arch/mips/kernel/unaligned.c

   1 /*
   2  * Handle unaligned accesses by emulation.
   3  *
   4  * This file is subject to the terms and conditions of the GNU General Public
   5  * License.  See the file "COPYING" in the main directory of this archive
   6  * for more details.
   7  *
   8  * Copyright (C) 1996, 1998, 1999, 2002 by Ralf Baechle
   9  * Copyright (C) 1999 Silicon Graphics, Inc.
  10  *
  11  * This file contains exception handler for address error exception with the
  12  * special capability to execute faulting instructions in software.  The
  13  * handler does not try to handle the case when the program counter points
  14  * to an address not aligned to a word boundary.
  15  *
  16  * Putting data to unaligned addresses is a bad practice even on Intel where
  17  * only the performance is affected.  Much worse is that such code is non-
  18  * portable.  Due to several programs that die on MIPS due to alignment
  19  * problems I decided to implement this handler anyway though I originally
  20  * didn't intend to do this at all for user code.
  21  *
  22  * For now I enable fixing of address errors by default to make life easier.
  23  * I however intend to disable this somewhen in the future when the alignment
  24  * problems with user programs have been fixed.  For programmers this is the
  25  * right way to go.
  26  *
  27  * Fixing address errors is a per process option.  The option is inherited
  28  * across fork(2) and execve(2) calls.  If you really want to use the
  29  * option in your user programs - I discourage the use of the software
  30  * emulation strongly - use the following code in your userland stuff:
  31  *
  32  * #include <sys/sysmips.h>
  33  *
  34  * ...
  35  * sysmips(MIPS_FIXADE, x);
  36  * ...
  37  *
  38  * The argument x is 0 for disabling software emulation, enabled otherwise.
  39  *
  40  * Below a little program to play around with this feature.
  41  *
  42  * #include <stdio.h>
  43  * #include <sys/sysmips.h>
  44  *
  45  * struct foo {
  46  *         unsigned char bar[8];
  47  * };
  48  *
  49  * main(int argc, char *argv[])
  50  * {
  51  *         struct foo x = {0, 1, 2, 3, 4, 5, 6, 7};
  52  *         unsigned int *p = (unsigned int *) (x.bar + 3);
  53  *         int i;
  54  *
  55  *         if (argc > 1)
  56  *                 sysmips(MIPS_FIXADE, atoi(argv[1]));
  57  *
  58  *         printf("*p = %08lx\n", *p);
  59  *
  60  *         *p = 0xdeadface;
  61  *
  62  *         for(i = 0; i <= 7; i++)
  63  *         printf("%02x ", x.bar[i]);
  64  *         printf("\n");
  65  * }
  66  *
  67  * Coprocessor loads are not supported; I think this case is unimportant
  68  * in the practice.
  69  *
  70  * TODO: Handle ndc (attempted store to doubleword in uncached memory)
  71  *       exception for the R6000.
  72  *       A store crossing a page boundary might be executed only partially.
  73  *       Undo the partial store in this case.
  74  */
  75 #include <linux/mm.h>
  76 #include <linux/signal.h>
  77 #include <linux/smp.h>
  78 #include <linux/sched.h>
  79 #include <linux/debugfs.h>
  80 #include <linux/perf_event.h>
  81
  82 #include <asm/asm.h>
  83 #include <asm/branch.h>
  84 #include <asm/byteorder.h>
  85 #include <asm/cop2.h>
  86 #include <asm/inst.h>
  87 #include <asm/uaccess.h>
  88
  89 #define STR(x)  __STR(x)
  90 #define __STR(x)  #x
  91
  92 enum {
  93         UNALIGNED_ACTION_QUIET,
  94         UNALIGNED_ACTION_SIGNAL,
  95         UNALIGNED_ACTION_SHOW,
  96 };
  97 #ifdef CONFIG_DEBUG_FS
  98 static u32 unaligned_instructions;
  99 static u32 unaligned_action;
 100 #else
 101 #define unaligned_action UNALIGNED_ACTION_QUIET
 102 #endif
 103 extern void show_registers(struct pt_regs *regs);
 104
 105 static void emulate_load_store_insn(struct pt_regs *regs,
 106         void __user *addr, unsigned int __user *pc)
 107 {
 108         union mips_instruction insn;
 109         unsigned long value;
 110         unsigned int res;
 111
 112         perf_sw_event(PERF_COUNT_SW_EMULATION_FAULTS, 1, regs, 0);
 113
 114         /*
 115          * This load never faults.
 116          */
 117         __get_user(insn.word, pc);
 118
 119         switch (insn.i_format.opcode) {
 120         /*
 121          * These are instructions that a compiler doesn't generate.  We
 122          * can assume therefore that the code is MIPS-aware and
 123          * really buggy.  Emulating these instructions would break the
 124          * semantics anyway.
 125          */
 126         case ll_op:
 127         case lld_op:
 128         case sc_op:
 129         case scd_op:
 130
 131         /*
 132          * For these instructions the only way to create an address
 133          * error is an attempted access to kernel/supervisor address
 134          * space.
 135          */
 136         case ldl_op:
 137         case ldr_op:
 138         case lwl_op:
 139         case lwr_op:
 140         case sdl_op:
 141         case sdr_op:
 142         case swl_op:
 143         case swr_op:
 144         case lb_op:
 145         case lbu_op:
 146         case sb_op:
 147                 goto sigbus;
 148
 149         /*
 150          * The remaining opcodes are the ones that are really of interest.
 151          */
 152         case lh_op:
 153                 if (!access_ok(VERIFY_READ, addr, 2))
 154                         goto sigbus;
 155
 156                 __asm__ __volatile__ (".set\tnoat\n"
 157 #ifdef __BIG_ENDIAN
 158                         "1:\tlb\t%0, 0(%2)\n"
 159                         "2:\tlbu\t$1, 1(%2)\n\t"
 160 #endif
 161 #ifdef __LITTLE_ENDIAN
 162                         "1:\tlb\t%0, 1(%2)\n"
 163                         "2:\tlbu\t$1, 0(%2)\n\t"
 164 #endif
 165                         "sll\t%0, 0x8\n\t"
 166                         "or\t%0, $1\n\t"
 167                         "li\t%1, 0\n"
 168                         "3:\t.set\tat\n\t"
 169                         ".section\t.fixup,\"ax\"\n\t"
 170                         "4:\tli\t%1, %3\n\t"
 171                         "j\t3b\n\t"
 172                         ".previous\n\t"
 173                         ".section\t__ex_table,\"a\"\n\t"
 174                         STR(PTR)"\t1b, 4b\n\t"
 175                         STR(PTR)"\t2b, 4b\n\t"
 176                         ".previous"
 177                         : "=&r" (value), "=r" (res)
 178                         : "r" (addr), "i" (-EFAULT));
 179                 if (res)
 180                         goto fault;
 181                 compute_return_epc(regs);
 182                 regs->regs[insn.i_format.rt] = value;
 183                 break;
 184
 185         case lw_op:
 186                 if (!access_ok(VERIFY_READ, addr, 4))
 187                         goto sigbus;
 188
 189                 __asm__ __volatile__ (
 190 #ifdef __BIG_ENDIAN
 191                         "1:\tlwl\t%0, (%2)\n"
 192                         "2:\tlwr\t%0, 3(%2)\n\t"
 193 #endif
 194 #ifdef __LITTLE_ENDIAN
 195                         "1:\tlwl\t%0, 3(%2)\n"
 196                         "2:\tlwr\t%0, (%2)\n\t"
 197 #endif
 198                         "li\t%1, 0\n"
 199                         "3:\t.section\t.fixup,\"ax\"\n\t"
 200                         "4:\tli\t%1, %3\n\t"
 201                         "j\t3b\n\t"
 202                         ".previous\n\t"
 203                         ".section\t__ex_table,\"a\"\n\t"
 204                         STR(PTR)"\t1b, 4b\n\t"
 205                         STR(PTR)"\t2b, 4b\n\t"
 206                         ".previous"
 207                         : "=&r" (value), "=r" (res)
 208                         : "r" (addr), "i" (-EFAULT));
 209                 if (res)
 210                         goto fault;
 211                 compute_return_epc(regs);
 212                 regs->regs[insn.i_format.rt] = value;
 213                 break;
 214
 215         case lhu_op:
 216                 if (!access_ok(VERIFY_READ, addr, 2))
 217                         goto sigbus;
 218
 219                 __asm__ __volatile__ (
 220                         ".set\tnoat\n"
 221 #ifdef __BIG_ENDIAN
 222                         "1:\tlbu\t%0, 0(%2)\n"
 223                         "2:\tlbu\t$1, 1(%2)\n\t"
 224 #endif
 225 #ifdef __LITTLE_ENDIAN
 226                         "1:\tlbu\t%0, 1(%2)\n"
 227                         "2:\tlbu\t$1, 0(%2)\n\t"
 228 #endif
 229                         "sll\t%0, 0x8\n\t"
 230                         "or\t%0, $1\n\t"
 231                         "li\t%1, 0\n"
 232                         "3:\t.set\tat\n\t"
 233                         ".section\t.fixup,\"ax\"\n\t"
 234                         "4:\tli\t%1, %3\n\t"
 235                         "j\t3b\n\t"
 236                         ".previous\n\t"
 237                         ".section\t__ex_table,\"a\"\n\t"
 238                         STR(PTR)"\t1b, 4b\n\t"
 239                         STR(PTR)"\t2b, 4b\n\t"
 240                         ".previous"
 241                         : "=&r" (value), "=r" (res)
 242                         : "r" (addr), "i" (-EFAULT));
 243                 if (res)
 244                         goto fault;
 245                 compute_return_epc(regs);
 246                 regs->regs[insn.i_format.rt] = value;
 247                 break;
 248
 249         case lwu_op:
 250 #ifdef CONFIG_64BIT
 251                 /*
 252                  * A 32-bit kernel might be running on a 64-bit processor.  But
 253                  * if we're on a 32-bit processor and an i-cache incoherency
 254                  * or race makes us see a 64-bit instruction here the sdl/sdr
 255                  * would blow up, so for now we don't handle unaligned 64-bit
 256                  * instructions on 32-bit kernels.
 257                  */
 258                 if (!access_ok(VERIFY_READ, addr, 4))
 259                         goto sigbus;
 260
 261                 __asm__ __volatile__ (
 262 #ifdef __BIG_ENDIAN
 263                         "1:\tlwl\t%0, (%2)\n"
 264                         "2:\tlwr\t%0, 3(%2)\n\t"
 265 #endif
 266 #ifdef __LITTLE_ENDIAN
 267                         "1:\tlwl\t%0, 3(%2)\n"
 268                         "2:\tlwr\t%0, (%2)\n\t"
 269 #endif
 270                         "dsll\t%0, %0, 32\n\t"
 271                         "dsrl\t%0, %0, 32\n\t"
 272                         "li\t%1, 0\n"
 273                         "3:\t.section\t.fixup,\"ax\"\n\t"
 274                         "4:\tli\t%1, %3\n\t"
 275                         "j\t3b\n\t"
 276                         ".previous\n\t"
 277                         ".section\t__ex_table,\"a\"\n\t"
 278                         STR(PTR)"\t1b, 4b\n\t"
 279                         STR(PTR)"\t2b, 4b\n\t"
 280                         ".previous"
 281                         : "=&r" (value), "=r" (res)
 282                         : "r" (addr), "i" (-EFAULT));
 283                 if (res)
 284                         goto fault;
 285                 compute_return_epc(regs);
 286                 regs->regs[insn.i_format.rt] = value;
 287                 break;
 288 #endif /* CONFIG_64BIT */
 289
 290                 /* Cannot handle 64-bit instructions in 32-bit kernel */
 291                 goto sigill;
 292
 293         case ld_op:
 294 #ifdef CONFIG_64BIT
 295                 /*
 296                  * A 32-bit kernel might be running on a 64-bit processor.  But
 297                  * if we're on a 32-bit processor and an i-cache incoherency
 298                  * or race makes us see a 64-bit instruction here the sdl/sdr
 299                  * would blow up, so for now we don't handle unaligned 64-bit
 300                  * instructions on 32-bit kernels.
 301                  */
 302                 if (!access_ok(VERIFY_READ, addr, 8))
 303                         goto sigbus;
 304
 305                 __asm__ __volatile__ (
 306 #ifdef __BIG_ENDIAN
 307                         "1:\tldl\t%0, (%2)\n"
 308                         "2:\tldr\t%0, 7(%2)\n\t"
 309 #endif
 310 #ifdef __LITTLE_ENDIAN
 311                         "1:\tldl\t%0, 7(%2)\n"
 312                         "2:\tldr\t%0, (%2)\n\t"
 313 #endif
 314                         "li\t%1, 0\n"
 315                         "3:\t.section\t.fixup,\"ax\"\n\t"
 316                         "4:\tli\t%1, %3\n\t"
 317                         "j\t3b\n\t"
 318                         ".previous\n\t"
 319                         ".section\t__ex_table,\"a\"\n\t"
 320                         STR(PTR)"\t1b, 4b\n\t"
 321                         STR(PTR)"\t2b, 4b\n\t"
 322                         ".previous"
 323                         : "=&r" (value), "=r" (res)
 324                         : "r" (addr), "i" (-EFAULT));
 325                 if (res)
 326                         goto fault;
 327                 compute_return_epc(regs);
 328                 regs->regs[insn.i_format.rt] = value;
 329                 break;
 330 #endif /* CONFIG_64BIT */
 331
 332                 /* Cannot handle 64-bit instructions in 32-bit kernel */
 333                 goto sigill;
 334
 335         case sh_op:
 336                 if (!access_ok(VERIFY_WRITE, addr, 2))
 337                         goto sigbus;
 338
 339                 value = regs->regs[insn.i_format.rt];
 340                 __asm__ __volatile__ (
 341 #ifdef __BIG_ENDIAN
 342                         ".set\tnoat\n"
 343                         "1:\tsb\t%1, 1(%2)\n\t"
 344                         "srl\t$1, %1, 0x8\n"
 345                         "2:\tsb\t$1, 0(%2)\n\t"
 346                         ".set\tat\n\t"
 347 #endif
 348 #ifdef __LITTLE_ENDIAN
 349                         ".set\tnoat\n"
 350                         "1:\tsb\t%1, 0(%2)\n\t"
 351                         "srl\t$1,%1, 0x8\n"
 352                         "2:\tsb\t$1, 1(%2)\n\t"
 353                         ".set\tat\n\t"
 354 #endif
 355                         "li\t%0, 0\n"
 356                         "3:\n\t"
 357                         ".section\t.fixup,\"ax\"\n\t"
 358                         "4:\tli\t%0, %3\n\t"
 359                         "j\t3b\n\t"
 360                         ".previous\n\t"
 361                         ".section\t__ex_table,\"a\"\n\t"
 362                         STR(PTR)"\t1b, 4b\n\t"
 363                         STR(PTR)"\t2b, 4b\n\t"
 364                         ".previous"
 365                         : "=r" (res)
 366                         : "r" (value), "r" (addr), "i" (-EFAULT));
 367                 if (res)
 368                         goto fault;
 369                 compute_return_epc(regs);
 370                 break;
 371
 372         case sw_op:
 373                 if (!access_ok(VERIFY_WRITE, addr, 4))
 374                         goto sigbus;
 375
 376                 value = regs->regs[insn.i_format.rt];
 377                 __asm__ __volatile__ (
 378 #ifdef __BIG_ENDIAN
 379                         "1:\tswl\t%1,(%2)\n"
 380                         "2:\tswr\t%1, 3(%2)\n\t"
 381 #endif
 382 #ifdef __LITTLE_ENDIAN
 383                         "1:\tswl\t%1, 3(%2)\n"
 384                         "2:\tswr\t%1, (%2)\n\t"
 385 #endif
 386                         "li\t%0, 0\n"
 387                         "3:\n\t"
 388                         ".section\t.fixup,\"ax\"\n\t"
 389                         "4:\tli\t%0, %3\n\t"
 390                         "j\t3b\n\t"
 391                         ".previous\n\t"
 392                         ".section\t__ex_table,\"a\"\n\t"
 393                         STR(PTR)"\t1b, 4b\n\t"
 394                         STR(PTR)"\t2b, 4b\n\t"
 395                         ".previous"
 396                 : "=r" (res)
 397                 : "r" (value), "r" (addr), "i" (-EFAULT));
 398                 if (res)
 399                         goto fault;
 400                 compute_return_epc(regs);
 401                 break;
 402
 403         case sd_op:
 404 #ifdef CONFIG_64BIT
 405                 /*
 406                  * A 32-bit kernel might be running on a 64-bit processor.  But
 407                  * if we're on a 32-bit processor and an i-cache incoherency
 408                  * or race makes us see a 64-bit instruction here the sdl/sdr
 409                  * would blow up, so for now we don't handle unaligned 64-bit
 410                  * instructions on 32-bit kernels.
 411                  */
 412                 if (!access_ok(VERIFY_WRITE, addr, 8))
 413                         goto sigbus;
 414
 415                 value = regs->regs[insn.i_format.rt];
 416                 __asm__ __volatile__ (
 417 #ifdef __BIG_ENDIAN
 418                         "1:\tsdl\t%1,(%2)\n"
 419                         "2:\tsdr\t%1, 7(%2)\n\t"
 420 #endif
 421 #ifdef __LITTLE_ENDIAN
 422                         "1:\tsdl\t%1, 7(%2)\n"
 423                         "2:\tsdr\t%1, (%2)\n\t"
 424 #endif
 425                         "li\t%0, 0\n"
 426                         "3:\n\t"
 427                         ".section\t.fixup,\"ax\"\n\t"
 428                         "4:\tli\t%0, %3\n\t"
 429                         "j\t3b\n\t"
 430                         ".previous\n\t"
 431                         ".section\t__ex_table,\"a\"\n\t"
 432                         STR(PTR)"\t1b, 4b\n\t"
 433                         STR(PTR)"\t2b, 4b\n\t"
 434                         ".previous"
 435                 : "=r" (res)
 436                 : "r" (value), "r" (addr), "i" (-EFAULT));
 437                 if (res)
 438                         goto fault;
 439                 compute_return_epc(regs);
 440                 break;
 441 #endif /* CONFIG_64BIT */
 442
 443                 /* Cannot handle 64-bit instructions in 32-bit kernel */
 444                 goto sigill;
 445
 446         case lwc1_op:
 447         case ldc1_op:
 448         case swc1_op:
 449         case sdc1_op:
 450                 /*
 451                  * I herewith declare: this does not happen.  So send SIGBUS.
 452                  */
 453                 goto sigbus;
 454
 455         /*
 456          * COP2 is available to implementor for application specific use.
 457          * It's up to applications to register a notifier chain and do
 458          * whatever they have to do, including possible sending of signals.
 459          */
 460         case lwc2_op:
 461                 cu2_notifier_call_chain(CU2_LWC2_OP, regs);
 462                 break;
 463
 464         case ldc2_op:
 465                 cu2_notifier_call_chain(CU2_LDC2_OP, regs);
 466                 break;
 467
 468         case swc2_op:
 469                 cu2_notifier_call_chain(CU2_SWC2_OP, regs);
 470                 break;
 471
 472         case sdc2_op:
 473                 cu2_notifier_call_chain(CU2_SDC2_OP, regs);
 474                 break;
 475
 476         default:
 477                 /*
 478                  * Pheeee...  We encountered an yet unknown instruction or
 479                  * cache coherence problem.  Die sucker, die ...
 480                  */
 481                 goto sigill;
 482         }
 483
 484 #ifdef CONFIG_DEBUG_FS
 485         unaligned_instructions++;
 486 #endif
 487
 488         return;
 489
 490 fault:
 491         /* Did we have an exception handler installed? */
 492         if (fixup_exception(regs))
 493                 return;
 494
 495         die_if_kernel("Unhandled kernel unaligned access", regs);
 496         force_sig(SIGSEGV, current);
 497
 498         return;
 499
 500 sigbus:
 501         die_if_kernel("Unhandled kernel unaligned access", regs);
 502         force_sig(SIGBUS, current);
 503
 504         return;
 505
 506 sigill:
 507         die_if_kernel("Unhandled kernel unaligned access or invalid instruction", regs);
 508         force_sig(SIGILL, current);
 509 }
 510
 511 asmlinkage void do_ade(struct pt_regs *regs)
 512 {
 513         unsigned int __user *pc;
 514         mm_segment_t seg;
 515
 516         perf_sw_event(PERF_COUNT_SW_ALIGNMENT_FAULTS,
 517                         1, regs, regs->cp0_badvaddr);
 518         /*
 519          * Did we catch a fault trying to load an instruction?
 520          * Or are we running in MIPS16 mode?
 521          */
 522         if ((regs->cp0_badvaddr == regs->cp0_epc) || (regs->cp0_epc & 0x1))
 523                 goto sigbus;
 524
 525         pc = (unsigned int __user *) exception_epc(regs);
 526         if (user_mode(regs) && !test_thread_flag(TIF_FIXADE))
 527                 goto sigbus;
 528         if (unaligned_action == UNALIGNED_ACTION_SIGNAL)
 529                 goto sigbus;
 530         else if (unaligned_action == UNALIGNED_ACTION_SHOW)
 531                 show_registers(regs);
 532
 533         /*
 534          * Do branch emulation only if we didn't forward the exception.
 535          * This is all so but ugly ...
 536          */
 537         seg = get_fs();
 538         if (!user_mode(regs))
 539                 set_fs(KERNEL_DS);
 540         emulate_load_store_insn(regs, (void __user *)regs->cp0_badvaddr, pc);
 541         set_fs(seg);
 542
 543         return;
 544
 545 sigbus:
 546         die_if_kernel("Kernel unaligned instruction access", regs);
 547         force_sig(SIGBUS, current);
 548
 549         /*
 550          * XXX On return from the signal handler we should advance the epc
 551          */
 552 }
 553
 554 #ifdef CONFIG_DEBUG_FS
 555 extern struct dentry *mips_debugfs_dir;
 556 static int __init debugfs_unaligned(void)
 557 {
 558         struct dentry *d;
 559
 560         if (!mips_debugfs_dir)
 561                 return -ENODEV;
 562         d = debugfs_create_u32("unaligned_instructions", S_IRUGO,
 563                                mips_debugfs_dir, &unaligned_instructions);
 564         if (!d)
 565                 return -ENOMEM;
 566         d = debugfs_create_u32("unaligned_action", S_IRUGO | S_IWUSR,
 567                                mips_debugfs_dir, &unaligned_action);
 568         if (!d)
 569                 return -ENOMEM;
 570         return 0;
 571 }
 572 __initcall(debugfs_unaligned);
 573 #endif