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vmemu
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more prepared to write virtual branch detection code now...

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John Doe 2 years ago
parent c35a646f64
commit 29a40b4421
3 changed files with 114 additions and 93 deletions
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2
deps/vmprofiler vendored

@ -1 +1 @@
Subproject commit b018ca7999b7a5bd372f56fad4d11f1f9033f255
Subproject commit c5df1338acfb22485387e4b96d26051640b3a931

33
include/vmemu_t.hpp
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@ -24,13 +24,22 @@ class emu_t {
uc_engine* uc;
const vm::vmctx_t* m_vm;
zydis_reg_t vip, vsp;
/// <summary>
/// current code trace...
/// </summary>
vm::instrs::hndlr_trace_t cc_trace;
/// <summary>
/// current virtual code block...
/// block...
/// </summary>
vm::instrs::vblk_t* cc_blk;
/// <summary>
/// set to true when emulating the vm enter...
/// current code virtual routine...
/// </summary>
bool m_vm_enter;
vm::instrs::vrtn_t* cc_vrtn;
/// <summary>
/// unicorn engine hook
@ -80,13 +89,21 @@ class emu_t {
static void int_callback(uc_engine* uc, std::uint32_t intno, emu_t* obj);
/// <summary>
/// determines if there is a JCC in the virtual instruction stream, if there
/// is returns a pair of image based addresses for both of the branches...
/// determines if its possible that the virtual instruction stream contains a
/// virtual JCC...
///
/// this simply checks to see if there are at least 3 LCONST that load 64bit
/// constant values...
///
/// it also checks if the last 2 LCONST's load image based addresses which
/// land inside of executable sections...
///
/// this function cannot be used to determine if there is a virtual branch or
/// not... it is only a useful/preliminary function...
/// </summary>
/// <param name="vinstrs">vector of virtual instructions...</param>
/// <returns>returns a pair of imaged based addresses, one for each branch
/// address... if there is no jcc then it returns nothing...</returns>
std::optional<std::pair<std::uintptr_t, std::uintptr_t>> has_jcc(
std::vector<vm::instrs::vinstr_t>& vinstrs);
/// <returns>returns true if there is at least 3 LCONST in the virtual
/// instruction stream that load 64bit values...</returns>
bool could_have_jcc(std::vector<vm::instrs::vinstr_t>& vinstrs);
};
} // namespace vm

172
src/vmemu_t.cpp
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@ -78,12 +78,12 @@ bool emu_t::emulate(std::uint32_t vmenter_rva, vm::instrs::vrtn_t& vrtn) {
cc_trace.m_vip = vip;
cc_trace.m_vsp = vsp;
vrtn.m_rva = vmenter_rva;
m_vm_enter = true;
vm::instrs::vblk_t blk;
blk.m_vip = {0ull, 0ull};
blk.m_cpu = {nullptr, nullptr};
cc_blk = &blk;
cc_vrtn = &vrtn;
std::printf("> beginning execution at = %p\n", rip);
if ((err = uc_emu_start(uc, rip, 0ull, 0ull, 0ull))) {
@ -91,9 +91,9 @@ bool emu_t::emulate(std::uint32_t vmenter_rva, vm::instrs::vrtn_t& vrtn) {
return false;
}
std::printf("> blk address = %p\n", blk.m_vip.img_base);
const auto jcc_result = has_jcc(blk.m_vinstrs);
std::printf("> jcc result = %d\n", jcc_result.has_value());
std::printf(
"> blk_%p, number of virtual instructions = %d, could have a jcc = %d\n",
blk.m_vip.img_base, blk.m_vinstrs.size(), could_have_jcc(blk.m_vinstrs));
return true;
}
@ -148,18 +148,17 @@ bool emu_t::code_exec_callback(uc_engine* uc,
if (instr.mnemonic == ZYDIS_MNEMONIC_INVALID)
return false;
// save the current cpu's context (all register values and such)...
// create a new emu_instr_t with this information... this info will be used by
// profiles to grab decrypted values and such...
uc_context* cpu_ctx;
uc_context_alloc(obj->uc, &cpu_ctx);
uc_context_save(obj->uc, cpu_ctx);
uc_context* ctx;
uc_context_alloc(uc, &ctx);
uc_context_save(uc, ctx);
std::uint8_t* stack = reinterpret_cast<std::uint8_t*>(malloc(STACK_SIZE));
uc_mem_read(uc, STACK_BASE, stack, STACK_SIZE);
// 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));
uc_mem_read(uc, STACK_BASE, obj->cc_trace.m_stack, STACK_SIZE);
}
vm::instrs::emu_instr_t emu_instr{instr, cpu_ctx, stack};
obj->cc_trace.m_instrs.push_back(emu_instr);
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 ||
@ -185,33 +184,32 @@ bool emu_t::code_exec_callback(uc_engine* uc,
obj->cc_trace.m_instrs.erase((rva_fetch + 1).base(),
obj->cc_trace.m_instrs.end());
// extract vip address out of the vm enter trace...
if (obj->m_vm_enter) {
auto vip_addr_set = std::find_if(
// set the virtual code block vip address information...
if (!obj->cc_blk->m_vip.rva || !obj->cc_blk->m_vip.img_base) {
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& emu_instr) -> bool {
const auto& i = emu_instr.m_instr;
[&vip = obj->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;
});
// get the cpu context from the instruction after the instruction that
// writes to vip...
--vip_addr_set;
uc_context* backup;
uc_context_alloc(uc, &backup);
uc_context_save(uc, backup);
uc_context_restore(uc, vip_addr_set->m_cpu);
uc_context_restore(uc, (vip_write - 1)->m_cpu);
auto uc_reg =
vm::instrs::reg_map[vip_write->m_instr.operands[0].reg.value];
std::uintptr_t vip_addr = 0ull;
uc_reg_read(uc, vm::instrs::reg_map[obj->vip], &vip_addr);
uc_reg_read(uc, uc_reg, &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);
obj->m_vm_enter = false;
} else {
const auto vinstr =
vm::instrs::determine(obj->vip, obj->vsp, obj->cc_trace);
@ -241,21 +239,25 @@ bool emu_t::code_exec_callback(uc_engine* uc,
obj->cc_blk->m_vinstrs.push_back(vinstr);
if (vinstr.mnemonic == vm::instrs::mnemonic_t::jmp) {
uc_context *b1, *b2;
uc_context_alloc(uc, &b1);
uc_context_alloc(uc, &b2);
uc_context_save(uc, b1);
uc_context_restore(uc, obj->cc_trace.m_instrs.begin()->m_cpu);
uc_context_save(uc, b2);
uc_context_restore(uc, b1);
uc_context *backup, *copy;
std::uint8_t* stack =
reinterpret_cast<std::uint8_t*>(malloc(STACK_SIZE));
// backup current unicorn-engine context...
uc_context_alloc(uc, &backup);
uc_context_alloc(uc, &copy);
uc_context_save(uc, backup);
std::memcpy(stack, obj->cc_trace.m_instrs.begin()->stack, STACK_SIZE);
// 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);
obj->cc_blk->m_cpu.ctx = b2;
obj->cc_blk->m_cpu.stack = stack;
// 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];
uc_mem_read(uc, STACK_BASE, obj->cc_blk->m_jmp.stack, STACK_SIZE);
}
if (vinstr.mnemonic == vm::instrs::mnemonic_t::jmp ||
@ -267,9 +269,9 @@ bool emu_t::code_exec_callback(uc_engine* uc,
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);
free(instr.stack);
});
free(obj->cc_trace.m_stack);
obj->cc_trace.m_instrs.clear();
}
return true;
@ -314,49 +316,51 @@ void emu_t::invalid_mem(uc_engine* uc,
}
}
std::optional<std::pair<std::uintptr_t, std::uintptr_t>> emu_t::has_jcc(
std::vector<vm::instrs::vinstr_t>& vinstrs) {
if (vinstrs.back().mnemonic == vm::instrs::mnemonic_t::vmexit)
return {};
// number of LCONST virtual instructions which load 64bit imm's...
const std::uint32_t lconst_num = std::accumulate(
vinstrs.begin(), vinstrs.end(), 0,
[&](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;
});
if (lconst_num < 3)
return {};
const auto lconst1 = std::find_if(
vinstrs.rbegin(), vinstrs.rend(), [&](vm::instrs::vinstr_t& v) -> bool {
return v.mnemonic == vm::instrs::mnemonic_t::lconst && v.imm.size == 64;
});
const auto lconst2 = std::find_if(
lconst1 + 1, vinstrs.rend(), [&](vm::instrs::vinstr_t& v) -> bool {
return v.mnemonic == vm::instrs::mnemonic_t::lconst && v.imm.size == 64;
});
static const auto exec_callbk = [&](uc_engine* uc, uint64_t address,
uint32_t size, emu_t* obj) {};
uc_context *backup, *br1, *br2;
uc_context_alloc(uc, &backup);
uc_context_alloc(uc, &br1);
uc_context_alloc(uc, &br2);
uc_context_save(uc, backup);
uc_context_restore(uc, cc_blk->m_cpu.ctx);
uc_mem_write(uc, STACK_BASE, cc_blk->m_cpu.stack, STACK_SIZE);
uc_context_restore(uc, backup);
uc_context_free(backup);
uc_context_free(br1);
uc_context_free(br2);
return {};
bool emu_t::could_have_jcc(std::vector<vm::instrs::vinstr_t>& vinstrs) {
// 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 false;
// 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 false;
const auto lconst2 = std::find_if(lconst1 + 1, vinstrs.rend(), lconst64_chk);
if (lconst2 == vinstrs.rend())
return false;
// 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 false;
// 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 false;
return true;
}
} // namespace vm
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