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hook.cpp
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hook.cpp
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#include <cinttypes>
#include <cstdint>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <vector>
#ifdef _WIN32
#define WIN32_LEAN_AND_MEAN
#include <windows.h>
#else
#include <sys/mman.h>
#endif // _WIN32
#include "interop.hpp"
namespace openloco::interop
{
static void* _hookTableAddress;
static int32_t _hookTableOffset;
static int32_t _maxHooks = 1000;
constexpr auto HOOK_BYTE_COUNT = 140;
static registers _hookRegisters;
// This macro writes a little-endian 4-byte long value into *data
// It is used to avoid type punning.
#define write_address_strictalias(data, addr) \
*(data + 0) = ((addr)&0x000000ff) >> 0; \
*(data + 1) = ((addr)&0x0000ff00) >> 8; \
*(data + 2) = ((addr)&0x00ff0000) >> 16; \
*(data + 3) = ((addr)&0xff000000) >> 24;
static void hookfunc(uintptr_t address, uintptr_t hookAddress, int32_t stacksize)
{
int32_t i = 0;
uint8_t data[HOOK_BYTE_COUNT] = { 0 };
uintptr_t registerAddress = (uintptr_t)&_hookRegisters;
data[i++] = 0x89; // mov [_hookRegisters], eax
data[i++] = (0b000 << 3) | 0b101;
write_address_strictalias(&data[i], registerAddress);
i += 4;
data[i++] = 0x89; // mov [_hookRegisters + 4], ebx
data[i++] = (0b011 << 3) | 0b101;
write_address_strictalias(&data[i], registerAddress + 4);
i += 4;
data[i++] = 0x89; // mov [_hookRegisters + 8], ecx
data[i++] = (0b001 << 3) | 0b101;
write_address_strictalias(&data[i], registerAddress + 8);
i += 4;
data[i++] = 0x89; // mov [_hookRegisters + 12], edx
data[i++] = (0b010 << 3) | 0b101;
write_address_strictalias(&data[i], registerAddress + 12);
i += 4;
data[i++] = 0x89; // mov [_hookRegisters + 16], esi
data[i++] = (0b110 << 3) | 0b101;
write_address_strictalias(&data[i], registerAddress + 16);
i += 4;
data[i++] = 0x89; // mov [_hookRegisters + 20], edi
data[i++] = (0b111 << 3) | 0b101;
write_address_strictalias(&data[i], registerAddress + 20);
i += 4;
data[i++] = 0x89; // mov [_hookRegisters + 24], ebp
data[i++] = (0b101 << 3) | 0b101;
write_address_strictalias(&data[i], registerAddress + 24);
i += 4;
// work out distance to nearest 0xC
// (esp - numargs * 4) & 0xC
// move to align - 4
// save that amount
// push the registers to be on the stack to access as arguments
data[i++] = 0x68; // push _hookRegisters
write_address_strictalias(&data[i], registerAddress);
i += 4;
data[i++] = 0xE8; // call
write_address_strictalias(&data[i], hookAddress - address - i - 4);
i += 4;
data[i++] = 0x83; // add esp, 4
data[i++] = 0xC4;
data[i++] = 0x04;
data[i++] = 0x25; // and eax,0xff
data[i++] = 0xff;
data[i++] = 0x00;
data[i++] = 0x00;
data[i++] = 0x00;
data[i++] = 0xc1; // shl eax, 8
data[i++] = 0xe0;
data[i++] = 0x08;
data[i++] = 0x9e; // sahf
data[i++] = 0x9c; // pushf
data[i++] = 0x8B; // mov eax, [_hookRegisters]
data[i++] = (0b000 << 3) | 0b101;
write_address_strictalias(&data[i], registerAddress);
i += 4;
data[i++] = 0x8B; // mov ebx, [_hookRegisters + 4]
data[i++] = (0b011 << 3) | 0b101;
write_address_strictalias(&data[i], registerAddress + 4);
i += 4;
data[i++] = 0x8B; // mov ecx, [_hookRegisters + 8]
data[i++] = (0b001 << 3) | 0b101;
write_address_strictalias(&data[i], registerAddress + 8);
i += 4;
data[i++] = 0x8B; // mov edx, [_hookRegisters + 12]
data[i++] = (0b010 << 3) | 0b101;
write_address_strictalias(&data[i], registerAddress + 12);
i += 4;
data[i++] = 0x8B; // mov esi, [_hookRegisters + 16]
data[i++] = (0b110 << 3) | 0b101;
write_address_strictalias(&data[i], registerAddress + 16);
i += 4;
data[i++] = 0x8B; // mov edi, [_hookRegisters + 20]
data[i++] = (0b111 << 3) | 0b101;
write_address_strictalias(&data[i], registerAddress + 20);
i += 4;
data[i++] = 0x8B; // mov ebp, [_hookRegisters + 24]
data[i++] = (0b101 << 3) | 0b101;
write_address_strictalias(&data[i], registerAddress + 24);
i += 4;
data[i++] = 0x9d; // popf
data[i++] = 0xC3; // retn
#ifdef _WIN32
WriteProcessMemory(GetCurrentProcess(), (LPVOID)address, data, i, 0);
#else
// We own the pages with PROT_WRITE | PROT_EXEC, we can simply just memcpy the data
memcpy((void*)address, data, i);
#endif // _WIN32
}
void register_hook(uintptr_t address, hook_function function)
{
if (!_hookTableAddress)
{
size_t size = _maxHooks * HOOK_BYTE_COUNT;
#ifdef _WIN32
_hookTableAddress = VirtualAllocEx(GetCurrentProcess(), NULL, size, MEM_COMMIT, PAGE_EXECUTE_READWRITE);
#else
_hookTableAddress = mmap(NULL, size, PROT_EXEC | PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
if (_hookTableAddress == MAP_FAILED)
{
perror("mmap");
exit(1);
}
#endif // _WIN32
}
if (_hookTableOffset > _maxHooks)
{
return;
}
uint32_t hookaddress = (uint32_t)_hookTableAddress + (_hookTableOffset * HOOK_BYTE_COUNT);
uint8_t data[9];
int32_t i = 0;
data[i++] = 0xE9; // jmp
write_address_strictalias(&data[i], hookaddress - address - i - 4);
i += 4;
data[i++] = 0xC3; // retn
write_memory(address, data, i);
hookfunc(hookaddress, (uintptr_t)function, 0);
_hookTableOffset++;
}
void register_hook_stub(uintptr_t address)
{
static uintptr_t passAddress;
passAddress = address;
register_hook(
address,
[](registers& regs) -> uint8_t {
std::printf(" fn %" PRIuPTR "\n", passAddress);
return 0;
});
}
void write_ret(uint32_t address)
{
uint8_t opcode = 0xC3;
write_memory(address, &opcode, sizeof(opcode));
}
void write_jmp(uint32_t address, void* fn)
{
uint8_t data[5] = { 0 };
data[0] = 0xE9; // JMP
auto addr = reinterpret_cast<uintptr_t>(fn);
write_address_strictalias(&data[1], addr - address - 5);
write_memory(address, data, sizeof(data));
}
static void* _smallHooks;
static uint8_t* _offset;
static void* make_jump(uint32_t address, void* fn)
{
if (!_smallHooks)
{
size_t size = 20 * 500;
#ifdef _WIN32
_hookTableAddress = VirtualAllocEx(GetCurrentProcess(), NULL, size, MEM_COMMIT, PAGE_EXECUTE_READWRITE);
#else
_smallHooks = mmap(NULL, size, PROT_EXEC | PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
if (_smallHooks == MAP_FAILED)
{
perror("mmap");
exit(1);
}
_offset = static_cast<uint8_t*>(_smallHooks);
#endif // _WIN32
}
int i = 0;
_offset[i++] = 0x58; // POP EAX
_offset[i++] = 0x68; // PUSH
write_address_strictalias(&_offset[i], address);
i += 4;
_offset[i++] = 0x50; // PUSH EAX
uintptr_t base = reinterpret_cast<uintptr_t>(_offset);
uintptr_t addr = reinterpret_cast<uintptr_t>(fn);
_offset[i++] = 0xE9; // JMP
write_address_strictalias(&_offset[i], addr - base - 12);
i += 4;
uint8_t* ptr = _offset;
_offset += i;
return ptr;
}
void hook_dump(uint32_t address, void* fn)
{
uint8_t data[4] = { 0 };
void* hook = make_jump(address, fn);
uintptr_t addr = reinterpret_cast<uintptr_t>(hook);
write_address_strictalias(&data[0], addr);
write_memory(address, data, sizeof(data));
}
void hook_lib(uint32_t address, void* fn)
{
uint8_t data[4] = { 0 };
uintptr_t addr = reinterpret_cast<uintptr_t>(fn);
write_address_strictalias(&data[0], addr);
write_memory(address, data, sizeof(data));
}
void write_nop(uint32_t address, size_t count)
{
std::vector<uint8_t> buffer(count, 0x90);
write_memory(address, buffer.data(), buffer.size());
}
}