arch/powerpc/lib/code-patching.c

   1 /*
   2  *  Copyright 2008 Michael Ellerman, IBM Corporation.
   3  *
   4  *  This program is free software; you can redistribute it and/or
   5  *  modify it under the terms of the GNU General Public License
   6  *  as published by the Free Software Foundation; either version
   7  *  2 of the License, or (at your option) any later version.
   8  */
   9
  10 #include <linux/kernel.h>
  11 #include <linux/vmalloc.h>
  12 #include <linux/init.h>
  13 #include <linux/mm.h>
  14 #include <asm/page.h>
  15 #include <asm/code-patching.h>
  16 #include <linux/uaccess.h>
  17 #include <linux/kprobes.h>
  18
  19
  20 int patch_instruction(unsigned int *addr, unsigned int instr)
  21 {
  22         int err;
  23
  24         __put_user_size(instr, addr, 4, err);
  25         if (err)
  26                 return err;
  27         asm ("dcbst 0, %0; sync; icbi 0,%0; sync; isync" : : "r" (addr));
  28         return 0;
  29 }
  30
  31 int patch_branch(unsigned int *addr, unsigned long target, int flags)
  32 {
  33         return patch_instruction(addr, create_branch(addr, target, flags));
  34 }
  35
  36 bool is_offset_in_branch_range(long offset)
  37 {
  38         /*
  39          * Powerpc branch instruction is :
  40          *
  41          *  0         6                 30   31
  42          *  +---------+----------------+---+---+
  43          *  | opcode  |     LI         |AA |LK |
  44          *  +---------+----------------+---+---+
  45          *  Where AA = 0 and LK = 0
  46          *
  47          * LI is a signed 24 bits integer. The real branch offset is computed
  48          * by: imm32 = SignExtend(LI:'0b00', 32);
  49          *
  50          * So the maximum forward branch should be:
  51          *   (0x007fffff << 2) = 0x01fffffc =  0x1fffffc
  52          * The maximum backward branch should be:
  53          *   (0xff800000 << 2) = 0xfe000000 = -0x2000000
  54          */
  55         return (offset >= -0x2000000 && offset <= 0x1fffffc && !(offset & 0x3));
  56 }
  57
  58 /*
  59  * Helper to check if a given instruction is a conditional branch
  60  * Derived from the conditional checks in analyse_instr()
  61  */
  62 bool __kprobes is_conditional_branch(unsigned int instr)
  63 {
  64         unsigned int opcode = instr >> 26;
  65
  66         if (opcode == 16)       /* bc, bca, bcl, bcla */
  67                 return true;
  68         if (opcode == 19) {
  69                 switch ((instr >> 1) & 0x3ff) {
  70                 case 16:        /* bclr, bclrl */
  71                 case 528:       /* bcctr, bcctrl */
  72                 case 560:       /* bctar, bctarl */
  73                         return true;
  74                 }
  75         }
  76         return false;
  77 }
  78
  79 unsigned int create_branch(const unsigned int *addr,
  80                            unsigned long target, int flags)
  81 {
  82         unsigned int instruction;
  83         long offset;
  84
  85         offset = target;
  86         if (! (flags & BRANCH_ABSOLUTE))
  87                 offset = offset - (unsigned long)addr;
  88
  89         /* Check we can represent the target in the instruction format */
  90         if (!is_offset_in_branch_range(offset))
  91                 return 0;
  92
  93         /* Mask out the flags and target, so they don't step on each other. */
  94         instruction = 0x48000000 | (flags & 0x3) | (offset & 0x03FFFFFC);
  95
  96         return instruction;
  97 }
  98
  99 unsigned int create_cond_branch(const unsigned int *addr,
 100                                 unsigned long target, int flags)
 101 {
 102         unsigned int instruction;
 103         long offset;
 104
 105         offset = target;
 106         if (! (flags & BRANCH_ABSOLUTE))
 107                 offset = offset - (unsigned long)addr;
 108
 109         /* Check we can represent the target in the instruction format */
 110         if (offset < -0x8000 || offset > 0x7FFF || offset & 0x3)
 111                 return 0;
 112
 113         /* Mask out the flags and target, so they don't step on each other. */
 114         instruction = 0x40000000 | (flags & 0x3FF0003) | (offset & 0xFFFC);
 115
 116         return instruction;
 117 }
 118
 119 static unsigned int branch_opcode(unsigned int instr)
 120 {
 121         return (instr >> 26) & 0x3F;
 122 }
 123
 124 static int instr_is_branch_iform(unsigned int instr)
 125 {
 126         return branch_opcode(instr) == 18;
 127 }
 128
 129 static int instr_is_branch_bform(unsigned int instr)
 130 {
 131         return branch_opcode(instr) == 16;
 132 }
 133
 134 int instr_is_relative_branch(unsigned int instr)
 135 {
 136         if (instr & BRANCH_ABSOLUTE)
 137                 return 0;
 138
 139         return instr_is_branch_iform(instr) || instr_is_branch_bform(instr);
 140 }
 141
 142 static unsigned long branch_iform_target(const unsigned int *instr)
 143 {
 144         signed long imm;
 145
 146         imm = *instr & 0x3FFFFFC;
 147
 148         /* If the top bit of the immediate value is set this is negative */
 149         if (imm & 0x2000000)
 150                 imm -= 0x4000000;
 151
 152         if ((*instr & BRANCH_ABSOLUTE) == 0)
 153                 imm += (unsigned long)instr;
 154
 155         return (unsigned long)imm;
 156 }
 157
 158 static unsigned long branch_bform_target(const unsigned int *instr)
 159 {
 160         signed long imm;
 161
 162         imm = *instr & 0xFFFC;
 163
 164         /* If the top bit of the immediate value is set this is negative */
 165         if (imm & 0x8000)
 166                 imm -= 0x10000;
 167
 168         if ((*instr & BRANCH_ABSOLUTE) == 0)
 169                 imm += (unsigned long)instr;
 170
 171         return (unsigned long)imm;
 172 }
 173
 174 unsigned long branch_target(const unsigned int *instr)
 175 {
 176         if (instr_is_branch_iform(*instr))
 177                 return branch_iform_target(instr);
 178         else if (instr_is_branch_bform(*instr))
 179                 return branch_bform_target(instr);
 180
 181         return 0;
 182 }
 183
 184 int instr_is_branch_to_addr(const unsigned int *instr, unsigned long addr)
 185 {
 186         if (instr_is_branch_iform(*instr) || instr_is_branch_bform(*instr))
 187                 return branch_target(instr) == addr;
 188
 189         return 0;
 190 }
 191
 192 unsigned int translate_branch(const unsigned int *dest, const unsigned int *src)
 193 {
 194         unsigned long target;
 195
 196         target = branch_target(src);
 197
 198         if (instr_is_branch_iform(*src))
 199                 return create_branch(dest, target, *src);
 200         else if (instr_is_branch_bform(*src))
 201                 return create_cond_branch(dest, target, *src);
 202
 203         return 0;
 204 }
 205
 206 #ifdef CONFIG_PPC_BOOK3E_64
 207 void __patch_exception(int exc, unsigned long addr)
 208 {
 209         extern unsigned int interrupt_base_book3e;
 210         unsigned int *ibase = &interrupt_base_book3e;
 211
 212         /* Our exceptions vectors start with a NOP and -then- a branch
 213          * to deal with single stepping from userspace which stops on
 214          * the second instruction. Thus we need to patch the second
 215          * instruction of the exception, not the first one
 216          */
 217
 218         patch_branch(ibase + (exc / 4) + 1, addr, 0);
 219 }
 220 #endif
 221
 222 #ifdef CONFIG_CODE_PATCHING_SELFTEST
 223
 224 static void __init test_trampoline(void)
 225 {
 226         asm ("nop;\n");
 227 }
 228
 229 #define check(x)        \
 230         if (!(x)) printk("code-patching: test failed at line %d\n", __LINE__);
 231
 232 static void __init test_branch_iform(void)
 233 {
 234         unsigned int instr;
 235         unsigned long addr;
 236
 237         addr = (unsigned long)&instr;
 238
 239         /* The simplest case, branch to self, no flags */
 240         check(instr_is_branch_iform(0x48000000));
 241         /* All bits of target set, and flags */
 242         check(instr_is_branch_iform(0x4bffffff));
 243         /* High bit of opcode set, which is wrong */
 244         check(!instr_is_branch_iform(0xcbffffff));
 245         /* Middle bits of opcode set, which is wrong */
 246         check(!instr_is_branch_iform(0x7bffffff));
 247
 248         /* Simplest case, branch to self with link */
 249         check(instr_is_branch_iform(0x48000001));
 250         /* All bits of targets set */
 251         check(instr_is_branch_iform(0x4bfffffd));
 252         /* Some bits of targets set */
 253         check(instr_is_branch_iform(0x4bff00fd));
 254         /* Must be a valid branch to start with */
 255         check(!instr_is_branch_iform(0x7bfffffd));
 256
 257         /* Absolute branch to 0x100 */
 258         instr = 0x48000103;
 259         check(instr_is_branch_to_addr(&instr, 0x100));
 260         /* Absolute branch to 0x420fc */
 261         instr = 0x480420ff;
 262         check(instr_is_branch_to_addr(&instr, 0x420fc));
 263         /* Maximum positive relative branch, + 20MB - 4B */
 264         instr = 0x49fffffc;
 265         check(instr_is_branch_to_addr(&instr, addr + 0x1FFFFFC));
 266         /* Smallest negative relative branch, - 4B */
 267         instr = 0x4bfffffc;
 268         check(instr_is_branch_to_addr(&instr, addr - 4));
 269         /* Largest negative relative branch, - 32 MB */
 270         instr = 0x4a000000;
 271         check(instr_is_branch_to_addr(&instr, addr - 0x2000000));
 272
 273         /* Branch to self, with link */
 274         instr = create_branch(&instr, addr, BRANCH_SET_LINK);
 275         check(instr_is_branch_to_addr(&instr, addr));
 276
 277         /* Branch to self - 0x100, with link */
 278         instr = create_branch(&instr, addr - 0x100, BRANCH_SET_LINK);
 279         check(instr_is_branch_to_addr(&instr, addr - 0x100));
 280
 281         /* Branch to self + 0x100, no link */
 282         instr = create_branch(&instr, addr + 0x100, 0);
 283         check(instr_is_branch_to_addr(&instr, addr + 0x100));
 284
 285         /* Maximum relative negative offset, - 32 MB */
 286         instr = create_branch(&instr, addr - 0x2000000, BRANCH_SET_LINK);
 287         check(instr_is_branch_to_addr(&instr, addr - 0x2000000));
 288
 289         /* Out of range relative negative offset, - 32 MB + 4*/
 290         instr = create_branch(&instr, addr - 0x2000004, BRANCH_SET_LINK);
 291         check(instr == 0);
 292
 293         /* Out of range relative positive offset, + 32 MB */
 294         instr = create_branch(&instr, addr + 0x2000000, BRANCH_SET_LINK);
 295         check(instr == 0);
 296
 297         /* Unaligned target */
 298         instr = create_branch(&instr, addr + 3, BRANCH_SET_LINK);
 299         check(instr == 0);
 300
 301         /* Check flags are masked correctly */
 302         instr = create_branch(&instr, addr, 0xFFFFFFFC);
 303         check(instr_is_branch_to_addr(&instr, addr));
 304         check(instr == 0x48000000);
 305 }
 306
 307 static void __init test_create_function_call(void)
 308 {
 309         unsigned int *iptr;
 310         unsigned long dest;
 311
 312         /* Check we can create a function call */
 313         iptr = (unsigned int *)ppc_function_entry(test_trampoline);
 314         dest = ppc_function_entry(test_create_function_call);
 315         patch_instruction(iptr, create_branch(iptr, dest, BRANCH_SET_LINK));
 316         check(instr_is_branch_to_addr(iptr, dest));
 317 }
 318
 319 static void __init test_branch_bform(void)
 320 {
 321         unsigned long addr;
 322         unsigned int *iptr, instr, flags;
 323
 324         iptr = &instr;
 325         addr = (unsigned long)iptr;
 326
 327         /* The simplest case, branch to self, no flags */
 328         check(instr_is_branch_bform(0x40000000));
 329         /* All bits of target set, and flags */
 330         check(instr_is_branch_bform(0x43ffffff));
 331         /* High bit of opcode set, which is wrong */
 332         check(!instr_is_branch_bform(0xc3ffffff));
 333         /* Middle bits of opcode set, which is wrong */
 334         check(!instr_is_branch_bform(0x7bffffff));
 335
 336         /* Absolute conditional branch to 0x100 */
 337         instr = 0x43ff0103;
 338         check(instr_is_branch_to_addr(&instr, 0x100));
 339         /* Absolute conditional branch to 0x20fc */
 340         instr = 0x43ff20ff;
 341         check(instr_is_branch_to_addr(&instr, 0x20fc));
 342         /* Maximum positive relative conditional branch, + 32 KB - 4B */
 343         instr = 0x43ff7ffc;
 344         check(instr_is_branch_to_addr(&instr, addr + 0x7FFC));
 345         /* Smallest negative relative conditional branch, - 4B */
 346         instr = 0x43fffffc;
 347         check(instr_is_branch_to_addr(&instr, addr - 4));
 348         /* Largest negative relative conditional branch, - 32 KB */
 349         instr = 0x43ff8000;
 350         check(instr_is_branch_to_addr(&instr, addr - 0x8000));
 351
 352         /* All condition code bits set & link */
 353         flags = 0x3ff000 | BRANCH_SET_LINK;
 354
 355         /* Branch to self */
 356         instr = create_cond_branch(iptr, addr, flags);
 357         check(instr_is_branch_to_addr(&instr, addr));
 358
 359         /* Branch to self - 0x100 */
 360         instr = create_cond_branch(iptr, addr - 0x100, flags);
 361         check(instr_is_branch_to_addr(&instr, addr - 0x100));
 362
 363         /* Branch to self + 0x100 */
 364         instr = create_cond_branch(iptr, addr + 0x100, flags);
 365         check(instr_is_branch_to_addr(&instr, addr + 0x100));
 366
 367         /* Maximum relative negative offset, - 32 KB */
 368         instr = create_cond_branch(iptr, addr - 0x8000, flags);
 369         check(instr_is_branch_to_addr(&instr, addr - 0x8000));
 370
 371         /* Out of range relative negative offset, - 32 KB + 4*/
 372         instr = create_cond_branch(iptr, addr - 0x8004, flags);
 373         check(instr == 0);
 374
 375         /* Out of range relative positive offset, + 32 KB */
 376         instr = create_cond_branch(iptr, addr + 0x8000, flags);
 377         check(instr == 0);
 378
 379         /* Unaligned target */
 380         instr = create_cond_branch(iptr, addr + 3, flags);
 381         check(instr == 0);
 382
 383         /* Check flags are masked correctly */
 384         instr = create_cond_branch(iptr, addr, 0xFFFFFFFC);
 385         check(instr_is_branch_to_addr(&instr, addr));
 386         check(instr == 0x43FF0000);
 387 }
 388
 389 static void __init test_translate_branch(void)
 390 {
 391         unsigned long addr;
 392         unsigned int *p, *q;
 393         void *buf;
 394
 395         buf = vmalloc(PAGE_ALIGN(0x2000000 + 1));
 396         check(buf);
 397         if (!buf)
 398                 return;
 399
 400         /* Simple case, branch to self moved a little */
 401         p = buf;
 402         addr = (unsigned long)p;
 403         patch_branch(p, addr, 0);
 404         check(instr_is_branch_to_addr(p, addr));
 405         q = p + 1;
 406         patch_instruction(q, translate_branch(q, p));
 407         check(instr_is_branch_to_addr(q, addr));
 408
 409         /* Maximum negative case, move b . to addr + 32 MB */
 410         p = buf;
 411         addr = (unsigned long)p;
 412         patch_branch(p, addr, 0);
 413         q = buf + 0x2000000;
 414         patch_instruction(q, translate_branch(q, p));
 415         check(instr_is_branch_to_addr(p, addr));
 416         check(instr_is_branch_to_addr(q, addr));
 417         check(*q == 0x4a000000);
 418
 419         /* Maximum positive case, move x to x - 32 MB + 4 */
 420         p = buf + 0x2000000;
 421         addr = (unsigned long)p;
 422         patch_branch(p, addr, 0);
 423         q = buf + 4;
 424         patch_instruction(q, translate_branch(q, p));
 425         check(instr_is_branch_to_addr(p, addr));
 426         check(instr_is_branch_to_addr(q, addr));
 427         check(*q == 0x49fffffc);
 428
 429         /* Jump to x + 16 MB moved to x + 20 MB */
 430         p = buf;
 431         addr = 0x1000000 + (unsigned long)buf;
 432         patch_branch(p, addr, BRANCH_SET_LINK);
 433         q = buf + 0x1400000;
 434         patch_instruction(q, translate_branch(q, p));
 435         check(instr_is_branch_to_addr(p, addr));
 436         check(instr_is_branch_to_addr(q, addr));
 437
 438         /* Jump to x + 16 MB moved to x - 16 MB + 4 */
 439         p = buf + 0x1000000;
 440         addr = 0x2000000 + (unsigned long)buf;
 441         patch_branch(p, addr, 0);
 442         q = buf + 4;
 443         patch_instruction(q, translate_branch(q, p));
 444         check(instr_is_branch_to_addr(p, addr));
 445         check(instr_is_branch_to_addr(q, addr));
 446
 447
 448         /* Conditional branch tests */
 449
 450         /* Simple case, branch to self moved a little */
 451         p = buf;
 452         addr = (unsigned long)p;
 453         patch_instruction(p, create_cond_branch(p, addr, 0));
 454         check(instr_is_branch_to_addr(p, addr));
 455         q = p + 1;
 456         patch_instruction(q, translate_branch(q, p));
 457         check(instr_is_branch_to_addr(q, addr));
 458
 459         /* Maximum negative case, move b . to addr + 32 KB */
 460         p = buf;
 461         addr = (unsigned long)p;
 462         patch_instruction(p, create_cond_branch(p, addr, 0xFFFFFFFC));
 463         q = buf + 0x8000;
 464         patch_instruction(q, translate_branch(q, p));
 465         check(instr_is_branch_to_addr(p, addr));
 466         check(instr_is_branch_to_addr(q, addr));
 467         check(*q == 0x43ff8000);
 468
 469         /* Maximum positive case, move x to x - 32 KB + 4 */
 470         p = buf + 0x8000;
 471         addr = (unsigned long)p;
 472         patch_instruction(p, create_cond_branch(p, addr, 0xFFFFFFFC));
 473         q = buf + 4;
 474         patch_instruction(q, translate_branch(q, p));
 475         check(instr_is_branch_to_addr(p, addr));
 476         check(instr_is_branch_to_addr(q, addr));
 477         check(*q == 0x43ff7ffc);
 478
 479         /* Jump to x + 12 KB moved to x + 20 KB */
 480         p = buf;
 481         addr = 0x3000 + (unsigned long)buf;
 482         patch_instruction(p, create_cond_branch(p, addr, BRANCH_SET_LINK));
 483         q = buf + 0x5000;
 484         patch_instruction(q, translate_branch(q, p));
 485         check(instr_is_branch_to_addr(p, addr));
 486         check(instr_is_branch_to_addr(q, addr));
 487
 488         /* Jump to x + 8 KB moved to x - 8 KB + 4 */
 489         p = buf + 0x2000;
 490         addr = 0x4000 + (unsigned long)buf;
 491         patch_instruction(p, create_cond_branch(p, addr, 0));
 492         q = buf + 4;
 493         patch_instruction(q, translate_branch(q, p));
 494         check(instr_is_branch_to_addr(p, addr));
 495         check(instr_is_branch_to_addr(q, addr));
 496
 497         /* Free the buffer we were using */
 498         vfree(buf);
 499 }
 500
 501 static int __init test_code_patching(void)
 502 {
 503         printk(KERN_DEBUG "Running code patching self-tests ...\n");
 504
 505         test_branch_iform();
 506         test_branch_bform();
 507         test_create_function_call();
 508         test_translate_branch();
 509
 510         return 0;
 511 }
 512 late_initcall(test_code_patching);
 513
 514 #endif /* CONFIG_CODE_PATCHING_SELFTEST */