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      1 /*
      2  * Copyright (C) 2007 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 #include "linker.h"
     18 
     19 #include <dlfcn.h>
     20 #include <pthread.h>
     21 #include <stdio.h>
     22 #include <stdlib.h>
     23 #include <android/dlext.h>
     24 
     25 #include <bionic/pthread_internal.h>
     26 #include "private/bionic_tls.h"
     27 #include "private/ScopedPthreadMutexLocker.h"
     28 #include "private/ThreadLocalBuffer.h"
     29 
     30 /* This file hijacks the symbols stubbed out in libdl.so. */
     31 
     32 static pthread_mutex_t g_dl_mutex = PTHREAD_RECURSIVE_MUTEX_INITIALIZER;
     33 
     34 static const char* __bionic_set_dlerror(char* new_value) {
     35   char** dlerror_slot = &reinterpret_cast<char**>(__get_tls())[TLS_SLOT_DLERROR];
     36 
     37   const char* old_value = *dlerror_slot;
     38   *dlerror_slot = new_value;
     39   return old_value;
     40 }
     41 
     42 static void __bionic_format_dlerror(const char* msg, const char* detail) {
     43   char* buffer = __get_thread()->dlerror_buffer;
     44   strlcpy(buffer, msg, __BIONIC_DLERROR_BUFFER_SIZE);
     45   if (detail != NULL) {
     46     strlcat(buffer, ": ", __BIONIC_DLERROR_BUFFER_SIZE);
     47     strlcat(buffer, detail, __BIONIC_DLERROR_BUFFER_SIZE);
     48   }
     49 
     50   __bionic_set_dlerror(buffer);
     51 }
     52 
     53 const char* dlerror() {
     54   const char* old_value = __bionic_set_dlerror(NULL);
     55   return old_value;
     56 }
     57 
     58 void android_get_LD_LIBRARY_PATH(char* buffer, size_t buffer_size) {
     59   ScopedPthreadMutexLocker locker(&g_dl_mutex);
     60   do_android_get_LD_LIBRARY_PATH(buffer, buffer_size);
     61 }
     62 
     63 void android_update_LD_LIBRARY_PATH(const char* ld_library_path) {
     64   ScopedPthreadMutexLocker locker(&g_dl_mutex);
     65   do_android_update_LD_LIBRARY_PATH(ld_library_path);
     66 }
     67 
     68 static void* dlopen_ext(const char* filename, int flags, const android_dlextinfo* extinfo) {
     69   ScopedPthreadMutexLocker locker(&g_dl_mutex);
     70   soinfo* result = do_dlopen(filename, flags, extinfo);
     71   if (result == NULL) {
     72     __bionic_format_dlerror("dlopen failed", linker_get_error_buffer());
     73     return NULL;
     74   }
     75   return result;
     76 }
     77 
     78 void* android_dlopen_ext(const char* filename, int flags, const android_dlextinfo* extinfo) {
     79   return dlopen_ext(filename, flags, extinfo);
     80 }
     81 
     82 void* dlopen(const char* filename, int flags) {
     83   return dlopen_ext(filename, flags, NULL);
     84 }
     85 
     86 void* dlsym(void* handle, const char* symbol) {
     87   ScopedPthreadMutexLocker locker(&g_dl_mutex);
     88 
     89 #if !defined(__LP64__)
     90   if (handle == NULL) {
     91     __bionic_format_dlerror("dlsym library handle is null", NULL);
     92     return NULL;
     93   }
     94 #endif
     95 
     96   if (symbol == NULL) {
     97     __bionic_format_dlerror("dlsym symbol name is null", NULL);
     98     return NULL;
     99   }
    100 
    101   soinfo* found = NULL;
    102   ElfW(Sym)* sym = NULL;
    103   if (handle == RTLD_DEFAULT) {
    104     sym = dlsym_linear_lookup(symbol, &found, NULL);
    105   } else if (handle == RTLD_NEXT) {
    106     void* caller_addr = __builtin_return_address(0);
    107     soinfo* si = find_containing_library(caller_addr);
    108 
    109     sym = NULL;
    110     if (si && si->next) {
    111       sym = dlsym_linear_lookup(symbol, &found, si->next);
    112     }
    113   } else {
    114     sym = dlsym_handle_lookup(reinterpret_cast<soinfo*>(handle), &found, symbol);
    115   }
    116 
    117   if (sym != NULL) {
    118     unsigned bind = ELF_ST_BIND(sym->st_info);
    119 
    120     if ((bind == STB_GLOBAL || bind == STB_WEAK) && sym->st_shndx != 0) {
    121       return reinterpret_cast<void*>(sym->st_value + found->load_bias);
    122     }
    123 
    124     __bionic_format_dlerror("symbol found but not global", symbol);
    125     return NULL;
    126   } else {
    127     __bionic_format_dlerror("undefined symbol", symbol);
    128     return NULL;
    129   }
    130 }
    131 
    132 int dladdr(const void* addr, Dl_info* info) {
    133   ScopedPthreadMutexLocker locker(&g_dl_mutex);
    134 
    135   // Determine if this address can be found in any library currently mapped.
    136   soinfo* si = find_containing_library(addr);
    137   if (si == NULL) {
    138     return 0;
    139   }
    140 
    141   memset(info, 0, sizeof(Dl_info));
    142 
    143   info->dli_fname = si->name;
    144   // Address at which the shared object is loaded.
    145   info->dli_fbase = reinterpret_cast<void*>(si->base);
    146 
    147   // Determine if any symbol in the library contains the specified address.
    148   ElfW(Sym)* sym = dladdr_find_symbol(si, addr);
    149   if (sym != NULL) {
    150     info->dli_sname = si->strtab + sym->st_name;
    151     info->dli_saddr = reinterpret_cast<void*>(si->load_bias + sym->st_value);
    152   }
    153 
    154   return 1;
    155 }
    156 
    157 int dlclose(void* handle) {
    158   ScopedPthreadMutexLocker locker(&g_dl_mutex);
    159   do_dlclose(reinterpret_cast<soinfo*>(handle));
    160   // dlclose has no defined errors.
    161   return 0;
    162 }
    163 
    164 // name_offset: starting index of the name in libdl_info.strtab
    165 #define ELF32_SYM_INITIALIZER(name_offset, value, shndx) \
    166     { name_offset, \
    167       reinterpret_cast<Elf32_Addr>(reinterpret_cast<void*>(value)), \
    168       /* st_size */ 0, \
    169       (shndx == 0) ? 0 : (STB_GLOBAL << 4), \
    170       /* st_other */ 0, \
    171       shndx, \
    172     }
    173 
    174 #define ELF64_SYM_INITIALIZER(name_offset, value, shndx) \
    175     { name_offset, \
    176       (shndx == 0) ? 0 : (STB_GLOBAL << 4), \
    177       /* st_other */ 0, \
    178       shndx, \
    179       reinterpret_cast<Elf64_Addr>(reinterpret_cast<void*>(value)), \
    180       /* st_size */ 0, \
    181     }
    182 
    183 #if defined(__arm__)
    184   // 0000000 00011111 111112 22222222 2333333 3333444444444455555555556666666 6667777777777888888888899999 9999900000000001 1111111112222222222 333333333344444444445
    185   // 0123456 78901234 567890 12345678 9012345 6789012345678901234567890123456 7890123456789012345678901234 5678901234567890 1234567890123456789 012345678901234567890
    186 #  define ANDROID_LIBDL_STRTAB \
    187     "dlopen\0dlclose\0dlsym\0dlerror\0dladdr\0android_update_LD_LIBRARY_PATH\0android_get_LD_LIBRARY_PATH\0dl_iterate_phdr\0android_dlopen_ext\0dl_unwind_find_exidx\0"
    188 #elif defined(__aarch64__) || defined(__i386__) || defined(__mips__) || defined(__x86_64__)
    189   // 0000000 00011111 111112 22222222 2333333 3333444444444455555555556666666 6667777777777888888888899999 9999900000000001 1111111112222222222
    190   // 0123456 78901234 567890 12345678 9012345 6789012345678901234567890123456 7890123456789012345678901234 5678901234567890 1234567890123456789
    191 #  define ANDROID_LIBDL_STRTAB \
    192     "dlopen\0dlclose\0dlsym\0dlerror\0dladdr\0android_update_LD_LIBRARY_PATH\0android_get_LD_LIBRARY_PATH\0dl_iterate_phdr\0android_dlopen_ext\0"
    193 #else
    194 #  error Unsupported architecture. Only arm, arm64, mips, mips64, x86 and x86_64 are presently supported.
    195 #endif
    196 
    197 static ElfW(Sym) g_libdl_symtab[] = {
    198   // Total length of libdl_info.strtab, including trailing 0.
    199   // This is actually the STH_UNDEF entry. Technically, it's
    200   // supposed to have st_name == 0, but instead, it points to an index
    201   // in the strtab with a \0 to make iterating through the symtab easier.
    202   ELFW(SYM_INITIALIZER)(sizeof(ANDROID_LIBDL_STRTAB) - 1, NULL, 0),
    203   ELFW(SYM_INITIALIZER)(  0, &dlopen, 1),
    204   ELFW(SYM_INITIALIZER)(  7, &dlclose, 1),
    205   ELFW(SYM_INITIALIZER)( 15, &dlsym, 1),
    206   ELFW(SYM_INITIALIZER)( 21, &dlerror, 1),
    207   ELFW(SYM_INITIALIZER)( 29, &dladdr, 1),
    208   ELFW(SYM_INITIALIZER)( 36, &android_update_LD_LIBRARY_PATH, 1),
    209   ELFW(SYM_INITIALIZER)( 67, &android_get_LD_LIBRARY_PATH, 1),
    210   ELFW(SYM_INITIALIZER)( 95, &dl_iterate_phdr, 1),
    211   ELFW(SYM_INITIALIZER)(111, &android_dlopen_ext, 1),
    212 #if defined(__arm__)
    213   ELFW(SYM_INITIALIZER)(130, &dl_unwind_find_exidx, 1),
    214 #endif
    215 };
    216 
    217 // Fake out a hash table with a single bucket.
    218 //
    219 // A search of the hash table will look through g_libdl_symtab starting with index 1, then
    220 // use g_libdl_chains to find the next index to look at. g_libdl_chains should be set up to
    221 // walk through every element in g_libdl_symtab, and then end with 0 (sentinel value).
    222 //
    223 // That is, g_libdl_chains should look like { 0, 2, 3, ... N, 0 } where N is the number
    224 // of actual symbols, or nelems(g_libdl_symtab)-1 (since the first element of g_libdl_symtab is not
    225 // a real symbol). (See soinfo_elf_lookup().)
    226 //
    227 // Note that adding any new symbols here requires stubbing them out in libdl.
    228 static unsigned g_libdl_buckets[1] = { 1 };
    229 #if defined(__arm__)
    230 static unsigned g_libdl_chains[] = { 0, 2, 3, 4, 5, 6, 7, 8, 9, 10, 0 };
    231 #else
    232 static unsigned g_libdl_chains[] = { 0, 2, 3, 4, 5, 6, 7, 8, 9, 0 };
    233 #endif
    234 
    235 // Defined as global because we do not yet have access
    236 // to synchronization functions __cxa_guard_* needed
    237 // to define statics inside functions.
    238 static soinfo __libdl_info;
    239 
    240 // This is used by the dynamic linker. Every process gets these symbols for free.
    241 soinfo* get_libdl_info() {
    242   if (__libdl_info.name[0] == '\0') {
    243     // initialize
    244     strncpy(__libdl_info.name, "libdl.so", sizeof(__libdl_info.name));
    245     __libdl_info.flags = FLAG_LINKED | FLAG_NEW_SOINFO;
    246     __libdl_info.strtab = ANDROID_LIBDL_STRTAB;
    247     __libdl_info.symtab = g_libdl_symtab;
    248     __libdl_info.nbucket = sizeof(g_libdl_buckets)/sizeof(unsigned);
    249     __libdl_info.nchain = sizeof(g_libdl_chains)/sizeof(unsigned);
    250     __libdl_info.bucket = g_libdl_buckets;
    251     __libdl_info.chain = g_libdl_chains;
    252     __libdl_info.has_DT_SYMBOLIC = true;
    253   }
    254 
    255   return &__libdl_info;
    256 }
    257