/* * arch/arm64/kernel/probes/decode-insn.c * * Copyright (C) 2013 Linaro Limited. * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License version 2 as * published by the Free Software Foundation. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU * General Public License for more details. */ #include <linux/kernel.h> #include <linux/kprobes.h> #include <linux/module.h> #include <linux/kallsyms.h> #include <asm/insn.h> #include <asm/sections.h> #include "decode-insn.h" #include "simulate-insn.h" static bool __kprobes aarch64_insn_is_steppable(u32 insn) { /* * Branch instructions will write a new value into the PC which is * likely to be relative to the XOL address and therefore invalid. * Deliberate generation of an exception during stepping is also not * currently safe. Lastly, MSR instructions can do any number of nasty * things we can't handle during single-stepping. */ if (aarch64_get_insn_class(insn) == AARCH64_INSN_CLS_BR_SYS) { if (aarch64_insn_is_branch(insn) || aarch64_insn_is_msr_imm(insn) || aarch64_insn_is_msr_reg(insn) || aarch64_insn_is_exception(insn) || aarch64_insn_is_eret(insn)) return false; /* * The MRS instruction may not return a correct value when * executing in the single-stepping environment. We do make one * exception, for reading the DAIF bits. */ if (aarch64_insn_is_mrs(insn)) return aarch64_insn_extract_system_reg(insn) != AARCH64_INSN_SPCLREG_DAIF; /* * The HINT instruction is is problematic when single-stepping, * except for the NOP case. */ if (aarch64_insn_is_hint(insn)) return aarch64_insn_is_nop(insn); return true; } /* * Instructions which load PC relative literals are not going to work * when executed from an XOL slot. Instructions doing an exclusive * load/store are not going to complete successfully when single-step * exception handling happens in the middle of the sequence. */ if (aarch64_insn_uses_literal(insn) || aarch64_insn_is_exclusive(insn)) return false; return true; } /* Return: * INSN_REJECTED If instruction is one not allowed to kprobe, * INSN_GOOD If instruction is supported and uses instruction slot, * INSN_GOOD_NO_SLOT If instruction is supported but doesn't use its slot. */ enum probe_insn __kprobes arm_probe_decode_insn(probe_opcode_t insn, struct arch_probe_insn *api) { /* * Instructions reading or modifying the PC won't work from the XOL * slot. */ if (aarch64_insn_is_steppable(insn)) return INSN_GOOD; if (aarch64_insn_is_bcond(insn)) { api->handler = simulate_b_cond; } else if (aarch64_insn_is_cbz(insn) || aarch64_insn_is_cbnz(insn)) { api->handler = simulate_cbz_cbnz; } else if (aarch64_insn_is_tbz(insn) || aarch64_insn_is_tbnz(insn)) { api->handler = simulate_tbz_tbnz; } else if (aarch64_insn_is_adr_adrp(insn)) { api->handler = simulate_adr_adrp; } else if (aarch64_insn_is_b(insn) || aarch64_insn_is_bl(insn)) { api->handler = simulate_b_bl; } else if (aarch64_insn_is_br(insn) || aarch64_insn_is_blr(insn) || aarch64_insn_is_ret(insn)) { api->handler = simulate_br_blr_ret; } else if (aarch64_insn_is_ldr_lit(insn)) { api->handler = simulate_ldr_literal; } else if (aarch64_insn_is_ldrsw_lit(insn)) { api->handler = simulate_ldrsw_literal; } else { /* * Instruction cannot be stepped out-of-line and we don't * (yet) simulate it. */ return INSN_REJECTED; } return INSN_GOOD_NO_SLOT; } #ifdef CONFIG_KPROBES static bool __kprobes is_probed_address_atomic(kprobe_opcode_t *scan_start, kprobe_opcode_t *scan_end) { while (scan_start >= scan_end) { /* * atomic region starts from exclusive load and ends with * exclusive store. */ if (aarch64_insn_is_store_ex(le32_to_cpu(*scan_start))) return false; else if (aarch64_insn_is_load_ex(le32_to_cpu(*scan_start))) return true; scan_start--; } return false; } enum probe_insn __kprobes arm_kprobe_decode_insn(kprobe_opcode_t *addr, struct arch_specific_insn *asi) { enum probe_insn decoded; probe_opcode_t insn = le32_to_cpu(*addr); probe_opcode_t *scan_end = NULL; unsigned long size = 0, offset = 0; /* * If there's a symbol defined in front of and near enough to * the probe address assume it is the entry point to this * code and use it to further limit how far back we search * when determining if we're in an atomic sequence. If we could * not find any symbol skip the atomic test altogether as we * could otherwise end up searching irrelevant text/literals. * KPROBES depends on KALLSYMS so this last case should never * happen. */ if (kallsyms_lookup_size_offset((unsigned long) addr, &size, &offset)) { if (offset < (MAX_ATOMIC_CONTEXT_SIZE*sizeof(kprobe_opcode_t))) scan_end = addr - (offset / sizeof(kprobe_opcode_t)); else scan_end = addr - MAX_ATOMIC_CONTEXT_SIZE; } decoded = arm_probe_decode_insn(insn, &asi->api); if (decoded != INSN_REJECTED && scan_end) if (is_probed_address_atomic(addr - 1, scan_end)) return INSN_REJECTED; return decoded; } #endif