LXR linux/mm/process_vm

   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/mm.h>
   9#include <linux/uio.h>
  10#include <linux/sched.h>
  11#include <linux/sched/mm.h>
  12#include <linux/highmem.h>
  13#include <linux/ptrace.h>
  14#include <linux/slab.h>
  15#include <linux/syscalls.h>
  16
  17#ifdef CONFIG_COMPAT
  18#include <linux/compat.h>
  19#endif
  20
  21/**
  22 * process_vm_rw_pages - read/write pages from task specified
  23 * @pages: array of pointers to pages we want to copy
  24 * @offset: offset in page to start copying from/to
  25 * @len: number of bytes to copy
  26 * @iter: where to copy to/from locally
  27 * @vm_write: 0 means copy from, 1 means copy to
  28 * Returns 0 on success, error code otherwise
  29 */
  30static int process_vm_rw_pages(struct page **pages,
  31                               unsigned offset,
  32                               size_t len,
  33                               struct iov_iter *iter,
  34                               int vm_write)
  35{
  36        /* Do the copy for each page */
  37        while (len && iov_iter_count(iter)) {
  38                struct page *page = *pages++;
  39                size_t copy = PAGE_SIZE - offset;
  40                size_t copied;
  41
  42                if (copy > len)
  43                        copy = len;
  44
  45                if (vm_write)
  46                        copied = copy_page_from_iter(page, offset, copy, iter);
  47                else
  48                        copied = copy_page_to_iter(page, offset, copy, iter);
  49
  50                len -= copied;
  51                if (copied < copy && iov_iter_count(iter))
  52                        return -EFAULT;
  53                offset = 0;
  54        }
  55        return 0;
  56}
  57
  58/* Maximum number of pages kmalloc'd to hold struct page's during copy */
  59#define PVM_MAX_KMALLOC_PAGES (PAGE_SIZE * 2)
  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 */
  73static 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 long max_pages_per_loop = PVM_MAX_KMALLOC_PAGES
  86                / sizeof(struct pages *);
  87        unsigned int flags = 0;
  88
  89        /* Work out address and page range required */
  90        if (len == 0)
  91                return 0;
  92        nr_pages = (addr + len - 1) / PAGE_SIZE - addr / PAGE_SIZE + 1;
  93
  94        if (vm_write)
  95                flags |= FOLL_WRITE;
  96
  97        while (!rc && nr_pages && iov_iter_count(iter)) {
  98                int pinned_pages = min(nr_pages, max_pages_per_loop);
  99                int locked = 1;
 100                size_t bytes;
 101
 102                /*
 103                 * Get the pages we're interested in.  We must
 104                 * access remotely because task/mm might not
 105                 * current/current->mm
 106                 */
 107                mmap_read_lock(mm);
 108                pinned_pages = pin_user_pages_remote(mm, pa, pinned_pages,
 109                                                     flags, process_pages,
 110                                                     NULL, &locked);
 111                if (locked)
 112                        mmap_read_unlock(mm);
 113                if (pinned_pages <= 0)
 114                        return -EFAULT;
 115
 116                bytes = pinned_pages * PAGE_SIZE - start_offset;
 117                if (bytes > len)
 118                        bytes = len;
 119
 120                rc = process_vm_rw_pages(process_pages,
 121                                         start_offset, bytes, iter,
 122                                         vm_write);
 123                len -= bytes;
 124                start_offset = 0;
 125                nr_pages -= pinned_pages;
 126                pa += pinned_pages * PAGE_SIZE;
 127
 128                /* If vm_write is set, the pages need to be made dirty: */
 129                unpin_user_pages_dirty_lock(process_pages, pinned_pages,
 130                                            vm_write);
 131        }
 132
 133        return rc;
 134}
 135
 136/* Maximum number of entries for process pages array
 137   which lives on stack */
 138#define PVM_MAX_PP_ARRAY_COUNT 16
 139
 140/**
 141 * process_vm_rw_core - core of reading/writing pages from task specified
 142 * @pid: PID of process to read/write from/to
 143 * @iter: where to copy to/from locally
 144 * @rvec: iovec array specifying where to copy to/from in the other process
 145 * @riovcnt: size of rvec array
 146 * @flags: currently unused
 147 * @vm_write: 0 if reading from other process, 1 if writing to other process
 148 *
 149 * Returns the number of bytes read/written or error code. May
 150 *  return less bytes than expected if an error occurs during the copying
 151 *  process.
 152 */
 153static ssize_t process_vm_rw_core(pid_t pid, struct iov_iter *iter,
 154                                  const struct iovec *rvec,
 155                                  unsigned long riovcnt,
 156                                  unsigned long flags, int vm_write)
 157{
 158        struct task_struct *task;
 159        struct page *pp_stack[PVM_MAX_PP_ARRAY_COUNT];
 160        struct page **process_pages = pp_stack;
 161        struct mm_struct *mm;
 162        unsigned long i;
 163        ssize_t rc = 0;
 164        unsigned long nr_pages = 0;
 165        unsigned long nr_pages_iov;
 166        ssize_t iov_len;
 167        size_t total_len = iov_iter_count(iter);
 168
 169        /*
 170         * Work out how many pages of struct pages we're going to need
 171         * when eventually calling get_user_pages
 172         */
 173        for (i = 0; i < riovcnt; i++) {
 174                iov_len = rvec[i].iov_len;
 175                if (iov_len > 0) {
 176                        nr_pages_iov = ((unsigned long)rvec[i].iov_base
 177                                        + iov_len)
 178                                / PAGE_SIZE - (unsigned long)rvec[i].iov_base
 179                                / PAGE_SIZE + 1;
 180                        nr_pages = max(nr_pages, nr_pages_iov);
 181                }
 182        }
 183
 184        if (nr_pages == 0)
 185                return 0;
 186
 187        if (nr_pages > PVM_MAX_PP_ARRAY_COUNT) {
 188                /* For reliability don't try to kmalloc more than
 189                   2 pages worth */
 190                process_pages = kmalloc(min_t(size_t, PVM_MAX_KMALLOC_PAGES,
 191                                              sizeof(struct pages *)*nr_pages),
 192                                        GFP_KERNEL);
 193
 194                if (!process_pages)
 195                        return -ENOMEM;
 196        }
 197
 198        /* Get process information */
 199        task = find_get_task_by_vpid(pid);
 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
 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 *
 252 * Returns the number of bytes read/written or error code. May
 253 *  return less bytes than expected if an error occurs during the copying
 254 *  process.
 255 */
 256static ssize_t process_vm_rw(pid_t pid,
 257                             const struct iovec __user *lvec,
 258                             unsigned long liovcnt,
 259                             const struct iovec __user *rvec,
 260                             unsigned long riovcnt,
 261                             unsigned long flags, int vm_write)
 262{
 263        struct iovec iovstack_l[UIO_FASTIOV];
 264        struct iovec iovstack_r[UIO_FASTIOV];
 265        struct iovec *iov_l = iovstack_l;
 266        struct iovec *iov_r = iovstack_r;
 267        struct iov_iter iter;
 268        ssize_t rc;
 269        int dir = vm_write ? WRITE : READ;
 270
 271        if (flags != 0)
 272                return -EINVAL;
 273
 274        /* Check iovecs */
 275        rc = import_iovec(dir, lvec, liovcnt, UIO_FASTIOV, &iov_l, &iter);
 276        if (rc < 0)
 277                return rc;
 278        if (!iov_iter_count(&iter))
 279                goto free_iovecs;
 280
 281        rc = rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt, UIO_FASTIOV,
 282                                   iovstack_r, &iov_r);
 283        if (rc <= 0)
 284                goto free_iovecs;
 285
 286        rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write);
 287
 288free_iovecs:
 289        if (iov_r != iovstack_r)
 290                kfree(iov_r);
 291        kfree(iov_l);
 292
 293        return rc;
 294}
 295
 296SYSCALL_DEFINE6(process_vm_readv, pid_t, pid, const struct iovec __user *, lvec,
 297                unsigned long, liovcnt, const struct iovec __user *, rvec,
 298                unsigned long, riovcnt, unsigned long, flags)
 299{
 300        return process_vm_rw(pid, lvec, liovcnt, rvec, riovcnt, flags, 0);
 301}
 302
 303SYSCALL_DEFINE6(process_vm_writev, pid_t, pid,
 304                const struct iovec __user *, lvec,
 305                unsigned long, liovcnt, const struct iovec __user *, rvec,
 306                unsigned long, riovcnt, unsigned long, flags)
 307{
 308        return process_vm_rw(pid, lvec, liovcnt, rvec, riovcnt, flags, 1);
 309}
 310
 311#ifdef CONFIG_COMPAT
 312
 313static ssize_t
 314compat_process_vm_rw(compat_pid_t pid,
 315                     const struct compat_iovec __user *lvec,
 316                     unsigned long liovcnt,
 317                     const struct compat_iovec __user *rvec,
 318                     unsigned long riovcnt,
 319                     unsigned long flags, int vm_write)
 320{
 321        struct iovec iovstack_l[UIO_FASTIOV];
 322        struct iovec iovstack_r[UIO_FASTIOV];
 323        struct iovec *iov_l = iovstack_l;
 324        struct iovec *iov_r = iovstack_r;
 325        struct iov_iter iter;
 326        ssize_t rc = -EFAULT;
 327        int dir = vm_write ? WRITE : READ;
 328
 329        if (flags != 0)
 330                return -EINVAL;
 331
 332        rc = compat_import_iovec(dir, lvec, liovcnt, UIO_FASTIOV, &iov_l, &iter);
 333        if (rc < 0)
 334                return rc;
 335        if (!iov_iter_count(&iter))
 336                goto free_iovecs;
 337        rc = compat_rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt,
 338                                          UIO_FASTIOV, iovstack_r,
 339                                          &iov_r);
 340        if (rc <= 0)
 341                goto free_iovecs;
 342
 343        rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write);
 344
 345free_iovecs:
 346        if (iov_r != iovstack_r)
 347                kfree(iov_r);
 348        kfree(iov_l);
 349        return rc;
 350}
 351
 352COMPAT_SYSCALL_DEFINE6(process_vm_readv, compat_pid_t, pid,
 353                       const struct compat_iovec __user *, lvec,
 354                       compat_ulong_t, liovcnt,
 355                       const struct compat_iovec __user *, rvec,
 356                       compat_ulong_t, riovcnt,
 357                       compat_ulong_t, flags)
 358{
 359        return compat_process_vm_rw(pid, lvec, liovcnt, rvec,
 360                                    riovcnt, flags, 0);
 361}
 362
 363COMPAT_SYSCALL_DEFINE6(process_vm_writev, compat_pid_t, pid,
 364                       const struct compat_iovec __user *, lvec,
 365                       compat_ulong_t, liovcnt,
 366                       const struct compat_iovec __user *, rvec,
 367                       compat_ulong_t, riovcnt,
 368                       compat_ulong_t, flags)
 369{
 370        return compat_process_vm_rw(pid, lvec, liovcnt, rvec,
 371                                    riovcnt, flags, 1);
 372}
 373
 374#endif
 375