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X64: Handle DT_INIT-style initializer (part of #21)

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Katy Coe
2020-02-14 15:12:13 +01:00
parent ee93343ff8
commit 6ec5c06fbc
1 changed files with 102 additions and 42 deletions
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144
Il2CppInspector.Common/Architectures/Il2CppBinaryX64.cs
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@@ -1,10 +1,11 @@
/*
Copyright 2019 Katy Coe - http://www.hearthcode.org - http://www.djkaty.com
Copyright 2019-2020 Katy Coe - http://www.hearthcode.org - http://www.djkaty.com
All rights reserved.
*/
using System;
using System.ComponentModel.Design;
using System.Linq;
namespace Il2CppInspector
@@ -15,30 +16,28 @@ namespace Il2CppInspector
public Il2CppBinaryX64(IFileFormatReader stream, uint codeRegistration, uint metadataRegistration) : base(stream, codeRegistration, metadataRegistration) { }
// Format of 64-bit LEA:
// 0x48 - REX prefix signifying 64-bit mode with 64-bit operand size (REX prefix bits: Volume 2A, page 2-9)
// 0x48/0x4C - REX prefix signifying 64-bit mode with 64-bit operand size (REX prefix bits: Volume 2A, page 2-9) (bit 2 is register bit 3)
// 8x8D - LEA opcode (8D /r, LEA r64, m)
// 0xX5 - bottom 3 bits = 101 to indicate subsequent operand is a 32-bit displacement; middle 3 bits = register number; top 2 bits = 00
// Bytes 03-06 - 32-bit displacement
// Register numbers: 00 = RAX, 01 = RCX, 10 = RDX, 11 = RBX
// Register numbers: 00b = RAX, 01b = RCX, 10b = RDX, 11b = RBX
// See: https://software.intel.com/sites/default/files/managed/39/c5/325462-sdm-vol-1-2abcd-3abcd.pdf
// Chapter 2.1, 2.1.3, 2.1.5 table 2-2, page 3-537
// NOTE: There is a chance of false positives because of x86's variable instruction length architecture
private (int foundOffset, int reg, uint operand)? findLea(byte[] buff, int offset, int searchDistance) {
// Find first LEA but don't search too far
var opcode = new byte[] { 0x48, 0x8D };
// Find first LEA but don't search too far (either 0x48 0x8D, or 0x4C 0x8D)
int i, index;
for (i = offset, index = 0; i < offset + searchDistance && i < buff.Length && index < opcode.Length; i++)
if (buff[i] != opcode[index++]) {
for (i = offset, index = 0; i < offset + searchDistance && i < buff.Length && index < 2; i++)
if (index == 1 && buff[i] != 0x8D)
index = 0;
// Maybe we're starting a new match
if (buff[i] != opcode[index++])
index = 0;
else if (index != 0 || buff[i] == 0x48 || buff[i] == 0x4C) {
++index;
}
if (index < opcode.Length)
if (index < 2)
return null;
var lea = getLea(buff, (int) i - 2);
@@ -47,20 +46,27 @@ namespace Il2CppInspector
}
private (int reg, uint operand)? getLea(byte[] buff, int offset) {
if (buff[offset] != 0x48 || buff[offset + 1] != 0x8D)
if ((buff[offset] != 0x48 && buff[offset] != 0x4C) || buff[offset + 1] != 0x8D)
return null;
// Found LEA RnX, [RIP + disp32]
var reg = (buff[offset + 2] >> 3) & 7;
var reg = ((buff[offset + 2] >> 3) & 7) + ((buff[offset] << 1) & 8);
var operand = BitConverter.ToUInt32(buff, offset + 3);
return (reg, operand);
}
// 0x40 to set 64-bit mode with 32-bit register size, 0x50+rd to push specified register number
// REX 0x40 to set 64-bit mode with 32-bit register size, 0x50+rd to push specified register number
// Volume 2B, page 4-511
private bool isPushR32(byte[] buff, int offset) => buff[offset] == 0x40 && buff[offset + 1] >= 0x50 && buff[offset + 1] < 0x58;
// REX 0x40 to set 64-bit mode with 64-bit register size, register bit 3 in REX bit 0; bottom 3 bits of opcode are register bits 0-2
private bool isPushR64(byte[] buff, int offset) => (buff[offset] == 0x40 || buff[offset] == 0x41) && buff[offset + 1] >= 0x50 && buff[offset + 1] <= 0x57;
// push rbp is a one-byte instruction encoded as 0x55
// mov rbp, rsp is a 3-byte instruction encoded as 0x48 0x89 0xE5
private bool isPrologue(byte[] buff, int offset) => buff[offset] == 0x55 && buff[offset + 1] == 0x48 && buff[offset + 2] == 0x89 && buff[offset + 3] == 0xE5;
// 0b0100_0X0Y to set 64-bit mode, 0x33 for XOR, 0b11_XXX_YYY for register numbers
// Volume 2C, page 5-278
private (int reg_op1, int reg_op2)? getXorR64R64(byte[] buff, int offset) {
@@ -72,6 +78,19 @@ namespace Il2CppInspector
protected override (ulong, ulong) ConsiderCode(IFileFormatReader image, uint loc) {
// Setup
var buffSize = 0x66; // minimum number of bytes to process the longest expected function
var leaSize = 7; // the length of an LEA instruction with a 64-bit register operand and a 32-bit memory operand
var xorSize = 3; // the length of a XOR instruction of two 64-bit registers
var pushSize = 2; // the length of a PUSH instruction with a 64-bit register
int RAX = 0, RBX = 3, RCX = 1, RDX = 2, R8 = 8;
ulong pCgr = 0; // the point to the code registration function
image.Position = loc;
var buff = image.ReadBytes(buffSize);
// We have seen two versions of the initializer:
// 1. Regular version
// 2. Inlined version with il2cpp::utils::RegisterRuntimeInitializeAndCleanup(CallbackFunction, CallbackFunction, order)
@@ -80,21 +99,17 @@ namespace Il2CppInspector
// Version 2 has a standard prologue and loads the wanted pointer into rax (lea rax)
(int reg, uint operand)? lea;
ulong pCgr = 0;
image.Position = loc;
var buff = image.ReadBytes(0x20); // arbitrary number of bytes, but enough to process the function
// Check for regular version
var xor = getXorR64R64(buff, 0); // 3 bytes
var xor = getXorR64R64(buff, 0);
if (xor != null && xor.Value.reg_op1 == xor.Value.reg_op2) {
lea = getLea(buff, 3); // 7 bytes
lea = getLea(buff, xorSize);
if (lea != null) {
xor = getXorR64R64(buff, 10);
xor = getXorR64R64(buff, xorSize + leaSize);
if (xor != null && xor.Value.reg_op1 == xor.Value.reg_op2) {
// We found Il2CppCodegenRegistration(void)
pCgr = image.GlobalOffset + loc + 10 + lea.Value.operand;
pCgr = image.GlobalOffset + loc + (ulong) (xorSize + leaSize) + lea.Value.operand;
}
}
}
@@ -104,25 +119,21 @@ namespace Il2CppInspector
// Check for prologue
if (isPushR32(buff, 0)) {
// Linear sweep for LEA
var leaInlined = findLea(buff, 2, 0x1E); // 0x20 - 2
// LEA is 7 bytes long
var leaInlined = findLea(buff, pushSize, buffSize - pushSize);
if (leaInlined != null)
pCgr = image.GlobalOffset + loc + (uint) leaInlined.Value.foundOffset + 7 + leaInlined.Value.operand;
pCgr = image.GlobalOffset + loc + (uint) leaInlined.Value.foundOffset + (uint) leaSize + leaInlined.Value.operand;
}
}
var okToContinue = pCgr != 0;
// Assume we've found the pointer to Il2CppCodegenRegistration(void) and jump there
if (okToContinue) {
if (pCgr != 0) {
try {
Image.Position = Image.MapVATR(pCgr);
}
// Couldn't map virtual address to data in file, so it's not this function
catch (InvalidOperationException) {
okToContinue = false;
pCgr = 0;
}
}
@@ -132,29 +143,38 @@ namespace Il2CppInspector
// 1. il2cpp::vm::MetadataCache::Register is called directly with arguments in rcx, rdx and r8 (lea, lea, lea, jmp)
// 2. The two functions being inlined. The arguments are loaded sequentially into rax after the prologue
// By ignoring the REX R flag (bit 2 of the instruction prefix) which specifies an extension bit to the register operand,
// we skip over "lea r8". This will leave us with two LEAs containing our desired pointers.
if (pCgr != 0) {
var buff2Size = 0x40;
var buff2 = image.ReadBytes(buffSize);
var offset = 0;
if (okToContinue) {
buff = image.ReadBytes(0x40);
(int foundOffset, int reg, uint operand)? lea1 = null, lea2 = null;
// We skip over "lea r8". This will leave us with two LEAs containing our desired pointers.
while (offset + leaSize < buff2Size && (!lea1.HasValue || lea1.Value.reg == R8)) {
lea1 = findLea(buff2, offset, buff2Size - (offset + leaSize));
offset = lea1?.foundOffset + leaSize ?? buff2Size;
}
// LEA is 7 bytes long
var lea1 = findLea(buff, 0, 0x40 - 7);
if (lea1 != null) {
var lea2 = findLea(buff, lea1.Value.foundOffset + 7, 0x40 - lea1.Value.foundOffset - 7);
while (offset + leaSize < buff2Size && (!lea2.HasValue || lea2.Value.reg == R8)) {
lea2 = findLea(buff2, offset, buff2Size - (offset + leaSize));
offset = lea2?.foundOffset + leaSize ?? buff2Size;
}
if (lea2 != null) {
// Use the original pointer found, not the file location + GlobalOffset because the data may be in a different section
var ptr1 = pCgr + (uint) lea1.Value.foundOffset + 7 + lea1.Value.operand;
var ptr2 = pCgr + (uint) lea2.Value.foundOffset + 7 + lea2.Value.operand;
var ptr1 = pCgr + (uint) lea1.Value.foundOffset + (uint) leaSize + lea1.Value.operand;
var ptr2 = pCgr + (uint) lea2.Value.foundOffset + (uint) leaSize + lea2.Value.operand;
// RCX and RDX argument passing?
if (lea1.Value.reg == 2 /* RDX */ && lea2.Value.reg == 1 /* RCX */)
if (lea1.Value.reg == RDX && lea2.Value.reg == RCX)
return (ptr2, ptr1);
// RAX sequential loading?
if (lea1.Value.reg == 0 /* RAX */ && lea2.Value.reg == 0 /* RAX */)
if (lea1.Value.reg == RAX && lea2.Value.reg == RAX)
return (ptr1, ptr2);
}
}
@@ -166,8 +186,48 @@ namespace Il2CppInspector
// 2. Pointer to final address of 2nd table loaded into rbx (lea rbx), runs backwards (8 bytes per entry) until finding 0xFFFFFFFF_FFFFFFFF
// The strategy: find these LEAs, acquire and merge the two function tables, then call ourselves in a loop to check each function address
// TODO: Implement DT_INIT analysis
// Expect function prologue and at least 3 64-bit register pushes (there are probably more)
if (!isPrologue(buff, 0) || !isPushR64(buff, 4) || !isPushR64(buff, 6) || !isPushR64(buff, 8))
return (0, 0);
// Find the start and end addresses of the first function table
var leaOfStart = findLea(buff, 10, buffSize - 10);
if (leaOfStart == null || leaOfStart.Value.reg != RBX) // Most be lea rbx
return (0, 0);
var leaOfEnd = findLea(buff, leaOfStart.Value.foundOffset + leaSize, buffSize - (leaOfStart.Value.foundOffset + leaSize));
if (leaOfEnd == null || leaOfEnd.Value.reg == RBX) // Must be lea with any register besides rbx
return (0, 0);
var ptrStart1 = leaOfStart.Value.foundOffset + leaSize + leaOfStart.Value.operand;
var ptrEnd1 = leaOfEnd .Value.foundOffset + leaSize + leaOfEnd .Value.operand;
// Find the address of the last item in the second function table
var leaOfLastItem = findLea(buff, leaOfEnd.Value.foundOffset + leaSize, buffSize - (leaOfEnd.Value.foundOffset + leaSize));
if (leaOfLastItem == null || leaOfLastItem.Value.reg != 0b11) // Must be lea rbx
return (0, 0);
var entrySize = 8; // 64-bit array entries
var ptrEnd2 = leaOfLastItem.Value.foundOffset + leaSize + leaOfLastItem.Value.operand + entrySize;
// Work backwards to find the address of the first item in the second function table
var ptrStart2 = ptrEnd2;
while (image.ReadUInt64(image.MapVATR((ulong) ptrStart2)) != 0xFFFF_FFFF_FFFF_FFFF)
ptrStart2 -= entrySize;
ptrStart2 += entrySize;
// Acquire both function tables
var funcs1 = image.ReadMappedWordArray((ulong) ptrStart1, (int) (ptrEnd1 - ptrStart1) / entrySize);
var funcs2 = image.ReadMappedWordArray((ulong) ptrStart2, (int) (ptrEnd2 - ptrStart2) / entrySize);
// Check every function
var funcs = funcs1.Concat(funcs2);
foreach (var pFunc in funcs) {
var result = ConsiderCode(image, image.MapVATR((ulong) pFunc));
if (result != (0, 0))
return result;
}
return (0, 0);
}
}