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- // Copyright 2016 The Chromium Authors. All rights reserved.
- // Use of this source code is governed by a BSD-style license that can be
- // found in the LICENSE file.
- #include "courgette/rel32_finder_x64.h"
- namespace courgette {
- Rel32FinderX64::Rel32FinderX64(RVA relocs_start_rva,
- RVA relocs_end_rva,
- RVA size_of_image)
- : Rel32Finder(relocs_start_rva, relocs_end_rva),
- size_of_image_(size_of_image) {}
- // Scan for opcodes matching the following instructions :
- // rel32 JMP/CALL
- // rip MOV/LEA
- // Jcc (excluding JPO/JPE)
- // Falsely detected rel32 that collide with known abs32 or that point outside
- // valid regions are discarded.
- void Rel32FinderX64::Find(const uint8_t* start_pointer,
- const uint8_t* end_pointer,
- RVA start_rva,
- RVA end_rva,
- const std::vector<RVA>& abs32_locations) {
- // Quick way to convert from Pointer to RVA within a single Section is to
- // subtract |adjust_pointer_to_rva|.
- const uint8_t* const adjust_pointer_to_rva = start_pointer - start_rva;
- std::vector<RVA>::const_iterator abs32_pos = abs32_locations.begin();
- // Find the rel32 relocations.
- const uint8_t* p = start_pointer;
- while (p < end_pointer) {
- RVA current_rva = static_cast<RVA>(p - adjust_pointer_to_rva);
- // Skip the base reloation table if we encounter it.
- // Note: We're not bothering to handle the edge case where a Rel32 pointer
- // collides with |relocs_start_rva_| by being {1, 2, 3}-bytes before it.
- if (current_rva >= relocs_start_rva_ && current_rva < relocs_end_rva_) {
- p += relocs_end_rva_ - current_rva;
- continue;
- }
- // Heuristic discovery of rel32 locations in instruction stream: are the
- // next few bytes the start of an instruction containing a rel32
- // addressing mode?
- const uint8_t* rel32 = nullptr;
- bool is_rip_relative = false;
- if (p + 5 <= end_pointer) {
- if (p[0] == 0xE8 || p[0] == 0xE9) // jmp rel32 and call rel32
- rel32 = p + 1;
- }
- if (p + 6 <= end_pointer) {
- if (p[0] == 0x0F && (p[1] & 0xF0) == 0x80) { // Jcc long form
- if (p[1] != 0x8A && p[1] != 0x8B) // JPE/JPO unlikely
- rel32 = p + 2;
- } else if ((p[0] == 0xFF &&
- (p[1] == 0x15 || p[1] == 0x25)) ||
- ((p[0] == 0x89 || p[0] == 0x8B || p[0] == 0x8D) &&
- (p[1] & 0xC7) == 0x05)) {
- // 6-byte instructions:
- // [2-byte opcode] [disp32]:
- // Opcode
- // FF 15: call QWORD PTR [rip+disp32]
- // FF 25: jmp QWORD PTR [rip+disp32]
- //
- // [1-byte opcode] [ModR/M] [disp32]:
- // Opcode
- // 89: mov DWORD PTR [rip+disp32],reg
- // 8B: mov reg,DWORD PTR [rip+disp32]
- // 8D: lea reg,[rip+disp32]
- // ModR/M : MMRRRMMM
- // MM = 00 & MMM = 101 => rip+disp32
- // RRR: selects reg operand from [eax|ecx|...|edi]
- rel32 = p + 2;
- is_rip_relative = true;
- }
- }
- // TODO(huangs): Maybe skip checking prefixes,
- // and let 6-byte instructions take care of this?
- if (p + 7 <= end_pointer) {
- if (((p[0] & 0xF2) == 0x40 || p[0] == 0x66) &&
- (p[1] == 0x89 || p[1] == 0x8B || p[1] == 0x8D) &&
- (p[2] & 0xC7) == 0x05) {
- // 7-byte instructions:
- // [REX.W prefix] [1-byte opcode] [ModR/M] [disp32]
- // REX Prefix : 0100WR0B
- // W: 0 = Default Operation Size
- // 1 = 64 Bit Operand Size
- // R: 0 = REG selects from [rax|rcx|...|rdi].
- // 1 = REG selects from [r9|r10|...|r15].
- // B: ModR/M r/m field extension (not used).
- // Opcode
- // 89: mov QWORD PTR [rip+disp32],reg
- // 8B: mov reg,QWORD PTR [rip+disp32]
- // 8D: lea reg,[rip+disp32]
- // ModR/M : MMRRRMMM
- // MM = 00 & MMM = 101 => rip+disp32
- // RRR: selects reg operand
- //
- // 66 [1-byte opcode] [ModR/M] [disp32]
- // Prefix
- // 66: Operand size override
- // Opcode
- // 89: mov WORD PTR [rip+disp32],reg
- // 8B: mov reg,WORD PTR [rip+disp32]
- // 8D: lea reg,[rip+disp32]
- // ModR/M : MMRRRMMM
- // MM = 00 & MMM = 101 = rip+disp32
- // RRR selects reg operand from [ax|cx|...|di]
- rel32 = p + 3;
- is_rip_relative = true;
- }
- }
- if (rel32) {
- RVA rel32_rva = static_cast<RVA>(rel32 - adjust_pointer_to_rva);
- // Is there an abs32 reloc overlapping the candidate?
- while (abs32_pos != abs32_locations.end() && *abs32_pos < rel32_rva - 3)
- ++abs32_pos;
- // Now: (*abs32_pos > rel32_rva - 4) i.e. the lowest addressed 4-byte
- // region that could overlap rel32_rva.
- if (abs32_pos != abs32_locations.end()) {
- if (*abs32_pos < rel32_rva + 4) {
- // Beginning of abs32 reloc is before end of rel32 reloc so they
- // overlap. Skip four bytes past the abs32 reloc.
- p += (*abs32_pos + 4) - current_rva;
- continue;
- }
- }
- // + 4 since offset is relative to start of next instruction.
- RVA target_rva = rel32_rva + 4 + Read32LittleEndian(rel32);
- // To be valid, rel32 target must be within image, and within this
- // section.
- if (target_rva < size_of_image_ && // Subsumes rva != kUnassignedRVA.
- (is_rip_relative ||
- (start_rva <= target_rva && target_rva < end_rva))) {
- rel32_locations_.push_back(rel32_rva);
- #if COURGETTE_HISTOGRAM_TARGETS
- ++rel32_target_rvas_[target_rva];
- #endif
- p = rel32 + 4;
- continue;
- }
- }
- p += 1;
- }
- }
- } // namespace courgette
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