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re-writing branch emulation so its not stinky code

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_xeroxz 3 years ago
parent 32b90cdccc
commit 4918ed0a38
3 changed files with 92 additions and 105 deletions
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2
deps/vmprofiler vendored

@ -1 +1 @@
Subproject commit 322a8bcf97d47a6d792c97d803429303106958da
Subproject commit b88c7b9321ea64989666ac19534d425b40369c6f

7
include/vmemu_t.hpp
Unescape View File

@ -23,7 +23,6 @@ class emu_t {
private:
uc_engine* uc;
const vm::vmctx_t* m_vm;
zydis_reg_t vip, vsp;
/// <summary>
/// used in branch_pred_spec_exec to count legit SREG virtual instructions...
@ -125,11 +124,5 @@ class emu_t {
/// <param name="branch_addr"></param>
/// <returns></returns>
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

184
src/vmemu_t.cpp
Unescape View File

@ -1,11 +1,7 @@
#include <vmemu_t.hpp>
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());
auto br_info = could_have_jcc(cc_blk->m_vinstrs);
if (br_info.has_value()) {
auto [br1, br2] = br_info.value();
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);
// 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;
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 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);
}
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);
// keep track of the emulated blocks... by their addresses...
std::vector<std::uintptr_t> blk_addrs;
blk_addrs.push_back(blk.m_vip.img_base);
uc_context_restore(uc, backup);
uc_context_free(backup);
uc_mem_write(uc, STACK_BASE, stack, STACK_SIZE);
delete stack;
// 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);
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);
// 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);
}
}
}
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;
uc_context_alloc(uc, &backup);
uc_context_save(uc, backup);
uc_mem_read(uc, STACK_BASE, stack_backup, STACK_SIZE);
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<std::uint8_t*>(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<std::uint8_t>::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;
}

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