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Process ELF32 relocations

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This commit is contained in:
Katy Coe
2019-10-22 00:37:16 +02:00
parent a8aa618aee
commit c88f058a39
2 changed files with 150 additions and 8 deletions
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119
Il2CppInspector/FileFormatReaders/ElfReader.cs
View File

@@ -7,6 +7,7 @@
using System;
using System.Collections.Generic;
using System.Data.Common;
using System.Diagnostics;
using System.IO;
using System.Linq;
@@ -15,7 +16,48 @@ namespace Il2CppInspector
{
internal class ElfReader : FileFormatReader<ElfReader>
{
private program_header_table[] program_header_table;
// Internal relocation entry helper
private struct ElfReloc
{
public Elf Type;
public uint Offset;
public uint? Addend;
public uint SymbolTable;
public uint SymbolIndex;
// Equality based on target address
public override bool Equals(object obj) => obj is ElfReloc reloc && Equals(reloc);
public bool Equals(ElfReloc other) {
return Offset == other.Offset;
}
public override int GetHashCode() {
unchecked {
var hashCode = (int)Type;
hashCode = (hashCode * 397) ^ (int)Offset;
hashCode = (hashCode * 397) ^ Addend.GetHashCode();
hashCode = (hashCode * 397) ^ (int)SymbolTable;
hashCode = (hashCode * 397) ^ (int)SymbolIndex;
return hashCode;
}
}
// Cast operators (makes the below code MUCH easier to read)
public ElfReloc(elf_32_rel rel, uint symbolTable) {
Type = (Elf) (rel.r_info & 0xff);
Offset = rel.r_offset;
Addend = null;
SymbolIndex = rel.r_info >> 8; // r_info >> 8 is an index into the symbol table
SymbolTable = symbolTable;
}
public ElfReloc(elf_32_rela rela, uint symbolTable)
: this(new elf_32_rel { r_info = rela.r_info, r_offset = rela.r_offset }, symbolTable) =>
Addend = rela.r_addend;
}
private elf_32_phdr[] program_header_table;
private elf_32_shdr[] section_header_table;
private elf_32_dynamic[] dynamic_table;
private elf_header elf_header;
@@ -35,7 +77,8 @@ namespace Il2CppInspector
public override int Bits => (elf_header.m_arch == (uint) Elf.ELFCLASS64) ? 64 : 32;
private elf_32_shdr getSection(Elf sectionIndex) => section_header_table.FirstOrDefault(x => x.sh_type == (uint) sectionIndex);
private program_header_table getProgramHeader(Elf programIndex) => program_header_table.FirstOrDefault(x => x.p_type == (uint) programIndex);
private IEnumerable<elf_32_shdr> getSections(Elf sectionIndex) => section_header_table.Where(x => x.sh_type == (uint)sectionIndex);
private elf_32_phdr getProgramHeader(Elf programIndex) => program_header_table.FirstOrDefault(x => x.p_type == (uint) programIndex);
private elf_32_dynamic getDynamic(Elf dynamicIndex) => dynamic_table?.FirstOrDefault(x => x.d_tag == (uint) dynamicIndex);
protected override bool Init() {
@@ -51,10 +94,10 @@ namespace Il2CppInspector
return false;
}
program_header_table = ReadArray<program_header_table>(elf_header.e_phoff, elf_header.e_phnum);
program_header_table = ReadArray<elf_32_phdr>(elf_header.e_phoff, elf_header.e_phnum);
section_header_table = ReadArray<elf_32_shdr>(elf_header.e_shoff, elf_header.e_shnum);
if (getProgramHeader(Elf.PT_DYNAMIC) is program_header_table PT_DYNAMIC)
if (getProgramHeader(Elf.PT_DYNAMIC) is elf_32_phdr PT_DYNAMIC)
dynamic_table = ReadArray<elf_32_dynamic>(PT_DYNAMIC.p_offset, (int) PT_DYNAMIC.p_filesz / 8 /* sizeof(elf_32_dynamic) */);
// Get global offset table
@@ -63,7 +106,73 @@ namespace Il2CppInspector
throw new InvalidOperationException("Unable to get GLOBAL_OFFSET_TABLE from PT_DYNAMIC");
GlobalOffset = (uint) _GLOBAL_OFFSET_TABLE_;
// TODO: Find all relocations
// Find all relocations; target address => (rela header (rels are converted to rela), symbol table base address, is rela?)
var rels = new HashSet<ElfReloc>();
// Two types: add value from offset in image, and add value from specified addend
foreach (var relSection in getSections(Elf.SHT_REL))
rels.UnionWith(
from rel in ReadArray<elf_32_rel>(relSection.sh_offset, (int) (relSection.sh_size / relSection.sh_entsize))
select new ElfReloc(rel, section_header_table[relSection.sh_link].sh_offset));
foreach (var relaSection in getSections(Elf.SHT_RELA))
rels.UnionWith(
from rela in ReadArray<elf_32_rela>(relaSection.sh_offset, (int)(relaSection.sh_size / relaSection.sh_entsize))
select new ElfReloc(rela, section_header_table[relaSection.sh_link].sh_offset));
// Relocations in dynamic section
if (getDynamic(Elf.DT_REL) is elf_32_dynamic dt_rel) {
var dt_rel_count = getDynamic(Elf.DT_RELSZ).d_un / getDynamic(Elf.DT_RELENT).d_un;
var dt_rel_list = ReadArray<elf_32_rel>(MapVATR(dt_rel.d_un), (int) dt_rel_count);
var dt_symtab = getDynamic(Elf.DT_SYMTAB).d_un;
rels.UnionWith(from rel in dt_rel_list select new ElfReloc(rel, dt_symtab));
}
if (getDynamic(Elf.DT_RELA) is elf_32_dynamic dt_rela) {
var dt_rela_count = getDynamic(Elf.DT_RELASZ).d_un / getDynamic(Elf.DT_RELAENT).d_un;
var dt_rela_list = ReadArray<elf_32_rela>(MapVATR(dt_rela.d_un), (int) dt_rela_count);
var dt_symtab = getDynamic(Elf.DT_SYMTAB).d_un;
rels.UnionWith(from rela in dt_rela_list select new ElfReloc(rela, dt_symtab));
}
// Process relocations
// WARNING: This modifies the stream passed in the constructor
if (BaseStream is FileStream)
throw new InvalidOperationException("Input stream to ElfReader is a file. Please supply a mutable stream source.");
var writer = new BinaryWriter(BaseStream);
foreach (var rel in rels) {
var symValue = ReadObject<elf_32_sym>(rel.SymbolTable + rel.SymbolIndex * 16 /* sizeof(elf_32_sym) */).st_value; // S
// The addend is specified in the struct for rela, and comes from the target location for rel
Position = MapVATR(rel.Offset);
var addend = rel.Addend ?? ReadUInt32(); // A
// Only handle relocation types we understand, skip the rest
// Relocation types from https://docs.oracle.com/cd/E23824_01/html/819-0690/chapter6-54839.html#scrolltoc
// and https://studfiles.net/preview/429210/page:18/
(uint newValue, bool recognized) result = (rel.Type, (Elf) elf_header.e_machine) switch {
(Elf.R_ARM_ABS32, Elf.EM_ARM) => (symValue + addend, true), // S + A
(Elf.R_ARM_REL32, Elf.EM_ARM) => (symValue - rel.Offset + addend, true), // S - P + A
(Elf.R_ARM_COPY, Elf.EM_ARM) => (symValue, true), // S
(Elf.R_386_32, Elf.EM_386) => (symValue + addend, true), // S + A
(Elf.R_386_PC32, Elf.EM_386) => (symValue + addend - rel.Offset, true), // S + A - P
(Elf.R_386_GLOB_DAT, Elf.EM_386) => (symValue, true), // S
(Elf.R_386_JMP_SLOT, Elf.EM_386) => (symValue, true), // S
(Elf.R_AMD64_64, Elf.EM_AARCH64) => (symValue + addend, true), // S + A
_ => (0, false)
};
if (result.recognized) {
Position = MapVATR(rel.Offset);
writer.Write(result.newValue);
}
}
Console.WriteLine($"Processed {rels.Count} relocations");
return true;
}

37
Il2CppInspector/FileFormatReaders/FormatLayouts/Elf.cs
View File

@@ -31,13 +31,33 @@ namespace Il2CppInspector
// SHTs
SHT_SYMTAB = 2,
SHT_STRTAB = 3,
SHT_RELA = 4,
SHT_REL = 9,
SHT_DYNSYM = 11,
// dynamic sections
DT_STRTAB = 5,
DT_SYMTAB = 6,
DT_RELA = 7,
DT_RELASZ = 8,
DT_RELAENT = 9,
DT_REL = 17,
DT_RELSZ = 18,
DT_RELENT = 19,
DT_INIT_ARRAY = 25,
DT_INIT_ARRAYSZ = 27
DT_INIT_ARRAYSZ = 27,
// relocation types
R_ARM_ABS32 = 2,
R_ARM_REL32 = 3,
R_ARM_COPY = 20,
R_386_32 = 1,
R_386_PC32 = 2,
R_386_GLOB_DAT = 6,
R_386_JMP_SLOT = 7,
R_AMD64_64 = 1
}
#pragma warning disable CS0649
@@ -90,7 +110,7 @@ namespace Il2CppInspector
public ushort e_shtrndx;
}
internal class program_header_table
internal class elf_32_phdr
{
public uint p_type;
public uint p_offset;
@@ -132,5 +152,18 @@ namespace Il2CppInspector
public uint d_tag;
public uint d_un;
}
internal class elf_32_rel
{
public uint r_offset;
public uint r_info;
}
internal class elf_32_rela
{
public uint r_offset;
public uint r_info;
public uint r_addend;
}
#pragma warning restore CS0649
}