drivers/tty/vt/vc_screen.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Provide access to virtual console memory.
   4  * /dev/vcs0: 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  * aeb@cwi.nl - efter Friedas begravelse - 950211
  23  *
  24  * machek@k332.feld.cvut.cz - 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 <asm/unaligned.h>
  52
  53 #undef attr
  54 #undef org
  55 #undef addr
  56 #define HEADER_SIZE     4
  57
  58 #define CON_BUF_SIZE (CONFIG_BASE_SMALL ? 256 : PAGE_SIZE)
  59
  60 /*
  61  * Our minor space:
  62  *
  63  *   0 ... 63   glyph mode without attributes
  64  *  64 ... 127  unicode mode without attributes
  65  * 128 ... 191  glyph mode with attributes
  66  * 192 ... 255  unused (reserved for unicode with attributes)
  67  *
  68  * This relies on MAX_NR_CONSOLES being  <= 63, meaning 63 actual consoles
  69  * with minors 0, 64, 128 and 192 being proxies for the foreground console.
  70  */
  71 #if MAX_NR_CONSOLES > 63
  72 #warning "/dev/vcs* devices may not accommodate more than 63 consoles"
  73 #endif
  74
  75 #define console(inode)          (iminor(inode) & 63)
  76 #define use_unicode(inode)      (iminor(inode) & 64)
  77 #define use_attributes(inode)   (iminor(inode) & 128)
  78
  79
  80 struct vcs_poll_data {
  81         struct notifier_block notifier;
  82         unsigned int cons_num;
  83         bool seen_last_update;
  84         wait_queue_head_t waitq;
  85         struct fasync_struct *fasync;
  86 };
  87
  88 static int
  89 vcs_notifier(struct notifier_block *nb, unsigned long code, void *_param)
  90 {
  91         struct vt_notifier_param *param = _param;
  92         struct vc_data *vc = param->vc;
  93         struct vcs_poll_data *poll =
  94                 container_of(nb, struct vcs_poll_data, notifier);
  95         int currcons = poll->cons_num;
  96
  97         if (code != VT_UPDATE)
  98                 return NOTIFY_DONE;
  99
 100         if (currcons == 0)
 101                 currcons = fg_console;
 102         else
 103                 currcons--;
 104         if (currcons != vc->vc_num)
 105                 return NOTIFY_DONE;
 106
 107         poll->seen_last_update = false;
 108         wake_up_interruptible(&poll->waitq);
 109         kill_fasync(&poll->fasync, SIGIO, POLL_IN);
 110         return NOTIFY_OK;
 111 }
 112
 113 static void
 114 vcs_poll_data_free(struct vcs_poll_data *poll)
 115 {
 116         unregister_vt_notifier(&poll->notifier);
 117         kfree(poll);
 118 }
 119
 120 static struct vcs_poll_data *
 121 vcs_poll_data_get(struct file *file)
 122 {
 123         struct vcs_poll_data *poll = file->private_data, *kill = NULL;
 124
 125         if (poll)
 126                 return poll;
 127
 128         poll = kzalloc(sizeof(*poll), GFP_KERNEL);
 129         if (!poll)
 130                 return NULL;
 131         poll->cons_num = console(file_inode(file));
 132         init_waitqueue_head(&poll->waitq);
 133         poll->notifier.notifier_call = vcs_notifier;
 134         if (register_vt_notifier(&poll->notifier) != 0) {
 135                 kfree(poll);
 136                 return NULL;
 137         }
 138
 139         /*
 140          * This code may be called either through ->poll() or ->fasync().
 141          * If we have two threads using the same file descriptor, they could
 142          * both enter this function, both notice that the structure hasn't
 143          * been allocated yet and go ahead allocating it in parallel, but
 144          * only one of them must survive and be shared otherwise we'd leak
 145          * memory with a dangling notifier callback.
 146          */
 147         spin_lock(&file->f_lock);
 148         if (!file->private_data) {
 149                 file->private_data = poll;
 150         } else {
 151                 /* someone else raced ahead of us */
 152                 kill = poll;
 153                 poll = file->private_data;
 154         }
 155         spin_unlock(&file->f_lock);
 156         if (kill)
 157                 vcs_poll_data_free(kill);
 158
 159         return poll;
 160 }
 161
 162 /*
 163  * Returns VC for inode.
 164  * Must be called with console_lock.
 165  */
 166 static struct vc_data*
 167 vcs_vc(struct inode *inode, int *viewed)
 168 {
 169         unsigned int currcons = console(inode);
 170
 171         WARN_CONSOLE_UNLOCKED();
 172
 173         if (currcons == 0) {
 174                 currcons = fg_console;
 175                 if (viewed)
 176                         *viewed = 1;
 177         } else {
 178                 currcons--;
 179                 if (viewed)
 180                         *viewed = 0;
 181         }
 182         return vc_cons[currcons].d;
 183 }
 184
 185 /*
 186  * Returns size for VC carried by inode.
 187  * Must be called with console_lock.
 188  */
 189 static int
 190 vcs_size(struct inode *inode)
 191 {
 192         int size;
 193         struct vc_data *vc;
 194
 195         WARN_CONSOLE_UNLOCKED();
 196
 197         vc = vcs_vc(inode, NULL);
 198         if (!vc)
 199                 return -ENXIO;
 200
 201         size = vc->vc_rows * vc->vc_cols;
 202
 203         if (use_attributes(inode)) {
 204                 if (use_unicode(inode))
 205                         return -EOPNOTSUPP;
 206                 size = 2*size + HEADER_SIZE;
 207         } else if (use_unicode(inode))
 208                 size *= 4;
 209         return size;
 210 }
 211
 212 static loff_t vcs_lseek(struct file *file, loff_t offset, int orig)
 213 {
 214         int size;
 215
 216         console_lock();
 217         size = vcs_size(file_inode(file));
 218         console_unlock();
 219         if (size < 0)
 220                 return size;
 221         return fixed_size_llseek(file, offset, orig, size);
 222 }
 223
 224
 225 static ssize_t
 226 vcs_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
 227 {
 228         struct inode *inode = file_inode(file);
 229         struct vc_data *vc;
 230         struct vcs_poll_data *poll;
 231         long pos, read;
 232         int attr, uni_mode, row, col, maxcol, viewed;
 233         unsigned short *org = NULL;
 234         ssize_t ret;
 235         char *con_buf;
 236
 237         con_buf = (char *) __get_free_page(GFP_KERNEL);
 238         if (!con_buf)
 239                 return -ENOMEM;
 240
 241         pos = *ppos;
 242
 243         /* Select the proper current console and verify
 244          * sanity of the situation under the console lock.
 245          */
 246         console_lock();
 247
 248         uni_mode = use_unicode(inode);
 249         attr = use_attributes(inode);
 250         ret = -ENXIO;
 251         vc = vcs_vc(inode, &viewed);
 252         if (!vc)
 253                 goto unlock_out;
 254
 255         ret = -EINVAL;
 256         if (pos < 0)
 257                 goto unlock_out;
 258         /* we enforce 32-bit alignment for pos and count in unicode mode */
 259         if (uni_mode && (pos | count) & 3)
 260                 goto unlock_out;
 261
 262         poll = file->private_data;
 263         if (count && poll)
 264                 poll->seen_last_update = true;
 265         read = 0;
 266         ret = 0;
 267         while (count) {
 268                 char *con_buf0, *con_buf_start;
 269                 long this_round, size;
 270                 ssize_t orig_count;
 271                 long p = pos;
 272
 273                 /* Check whether we are above size each round,
 274                  * as copy_to_user at the end of this loop
 275                  * could sleep.
 276                  */
 277                 size = vcs_size(inode);
 278                 if (size < 0) {
 279                         if (read)
 280                                 break;
 281                         ret = size;
 282                         goto unlock_out;
 283                 }
 284                 if (pos >= size)
 285                         break;
 286                 if (count > size - pos)
 287                         count = size - pos;
 288
 289                 this_round = count;
 290                 if (this_round > CON_BUF_SIZE)
 291                         this_round = CON_BUF_SIZE;
 292
 293                 /* Perform the whole read into the local con_buf.
 294                  * Then we can drop the console spinlock and safely
 295                  * attempt to move it to userspace.
 296                  */
 297
 298                 con_buf_start = con_buf0 = con_buf;
 299                 orig_count = this_round;
 300                 maxcol = vc->vc_cols;
 301                 if (uni_mode) {
 302                         unsigned int nr;
 303
 304                         ret = vc_uniscr_check(vc);
 305                         if (ret)
 306                                 break;
 307                         p /= 4;
 308                         row = p / vc->vc_cols;
 309                         col = p % maxcol;
 310                         nr = maxcol - col;
 311                         do {
 312                                 if (nr > this_round/4)
 313                                         nr = this_round/4;
 314                                 vc_uniscr_copy_line(vc, con_buf0, viewed,
 315                                                     row, col, nr);
 316                                 con_buf0 += nr * 4;
 317                                 this_round -= nr * 4;
 318                                 row++;
 319                                 col = 0;
 320                                 nr = maxcol;
 321                         } while (this_round);
 322                 } else if (!attr) {
 323                         org = screen_pos(vc, p, viewed);
 324                         col = p % maxcol;
 325                         p += maxcol - col;
 326                         while (this_round-- > 0) {
 327                                 *con_buf0++ = (vcs_scr_readw(vc, org++) & 0xff);
 328                                 if (++col == maxcol) {
 329                                         org = screen_pos(vc, p, viewed);
 330                                         col = 0;
 331                                         p += maxcol;
 332                                 }
 333                         }
 334                 } else {
 335                         if (p < HEADER_SIZE) {
 336                                 size_t tmp_count;
 337
 338                                 con_buf0[0] = (char)vc->vc_rows;
 339                                 con_buf0[1] = (char)vc->vc_cols;
 340                                 getconsxy(vc, con_buf0 + 2);
 341
 342                                 con_buf_start += p;
 343                                 this_round += p;
 344                                 if (this_round > CON_BUF_SIZE) {
 345                                         this_round = CON_BUF_SIZE;
 346                                         orig_count = this_round - p;
 347                                 }
 348
 349                                 tmp_count = HEADER_SIZE;
 350                                 if (tmp_count > this_round)
 351                                         tmp_count = this_round;
 352
 353                                 /* Advance state pointers and move on. */
 354                                 this_round -= tmp_count;
 355                                 p = HEADER_SIZE;
 356                                 con_buf0 = con_buf + HEADER_SIZE;
 357                                 /* If this_round >= 0, then p is even... */
 358                         } else if (p & 1) {
 359                                 /* Skip first byte for output if start address is odd
 360                                  * Update region sizes up/down depending on free
 361                                  * space in buffer.
 362                                  */
 363                                 con_buf_start++;
 364                                 if (this_round < CON_BUF_SIZE)
 365                                         this_round++;
 366                                 else
 367                                         orig_count--;
 368                         }
 369                         if (this_round > 0) {
 370                                 unsigned short *tmp_buf = (unsigned short *)con_buf0;
 371
 372                                 p -= HEADER_SIZE;
 373                                 p /= 2;
 374                                 col = p % maxcol;
 375
 376                                 org = screen_pos(vc, p, viewed);
 377                                 p += maxcol - col;
 378
 379                                 /* Buffer has even length, so we can always copy
 380                                  * character + attribute. We do not copy last byte
 381                                  * to userspace if this_round is odd.
 382                                  */
 383                                 this_round = (this_round + 1) >> 1;
 384
 385                                 while (this_round) {
 386                                         *tmp_buf++ = vcs_scr_readw(vc, org++);
 387                                         this_round --;
 388                                         if (++col == maxcol) {
 389                                                 org = screen_pos(vc, p, viewed);
 390                                                 col = 0;
 391                                                 p += maxcol;
 392                                         }
 393                                 }
 394                         }
 395                 }
 396
 397                 /* Finally, release the console semaphore while we push
 398                  * all the data to userspace from our temporary buffer.
 399                  *
 400                  * AKPM: Even though it's a semaphore, we should drop it because
 401                  * the pagefault handling code may want to call printk().
 402                  */
 403
 404                 console_unlock();
 405                 ret = copy_to_user(buf, con_buf_start, orig_count);
 406                 console_lock();
 407
 408                 if (ret) {
 409                         read += (orig_count - ret);
 410                         ret = -EFAULT;
 411                         break;
 412                 }
 413                 buf += orig_count;
 414                 pos += orig_count;
 415                 read += orig_count;
 416                 count -= orig_count;
 417         }
 418         *ppos += read;
 419         if (read)
 420                 ret = read;
 421 unlock_out:
 422         console_unlock();
 423         free_page((unsigned long) con_buf);
 424         return ret;
 425 }
 426
 427 static ssize_t
 428 vcs_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
 429 {
 430         struct inode *inode = file_inode(file);
 431         struct vc_data *vc;
 432         long pos;
 433         long attr, size, written;
 434         char *con_buf0;
 435         int col, maxcol, viewed;
 436         u16 *org0 = NULL, *org = NULL;
 437         size_t ret;
 438         char *con_buf;
 439
 440         con_buf = (char *) __get_free_page(GFP_KERNEL);
 441         if (!con_buf)
 442                 return -ENOMEM;
 443
 444         pos = *ppos;
 445
 446         /* Select the proper current console and verify
 447          * sanity of the situation under the console lock.
 448          */
 449         console_lock();
 450
 451         attr = use_attributes(inode);
 452         ret = -ENXIO;
 453         vc = vcs_vc(inode, &viewed);
 454         if (!vc)
 455                 goto unlock_out;
 456
 457         size = vcs_size(inode);
 458         ret = -EINVAL;
 459         if (pos < 0 || pos > size)
 460                 goto unlock_out;
 461         if (count > size - pos)
 462                 count = size - pos;
 463         written = 0;
 464         while (count) {
 465                 long this_round = count;
 466                 size_t orig_count;
 467                 long p;
 468
 469                 if (this_round > CON_BUF_SIZE)
 470                         this_round = CON_BUF_SIZE;
 471
 472                 /* Temporarily drop the console lock so that we can read
 473                  * in the write data from userspace safely.
 474                  */
 475                 console_unlock();
 476                 ret = copy_from_user(con_buf, buf, this_round);
 477                 console_lock();
 478
 479                 if (ret) {
 480                         this_round -= ret;
 481                         if (!this_round) {
 482                                 /* Abort loop if no data were copied. Otherwise
 483                                  * fail with -EFAULT.
 484                                  */
 485                                 if (written)
 486                                         break;
 487                                 ret = -EFAULT;
 488                                 goto unlock_out;
 489                         }
 490                 }
 491
 492                 /* The vcs_size might have changed while we slept to grab
 493                  * the user buffer, so recheck.
 494                  * Return data written up to now on failure.
 495                  */
 496                 size = vcs_size(inode);
 497                 if (size < 0) {
 498                         if (written)
 499                                 break;
 500                         ret = size;
 501                         goto unlock_out;
 502                 }
 503                 if (pos >= size)
 504                         break;
 505                 if (this_round > size - pos)
 506                         this_round = size - pos;
 507
 508                 /* OK, now actually push the write to the console
 509                  * under the lock using the local kernel buffer.
 510                  */
 511
 512                 con_buf0 = con_buf;
 513                 orig_count = this_round;
 514                 maxcol = vc->vc_cols;
 515                 p = pos;
 516                 if (!attr) {
 517                         org0 = org = screen_pos(vc, p, viewed);
 518                         col = p % maxcol;
 519                         p += maxcol - col;
 520
 521                         while (this_round > 0) {
 522                                 unsigned char c = *con_buf0++;
 523
 524                                 this_round--;
 525                                 vcs_scr_writew(vc,
 526                                                (vcs_scr_readw(vc, org) & 0xff00) | c, org);
 527                                 org++;
 528                                 if (++col == maxcol) {
 529                                         org = screen_pos(vc, p, viewed);
 530                                         col = 0;
 531                                         p += maxcol;
 532                                 }
 533                         }
 534                 } else {
 535                         if (p < HEADER_SIZE) {
 536                                 char header[HEADER_SIZE];
 537
 538                                 getconsxy(vc, header + 2);
 539                                 while (p < HEADER_SIZE && this_round > 0) {
 540                                         this_round--;
 541                                         header[p++] = *con_buf0++;
 542                                 }
 543                                 if (!viewed)
 544                                         putconsxy(vc, header + 2);
 545                         }
 546                         p -= HEADER_SIZE;
 547                         col = (p/2) % maxcol;
 548                         if (this_round > 0) {
 549                                 org0 = org = screen_pos(vc, p/2, viewed);
 550                                 if ((p & 1) && this_round > 0) {
 551                                         char c;
 552
 553                                         this_round--;
 554                                         c = *con_buf0++;
 555 #ifdef __BIG_ENDIAN
 556                                         vcs_scr_writew(vc, c |
 557                                              (vcs_scr_readw(vc, org) & 0xff00), org);
 558 #else
 559                                         vcs_scr_writew(vc, (c << 8) |
 560                                              (vcs_scr_readw(vc, org) & 0xff), org);
 561 #endif
 562                                         org++;
 563                                         p++;
 564                                         if (++col == maxcol) {
 565                                                 org = screen_pos(vc, p/2, viewed);
 566                                                 col = 0;
 567                                         }
 568                                 }
 569                                 p /= 2;
 570                                 p += maxcol - col;
 571                         }
 572                         while (this_round > 1) {
 573                                 unsigned short w;
 574
 575                                 w = get_unaligned(((unsigned short *)con_buf0));
 576                                 vcs_scr_writew(vc, w, org++);
 577                                 con_buf0 += 2;
 578                                 this_round -= 2;
 579                                 if (++col == maxcol) {
 580                                         org = screen_pos(vc, p, viewed);
 581                                         col = 0;
 582                                         p += maxcol;
 583                                 }
 584                         }
 585                         if (this_round > 0) {
 586                                 unsigned char c;
 587
 588                                 c = *con_buf0++;
 589 #ifdef __BIG_ENDIAN
 590                                 vcs_scr_writew(vc, (vcs_scr_readw(vc, org) & 0xff) | (c << 8), org);
 591 #else
 592                                 vcs_scr_writew(vc, (vcs_scr_readw(vc, org) & 0xff00) | c, org);
 593 #endif
 594                         }
 595                 }
 596                 count -= orig_count;
 597                 written += orig_count;
 598                 buf += orig_count;
 599                 pos += orig_count;
 600                 if (org0)
 601                         update_region(vc, (unsigned long)(org0), org - org0);
 602         }
 603         *ppos += written;
 604         ret = written;
 605         if (written)
 606                 vcs_scr_updated(vc);
 607
 608 unlock_out:
 609         console_unlock();
 610         free_page((unsigned long) con_buf);
 611         return ret;
 612 }
 613
 614 static __poll_t
 615 vcs_poll(struct file *file, poll_table *wait)
 616 {
 617         struct vcs_poll_data *poll = vcs_poll_data_get(file);
 618         __poll_t ret = DEFAULT_POLLMASK|EPOLLERR|EPOLLPRI;
 619
 620         if (poll) {
 621                 poll_wait(file, &poll->waitq, wait);
 622                 if (poll->seen_last_update)
 623                         ret = DEFAULT_POLLMASK;
 624         }
 625         return ret;
 626 }
 627
 628 static int
 629 vcs_fasync(int fd, struct file *file, int on)
 630 {
 631         struct vcs_poll_data *poll = file->private_data;
 632
 633         if (!poll) {
 634                 /* don't allocate anything if all we want is disable fasync */
 635                 if (!on)
 636                         return 0;
 637                 poll = vcs_poll_data_get(file);
 638                 if (!poll)
 639                         return -ENOMEM;
 640         }
 641
 642         return fasync_helper(fd, file, on, &poll->fasync);
 643 }
 644
 645 static int
 646 vcs_open(struct inode *inode, struct file *filp)
 647 {
 648         unsigned int currcons = console(inode);
 649         bool attr = use_attributes(inode);
 650         bool uni_mode = use_unicode(inode);
 651         int ret = 0;
 652
 653         /* we currently don't support attributes in unicode mode */
 654         if (attr && uni_mode)
 655                 return -EOPNOTSUPP;
 656
 657         console_lock();
 658         if(currcons && !vc_cons_allocated(currcons-1))
 659                 ret = -ENXIO;
 660         console_unlock();
 661         return ret;
 662 }
 663
 664 static int vcs_release(struct inode *inode, struct file *file)
 665 {
 666         struct vcs_poll_data *poll = file->private_data;
 667
 668         if (poll)
 669                 vcs_poll_data_free(poll);
 670         return 0;
 671 }
 672
 673 static const struct file_operations vcs_fops = {
 674         .llseek         = vcs_lseek,
 675         .read           = vcs_read,
 676         .write          = vcs_write,
 677         .poll           = vcs_poll,
 678         .fasync         = vcs_fasync,
 679         .open           = vcs_open,
 680         .release        = vcs_release,
 681 };
 682
 683 static struct class *vc_class;
 684
 685 void vcs_make_sysfs(int index)
 686 {
 687         device_create(vc_class, NULL, MKDEV(VCS_MAJOR, index + 1), NULL,
 688                       "vcs%u", index + 1);
 689         device_create(vc_class, NULL, MKDEV(VCS_MAJOR, index + 65), NULL,
 690                       "vcsu%u", index + 1);
 691         device_create(vc_class, NULL, MKDEV(VCS_MAJOR, index + 129), NULL,
 692                       "vcsa%u", index + 1);
 693 }
 694
 695 void vcs_remove_sysfs(int index)
 696 {
 697         device_destroy(vc_class, MKDEV(VCS_MAJOR, index + 1));
 698         device_destroy(vc_class, MKDEV(VCS_MAJOR, index + 65));
 699         device_destroy(vc_class, MKDEV(VCS_MAJOR, index + 129));
 700 }
 701
 702 int __init vcs_init(void)
 703 {
 704         unsigned int i;
 705
 706         if (register_chrdev(VCS_MAJOR, "vcs", &vcs_fops))
 707                 panic("unable to get major %d for vcs device", VCS_MAJOR);
 708         vc_class = class_create(THIS_MODULE, "vc");
 709
 710         device_create(vc_class, NULL, MKDEV(VCS_MAJOR, 0), NULL, "vcs");
 711         device_create(vc_class, NULL, MKDEV(VCS_MAJOR, 64), NULL, "vcsu");
 712         device_create(vc_class, NULL, MKDEV(VCS_MAJOR, 128), NULL, "vcsa");
 713         for (i = 0; i < MIN_NR_CONSOLES; i++)
 714                 vcs_make_sysfs(i);
 715         return 0;
 716 }