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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