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

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * arch/arm64/kernel/probes/decode-insn.c
   4  *
   5  * Copyright (C) 2013 Linaro Limited.
   6  */
   7
   8 #include <linux/kernel.h>
   9 #include <linux/kprobes.h>
  10 #include <linux/module.h>
  11 #include <linux/kallsyms.h>
  12 #include <asm/insn.h>
  13 #include <asm/sections.h>
  14
  15 #include "decode-insn.h"
  16 #include "simulate-insn.h"
  17
  18 static bool __kprobes aarch64_insn_is_steppable(u32 insn)
  19 {
  20         /*
  21          * Branch instructions will write a new value into the PC which is
  22          * likely to be relative to the XOL address and therefore invalid.
  23          * Deliberate generation of an exception during stepping is also not
  24          * currently safe. Lastly, MSR instructions can do any number of nasty
  25          * things we can't handle during single-stepping.
  26          */
  27         if (aarch64_get_insn_class(insn) == AARCH64_INSN_CLS_BR_SYS) {
  28                 if (aarch64_insn_is_branch(insn) ||
  29                     aarch64_insn_is_msr_imm(insn) ||
  30                     aarch64_insn_is_msr_reg(insn) ||
  31                     aarch64_insn_is_exception(insn) ||
  32                     aarch64_insn_is_eret(insn) ||
  33                     aarch64_insn_is_eret_auth(insn))
  34                         return false;
  35
  36                 /*
  37                  * The MRS instruction may not return a correct value when
  38                  * executing in the single-stepping environment. We do make one
  39                  * exception, for reading the DAIF bits.
  40                  */
  41                 if (aarch64_insn_is_mrs(insn))
  42                         return aarch64_insn_extract_system_reg(insn)
  43                              != AARCH64_INSN_SPCLREG_DAIF;
  44
  45                 /*
  46                  * The HINT instruction is steppable only if it is in whitelist
  47                  * and the rest of other such instructions are blocked for
  48                  * single stepping as they may cause exception or other
  49                  * unintended behaviour.
  50                  */
  51                 if (aarch64_insn_is_hint(insn))
  52                         return aarch64_insn_is_steppable_hint(insn);
  53
  54                 return true;
  55         }
  56
  57         /*
  58          * Instructions which load PC relative literals are not going to work
  59          * when executed from an XOL slot. Instructions doing an exclusive
  60          * load/store are not going to complete successfully when single-step
  61          * exception handling happens in the middle of the sequence.
  62          */
  63         if (aarch64_insn_uses_literal(insn) ||
  64             aarch64_insn_is_exclusive(insn))
  65                 return false;
  66
  67         return true;
  68 }
  69
  70 /* Return:
  71  *   INSN_REJECTED     If instruction is one not allowed to kprobe,
  72  *   INSN_GOOD         If instruction is supported and uses instruction slot,
  73  *   INSN_GOOD_NO_SLOT If instruction is supported but doesn't use its slot.
  74  */
  75 enum probe_insn __kprobes
  76 arm_probe_decode_insn(probe_opcode_t insn, struct arch_probe_insn *api)
  77 {
  78         /*
  79          * Instructions reading or modifying the PC won't work from the XOL
  80          * slot.
  81          */
  82         if (aarch64_insn_is_steppable(insn))
  83                 return INSN_GOOD;
  84
  85         if (aarch64_insn_is_bcond(insn)) {
  86                 api->handler = simulate_b_cond;
  87         } else if (aarch64_insn_is_cbz(insn) ||
  88             aarch64_insn_is_cbnz(insn)) {
  89                 api->handler = simulate_cbz_cbnz;
  90         } else if (aarch64_insn_is_tbz(insn) ||
  91             aarch64_insn_is_tbnz(insn)) {
  92                 api->handler = simulate_tbz_tbnz;
  93         } else if (aarch64_insn_is_adr_adrp(insn)) {
  94                 api->handler = simulate_adr_adrp;
  95         } else if (aarch64_insn_is_b(insn) ||
  96             aarch64_insn_is_bl(insn)) {
  97                 api->handler = simulate_b_bl;
  98         } else if (aarch64_insn_is_br(insn) ||
  99             aarch64_insn_is_blr(insn) ||
 100             aarch64_insn_is_ret(insn)) {
 101                 api->handler = simulate_br_blr_ret;
 102         } else if (aarch64_insn_is_ldr_lit(insn)) {
 103                 api->handler = simulate_ldr_literal;
 104         } else if (aarch64_insn_is_ldrsw_lit(insn)) {
 105                 api->handler = simulate_ldrsw_literal;
 106         } else {
 107                 /*
 108                  * Instruction cannot be stepped out-of-line and we don't
 109                  * (yet) simulate it.
 110                  */
 111                 return INSN_REJECTED;
 112         }
 113
 114         return INSN_GOOD_NO_SLOT;
 115 }
 116
 117 #ifdef CONFIG_KPROBES
 118 static bool __kprobes
 119 is_probed_address_atomic(kprobe_opcode_t *scan_start, kprobe_opcode_t *scan_end)
 120 {
 121         while (scan_start >= scan_end) {
 122                 /*
 123                  * atomic region starts from exclusive load and ends with
 124                  * exclusive store.
 125                  */
 126                 if (aarch64_insn_is_store_ex(le32_to_cpu(*scan_start)))
 127                         return false;
 128                 else if (aarch64_insn_is_load_ex(le32_to_cpu(*scan_start)))
 129                         return true;
 130                 scan_start--;
 131         }
 132
 133         return false;
 134 }
 135
 136 enum probe_insn __kprobes
 137 arm_kprobe_decode_insn(kprobe_opcode_t *addr, struct arch_specific_insn *asi)
 138 {
 139         enum probe_insn decoded;
 140         probe_opcode_t insn = le32_to_cpu(*addr);
 141         probe_opcode_t *scan_end = NULL;
 142         unsigned long size = 0, offset = 0;
 143
 144         /*
 145          * If there's a symbol defined in front of and near enough to
 146          * the probe address assume it is the entry point to this
 147          * code and use it to further limit how far back we search
 148          * when determining if we're in an atomic sequence. If we could
 149          * not find any symbol skip the atomic test altogether as we
 150          * could otherwise end up searching irrelevant text/literals.
 151          * KPROBES depends on KALLSYMS so this last case should never
 152          * happen.
 153          */
 154         if (kallsyms_lookup_size_offset((unsigned long) addr, &size, &offset)) {
 155                 if (offset < (MAX_ATOMIC_CONTEXT_SIZE*sizeof(kprobe_opcode_t)))
 156                         scan_end = addr - (offset / sizeof(kprobe_opcode_t));
 157                 else
 158                         scan_end = addr - MAX_ATOMIC_CONTEXT_SIZE;
 159         }
 160         decoded = arm_probe_decode_insn(insn, &asi->api);
 161
 162         if (decoded != INSN_REJECTED && scan_end)
 163                 if (is_probed_address_atomic(addr - 1, scan_end))
 164                         return INSN_REJECTED;
 165
 166         return decoded;
 167 }
 168 #endif