1 /*
2  * Copyright (C) 2014 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 __ANDROID_DLEXT_H__
18 #define __ANDROID_DLEXT_H__
19 
20 #include <stdbool.h>
21 #include <stddef.h>
22 #include <stdint.h>
23 #include <sys/cdefs.h>
24 #include <sys/types.h>  /* for off64_t */
25 
26 /**
27  * @addtogroup libdl Dynamic Linker
28  * @{
29  */
30 
31 /**
32  * \file
33  * Advanced dynamic library opening support. Most users will want to use
34  * the standard [dlopen(3)](http://man7.org/linux/man-pages/man3/dlopen.3.html)
35  * functionality in `<dlfcn.h>` instead.
36  */
37 
38 __BEGIN_DECLS
39 
40 /** Bitfield definitions for `android_dlextinfo::flags`. */
41 enum {
42   /**
43    * When set, the `reserved_addr` and `reserved_size` fields must point to an
44    * already-reserved region of address space which will be used to load the
45    * library if it fits.
46    *
47    * If the reserved region is not large enough, loading will fail.
48    */
49   ANDROID_DLEXT_RESERVED_ADDRESS      = 0x1,
50 
51   /**
52    * Like `ANDROID_DLEXT_RESERVED_ADDRESS`, but if the reserved region is not large enough,
53    * the linker will choose an available address instead.
54    */
55   ANDROID_DLEXT_RESERVED_ADDRESS_HINT = 0x2,
56 
57   /**
58    * When set, write the GNU RELRO section of the mapped library to `relro_fd`
59    * after relocation has been performed, to allow it to be reused by another
60    * process loading the same library at the same address. This implies
61    * `ANDROID_DLEXT_USE_RELRO`.
62    *
63    * This is mainly useful for the system WebView implementation.
64    */
65   ANDROID_DLEXT_WRITE_RELRO           = 0x4,
66 
67   /**
68    * When set, compare the GNU RELRO section of the mapped library to `relro_fd`
69    * after relocation has been performed, and replace any relocated pages that
70    * are identical with a version mapped from the file.
71    *
72    * This is mainly useful for the system WebView implementation.
73    */
74   ANDROID_DLEXT_USE_RELRO             = 0x8,
75 
76   /**
77    * Use `library_fd` instead of opening the file by name.
78    * The filename parameter is still used to identify the library.
79    */
80   ANDROID_DLEXT_USE_LIBRARY_FD        = 0x10,
81 
82   /**
83    * If opening a library using `library_fd` read it starting at `library_fd_offset`.
84    * This is mainly useful for loading a library stored within another file (such as uncompressed
85    * inside a ZIP archive).
86    * This flag is only valid when `ANDROID_DLEXT_USE_LIBRARY_FD` is set.
87    */
88   ANDROID_DLEXT_USE_LIBRARY_FD_OFFSET    = 0x20,
89 
90   /**
91    * When set, do not use `stat(2)` to check if the library has already been loaded.
92    *
93    * This flag allows forced loading of the library in the case when for some
94    * reason multiple ELF files share the same filename (because the already-loaded
95    * library has been removed and overwritten, for example).
96    *
97    * Note that if the library has the same `DT_SONAME` as an old one and some other
98    * library has the soname in its `DT_NEEDED` list, the first one will be used to resolve any
99    * dependencies.
100    */
101   ANDROID_DLEXT_FORCE_LOAD = 0x40,
102 
103   // Historically we had two other options for ART.
104   // They were last available in Android P.
105   // Reuse these bits last!
106   // ANDROID_DLEXT_FORCE_FIXED_VADDR = 0x80
107   // ANDROID_DLEXT_LOAD_AT_FIXED_ADDRESS = 0x100
108 
109   /**
110    * This flag used to load library in a different namespace. The namespace is
111    * specified in `library_namespace`.
112    *
113    * This flag is for internal use only (since there is no NDK API for namespaces).
114    */
115   ANDROID_DLEXT_USE_NAMESPACE = 0x200,
116 
117   /**
118    * Instructs dlopen to apply `ANDROID_DLEXT_RESERVED_ADDRESS`,
119    * `ANDROID_DLEXT_RESERVED_ADDRESS_HINT`, `ANDROID_DLEXT_WRITE_RELRO` and
120    * `ANDROID_DLEXT_USE_RELRO` to any libraries loaded as dependencies of the
121    * main library as well.
122    *
123    * This means that if the main library depends on one or more not-already-loaded libraries, they
124    * will be loaded consecutively into the region starting at `reserved_addr`, and `reserved_size`
125    * must be large enough to contain all of the libraries. The libraries will be loaded in the
126    * deterministic order constructed from the DT_NEEDED entries, rather than the more secure random
127    * order used by default.
128    *
129    * Each library's GNU RELRO sections will be written out to `relro_fd` in the same order they were
130    * loaded. This will mean that the resulting file is dependent on which of the libraries were
131    * already loaded, as only the newly loaded libraries will be included, not any already-loaded
132    * dependencies. The caller should ensure that the set of libraries newly loaded is consistent
133    * for this to be effective.
134    *
135    * This is mainly useful for the system WebView implementation.
136    */
137   ANDROID_DLEXT_RESERVED_ADDRESS_RECURSIVE = 0x400,
138 
139 
140   /** Mask of valid bits. */
141   ANDROID_DLEXT_VALID_FLAG_BITS       = ANDROID_DLEXT_RESERVED_ADDRESS |
142                                         ANDROID_DLEXT_RESERVED_ADDRESS_HINT |
143                                         ANDROID_DLEXT_WRITE_RELRO |
144                                         ANDROID_DLEXT_USE_RELRO |
145                                         ANDROID_DLEXT_USE_LIBRARY_FD |
146                                         ANDROID_DLEXT_USE_LIBRARY_FD_OFFSET |
147                                         ANDROID_DLEXT_FORCE_LOAD |
148                                         ANDROID_DLEXT_USE_NAMESPACE |
149                                         ANDROID_DLEXT_RESERVED_ADDRESS_RECURSIVE,
150 };
151 
152 struct android_namespace_t;
153 
154 /** Used to pass Android-specific arguments to `android_dlopen_ext`. */
155 typedef struct {
156   /** A bitmask of `ANDROID_DLEXT_` enum values. */
157   uint64_t flags;
158 
159   /** Used by `ANDROID_DLEXT_RESERVED_ADDRESS` and `ANDROID_DLEXT_RESERVED_ADDRESS_HINT`. */
160   void*   reserved_addr;
161   /** Used by `ANDROID_DLEXT_RESERVED_ADDRESS` and `ANDROID_DLEXT_RESERVED_ADDRESS_HINT`. */
162   size_t  reserved_size;
163 
164   /** Used by `ANDROID_DLEXT_WRITE_RELRO` and `ANDROID_DLEXT_USE_RELRO`. */
165   int     relro_fd;
166 
167   /** Used by `ANDROID_DLEXT_USE_LIBRARY_FD`. */
168   int     library_fd;
169   /** Used by `ANDROID_DLEXT_USE_LIBRARY_FD_OFFSET` */
170   off64_t library_fd_offset;
171 
172   /** Used by `ANDROID_DLEXT_USE_NAMESPACE`. */
173   struct android_namespace_t* library_namespace;
174 } android_dlextinfo;
175 
176 /**
177  * Opens the given library. The `__filename` and `__flags` arguments are
178  * the same as for [dlopen(3)](http://man7.org/linux/man-pages/man3/dlopen.3.html),
179  * with the Android-specific flags supplied via the `flags` member of `__info`.
180  *
181  * Available since API level 21.
182  */
183 void* android_dlopen_ext(const char* __filename, int __flags, const android_dlextinfo* __info)
184   __INTRODUCED_IN(21);
185 
186 __END_DECLS
187 
188 /** @} */
189 
190 #endif
191