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Linux/mm/process_vm_access.c

  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  */
 33 static 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  */
 77 static 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         unsigned int flags = 0;
 92 
 93         /* Work out address and page range required */
 94         if (len == 0)
 95                 return 0;
 96         nr_pages = (addr + len - 1) / PAGE_SIZE - addr / PAGE_SIZE + 1;
 97 
 98         if (vm_write)
 99                 flags |= FOLL_WRITE;
100 
101         while (!rc && nr_pages && iov_iter_count(iter)) {
102                 int pages = min(nr_pages, max_pages_per_loop);
103                 int locked = 1;
104                 size_t bytes;
105 
106                 /*
107                  * Get the pages we're interested in.  We must
108                  * access remotely because task/mm might not
109                  * current/current->mm
110                  */
111                 down_read(&mm->mmap_sem);
112                 pages = get_user_pages_remote(task, mm, pa, pages, flags,
113                                               process_pages, NULL, &locked);
114                 if (locked)
115                         up_read(&mm->mmap_sem);
116                 if (pages <= 0)
117                         return -EFAULT;
118 
119                 bytes = pages * PAGE_SIZE - start_offset;
120                 if (bytes > len)
121                         bytes = len;
122 
123                 rc = process_vm_rw_pages(process_pages,
124                                          start_offset, bytes, iter,
125                                          vm_write);
126                 len -= bytes;
127                 start_offset = 0;
128                 nr_pages -= pages;
129                 pa += pages * PAGE_SIZE;
130                 while (pages)
131                         put_page(process_pages[--pages]);
132         }
133 
134         return rc;
135 }
136 
137 /* Maximum number of entries for process pages array
138    which lives on stack */
139 #define PVM_MAX_PP_ARRAY_COUNT 16
140 
141 /**
142  * process_vm_rw_core - core of reading/writing pages from task specified
143  * @pid: PID of process to read/write from/to
144  * @iter: where to copy to/from locally
145  * @rvec: iovec array specifying where to copy to/from in the other process
146  * @riovcnt: size of rvec array
147  * @flags: currently unused
148  * @vm_write: 0 if reading from other process, 1 if writing to other process
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  */
153 static 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         rcu_read_lock();
200         task = find_task_by_vpid(pid);
201         if (task)
202                 get_task_struct(task);
203         rcu_read_unlock();
204         if (!task) {
205                 rc = -ESRCH;
206                 goto free_proc_pages;
207         }
208 
209         mm = mm_access(task, PTRACE_MODE_ATTACH_REALCREDS);
210         if (!mm || IS_ERR(mm)) {
211                 rc = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH;
212                 /*
213                  * Explicitly map EACCES to EPERM as EPERM is a more a
214                  * appropriate error code for process_vw_readv/writev
215                  */
216                 if (rc == -EACCES)
217                         rc = -EPERM;
218                 goto put_task_struct;
219         }
220 
221         for (i = 0; i < riovcnt && iov_iter_count(iter) && !rc; i++)
222                 rc = process_vm_rw_single_vec(
223                         (unsigned long)rvec[i].iov_base, rvec[i].iov_len,
224                         iter, process_pages, mm, task, vm_write);
225 
226         /* copied = space before - space after */
227         total_len -= iov_iter_count(iter);
228 
229         /* If we have managed to copy any data at all then
230            we return the number of bytes copied. Otherwise
231            we return the error code */
232         if (total_len)
233                 rc = total_len;
234 
235         mmput(mm);
236 
237 put_task_struct:
238         put_task_struct(task);
239 
240 free_proc_pages:
241         if (process_pages != pp_stack)
242                 kfree(process_pages);
243         return rc;
244 }
245 
246 /**
247  * process_vm_rw - check iovecs before calling core routine
248  * @pid: PID of process to read/write from/to
249  * @lvec: iovec array specifying where to copy to/from locally
250  * @liovcnt: size of lvec array
251  * @rvec: iovec array specifying where to copy to/from in the other process
252  * @riovcnt: size of rvec array
253  * @flags: currently unused
254  * @vm_write: 0 if reading from other process, 1 if writing to other process
255  * Returns the number of bytes read/written or error code. May
256  *  return less bytes than expected if an error occurs during the copying
257  *  process.
258  */
259 static ssize_t process_vm_rw(pid_t pid,
260                              const struct iovec __user *lvec,
261                              unsigned long liovcnt,
262                              const struct iovec __user *rvec,
263                              unsigned long riovcnt,
264                              unsigned long flags, int vm_write)
265 {
266         struct iovec iovstack_l[UIO_FASTIOV];
267         struct iovec iovstack_r[UIO_FASTIOV];
268         struct iovec *iov_l = iovstack_l;
269         struct iovec *iov_r = iovstack_r;
270         struct iov_iter iter;
271         ssize_t rc;
272         int dir = vm_write ? WRITE : READ;
273 
274         if (flags != 0)
275                 return -EINVAL;
276 
277         /* Check iovecs */
278         rc = import_iovec(dir, lvec, liovcnt, UIO_FASTIOV, &iov_l, &iter);
279         if (rc < 0)
280                 return rc;
281         if (!iov_iter_count(&iter))
282                 goto free_iovecs;
283 
284         rc = rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt, UIO_FASTIOV,
285                                    iovstack_r, &iov_r);
286         if (rc <= 0)
287                 goto free_iovecs;
288 
289         rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write);
290 
291 free_iovecs:
292         if (iov_r != iovstack_r)
293                 kfree(iov_r);
294         kfree(iov_l);
295 
296         return rc;
297 }
298 
299 SYSCALL_DEFINE6(process_vm_readv, pid_t, pid, 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, 0);
304 }
305 
306 SYSCALL_DEFINE6(process_vm_writev, pid_t, pid,
307                 const struct iovec __user *, lvec,
308                 unsigned long, liovcnt, const struct iovec __user *, rvec,
309                 unsigned long, riovcnt, unsigned long, flags)
310 {
311         return process_vm_rw(pid, lvec, liovcnt, rvec, riovcnt, flags, 1);
312 }
313 
314 #ifdef CONFIG_COMPAT
315 
316 static ssize_t
317 compat_process_vm_rw(compat_pid_t pid,
318                      const struct compat_iovec __user *lvec,
319                      unsigned long liovcnt,
320                      const struct compat_iovec __user *rvec,
321                      unsigned long riovcnt,
322                      unsigned long flags, int vm_write)
323 {
324         struct iovec iovstack_l[UIO_FASTIOV];
325         struct iovec iovstack_r[UIO_FASTIOV];
326         struct iovec *iov_l = iovstack_l;
327         struct iovec *iov_r = iovstack_r;
328         struct iov_iter iter;
329         ssize_t rc = -EFAULT;
330         int dir = vm_write ? WRITE : READ;
331 
332         if (flags != 0)
333                 return -EINVAL;
334 
335         rc = compat_import_iovec(dir, lvec, liovcnt, UIO_FASTIOV, &iov_l, &iter);
336         if (rc < 0)
337                 return rc;
338         if (!iov_iter_count(&iter))
339                 goto free_iovecs;
340         rc = compat_rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt,
341                                           UIO_FASTIOV, iovstack_r,
342                                           &iov_r);
343         if (rc <= 0)
344                 goto free_iovecs;
345 
346         rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write);
347 
348 free_iovecs:
349         if (iov_r != iovstack_r)
350                 kfree(iov_r);
351         kfree(iov_l);
352         return rc;
353 }
354 
355 COMPAT_SYSCALL_DEFINE6(process_vm_readv, compat_pid_t, pid,
356                        const struct compat_iovec __user *, lvec,
357                        compat_ulong_t, liovcnt,
358                        const struct compat_iovec __user *, rvec,
359                        compat_ulong_t, riovcnt,
360                        compat_ulong_t, flags)
361 {
362         return compat_process_vm_rw(pid, lvec, liovcnt, rvec,
363                                     riovcnt, flags, 0);
364 }
365 
366 COMPAT_SYSCALL_DEFINE6(process_vm_writev, compat_pid_t, pid,
367                        const struct compat_iovec __user *, lvec,
368                        compat_ulong_t, liovcnt,
369                        const struct compat_iovec __user *, rvec,
370                        compat_ulong_t, riovcnt,
371                        compat_ulong_t, flags)
372 {
373         return compat_process_vm_rw(pid, lvec, liovcnt, rvec,
374                                     riovcnt, flags, 1);
375 }
376 
377 #endif
378 

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