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90 lines
2.8 KiB
90 lines
2.8 KiB
/*
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* Copyright (C) 2023 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include <elf.h>
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#include <stdio.h>
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#include <iostream>
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#include <string>
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#include "./elf.h"
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namespace shell_as {
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namespace {
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// The base address of a PIE binary when loaded with ASLR disabled.
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#if defined(__arm__) || defined(__aarch64__)
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constexpr uint64_t k32BitImageBase = 0xAAAAA000;
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constexpr uint64_t k64BitImageBase = 0x5555555000;
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#else
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constexpr uint64_t k32BitImageBase = 0x56555000;
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constexpr uint64_t k64BitImageBase = 0x555555554000;
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#endif
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} // namespace
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bool GetElfEntryPoint(const pid_t process_id, uint64_t* entry_address,
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bool* is_arm_mode) {
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uint8_t elf_header_buffer[sizeof(Elf64_Ehdr)];
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std::string exe_path = "/proc/" + std::to_string(process_id) + "/exe";
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FILE* exe_file = fopen(exe_path.c_str(), "rb");
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if (exe_file == nullptr) {
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std::cerr << "Unable to open executable of process " << process_id
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<< std::endl;
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return false;
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}
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int read_size =
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fread(elf_header_buffer, sizeof(elf_header_buffer), 1, exe_file);
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fclose(exe_file);
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if (read_size <= 0) {
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std::cerr << "Unable to read executable of process " << process_id
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<< std::endl;
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return false;
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}
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const Elf32_Ehdr* file_header_32 = (Elf32_Ehdr*)elf_header_buffer;
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const Elf64_Ehdr* file_header_64 = (Elf64_Ehdr*)elf_header_buffer;
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// The first handful of bytes of a header do not depend on whether the file is
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// 32bit vs 64bit.
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const bool is_pie_binary = file_header_32->e_type == ET_DYN;
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if (file_header_32->e_ident[EI_CLASS] == ELFCLASS32) {
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*entry_address =
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file_header_32->e_entry + (is_pie_binary ? k32BitImageBase : 0);
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} else if (file_header_32->e_ident[EI_CLASS] == ELFCLASS64) {
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*entry_address =
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file_header_64->e_entry + (is_pie_binary ? k64BitImageBase : 0);
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} else {
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return false;
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}
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*is_arm_mode = false;
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#if defined(__arm__)
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if ((*entry_address & 1) == 0) {
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*is_arm_mode = true;
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}
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// The entry address for ARM Elf binaries is branched to using a BX
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// instruction. The low bit of these instructions indicates the instruction
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// set of the code that is being jumped to. A low bit of 1 indicates thumb
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// mode while a low bit of 0 indicates ARM mode.
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*entry_address &= ~1;
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#endif
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return true;
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}
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} // namespace shell_as
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