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1 // Copyright (c) 2012, Google Inc.
2 // All rights reserved.
3 //
4 // Redistribution and use in source and binary forms, with or without
5 // modification, are permitted provided that the following conditions are
6 // met:
7 //
8 //     * Redistributions of source code must retain the above copyright
9 // notice, this list of conditions and the following disclaimer.
10 //     * Redistributions in binary form must reproduce the above
11 // copyright notice, this list of conditions and the following disclaimer
12 // in the documentation and/or other materials provided with the
13 // distribution.
14 //     * Neither the name of Google Inc. nor the names of its
15 // contributors may be used to endorse or promote products derived from
16 // this software without specific prior written permission.
17 //
18 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
19 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
20 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
21 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
22 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
23 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
24 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
25 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
26 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
27 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
28 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
29 
30 #include "common/linux/elfutils.h"
31 
32 #include <assert.h>
33 #include <string.h>
34 
35 #include "common/linux/linux_libc_support.h"
36 #include "common/linux/elfutils-inl.h"
37 
38 namespace google_breakpad {
39 
40 namespace {
41 
42 template<typename ElfClass>
FindElfClassSection(const char * elf_base,const char * section_name,typename ElfClass::Word section_type,const void ** section_start,size_t * section_size)43 void FindElfClassSection(const char *elf_base,
44                          const char *section_name,
45                          typename ElfClass::Word section_type,
46                          const void **section_start,
47                          size_t *section_size) {
48   typedef typename ElfClass::Ehdr Ehdr;
49   typedef typename ElfClass::Shdr Shdr;
50 
51   assert(elf_base);
52   assert(section_start);
53   assert(section_size);
54 
55   assert(my_strncmp(elf_base, ELFMAG, SELFMAG) == 0);
56 
57   const Ehdr* elf_header = reinterpret_cast<const Ehdr*>(elf_base);
58   assert(elf_header->e_ident[EI_CLASS] == ElfClass::kClass);
59 
60   const Shdr* sections =
61     GetOffset<ElfClass, Shdr>(elf_header, elf_header->e_shoff);
62   const Shdr* section_names = sections + elf_header->e_shstrndx;
63   const char* names =
64     GetOffset<ElfClass, char>(elf_header, section_names->sh_offset);
65   const char *names_end = names + section_names->sh_size;
66 
67   const Shdr* section =
68     FindElfSectionByName<ElfClass>(section_name, section_type,
69                                    sections, names, names_end,
70                                    elf_header->e_shnum);
71 
72   if (section != NULL && section->sh_size > 0) {
73     *section_start = elf_base + section->sh_offset;
74     *section_size = section->sh_size;
75   }
76 }
77 
78 template<typename ElfClass>
FindElfClassSegment(const char * elf_base,typename ElfClass::Word segment_type,const void ** segment_start,size_t * segment_size)79 void FindElfClassSegment(const char *elf_base,
80                          typename ElfClass::Word segment_type,
81                          const void **segment_start,
82                          size_t *segment_size) {
83   typedef typename ElfClass::Ehdr Ehdr;
84   typedef typename ElfClass::Phdr Phdr;
85 
86   assert(elf_base);
87   assert(segment_start);
88   assert(segment_size);
89 
90   assert(my_strncmp(elf_base, ELFMAG, SELFMAG) == 0);
91 
92   const Ehdr* elf_header = reinterpret_cast<const Ehdr*>(elf_base);
93   assert(elf_header->e_ident[EI_CLASS] == ElfClass::kClass);
94 
95   const Phdr* phdrs =
96     GetOffset<ElfClass, Phdr>(elf_header, elf_header->e_phoff);
97 
98   for (int i = 0; i < elf_header->e_phnum; ++i) {
99     if (phdrs[i].p_type == segment_type) {
100       *segment_start = elf_base + phdrs[i].p_offset;
101       *segment_size = phdrs[i].p_filesz;
102       return;
103     }
104   }
105 }
106 
107 }  // namespace
108 
IsValidElf(const void * elf_base)109 bool IsValidElf(const void* elf_base) {
110   return my_strncmp(reinterpret_cast<const char*>(elf_base),
111                     ELFMAG, SELFMAG) == 0;
112 }
113 
ElfClass(const void * elf_base)114 int ElfClass(const void* elf_base) {
115   const ElfW(Ehdr)* elf_header =
116     reinterpret_cast<const ElfW(Ehdr)*>(elf_base);
117 
118   return elf_header->e_ident[EI_CLASS];
119 }
120 
FindElfSection(const void * elf_mapped_base,const char * section_name,uint32_t section_type,const void ** section_start,size_t * section_size,int * elfclass)121 bool FindElfSection(const void *elf_mapped_base,
122                     const char *section_name,
123                     uint32_t section_type,
124                     const void **section_start,
125                     size_t *section_size,
126                     int *elfclass) {
127   assert(elf_mapped_base);
128   assert(section_start);
129   assert(section_size);
130 
131   *section_start = NULL;
132   *section_size = 0;
133 
134   if (!IsValidElf(elf_mapped_base))
135     return false;
136 
137   int cls = ElfClass(elf_mapped_base);
138   if (elfclass) {
139     *elfclass = cls;
140   }
141 
142   const char* elf_base =
143     static_cast<const char*>(elf_mapped_base);
144 
145   if (cls == ELFCLASS32) {
146     FindElfClassSection<ElfClass32>(elf_base, section_name, section_type,
147                                     section_start, section_size);
148     return *section_start != NULL;
149   } else if (cls == ELFCLASS64) {
150     FindElfClassSection<ElfClass64>(elf_base, section_name, section_type,
151                                     section_start, section_size);
152     return *section_start != NULL;
153   }
154 
155   return false;
156 }
157 
FindElfSegment(const void * elf_mapped_base,uint32_t segment_type,const void ** segment_start,size_t * segment_size,int * elfclass)158 bool FindElfSegment(const void *elf_mapped_base,
159                     uint32_t segment_type,
160                     const void **segment_start,
161                     size_t *segment_size,
162                     int *elfclass) {
163   assert(elf_mapped_base);
164   assert(segment_start);
165   assert(segment_size);
166 
167   *segment_start = NULL;
168   *segment_size = 0;
169 
170   if (!IsValidElf(elf_mapped_base))
171     return false;
172 
173   int cls = ElfClass(elf_mapped_base);
174   if (elfclass) {
175     *elfclass = cls;
176   }
177 
178   const char* elf_base =
179     static_cast<const char*>(elf_mapped_base);
180 
181   if (cls == ELFCLASS32) {
182     FindElfClassSegment<ElfClass32>(elf_base, segment_type,
183                                     segment_start, segment_size);
184     return *segment_start != NULL;
185   } else if (cls == ELFCLASS64) {
186     FindElfClassSegment<ElfClass64>(elf_base, segment_type,
187                                     segment_start, segment_size);
188     return *segment_start != NULL;
189   }
190 
191   return false;
192 }
193 
194 }  // namespace google_breakpad
195