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Linux/mm/process_vm_access.c

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  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  * @task: task to read/write from
 27  * @mm: mm for task
 28  * @process_pages: struct pages area that can store at least
 29  *  nr_pages_to_copy struct page pointers
 30  * @pa: address of page in task to start copying from/to
 31  * @start_offset: offset in page to start copying from/to
 32  * @len: number of bytes to copy
 33  * @lvec: iovec array specifying where to copy to/from
 34  * @lvec_cnt: number of elements in iovec array
 35  * @lvec_current: index in iovec array we are up to
 36  * @lvec_offset: offset in bytes from current iovec iov_base we are up to
 37  * @vm_write: 0 means copy from, 1 means copy to
 38  * @nr_pages_to_copy: number of pages to copy
 39  * @bytes_copied: returns number of bytes successfully copied
 40  * Returns 0 on success, error code otherwise
 41  */
 42 static int process_vm_rw_pages(struct task_struct *task,
 43                                struct mm_struct *mm,
 44                                struct page **process_pages,
 45                                unsigned long pa,
 46                                unsigned long start_offset,
 47                                unsigned long len,
 48                                const struct iovec *lvec,
 49                                unsigned long lvec_cnt,
 50                                unsigned long *lvec_current,
 51                                size_t *lvec_offset,
 52                                int vm_write,
 53                                unsigned int nr_pages_to_copy,
 54                                ssize_t *bytes_copied)
 55 {
 56         int pages_pinned;
 57         void *target_kaddr;
 58         int pgs_copied = 0;
 59         int j;
 60         int ret;
 61         ssize_t bytes_to_copy;
 62         ssize_t rc = 0;
 63 
 64         *bytes_copied = 0;
 65 
 66         /* Get the pages we're interested in */
 67         down_read(&mm->mmap_sem);
 68         pages_pinned = get_user_pages(task, mm, pa,
 69                                       nr_pages_to_copy,
 70                                       vm_write, 0, process_pages, NULL);
 71         up_read(&mm->mmap_sem);
 72 
 73         if (pages_pinned != nr_pages_to_copy) {
 74                 rc = -EFAULT;
 75                 goto end;
 76         }
 77 
 78         /* Do the copy for each page */
 79         for (pgs_copied = 0;
 80              (pgs_copied < nr_pages_to_copy) && (*lvec_current < lvec_cnt);
 81              pgs_copied++) {
 82                 /* Make sure we have a non zero length iovec */
 83                 while (*lvec_current < lvec_cnt
 84                        && lvec[*lvec_current].iov_len == 0)
 85                         (*lvec_current)++;
 86                 if (*lvec_current == lvec_cnt)
 87                         break;
 88 
 89                 /*
 90                  * Will copy smallest of:
 91                  * - bytes remaining in page
 92                  * - bytes remaining in destination iovec
 93                  */
 94                 bytes_to_copy = min_t(ssize_t, PAGE_SIZE - start_offset,
 95                                       len - *bytes_copied);
 96                 bytes_to_copy = min_t(ssize_t, bytes_to_copy,
 97                                       lvec[*lvec_current].iov_len
 98                                       - *lvec_offset);
 99 
100                 target_kaddr = kmap(process_pages[pgs_copied]) + start_offset;
101 
102                 if (vm_write)
103                         ret = copy_from_user(target_kaddr,
104                                              lvec[*lvec_current].iov_base
105                                              + *lvec_offset,
106                                              bytes_to_copy);
107                 else
108                         ret = copy_to_user(lvec[*lvec_current].iov_base
109                                            + *lvec_offset,
110                                            target_kaddr, bytes_to_copy);
111                 kunmap(process_pages[pgs_copied]);
112                 if (ret) {
113                         *bytes_copied += bytes_to_copy - ret;
114                         pgs_copied++;
115                         rc = -EFAULT;
116                         goto end;
117                 }
118                 *bytes_copied += bytes_to_copy;
119                 *lvec_offset += bytes_to_copy;
120                 if (*lvec_offset == lvec[*lvec_current].iov_len) {
121                         /*
122                          * Need to copy remaining part of page into the
123                          * next iovec if there are any bytes left in page
124                          */
125                         (*lvec_current)++;
126                         *lvec_offset = 0;
127                         start_offset = (start_offset + bytes_to_copy)
128                                 % PAGE_SIZE;
129                         if (start_offset)
130                                 pgs_copied--;
131                 } else {
132                         start_offset = 0;
133                 }
134         }
135 
136 end:
137         if (vm_write) {
138                 for (j = 0; j < pages_pinned; j++) {
139                         if (j < pgs_copied)
140                                 set_page_dirty_lock(process_pages[j]);
141                         put_page(process_pages[j]);
142                 }
143         } else {
144                 for (j = 0; j < pages_pinned; j++)
145                         put_page(process_pages[j]);
146         }
147 
148         return rc;
149 }
150 
151 /* Maximum number of pages kmalloc'd to hold struct page's during copy */
152 #define PVM_MAX_KMALLOC_PAGES (PAGE_SIZE * 2)
153 
154 /**
155  * process_vm_rw_single_vec - read/write pages from task specified
156  * @addr: start memory address of target process
157  * @len: size of area to copy to/from
158  * @lvec: iovec array specifying where to copy to/from locally
159  * @lvec_cnt: number of elements in iovec array
160  * @lvec_current: index in iovec array we are up to
161  * @lvec_offset: offset in bytes from current iovec iov_base we are up to
162  * @process_pages: struct pages area that can store at least
163  *  nr_pages_to_copy struct page pointers
164  * @mm: mm for task
165  * @task: task to read/write from
166  * @vm_write: 0 means copy from, 1 means copy to
167  * @bytes_copied: returns number of bytes successfully copied
168  * Returns 0 on success or on failure error code
169  */
170 static int process_vm_rw_single_vec(unsigned long addr,
171                                     unsigned long len,
172                                     const struct iovec *lvec,
173                                     unsigned long lvec_cnt,
174                                     unsigned long *lvec_current,
175                                     size_t *lvec_offset,
176                                     struct page **process_pages,
177                                     struct mm_struct *mm,
178                                     struct task_struct *task,
179                                     int vm_write,
180                                     ssize_t *bytes_copied)
181 {
182         unsigned long pa = addr & PAGE_MASK;
183         unsigned long start_offset = addr - pa;
184         unsigned long nr_pages;
185         ssize_t bytes_copied_loop;
186         ssize_t rc = 0;
187         unsigned long nr_pages_copied = 0;
188         unsigned long nr_pages_to_copy;
189         unsigned long max_pages_per_loop = PVM_MAX_KMALLOC_PAGES
190                 / sizeof(struct pages *);
191 
192         *bytes_copied = 0;
193 
194         /* Work out address and page range required */
195         if (len == 0)
196                 return 0;
197         nr_pages = (addr + len - 1) / PAGE_SIZE - addr / PAGE_SIZE + 1;
198 
199         while ((nr_pages_copied < nr_pages) && (*lvec_current < lvec_cnt)) {
200                 nr_pages_to_copy = min(nr_pages - nr_pages_copied,
201                                        max_pages_per_loop);
202 
203                 rc = process_vm_rw_pages(task, mm, process_pages, pa,
204                                          start_offset, len,
205                                          lvec, lvec_cnt,
206                                          lvec_current, lvec_offset,
207                                          vm_write, nr_pages_to_copy,
208                                          &bytes_copied_loop);
209                 start_offset = 0;
210                 *bytes_copied += bytes_copied_loop;
211 
212                 if (rc < 0) {
213                         return rc;
214                 } else {
215                         len -= bytes_copied_loop;
216                         nr_pages_copied += nr_pages_to_copy;
217                         pa += nr_pages_to_copy * PAGE_SIZE;
218                 }
219         }
220 
221         return rc;
222 }
223 
224 /* Maximum number of entries for process pages array
225    which lives on stack */
226 #define PVM_MAX_PP_ARRAY_COUNT 16
227 
228 /**
229  * process_vm_rw_core - core of reading/writing pages from task specified
230  * @pid: PID of process to read/write from/to
231  * @lvec: iovec array specifying where to copy to/from locally
232  * @liovcnt: size of lvec array
233  * @rvec: iovec array specifying where to copy to/from in the other process
234  * @riovcnt: size of rvec array
235  * @flags: currently unused
236  * @vm_write: 0 if reading from other process, 1 if writing to other process
237  * Returns the number of bytes read/written or error code. May
238  *  return less bytes than expected if an error occurs during the copying
239  *  process.
240  */
241 static ssize_t process_vm_rw_core(pid_t pid, const struct iovec *lvec,
242                                   unsigned long liovcnt,
243                                   const struct iovec *rvec,
244                                   unsigned long riovcnt,
245                                   unsigned long flags, int vm_write)
246 {
247         struct task_struct *task;
248         struct page *pp_stack[PVM_MAX_PP_ARRAY_COUNT];
249         struct page **process_pages = pp_stack;
250         struct mm_struct *mm;
251         unsigned long i;
252         ssize_t rc = 0;
253         ssize_t bytes_copied_loop;
254         ssize_t bytes_copied = 0;
255         unsigned long nr_pages = 0;
256         unsigned long nr_pages_iov;
257         unsigned long iov_l_curr_idx = 0;
258         size_t iov_l_curr_offset = 0;
259         ssize_t iov_len;
260 
261         /*
262          * Work out how many pages of struct pages we're going to need
263          * when eventually calling get_user_pages
264          */
265         for (i = 0; i < riovcnt; i++) {
266                 iov_len = rvec[i].iov_len;
267                 if (iov_len > 0) {
268                         nr_pages_iov = ((unsigned long)rvec[i].iov_base
269                                         + iov_len)
270                                 / PAGE_SIZE - (unsigned long)rvec[i].iov_base
271                                 / PAGE_SIZE + 1;
272                         nr_pages = max(nr_pages, nr_pages_iov);
273                 }
274         }
275 
276         if (nr_pages == 0)
277                 return 0;
278 
279         if (nr_pages > PVM_MAX_PP_ARRAY_COUNT) {
280                 /* For reliability don't try to kmalloc more than
281                    2 pages worth */
282                 process_pages = kmalloc(min_t(size_t, PVM_MAX_KMALLOC_PAGES,
283                                               sizeof(struct pages *)*nr_pages),
284                                         GFP_KERNEL);
285 
286                 if (!process_pages)
287                         return -ENOMEM;
288         }
289 
290         /* Get process information */
291         rcu_read_lock();
292         task = find_task_by_vpid(pid);
293         if (task)
294                 get_task_struct(task);
295         rcu_read_unlock();
296         if (!task) {
297                 rc = -ESRCH;
298                 goto free_proc_pages;
299         }
300 
301         mm = mm_access(task, PTRACE_MODE_ATTACH_REALCREDS);
302         if (!mm || IS_ERR(mm)) {
303                 rc = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH;
304                 /*
305                  * Explicitly map EACCES to EPERM as EPERM is a more a
306                  * appropriate error code for process_vw_readv/writev
307                  */
308                 if (rc == -EACCES)
309                         rc = -EPERM;
310                 goto put_task_struct;
311         }
312 
313         for (i = 0; i < riovcnt && iov_l_curr_idx < liovcnt; i++) {
314                 rc = process_vm_rw_single_vec(
315                         (unsigned long)rvec[i].iov_base, rvec[i].iov_len,
316                         lvec, liovcnt, &iov_l_curr_idx, &iov_l_curr_offset,
317                         process_pages, mm, task, vm_write, &bytes_copied_loop);
318                 bytes_copied += bytes_copied_loop;
319                 if (rc != 0) {
320                         /* If we have managed to copy any data at all then
321                            we return the number of bytes copied. Otherwise
322                            we return the error code */
323                         if (bytes_copied)
324                                 rc = bytes_copied;
325                         goto put_mm;
326                 }
327         }
328 
329         rc = bytes_copied;
330 put_mm:
331         mmput(mm);
332 
333 put_task_struct:
334         put_task_struct(task);
335 
336 free_proc_pages:
337         if (process_pages != pp_stack)
338                 kfree(process_pages);
339         return rc;
340 }
341 
342 /**
343  * process_vm_rw - check iovecs before calling core routine
344  * @pid: PID of process to read/write from/to
345  * @lvec: iovec array specifying where to copy to/from locally
346  * @liovcnt: size of lvec array
347  * @rvec: iovec array specifying where to copy to/from in the other process
348  * @riovcnt: size of rvec array
349  * @flags: currently unused
350  * @vm_write: 0 if reading from other process, 1 if writing to other process
351  * Returns the number of bytes read/written or error code. May
352  *  return less bytes than expected if an error occurs during the copying
353  *  process.
354  */
355 static ssize_t process_vm_rw(pid_t pid,
356                              const struct iovec __user *lvec,
357                              unsigned long liovcnt,
358                              const struct iovec __user *rvec,
359                              unsigned long riovcnt,
360                              unsigned long flags, int vm_write)
361 {
362         struct iovec iovstack_l[UIO_FASTIOV];
363         struct iovec iovstack_r[UIO_FASTIOV];
364         struct iovec *iov_l = iovstack_l;
365         struct iovec *iov_r = iovstack_r;
366         ssize_t rc;
367 
368         if (flags != 0)
369                 return -EINVAL;
370 
371         /* Check iovecs */
372         if (vm_write)
373                 rc = rw_copy_check_uvector(WRITE, lvec, liovcnt, UIO_FASTIOV,
374                                            iovstack_l, &iov_l);
375         else
376                 rc = rw_copy_check_uvector(READ, lvec, liovcnt, UIO_FASTIOV,
377                                            iovstack_l, &iov_l);
378         if (rc <= 0)
379                 goto free_iovecs;
380 
381         rc = rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt, UIO_FASTIOV,
382                                    iovstack_r, &iov_r);
383         if (rc <= 0)
384                 goto free_iovecs;
385 
386         rc = process_vm_rw_core(pid, iov_l, liovcnt, iov_r, riovcnt, flags,
387                                 vm_write);
388 
389 free_iovecs:
390         if (iov_r != iovstack_r)
391                 kfree(iov_r);
392         if (iov_l != iovstack_l)
393                 kfree(iov_l);
394 
395         return rc;
396 }
397 
398 SYSCALL_DEFINE6(process_vm_readv, pid_t, pid, const struct iovec __user *, lvec,
399                 unsigned long, liovcnt, const struct iovec __user *, rvec,
400                 unsigned long, riovcnt, unsigned long, flags)
401 {
402         return process_vm_rw(pid, lvec, liovcnt, rvec, riovcnt, flags, 0);
403 }
404 
405 SYSCALL_DEFINE6(process_vm_writev, pid_t, pid,
406                 const struct iovec __user *, lvec,
407                 unsigned long, liovcnt, const struct iovec __user *, rvec,
408                 unsigned long, riovcnt, unsigned long, flags)
409 {
410         return process_vm_rw(pid, lvec, liovcnt, rvec, riovcnt, flags, 1);
411 }
412 
413 #ifdef CONFIG_COMPAT
414 
415 asmlinkage ssize_t
416 compat_process_vm_rw(compat_pid_t pid,
417                      const struct compat_iovec __user *lvec,
418                      unsigned long liovcnt,
419                      const struct compat_iovec __user *rvec,
420                      unsigned long riovcnt,
421                      unsigned long flags, int vm_write)
422 {
423         struct iovec iovstack_l[UIO_FASTIOV];
424         struct iovec iovstack_r[UIO_FASTIOV];
425         struct iovec *iov_l = iovstack_l;
426         struct iovec *iov_r = iovstack_r;
427         ssize_t rc = -EFAULT;
428 
429         if (flags != 0)
430                 return -EINVAL;
431 
432         if (vm_write)
433                 rc = compat_rw_copy_check_uvector(WRITE, lvec, liovcnt,
434                                                   UIO_FASTIOV, iovstack_l,
435                                                   &iov_l);
436         else
437                 rc = compat_rw_copy_check_uvector(READ, lvec, liovcnt,
438                                                   UIO_FASTIOV, iovstack_l,
439                                                   &iov_l);
440         if (rc <= 0)
441                 goto free_iovecs;
442         rc = compat_rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt,
443                                           UIO_FASTIOV, iovstack_r,
444                                           &iov_r);
445         if (rc <= 0)
446                 goto free_iovecs;
447 
448         rc = process_vm_rw_core(pid, iov_l, liovcnt, iov_r, riovcnt, flags,
449                            vm_write);
450 
451 free_iovecs:
452         if (iov_r != iovstack_r)
453                 kfree(iov_r);
454         if (iov_l != iovstack_l)
455                 kfree(iov_l);
456         return rc;
457 }
458 
459 asmlinkage ssize_t
460 compat_sys_process_vm_readv(compat_pid_t pid,
461                             const struct compat_iovec __user *lvec,
462                             unsigned long liovcnt,
463                             const struct compat_iovec __user *rvec,
464                             unsigned long riovcnt,
465                             unsigned long flags)
466 {
467         return compat_process_vm_rw(pid, lvec, liovcnt, rvec,
468                                     riovcnt, flags, 0);
469 }
470 
471 asmlinkage ssize_t
472 compat_sys_process_vm_writev(compat_pid_t pid,
473                              const struct compat_iovec __user *lvec,
474                              unsigned long liovcnt,
475                              const struct compat_iovec __user *rvec,
476                              unsigned long riovcnt,
477                              unsigned long flags)
478 {
479         return compat_process_vm_rw(pid, lvec, liovcnt, rvec,
480                                     riovcnt, flags, 1);
481 }
482 
483 #endif
484 

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