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