| // Copyright 2015 The Chromium Authors |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| #include "courgette/rel32_finder_x86.h" |
| |
| namespace courgette { |
| |
| Rel32FinderX86::Rel32FinderX86(RVA relocs_start_rva, RVA relocs_end_rva) |
| : Rel32Finder(relocs_start_rva, relocs_end_rva) {} |
| |
| // Scan for opcodes matching the following instructions : |
| // rel32 JMP/CALL |
| // Jcc (excluding JPO/JPE) |
| // Falsely detected rel32 that collide with known abs32 or that point outside |
| // valid regions are discarded. |
| void Rel32FinderX86::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; |
| |
| 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; |
| } |
| } |
| 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); |
| // Valid, rel32 target must be within image, and within this section. |
| // Subsumes |target_rva| != |kUnassignedRVA|. |
| if (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 |