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 
37 static 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
48 static inline int valid_phys_addr_range(phys_addr_t addr, size_t count)
49 {
50 	return addr + count <= __pa(high_memory);
51 }
52 
53 static 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
60 static inline int page_is_allowed(unsigned long pfn)
61 {
62 	return devmem_is_allowed(pfn);
63 }
64 #else
65 static inline int page_is_allowed(unsigned long pfn)
66 {
67 	return 1;
68 }
69 #endif
70 
71 static 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  */
82 static 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(p, 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(p, count);
121 
122 		err = -EPERM;
123 		allowed = page_is_allowed(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(buf, 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(p);
138 			if (!ptr)
139 				goto failed;
140 
141 			probe = copy_from_kernel_nofault(bounce, ptr, sz);
142 			unxlate_dev_mem_ptr(p, ptr);
143 			if (probe)
144 				goto failed;
145 
146 			remaining = copy_to_user(buf, bounce, 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(bounce);
160 
161 	*ppos += read;
162 	return read;
163 
164 failed:
165 	kfree(bounce);
166 	return err;
167 }
168 
169 static 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(p, 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(p, count);
201 
202 		allowed = page_is_allowed(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(p);
214 			if (!ptr) {
215 				if (written)
216 					break;
217 				return -EFAULT;
218 			}
219 
220 			copied = copy_from_user(ptr, buf, sz);
221 			unxlate_dev_mem_ptr(p, 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 
242 int __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
256 static 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 
269 static 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
283 static 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 */
295 static 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 
301 static 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 */
307 static inline int private_mapping_ok(struct vm_area_struct *vma)
308 {
309 	return is_nommu_shared_mapping(vma->vm_flags);
310 }
311 #else
312 
313 static inline int private_mapping_ok(struct vm_area_struct *vma)
314 {
315 	return 1;
316 }
317 #endif
318 
319 static const struct vm_operations_struct mmap_mem_ops = {
320 #ifdef CONFIG_HAVE_IOREMAP_PROT
321 	.access = generic_access_phys
322 #endif
323 };
324 
325 static 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(vma->vm_pgoff, size))
339 		return -EINVAL;
340 
341 	if (!private_mapping_ok(vma))
342 		return -ENOSYS;
343 
344 	if (!range_is_allowed(vma->vm_pgoff, size))
345 		return -EPERM;
346 
347 	if (!phys_mem_access_prot_allowed(file, vma->vm_pgoff, size,
348 						&vma->vm_page_prot))
349 		return -EINVAL;
350 
351 	vma->vm_page_prot = phys_mem_access_prot(file, vma->vm_pgoff,
352 						 size,
353 						 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 			    vma->vm_start,
360 			    vma->vm_pgoff,
361 			    size,
362 			    vma->vm_page_prot)) {
363 		return -EAGAIN;
364 	}
365 	return 0;
366 }
367 
368 #ifdef CONFIG_DEVPORT
369 static 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 
387 static 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(c, i);
404 		i++;
405 		tmp++;
406 	}
407 	*ppos = i;
408 	return tmp-buf;
409 }
410 #endif
411 
412 static ssize_t read_null(struct file *file, char __user *buf,
413 			 size_t count, loff_t *ppos)
414 {
415 	return 0;
416 }
417 
418 static ssize_t write_null(struct file *file, const char __user *buf,
419 			  size_t count, loff_t *ppos)
420 {
421 	return count;
422 }
423 
424 static ssize_t read_iter_null(struct kiocb *iocb, struct iov_iter *to)
425 {
426 	return 0;
427 }
428 
429 static ssize_t write_iter_null(struct kiocb *iocb, struct iov_iter *from)
430 {
431 	size_t count = iov_iter_count(from);
432 	iov_iter_advance(from, count);
433 	return count;
434 }
435 
436 static 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 
442 static 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, pipe_to_null);
446 }
447 
448 static int uring_cmd_null(struct io_uring_cmd *ioucmd, unsigned int issue_flags)
449 {
450 	return 0;
451 }
452 
453 static ssize_t read_iter_zero(struct kiocb *iocb, struct iov_iter *iter)
454 {
455 	size_t written = 0;
456 
457 	while (iov_iter_count(iter)) {
458 		size_t chunk = iov_iter_count(iter), n;
459 
460 		if (chunk > PAGE_SIZE)
461 			chunk = PAGE_SIZE;	/* Just for latency reasons */
462 		n = iov_iter_zero(chunk, iter);
463 		if (!n && iov_iter_count(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 
477 static 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(buf + cleared, 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 
504 static 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 static unsigned long get_unmapped_area_zero(struct file *file,
516 				unsigned long addr, unsigned long len,
517 				unsigned long pgoff, unsigned long flags)
518 {
519 #ifdef CONFIG_MMU
520 	if (flags & MAP_SHARED) {
521 		/*
522 		 * mmap_zero() will call shmem_zero_setup() to create a file,
523 		 * so use shmem's get_unmapped_area in case it can be huge;
524 		 * and pass NULL for file as in mmap.c's get_unmapped_area(),
525 		 * so as not to confuse shmem with our handle on "/dev/zero".
526 		 */
527 		return shmem_get_unmapped_area(NULL, addr, len, pgoff, flags);
528 	}
529 
530 	/* Otherwise flags & MAP_PRIVATE: with no shmem object beneath it */
531 	return mm_get_unmapped_area(current->mm, file, addr, len, pgoff, flags);
532 #else
533 	return -ENOSYS;
534 #endif
535 }
536 
537 static ssize_t write_full(struct file *file, const char __user *buf,
538 			  size_t count, loff_t *ppos)
539 {
540 	return -ENOSPC;
541 }
542 
543 /*
544  * Special lseek() function for /dev/null and /dev/zero.  Most notably, you
545  * can fopen() both devices with "a" now.  This was previously impossible.
546  * -- SRB.
547  */
548 static loff_t null_lseek(struct file *file, loff_t offset, int orig)
549 {
550 	return file->f_pos = 0;
551 }
552 
553 /*
554  * The memory devices use the full 32/64 bits of the offset, and so we cannot
555  * check against negative addresses: they are ok. The return value is weird,
556  * though, in that case (0).
557  *
558  * also note that seeking relative to the "end of file" isn't supported:
559  * it has no meaning, so it returns -EINVAL.
560  */
561 static loff_t memory_lseek(struct file *file, loff_t offset, int orig)
562 {
563 	loff_t ret;
564 
565 	inode_lock(file_inode(file));
566 	switch (orig) {
567 	case SEEK_CUR:
568 		offset += file->f_pos;
569 		fallthrough;
570 	case SEEK_SET:
571 		/* to avoid userland mistaking f_pos=-9 as -EBADF=-9 */
572 		if ((unsigned long long)offset >= -MAX_ERRNO) {
573 			ret = -EOVERFLOW;
574 			break;
575 		}
576 		file->f_pos = offset;
577 		ret = file->f_pos;
578 		force_successful_syscall_return();
579 		break;
580 	default:
581 		ret = -EINVAL;
582 	}
583 	inode_unlock(file_inode(file));
584 	return ret;
585 }
586 
587 static int open_port(struct inode *inode, struct file *filp)
588 {
589 	int rc;
590 
591 	if (!capable(CAP_SYS_RAWIO))
592 		return -EPERM;
593 
594 	rc = security_locked_down(LOCKDOWN_DEV_MEM);
595 	if (rc)
596 		return rc;
597 
598 	if (iminor(inode) != DEVMEM_MINOR)
599 		return 0;
600 
601 	/*
602 	 * Use a unified address space to have a single point to manage
603 	 * revocations when drivers want to take over a /dev/mem mapped
604 	 * range.
605 	 */
606 	filp->f_mapping = iomem_get_mapping();
607 
608 	return 0;
609 }
610 
611 #define zero_lseek	null_lseek
612 #define full_lseek      null_lseek
613 #define write_zero	write_null
614 #define write_iter_zero	write_iter_null
615 #define splice_write_zero	splice_write_null
616 #define open_mem	open_port
617 
618 static const struct file_operations __maybe_unused mem_fops = {
619 	.llseek		= memory_lseek,
620 	.read		= read_mem,
621 	.write		= write_mem,
622 	.mmap		= mmap_mem,
623 	.open		= open_mem,
624 #ifndef CONFIG_MMU
625 	.get_unmapped_area = get_unmapped_area_mem,
626 	.mmap_capabilities = memory_mmap_capabilities,
627 #endif
628 	.fop_flags	= FOP_UNSIGNED_OFFSET,
629 };
630 
631 static const struct file_operations null_fops = {
632 	.llseek		= null_lseek,
633 	.read		= read_null,
634 	.write		= write_null,
635 	.read_iter	= read_iter_null,
636 	.write_iter	= write_iter_null,
637 	.splice_write	= splice_write_null,
638 	.uring_cmd	= uring_cmd_null,
639 };
640 
641 #ifdef CONFIG_DEVPORT
642 static const struct file_operations port_fops = {
643 	.llseek		= memory_lseek,
644 	.read		= read_port,
645 	.write		= write_port,
646 	.open		= open_port,
647 };
648 #endif
649 
650 static const struct file_operations zero_fops = {
651 	.llseek		= zero_lseek,
652 	.write		= write_zero,
653 	.read_iter	= read_iter_zero,
654 	.read		= read_zero,
655 	.write_iter	= write_iter_zero,
656 	.splice_read	= copy_splice_read,
657 	.splice_write	= splice_write_zero,
658 	.mmap		= mmap_zero,
659 	.get_unmapped_area = get_unmapped_area_zero,
660 #ifndef CONFIG_MMU
661 	.mmap_capabilities = zero_mmap_capabilities,
662 #endif
663 };
664 
665 static const struct file_operations full_fops = {
666 	.llseek		= full_lseek,
667 	.read_iter	= read_iter_zero,
668 	.write		= write_full,
669 	.splice_read	= copy_splice_read,
670 };
671 
672 static const struct memdev {
673 	const char *name;
674 	const struct file_operations *fops;
675 	fmode_t fmode;
676 	umode_t mode;
677 } devlist[] = {
678 #ifdef CONFIG_DEVMEM
679 	[DEVMEM_MINOR] = { "mem", &mem_fops, 0, 0 },
680 #endif
681 	[3] = { "null", &null_fops, FMODE_NOWAIT, 0666 },
682 #ifdef CONFIG_DEVPORT
683 	[4] = { "port", &port_fops, 0, 0 },
684 #endif
685 	[5] = { "zero", &zero_fops, FMODE_NOWAIT, 0666 },
686 	[7] = { "full", &full_fops, 0, 0666 },
687 	[8] = { "random", &random_fops, FMODE_NOWAIT, 0666 },
688 	[9] = { "urandom", &urandom_fops, FMODE_NOWAIT, 0666 },
689 #ifdef CONFIG_PRINTK
690 	[11] = { "kmsg", &kmsg_fops, 0, 0644 },
691 #endif
692 };
693 
694 static int memory_open(struct inode *inode, struct file *filp)
695 {
696 	int minor;
697 	const struct memdev *dev;
698 
699 	minor = iminor(inode);
700 	if (minor >= ARRAY_SIZE(devlist))
701 		return -ENXIO;
702 
703 	dev = &devlist[minor];
704 	if (!dev->fops)
705 		return -ENXIO;
706 
707 	filp->f_op = dev->fops;
708 	filp->f_mode |= dev->fmode;
709 
710 	if (dev->fops->open)
711 		return dev->fops->open(inode, filp);
712 
713 	return 0;
714 }
715 
716 static const struct file_operations memory_fops = {
717 	.open = memory_open,
718 	.llseek = noop_llseek,
719 };
720 
721 static char *mem_devnode(const struct device *dev, umode_t *mode)
722 {
723 	if (mode && devlist[MINOR(dev->devt)].mode)
724 		*mode = devlist[MINOR(dev->devt)].mode;
725 	return NULL;
726 }
727 
728 static const struct class mem_class = {
729 	.name		= "mem",
730 	.devnode	= mem_devnode,
731 };
732 
733 static int __init chr_dev_init(void)
734 {
735 	int retval;
736 	int minor;
737 
738 	if (register_chrdev(MEM_MAJOR, "mem", &memory_fops))
739 		printk("unable to get major %d for memory devs\n", MEM_MAJOR);
740 
741 	retval = class_register(&mem_class);
742 	if (retval)
743 		return retval;
744 
745 	for (minor = 1; minor < ARRAY_SIZE(devlist); minor++) {
746 		if (!devlist[minor].name)
747 			continue;
748 
749 		/*
750 		 * Create /dev/port?
751 		 */
752 		if ((minor == DEVPORT_MINOR) && !arch_has_dev_port())
753 			continue;
754 
755 		device_create(&mem_class, NULL, MKDEV(MEM_MAJOR, minor),
756 			      NULL, devlist[minor].name);
757 	}
758 
759 	return tty_init();
760 }
761 
762 fs_initcall(chr_dev_init);
763