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1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Provide access to virtual console memory.
4 * /dev/vcs: the screen as it is being viewed right now (possibly scrolled)
5 * /dev/vcsN: the screen of /dev/ttyN (1 <= N <= 63)
6 * [minor: N]
7 *
8 * /dev/vcsaN: idem, but including attributes, and prefixed with
9 * the 4 bytes lines,columns,x,y (as screendump used to give).
10 * Attribute/character pair is in native endianity.
11 * [minor: N+128]
12 *
13 * /dev/vcsuN: similar to /dev/vcsaN but using 4-byte unicode values
14 * instead of 1-byte screen glyph values.
15 * [minor: N+64]
16 *
17 * /dev/vcsuaN: same idea as /dev/vcsaN for unicode (not yet implemented).
18 *
19 * This replaces screendump and part of selection, so that the system
20 * administrator can control access using file system permissions.
21 *
22 * [email protected] - efter Friedas begravelse - 950211
23 *
24 * [email protected] - modified not to send characters to wrong console
25 * - fixed some fatal off-by-one bugs (0-- no longer == -1 -> looping and looping and looping...)
26 * - making it shorter - scr_readw are macros which expand in PRETTY long code
27 */
28
29#include <linux/kernel.h>
30#include <linux/major.h>
31#include <linux/errno.h>
32#include <linux/export.h>
33#include <linux/tty.h>
34#include <linux/interrupt.h>
35#include <linux/mm.h>
36#include <linux/init.h>
37#include <linux/vt_kern.h>
38#include <linux/selection.h>
39#include <linux/kbd_kern.h>
40#include <linux/console.h>
41#include <linux/device.h>
42#include <linux/sched.h>
43#include <linux/fs.h>
44#include <linux/poll.h>
45#include <linux/signal.h>
46#include <linux/slab.h>
47#include <linux/notifier.h>
48
49#include <linux/uaccess.h>
50#include <asm/byteorder.h>
51#include <linux/unaligned.h>
52
53#define HEADER_SIZE 4u
54#define CON_BUF_SIZE (IS_ENABLED(CONFIG_BASE_SMALL) ? 256 : PAGE_SIZE)
55
56/*
57 * Our minor space:
58 *
59 * 0 ... 63 glyph mode without attributes
60 * 64 ... 127 unicode mode without attributes
61 * 128 ... 191 glyph mode with attributes
62 * 192 ... 255 unused (reserved for unicode with attributes)
63 *
64 * This relies on MAX_NR_CONSOLES being <= 63, meaning 63 actual consoles
65 * with minors 0, 64, 128 and 192 being proxies for the foreground console.
66 */
67#if MAX_NR_CONSOLES > 63
68#warning "/dev/vcs* devices may not accommodate more than 63 consoles"
69#endif
70
71#define console(inode) (iminor(inode) & 63)
72#define use_unicode(inode) (iminor(inode) & 64)
73#define use_attributes(inode) (iminor(inode) & 128)
74
75struct vcs_poll_data {
76 struct notifier_block notifier;
77 unsigned int cons_num;
78 int event;
79 wait_queue_head_t waitq;
80 struct fasync_struct *fasync;
81};
82
83static int
84vcs_notifier(struct notifier_block *nb, unsigned long code, void *_param)
85{
86 struct vt_notifier_param *param = _param;
87 struct vc_data *vc = param->vc;
88 struct vcs_poll_data *poll =
89 container_of(nb, struct vcs_poll_data, notifier);
90 int currcons = poll->cons_num;
91 int fa_band;
92
93 switch (code) {
94 case VT_UPDATE:
95 fa_band = POLL_PRI;
96 break;
97 case VT_DEALLOCATE:
98 fa_band = POLL_HUP;
99 break;
100 default:
101 return NOTIFY_DONE;
102 }
103
104 if (currcons == 0)
105 currcons = fg_console;
106 else
107 currcons--;
108 if (currcons != vc->vc_num)
109 return NOTIFY_DONE;
110
111 poll->event = code;
112 wake_up_interruptible(&poll->waitq);
113 kill_fasync(&poll->fasync, SIGIO, fa_band);
114 return NOTIFY_OK;
115}
116
117static void
118vcs_poll_data_free(struct vcs_poll_data *poll)
119{
120 unregister_vt_notifier(&poll->notifier);
121 kfree(poll);
122}
123
124static struct vcs_poll_data *
125vcs_poll_data_get(struct file *file)
126{
127 struct vcs_poll_data *poll = file->private_data, *kill = NULL;
128
129 if (poll)
130 return poll;
131
132 poll = kzalloc_obj(*poll);
133 if (!poll)
134 return NULL;
135 poll->cons_num = console(file_inode(file));
136 init_waitqueue_head(&poll->waitq);
137 poll->notifier.notifier_call = vcs_notifier;
138 /*
139 * In order not to lose any update event, we must pretend one might
140 * have occurred before we have a chance to register our notifier.
141 * This is also how user space has come to detect which kernels
142 * support POLLPRI on /dev/vcs* devices i.e. using poll() with
143 * POLLPRI and a zero timeout.
144 */
145 poll->event = VT_UPDATE;
146
147 if (register_vt_notifier(&poll->notifier) != 0) {
148 kfree(poll);
149 return NULL;
150 }
151
152 /*
153 * This code may be called either through ->poll() or ->fasync().
154 * If we have two threads using the same file descriptor, they could
155 * both enter this function, both notice that the structure hasn't
156 * been allocated yet and go ahead allocating it in parallel, but
157 * only one of them must survive and be shared otherwise we'd leak
158 * memory with a dangling notifier callback.
159 */
160 spin_lock(&file->f_lock);
161 if (!file->private_data) {
162 file->private_data = poll;
163 } else {
164 /* someone else raced ahead of us */
165 kill = poll;
166 poll = file->private_data;
167 }
168 spin_unlock(&file->f_lock);
169 if (kill)
170 vcs_poll_data_free(kill);
171
172 return poll;
173}
174
175/**
176 * vcs_vc - return VC for @inode
177 * @inode: inode for which to return a VC
178 * @viewed: returns whether this console is currently foreground (viewed)
179 *
180 * Must be called with console_lock.
181 */
182static struct vc_data *vcs_vc(struct inode *inode, bool *viewed)
183{
184 unsigned int currcons = console(inode);
185
186 WARN_CONSOLE_UNLOCKED();
187
188 if (currcons == 0) {
189 currcons = fg_console;
190 if (viewed)
191 *viewed = true;
192 } else {
193 currcons--;
194 if (viewed)
195 *viewed = false;
196 }
197 return vc_cons[currcons].d;
198}
199
200/**
201 * vcs_size - return size for a VC in @vc
202 * @vc: which VC
203 * @attr: does it use attributes?
204 * @unicode: is it unicode?
205 *
206 * Must be called with console_lock.
207 */
208static int vcs_size(const struct vc_data *vc, bool attr, bool unicode)
209{
210 int size;
211
212 WARN_CONSOLE_UNLOCKED();
213
214 size = vc->vc_rows * vc->vc_cols;
215
216 if (attr) {
217 if (unicode)
218 return -EOPNOTSUPP;
219
220 size = 2 * size + HEADER_SIZE;
221 } else if (unicode)
222 size *= 4;
223
224 return size;
225}
226
227static loff_t vcs_lseek(struct file *file, loff_t offset, int orig)
228{
229 struct inode *inode = file_inode(file);
230 struct vc_data *vc;
231 int size;
232
233 scoped_guard(console_lock) {
234 vc = vcs_vc(inode, NULL);
235 if (!vc)
236 return -ENXIO;
237
238 size = vcs_size(vc, use_attributes(inode), use_unicode(inode));
239 }
240 if (size < 0)
241 return size;
242 return fixed_size_llseek(file, offset, orig, size);
243}
244
245static int vcs_read_buf_uni(struct vc_data *vc, char *con_buf,
246 unsigned int pos, unsigned int count, bool viewed)
247{
248 unsigned int nr, row, col, maxcol = vc->vc_cols;
249 int ret;
250
251 ret = vc_uniscr_check(vc);
252 if (ret)
253 return ret;
254
255 pos /= 4;
256 row = pos / maxcol;
257 col = pos % maxcol;
258 nr = maxcol - col;
259 do {
260 if (nr > count / 4)
261 nr = count / 4;
262 vc_uniscr_copy_line(vc, con_buf, viewed, row, col, nr);
263 con_buf += nr * 4;
264 count -= nr * 4;
265 row++;
266 col = 0;
267 nr = maxcol;
268 } while (count);
269
270 return 0;
271}
272
273static void vcs_read_buf_noattr(const struct vc_data *vc, char *con_buf,
274 unsigned int pos, unsigned int count, bool viewed)
275{
276 u16 *org;
277 unsigned int col, maxcol = vc->vc_cols;
278
279 org = screen_pos(vc, pos, viewed);
280 col = pos % maxcol;
281 pos += maxcol - col;
282
283 while (count-- > 0) {
284 *con_buf++ = (vcs_scr_readw(vc, org++) & 0xff);
285 if (++col == maxcol) {
286 org = screen_pos(vc, pos, viewed);
287 col = 0;
288 pos += maxcol;
289 }
290 }
291}
292
293static unsigned int vcs_read_buf(const struct vc_data *vc, char *con_buf,
294 unsigned int pos, unsigned int count, bool viewed,
295 unsigned int *skip)
296{
297 u16 *org, *con_buf16;
298 unsigned int col, maxcol = vc->vc_cols;
299 unsigned int filled = count;
300
301 if (pos < HEADER_SIZE) {
302 /* clamp header values if they don't fit */
303 con_buf[0] = min(vc->vc_rows, 0xFFu);
304 con_buf[1] = min(vc->vc_cols, 0xFFu);
305 getconsxy(vc, con_buf + 2);
306
307 *skip += pos;
308 count += pos;
309 if (count > CON_BUF_SIZE) {
310 count = CON_BUF_SIZE;
311 filled = count - pos;
312 }
313
314 /* Advance state pointers and move on. */
315 count -= min(HEADER_SIZE, count);
316 pos = HEADER_SIZE;
317 con_buf += HEADER_SIZE;
318 /* If count >= 0, then pos is even... */
319 } else if (pos & 1) {
320 /*
321 * Skip first byte for output if start address is odd. Update
322 * region sizes up/down depending on free space in buffer.
323 */
324 (*skip)++;
325 if (count < CON_BUF_SIZE)
326 count++;
327 else
328 filled--;
329 }
330
331 if (!count)
332 return filled;
333
334 pos -= HEADER_SIZE;
335 pos /= 2;
336 col = pos % maxcol;
337
338 org = screen_pos(vc, pos, viewed);
339 pos += maxcol - col;
340
341 /*
342 * Buffer has even length, so we can always copy character + attribute.
343 * We do not copy last byte to userspace if count is odd.
344 */
345 count = (count + 1) / 2;
346 con_buf16 = (u16 *)con_buf;
347
348 while (count) {
349 *con_buf16++ = vcs_scr_readw(vc, org++);
350 count--;
351 if (++col == maxcol) {
352 org = screen_pos(vc, pos, viewed);
353 col = 0;
354 pos += maxcol;
355 }
356 }
357
358 return filled;
359}
360
361static ssize_t
362vcs_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
363{
364 struct inode *inode = file_inode(file);
365 struct vc_data *vc;
366 struct vcs_poll_data *poll;
367 unsigned int read;
368 ssize_t ret;
369 loff_t pos;
370 bool viewed, attr, uni_mode;
371
372 char *con_buf __free(kfree) = kmalloc(PAGE_SIZE, GFP_KERNEL);
373 if (!con_buf)
374 return -ENOMEM;
375
376 pos = *ppos;
377
378 /* Select the proper current console and verify
379 * sanity of the situation under the console lock.
380 */
381 guard(console_lock)();
382
383 uni_mode = use_unicode(inode);
384 attr = use_attributes(inode);
385
386 if (pos < 0)
387 return -EINVAL;
388 /* we enforce 32-bit alignment for pos and count in unicode mode */
389 if (uni_mode && (pos | count) & 3)
390 return -EINVAL;
391
392 poll = file->private_data;
393 if (count && poll)
394 poll->event = 0;
395 read = 0;
396 ret = 0;
397 while (count) {
398 unsigned int this_round, skip = 0;
399 int size;
400
401 vc = vcs_vc(inode, &viewed);
402 if (!vc) {
403 ret = -ENXIO;
404 break;
405 }
406
407 /* Check whether we are above size each round,
408 * as copy_to_user at the end of this loop
409 * could sleep.
410 */
411 size = vcs_size(vc, attr, uni_mode);
412 if (size < 0) {
413 ret = size;
414 break;
415 }
416 if (pos >= size)
417 break;
418 if (count > size - pos)
419 count = size - pos;
420
421 this_round = count;
422 if (this_round > CON_BUF_SIZE)
423 this_round = CON_BUF_SIZE;
424
425 /* Perform the whole read into the local con_buf.
426 * Then we can drop the console spinlock and safely
427 * attempt to move it to userspace.
428 */
429
430 if (uni_mode) {
431 ret = vcs_read_buf_uni(vc, con_buf, pos, this_round,
432 viewed);
433 if (ret)
434 break;
435 } else if (!attr) {
436 vcs_read_buf_noattr(vc, con_buf, pos, this_round,
437 viewed);
438 } else {
439 this_round = vcs_read_buf(vc, con_buf, pos, this_round,
440 viewed, &skip);
441 }
442
443 /* Finally, release the console semaphore while we push
444 * all the data to userspace from our temporary buffer.
445 *
446 * AKPM: Even though it's a semaphore, we should drop it because
447 * the pagefault handling code may want to call printk().
448 */
449
450 console_unlock();
451 ret = copy_to_user(buf, con_buf + skip, this_round);
452 console_lock();
453
454 if (ret) {
455 read += this_round - ret;
456 ret = -EFAULT;
457 break;
458 }
459 buf += this_round;
460 pos += this_round;
461 read += this_round;
462 count -= this_round;
463 }
464 *ppos += read;
465 if (read)
466 return read;
467
468 return ret;
469}
470
471static u16 *vcs_write_buf_noattr(struct vc_data *vc, const char *con_buf,
472 unsigned int pos, unsigned int count, bool viewed, u16 **org0)
473{
474 u16 *org;
475 unsigned int col, maxcol = vc->vc_cols;
476
477 *org0 = org = screen_pos(vc, pos, viewed);
478 col = pos % maxcol;
479 pos += maxcol - col;
480
481 while (count > 0) {
482 unsigned char c = *con_buf++;
483
484 count--;
485 vcs_scr_writew(vc,
486 (vcs_scr_readw(vc, org) & 0xff00) | c, org);
487 org++;
488 if (++col == maxcol) {
489 org = screen_pos(vc, pos, viewed);
490 col = 0;
491 pos += maxcol;
492 }
493 }
494
495 return org;
496}
497
498/*
499 * Compilers (gcc 10) are unable to optimize the swap in cpu_to_le16. So do it
500 * the poor man way.
501 */
502static inline u16 vc_compile_le16(u8 hi, u8 lo)
503{
504#ifdef __BIG_ENDIAN
505 return (lo << 8u) | hi;
506#else
507 return (hi << 8u) | lo;
508#endif
509}
510
511static u16 *vcs_write_buf(struct vc_data *vc, const char *con_buf,
512 unsigned int pos, unsigned int count, bool viewed, u16 **org0)
513{
514 u16 *org;
515 unsigned int col, maxcol = vc->vc_cols;
516 unsigned char c;
517
518 /* header */
519 if (pos < HEADER_SIZE) {
520 char header[HEADER_SIZE];
521
522 getconsxy(vc, header + 2);
523 while (pos < HEADER_SIZE && count > 0) {
524 count--;
525 header[pos++] = *con_buf++;
526 }
527 if (!viewed)
528 putconsxy(vc, header + 2);
529 }
530
531 if (!count)
532 return NULL;
533
534 pos -= HEADER_SIZE;
535 col = (pos/2) % maxcol;
536
537 *org0 = org = screen_pos(vc, pos/2, viewed);
538
539 /* odd pos -- the first single character */
540 if (pos & 1) {
541 count--;
542 c = *con_buf++;
543 vcs_scr_writew(vc, vc_compile_le16(c, vcs_scr_readw(vc, org)),
544 org);
545 org++;
546 pos++;
547 if (++col == maxcol) {
548 org = screen_pos(vc, pos/2, viewed);
549 col = 0;
550 }
551 }
552
553 pos /= 2;
554 pos += maxcol - col;
555
556 /* even pos -- handle attr+character pairs */
557 while (count > 1) {
558 unsigned short w;
559
560 w = get_unaligned(((unsigned short *)con_buf));
561 vcs_scr_writew(vc, w, org++);
562 con_buf += 2;
563 count -= 2;
564 if (++col == maxcol) {
565 org = screen_pos(vc, pos, viewed);
566 col = 0;
567 pos += maxcol;
568 }
569 }
570
571 if (!count)
572 return org;
573
574 /* odd pos -- the remaining character */
575 c = *con_buf++;
576 vcs_scr_writew(vc, vc_compile_le16(vcs_scr_readw(vc, org) >> 8, c),
577 org);
578
579 return org;
580}
581
582static ssize_t
583vcs_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
584{
585 struct inode *inode = file_inode(file);
586 struct vc_data *vc;
587 u16 *org0, *org;
588 unsigned int written;
589 int size;
590 ssize_t ret;
591 loff_t pos;
592 bool viewed, attr;
593
594 if (use_unicode(inode))
595 return -EOPNOTSUPP;
596
597 char *con_buf __free(kfree) = kmalloc(PAGE_SIZE, GFP_KERNEL);
598 if (!con_buf)
599 return -ENOMEM;
600
601 pos = *ppos;
602
603 /* Select the proper current console and verify
604 * sanity of the situation under the console lock.
605 */
606 guard(console_lock)();
607
608 attr = use_attributes(inode);
609 vc = vcs_vc(inode, &viewed);
610 if (!vc)
611 return -ENXIO;
612
613 size = vcs_size(vc, attr, false);
614 if (size < 0)
615 return size;
616 if (pos < 0 || pos > size)
617 return -EINVAL;
618 if (count > size - pos)
619 count = size - pos;
620 written = 0;
621 while (count) {
622 unsigned int this_round = count;
623
624 if (this_round > CON_BUF_SIZE)
625 this_round = CON_BUF_SIZE;
626
627 /* Temporarily drop the console lock so that we can read
628 * in the write data from userspace safely.
629 */
630 console_unlock();
631 ret = copy_from_user(con_buf, buf, this_round);
632 console_lock();
633
634 /* The vc might have been freed or vcs_size might have changed
635 * while we slept to grab the user buffer; recheck here, before
636 * if (ret), so every break path below passes a fresh vc to the
637 * post-loop vcs_scr_updated(). Return data written so far.
638 */
639 vc = vcs_vc(inode, &viewed);
640 if (!vc) {
641 if (written)
642 break;
643 return -ENXIO;
644 }
645
646 if (ret) {
647 this_round -= ret;
648 if (!this_round) {
649 /* Abort loop if no data were copied. Otherwise
650 * fail with -EFAULT.
651 */
652 if (written)
653 break;
654 return -EFAULT;
655 }
656 }
657 size = vcs_size(vc, attr, false);
658 if (size < 0) {
659 if (written)
660 break;
661 return size;
662 }
663 if (pos >= size)
664 break;
665 if (this_round > size - pos)
666 this_round = size - pos;
667
668 /* OK, now actually push the write to the console
669 * under the lock using the local kernel buffer.
670 */
671
672 if (attr)
673 org = vcs_write_buf(vc, con_buf, pos, this_round,
674 viewed, &org0);
675 else
676 org = vcs_write_buf_noattr(vc, con_buf, pos, this_round,
677 viewed, &org0);
678
679 count -= this_round;
680 written += this_round;
681 buf += this_round;
682 pos += this_round;
683 if (org)
684 update_region(vc, (unsigned long)(org0), org - org0);
685 }
686 *ppos += written;
687 ret = written;
688 if (written && vc)
689 vcs_scr_updated(vc);
690
691 return ret;
692}
693
694static __poll_t
695vcs_poll(struct file *file, poll_table *wait)
696{
697 struct vcs_poll_data *poll = vcs_poll_data_get(file);
698 __poll_t ret = DEFAULT_POLLMASK|EPOLLERR;
699
700 if (poll) {
701 poll_wait(file, &poll->waitq, wait);
702 switch (poll->event) {
703 case VT_UPDATE:
704 ret = DEFAULT_POLLMASK|EPOLLPRI;
705 break;
706 case VT_DEALLOCATE:
707 ret = DEFAULT_POLLMASK|EPOLLHUP|EPOLLERR;
708 break;
709 case 0:
710 ret = DEFAULT_POLLMASK;
711 break;
712 }
713 }
714 return ret;
715}
716
717static int
718vcs_fasync(int fd, struct file *file, int on)
719{
720 struct vcs_poll_data *poll = file->private_data;
721
722 if (!poll) {
723 /* don't allocate anything if all we want is disable fasync */
724 if (!on)
725 return 0;
726 poll = vcs_poll_data_get(file);
727 if (!poll)
728 return -ENOMEM;
729 }
730
731 return fasync_helper(fd, file, on, &poll->fasync);
732}
733
734static int
735vcs_open(struct inode *inode, struct file *filp)
736{
737 unsigned int currcons = console(inode);
738 bool attr = use_attributes(inode);
739 bool uni_mode = use_unicode(inode);
740
741 /* we currently don't support attributes in unicode mode */
742 if (attr && uni_mode)
743 return -EOPNOTSUPP;
744
745 guard(console_lock)();
746
747 if (currcons && !vc_cons_allocated(currcons - 1))
748 return -ENXIO;
749
750 return 0;
751}
752
753static int vcs_release(struct inode *inode, struct file *file)
754{
755 struct vcs_poll_data *poll = file->private_data;
756
757 if (poll)
758 vcs_poll_data_free(poll);
759 return 0;
760}
761
762static const struct file_operations vcs_fops = {
763 .llseek = vcs_lseek,
764 .read = vcs_read,
765 .write = vcs_write,
766 .poll = vcs_poll,
767 .fasync = vcs_fasync,
768 .open = vcs_open,
769 .release = vcs_release,
770};
771
772static const struct class vc_class = {
773 .name = "vc",
774};
775
776void vcs_make_sysfs(int index)
777{
778 device_create(&vc_class, NULL, MKDEV(VCS_MAJOR, index + 1), NULL, "vcs%u", index + 1);
779 device_create(&vc_class, NULL, MKDEV(VCS_MAJOR, index + 65), NULL, "vcsu%u", index + 1);
780 device_create(&vc_class, NULL, MKDEV(VCS_MAJOR, index + 129), NULL, "vcsa%u", index + 1);
781}
782
783void vcs_remove_sysfs(int index)
784{
785 device_destroy(&vc_class, MKDEV(VCS_MAJOR, index + 1));
786 device_destroy(&vc_class, MKDEV(VCS_MAJOR, index + 65));
787 device_destroy(&vc_class, MKDEV(VCS_MAJOR, index + 129));
788}
789
790int __init vcs_init(void)
791{
792 unsigned int i;
793
794 if (register_chrdev(VCS_MAJOR, "vcs", &vcs_fops))
795 panic("unable to get major %d for vcs device", VCS_MAJOR);
796 if (class_register(&vc_class))
797 panic("unable to create vc_class");
798
799 device_create(&vc_class, NULL, MKDEV(VCS_MAJOR, 0), NULL, "vcs");
800 device_create(&vc_class, NULL, MKDEV(VCS_MAJOR, 64), NULL, "vcsu");
801 device_create(&vc_class, NULL, MKDEV(VCS_MAJOR, 128), NULL, "vcsa");
802 for (i = 0; i < MIN_NR_CONSOLES; i++)
803 vcs_make_sysfs(i);
804 return 0;
805}