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