From 4918ed0a3828c6cee430846848edbe3fa23a691a Mon Sep 17 00:00:00 2001 From: _xeroxz Date: Fri, 7 Jan 2022 15:39:55 -0800 Subject: [PATCH] re-writing branch emulation so its not stinky code --- deps/vmprofiler | 2 +- include/vmemu_t.hpp | 7 -- src/vmemu_t.cpp | 188 +++++++++++++++++++++----------------------- 3 files changed, 92 insertions(+), 105 deletions(-) diff --git a/deps/vmprofiler b/deps/vmprofiler index 322a8bc..b88c7b9 160000 --- a/deps/vmprofiler +++ b/deps/vmprofiler @@ -1 +1 @@ -Subproject commit 322a8bcf97d47a6d792c97d803429303106958da +Subproject commit b88c7b9321ea64989666ac19534d425b40369c6f diff --git a/include/vmemu_t.hpp b/include/vmemu_t.hpp index 1678916..72666b9 100644 --- a/include/vmemu_t.hpp +++ b/include/vmemu_t.hpp @@ -23,7 +23,6 @@ class emu_t { private: uc_engine* uc; const vm::vmctx_t* m_vm; - zydis_reg_t vip, vsp; /// /// used in branch_pred_spec_exec to count legit SREG virtual instructions... @@ -125,11 +124,5 @@ class emu_t { /// /// bool legit_branch(vm::instrs::vblk_t& vblk, std::uintptr_t branch_addr); - - void emulate_branch(uc_context* ctx, - std::uint8_t* stack, - std::uintptr_t branch_addr, - zydis_reg_t vsp, - vm::instrs::vblk_t& vblk); }; } // namespace vm diff --git a/src/vmemu_t.cpp b/src/vmemu_t.cpp index db7c562..181e6a3 100644 --- a/src/vmemu_t.cpp +++ b/src/vmemu_t.cpp @@ -1,11 +1,7 @@ #include namespace vm { -emu_t::emu_t(vm::vmctx_t* vm_ctx) - : m_vm(vm_ctx), - vip(vm_ctx->get_vip()), - vsp(vm_ctx->get_vsp()), - m_sreg_cnt(0u) {} +emu_t::emu_t(vm::vmctx_t* vm_ctx) : m_vm(vm_ctx) {} emu_t::~emu_t() { if (uc) @@ -64,6 +60,16 @@ bool emu_t::init() { 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; @@ -77,17 +83,8 @@ bool emu_t::emulate(std::uint32_t vmenter_rva, vm::instrs::vrtn_t& vrtn) { return false; } - cc_trace.m_uc = uc; - cc_trace.m_vip = vip; - cc_trace.m_vsp = vsp; - vrtn.m_rva = vmenter_rva; - - vm::instrs::vblk_t blk; - blk.m_vip = {0ull, 0ull}; - blk.m_vm = {vip, vsp}; - - cc_blk = &blk; - cc_vrtn = &vrtn; + 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))) { @@ -95,73 +92,67 @@ bool emu_t::emulate(std::uint32_t vmenter_rva, vm::instrs::vrtn_t& vrtn) { return false; } - auto res = could_have_jcc(blk.m_vinstrs); - std::printf("> blk_%p, number of virtual instructions = %d\n", - blk.m_vip.img_base, blk.m_vinstrs.size()); - - if (res.has_value()) { - const auto [b1, b2] = res.value(); - auto b1_legit = - legit_branch(blk, (b1 - m_vm->m_image_base) + m_vm->m_module_base); - auto b2_legit = - legit_branch(blk, (b2 - m_vm->m_image_base) + m_vm->m_module_base); - - if (b1_legit && b2_legit) { - blk.branches.push_back(b1); - blk.branches.push_back(b2); - blk.branch_type = vm::instrs::vbranch_type::jcc; - std::printf("> code block has jcc, b1 = %p, b2 = %p\n", b1, b2); - } else { - uc_context* backup; - std::uint8_t* stack = new std::uint8_t[STACK_SIZE]; - uc_mem_read(uc, STACK_BASE, stack, STACK_SIZE); - uc_context_alloc(uc, &backup); - uc_context_save(uc, backup); - uc_context_restore(uc, blk.m_jmp.ctx); + auto br_info = could_have_jcc(cc_blk->m_vinstrs); + if (br_info.has_value()) { + auto [br1, br2] = br_info.value(); - std::uintptr_t vsp_ptr = 0ull, branch_addr = 0ull; - uc_reg_read(uc, vm::instrs::reg_map[blk.m_vm.vsp], &vsp_ptr); - uc_mem_read(uc, vsp_ptr, &branch_addr, sizeof branch_addr); + // 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; - uc_context_restore(uc, backup); - uc_context_free(backup); - uc_mem_write(uc, STACK_BASE, stack, STACK_SIZE); - delete stack; - - blk.branches.push_back(branch_addr); - blk.branch_type = vm::instrs::vbranch_type::absolute; - std::printf("> code block has absolute jmp, b1 = %p\n", branch_addr); - } + 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); } - return true; -} -void emu_t::emulate_branch(uc_context* ctx, - std::uint8_t* stack, - std::uintptr_t branch_addr, - zydis_reg_t vsp, - vm::instrs::vblk_t& vblk) { - uc_context* backup; - std::uint8_t* stack_backup = new std::uint8_t[STACK_SIZE]; - std::uintptr_t vsp_addr = 0ull, rip = 0ull; + // keep track of the emulated blocks... by their addresses... + std::vector blk_addrs; + blk_addrs.push_back(blk.m_vip.img_base); - uc_context_alloc(uc, &backup); - uc_context_save(uc, backup); - uc_mem_read(uc, STACK_BASE, stack_backup, STACK_SIZE); + // 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) { + auto& blk = cc_vrtn->m_blks[idx]; + if (blk.branch_type != vm::instrs::vbranch_type::none) { + std::uintptr_t rip = 0ull, 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); + uc_reg_read(uc, UC_X86_REG_RIP, &rip); + + // 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; + + // 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); + uc_emu_start(uc, rip, 0ull, 0ull, 0ull); + } + } + } - uc_context_restore(uc, ctx); - uc_mem_write(uc, STACK_BASE, stack, STACK_SIZE); - uc_reg_read(uc, vm::instrs::reg_map[vsp], &vsp_addr); - uc_reg_read(uc, UC_X86_REG_RIP, &rip); - uc_mem_write(uc, vsp_addr, &branch_addr, sizeof branch_addr); + // 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); - cc_blk = &vblk; - uc_emu_start(uc, rip, 0u, 0u, 0u); + if (blk.m_jmp.stack) + delete[] blk.m_jmp.stack; + }); - uc_mem_write(uc, STACK_BASE, stack_backup, STACK_SIZE); - uc_context_restore(uc, backup); - uc_context_free(backup); - delete stack_backup; + return true; } void emu_t::int_callback(uc_engine* uc, std::uint32_t intno, emu_t* obj) { @@ -221,7 +212,7 @@ bool emu_t::branch_pred_spec_exec(uc_engine* uc, // 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 = reinterpret_cast(malloc(STACK_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); } @@ -239,7 +230,8 @@ bool emu_t::branch_pred_spec_exec(uc_engine* uc, // 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->vip](const vm::instrs::emu_instr_t& instr) -> bool { + [&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 && @@ -251,8 +243,7 @@ bool emu_t::branch_pred_spec_exec(uc_engine* uc, obj->cc_trace.m_instrs.erase((rva_fetch + 1).base(), obj->cc_trace.m_instrs.end()); - const auto vinstr = - vm::instrs::determine(obj->vip, obj->vsp, obj->cc_trace); + 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(), @@ -260,7 +251,7 @@ bool emu_t::branch_pred_spec_exec(uc_engine* uc, uc_context_free(instr.m_cpu); }); - free(obj->cc_trace.m_stack); + delete[] obj->cc_trace.m_stack; obj->cc_trace.m_instrs.clear(); if (vinstr.mnemonic != vm::instrs::mnemonic_t::jmp) { @@ -270,8 +261,7 @@ bool emu_t::branch_pred_spec_exec(uc_engine* uc, if (!vinstr.imm.has_imm) uc_emu_stop(uc); - if (vinstr.imm.size != 8 || - vinstr.imm.val > std::numeric_limits::max()) + if (vinstr.imm.size != 8 || vinstr.imm.val > 8 * VIRTUAL_REGISTER_COUNT) uc_emu_stop(uc); // -- stop after 10 legit SREG's... @@ -279,6 +269,7 @@ bool emu_t::branch_pred_spec_exec(uc_engine* uc, uc_emu_stop(uc); } } + return true; } bool emu_t::code_exec_callback(uc_engine* uc, @@ -325,7 +316,8 @@ bool emu_t::code_exec_callback(uc_engine* uc, // 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->vip](const vm::instrs::emu_instr_t& instr) -> bool { + [&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 && @@ -339,9 +331,10 @@ bool emu_t::code_exec_callback(uc_engine* uc, // 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->vip](vm::instrs::emu_instr_t& instr) -> bool { + [&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; @@ -364,9 +357,7 @@ bool emu_t::code_exec_callback(uc_engine* uc, uc_context_restore(uc, backup); uc_context_free(backup); } else { - const auto vinstr = - vm::instrs::determine(obj->vip, obj->vsp, obj->cc_trace); - + 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", @@ -383,8 +374,9 @@ bool emu_t::code_exec_callback(uc_engine* uc, inst_stream.push_back({instr.m_instr}); }); + std::printf("> err: please define the following vm handler:\n"); vm::utils::print(inst_stream); - std::getchar(); + return false; } if (obj->cc_blk->m_vinstrs.size()) { @@ -407,6 +399,7 @@ bool emu_t::code_exec_callback(uc_engine* uc, // set current code block virtual jmp instruction information... obj->cc_blk->m_jmp.ctx = copy; 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); } @@ -416,8 +409,6 @@ bool emu_t::code_exec_callback(uc_engine* uc, uc_emu_stop(obj->uc); } - obj->cc_trace.m_vip = obj->vip; - obj->cc_trace.m_vsp = obj->vsp; obj->cc_blk->m_vinstrs.push_back(vinstr); } @@ -427,7 +418,7 @@ bool emu_t::code_exec_callback(uc_engine* uc, uc_context_free(instr.m_cpu); }); - free(obj->cc_trace.m_stack); + delete[] obj->cc_trace.m_stack; obj->cc_trace.m_instrs.clear(); } return true; @@ -481,7 +472,7 @@ bool emu_t::legit_branch(vm::instrs::vblk_t& vblk, std::uintptr_t branch_addr) { (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... + // make a backup of the current emulation state... uc_context* backup; uc_context_alloc(uc, &backup); uc_context_save(uc, backup); @@ -492,25 +483,28 @@ bool emu_t::legit_branch(vm::instrs::vblk_t& vblk, std::uintptr_t branch_addr) { uc_context_restore(uc, vblk.m_jmp.ctx); uc_mem_write(uc, STACK_BASE, vblk.m_jmp.stack, STACK_SIZE); - std::uintptr_t vsp_ptr = 0ull, rip = 0ull; + // 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_ptr); - uc_mem_write(uc, vsp_ptr, &branch_addr, sizeof branch_addr); + 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... + // 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; + delete[] stack; // add normal execution callback back... 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; }