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                        set_page_dirty_lock(page);
  48                } else {
  49                        copied = copy_page_to_iter(page, offset, copy, iter);
  50                }
  51                len -= copied;
  52                if (copied < copy && iov_iter_count(iter))
  53                        return -EFAULT;
  54                offset = 0;
  55        }
  56        return 0;
  57}
  58
  59/* Maximum number of pages kmalloc'd to hold struct page's during copy */
  60#define PVM_MAX_KMALLOC_PAGES (PAGE_SIZE * 2)
  61
  62/**
  63 * process_vm_rw_single_vec - read/write pages from task specified
  64 * @addr: start memory address of target process
  65 * @len: size of area to copy to/from
  66 * @iter: where to copy to/from locally
  67 * @process_pages: struct pages area that can store at least
  68 *  nr_pages_to_copy struct page pointers
  69 * @mm: mm for task
  70 * @task: task to read/write from
  71 * @vm_write: 0 means copy from, 1 means copy to
  72 * Returns 0 on success or on failure error code
  73 */
  74static int process_vm_rw_single_vec(unsigned long addr,
  75                                    unsigned long len,
  76                                    struct iov_iter *iter,
  77                                    struct page **process_pages,
  78                                    struct mm_struct *mm,
  79                                    struct task_struct *task,
  80                                    int vm_write)
  81{
  82        unsigned long pa = addr & PAGE_MASK;
  83        unsigned long start_offset = addr - pa;
  84        unsigned long nr_pages;
  85        ssize_t rc = 0;
  86        unsigned long max_pages_per_loop = PVM_MAX_KMALLOC_PAGES
  87                / sizeof(struct pages *);
  88        unsigned int flags = 0;
  89
  90        /* Work out address and page range required */
  91        if (len == 0)
  92                return 0;
  93        nr_pages = (addr + len - 1) / PAGE_SIZE - addr / PAGE_SIZE + 1;
  94
  95        if (vm_write)
  96                flags |= FOLL_WRITE;
  97
  98        while (!rc && nr_pages && iov_iter_count(iter)) {
  99                int pages = min(nr_pages, max_pages_per_loop);
 100                int locked = 1;
 101                size_t bytes;
 102
 103                /*
 104                 * Get the pages we're interested in.  We must
 105                 * access remotely because task/mm might not
 106                 * current/current->mm
 107                 */
 108                down_read(&mm->mmap_sem);
 109                pages = get_user_pages_remote(task, mm, pa, pages, flags,
 110                                              process_pages, NULL, &locked);
 111                if (locked)
 112                        up_read(&mm->mmap_sem);
 113                if (pages <= 0)
 114                        return -EFAULT;
 115
 116                bytes = 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 -= pages;
 126                pa += pages * PAGE_SIZE;
 127                while (pages)
 128                        put_page(process_pages[--pages]);
 129        }
 130
 131        return rc;
 132}
 133
 134/* Maximum number of entries for process pages array
 135   which lives on stack */
 136#define PVM_MAX_PP_ARRAY_COUNT 16
 137
 138/**
 139 * process_vm_rw_core - core of reading/writing pages from task specified
 140 * @pid: PID of process to read/write from/to
 141 * @iter: where to copy to/from locally
 142 * @rvec: iovec array specifying where to copy to/from in the other process
 143 * @riovcnt: size of rvec array
 144 * @flags: currently unused
 145 * @vm_write: 0 if reading from other process, 1 if writing to other process
 146 *
 147 * Returns the number of bytes read/written or error code. May
 148 *  return less bytes than expected if an error occurs during the copying
 149 *  process.
 150 */
 151static ssize_t process_vm_rw_core(pid_t pid, struct iov_iter *iter,
 152                                  const struct iovec *rvec,
 153                                  unsigned long riovcnt,
 154                                  unsigned long flags, int vm_write)
 155{
 156        struct task_struct *task;
 157        struct page *pp_stack[PVM_MAX_PP_ARRAY_COUNT];
 158        struct page **process_pages = pp_stack;
 159        struct mm_struct *mm;
 160        unsigned long i;
 161        ssize_t rc = 0;
 162        unsigned long nr_pages = 0;
 163        unsigned long nr_pages_iov;
 164        ssize_t iov_len;
 165        size_t total_len = iov_iter_count(iter);
 166
 167        /*
 168         * Work out how many pages of struct pages we're going to need
 169         * when eventually calling get_user_pages
 170         */
 171        for (i = 0; i < riovcnt; i++) {
 172                iov_len = rvec[i].iov_len;
 173                if (iov_len > 0) {
 174                        nr_pages_iov = ((unsigned long)rvec[i].iov_base
 175                                        + iov_len)
 176                                / PAGE_SIZE - (unsigned long)rvec[i].iov_base
 177                                / PAGE_SIZE + 1;
 178                        nr_pages = max(nr_pages, nr_pages_iov);
 179                }
 180        }
 181
 182        if (nr_pages == 0)
 183                return 0;
 184
 185        if (nr_pages > PVM_MAX_PP_ARRAY_COUNT) {
 186                /* For reliability don't try to kmalloc more than
 187                   2 pages worth */
 188                process_pages = kmalloc(min_t(size_t, PVM_MAX_KMALLOC_PAGES,
 189                                              sizeof(struct pages *)*nr_pages),
 190                                        GFP_KERNEL);
 191
 192                if (!process_pages)
 193                        return -ENOMEM;
 194        }
 195
 196        /* Get process information */
 197        task = find_get_task_by_vpid(pid);
 198        if (!task) {
 199                rc = -ESRCH;
 200                goto free_proc_pages;
 201        }
 202
 203        mm = mm_access(task, PTRACE_MODE_ATTACH_REALCREDS);
 204        if (!mm || IS_ERR(mm)) {
 205                rc = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH;
 206                /*
 207                 * Explicitly map EACCES to EPERM as EPERM is a more a
 208                 * appropriate error code for process_vw_readv/writev
 209                 */
 210                if (rc == -EACCES)
 211                        rc = -EPERM;
 212                goto put_task_struct;
 213        }
 214
 215        for (i = 0; i < riovcnt && iov_iter_count(iter) && !rc; i++)
 216                rc = process_vm_rw_single_vec(
 217                        (unsigned long)rvec[i].iov_base, rvec[i].iov_len,
 218                        iter, process_pages, mm, task, vm_write);
 219
 220        /* copied = space before - space after */
 221        total_len -= iov_iter_count(iter);
 222
 223        /* If we have managed to copy any data at all then
 224           we return the number of bytes copied. Otherwise
 225           we return the error code */
 226        if (total_len)
 227                rc = total_len;
 228
 229        mmput(mm);
 230
 231put_task_struct:
 232        put_task_struct(task);
 233
 234free_proc_pages:
 235        if (process_pages != pp_stack)
 236                kfree(process_pages);
 237        return rc;
 238}
 239
 240/**
 241 * process_vm_rw - check iovecs before calling core routine
 242 * @pid: PID of process to read/write from/to
 243 * @lvec: iovec array specifying where to copy to/from locally
 244 * @liovcnt: size of lvec array
 245 * @rvec: iovec array specifying where to copy to/from in the other process
 246 * @riovcnt: size of rvec array
 247 * @flags: currently unused
 248 * @vm_write: 0 if reading from other process, 1 if writing to other process
 249 *
 250 * Returns the number of bytes read/written or error code. May
 251 *  return less bytes than expected if an error occurs during the copying
 252 *  process.
 253 */
 254static ssize_t process_vm_rw(pid_t pid,
 255                             const struct iovec __user *lvec,
 256                             unsigned long liovcnt,
 257                             const struct iovec __user *rvec,
 258                             unsigned long riovcnt,
 259                             unsigned long flags, int vm_write)
 260{
 261        struct iovec iovstack_l[UIO_FASTIOV];
 262        struct iovec iovstack_r[UIO_FASTIOV];
 263        struct iovec *iov_l = iovstack_l;
 264        struct iovec *iov_r = iovstack_r;
 265        struct iov_iter iter;
 266        ssize_t rc;
 267        int dir = vm_write ? WRITE : READ;
 268
 269        if (flags != 0)
 270                return -EINVAL;
 271
 272        /* Check iovecs */
 273        rc = import_iovec(dir, lvec, liovcnt, UIO_FASTIOV, &iov_l, &iter);
 274        if (rc < 0)
 275                return rc;
 276        if (!iov_iter_count(&iter))
 277                goto free_iovecs;
 278
 279        rc = rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt, UIO_FASTIOV,
 280                                   iovstack_r, &iov_r);
 281        if (rc <= 0)
 282                goto free_iovecs;
 283
 284        rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write);
 285
 286free_iovecs:
 287        if (iov_r != iovstack_r)
 288                kfree(iov_r);
 289        kfree(iov_l);
 290
 291        return rc;
 292}
 293
 294SYSCALL_DEFINE6(process_vm_readv, pid_t, pid, const struct iovec __user *, lvec,
 295                unsigned long, liovcnt, const struct iovec __user *, rvec,
 296                unsigned long, riovcnt, unsigned long, flags)
 297{
 298        return process_vm_rw(pid, lvec, liovcnt, rvec, riovcnt, flags, 0);
 299}
 300
 301SYSCALL_DEFINE6(process_vm_writev, pid_t, pid,
 302                const struct iovec __user *, lvec,
 303                unsigned long, liovcnt, const struct iovec __user *, rvec,
 304                unsigned long, riovcnt, unsigned long, flags)
 305{
 306        return process_vm_rw(pid, lvec, liovcnt, rvec, riovcnt, flags, 1);
 307}
 308
 309#ifdef CONFIG_COMPAT
 310
 311static ssize_t
 312compat_process_vm_rw(compat_pid_t pid,
 313                     const struct compat_iovec __user *lvec,
 314                     unsigned long liovcnt,
 315                     const struct compat_iovec __user *rvec,
 316                     unsigned long riovcnt,
 317                     unsigned long flags, int vm_write)
 318{
 319        struct iovec iovstack_l[UIO_FASTIOV];
 320        struct iovec iovstack_r[UIO_FASTIOV];
 321        struct iovec *iov_l = iovstack_l;
 322        struct iovec *iov_r = iovstack_r;
 323        struct iov_iter iter;
 324        ssize_t rc = -EFAULT;
 325        int dir = vm_write ? WRITE : READ;
 326
 327        if (flags != 0)
 328                return -EINVAL;
 329
 330        rc = compat_import_iovec(dir, lvec, liovcnt, UIO_FASTIOV, &iov_l, &iter);
 331        if (rc < 0)
 332                return rc;
 333        if (!iov_iter_count(&iter))
 334                goto free_iovecs;
 335        rc = compat_rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt,
 336                                          UIO_FASTIOV, iovstack_r,
 337                                          &iov_r);
 338        if (rc <= 0)
 339                goto free_iovecs;
 340
 341        rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write);
 342
 343free_iovecs:
 344        if (iov_r != iovstack_r)
 345                kfree(iov_r);
 346        kfree(iov_l);
 347        return rc;
 348}
 349
 350COMPAT_SYSCALL_DEFINE6(process_vm_readv, compat_pid_t, pid,
 351                       const struct compat_iovec __user *, lvec,
 352                       compat_ulong_t, liovcnt,
 353                       const struct compat_iovec __user *, rvec,
 354                       compat_ulong_t, riovcnt,
 355                       compat_ulong_t, flags)
 356{
 357        return compat_process_vm_rw(pid, lvec, liovcnt, rvec,
 358                                    riovcnt, flags, 0);
 359}
 360
 361COMPAT_SYSCALL_DEFINE6(process_vm_writev, compat_pid_t, pid,
 362                       const struct compat_iovec __user *, lvec,
 363                       compat_ulong_t, liovcnt,
 364                       const struct compat_iovec __user *, rvec,
 365                       compat_ulong_t, riovcnt,
 366                       compat_ulong_t, flags)
 367{
 368        return compat_process_vm_rw(pid, lvec, liovcnt, rvec,
 369                                    riovcnt, flags, 1);
 370}
 371
 372#endif
 373