw_pages(struct page **pages,
  35                               unsigned offset,
  36                               size_t len,
  37                               struct iov_iter *iter,
  38                               int vm_write)
  39{
  40        /* Do the copy for each page */
  41        while (len && iov_iter_count(iter)) {
  42                struct page *page = *pages++;
  43                size_t copy = PAGE_SIZE - offset;
  44                size_t copied;
  45
  46                if (copy > len)
  47                        copy = len;
  48
  49                if (vm_write) {
  50                        copied = copy_page_from_iter(page, offset, copy, iter);
  51                        set_page_dirty_lock(page);
  52                } else {
  53                        copied = copy_page_to_iter(page, offset, copy, iter);
  54                }
  55                len -= copied;
  56                if (copied < copy && iov_iter_count(iter))
  57                        return -EFAULT;
  58                offset = 0;
  59        }
  60        return 0;
  61}
  62
  63/* Maximum number of pages kmalloc'd to hold struct page's during copy */
  64#define PVM_MAX_KMALLOC_PAGES (PAGE_SIZE * 2)
  65
  66/**
  67 * process_vm_rw_single_vec - read/write pages from task specified
  68 * @addr: start memory address of target process
  69 * @len: size of area to copy to/from
  70 * @iter: where to copy to/from locally
  71 * @process_pages: struct pages area that can store at least
  72 *  nr_pages_to_copy struct page pointers
  73 * @mm: mm for task
  74 * @task: task to read/write from
  75 * @vm_write: 0 means copy from, 1 means copy to
  76 * Returns 0 on success or on failure error code
  77 */
  78static int process_vm_rw_single_vec(unsigned long addr,
  79                                    unsigned long len,
  80                                    struct iov_iter *iter,
  81                                    struct page **process_pages,
  82                                    struct mm_struct *mm,
  83                                    struct task_struct *task,
  84                                    int vm_write)
  85{
  86        unsigned long pa = addr & PAGE_MASK;
  87        unsigned long start_offset = addr - pa;
  88        unsigned long nr_pages;
  89        ssize_t rc = 0;
  90        unsigned long max_pages_per_loop = PVM_MAX_KMALLOC_PAGES
  91                / sizeof(struct pages *);
  92        unsigned int flags = 0;
  93
  94        /* Work out address and page range required */
  95        if (len == 0)
  96                return 0;
  97        nr_pages = (addr + len - 1) / PAGE_SIZE - addr / PAGE_SIZE + 1;
  98
  99        if (vm_write)
 100                flags |= FOLL_WRITE;
 101
 102        while (!rc && nr_pages && iov_iter_count(iter)) {
 103                int pages = min(nr_pages, max_pages_per_loop);
 104                int locked = 1;
 105                size_t bytes;
 106
 107                /*
 108                 * Get the pages we're interested in.  We must
 109                 * access remotely because task/mm might not
 110                 * current/current->mm
 111                 */
 112                down_read(&mm->mmap_sem);
 113                pages = get_user_pages_remote(task, mm, pa, pages, flags,
 114                                              process_pages, NULL, &locked);
 115                if (locked)
 116                        up_read(&mm->mmap_sem);
 117                if (pages <= 0)
 118                        return -EFAULT;
 119
 120                bytes = pages * PAGE_SIZE - start_offset;
 121                if (bytes > len)
 122                        bytes = len;
 123
 124                rc = process_vm_rw_pages(process_pages,
 125                                         start_offset, bytes, iter,
 126                                         vm_write);
 127                len -= bytes;
 128                start_offset = 0;
 129                nr_pages -= pages;
 130                pa += pages * PAGE_SIZE;
 131                while (pages)
 132                        put_page(process_pages[--pages]);
 133        }
 134
 135        return rc;
 136}
 137
 138/* Maximum number of entries for process pages array
 139   which lives on stack */
 140#define PVM_MAX_PP_ARRAY_COUNT 16
 141
 142/**
 143 * process_vm_rw_core - core of reading/writing pages from task specified
 144 * @pid: PID of process to read/write from/to
 145 * @iter: where to copy to/from locally
 146 * @rvec: iovec array specifying where to copy to/from in the other process
 147 * @riovcnt: size of rvec array
 148 * @flags: currently unused
 149 * @vm_write: 0 if reading from other process, 1 if writing to other process
 150 *
 151 * Returns the number of bytes read/written or error code. May
 152 *  return less bytes than expected if an error occurs during the copying
 153 *  process.
 154 */
 155static ssize_t process_vm_rw_core(pid_t pid, struct iov_iter *iter,
 156                                  const struct iovec *rvec,
 157                                  unsigned long riovcnt,
 158                                  unsigned long flags, int vm_write)
 159{
 160        struct task_struct *task;
 161        struct page *pp_stack[PVM_MAX_PP_ARRAY_COUNT];
 162        struct page **process_pages = pp_stack;
 163        struct mm_struct *mm;
 164        unsigned long i;
 165        ssize_t rc = 0;
 166        unsigned long nr_pages = 0;
 167        unsigned long nr_pages_iov;
 168        ssize_t iov_len;
 169        size_t total_len = iov_iter_count(iter);
 170
 171        /*
 172         * Work out how many pages of struct pages we're going to need
 173         * when eventually calling get_user_pages
 174         */
 175        for (i = 0; i < riovcnt; i++) {
 176                iov_len = rvec[i].iov_len;
 177                if (iov_len > 0) {
 178                        nr_pages_iov = ((unsigned long)rvec[i].iov_base
 179                                        + iov_len)
 180                                / PAGE_SIZE - (unsigned long)rvec[i].iov_base
 181                                / PAGE_SIZE + 1;
 182                        nr_pages = max(nr_pages, nr_pages_iov);
 183                }
 184        }
 185
 186        if (nr_pages == 0)
 187                return 0;
 188
 189        if (nr_pages > PVM_MAX_PP_ARRAY_COUNT) {
 190                /* For reliability don't try to kmalloc more than
 191                   2 pages worth */
 192                process_pages = kmalloc(min_t(size_t, PVM_MAX_KMALLOC_PAGES,
 193                                              sizeof(struct pages *)*nr_pages),
 194                                        GFP_KERNEL);
 195
 196                if (!process_pages)
 197                        return -ENOMEM;
 198        }
 199
 200        /* Get process information */
 201        task = find_get_task_by_vpid(pid);
 202        if (!task) {
 203                rc = -ESRCH;
 204                goto free_proc_pages;
 205        }
 206
 207        mm = mm_access(task, PTRACE_MODE_ATTACH_REALCREDS);
 208        if (!mm || IS_ERR(mm)) {
 209                rc = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH;
 210                /*
 211                 * Explicitly map EACCES to EPERM as EPERM is a more a
 212                 * appropriate error code for process_vw_readv/writev
 213                 */
 214                if (rc == -EACCES)
 215                        rc = -EPERM;
 216                goto put_task_struct;
 217        }
 218
 219        for (i = 0; i < riovcnt && iov_iter_count(iter) && !rc; i++)
 220                rc = process_vm_rw_single_vec(
 221                        (unsigned long)rvec[i].iov_base, rvec[i].iov_len,
 222                        iter, process_pages, mm, task, vm_write);
 223
 224        /* copied = space before - space after */
 225        total_len -= iov_iter_count(iter);
 226
 227        /* If we have managed to copy any data at all then
 228           we return the number of bytes copied. Otherwise
 229           we return the error code */
 230        if (total_len)
 231                rc = total_len;
 232
 233        mmput(mm);
 234
 235put_task_struct:
 236        put_task_struct(task);
 237
 238free_proc_pages:
 239        if (process_pages != pp_stack)
 240                kfree(process_pages);
 241        return rc;
 242}
 243
 244/**
 245 * process_vm_rw - check iovecs before calling core routine
 246 * @pid: PID of process to read/write from/to
 247 * @lvec: iovec array specifying where to copy to/from locally
 248 * @liovcnt: size of lvec array
 249 * @rvec: iovec array specifying where to copy to/from in the other process
 250 * @riovcnt: size of rvec array
 251 * @flags: currently unused
 252 * @vm_write: 0 if reading from other process, 1 if writing to other process
 253 *
 254 * Returns the number of bytes read/written or error code. May
 255 *  return less bytes than expected if an error occurs during the copying
 256 *  process.
 257 */
 258static ssize_t process_vm_rw(pid_t pid,
 259                             const struct iovec __user *lvec,
 260                             unsigned long liovcnt,
 261                             const struct iovec __user *rvec,
 262                             unsigned long riovcnt,
 263                             unsigned long flags, int vm_write)
 264{
 265        struct iovec iovstack_l[UIO_FASTIOV];
 266        struct iovec iovstack_r[UIO_FASTIOV];
 267        struct iovec *iov_l = iovstack_l;
 268        struct iovec *iov_r = iovstack_r;
 269        struct iov_iter iter;
 270        ssize_t rc;
 271        int dir = vm_write ? WRITE : READ;
 272
 273        if (flags != 0)
 274                return -EINVAL;
 275
 276        /* Check iovecs */
 277        rc = import_iovec(dir, lvec, liovcnt, UIO_FASTIOV, &iov_l, &iter);
 278        if (rc < 0)
 279                return rc;
 280        if (!iov_iter_count(&iter))
 281                goto free_iovecs;
 282
 283        rc = rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt, UIO_FASTIOV,
 284                                   iovstack_r, &iov_r);
 285        if (rc <= 0)
 286                goto free_iovecs;
 287
 288        rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write);
 289
 290free_iovecs:
 291        if (iov_r != iovstack_r)
 292                kfree(iov_r);
 293        kfree(iov_l);
 294
 295        return rc;
 296}
 297
 298SYSCALL_DEFINE6(process_vm_readv, pid_t, pid, const struct iovec __user *, lvec,
 299                unsigned long, liovcnt, const struct iovec __user *, rvec,
 300                unsigned long, riovcnt, unsigned long, flags)
 301{
 302        return process_vm_rw(pid, lvec, liovcnt, rvec, riovcnt, flags, 0);
 303}
 304
 305SYSCALL_DEFINE6(process_vm_writev, pid_t, pid,
 306                const struct iovec __user *, lvec,
 307                unsigned long, liovcnt, const struct iovec __user *, rvec,
 308                unsigned long, riovcnt, unsigned long, flags)
 309{
 310        return process_vm_rw(pid, lvec, liovcnt, rvec, riovcnt, flags, 1);
 311}
 312
 313#ifdef CONFIG_COMPAT
 314
 315static ssize_t
 316compat_process_vm_rw(compat_pid_t pid,
 317                     const struct compat_iovec __user *lvec,
 318                     unsigned long liovcnt,
 319                     const struct compat_iovec __user *rvec,
 320                     unsigned long riovcnt,
 321                     unsigned long flags, int vm_write)
 322{
 323        struct iovec iovstack_l[UIO_FASTIOV];
 324        struct iovec iovstack_r[UIO_FASTIOV];
 325        struct iovec *iov_l = iovstack_l;
 326        struct iovec *iov_r = iovstack_r;
 327        struct iov_iter iter;
 328        ssize_t rc = -EFAULT;
 329        int dir = vm_write ? WRITE : READ;
 330
 331        if (flags != 0)
 332                return -EINVAL;
 333
 334        rc = compat_import_iovec(dir, lvec, liovcnt, UIO_FASTIOV, &iov_l, &iter);
 335        if (rc < 0)
 336                return rc;
 337        if (!iov_iter_count(&iter))
 338                goto free_iovecs;
 339        rc = compat_rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt,
 340                                          UIO_FASTIOV, iovstack_r,
 341                                          &iov_r);
 342        if (rc <= 0)
 343                goto free_iovecs;
 344
 345        rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write);
 346
 347free_iovecs:
 348        if (iov_r != iovstack_r)
 349                kfree(iov_r);
 350        kfree(iov_l);
 351        return rc;
 352}
 353
 354COMPAT_SYSCALL_DEFINE6(process_vm_readv, 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, 0);
 363}
 364
 365COMPAT_SYSCALL_DEFINE6(process_vm_writev, compat_pid_t, pid,
 366                       const struct compat_iovec __user *, lvec,
 367                       compat_ulong_t, liovcnt,
 368                       const struct compat_iovec __user *, rvec,
 369                       compat_ulong_t, riovcnt,
 370                       compat_ulong_t, flags)
 371{
 372        return compat_process_vm_rw(pid, lvec, liovcnt, rvec,
 373                                    riovcnt, flags, 1);
 374}
 375
 376#endif
 377