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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 * @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 */
 33static 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 */
 77static 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
 92	/* Work out address and page range required */
 93	if (len == 0)
 94		return 0;
 95	nr_pages = (addr + len - 1) / PAGE_SIZE - addr / PAGE_SIZE + 1;
 96
 97	while (!rc && nr_pages && iov_iter_count(iter)) {
 98		int pages = min(nr_pages, max_pages_per_loop);
 99		size_t bytes;
100
101		/*
102		 * Get the pages we're interested in.  We must
103		 * add FOLL_REMOTE because task/mm might not
104		 * current/current->mm
105		 */
106		pages = __get_user_pages_unlocked(task, mm, pa, pages,
107						  vm_write, 0, process_pages,
108						  FOLL_REMOTE);
109		if (pages <= 0)
110			return -EFAULT;
111
112		bytes = pages * PAGE_SIZE - start_offset;
113		if (bytes > len)
114			bytes = len;
115
116		rc = process_vm_rw_pages(process_pages,
117					 start_offset, bytes, iter,
118					 vm_write);
119		len -= bytes;
120		start_offset = 0;
121		nr_pages -= pages;
122		pa += pages * PAGE_SIZE;
123		while (pages)
124			put_page(process_pages[--pages]);
125	}
126
127	return rc;
128}
129
130/* Maximum number of entries for process pages array
131   which lives on stack */
132#define PVM_MAX_PP_ARRAY_COUNT 16
133
134/**
135 * process_vm_rw_core - core of reading/writing pages from task specified
136 * @pid: PID of process to read/write from/to
137 * @iter: where to copy to/from locally
138 * @rvec: iovec array specifying where to copy to/from in the other process
139 * @riovcnt: size of rvec array
140 * @flags: currently unused
141 * @vm_write: 0 if reading from other process, 1 if writing to other process
142 * Returns the number of bytes read/written or error code. May
143 *  return less bytes than expected if an error occurs during the copying
144 *  process.
145 */
146static ssize_t process_vm_rw_core(pid_t pid, struct iov_iter *iter,
147				  const struct iovec *rvec,
148				  unsigned long riovcnt,
149				  unsigned long flags, int vm_write)
150{
151	struct task_struct *task;
152	struct page *pp_stack[PVM_MAX_PP_ARRAY_COUNT];
153	struct page **process_pages = pp_stack;
154	struct mm_struct *mm;
155	unsigned long i;
156	ssize_t rc = 0;
157	unsigned long nr_pages = 0;
158	unsigned long nr_pages_iov;
159	ssize_t iov_len;
160	size_t total_len = iov_iter_count(iter);
161
162	/*
163	 * Work out how many pages of struct pages we're going to need
164	 * when eventually calling get_user_pages
165	 */
166	for (i = 0; i < riovcnt; i++) {
167		iov_len = rvec[i].iov_len;
168		if (iov_len > 0) {
169			nr_pages_iov = ((unsigned long)rvec[i].iov_base
170					+ iov_len)
171				/ PAGE_SIZE - (unsigned long)rvec[i].iov_base
172				/ PAGE_SIZE + 1;
173			nr_pages = max(nr_pages, nr_pages_iov);
174		}
175	}
176
177	if (nr_pages == 0)
178		return 0;
179
180	if (nr_pages > PVM_MAX_PP_ARRAY_COUNT) {
181		/* For reliability don't try to kmalloc more than
182		   2 pages worth */
183		process_pages = kmalloc(min_t(size_t, PVM_MAX_KMALLOC_PAGES,
184					      sizeof(struct pages *)*nr_pages),
185					GFP_KERNEL);
186
187		if (!process_pages)
188			return -ENOMEM;
189	}
190
191	/* Get process information */
192	rcu_read_lock();
193	task = find_task_by_vpid(pid);
194	if (task)
195		get_task_struct(task);
196	rcu_read_unlock();
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 a
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 * Returns the number of bytes read/written or error code. May
249 *  return less bytes than expected if an error occurs during the copying
250 *  process.
251 */
252static ssize_t process_vm_rw(pid_t pid,
253			     const struct iovec __user *lvec,
254			     unsigned long liovcnt,
255			     const struct iovec __user *rvec,
256			     unsigned long riovcnt,
257			     unsigned long flags, int vm_write)
258{
259	struct iovec iovstack_l[UIO_FASTIOV];
260	struct iovec iovstack_r[UIO_FASTIOV];
261	struct iovec *iov_l = iovstack_l;
262	struct iovec *iov_r = iovstack_r;
263	struct iov_iter iter;
264	ssize_t rc;
265	int dir = vm_write ? WRITE : READ;
266
267	if (flags != 0)
268		return -EINVAL;
269
270	/* Check iovecs */
271	rc = import_iovec(dir, lvec, liovcnt, UIO_FASTIOV, &iov_l, &iter);
272	if (rc < 0)
273		return rc;
274	if (!iov_iter_count(&iter))
275		goto free_iovecs;
276
277	rc = rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt, UIO_FASTIOV,
278				   iovstack_r, &iov_r);
279	if (rc <= 0)
280		goto free_iovecs;
281
282	rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write);
283
284free_iovecs:
285	if (iov_r != iovstack_r)
286		kfree(iov_r);
287	kfree(iov_l);
288
289	return rc;
290}
291
292SYSCALL_DEFINE6(process_vm_readv, pid_t, pid, const struct iovec __user *, lvec,
293		unsigned long, liovcnt, const struct iovec __user *, rvec,
294		unsigned long, riovcnt,	unsigned long, flags)
295{
296	return process_vm_rw(pid, lvec, liovcnt, rvec, riovcnt, flags, 0);
297}
298
299SYSCALL_DEFINE6(process_vm_writev, pid_t, pid,
300		const struct iovec __user *, lvec,
301		unsigned long, liovcnt, const struct iovec __user *, rvec,
302		unsigned long, riovcnt,	unsigned long, flags)
303{
304	return process_vm_rw(pid, lvec, liovcnt, rvec, riovcnt, flags, 1);
305}
306
307#ifdef CONFIG_COMPAT
308
309static ssize_t
310compat_process_vm_rw(compat_pid_t pid,
311		     const struct compat_iovec __user *lvec,
312		     unsigned long liovcnt,
313		     const struct compat_iovec __user *rvec,
314		     unsigned long riovcnt,
315		     unsigned long flags, int vm_write)
316{
317	struct iovec iovstack_l[UIO_FASTIOV];
318	struct iovec iovstack_r[UIO_FASTIOV];
319	struct iovec *iov_l = iovstack_l;
320	struct iovec *iov_r = iovstack_r;
321	struct iov_iter iter;
322	ssize_t rc = -EFAULT;
323	int dir = vm_write ? WRITE : READ;
324
325	if (flags != 0)
326		return -EINVAL;
327
328	rc = compat_import_iovec(dir, lvec, liovcnt, UIO_FASTIOV, &iov_l, &iter);
329	if (rc < 0)
330		return rc;
331	if (!iov_iter_count(&iter))
332		goto free_iovecs;
333	rc = compat_rw_copy_check_uvector(CHECK_IOVEC_ONLY, rvec, riovcnt,
334					  UIO_FASTIOV, iovstack_r,
335					  &iov_r);
336	if (rc <= 0)
337		goto free_iovecs;
338
339	rc = process_vm_rw_core(pid, &iter, iov_r, riovcnt, flags, vm_write);
340
341free_iovecs:
342	if (iov_r != iovstack_r)
343		kfree(iov_r);
344	kfree(iov_l);
345	return rc;
346}
347
348COMPAT_SYSCALL_DEFINE6(process_vm_readv, compat_pid_t, pid,
349		       const struct compat_iovec __user *, lvec,
350		       compat_ulong_t, liovcnt,
351		       const struct compat_iovec __user *, rvec,
352		       compat_ulong_t, riovcnt,
353		       compat_ulong_t, flags)
354{
355	return compat_process_vm_rw(pid, lvec, liovcnt, rvec,
356				    riovcnt, flags, 0);
357}
358
359COMPAT_SYSCALL_DEFINE6(process_vm_writev, compat_pid_t, pid,
360		       const struct compat_iovec __user *, lvec,
361		       compat_ulong_t, liovcnt,
362		       const struct compat_iovec __user *, rvec,
363		       compat_ulong_t, riovcnt,
364		       compat_ulong_t, flags)
365{
366	return compat_process_vm_rw(pid, lvec, liovcnt, rvec,
367				    riovcnt, flags, 1);
368}
369
370#endif