xref: /openbmc/linux/mm/process_vm_access.c (revision 0b295316)
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  */
process_vm_rw_pages(struct page ** pages,unsigned offset,size_t len,struct iov_iter * iter,int vm_write)27 static 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  */
process_vm_rw_single_vec(unsigned long addr,unsigned long len,struct iov_iter * iter,struct page ** process_pages,struct mm_struct * mm,struct task_struct * task,int vm_write)70 static 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 						     &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  */
process_vm_rw_core(pid_t pid,struct iov_iter * iter,const struct iovec * rvec,unsigned long riovcnt,unsigned long flags,int vm_write)150 static 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 
230 put_task_struct:
231 	put_task_struct(task);
232 
233 free_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  */
process_vm_rw(pid_t pid,const struct iovec __user * lvec,unsigned long liovcnt,const struct iovec __user * rvec,unsigned long riovcnt,unsigned long flags,int vm_write)253 static 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 ? ITER_SOURCE : ITER_DEST;
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);
286 free_iov_l:
287 	kfree(iov_l);
288 	return rc;
289 }
290 
SYSCALL_DEFINE6(process_vm_readv,pid_t,pid,const struct iovec __user *,lvec,unsigned long,liovcnt,const struct iovec __user *,rvec,unsigned long,riovcnt,unsigned long,flags)291 SYSCALL_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 
SYSCALL_DEFINE6(process_vm_writev,pid_t,pid,const struct iovec __user *,lvec,unsigned long,liovcnt,const struct iovec __user *,rvec,unsigned long,riovcnt,unsigned long,flags)298 SYSCALL_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 }
305