1 /*
2  * Copyright (C) 2012 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 #ifndef ART_RUNTIME_ELF_FILE_IMPL_H_
18 #define ART_RUNTIME_ELF_FILE_IMPL_H_
19 
20 #include <map>
21 #include <memory>
22 #include <type_traits>
23 #include <vector>
24 
25 // Explicitly include our own elf.h to avoid Linux and other dependencies.
26 #include "./elf.h"
27 #include "mem_map.h"
28 
29 namespace art {
30 
31 template <typename ElfTypes>
32 class ElfFileImpl {
33  public:
34   using Elf_Addr = typename ElfTypes::Addr;
35   using Elf_Off = typename ElfTypes::Off;
36   using Elf_Half = typename ElfTypes::Half;
37   using Elf_Word = typename ElfTypes::Word;
38   using Elf_Sword = typename ElfTypes::Sword;
39   using Elf_Ehdr = typename ElfTypes::Ehdr;
40   using Elf_Shdr = typename ElfTypes::Shdr;
41   using Elf_Sym = typename ElfTypes::Sym;
42   using Elf_Rel = typename ElfTypes::Rel;
43   using Elf_Rela = typename ElfTypes::Rela;
44   using Elf_Phdr = typename ElfTypes::Phdr;
45   using Elf_Dyn = typename ElfTypes::Dyn;
46 
47   static ElfFileImpl* Open(File* file,
48                            bool writable,
49                            bool program_header_only,
50                            bool low_4gb,
51                            std::string* error_msg,
52                            uint8_t* requested_base = nullptr);
53   static ElfFileImpl* Open(File* file,
54                            int mmap_prot,
55                            int mmap_flags,
56                            bool low_4gb,
57                            std::string* error_msg);
58   ~ElfFileImpl();
59 
GetFilePath()60   const std::string& GetFilePath() const {
61     return file_path_;
62   }
63 
Begin()64   uint8_t* Begin() const {
65     return map_->Begin();
66   }
67 
End()68   uint8_t* End() const {
69     return map_->End();
70   }
71 
Size()72   size_t Size() const {
73     return map_->Size();
74   }
75 
76   Elf_Ehdr& GetHeader() const;
77 
78   Elf_Word GetProgramHeaderNum() const;
79   Elf_Phdr* GetProgramHeader(Elf_Word) const;
80 
81   Elf_Word GetSectionHeaderNum() const;
82   Elf_Shdr* GetSectionHeader(Elf_Word) const;
83   Elf_Shdr* FindSectionByType(Elf_Word type) const;
84   Elf_Shdr* FindSectionByName(const std::string& name) const;
85 
86   Elf_Shdr* GetSectionNameStringSection() const;
87 
88   // Find .dynsym using .hash for more efficient lookup than FindSymbolAddress.
89   const uint8_t* FindDynamicSymbolAddress(const std::string& symbol_name) const;
90 
91   static bool IsSymbolSectionType(Elf_Word section_type);
92   Elf_Word GetSymbolNum(Elf_Shdr&) const;
93   Elf_Sym* GetSymbol(Elf_Word section_type, Elf_Word i) const;
94 
95   // Find address of symbol in specified table, returning 0 if it is
96   // not found. See FindSymbolByName for an explanation of build_map.
97   Elf_Addr FindSymbolAddress(Elf_Word section_type,
98                              const std::string& symbol_name,
99                              bool build_map);
100 
101   // Lookup a string given string section and offset. Returns null for special 0 offset.
102   const char* GetString(Elf_Shdr&, Elf_Word) const;
103 
104   Elf_Word GetDynamicNum() const;
105   Elf_Dyn& GetDynamic(Elf_Word) const;
106 
107   Elf_Word GetRelNum(Elf_Shdr&) const;
108   Elf_Rel& GetRel(Elf_Shdr&, Elf_Word) const;
109 
110   Elf_Word GetRelaNum(Elf_Shdr&) const;
111   Elf_Rela& GetRela(Elf_Shdr&, Elf_Word) const;
112 
113   // Retrieves the expected size when the file is loaded at runtime. Returns true if successful.
114   bool GetLoadedSize(size_t* size, std::string* error_msg) const;
115 
116   // Load segments into memory based on PT_LOAD program headers.
117   // executable is true at run time, false at compile time.
118   bool Load(File* file, bool executable, bool low_4gb, std::string* error_msg);
119 
120   bool Fixup(Elf_Addr base_address);
121   bool FixupDynamic(Elf_Addr base_address);
122   bool FixupSectionHeaders(Elf_Addr base_address);
123   bool FixupProgramHeaders(Elf_Addr base_address);
124   bool FixupSymbols(Elf_Addr base_address, bool dynamic);
125   bool FixupRelocations(Elf_Addr base_address);
126   bool FixupDebugSections(Elf_Addr base_address_delta);
127   bool ApplyOatPatchesTo(const char* target_section_name, Elf_Addr base_address_delta);
128   static void ApplyOatPatches(const uint8_t* patches, const uint8_t* patches_end, Elf_Addr delta,
129                               uint8_t* to_patch, const uint8_t* to_patch_end);
130 
131   bool Strip(File* file, std::string* error_msg);
132 
133  private:
134   ElfFileImpl(File* file, bool writable, bool program_header_only, uint8_t* requested_base);
135 
136   bool Setup(File* file, int prot, int flags, bool low_4gb, std::string* error_msg);
137 
138   bool SetMap(File* file, MemMap* map, std::string* error_msg);
139 
140   uint8_t* GetProgramHeadersStart() const;
141   uint8_t* GetSectionHeadersStart() const;
142   Elf_Phdr& GetDynamicProgramHeader() const;
143   Elf_Dyn* GetDynamicSectionStart() const;
144   Elf_Sym* GetSymbolSectionStart(Elf_Word section_type) const;
145   const char* GetStringSectionStart(Elf_Word section_type) const;
146   Elf_Rel* GetRelSectionStart(Elf_Shdr&) const;
147   Elf_Rela* GetRelaSectionStart(Elf_Shdr&) const;
148   Elf_Word* GetHashSectionStart() const;
149   Elf_Word GetHashBucketNum() const;
150   Elf_Word GetHashChainNum() const;
151   Elf_Word GetHashBucket(size_t i, bool* ok) const;
152   Elf_Word GetHashChain(size_t i, bool* ok) const;
153 
154   typedef std::map<std::string, Elf_Sym*> SymbolTable;
155   SymbolTable** GetSymbolTable(Elf_Word section_type);
156 
157   bool ValidPointer(const uint8_t* start) const;
158 
159   const Elf_Sym* FindDynamicSymbol(const std::string& symbol_name) const;
160 
161   // Check that certain sections and their dependencies exist.
162   bool CheckSectionsExist(File* file, std::string* error_msg) const;
163 
164   // Check that the link of the first section links to the second section.
165   bool CheckSectionsLinked(const uint8_t* source, const uint8_t* target) const;
166 
167   // Check whether the offset is in range, and set to target to Begin() + offset if OK.
168   bool CheckAndSet(Elf32_Off offset, const char* label, uint8_t** target, std::string* error_msg);
169 
170   // Find symbol in specified table, returning null if it is not found.
171   //
172   // If build_map is true, builds a map to speed repeated access. The
173   // map does not included untyped symbol values (aka STT_NOTYPE)
174   // since they can contain duplicates. If build_map is false, the map
175   // will be used if it was already created. Typically build_map
176   // should be set unless only a small number of symbols will be
177   // looked up.
178   Elf_Sym* FindSymbolByName(Elf_Word section_type,
179                             const std::string& symbol_name,
180                             bool build_map);
181 
182   Elf_Phdr* FindProgamHeaderByType(Elf_Word type) const;
183 
184   Elf_Dyn* FindDynamicByType(Elf_Sword type) const;
185   Elf_Word FindDynamicValueByType(Elf_Sword type) const;
186 
187   // Lookup a string by section type. Returns null for special 0 offset.
188   const char* GetString(Elf_Word section_type, Elf_Word) const;
189 
190   const std::string file_path_;
191   const bool writable_;
192   const bool program_header_only_;
193 
194   // ELF header mapping. If program_header_only_ is false, will
195   // actually point to the entire elf file.
196   std::unique_ptr<MemMap> map_;
197   Elf_Ehdr* header_;
198   std::vector<MemMap*> segments_;
199 
200   // Pointer to start of first PT_LOAD program segment after Load()
201   // when program_header_only_ is true.
202   uint8_t* base_address_;
203 
204   // The program header should always available but use GetProgramHeadersStart() to be sure.
205   uint8_t* program_headers_start_;
206 
207   // Conditionally available values. Use accessors to ensure they exist if they are required.
208   uint8_t* section_headers_start_;
209   Elf_Phdr* dynamic_program_header_;
210   Elf_Dyn* dynamic_section_start_;
211   Elf_Sym* symtab_section_start_;
212   Elf_Sym* dynsym_section_start_;
213   char* strtab_section_start_;
214   char* dynstr_section_start_;
215   Elf_Word* hash_section_start_;
216 
217   SymbolTable* symtab_symbol_table_;
218   SymbolTable* dynsym_symbol_table_;
219 
220   // Override the 'base' p_vaddr in the first LOAD segment with this value (if non-null).
221   uint8_t* requested_base_;
222 
223   DISALLOW_COPY_AND_ASSIGN(ElfFileImpl);
224 };
225 
226 }  // namespace art
227 
228 #endif  // ART_RUNTIME_ELF_FILE_IMPL_H_
229