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  * This replaces screendump and part of selection, so that the system
  14  * administrator can control access using file system permissions.
  15  *
  16  * aeb@cwi.nl - efter Friedas begravelse - 950211
  17  *
  18  * machek@k332.feld.cvut.cz - modified not to send characters to wrong console
  19  *       - fixed some fatal off-by-one bugs (0-- no longer == -1 -> looping and looping and looping...)
  20  *       - making it shorter - scr_readw are macros which expand in PRETTY long code
  21  */
  22
  23 #include <linux/kernel.h>
  24 #include <linux/major.h>
  25 #include <linux/errno.h>
  26 #include <linux/export.h>
  27 #include <linux/tty.h>
  28 #include <linux/interrupt.h>
  29 #include <linux/mm.h>
  30 #include <linux/init.h>
  31 #include <linux/vt_kern.h>
  32 #include <linux/selection.h>
  33 #include <linux/kbd_kern.h>
  34 #include <linux/console.h>
  35 #include <linux/device.h>
  36 #include <linux/sched.h>
  37 #include <linux/fs.h>
  38 #include <linux/poll.h>
  39 #include <linux/signal.h>
  40 #include <linux/slab.h>
  41 #include <linux/notifier.h>
  42
  43 #include <linux/uaccess.h>
  44 #include <asm/byteorder.h>
  45 #include <asm/unaligned.h>
  46
  47 #undef attr
  48 #undef org
  49 #undef addr
  50 #define HEADER_SIZE     4
  51
  52 #define CON_BUF_SIZE (CONFIG_BASE_SMALL ? 256 : PAGE_SIZE)
  53
  54 struct vcs_poll_data {
  55         struct notifier_block notifier;
  56         unsigned int cons_num;
  57         bool seen_last_update;
  58         wait_queue_head_t waitq;
  59         struct fasync_struct *fasync;
  60 };
  61
  62 static int
  63 vcs_notifier(struct notifier_block *nb, unsigned long code, void *_param)
  64 {
  65         struct vt_notifier_param *param = _param;
  66         struct vc_data *vc = param->vc;
  67         struct vcs_poll_data *poll =
  68                 container_of(nb, struct vcs_poll_data, notifier);
  69         int currcons = poll->cons_num;
  70
  71         if (code != VT_UPDATE)
  72                 return NOTIFY_DONE;
  73
  74         if (currcons == 0)
  75                 currcons = fg_console;
  76         else
  77                 currcons--;
  78         if (currcons != vc->vc_num)
  79                 return NOTIFY_DONE;
  80
  81         poll->seen_last_update = false;
  82         wake_up_interruptible(&poll->waitq);
  83         kill_fasync(&poll->fasync, SIGIO, POLL_IN);
  84         return NOTIFY_OK;
  85 }
  86
  87 static void
  88 vcs_poll_data_free(struct vcs_poll_data *poll)
  89 {
  90         unregister_vt_notifier(&poll->notifier);
  91         kfree(poll);
  92 }
  93
  94 static struct vcs_poll_data *
  95 vcs_poll_data_get(struct file *file)
  96 {
  97         struct vcs_poll_data *poll = file->private_data, *kill = NULL;
  98
  99         if (poll)
 100                 return poll;
 101
 102         poll = kzalloc(sizeof(*poll), GFP_KERNEL);
 103         if (!poll)
 104                 return NULL;
 105         poll->cons_num = iminor(file_inode(file)) & 127;
 106         init_waitqueue_head(&poll->waitq);
 107         poll->notifier.notifier_call = vcs_notifier;
 108         if (register_vt_notifier(&poll->notifier) != 0) {
 109                 kfree(poll);
 110                 return NULL;
 111         }
 112
 113         /*
 114          * This code may be called either through ->poll() or ->fasync().
 115          * If we have two threads using the same file descriptor, they could
 116          * both enter this function, both notice that the structure hasn't
 117          * been allocated yet and go ahead allocating it in parallel, but
 118          * only one of them must survive and be shared otherwise we'd leak
 119          * memory with a dangling notifier callback.
 120          */
 121         spin_lock(&file->f_lock);
 122         if (!file->private_data) {
 123                 file->private_data = poll;
 124         } else {
 125                 /* someone else raced ahead of us */
 126                 kill = poll;
 127                 poll = file->private_data;
 128         }
 129         spin_unlock(&file->f_lock);
 130         if (kill)
 131                 vcs_poll_data_free(kill);
 132
 133         return poll;
 134 }
 135
 136 /*
 137  * Returns VC for inode.
 138  * Must be called with console_lock.
 139  */
 140 static struct vc_data*
 141 vcs_vc(struct inode *inode, int *viewed)
 142 {
 143         unsigned int currcons = iminor(inode) & 127;
 144
 145         WARN_CONSOLE_UNLOCKED();
 146
 147         if (currcons == 0) {
 148                 currcons = fg_console;
 149                 if (viewed)
 150                         *viewed = 1;
 151         } else {
 152                 currcons--;
 153                 if (viewed)
 154                         *viewed = 0;
 155         }
 156         return vc_cons[currcons].d;
 157 }
 158
 159 /*
 160  * Returns size for VC carried by inode.
 161  * Must be called with console_lock.
 162  */
 163 static int
 164 vcs_size(struct inode *inode)
 165 {
 166         int size;
 167         int minor = iminor(inode);
 168         struct vc_data *vc;
 169
 170         WARN_CONSOLE_UNLOCKED();
 171
 172         vc = vcs_vc(inode, NULL);
 173         if (!vc)
 174                 return -ENXIO;
 175
 176         size = vc->vc_rows * vc->vc_cols;
 177
 178         if (minor & 128)
 179                 size = 2*size + HEADER_SIZE;
 180         return size;
 181 }
 182
 183 static loff_t vcs_lseek(struct file *file, loff_t offset, int orig)
 184 {
 185         int size;
 186
 187         console_lock();
 188         size = vcs_size(file_inode(file));
 189         console_unlock();
 190         if (size < 0)
 191                 return size;
 192         return fixed_size_llseek(file, offset, orig, size);
 193 }
 194
 195
 196 static ssize_t
 197 vcs_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
 198 {
 199         struct inode *inode = file_inode(file);
 200         unsigned int currcons = iminor(inode);
 201         struct vc_data *vc;
 202         struct vcs_poll_data *poll;
 203         long pos;
 204         long attr, read;
 205         int col, maxcol, viewed;
 206         unsigned short *org = NULL;
 207         ssize_t ret;
 208         char *con_buf;
 209
 210         con_buf = (char *) __get_free_page(GFP_KERNEL);
 211         if (!con_buf)
 212                 return -ENOMEM;
 213
 214         pos = *ppos;
 215
 216         /* Select the proper current console and verify
 217          * sanity of the situation under the console lock.
 218          */
 219         console_lock();
 220
 221         attr = (currcons & 128);
 222         ret = -ENXIO;
 223         vc = vcs_vc(inode, &viewed);
 224         if (!vc)
 225                 goto unlock_out;
 226
 227         ret = -EINVAL;
 228         if (pos < 0)
 229                 goto unlock_out;
 230         poll = file->private_data;
 231         if (count && poll)
 232                 poll->seen_last_update = true;
 233         read = 0;
 234         ret = 0;
 235         while (count) {
 236                 char *con_buf0, *con_buf_start;
 237                 long this_round, size;
 238                 ssize_t orig_count;
 239                 long p = pos;
 240
 241                 /* Check whether we are above size each round,
 242                  * as copy_to_user at the end of this loop
 243                  * could sleep.
 244                  */
 245                 size = vcs_size(inode);
 246                 if (size < 0) {
 247                         if (read)
 248                                 break;
 249                         ret = size;
 250                         goto unlock_out;
 251                 }
 252                 if (pos >= size)
 253                         break;
 254                 if (count > size - pos)
 255                         count = size - pos;
 256
 257                 this_round = count;
 258                 if (this_round > CON_BUF_SIZE)
 259                         this_round = CON_BUF_SIZE;
 260
 261                 /* Perform the whole read into the local con_buf.
 262                  * Then we can drop the console spinlock and safely
 263                  * attempt to move it to userspace.
 264                  */
 265
 266                 con_buf_start = con_buf0 = con_buf;
 267                 orig_count = this_round;
 268                 maxcol = vc->vc_cols;
 269                 if (!attr) {
 270                         org = screen_pos(vc, p, viewed);
 271                         col = p % maxcol;
 272                         p += maxcol - col;
 273                         while (this_round-- > 0) {
 274                                 *con_buf0++ = (vcs_scr_readw(vc, org++) & 0xff);
 275                                 if (++col == maxcol) {
 276                                         org = screen_pos(vc, p, viewed);
 277                                         col = 0;
 278                                         p += maxcol;
 279                                 }
 280                         }
 281                 } else {
 282                         if (p < HEADER_SIZE) {
 283                                 size_t tmp_count;
 284
 285                                 con_buf0[0] = (char)vc->vc_rows;
 286                                 con_buf0[1] = (char)vc->vc_cols;
 287                                 getconsxy(vc, con_buf0 + 2);
 288
 289                                 con_buf_start += p;
 290                                 this_round += p;
 291                                 if (this_round > CON_BUF_SIZE) {
 292                                         this_round = CON_BUF_SIZE;
 293                                         orig_count = this_round - p;
 294                                 }
 295
 296                                 tmp_count = HEADER_SIZE;
 297                                 if (tmp_count > this_round)
 298                                         tmp_count = this_round;
 299
 300                                 /* Advance state pointers and move on. */
 301                                 this_round -= tmp_count;
 302                                 p = HEADER_SIZE;
 303                                 con_buf0 = con_buf + HEADER_SIZE;
 304                                 /* If this_round >= 0, then p is even... */
 305                         } else if (p & 1) {
 306                                 /* Skip first byte for output if start address is odd
 307                                  * Update region sizes up/down depending on free
 308                                  * space in buffer.
 309                                  */
 310                                 con_buf_start++;
 311                                 if (this_round < CON_BUF_SIZE)
 312                                         this_round++;
 313                                 else
 314                                         orig_count--;
 315                         }
 316                         if (this_round > 0) {
 317                                 unsigned short *tmp_buf = (unsigned short *)con_buf0;
 318
 319                                 p -= HEADER_SIZE;
 320                                 p /= 2;
 321                                 col = p % maxcol;
 322
 323                                 org = screen_pos(vc, p, viewed);
 324                                 p += maxcol - col;
 325
 326                                 /* Buffer has even length, so we can always copy
 327                                  * character + attribute. We do not copy last byte
 328                                  * to userspace if this_round is odd.
 329                                  */
 330                                 this_round = (this_round + 1) >> 1;
 331
 332                                 while (this_round) {
 333                                         *tmp_buf++ = vcs_scr_readw(vc, org++);
 334                                         this_round --;
 335                                         if (++col == maxcol) {
 336                                                 org = screen_pos(vc, p, viewed);
 337                                                 col = 0;
 338                                                 p += maxcol;
 339                                         }
 340                                 }
 341                         }
 342                 }
 343
 344                 /* Finally, release the console semaphore while we push
 345                  * all the data to userspace from our temporary buffer.
 346                  *
 347                  * AKPM: Even though it's a semaphore, we should drop it because
 348                  * the pagefault handling code may want to call printk().
 349                  */
 350
 351                 console_unlock();
 352                 ret = copy_to_user(buf, con_buf_start, orig_count);
 353                 console_lock();
 354
 355                 if (ret) {
 356                         read += (orig_count - ret);
 357                         ret = -EFAULT;
 358                         break;
 359                 }
 360                 buf += orig_count;
 361                 pos += orig_count;
 362                 read += orig_count;
 363                 count -= orig_count;
 364         }
 365         *ppos += read;
 366         if (read)
 367                 ret = read;
 368 unlock_out:
 369         console_unlock();
 370         free_page((unsigned long) con_buf);
 371         return ret;
 372 }
 373
 374 static ssize_t
 375 vcs_write(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
 376 {
 377         struct inode *inode = file_inode(file);
 378         unsigned int currcons = iminor(inode);
 379         struct vc_data *vc;
 380         long pos;
 381         long attr, size, written;
 382         char *con_buf0;
 383         int col, maxcol, viewed;
 384         u16 *org0 = NULL, *org = NULL;
 385         size_t ret;
 386         char *con_buf;
 387
 388         con_buf = (char *) __get_free_page(GFP_KERNEL);
 389         if (!con_buf)
 390                 return -ENOMEM;
 391
 392         pos = *ppos;
 393
 394         /* Select the proper current console and verify
 395          * sanity of the situation under the console lock.
 396          */
 397         console_lock();
 398
 399         attr = (currcons & 128);
 400         ret = -ENXIO;
 401         vc = vcs_vc(inode, &viewed);
 402         if (!vc)
 403                 goto unlock_out;
 404
 405         size = vcs_size(inode);
 406         ret = -EINVAL;
 407         if (pos < 0 || pos > size)
 408                 goto unlock_out;
 409         if (count > size - pos)
 410                 count = size - pos;
 411         written = 0;
 412         while (count) {
 413                 long this_round = count;
 414                 size_t orig_count;
 415                 long p;
 416
 417                 if (this_round > CON_BUF_SIZE)
 418                         this_round = CON_BUF_SIZE;
 419
 420                 /* Temporarily drop the console lock so that we can read
 421                  * in the write data from userspace safely.
 422                  */
 423                 console_unlock();
 424                 ret = copy_from_user(con_buf, buf, this_round);
 425                 console_lock();
 426
 427                 if (ret) {
 428                         this_round -= ret;
 429                         if (!this_round) {
 430                                 /* Abort loop if no data were copied. Otherwise
 431                                  * fail with -EFAULT.
 432                                  */
 433                                 if (written)
 434                                         break;
 435                                 ret = -EFAULT;
 436                                 goto unlock_out;
 437                         }
 438                 }
 439
 440                 /* The vcs_size might have changed while we slept to grab
 441                  * the user buffer, so recheck.
 442                  * Return data written up to now on failure.
 443                  */
 444                 size = vcs_size(inode);
 445                 if (size < 0) {
 446                         if (written)
 447                                 break;
 448                         ret = size;
 449                         goto unlock_out;
 450                 }
 451                 if (pos >= size)
 452                         break;
 453                 if (this_round > size - pos)
 454                         this_round = size - pos;
 455
 456                 /* OK, now actually push the write to the console
 457                  * under the lock using the local kernel buffer.
 458                  */
 459
 460                 con_buf0 = con_buf;
 461                 orig_count = this_round;
 462                 maxcol = vc->vc_cols;
 463                 p = pos;
 464                 if (!attr) {
 465                         org0 = org = screen_pos(vc, p, viewed);
 466                         col = p % maxcol;
 467                         p += maxcol - col;
 468
 469                         while (this_round > 0) {
 470                                 unsigned char c = *con_buf0++;
 471
 472                                 this_round--;
 473                                 vcs_scr_writew(vc,
 474                                                (vcs_scr_readw(vc, org) & 0xff00) | c, org);
 475                                 org++;
 476                                 if (++col == maxcol) {
 477                                         org = screen_pos(vc, p, viewed);
 478                                         col = 0;
 479                                         p += maxcol;
 480                                 }
 481                         }
 482                 } else {
 483                         if (p < HEADER_SIZE) {
 484                                 char header[HEADER_SIZE];
 485
 486                                 getconsxy(vc, header + 2);
 487                                 while (p < HEADER_SIZE && this_round > 0) {
 488                                         this_round--;
 489                                         header[p++] = *con_buf0++;
 490                                 }
 491                                 if (!viewed)
 492                                         putconsxy(vc, header + 2);
 493                         }
 494                         p -= HEADER_SIZE;
 495                         col = (p/2) % maxcol;
 496                         if (this_round > 0) {
 497                                 org0 = org = screen_pos(vc, p/2, viewed);
 498                                 if ((p & 1) && this_round > 0) {
 499                                         char c;
 500
 501                                         this_round--;
 502                                         c = *con_buf0++;
 503 #ifdef __BIG_ENDIAN
 504                                         vcs_scr_writew(vc, c |
 505                                              (vcs_scr_readw(vc, org) & 0xff00), org);
 506 #else
 507                                         vcs_scr_writew(vc, (c << 8) |
 508                                              (vcs_scr_readw(vc, org) & 0xff), org);
 509 #endif
 510                                         org++;
 511                                         p++;
 512                                         if (++col == maxcol) {
 513                                                 org = screen_pos(vc, p/2, viewed);
 514                                                 col = 0;
 515                                         }
 516                                 }
 517                                 p /= 2;
 518                                 p += maxcol - col;
 519                         }
 520                         while (this_round > 1) {
 521                                 unsigned short w;
 522
 523                                 w = get_unaligned(((unsigned short *)con_buf0));
 524                                 vcs_scr_writew(vc, w, org++);
 525                                 con_buf0 += 2;
 526                                 this_round -= 2;
 527                                 if (++col == maxcol) {
 528                                         org = screen_pos(vc, p, viewed);
 529                                         col = 0;
 530                                         p += maxcol;
 531                                 }
 532                         }
 533                         if (this_round > 0) {
 534                                 unsigned char c;
 535
 536                                 c = *con_buf0++;
 537 #ifdef __BIG_ENDIAN
 538                                 vcs_scr_writew(vc, (vcs_scr_readw(vc, org) & 0xff) | (c << 8), org);
 539 #else
 540                                 vcs_scr_writew(vc, (vcs_scr_readw(vc, org) & 0xff00) | c, org);
 541 #endif
 542                         }
 543                 }
 544                 count -= orig_count;
 545                 written += orig_count;
 546                 buf += orig_count;
 547                 pos += orig_count;
 548                 if (org0)
 549                         update_region(vc, (unsigned long)(org0), org - org0);
 550         }
 551         *ppos += written;
 552         ret = written;
 553         if (written)
 554                 vcs_scr_updated(vc);
 555
 556 unlock_out:
 557         console_unlock();
 558         free_page((unsigned long) con_buf);
 559         return ret;
 560 }
 561
 562 static __poll_t
 563 vcs_poll(struct file *file, poll_table *wait)
 564 {
 565         struct vcs_poll_data *poll = vcs_poll_data_get(file);
 566         __poll_t ret = DEFAULT_POLLMASK|EPOLLERR|EPOLLPRI;
 567
 568         if (poll) {
 569                 poll_wait(file, &poll->waitq, wait);
 570                 if (poll->seen_last_update)
 571                         ret = DEFAULT_POLLMASK;
 572         }
 573         return ret;
 574 }
 575
 576 static int
 577 vcs_fasync(int fd, struct file *file, int on)
 578 {
 579         struct vcs_poll_data *poll = file->private_data;
 580
 581         if (!poll) {
 582                 /* don't allocate anything if all we want is disable fasync */
 583                 if (!on)
 584                         return 0;
 585                 poll = vcs_poll_data_get(file);
 586                 if (!poll)
 587                         return -ENOMEM;
 588         }
 589
 590         return fasync_helper(fd, file, on, &poll->fasync);
 591 }
 592
 593 static int
 594 vcs_open(struct inode *inode, struct file *filp)
 595 {
 596         unsigned int currcons = iminor(inode) & 127;
 597         int ret = 0;
 598
 599         console_lock();
 600         if(currcons && !vc_cons_allocated(currcons-1))
 601                 ret = -ENXIO;
 602         console_unlock();
 603         return ret;
 604 }
 605
 606 static int vcs_release(struct inode *inode, struct file *file)
 607 {
 608         struct vcs_poll_data *poll = file->private_data;
 609
 610         if (poll)
 611                 vcs_poll_data_free(poll);
 612         return 0;
 613 }
 614
 615 static const struct file_operations vcs_fops = {
 616         .llseek         = vcs_lseek,
 617         .read           = vcs_read,
 618         .write          = vcs_write,
 619         .poll           = vcs_poll,
 620         .fasync         = vcs_fasync,
 621         .open           = vcs_open,
 622         .release        = vcs_release,
 623 };
 624
 625 static struct class *vc_class;
 626
 627 void vcs_make_sysfs(int index)
 628 {
 629         device_create(vc_class, NULL, MKDEV(VCS_MAJOR, index + 1), NULL,
 630                       "vcs%u", index + 1);
 631         device_create(vc_class, NULL, MKDEV(VCS_MAJOR, index + 129), NULL,
 632                       "vcsa%u", index + 1);
 633 }
 634
 635 void vcs_remove_sysfs(int index)
 636 {
 637         device_destroy(vc_class, MKDEV(VCS_MAJOR, index + 1));
 638         device_destroy(vc_class, MKDEV(VCS_MAJOR, index + 129));
 639 }
 640
 641 int __init vcs_init(void)
 642 {
 643         unsigned int i;
 644
 645         if (register_chrdev(VCS_MAJOR, "vcs", &vcs_fops))
 646                 panic("unable to get major %d for vcs device", VCS_MAJOR);
 647         vc_class = class_create(THIS_MODULE, "vc");
 648
 649         device_create(vc_class, NULL, MKDEV(VCS_MAJOR, 0), NULL, "vcs");
 650         device_create(vc_class, NULL, MKDEV(VCS_MAJOR, 128), NULL, "vcsa");
 651         for (i = 0; i < MIN_NR_CONSOLES; i++)
 652                 vcs_make_sysfs(i);
 653         return 0;
 654 }