arch/x86/kernel/kprobes/opt.c

   1 /*
   2  *  Kernel Probes Jump Optimization (Optprobes)
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License as published by
   6  * the Free Software Foundation; either version 2 of the License, or
   7  * (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, write to the Free Software
  16  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  17  *
  18  * Copyright (C) IBM Corporation, 2002, 2004
  19  * Copyright (C) Hitachi Ltd., 2012
  20  */
  21 #include <linux/kprobes.h>
  22 #include <linux/ptrace.h>
  23 #include <linux/string.h>
  24 #include <linux/slab.h>
  25 #include <linux/hardirq.h>
  26 #include <linux/preempt.h>
  27 #include <linux/extable.h>
  28 #include <linux/kdebug.h>
  29 #include <linux/kallsyms.h>
  30 #include <linux/ftrace.h>
  31 #include <linux/frame.h>
  32
  33 #include <asm/text-patching.h>
  34 #include <asm/cacheflush.h>
  35 #include <asm/desc.h>
  36 #include <asm/pgtable.h>
  37 #include <linux/uaccess.h>
  38 #include <asm/alternative.h>
  39 #include <asm/insn.h>
  40 #include <asm/debugreg.h>
  41 #include <asm/set_memory.h>
  42 #include <asm/sections.h>
  43 #include <asm/nospec-branch.h>
  44
  45 #include "common.h"
  46
  47 unsigned long __recover_optprobed_insn(kprobe_opcode_t *buf, unsigned long addr)
  48 {
  49         struct optimized_kprobe *op;
  50         struct kprobe *kp;
  51         long offs;
  52         int i;
  53
  54         for (i = 0; i < RELATIVEJUMP_SIZE; i++) {
  55                 kp = get_kprobe((void *)addr - i);
  56                 /* This function only handles jump-optimized kprobe */
  57                 if (kp && kprobe_optimized(kp)) {
  58                         op = container_of(kp, struct optimized_kprobe, kp);
  59                         /* If op is optimized or under unoptimizing */
  60                         if (list_empty(&op->list) || optprobe_queued_unopt(op))
  61                                 goto found;
  62                 }
  63         }
  64
  65         return addr;
  66 found:
  67         /*
  68          * If the kprobe can be optimized, original bytes which can be
  69          * overwritten by jump destination address. In this case, original
  70          * bytes must be recovered from op->optinsn.copied_insn buffer.
  71          */
  72         if (probe_kernel_read(buf, (void *)addr,
  73                 MAX_INSN_SIZE * sizeof(kprobe_opcode_t)))
  74                 return 0UL;
  75
  76         if (addr == (unsigned long)kp->addr) {
  77                 buf[0] = kp->opcode;
  78                 memcpy(buf + 1, op->optinsn.copied_insn, RELATIVE_ADDR_SIZE);
  79         } else {
  80                 offs = addr - (unsigned long)kp->addr - 1;
  81                 memcpy(buf, op->optinsn.copied_insn + offs, RELATIVE_ADDR_SIZE - offs);
  82         }
  83
  84         return (unsigned long)buf;
  85 }
  86
  87 /* Insert a move instruction which sets a pointer to eax/rdi (1st arg). */
  88 static void synthesize_set_arg1(kprobe_opcode_t *addr, unsigned long val)
  89 {
  90 #ifdef CONFIG_X86_64
  91         *addr++ = 0x48;
  92         *addr++ = 0xbf;
  93 #else
  94         *addr++ = 0xb8;
  95 #endif
  96         *(unsigned long *)addr = val;
  97 }
  98
  99 asm (
 100                         "optprobe_template_func:\n"
 101                         ".global optprobe_template_entry\n"
 102                         "optprobe_template_entry:\n"
 103 #ifdef CONFIG_X86_64
 104                         /* We don't bother saving the ss register */
 105                         "       pushq %rsp\n"
 106                         "       pushfq\n"
 107                         SAVE_REGS_STRING
 108                         "       movq %rsp, %rsi\n"
 109                         ".global optprobe_template_val\n"
 110                         "optprobe_template_val:\n"
 111                         ASM_NOP5
 112                         ASM_NOP5
 113                         ".global optprobe_template_call\n"
 114                         "optprobe_template_call:\n"
 115                         ASM_NOP5
 116                         /* Move flags to rsp */
 117                         "       movq 144(%rsp), %rdx\n"
 118                         "       movq %rdx, 152(%rsp)\n"
 119                         RESTORE_REGS_STRING
 120                         /* Skip flags entry */
 121                         "       addq $8, %rsp\n"
 122                         "       popfq\n"
 123 #else /* CONFIG_X86_32 */
 124                         "       pushf\n"
 125                         SAVE_REGS_STRING
 126                         "       movl %esp, %edx\n"
 127                         ".global optprobe_template_val\n"
 128                         "optprobe_template_val:\n"
 129                         ASM_NOP5
 130                         ".global optprobe_template_call\n"
 131                         "optprobe_template_call:\n"
 132                         ASM_NOP5
 133                         RESTORE_REGS_STRING
 134                         "       addl $4, %esp\n"        /* skip cs */
 135                         "       popf\n"
 136 #endif
 137                         ".global optprobe_template_end\n"
 138                         "optprobe_template_end:\n"
 139                         ".type optprobe_template_func, @function\n"
 140                         ".size optprobe_template_func, .-optprobe_template_func\n");
 141
 142 void optprobe_template_func(void);
 143 STACK_FRAME_NON_STANDARD(optprobe_template_func);
 144 NOKPROBE_SYMBOL(optprobe_template_func);
 145 NOKPROBE_SYMBOL(optprobe_template_entry);
 146 NOKPROBE_SYMBOL(optprobe_template_val);
 147 NOKPROBE_SYMBOL(optprobe_template_call);
 148 NOKPROBE_SYMBOL(optprobe_template_end);
 149
 150 #define TMPL_MOVE_IDX \
 151         ((long)&optprobe_template_val - (long)&optprobe_template_entry)
 152 #define TMPL_CALL_IDX \
 153         ((long)&optprobe_template_call - (long)&optprobe_template_entry)
 154 #define TMPL_END_IDX \
 155         ((long)&optprobe_template_end - (long)&optprobe_template_entry)
 156
 157 #define INT3_SIZE sizeof(kprobe_opcode_t)
 158
 159 /* Optimized kprobe call back function: called from optinsn */
 160 static void
 161 optimized_callback(struct optimized_kprobe *op, struct pt_regs *regs)
 162 {
 163         struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 164         unsigned long flags;
 165
 166         /* This is possible if op is under delayed unoptimizing */
 167         if (kprobe_disabled(&op->kp))
 168                 return;
 169
 170         local_irq_save(flags);
 171         if (kprobe_running()) {
 172                 kprobes_inc_nmissed_count(&op->kp);
 173         } else {
 174                 /* Save skipped registers */
 175 #ifdef CONFIG_X86_64
 176                 regs->cs = __KERNEL_CS;
 177 #else
 178                 regs->cs = __KERNEL_CS | get_kernel_rpl();
 179                 regs->gs = 0;
 180 #endif
 181                 regs->ip = (unsigned long)op->kp.addr + INT3_SIZE;
 182                 regs->orig_ax = ~0UL;
 183
 184                 __this_cpu_write(current_kprobe, &op->kp);
 185                 kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 186                 opt_pre_handler(&op->kp, regs);
 187                 __this_cpu_write(current_kprobe, NULL);
 188         }
 189         local_irq_restore(flags);
 190 }
 191 NOKPROBE_SYMBOL(optimized_callback);
 192
 193 static int copy_optimized_instructions(u8 *dest, u8 *src)
 194 {
 195         struct insn insn;
 196         int len = 0, ret;
 197
 198         while (len < RELATIVEJUMP_SIZE) {
 199                 ret = __copy_instruction(dest + len, src + len, &insn);
 200                 if (!ret || !can_boost(&insn, src + len))
 201                         return -EINVAL;
 202                 len += ret;
 203         }
 204         /* Check whether the address range is reserved */
 205         if (ftrace_text_reserved(src, src + len - 1) ||
 206             alternatives_text_reserved(src, src + len - 1) ||
 207             jump_label_text_reserved(src, src + len - 1))
 208                 return -EBUSY;
 209
 210         return len;
 211 }
 212
 213 /* Check whether insn is indirect jump */
 214 static int __insn_is_indirect_jump(struct insn *insn)
 215 {
 216         return ((insn->opcode.bytes[0] == 0xff &&
 217                 (X86_MODRM_REG(insn->modrm.value) & 6) == 4) || /* Jump */
 218                 insn->opcode.bytes[0] == 0xea); /* Segment based jump */
 219 }
 220
 221 /* Check whether insn jumps into specified address range */
 222 static int insn_jump_into_range(struct insn *insn, unsigned long start, int len)
 223 {
 224         unsigned long target = 0;
 225
 226         switch (insn->opcode.bytes[0]) {
 227         case 0xe0:      /* loopne */
 228         case 0xe1:      /* loope */
 229         case 0xe2:      /* loop */
 230         case 0xe3:      /* jcxz */
 231         case 0xe9:      /* near relative jump */
 232         case 0xeb:      /* short relative jump */
 233                 break;
 234         case 0x0f:
 235                 if ((insn->opcode.bytes[1] & 0xf0) == 0x80) /* jcc near */
 236                         break;
 237                 return 0;
 238         default:
 239                 if ((insn->opcode.bytes[0] & 0xf0) == 0x70) /* jcc short */
 240                         break;
 241                 return 0;
 242         }
 243         target = (unsigned long)insn->next_byte + insn->immediate.value;
 244
 245         return (start <= target && target <= start + len);
 246 }
 247
 248 static int insn_is_indirect_jump(struct insn *insn)
 249 {
 250         int ret = __insn_is_indirect_jump(insn);
 251
 252 #ifdef CONFIG_RETPOLINE
 253         /*
 254          * Jump to x86_indirect_thunk_* is treated as an indirect jump.
 255          * Note that even with CONFIG_RETPOLINE=y, the kernel compiled with
 256          * older gcc may use indirect jump. So we add this check instead of
 257          * replace indirect-jump check.
 258          */
 259         if (!ret)
 260                 ret = insn_jump_into_range(insn,
 261                                 (unsigned long)__indirect_thunk_start,
 262                                 (unsigned long)__indirect_thunk_end -
 263                                 (unsigned long)__indirect_thunk_start);
 264 #endif
 265         return ret;
 266 }
 267
 268 /* Decode whole function to ensure any instructions don't jump into target */
 269 static int can_optimize(unsigned long paddr)
 270 {
 271         unsigned long addr, size = 0, offset = 0;
 272         struct insn insn;
 273         kprobe_opcode_t buf[MAX_INSN_SIZE];
 274
 275         /* Lookup symbol including addr */
 276         if (!kallsyms_lookup_size_offset(paddr, &size, &offset))
 277                 return 0;
 278
 279         /*
 280          * Do not optimize in the entry code due to the unstable
 281          * stack handling and registers setup.
 282          */
 283         if (((paddr >= (unsigned long)__entry_text_start) &&
 284              (paddr <  (unsigned long)__entry_text_end)) ||
 285             ((paddr >= (unsigned long)__irqentry_text_start) &&
 286              (paddr <  (unsigned long)__irqentry_text_end)))
 287                 return 0;
 288
 289         /* Check there is enough space for a relative jump. */
 290         if (size - offset < RELATIVEJUMP_SIZE)
 291                 return 0;
 292
 293         /* Decode instructions */
 294         addr = paddr - offset;
 295         while (addr < paddr - offset + size) { /* Decode until function end */
 296                 unsigned long recovered_insn;
 297                 if (search_exception_tables(addr))
 298                         /*
 299                          * Since some fixup code will jumps into this function,
 300                          * we can't optimize kprobe in this function.
 301                          */
 302                         return 0;
 303                 recovered_insn = recover_probed_instruction(buf, addr);
 304                 if (!recovered_insn)
 305                         return 0;
 306                 kernel_insn_init(&insn, (void *)recovered_insn, MAX_INSN_SIZE);
 307                 insn_get_length(&insn);
 308                 /* Another subsystem puts a breakpoint */
 309                 if (insn.opcode.bytes[0] == BREAKPOINT_INSTRUCTION)
 310                         return 0;
 311                 /* Recover address */
 312                 insn.kaddr = (void *)addr;
 313                 insn.next_byte = (void *)(addr + insn.length);
 314                 /* Check any instructions don't jump into target */
 315                 if (insn_is_indirect_jump(&insn) ||
 316                     insn_jump_into_range(&insn, paddr + INT3_SIZE,
 317                                          RELATIVE_ADDR_SIZE))
 318                         return 0;
 319                 addr += insn.length;
 320         }
 321
 322         return 1;
 323 }
 324
 325 /* Check optimized_kprobe can actually be optimized. */
 326 int arch_check_optimized_kprobe(struct optimized_kprobe *op)
 327 {
 328         int i;
 329         struct kprobe *p;
 330
 331         for (i = 1; i < op->optinsn.size; i++) {
 332                 p = get_kprobe(op->kp.addr + i);
 333                 if (p && !kprobe_disarmed(p))
 334                         return -EEXIST;
 335         }
 336
 337         return 0;
 338 }
 339
 340 /* Check the addr is within the optimized instructions. */
 341 int arch_within_optimized_kprobe(struct optimized_kprobe *op,
 342                                  unsigned long addr)
 343 {
 344         return ((unsigned long)op->kp.addr <= addr &&
 345                 (unsigned long)op->kp.addr + op->optinsn.size > addr);
 346 }
 347
 348 /* Free optimized instruction slot */
 349 static
 350 void __arch_remove_optimized_kprobe(struct optimized_kprobe *op, int dirty)
 351 {
 352         if (op->optinsn.insn) {
 353                 free_optinsn_slot(op->optinsn.insn, dirty);
 354                 op->optinsn.insn = NULL;
 355                 op->optinsn.size = 0;
 356         }
 357 }
 358
 359 void arch_remove_optimized_kprobe(struct optimized_kprobe *op)
 360 {
 361         __arch_remove_optimized_kprobe(op, 1);
 362 }
 363
 364 /*
 365  * Copy replacing target instructions
 366  * Target instructions MUST be relocatable (checked inside)
 367  * This is called when new aggr(opt)probe is allocated or reused.
 368  */
 369 int arch_prepare_optimized_kprobe(struct optimized_kprobe *op,
 370                                   struct kprobe *__unused)
 371 {
 372         u8 *buf;
 373         int ret;
 374         long rel;
 375
 376         if (!can_optimize((unsigned long)op->kp.addr))
 377                 return -EILSEQ;
 378
 379         op->optinsn.insn = get_optinsn_slot();
 380         if (!op->optinsn.insn)
 381                 return -ENOMEM;
 382
 383         /*
 384          * Verify if the address gap is in 2GB range, because this uses
 385          * a relative jump.
 386          */
 387         rel = (long)op->optinsn.insn - (long)op->kp.addr + RELATIVEJUMP_SIZE;
 388         if (abs(rel) > 0x7fffffff) {
 389                 __arch_remove_optimized_kprobe(op, 0);
 390                 return -ERANGE;
 391         }
 392
 393         buf = (u8 *)op->optinsn.insn;
 394         set_memory_rw((unsigned long)buf & PAGE_MASK, 1);
 395
 396         /* Copy instructions into the out-of-line buffer */
 397         ret = copy_optimized_instructions(buf + TMPL_END_IDX, op->kp.addr);
 398         if (ret < 0) {
 399                 __arch_remove_optimized_kprobe(op, 0);
 400                 return ret;
 401         }
 402         op->optinsn.size = ret;
 403
 404         /* Copy arch-dep-instance from template */
 405         memcpy(buf, &optprobe_template_entry, TMPL_END_IDX);
 406
 407         /* Set probe information */
 408         synthesize_set_arg1(buf + TMPL_MOVE_IDX, (unsigned long)op);
 409
 410         /* Set probe function call */
 411         synthesize_relcall(buf + TMPL_CALL_IDX, optimized_callback);
 412
 413         /* Set returning jmp instruction at the tail of out-of-line buffer */
 414         synthesize_reljump(buf + TMPL_END_IDX + op->optinsn.size,
 415                            (u8 *)op->kp.addr + op->optinsn.size);
 416
 417         set_memory_ro((unsigned long)buf & PAGE_MASK, 1);
 418
 419         flush_icache_range((unsigned long) buf,
 420                            (unsigned long) buf + TMPL_END_IDX +
 421                            op->optinsn.size + RELATIVEJUMP_SIZE);
 422         return 0;
 423 }
 424
 425 /*
 426  * Replace breakpoints (int3) with relative jumps.
 427  * Caller must call with locking kprobe_mutex and text_mutex.
 428  */
 429 void arch_optimize_kprobes(struct list_head *oplist)
 430 {
 431         struct optimized_kprobe *op, *tmp;
 432         u8 insn_buf[RELATIVEJUMP_SIZE];
 433
 434         list_for_each_entry_safe(op, tmp, oplist, list) {
 435                 s32 rel = (s32)((long)op->optinsn.insn -
 436                         ((long)op->kp.addr + RELATIVEJUMP_SIZE));
 437
 438                 WARN_ON(kprobe_disabled(&op->kp));
 439
 440                 /* Backup instructions which will be replaced by jump address */
 441                 memcpy(op->optinsn.copied_insn, op->kp.addr + INT3_SIZE,
 442                        RELATIVE_ADDR_SIZE);
 443
 444                 insn_buf[0] = RELATIVEJUMP_OPCODE;
 445                 *(s32 *)(&insn_buf[1]) = rel;
 446
 447                 text_poke_bp(op->kp.addr, insn_buf, RELATIVEJUMP_SIZE,
 448                              op->optinsn.insn);
 449
 450                 list_del_init(&op->list);
 451         }
 452 }
 453
 454 /* Replace a relative jump with a breakpoint (int3).  */
 455 void arch_unoptimize_kprobe(struct optimized_kprobe *op)
 456 {
 457         u8 insn_buf[RELATIVEJUMP_SIZE];
 458
 459         /* Set int3 to first byte for kprobes */
 460         insn_buf[0] = BREAKPOINT_INSTRUCTION;
 461         memcpy(insn_buf + 1, op->optinsn.copied_insn, RELATIVE_ADDR_SIZE);
 462         text_poke_bp(op->kp.addr, insn_buf, RELATIVEJUMP_SIZE,
 463                      op->optinsn.insn);
 464 }
 465
 466 /*
 467  * Recover original instructions and breakpoints from relative jumps.
 468  * Caller must call with locking kprobe_mutex.
 469  */
 470 extern void arch_unoptimize_kprobes(struct list_head *oplist,
 471                                     struct list_head *done_list)
 472 {
 473         struct optimized_kprobe *op, *tmp;
 474
 475         list_for_each_entry_safe(op, tmp, oplist, list) {
 476                 arch_unoptimize_kprobe(op);
 477                 list_move(&op->list, done_list);
 478         }
 479 }
 480
 481 int setup_detour_execution(struct kprobe *p, struct pt_regs *regs, int reenter)
 482 {
 483         struct optimized_kprobe *op;
 484
 485         if (p->flags & KPROBE_FLAG_OPTIMIZED) {
 486                 /* This kprobe is really able to run optimized path. */
 487                 op = container_of(p, struct optimized_kprobe, kp);
 488                 /* Detour through copied instructions */
 489                 regs->ip = (unsigned long)op->optinsn.insn + TMPL_END_IDX;
 490                 if (!reenter)
 491                         reset_current_kprobe();
 492                 preempt_enable_no_resched();
 493                 return 1;
 494         }
 495         return 0;
 496 }
 497 NOKPROBE_SYMBOL(setup_detour_execution);