#include #include namespace vm { emu_t::emu_t(vm::vmctx_t* vm_ctx) : m_vm(vm_ctx) {} emu_t::~emu_t() { if (uc) uc_close(uc); } bool emu_t::init() { uc_err err; if ((err = uc_open(UC_ARCH_X86, UC_MODE_64, &uc))) { std::printf("> uc_open err = %d\n", err); return false; } if ((err = uc_mem_map(uc, STACK_BASE, STACK_SIZE, UC_PROT_ALL))) { std::printf("> uc_mem_map stack err, reason = %d\n", err); return false; } if ((err = uc_mem_map(uc, m_vm->m_module_base, m_vm->m_image_size, UC_PROT_ALL))) { std::printf("> map memory failed, reason = %d\n", err); return false; } if ((err = uc_mem_write(uc, m_vm->m_module_base, reinterpret_cast(m_vm->m_module_base), m_vm->m_image_size))) { std::printf("> failed to write memory... reason = %d\n", err); return false; } if ((err = uc_hook_add(uc, &code_exec_hook, UC_HOOK_CODE, (void*)&vm::emu_t::code_exec_callback, this, m_vm->m_module_base, m_vm->m_module_base + m_vm->m_image_size))) { std::printf("> uc_hook_add error, reason = %d\n", err); return false; } if ((err = uc_hook_add(uc, &int_hook, UC_HOOK_INTR, (void*)&vm::emu_t::int_callback, this, 0ull, 0ull))) { std::printf("> uc_hook_add error, reason = %d\n", err); return false; } if ((err = uc_hook_add(uc, &invalid_mem_hook, UC_HOOK_MEM_READ_UNMAPPED | UC_HOOK_MEM_WRITE_UNMAPPED | UC_HOOK_MEM_FETCH_UNMAPPED, (void*)&vm::emu_t::invalid_mem, this, true, false))) { std::printf("> uc_hook_add error, reason = %d\n", err); return false; } return true; } bool emu_t::emulate(std::uint32_t vmenter_rva, vm::instrs::vrtn_t& vrtn) { uc_err err; vrtn.m_rva = vmenter_rva; auto& blk = vrtn.m_blks.emplace_back(); blk.m_vip = {0ull, 0ull}; blk.m_vm = {m_vm->get_vip(), m_vm->get_vsp()}; cc_blk = &blk; cc_vrtn = &vrtn; cc_trace.m_uc = uc; std::uintptr_t rip = vmenter_rva + m_vm->m_module_base, rsp = STACK_BASE + STACK_SIZE - PAGE_4KB; if ((err = uc_reg_write(uc, UC_X86_REG_RSP, &rsp))) { std::printf("> uc_reg_write error, reason = %d\n", err); return false; } if ((err = uc_reg_write(uc, UC_X86_REG_RIP, &rip))) { std::printf("> uc_reg_write error, reason = %d\n", err); return false; } cc_trace.m_vip = cc_blk->m_vm.vip; cc_trace.m_vsp = cc_blk->m_vm.vsp; std::printf("> beginning execution at = %p\n", rip); if ((err = uc_emu_start(uc, rip, 0ull, 0ull, 0ull))) { std::printf("> error starting emu... reason = %d\n", err); return false; } extract_branch_data(); std::printf("> emulated blk_%p\n\n", cc_blk->m_vip.img_base); // keep track of the emulated blocks... by their addresses... std::vector blk_addrs; blk_addrs.push_back(blk.m_vip.rva + m_vm->m_module_base); // the vector containing the vblk's grows inside of this for loop // thus we cannot use an advanced for loop (which uses itr's)... for (auto idx = 0u; idx < cc_vrtn->m_blks.size(); ++idx) { vm::instrs::vblk_t blk = cc_vrtn->m_blks[idx]; if (blk.branch_type != vm::instrs::vbranch_type::none) { // force the emulation of all branches... for (const auto br : blk.branches) { // only emulate blocks that havent been emulated before... if (std::find(blk_addrs.begin(), blk_addrs.end(), br) != blk_addrs.end()) continue; std::uintptr_t vsp = 0ull; uc_context_restore(uc, blk.m_jmp.ctx); uc_mem_write(uc, STACK_BASE, blk.m_jmp.stack, STACK_SIZE); uc_reg_read(uc, vm::instrs::reg_map[blk.m_vm.vsp], &vsp); // setup new cc_blk... auto& new_blk = vrtn.m_blks.emplace_back(); new_blk.m_vip = {0ull, 0ull}; new_blk.m_vm = {blk.m_jmp.m_vm.vip, blk.m_jmp.m_vm.vsp}; cc_blk = &new_blk; // emulate the branch... uc_mem_write(uc, vsp, &br, sizeof br); std::printf("> beginning execution at = %p\n", blk.m_jmp.rip); if ((err = uc_emu_start(uc, blk.m_jmp.rip, 0ull, 0ull, 0ull))) { std::printf("> error starting emu... reason = %d\n", err); return false; } extract_branch_data(); std::printf("> emulated blk_%p\n", cc_blk->m_vip.img_base); } } } // free all virtual code block virtual jmp information... std::for_each(vrtn.m_blks.begin(), vrtn.m_blks.end(), [&](vm::instrs::vblk_t& blk) { if (blk.m_jmp.ctx) uc_context_free(blk.m_jmp.ctx); if (blk.m_jmp.stack) delete[] blk.m_jmp.stack; }); return true; } void emu_t::extract_branch_data() { auto br_info = could_have_jcc(cc_blk->m_vinstrs); if (br_info.has_value()) { auto [br1, br2] = br_info.value(); // convert to absolute addresses... br1 -= m_vm->m_image_base; br2 -= m_vm->m_image_base; br1 += m_vm->m_module_base; br2 += m_vm->m_module_base; auto br1_legit = legit_branch(*cc_blk, br1); auto br2_legit = legit_branch(*cc_blk, br2); std::printf("> br1 legit: %d, br2 legit: %d\n", br1_legit, br2_legit); if (br1_legit && br2_legit) { std::printf("> virtual jcc uncovered... br1 = %p, br2 = %p\n", br1, br2); cc_blk->branch_type = vm::instrs::vbranch_type::jcc; cc_blk->branches.push_back(br1); cc_blk->branches.push_back(br2); } else if (br1_legit || br2_legit) { std::printf("> absolute virtual jmp uncovered... branch = %p\n", br1_legit ? br1 : br2); cc_blk->branch_type = vm::instrs::vbranch_type::absolute; cc_blk->branches.push_back(br1_legit ? br1 : br2); } else { std::printf("> unknown branch type...\n"); } } else if (cc_blk->m_vinstrs.back().mnemonic == vm::instrs::mnemonic_t::vmexit) { cc_blk->branch_type = vm::instrs::vbranch_type::none; } else if (cc_blk->m_vinstrs.back().mnemonic == vm::instrs::mnemonic_t::jmp) { // see if there is 1 lconst... if (auto last_lconst = std::find_if( cc_blk->m_vinstrs.rbegin(), cc_blk->m_vinstrs.rend(), [&](vm::instrs::vinstr_t& vinstr) -> bool { return vinstr.mnemonic == vm::instrs::mnemonic_t::lconst && vinstr.imm.size == 64; }); last_lconst != cc_blk->m_vinstrs.rend()) { const auto imm_img_based = last_lconst->imm.val; const auto imm_mod_based = (imm_img_based - m_vm->m_image_base) + m_vm->m_module_base; // check to see if the imm is inside of the module... and if the ptr lands // inside of an executable section... then lastly check to see if its a // legit branch or not... if (imm_img_based >= m_vm->m_image_base && imm_img_based < m_vm->m_image_base + m_vm->m_image_size && vm::utils::scn::executable(m_vm->m_module_base, imm_mod_based)) { cc_blk->branches.push_back(imm_mod_based); cc_blk->branch_type = vm::instrs::vbranch_type::absolute; } } else { std::printf("> jump table detected... review instruction stream...\n"); uc_emu_stop(uc); } } } void emu_t::int_callback(uc_engine* uc, std::uint32_t intno, emu_t* obj) { uc_err err; std::uintptr_t rip = 0ull; static thread_local zydis_decoded_instr_t instr; if ((err = uc_reg_read(uc, UC_X86_REG_RIP, &rip))) { std::printf("> failed to read rip... reason = %d\n", err); return; } if (!ZYAN_SUCCESS(ZydisDecoderDecodeBuffer(vm::utils::g_decoder.get(), reinterpret_cast(rip), PAGE_4KB, &instr))) { std::printf("> failed to decode instruction at = 0x%p\n", rip); if ((err = uc_emu_stop(uc))) { std::printf("> failed to stop emulation, exiting... reason = %d\n", err); exit(0); } return; } // advance rip over the instruction that caused the exception... this is // usually a division by 0... rip += instr.length; if ((err = uc_reg_write(uc, UC_X86_REG_RIP, &rip))) { std::printf("> failed to write rip... reason = %d\n", err); return; } } bool emu_t::branch_pred_spec_exec(uc_engine* uc, uint64_t address, uint32_t size, emu_t* obj) { uc_err err; static thread_local zydis_decoded_instr_t instr; if (!ZYAN_SUCCESS(ZydisDecoderDecodeBuffer(vm::utils::g_decoder.get(), reinterpret_cast(address), PAGE_4KB, &instr))) { std::printf("> failed to decode instruction at = 0x%p\n", address); if ((err = uc_emu_stop(uc))) { std::printf("> failed to stop emulation, exiting... reason = %d\n", err); exit(0); } return false; } if (instr.mnemonic == ZYDIS_MNEMONIC_INVALID) return false; uc_context* ctx; uc_context_alloc(uc, &ctx); uc_context_save(uc, ctx); // if this is the first instruction of this handler then save the stack... if (!obj->cc_trace.m_instrs.size()) { obj->cc_trace.m_stack = new std::uint8_t[STACK_SIZE]; uc_mem_read(uc, STACK_BASE, obj->cc_trace.m_stack, STACK_SIZE); } obj->cc_trace.m_instrs.push_back({instr, ctx}); // RET or JMP REG means the end of a vm handler... if (instr.mnemonic == ZYDIS_MNEMONIC_RET || (instr.mnemonic == ZYDIS_MNEMONIC_JMP && instr.operands[0].type == ZYDIS_OPERAND_TYPE_REGISTER)) { // deobfuscate the instruction stream before profiling... // makes it easier for profiles to be correct... vm::instrs::deobfuscate(obj->cc_trace); // find the last MOV REG, DWORD PTR [VIP] in the instruction stream, then // remove any instructions from this instruction to the JMP/RET... const auto rva_fetch = std::find_if( obj->cc_trace.m_instrs.rbegin(), obj->cc_trace.m_instrs.rend(), [& vip = obj->cc_trace.m_vip]( const vm::instrs::emu_instr_t& instr) -> bool { const auto& i = instr.m_instr; return i.mnemonic == ZYDIS_MNEMONIC_MOV && i.operands[0].type == ZYDIS_OPERAND_TYPE_REGISTER && i.operands[1].type == ZYDIS_OPERAND_TYPE_MEMORY && i.operands[1].mem.base == vip && i.operands[1].size == 32; }); if (rva_fetch != obj->cc_trace.m_instrs.rend()) obj->cc_trace.m_instrs.erase((rva_fetch + 1).base(), obj->cc_trace.m_instrs.end()); const auto vinstr = vm::instrs::determine(obj->cc_trace); // -- free the trace since we will start a new one... std::for_each(obj->cc_trace.m_instrs.begin(), obj->cc_trace.m_instrs.end(), [&](const vm::instrs::emu_instr_t& instr) { uc_context_free(instr.m_cpu); }); delete[] obj->cc_trace.m_stack; obj->cc_trace.m_instrs.clear(); if (vinstr.mnemonic != vm::instrs::mnemonic_t::jmp) { if (vinstr.mnemonic != vm::instrs::mnemonic_t::sreg) uc_emu_stop(uc); if (!vinstr.imm.has_imm) uc_emu_stop(uc); if (vinstr.imm.size != 8 || vinstr.imm.val > 8 * VIRTUAL_REGISTER_COUNT) uc_emu_stop(uc); // -- stop after 10 legit SREG's... if (++obj->m_sreg_cnt == 10) uc_emu_stop(uc); } } return true; } bool emu_t::code_exec_callback(uc_engine* uc, uint64_t address, uint32_t size, emu_t* obj) { uc_err err; static thread_local zydis_decoded_instr_t instr; if (!ZYAN_SUCCESS(ZydisDecoderDecodeBuffer(vm::utils::g_decoder.get(), reinterpret_cast(address), PAGE_4KB, &instr))) { std::printf("> failed to decode instruction at = 0x%p\n", address); if ((err = uc_emu_stop(uc))) { std::printf("> failed to stop emulation, exiting... reason = %d\n", err); exit(0); } return false; } if (instr.mnemonic == ZYDIS_MNEMONIC_INVALID) return false; uc_context* ctx; uc_context_alloc(uc, &ctx); uc_context_save(uc, ctx); // if this is the first instruction of this handler then save the stack... if (!obj->cc_trace.m_instrs.size()) { obj->cc_trace.m_stack = new std::uint8_t[STACK_SIZE]; obj->cc_trace.m_begin = address; uc_mem_read(uc, STACK_BASE, obj->cc_trace.m_stack, STACK_SIZE); } obj->cc_trace.m_instrs.push_back({instr, ctx}); // RET or JMP REG means the end of a vm handler... if (instr.mnemonic == ZYDIS_MNEMONIC_RET || (instr.mnemonic == ZYDIS_MNEMONIC_JMP && instr.operands[0].type == ZYDIS_OPERAND_TYPE_REGISTER)) { // deobfuscate the instruction stream before profiling... // makes it easier for profiles to be correct... vm::instrs::deobfuscate(obj->cc_trace); // find the last MOV REG, DWORD PTR [VIP] in the instruction stream, then // remove any instructions from this instruction to the JMP/RET... const auto rva_fetch = std::find_if( obj->cc_trace.m_instrs.rbegin(), obj->cc_trace.m_instrs.rend(), [& vip = obj->cc_trace.m_vip]( const vm::instrs::emu_instr_t& instr) -> bool { const auto& i = instr.m_instr; return i.mnemonic == ZYDIS_MNEMONIC_MOV && i.operands[0].type == ZYDIS_OPERAND_TYPE_REGISTER && i.operands[1].type == ZYDIS_OPERAND_TYPE_MEMORY && i.operands[1].mem.base == vip && i.operands[1].size == 32; }); if (rva_fetch != obj->cc_trace.m_instrs.rend()) obj->cc_trace.m_instrs.erase((rva_fetch + 1).base(), obj->cc_trace.m_instrs.end()); // set the virtual code block vip address information... if (!obj->cc_blk->m_vip.rva || !obj->cc_blk->m_vip.img_base) { // find the last write done to VIP... auto vip_write = std::find_if( obj->cc_trace.m_instrs.rbegin(), obj->cc_trace.m_instrs.rend(), [& vip = obj->cc_trace.m_vip](vm::instrs::emu_instr_t& instr) -> bool { const auto& i = instr.m_instr; return i.operands[0].type == ZYDIS_OPERAND_TYPE_REGISTER && i.operands[0].reg.value == vip; }); uc_context* backup; uc_context_alloc(uc, &backup); uc_context_save(uc, backup); uc_context_restore(uc, (--vip_write)->m_cpu); std::uintptr_t vip_addr = 0ull; uc_reg_read(uc, vm::instrs::reg_map[obj->cc_trace.m_vip], &vip_addr); obj->cc_blk->m_vip.rva = vip_addr -= obj->m_vm->m_module_base; obj->cc_blk->m_vip.img_base = vip_addr += obj->m_vm->m_image_base; uc_context_restore(uc, backup); uc_context_free(backup); } else { const auto vinstr = vm::instrs::determine(obj->cc_trace); if (vinstr.mnemonic != vm::instrs::mnemonic_t::unknown) { if (vinstr.imm.has_imm) std::printf("> %s %p\n", vm::instrs::get_profile(vinstr.mnemonic)->name.c_str(), vinstr.imm.val); else std::printf("> %s\n", vm::instrs::get_profile(vinstr.mnemonic)->name.c_str()); } else { zydis_rtn_t inst_stream; std::for_each(obj->cc_trace.m_instrs.begin(), obj->cc_trace.m_instrs.end(), [&](vm::instrs::emu_instr_t& instr) { inst_stream.push_back({instr.m_instr}); }); std::printf( "> err: please define the following vm handler (at = %p):\n", (obj->cc_trace.m_begin - obj->m_vm->m_module_base) + obj->m_vm->m_image_base); vm::utils::print(inst_stream); uc_emu_stop(uc); return false; } if (obj->cc_blk->m_vinstrs.size()) { if (vinstr.mnemonic == vm::instrs::mnemonic_t::jmp) { uc_context *backup, *copy; // backup current unicorn-engine context... uc_context_alloc(uc, &backup); uc_context_alloc(uc, ©); uc_context_save(uc, backup); // make a copy of the first cpu context of the jmp handler... uc_context_restore(uc, obj->cc_trace.m_instrs.begin()->m_cpu); uc_context_save(uc, copy); // restore the unicorn-engine context... also free the backup... uc_context_restore(uc, backup); uc_context_free(backup); // set current code block virtual jmp instruction information... obj->cc_blk->m_jmp.ctx = copy; obj->cc_blk->m_jmp.rip = obj->cc_trace.m_begin; obj->cc_blk->m_jmp.stack = new std::uint8_t[STACK_SIZE]; obj->cc_blk->m_jmp.m_vm = {obj->cc_trace.m_vip, obj->cc_trace.m_vsp}; std::memcpy(obj->cc_blk->m_jmp.stack, obj->cc_trace.m_stack, STACK_SIZE); } if (vinstr.mnemonic == vm::instrs::mnemonic_t::jmp || vinstr.mnemonic == vm::instrs::mnemonic_t::vmexit) uc_emu_stop(obj->uc); } obj->cc_blk->m_vinstrs.push_back(vinstr); } // -- free the trace since we will start a new one... std::for_each(obj->cc_trace.m_instrs.begin(), obj->cc_trace.m_instrs.end(), [&](const vm::instrs::emu_instr_t& instr) { uc_context_free(instr.m_cpu); }); delete[] obj->cc_trace.m_stack; obj->cc_trace.m_instrs.clear(); } return true; } void emu_t::invalid_mem(uc_engine* uc, uc_mem_type type, uint64_t address, int size, int64_t value, emu_t* obj) { switch (type) { case UC_MEM_READ_UNMAPPED: { uc_mem_map(uc, address & ~0xFFFull, PAGE_4KB, UC_PROT_ALL); std::printf(">>> reading invalid memory at address = %p, size = 0x%x\n", address, size); break; } case UC_MEM_WRITE_UNMAPPED: { uc_mem_map(uc, address & ~0xFFFull, PAGE_4KB, UC_PROT_ALL); std::printf( ">>> writing invalid memory at address = %p, size = 0x%x, val = " "0x%x\n", address, size, value); break; } case UC_MEM_FETCH_UNMAPPED: { std::printf(">>> fetching invalid instructions at address = %p\n", address); break; } default: break; } } bool emu_t::legit_branch(vm::instrs::vblk_t& vblk, std::uintptr_t branch_addr) { // remove normal execution callback... uc_hook_del(uc, code_exec_hook); // add branch pred hook... uc_hook_add(uc, &branch_pred_hook, UC_HOOK_CODE, (void*)&vm::emu_t::branch_pred_spec_exec, this, m_vm->m_module_base, m_vm->m_module_base + m_vm->m_image_size); // make a backup of the current emulation state... uc_context* backup; uc_context_alloc(uc, &backup); uc_context_save(uc, backup); std::uint8_t* stack = new std::uint8_t[STACK_SIZE]; uc_mem_read(uc, STACK_BASE, stack, STACK_SIZE); // restore cpu and stack back to the virtual jump handler... uc_context_restore(uc, vblk.m_jmp.ctx); uc_mem_write(uc, STACK_BASE, vblk.m_jmp.stack, STACK_SIZE); // force the virtual machine to try and emulate the branch address... std::uintptr_t vsp = 0ull, rip = 0ull; uc_reg_read(uc, UC_X86_REG_RIP, &rip); uc_reg_read(uc, vm::instrs::reg_map[vblk.m_vm.vsp], &vsp); uc_mem_write(uc, vsp, &branch_addr, sizeof branch_addr); m_sreg_cnt = 0u; uc_emu_start(uc, rip, 0ull, 0ull, 0ull); // restore original cpu and stack... uc_mem_write(uc, STACK_BASE, stack, STACK_SIZE); uc_context_restore(uc, backup); uc_context_free(backup); delete[] stack; // add normal execution callback back... uc_hook_del(uc, branch_pred_hook); uc_hook_add(uc, &code_exec_hook, UC_HOOK_CODE, (void*)&vm::emu_t::code_exec_callback, this, m_vm->m_module_base, m_vm->m_module_base + m_vm->m_image_size); // we will consider this a legit branch if there is at least 10 // SREG instructions... return m_sreg_cnt == 10; } std::optional> emu_t::could_have_jcc( std::vector& vinstrs) { if (vinstrs.back().mnemonic == vm::instrs::mnemonic_t::vmexit) return {}; // check to see if there is at least 3 LCONST %i64's if (std::accumulate( vinstrs.begin(), vinstrs.end(), 0u, [&](std::uint32_t val, vm::instrs::vinstr_t& v) -> std::uint32_t { return v.mnemonic == vm::instrs::mnemonic_t::lconst && v.imm.size == 64 ? ++val : val; }) < 3) return {}; // extract the lconst64's out of the virtual instruction stream... static const auto lconst64_chk = [&](vm::instrs::vinstr_t& v) -> bool { return v.mnemonic == vm::instrs::mnemonic_t::lconst && v.imm.size == 64; }; const auto lconst1 = std::find_if(vinstrs.rbegin(), vinstrs.rend(), lconst64_chk); if (lconst1 == vinstrs.rend()) return {}; const auto lconst2 = std::find_if(lconst1 + 1, vinstrs.rend(), lconst64_chk); if (lconst2 == vinstrs.rend()) return {}; // check to see if the imm val is inside of the image... if (lconst1->imm.val > m_vm->m_image_base + m_vm->m_image_size || lconst1->imm.val < m_vm->m_image_base || lconst2->imm.val > m_vm->m_image_base + m_vm->m_image_size || lconst2->imm.val < m_vm->m_image_base) return {}; // check to see if the imm's points to something inside of an executable // section... if (!vm::utils::scn::executable( m_vm->m_module_base, (lconst1->imm.val - m_vm->m_image_base) + m_vm->m_module_base) || !vm::utils::scn::executable( m_vm->m_module_base, (lconst2->imm.val - m_vm->m_image_base) + m_vm->m_module_base)) return {}; return {{lconst1->imm.val, lconst2->imm.val}}; } } // namespace vm