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Implement two-step address load linear sweep for Thumb-2 functions

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This commit is contained in:
Katy Coe
2019-10-27 22:01:48 +01:00
parent b863cf74b8
commit 7467873d0a
1 changed files with 203 additions and 40 deletions
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243
Il2CppInspector/Il2CppBinaryARM.cs
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@@ -6,6 +6,7 @@
*/
using System;
using System.Collections.Generic;
using System.Linq;
namespace Il2CppInspector
@@ -16,6 +17,165 @@ namespace Il2CppInspector
public Il2CppBinaryARM(IFileFormatReader stream, uint codeRegistration, uint metadataRegistration) : base(stream, codeRegistration, metadataRegistration) { }
// Thumb 2 Supplement Reference Manual: http://class.ece.iastate.edu/cpre288/resources/docs/Thumb-2SupplementReferenceManual.pdf
// Section 3.1
private uint getNextThumbInstruction(IFileFormatReader image) {
// Assume 16-bit
uint inst = image.ReadUInt16();
// Is 32-bit?
if (inst.Bits(13, 15) == 0b111)
if (inst.Bits(11, 2) != 0b00)
inst = (inst << 16) + image.ReadUInt16();
return inst;
}
// Page 4-166 (MOVS encoding T1, MOVW encoding T3), Page 4-171 (MOVT)
// In Thumb, an 8-byte MOV instruction is MOVW followed by MOVT
private enum Thumb : uint
{
MovW = 0b100100,
MovT = 0b101100
}
private (uint reg_d, ushort imm)? getMovImm(uint inst, Thumb movType) {
uint reg_d, imm;
// Encoding T1
if (inst.Bits(11, 21) == 0b00100 && movType == Thumb.MovW) {
imm = inst.Bits(0, 8);
reg_d = inst.Bits(8, 3);
return (reg_d, (ushort) imm);
}
// Encoding T3
if (inst.Bits(20, 6) != (uint) movType || inst.Bits(27, 5) != 0b11110 || inst.Bits(15, 1) != 0)
return null;
imm = (inst.Bits(16, 4) << 12) + (inst.Bits(26, 1) << 11) + (inst.Bits(12, 3) << 8) + inst.Bits(0, 8);
reg_d = inst.Bits(8, 4);
return (reg_d, (ushort) imm);
}
// Section 4.6.4 (ADD encoding T2)
private (uint reg_dn, uint reg_m)? getAddReg(uint inst) {
if (inst.Bits(8, 8) != 0b_0100_0100)
return null;
var reg_dn = (inst.Bits(7, 1) << 3) + inst.Bits(0, 3);
var reg_m = inst.Bits(3, 4);
return (reg_dn, reg_m);
}
// Section 4.6.43 (LDR encoding T1)
private (uint reg_n, uint reg_t, ushort imm)? getLdrImm(uint inst) {
if (inst.Bits(11, 5) != 0b_01101)
return null;
var reg_n = inst.Bits(3, 3);
var reg_t = inst.Bits(0, 3);
var imm = inst.Bits(6, 5);
return (reg_n, reg_t, (ushort) imm);
}
// Section 4.6.12 (B.W encoding T4; for encoding T3, flip bit 12)
private bool isBW(uint inst) => inst.Bits(27, 5) == 0b11110 && inst.Bits(14, 2) == 0b10 && inst.Bits(12, 1) == 1;
// Sweep a Thumb function and return the register values at the end (register number => value)
private Dictionary<uint, uint> sweepThumbForAddressLoads(List<uint> func, uint baseAddress, IFileFormatReader image) {
// List of registers and addresses loaded into them
var regs = new Dictionary<uint, uint>();
// Program counter is R15 in ARM
// https://www.scss.tcd.ie/~waldroj/3d1/arm_arm.pdf states:
// For a Thumb instruction, the value read is the address of the instruction plus 4 bytes
regs.Add(15, baseAddress + 4);
// Iterate each instruction
foreach (var inst in func) {
var accepted = false;
// Is it a MOVW?
if (getMovImm(inst, Thumb.MovW) is (uint movw_reg_d, ushort movw_imm)) {
if (regs.ContainsKey(movw_reg_d))
regs[movw_reg_d] = movw_imm; // Clears top 16 bits
else
regs.Add(movw_reg_d, movw_imm);
accepted = true;
}
// Is it a MOVT?
if (getMovImm(inst, Thumb.MovT) is (uint movt_reg_d, ushort movt_imm)) {
if (regs.ContainsKey(movt_reg_d))
regs[movt_reg_d] |= (uint) movt_imm << 16;
else
regs.Add(movt_reg_d, (uint) movt_imm << 16);
accepted = true;
}
// Is it a pointer de-reference (LDR Rt, [Rn, #imm])?
if (getLdrImm(inst) is (uint ldr_reg_n, uint ldr_reg_t, ushort ldr_imm)) {
// The code below works in the generic case for all Rt, Rn and #imm,
// but for our scan we want to restrict it such that Rt == Rn and #imm == 0
// otherwise we might pick up functions we don't want
if (ldr_reg_n == ldr_reg_t && ldr_imm == 0)
if (regs.ContainsKey(ldr_reg_n)) {
var offset = (regs[ldr_reg_n] & 0xffff_fffe) + ldr_imm;
var value = image.ReadUInt32(image.MapVATR(offset));
if (regs.ContainsKey(ldr_reg_t))
regs[ldr_reg_t] = value;
else
regs.Add(ldr_reg_t, value);
accepted = true;
}
}
// Is it an ADD Rdn, Rm?
if (getAddReg(inst) is (uint add_reg_dn, uint add_reg_m)) {
if (regs.ContainsKey(add_reg_dn) && regs.ContainsKey(add_reg_m)) {
regs[add_reg_dn] += regs[add_reg_m];
accepted = true;
}
}
// is it the end?
if (isBW(inst))
accepted = true;
// In our scan, we will ONLY accept one of the above instructions
if (!accepted)
return null;
// Advance program counter which we need to calculate ADDs with PC as operand correctly
regs[15] += inst.Bits(29, 3) == 0b111 ? 4u : 2u;
}
return regs;
}
// Get a Thumb function that ends in B.W
private List<uint> getThumbFunctionAtFileOffset(IFileFormatReader image, uint loc, uint maxLength) {
// Read a function that ends in a hard branch (B.W) or exceeds maxLength instructions
var func = new List<uint>();
uint inst;
image.Position = loc;
do {
inst = getNextThumbInstruction(image);
func.Add(inst);
} while (!isBW(inst) && func.Count < maxLength);
return func;
}
protected override (ulong, ulong) ConsiderCode(IFileFormatReader image, uint loc) {
// Assembly bytes to search for at start of each function
ulong metadataRegistration, codeRegistration;
@@ -29,6 +189,7 @@ namespace Il2CppInspector
if (new byte[] { 0x1c, 0x0, 0x9f, 0xe5, 0x1c, 0x10, 0x9f, 0xe5, 0x1c, 0x20, 0x9f, 0xe5 }.SequenceEqual(buff)) {
// Get offset to all addresses
// The +8 is because in ARM, PC always contains the currently executing instruction + 8
var offset = image.ReadUInt32(loc + 0x24) + loc + 0xc + 8;
// Get pointer to Il2CppCodegenRegistration(void)
@@ -68,52 +229,54 @@ namespace Il2CppInspector
return (codeRegistration, metadataRegistration);
}
// ARMv7 Thumb (T1) metadata v23
// void Il2CppCodeRegistration()
// Thumb-2
// We use a method similar to the linear sweep in Il2CppBinaryARM64; see the comments there for details
loc &= 0xffff_fffe;
image.Position = loc;
// Check for ADD Rx, PC in relevant parts of function
buff = image.ReadBytes(0x20);
if (buff[0x0C] == 0x79 && buff[0x0D] == 0x44 && // ADD R1, PC
buff[0x16] == 0x78 && buff[0x17] == 0x44 && // ADD R0, PC
buff[0x1E] == 0x7A && buff[0x1F] == 0x44) // ADD R2, PC
{
// Follow path to metadata pointer
var ppMetadata = decodeMovImm32(buff) + loc + 0x10;
image.Position = ppMetadata;
metadataRegistration = image.ReadUInt32();
// Load function into memory
// In practice, the longest function length we need is not generally longer than 11 instructions
var func = getThumbFunctionAtFileOffset(image, loc, 11);
// Follow path to code pointer
var pCode = decodeMovImm32(buff.Skip(8).Take(4).Concat(buff.Skip(14).Take(4)).ToArray());
codeRegistration = pCode + loc + 0x1A + image.GlobalOffset;
// Don't accept functions longer than 10 instructions (in this case, the last instruction won't be a B.W)
if (!isBW(func[^1]))
return (0, 0);
return (codeRegistration, metadataRegistration);
// Get a list of registers and values in them at the end of the function
var regs = sweepThumbForAddressLoads(func, (uint) image.GlobalOffset + loc, image);
if (regs == null)
return (0, 0);
uint r0, r1;
// Is it the Il2CppCodeRegistration.cpp initializer?
// R0-R3 + PC will be set and they will be the only registers set
// R2 and R3 must be zero
if (regs.Count() == 5 && regs.TryGetValue(0, out _) && regs.TryGetValue(1, out r1)
&& regs.TryGetValue(2, out uint r2) && regs.TryGetValue(3, out uint r3)) {
if (r2 == 0 && r3 == 0) {
// Load up the function whose address is in R1
func = getThumbFunctionAtFileOffset(image, image.MapVATR(r1 & 0xffff_fffe), 11);
if (!isBW(func[^1]))
return (0, 0);
regs = sweepThumbForAddressLoads(func, r1 & 0xffff_fffe, image);
}
}
// ARMv7 Thumb (T1)
// http://liris.cnrs.fr/~mmrissa/lib/exe/fetch.php?media=armv7-a-r-manual.pdf - A8.8.106
// http://armconverter.com/hextoarm/
var bytes = new byte[] { 0x2d, 0xe9, 0x00, 0x48, 0xeb, 0x46 };
image.Position = loc;
buff = image.ReadBytes(6);
if (!bytes.SequenceEqual(buff))
return (0, 0);
bytes = new byte[] { 0x00, 0x23, 0x00, 0x22, 0xbd, 0xe8, 0x00, 0x48 };
image.Position += 0x10;
buff = image.ReadBytes(8);
if (!bytes.SequenceEqual(buff))
return (0, 0);
image.Position = loc + 6;
image.Position = (image.MapVATR(decodeMovImm32(image.ReadBytes(8))) & 0xfffffffc) + 0x0e;
metadataRegistration = decodeMovImm32(image.ReadBytes(8));
codeRegistration = decodeMovImm32(image.ReadBytes(8));
return (codeRegistration, metadataRegistration);
}
// Is it Il2CppCodegenRegistration(void)?
// In v21 and later, R0-R2 + PC will be set and they will be the only registers set
// Pre-v21, R0-R1 + PC will be the only registers set
private uint decodeMovImm32(byte[] asm) {
ushort low = (ushort) (asm[2] + ((asm[3] & 0x70) << 4) + ((asm[1] & 0x04) << 9) + ((asm[0] & 0x0f) << 12));
ushort high = (ushort) (asm[6] + ((asm[7] & 0x70) << 4) + ((asm[5] & 0x04) << 9) + ((asm[4] & 0x0f) << 12));
return (uint) ((high << 16) + low);
if (image.Version >= 21 && regs.Count == 4 && regs.TryGetValue(0, out r0) && regs.TryGetValue(1, out r1) && regs.TryGetValue(2, out uint _))
return (r0 & 0xffff_fffe, r1 & 0xffff_fffe);
if (image.Version < 21 && regs.Count == 3 && regs.TryGetValue(0, out r0) && regs.TryGetValue(1, out r1))
return (r0 & 0xffff_fffe, r1 & 0xffff_fffe);
return (0, 0);
}
}
}
}