arch/arm64/kernel/probes/decode-insn.c

   1 /*
   2  * arch/arm64/kernel/probes/decode-insn.c
   3  *
   4  * Copyright (C) 2013 Linaro Limited.
   5  *
   6  * This program is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License version 2 as
   8  * published by the Free Software Foundation.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13  * General Public License for more details.
  14  */
  15
  16 #include <linux/kernel.h>
  17 #include <linux/kprobes.h>
  18 #include <linux/module.h>
  19 #include <linux/kallsyms.h>
  20 #include <asm/insn.h>
  21 #include <asm/sections.h>
  22
  23 #include "decode-insn.h"
  24 #include "simulate-insn.h"
  25
  26 static bool __kprobes aarch64_insn_is_steppable(u32 insn)
  27 {
  28         /*
  29          * Branch instructions will write a new value into the PC which is
  30          * likely to be relative to the XOL address and therefore invalid.
  31          * Deliberate generation of an exception during stepping is also not
  32          * currently safe. Lastly, MSR instructions can do any number of nasty
  33          * things we can't handle during single-stepping.
  34          */
  35         if (aarch64_get_insn_class(insn) == AARCH64_INSN_CLS_BR_SYS) {
  36                 if (aarch64_insn_is_branch(insn) ||
  37                     aarch64_insn_is_msr_imm(insn) ||
  38                     aarch64_insn_is_msr_reg(insn) ||
  39                     aarch64_insn_is_exception(insn) ||
  40                     aarch64_insn_is_eret(insn))
  41                         return false;
  42
  43                 /*
  44                  * The MRS instruction may not return a correct value when
  45                  * executing in the single-stepping environment. We do make one
  46                  * exception, for reading the DAIF bits.
  47                  */
  48                 if (aarch64_insn_is_mrs(insn))
  49                         return aarch64_insn_extract_system_reg(insn)
  50                              != AARCH64_INSN_SPCLREG_DAIF;
  51
  52                 /*
  53                  * The HINT instruction is is problematic when single-stepping,
  54                  * except for the NOP case.
  55                  */
  56                 if (aarch64_insn_is_hint(insn))
  57                         return aarch64_insn_is_nop(insn);
  58
  59                 return true;
  60         }
  61
  62         /*
  63          * Instructions which load PC relative literals are not going to work
  64          * when executed from an XOL slot. Instructions doing an exclusive
  65          * load/store are not going to complete successfully when single-step
  66          * exception handling happens in the middle of the sequence.
  67          */
  68         if (aarch64_insn_uses_literal(insn) ||
  69             aarch64_insn_is_exclusive(insn))
  70                 return false;
  71
  72         return true;
  73 }
  74
  75 /* Return:
  76  *   INSN_REJECTED     If instruction is one not allowed to kprobe,
  77  *   INSN_GOOD         If instruction is supported and uses instruction slot,
  78  *   INSN_GOOD_NO_SLOT If instruction is supported but doesn't use its slot.
  79  */
  80 enum probe_insn __kprobes
  81 arm_probe_decode_insn(probe_opcode_t insn, struct arch_probe_insn *api)
  82 {
  83         /*
  84          * Instructions reading or modifying the PC won't work from the XOL
  85          * slot.
  86          */
  87         if (aarch64_insn_is_steppable(insn))
  88                 return INSN_GOOD;
  89
  90         if (aarch64_insn_is_bcond(insn)) {
  91                 api->handler = simulate_b_cond;
  92         } else if (aarch64_insn_is_cbz(insn) ||
  93             aarch64_insn_is_cbnz(insn)) {
  94                 api->handler = simulate_cbz_cbnz;
  95         } else if (aarch64_insn_is_tbz(insn) ||
  96             aarch64_insn_is_tbnz(insn)) {
  97                 api->handler = simulate_tbz_tbnz;
  98         } else if (aarch64_insn_is_adr_adrp(insn)) {
  99                 api->handler = simulate_adr_adrp;
 100         } else if (aarch64_insn_is_b(insn) ||
 101             aarch64_insn_is_bl(insn)) {
 102                 api->handler = simulate_b_bl;
 103         } else if (aarch64_insn_is_br(insn) ||
 104             aarch64_insn_is_blr(insn) ||
 105             aarch64_insn_is_ret(insn)) {
 106                 api->handler = simulate_br_blr_ret;
 107         } else if (aarch64_insn_is_ldr_lit(insn)) {
 108                 api->handler = simulate_ldr_literal;
 109         } else if (aarch64_insn_is_ldrsw_lit(insn)) {
 110                 api->handler = simulate_ldrsw_literal;
 111         } else {
 112                 /*
 113                  * Instruction cannot be stepped out-of-line and we don't
 114                  * (yet) simulate it.
 115                  */
 116                 return INSN_REJECTED;
 117         }
 118
 119         return INSN_GOOD_NO_SLOT;
 120 }
 121
 122 #ifdef CONFIG_KPROBES
 123 static bool __kprobes
 124 is_probed_address_atomic(kprobe_opcode_t *scan_start, kprobe_opcode_t *scan_end)
 125 {
 126         while (scan_start >= scan_end) {
 127                 /*
 128                  * atomic region starts from exclusive load and ends with
 129                  * exclusive store.
 130                  */
 131                 if (aarch64_insn_is_store_ex(le32_to_cpu(*scan_start)))
 132                         return false;
 133                 else if (aarch64_insn_is_load_ex(le32_to_cpu(*scan_start)))
 134                         return true;
 135                 scan_start--;
 136         }
 137
 138         return false;
 139 }
 140
 141 enum probe_insn __kprobes
 142 arm_kprobe_decode_insn(kprobe_opcode_t *addr, struct arch_specific_insn *asi)
 143 {
 144         enum probe_insn decoded;
 145         probe_opcode_t insn = le32_to_cpu(*addr);
 146         probe_opcode_t *scan_end = NULL;
 147         unsigned long size = 0, offset = 0;
 148
 149         /*
 150          * If there's a symbol defined in front of and near enough to
 151          * the probe address assume it is the entry point to this
 152          * code and use it to further limit how far back we search
 153          * when determining if we're in an atomic sequence. If we could
 154          * not find any symbol skip the atomic test altogether as we
 155          * could otherwise end up searching irrelevant text/literals.
 156          * KPROBES depends on KALLSYMS so this last case should never
 157          * happen.
 158          */
 159         if (kallsyms_lookup_size_offset((unsigned long) addr, &size, &offset)) {
 160                 if (offset < (MAX_ATOMIC_CONTEXT_SIZE*sizeof(kprobe_opcode_t)))
 161                         scan_end = addr - (offset / sizeof(kprobe_opcode_t));
 162                 else
 163                         scan_end = addr - MAX_ATOMIC_CONTEXT_SIZE;
 164         }
 165         decoded = arm_probe_decode_insn(insn, &asi->api);
 166
 167         if (decoded != INSN_REJECTED && scan_end)
 168                 if (is_probed_address_atomic(addr - 1, scan_end))
 169                         return INSN_REJECTED;
 170
 171         return decoded;
 172 }
 173 #endif