Root/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 * @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 */
42static 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
136end:
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 */
170static 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 */
241static 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);
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;
330put_mm:
331    mmput(mm);
332
333put_task_struct:
334    put_task_struct(task);
335
336free_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 */
355static 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
389free_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
398SYSCALL_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
405SYSCALL_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
415asmlinkage ssize_t
416compat_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
451free_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
459asmlinkage ssize_t
460compat_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
471asmlinkage ssize_t
472compat_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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