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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/sched/mm.h>
 16 #include <linux/highmem.h>
 17 #include <linux/ptrace.h>
 18 #include <linux/slab.h>
 19 #include <linux/syscalls.h>
 20 
 21 #ifdef CONFIG_COMPAT
 22 #include <linux/compat.h>
 23 #endif
 24 
 25 /**
 26  * process_vm_rw_pages - read/write pages from task specified
 27  * @pages: array of pointers to pages we want to copy
 28  * @offset: offset in page to start copying from/to
 29  * @len: number of bytes to copy
 30  * @iter: where to copy to/from locally
 31  * @vm_write: 0 means copy from, 1 means copy to
 32  * Returns 0 on success, error code otherwise
 33  */
 34 static int process_vm_rw_pages(struct page **pages,
 35                                unsigned offset,
 36                                size_t len,
 37                                struct iov_iter *iter,
 38                                int vm_write)
 39 {
 40         /* Do the copy for each page */
 41         while (len && iov_iter_count(iter)) {
 42                 struct page *page = *pages++;
 43                 size_t copy = PAGE_SIZE - offset;
 44                 size_t copied;
 45 
 46                 if (copy > len)
 47                         copy = len;
 48 
 49                 if (vm_write) {
 50                         copied = copy_page_from_iter(page, offset, copy, iter);
 51                         set_page_dirty_lock(page);
 52                 } else {
 53                         copied = copy_page_to_iter(page, offset, copy, iter);
 54                 }
 55                 len -= copied;
 56                 if (copied < copy && iov_iter_count(iter))
 57                         return -EFAULT;
 58                 offset = 0;
 59         }
 60         return 0;
 61 }
 62 
 63 /* Maximum number of pages kmalloc'd to hold struct page's during copy */
 64 #define PVM_MAX_KMALLOC_PAGES (PAGE_SIZE * 2)
 65 
 66 /**
 67  * process_vm_rw_single_vec - read/write pages from task specified
 68  * @addr: start memory address of target process
 69  * @len: size of area to copy to/from
 70  * @iter: where to copy to/from locally
 71  * @process_pages: struct pages area that can store at least
 72  *  nr_pages_to_copy struct page pointers
 73  * @mm: mm for task
 74  * @task: task to read/write from
 75  * @vm_write: 0 means copy from, 1 means copy to
 76  * Returns 0 on success or on failure error code
 77  */
 78 static int process_vm_rw_single_vec(unsigned long addr,
 79                                     unsigned long len,
 80                                     struct iov_iter *iter,
 81                                     struct page **process_pages,
 82                                     struct mm_struct *mm,
 83                                     struct task_struct *task,
 84                                     int vm_write)
 85 {
 86         unsigned long pa = addr & PAGE_MASK;
 87         unsigned long start_offset = addr - pa;
 88         unsigned long nr_pages;
 89         ssize_t rc = 0;
 90         unsigned long max_pages_per_loop = PVM_MAX_KMALLOC_PAGES
 91                 / sizeof(struct pages *);
 92         unsigned int flags = 0;
 93 
 94         /* Work out address and page range required */
 95         if (len == 0)
 96                 return 0;
 97         nr_pages = (addr + len - 1) / PAGE_SIZE - addr / PAGE_SIZE + 1;
 98 
 99         if (vm_write)
100                 flags |= FOLL_WRITE;
101 
102         while (!rc && nr_pages && iov_iter_count(iter)) {
103                 int pages = min(nr_pages, max_pages_per_loop);
104                 int locked = 1;
105                 size_t bytes;
106 
107                 /*
108                  * Get the pages we're interested in.  We must
109                  * access remotely because task/mm might not
110                  * current/current->mm
111                  */
112                 down_read(&mm->mmap_sem);
113                 pages = get_user_pages_remote(task, mm, pa, pages, flags,
114                                               process_pages, NULL, &locked);
115                 if (locked)
116                         up_read(&mm->mmap_sem);
117                 if (pages <= 0)
118                         return -EFAULT;
119 
120                 bytes = pages * PAGE_SIZE - start_offset;
121                 if (bytes > len)
122                         bytes = len;
123 
124                 rc = process_vm_rw_pages(process_pages,
125                                          start_offset, bytes, iter,
126                                          vm_write);
127                 len -= bytes;
128                 start_offset = 0;
129                 nr_pages -= pages;
130                 pa += pages * PAGE_SIZE;
131                 while (pages)
132                         put_page(process_pages[--pages]);
133         }
134 
135         return rc;
136 }
137 
138 /* Maximum number of entries for process pages array
139    which lives on stack */
140 #define PVM_MAX_PP_ARRAY_COUNT 16
141 
142 /**
143  * process_vm_rw_core - core of reading/writing pages from task specified
144  * @pid: PID of process to read/write from/to
145  * @iter: where to copy to/from locally
146  * @rvec: iovec array specifying where to copy to/from in the other process
147  * @riovcnt: size of rvec array
148  * @flags: currently unused
149  * @vm_write: 0 if reading from other process, 1 if writing to other process
150  *
151  * Returns the number of bytes read/written or error code. May
152  *  return less bytes than expected if an error occurs during the copying
153  *  process.
154  */
155 static ssize_t process_vm_rw_core(pid_t pid, struct iov_iter *iter,
156                                   const struct iovec *rvec,
157                                   unsigned long riovcnt,
158                                   unsigned long flags, int vm_write)
159 {
160         struct task_struct *task;
161         struct page *pp_stack[PVM_MAX_PP_ARRAY_COUNT];
162         struct page **process_pages = pp_stack;
163         struct mm_struct *mm;
164         unsigned long i;
165         ssize_t rc = 0;
166         unsigned long nr_pages = 0;
167         unsigned long nr_pages_iov;
168         ssize_t iov_len;
169         size_t total_len = iov_iter_count(iter);
170 
171         /*
172          * Work out how many pages of struct pages we're going to need
173          * when eventually calling get_user_pages
174          */
175         for (i = 0; i < riovcnt; i++) {
176                 iov_len = rvec[i].iov_len;
177                 if (iov_len > 0) {
178                         nr_pages_iov = ((unsigned long)rvec[i].iov_base
179                                         + iov_len)
180                                 / PAGE_SIZE - (unsigned long)rvec[i].iov_base
181                                 / PAGE_SIZE + 1;
182                         nr_pages = max(nr_pages, nr_pages_iov);
183                 }
184         }
185 
186         if (nr_pages == 0)
187                 return 0;
188 
189         if (nr_pages > PVM_MAX_PP_ARRAY_COUNT) {
190                 /* For reliability don't try to kmalloc more than
191                    2 pages worth */
192                 process_pages = kmalloc(min_t(size_t, PVM_MAX_KMALLOC_PAGES,
193                                               sizeof(struct pages *)*nr_pages),
194                                         GFP_KERNEL);
195 
196                 if (!process_pages)
197                         return -ENOMEM;
198         }
199 
200         /* Get process information */
201         task = find_get_task_by_vpid(pid);
202         if (!task) {
203                 rc = -ESRCH;
204                 goto free_proc_pages;
205         }
206 
207         mm = mm_access(task, PTRACE_MODE_ATTACH_REALCREDS);
208         if (!mm || IS_ERR(mm)) {
209                 rc = IS_ERR(mm) ? PTR_ERR(mm) : -ESRCH;
210                 /*
211                  * Explicitly map EACCES to EPERM as EPERM is a more a
212                  * appropriate error code for process_vw_readv/writev
213                  */
214                 if (rc == -EACCES)
215                         rc = -EPERM;
216                 goto put_task_struct;
217         }
218 
219         for (i = 0; i < riovcnt && iov_iter_count(iter) && !rc; i++)
220                 rc = process_vm_rw_single_vec(
221                         (unsigned long)rvec[i].iov_base, rvec[i].iov_len,
222                         iter, process_pages, mm, task, vm_write);
223 
224         /* copied = space before - space after */
225         total_len -= iov_iter_count(iter);
226 
227         /* If we have managed to copy any data at all then
228            we return the number of bytes copied. Otherwise
229            we return the error code */
230         if (total_len)
231                 rc = total_len;
232 
233         mmput(mm);
234 
235 put_task_struct:
236         put_task_struct(task);
237 
238 free_proc_pages:
239         if (process_pages != pp_stack)
240                 kfree(process_pages);
241         return rc;
242 }
243 
244 /**
245  * process_vm_rw - check iovecs before calling core routine
246  * @pid: PID of process to read/write from/to
247  * @lvec: iovec array specifying where to copy to/from locally
248  * @liovcnt: size of lvec array
249  * @rvec: iovec array specifying where to copy to/from in the other process
250  * @riovcnt: size of rvec array
251  * @flags: currently unused
252  * @vm_write: 0 if reading from other process, 1 if writing to other process
253  *
254  * Returns the number of bytes read/written or error code. May
255  *  return less bytes than expected if an error occurs during the copying
256  *  process.
257  */
258 static ssize_t process_vm_rw(pid_t pid,
259                              const struct iovec __user *lvec,
260                              unsigned long liovcnt,
261                              const struct iovec __user *rvec,
262                              unsigned long riovcnt,
263                              unsigned long flags, int vm_write)
264 {
265         struct iovec iovstack_l[UIO_FASTIOV];
266         struct iovec iovstack_r[UIO_FASTIOV];
267         struct iovec *iov_l = iovstack_l;
268         struct iovec *iov_r = iovstack_r;
269         struct iov_iter iter;
270         ssize_t rc;
271         int dir = vm_write ? WRITE : READ;
272 
273         if (flags != 0)
274                 return -EINVAL;
275 
276         /* Check iovecs */
277         rc = import_iovec(dir, lvec, liovcnt, UIO_FASTIOV, &iov_l, &iter);
278         if (rc < 0)
279                 return rc;
280         if (!iov_iter_count(&iter))
281                 goto free_iovecs;
282 
283         rc = rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt, UIO_FASTIOV,
284                                    iovstack_r, &iov_r);
285         if (rc <= 0)
286                 goto free_iovecs;
287 
288         rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write);
289 
290 free_iovecs:
291         if (iov_r != iovstack_r)
292                 kfree(iov_r);
293         kfree(iov_l);
294 
295         return rc;
296 }
297 
298 SYSCALL_DEFINE6(process_vm_readv, pid_t, pid, const struct iovec __user *, lvec,
299                 unsigned long, liovcnt, const struct iovec __user *, rvec,
300                 unsigned long, riovcnt, unsigned long, flags)
301 {
302         return process_vm_rw(pid, lvec, liovcnt, rvec, riovcnt, flags, 0);
303 }
304 
305 SYSCALL_DEFINE6(process_vm_writev, pid_t, pid,
306                 const struct iovec __user *, lvec,
307                 unsigned long, liovcnt, const struct iovec __user *, rvec,
308                 unsigned long, riovcnt, unsigned long, flags)
309 {
310         return process_vm_rw(pid, lvec, liovcnt, rvec, riovcnt, flags, 1);
311 }
312 
313 #ifdef CONFIG_COMPAT
314 
315 static ssize_t
316 compat_process_vm_rw(compat_pid_t pid,
317                      const struct compat_iovec __user *lvec,
318                      unsigned long liovcnt,
319                      const struct compat_iovec __user *rvec,
320                      unsigned long riovcnt,
321                      unsigned long flags, int vm_write)
322 {
323         struct iovec iovstack_l[UIO_FASTIOV];
324         struct iovec iovstack_r[UIO_FASTIOV];
325         struct iovec *iov_l = iovstack_l;
326         struct iovec *iov_r = iovstack_r;
327         struct iov_iter iter;
328         ssize_t rc = -EFAULT;
329         int dir = vm_write ? WRITE : READ;
330 
331         if (flags != 0)
332                 return -EINVAL;
333 
334         rc = compat_import_iovec(dir, lvec, liovcnt, UIO_FASTIOV, &iov_l, &iter);
335         if (rc < 0)
336                 return rc;
337         if (!iov_iter_count(&iter))
338                 goto free_iovecs;
339         rc = compat_rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt,
340                                           UIO_FASTIOV, iovstack_r,
341                                           &iov_r);
342         if (rc <= 0)
343                 goto free_iovecs;
344 
345         rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write);
346 
347 free_iovecs:
348         if (iov_r != iovstack_r)
349                 kfree(iov_r);
350         kfree(iov_l);
351         return rc;
352 }
353 
354 COMPAT_SYSCALL_DEFINE6(process_vm_readv, compat_pid_t, pid,
355                        const struct compat_iovec __user *, lvec,
356                        compat_ulong_t, liovcnt,
357                        const struct compat_iovec __user *, rvec,
358                        compat_ulong_t, riovcnt,
359                        compat_ulong_t, flags)
360 {
361         return compat_process_vm_rw(pid, lvec, liovcnt, rvec,
362                                     riovcnt, flags, 0);
363 }
364 
365 COMPAT_SYSCALL_DEFINE6(process_vm_writev, compat_pid_t, pid,
366                        const struct compat_iovec __user *, lvec,
367                        compat_ulong_t, liovcnt,
368                        const struct compat_iovec __user *, rvec,
369                        compat_ulong_t, riovcnt,
370                        compat_ulong_t, flags)
371 {
372         return compat_process_vm_rw(pid, lvec, liovcnt, rvec,
373                                     riovcnt, flags, 1);
374 }
375 
376 #endif
377 

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