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- // Copyright 2015 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_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
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