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