1// SPDX-License-Identifier: GPL-2.0
2/*
3 * linux/drivers/char/mem.c
4 *
5 * Copyright (C) 1991, 1992 Linus Torvalds
6 *
7 * Added devfs support.
8 * Jan-11-1998, C. Scott Ananian <cananian@alumni.princeton.edu>
9 * Shared /dev/zero mmapping support, Feb 2000, Kanoj Sarcar <kanoj@sgi.com>
10 */
11
12#include <linux/mm.h>
13#include <linux/miscdevice.h>
14#include <linux/slab.h>
15#include <linux/vmalloc.h>
16#include <linux/mman.h>
17#include <linux/random.h>
18#include <linux/init.h>
19#include <linux/tty.h>
20#include <linux/capability.h>
21#include <linux/ptrace.h>
22#include <linux/device.h>
23#include <linux/highmem.h>
24#include <linux/backing-dev.h>
25#include <linux/shmem_fs.h>
26#include <linux/splice.h>
27#include <linux/pfn.h>
28#include <linux/export.h>
29#include <linux/io.h>
30#include <linux/uio.h>
31#include <linux/uaccess.h>
32#include <linux/security.h>
33
34#define DEVMEM_MINOR 1
35#define DEVPORT_MINOR 4
36
37static inline unsigned long size_inside_page(unsigned long start,
38 unsigned long size)
39{
40 unsigned long sz;
41
42 sz = PAGE_SIZE - (start & (PAGE_SIZE - 1));
43
44 return min(sz, size);
45}
46
47#ifndef ARCH_HAS_VALID_PHYS_ADDR_RANGE
48static inline int valid_phys_addr_range(phys_addr_t addr, size_t count)
49{
50 return addr + count <= __pa(high_memory);
51}
52
53static inline int valid_mmap_phys_addr_range(unsigned long pfn, size_t size)
54{
55 return 1;
56}
57#endif
58
59#ifdef CONFIG_STRICT_DEVMEM
60static inline int page_is_allowed(unsigned long pfn)
61{
62 return devmem_is_allowed(pfn);
63}
64#else
65static inline int page_is_allowed(unsigned long pfn)
66{
67 return 1;
68}
69#endif
70
71static inline bool should_stop_iteration(void)
72{
73 if (need_resched())
74 cond_resched();
75 return signal_pending(current);
76}
77
78/*
79 * This funcion reads the *physical* memory. The f_pos points directly to the
80 * memory location.
81 */
82static ssize_t read_mem(struct file *file, char __user *buf,
83 size_t count, loff_t *ppos)
84{
85 phys_addr_t p = *ppos;
86 ssize_t read, sz;
87 void *ptr;
88 char *bounce;
89 int err;
90
91 if (p != *ppos)
92 return 0;
93
94 if (!valid_phys_addr_range(addr: p, size: count))
95 return -EFAULT;
96 read = 0;
97#ifdef __ARCH_HAS_NO_PAGE_ZERO_MAPPED
98 /* we don't have page 0 mapped on sparc and m68k.. */
99 if (p < PAGE_SIZE) {
100 sz = size_inside_page(p, count);
101 if (sz > 0) {
102 if (clear_user(buf, sz))
103 return -EFAULT;
104 buf += sz;
105 p += sz;
106 count -= sz;
107 read += sz;
108 }
109 }
110#endif
111
112 bounce = kmalloc(PAGE_SIZE, GFP_KERNEL);
113 if (!bounce)
114 return -ENOMEM;
115
116 while (count > 0) {
117 unsigned long remaining;
118 int allowed, probe;
119
120 sz = size_inside_page(start: p, size: count);
121
122 err = -EPERM;
123 allowed = page_is_allowed(pfn: p >> PAGE_SHIFT);
124 if (!allowed)
125 goto failed;
126
127 err = -EFAULT;
128 if (allowed == 2) {
129 /* Show zeros for restricted memory. */
130 remaining = clear_user(to: buf, n: sz);
131 } else {
132 /*
133 * On ia64 if a page has been mapped somewhere as
134 * uncached, then it must also be accessed uncached
135 * by the kernel or data corruption may occur.
136 */
137 ptr = xlate_dev_mem_ptr(phys: p);
138 if (!ptr)
139 goto failed;
140
141 probe = copy_from_kernel_nofault(dst: bounce, src: ptr, size: sz);
142 unxlate_dev_mem_ptr(phys: p, addr: ptr);
143 if (probe)
144 goto failed;
145
146 remaining = copy_to_user(to: buf, from: bounce, n: sz);
147 }
148
149 if (remaining)
150 goto failed;
151
152 buf += sz;
153 p += sz;
154 count -= sz;
155 read += sz;
156 if (should_stop_iteration())
157 break;
158 }
159 kfree(objp: bounce);
160
161 *ppos += read;
162 return read;
163
164failed:
165 kfree(objp: bounce);
166 return err;
167}
168
169static ssize_t write_mem(struct file *file, const char __user *buf,
170 size_t count, loff_t *ppos)
171{
172 phys_addr_t p = *ppos;
173 ssize_t written, sz;
174 unsigned long copied;
175 void *ptr;
176
177 if (p != *ppos)
178 return -EFBIG;
179
180 if (!valid_phys_addr_range(addr: p, size: count))
181 return -EFAULT;
182
183 written = 0;
184
185#ifdef __ARCH_HAS_NO_PAGE_ZERO_MAPPED
186 /* we don't have page 0 mapped on sparc and m68k.. */
187 if (p < PAGE_SIZE) {
188 sz = size_inside_page(p, count);
189 /* Hmm. Do something? */
190 buf += sz;
191 p += sz;
192 count -= sz;
193 written += sz;
194 }
195#endif
196
197 while (count > 0) {
198 int allowed;
199
200 sz = size_inside_page(start: p, size: count);
201
202 allowed = page_is_allowed(pfn: p >> PAGE_SHIFT);
203 if (!allowed)
204 return -EPERM;
205
206 /* Skip actual writing when a page is marked as restricted. */
207 if (allowed == 1) {
208 /*
209 * On ia64 if a page has been mapped somewhere as
210 * uncached, then it must also be accessed uncached
211 * by the kernel or data corruption may occur.
212 */
213 ptr = xlate_dev_mem_ptr(phys: p);
214 if (!ptr) {
215 if (written)
216 break;
217 return -EFAULT;
218 }
219
220 copied = copy_from_user(to: ptr, from: buf, n: sz);
221 unxlate_dev_mem_ptr(phys: p, addr: ptr);
222 if (copied) {
223 written += sz - copied;
224 if (written)
225 break;
226 return -EFAULT;
227 }
228 }
229
230 buf += sz;
231 p += sz;
232 count -= sz;
233 written += sz;
234 if (should_stop_iteration())
235 break;
236 }
237
238 *ppos += written;
239 return written;
240}
241
242int __weak phys_mem_access_prot_allowed(struct file *file,
243 unsigned long pfn, unsigned long size, pgprot_t *vma_prot)
244{
245 return 1;
246}
247
248#ifndef __HAVE_PHYS_MEM_ACCESS_PROT
249
250/*
251 * Architectures vary in how they handle caching for addresses
252 * outside of main memory.
253 *
254 */
255#ifdef pgprot_noncached
256static int uncached_access(struct file *file, phys_addr_t addr)
257{
258 /*
259 * Accessing memory above the top the kernel knows about or through a
260 * file pointer
261 * that was marked O_DSYNC will be done non-cached.
262 */
263 if (file->f_flags & O_DSYNC)
264 return 1;
265 return addr >= __pa(high_memory);
266}
267#endif
268
269static pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
270 unsigned long size, pgprot_t vma_prot)
271{
272#ifdef pgprot_noncached
273 phys_addr_t offset = pfn << PAGE_SHIFT;
274
275 if (uncached_access(file, offset))
276 return pgprot_noncached(vma_prot);
277#endif
278 return vma_prot;
279}
280#endif
281
282#ifndef CONFIG_MMU
283static unsigned long get_unmapped_area_mem(struct file *file,
284 unsigned long addr,
285 unsigned long len,
286 unsigned long pgoff,
287 unsigned long flags)
288{
289 if (!valid_mmap_phys_addr_range(pgoff, len))
290 return (unsigned long) -EINVAL;
291 return pgoff << PAGE_SHIFT;
292}
293
294/* permit direct mmap, for read, write or exec */
295static unsigned memory_mmap_capabilities(struct file *file)
296{
297 return NOMMU_MAP_DIRECT |
298 NOMMU_MAP_READ | NOMMU_MAP_WRITE | NOMMU_MAP_EXEC;
299}
300
301static unsigned zero_mmap_capabilities(struct file *file)
302{
303 return NOMMU_MAP_COPY;
304}
305
306/* can't do an in-place private mapping if there's no MMU */
307static inline int private_mapping_ok(struct vm_area_struct *vma)
308{
309 return is_nommu_shared_mapping(vma->vm_flags);
310}
311#else
312
313static inline int private_mapping_ok(struct vm_area_struct *vma)
314{
315 return 1;
316}
317#endif
318
319static const struct vm_operations_struct mmap_mem_ops = {
320#ifdef CONFIG_HAVE_IOREMAP_PROT
321 .access = generic_access_phys
322#endif
323};
324
325static int mmap_mem(struct file *file, struct vm_area_struct *vma)
326{
327 size_t size = vma->vm_end - vma->vm_start;
328 phys_addr_t offset = (phys_addr_t)vma->vm_pgoff << PAGE_SHIFT;
329
330 /* Does it even fit in phys_addr_t? */
331 if (offset >> PAGE_SHIFT != vma->vm_pgoff)
332 return -EINVAL;
333
334 /* It's illegal to wrap around the end of the physical address space. */
335 if (offset + (phys_addr_t)size - 1 < offset)
336 return -EINVAL;
337
338 if (!valid_mmap_phys_addr_range(pfn: vma->vm_pgoff, size))
339 return -EINVAL;
340
341 if (!private_mapping_ok(vma))
342 return -ENOSYS;
343
344 if (!range_is_allowed(pfn: vma->vm_pgoff, size))
345 return -EPERM;
346
347 if (!phys_mem_access_prot_allowed(file, pfn: vma->vm_pgoff, size,
348 vma_prot: &vma->vm_page_prot))
349 return -EINVAL;
350
351 vma->vm_page_prot = phys_mem_access_prot(file, pfn: vma->vm_pgoff,
352 size,
353 vma_prot: vma->vm_page_prot);
354
355 vma->vm_ops = &mmap_mem_ops;
356
357 /* Remap-pfn-range will mark the range VM_IO */
358 if (remap_pfn_range(vma,
359 addr: vma->vm_start,
360 pfn: vma->vm_pgoff,
361 size,
362 vma->vm_page_prot)) {
363 return -EAGAIN;
364 }
365 return 0;
366}
367
368#ifdef CONFIG_DEVPORT
369static ssize_t read_port(struct file *file, char __user *buf,
370 size_t count, loff_t *ppos)
371{
372 unsigned long i = *ppos;
373 char __user *tmp = buf;
374
375 if (!access_ok(buf, count))
376 return -EFAULT;
377 while (count-- > 0 && i < 65536) {
378 if (__put_user(inb(i), tmp) < 0)
379 return -EFAULT;
380 i++;
381 tmp++;
382 }
383 *ppos = i;
384 return tmp-buf;
385}
386
387static ssize_t write_port(struct file *file, const char __user *buf,
388 size_t count, loff_t *ppos)
389{
390 unsigned long i = *ppos;
391 const char __user *tmp = buf;
392
393 if (!access_ok(buf, count))
394 return -EFAULT;
395 while (count-- > 0 && i < 65536) {
396 char c;
397
398 if (__get_user(c, tmp)) {
399 if (tmp > buf)
400 break;
401 return -EFAULT;
402 }
403 outb(value: c, port: i);
404 i++;
405 tmp++;
406 }
407 *ppos = i;
408 return tmp-buf;
409}
410#endif
411
412static ssize_t read_null(struct file *file, char __user *buf,
413 size_t count, loff_t *ppos)
414{
415 return 0;
416}
417
418static ssize_t write_null(struct file *file, const char __user *buf,
419 size_t count, loff_t *ppos)
420{
421 return count;
422}
423
424static ssize_t read_iter_null(struct kiocb *iocb, struct iov_iter *to)
425{
426 return 0;
427}
428
429static ssize_t write_iter_null(struct kiocb *iocb, struct iov_iter *from)
430{
431 size_t count = iov_iter_count(i: from);
432 iov_iter_advance(i: from, bytes: count);
433 return count;
434}
435
436static int pipe_to_null(struct pipe_inode_info *info, struct pipe_buffer *buf,
437 struct splice_desc *sd)
438{
439 return sd->len;
440}
441
442static ssize_t splice_write_null(struct pipe_inode_info *pipe, struct file *out,
443 loff_t *ppos, size_t len, unsigned int flags)
444{
445 return splice_from_pipe(pipe, out, ppos, len, flags, actor: pipe_to_null);
446}
447
448static int uring_cmd_null(struct io_uring_cmd *ioucmd, unsigned int issue_flags)
449{
450 return 0;
451}
452
453static ssize_t read_iter_zero(struct kiocb *iocb, struct iov_iter *iter)
454{
455 size_t written = 0;
456
457 while (iov_iter_count(i: iter)) {
458 size_t chunk = iov_iter_count(i: iter), n;
459
460 if (chunk > PAGE_SIZE)
461 chunk = PAGE_SIZE; /* Just for latency reasons */
462 n = iov_iter_zero(bytes: chunk, iter);
463 if (!n && iov_iter_count(i: iter))
464 return written ? written : -EFAULT;
465 written += n;
466 if (signal_pending(current))
467 return written ? written : -ERESTARTSYS;
468 if (!need_resched())
469 continue;
470 if (iocb->ki_flags & IOCB_NOWAIT)
471 return written ? written : -EAGAIN;
472 cond_resched();
473 }
474 return written;
475}
476
477static ssize_t read_zero(struct file *file, char __user *buf,
478 size_t count, loff_t *ppos)
479{
480 size_t cleared = 0;
481
482 while (count) {
483 size_t chunk = min_t(size_t, count, PAGE_SIZE);
484 size_t left;
485
486 left = clear_user(to: buf + cleared, n: chunk);
487 if (unlikely(left)) {
488 cleared += (chunk - left);
489 if (!cleared)
490 return -EFAULT;
491 break;
492 }
493 cleared += chunk;
494 count -= chunk;
495
496 if (signal_pending(current))
497 break;
498 cond_resched();
499 }
500
501 return cleared;
502}
503
504static int mmap_zero(struct file *file, struct vm_area_struct *vma)
505{
506#ifndef CONFIG_MMU
507 return -ENOSYS;
508#endif
509 if (vma->vm_flags & VM_SHARED)
510 return shmem_zero_setup(vma);
511 vma_set_anonymous(vma);
512 return 0;
513}
514
515#ifndef CONFIG_MMU
516static unsigned long get_unmapped_area_zero(struct file *file,
517 unsigned long addr, unsigned long len,
518 unsigned long pgoff, unsigned long flags)
519{
520 return -ENOSYS;
521}
522#else
523static unsigned long get_unmapped_area_zero(struct file *file,
524 unsigned long addr, unsigned long len,
525 unsigned long pgoff, unsigned long flags)
526{
527 if (flags & MAP_SHARED) {
528 /*
529 * mmap_zero() will call shmem_zero_setup() to create a file,
530 * so use shmem's get_unmapped_area in case it can be huge;
531 * and pass NULL for file as in mmap.c's get_unmapped_area(),
532 * so as not to confuse shmem with our handle on "/dev/zero".
533 */
534 return shmem_get_unmapped_area(NULL, addr, len, pgoff, flags);
535 }
536
537 /*
538 * Otherwise flags & MAP_PRIVATE: with no shmem object beneath it,
539 * attempt to map aligned to huge page size if possible, otherwise we
540 * fall back to system page size mappings.
541 */
542#ifdef CONFIG_TRANSPARENT_HUGEPAGE
543 return thp_get_unmapped_area(file, addr, len, pgoff, flags);
544#else
545 return mm_get_unmapped_area(current->mm, filp: file, addr, len, pgoff, flags);
546#endif
547}
548#endif /* CONFIG_MMU */
549
550static ssize_t write_full(struct file *file, const char __user *buf,
551 size_t count, loff_t *ppos)
552{
553 return -ENOSPC;
554}
555
556/*
557 * Special lseek() function for /dev/null and /dev/zero. Most notably, you
558 * can fopen() both devices with "a" now. This was previously impossible.
559 * -- SRB.
560 */
561static loff_t null_lseek(struct file *file, loff_t offset, int orig)
562{
563 return file->f_pos = 0;
564}
565
566/*
567 * The memory devices use the full 32/64 bits of the offset, and so we cannot
568 * check against negative addresses: they are ok. The return value is weird,
569 * though, in that case (0).
570 *
571 * also note that seeking relative to the "end of file" isn't supported:
572 * it has no meaning, so it returns -EINVAL.
573 */
574static loff_t memory_lseek(struct file *file, loff_t offset, int orig)
575{
576 loff_t ret;
577
578 inode_lock(inode: file_inode(f: file));
579 switch (orig) {
580 case SEEK_CUR:
581 offset += file->f_pos;
582 fallthrough;
583 case SEEK_SET:
584 /* to avoid userland mistaking f_pos=-9 as -EBADF=-9 */
585 if ((unsigned long long)offset >= -MAX_ERRNO) {
586 ret = -EOVERFLOW;
587 break;
588 }
589 file->f_pos = offset;
590 ret = file->f_pos;
591 force_successful_syscall_return();
592 break;
593 default:
594 ret = -EINVAL;
595 }
596 inode_unlock(inode: file_inode(f: file));
597 return ret;
598}
599
600static int open_port(struct inode *inode, struct file *filp)
601{
602 int rc;
603
604 if (!capable(CAP_SYS_RAWIO))
605 return -EPERM;
606
607 rc = security_locked_down(what: LOCKDOWN_DEV_MEM);
608 if (rc)
609 return rc;
610
611 if (iminor(inode) != DEVMEM_MINOR)
612 return 0;
613
614 /*
615 * Use a unified address space to have a single point to manage
616 * revocations when drivers want to take over a /dev/mem mapped
617 * range.
618 */
619 filp->f_mapping = iomem_get_mapping();
620
621 return 0;
622}
623
624#define zero_lseek null_lseek
625#define full_lseek null_lseek
626#define write_zero write_null
627#define write_iter_zero write_iter_null
628#define splice_write_zero splice_write_null
629#define open_mem open_port
630
631static const struct file_operations __maybe_unused mem_fops = {
632 .llseek = memory_lseek,
633 .read = read_mem,
634 .write = write_mem,
635 .mmap = mmap_mem,
636 .open = open_mem,
637#ifndef CONFIG_MMU
638 .get_unmapped_area = get_unmapped_area_mem,
639 .mmap_capabilities = memory_mmap_capabilities,
640#endif
641 .fop_flags = FOP_UNSIGNED_OFFSET,
642};
643
644static const struct file_operations null_fops = {
645 .llseek = null_lseek,
646 .read = read_null,
647 .write = write_null,
648 .read_iter = read_iter_null,
649 .write_iter = write_iter_null,
650 .splice_write = splice_write_null,
651 .uring_cmd = uring_cmd_null,
652};
653
654#ifdef CONFIG_DEVPORT
655static const struct file_operations port_fops = {
656 .llseek = memory_lseek,
657 .read = read_port,
658 .write = write_port,
659 .open = open_port,
660};
661#endif
662
663static const struct file_operations zero_fops = {
664 .llseek = zero_lseek,
665 .write = write_zero,
666 .read_iter = read_iter_zero,
667 .read = read_zero,
668 .write_iter = write_iter_zero,
669 .splice_read = copy_splice_read,
670 .splice_write = splice_write_zero,
671 .mmap = mmap_zero,
672 .get_unmapped_area = get_unmapped_area_zero,
673#ifndef CONFIG_MMU
674 .mmap_capabilities = zero_mmap_capabilities,
675#endif
676};
677
678static const struct file_operations full_fops = {
679 .llseek = full_lseek,
680 .read_iter = read_iter_zero,
681 .write = write_full,
682 .splice_read = copy_splice_read,
683};
684
685static const struct memdev {
686 const char *name;
687 const struct file_operations *fops;
688 fmode_t fmode;
689 umode_t mode;
690} devlist[] = {
691#ifdef CONFIG_DEVMEM
692 [DEVMEM_MINOR] = { "mem", &mem_fops, 0, 0 },
693#endif
694 [3] = { .name: "null", .fops: &null_fops, FMODE_NOWAIT, .mode: 0666 },
695#ifdef CONFIG_DEVPORT
696 [4] = { .name: "port", .fops: &port_fops, .fmode: 0, .mode: 0 },
697#endif
698 [5] = { .name: "zero", .fops: &zero_fops, FMODE_NOWAIT, .mode: 0666 },
699 [7] = { .name: "full", .fops: &full_fops, .fmode: 0, .mode: 0666 },
700 [8] = { .name: "random", .fops: &random_fops, FMODE_NOWAIT, .mode: 0666 },
701 [9] = { .name: "urandom", .fops: &urandom_fops, FMODE_NOWAIT, .mode: 0666 },
702#ifdef CONFIG_PRINTK
703 [11] = { .name: "kmsg", .fops: &kmsg_fops, .fmode: 0, .mode: 0644 },
704#endif
705};
706
707static int memory_open(struct inode *inode, struct file *filp)
708{
709 int minor;
710 const struct memdev *dev;
711
712 minor = iminor(inode);
713 if (minor >= ARRAY_SIZE(devlist))
714 return -ENXIO;
715
716 dev = &devlist[minor];
717 if (!dev->fops)
718 return -ENXIO;
719
720 filp->f_op = dev->fops;
721 filp->f_mode |= dev->fmode;
722
723 if (dev->fops->open)
724 return dev->fops->open(inode, filp);
725
726 return 0;
727}
728
729static const struct file_operations memory_fops = {
730 .open = memory_open,
731 .llseek = noop_llseek,
732};
733
734static char *mem_devnode(const struct device *dev, umode_t *mode)
735{
736 if (mode && devlist[MINOR(dev->devt)].mode)
737 *mode = devlist[MINOR(dev->devt)].mode;
738 return NULL;
739}
740
741static const struct class mem_class = {
742 .name = "mem",
743 .devnode = mem_devnode,
744};
745
746static int __init chr_dev_init(void)
747{
748 int retval;
749 int minor;
750
751 if (register_chrdev(MEM_MAJOR, name: "mem", fops: &memory_fops))
752 printk("unable to get major %d for memory devs\n", MEM_MAJOR);
753
754 retval = class_register(class: &mem_class);
755 if (retval)
756 return retval;
757
758 for (minor = 1; minor < ARRAY_SIZE(devlist); minor++) {
759 if (!devlist[minor].name)
760 continue;
761
762 /*
763 * Create /dev/port?
764 */
765 if ((minor == DEVPORT_MINOR) && !arch_has_dev_port())
766 continue;
767
768 device_create(cls: &mem_class, NULL, MKDEV(MEM_MAJOR, minor),
769 NULL, fmt: devlist[minor].name);
770 }
771
772 return tty_init();
773}
774
775fs_initcall(chr_dev_init);
776