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}