/* * Copyright (C) 2008, 2009 The Android Open Source Project * All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * * Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * * Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in * the documentation and/or other materials provided with the * distribution. * * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. */ #include #include #include #include #include #include #include #include #include #include #include #include #include // Private C library headers. #include #include #include "linker.h" #include "linker_debug.h" #include "linker_environ.h" #include "linker_format.h" #include "linker_phdr.h" #define ALLOW_SYMBOLS_FROM_MAIN 1 #define SO_MAX 128 /* Assume average path length of 64 and max 8 paths */ #define LDPATH_BUFSIZE 512 #define LDPATH_MAX 8 #define LDPRELOAD_BUFSIZE 512 #define LDPRELOAD_MAX 8 /* >>> IMPORTANT NOTE - READ ME BEFORE MODIFYING <<< * * Do NOT use malloc() and friends or pthread_*() code here. * Don't use printf() either; it's caused mysterious memory * corruption in the past. * The linker runs before we bring up libc and it's easiest * to make sure it does not depend on any complex libc features * * open issues / todo: * * - are we doing everything we should for ARM_COPY relocations? * - cleaner error reporting * - after linking, set as much stuff as possible to READONLY * and NOEXEC * - linker hardcodes PAGE_SIZE and PAGE_MASK because the kernel * headers provide versions that are negative... * - allocate space for soinfo structs dynamically instead of * having a hard limit (SO_MAX) */ static int soinfo_link_image(soinfo *si); static int socount = 0; static soinfo sopool[SO_MAX]; static soinfo *freelist = NULL; static soinfo *solist = &libdl_info; static soinfo *sonext = &libdl_info; #if ALLOW_SYMBOLS_FROM_MAIN static soinfo *somain; /* main process, always the one after libdl_info */ #endif static char ldpaths_buf[LDPATH_BUFSIZE]; static const char *ldpaths[LDPATH_MAX + 1]; static char ldpreloads_buf[LDPRELOAD_BUFSIZE]; static const char *ldpreload_names[LDPRELOAD_MAX + 1]; static soinfo *preloads[LDPRELOAD_MAX + 1]; #if LINKER_DEBUG int debug_verbosity; #endif static int pid; /* This boolean is set if the program being loaded is setuid */ static bool program_is_setuid; enum RelocationKind { kRelocAbsolute = 0, kRelocRelative, kRelocCopy, kRelocSymbol, kRelocMax }; #if STATS struct linker_stats_t { int count[kRelocMax]; }; static linker_stats_t linker_stats; static void count_relocation(RelocationKind kind) { ++linker_stats.count[kind]; } #else static void count_relocation(RelocationKind) { } #endif #if COUNT_PAGES static unsigned bitmask[4096]; #define MARK(offset) \ do { \ bitmask[((offset) >> 12) >> 3] |= (1 << (((offset) >> 12) & 7)); \ } while(0) #else #define MARK(x) do {} while (0) #endif // You shouldn't try to call memory-allocating functions in the dynamic linker. // Guard against the most obvious ones. #define DISALLOW_ALLOCATION(return_type, name, ...) \ return_type name __VA_ARGS__ \ { \ const char* msg = "ERROR: " #name " called from the dynamic linker!\n"; \ __libc_android_log_write(ANDROID_LOG_FATAL, "linker", msg); \ write(2, msg, sizeof(msg)); \ abort(); \ } #define UNUSED __attribute__((unused)) DISALLOW_ALLOCATION(void*, malloc, (size_t u UNUSED)); DISALLOW_ALLOCATION(void, free, (void* u UNUSED)); DISALLOW_ALLOCATION(void*, realloc, (void* u1 UNUSED, size_t u2 UNUSED)); DISALLOW_ALLOCATION(void*, calloc, (size_t u1 UNUSED, size_t u2 UNUSED)); static char tmp_err_buf[768]; static char __linker_dl_err_buf[768]; #define BASENAME(s) (strrchr(s, '/') != NULL ? strrchr(s, '/') + 1 : s) #define DL_ERR(fmt, x...) \ do { \ format_buffer(__linker_dl_err_buf, sizeof(__linker_dl_err_buf), \ "%s(%s:%d): " fmt, \ __FUNCTION__, BASENAME(__FILE__), __LINE__, ##x); \ ERROR(fmt "\n", ##x); \ } while(0) const char *linker_get_error(void) { return (const char *)&__linker_dl_err_buf[0]; } /* * This function is an empty stub where GDB locates a breakpoint to get notified * about linker activity. */ extern "C" void __attribute__((noinline)) __attribute__((visibility("default"))) rtld_db_dlactivity(void); static r_debug _r_debug = {1, NULL, &rtld_db_dlactivity, RT_CONSISTENT, 0}; static link_map* r_debug_tail = 0; static pthread_mutex_t _r_debug_lock = PTHREAD_MUTEX_INITIALIZER; static void insert_soinfo_into_debug_map(soinfo * info) { // Copy the necessary fields into the debug structure. link_map* map = &(info->linkmap); map->l_addr = info->base; map->l_name = (char*) info->name; map->l_ld = (uintptr_t)info->dynamic; /* Stick the new library at the end of the list. * gdb tends to care more about libc than it does * about leaf libraries, and ordering it this way * reduces the back-and-forth over the wire. */ if (r_debug_tail) { r_debug_tail->l_next = map; map->l_prev = r_debug_tail; map->l_next = 0; } else { _r_debug.r_map = map; map->l_prev = 0; map->l_next = 0; } r_debug_tail = map; } static void remove_soinfo_from_debug_map(soinfo* info) { link_map* map = &(info->linkmap); if (r_debug_tail == map) { r_debug_tail = map->l_prev; } if (map->l_prev) { map->l_prev->l_next = map->l_next; } if (map->l_next) { map->l_next->l_prev = map->l_prev; } } static void notify_gdb_of_load(soinfo* info) { if (info->flags & FLAG_EXE) { // GDB already knows about the main executable return; } pthread_mutex_lock(&_r_debug_lock); _r_debug.r_state = RT_ADD; rtld_db_dlactivity(); insert_soinfo_into_debug_map(info); _r_debug.r_state = RT_CONSISTENT; rtld_db_dlactivity(); pthread_mutex_unlock(&_r_debug_lock); } static void notify_gdb_of_unload(soinfo* info) { if (info->flags & FLAG_EXE) { // GDB already knows about the main executable return; } pthread_mutex_lock(&_r_debug_lock); _r_debug.r_state = RT_DELETE; rtld_db_dlactivity(); remove_soinfo_from_debug_map(info); _r_debug.r_state = RT_CONSISTENT; rtld_db_dlactivity(); pthread_mutex_unlock(&_r_debug_lock); } extern "C" void notify_gdb_of_libraries() { _r_debug.r_state = RT_ADD; rtld_db_dlactivity(); _r_debug.r_state = RT_CONSISTENT; rtld_db_dlactivity(); } static soinfo *soinfo_alloc(const char *name) { if (strlen(name) >= SOINFO_NAME_LEN) { DL_ERR("library name \"%s\" too long", name); return NULL; } /* The freelist is populated when we call soinfo_free(), which in turn is done only by dlclose(), which is not likely to be used. */ if (!freelist) { if (socount == SO_MAX) { DL_ERR("too many libraries when loading \"%s\"", name); return NULL; } freelist = sopool + socount++; freelist->next = NULL; } soinfo* si = freelist; freelist = freelist->next; /* Make sure we get a clean block of soinfo */ memset(si, 0, sizeof(soinfo)); strlcpy((char*) si->name, name, sizeof(si->name)); sonext->next = si; si->next = NULL; si->refcount = 0; sonext = si; TRACE("%5d name %s: allocated soinfo @ %p\n", pid, name, si); return si; } static void soinfo_free(soinfo* si) { if (si == NULL) { return; } soinfo *prev = NULL, *trav; TRACE("%5d name %s: freeing soinfo @ %p\n", pid, si->name, si); for(trav = solist; trav != NULL; trav = trav->next){ if (trav == si) break; prev = trav; } if (trav == NULL) { /* si was not ni solist */ DL_ERR("name \"%s\" is not in solist!", si->name); return; } /* prev will never be NULL, because the first entry in solist is always the static libdl_info. */ prev->next = si->next; if (si == sonext) sonext = prev; si->next = freelist; freelist = si; } #ifdef ANDROID_ARM_LINKER /* For a given PC, find the .so that it belongs to. * Returns the base address of the .ARM.exidx section * for that .so, and the number of 8-byte entries * in that section (via *pcount). * * Intended to be called by libc's __gnu_Unwind_Find_exidx(). * * This function is exposed via dlfcn.c and libdl.so. */ _Unwind_Ptr dl_unwind_find_exidx(_Unwind_Ptr pc, int *pcount) { soinfo *si; unsigned addr = (unsigned)pc; for (si = solist; si != 0; si = si->next){ if ((addr >= si->base) && (addr < (si->base + si->size))) { *pcount = si->ARM_exidx_count; return (_Unwind_Ptr)si->ARM_exidx; } } *pcount = 0; return NULL; } #elif defined(ANDROID_X86_LINKER) || defined(ANDROID_MIPS_LINKER) /* Here, we only have to provide a callback to iterate across all the * loaded libraries. gcc_eh does the rest. */ int dl_iterate_phdr(int (*cb)(dl_phdr_info *info, size_t size, void *data), void *data) { int rv = 0; for (soinfo* si = solist; si != NULL; si = si->next) { dl_phdr_info dl_info; dl_info.dlpi_addr = si->linkmap.l_addr; dl_info.dlpi_name = si->linkmap.l_name; dl_info.dlpi_phdr = si->phdr; dl_info.dlpi_phnum = si->phnum; rv = cb(&dl_info, sizeof(dl_phdr_info), data); if (rv != 0) { break; } } return rv; } #endif static Elf32_Sym *soinfo_elf_lookup(soinfo *si, unsigned hash, const char *name) { Elf32_Sym *s; Elf32_Sym *symtab = si->symtab; const char *strtab = si->strtab; unsigned n; TRACE_TYPE(LOOKUP, "%5d SEARCH %s in %s@0x%08x %08x %d\n", pid, name, si->name, si->base, hash, hash % si->nbucket); n = hash % si->nbucket; for(n = si->bucket[hash % si->nbucket]; n != 0; n = si->chain[n]){ s = symtab + n; if(strcmp(strtab + s->st_name, name)) continue; /* only concern ourselves with global and weak symbol definitions */ switch(ELF32_ST_BIND(s->st_info)){ case STB_GLOBAL: case STB_WEAK: if(s->st_shndx == SHN_UNDEF) continue; TRACE_TYPE(LOOKUP, "%5d FOUND %s in %s (%08x) %d\n", pid, name, si->name, s->st_value, s->st_size); return s; } } return NULL; } static unsigned elfhash(const char *_name) { const unsigned char *name = (const unsigned char *) _name; unsigned h = 0, g; while(*name) { h = (h << 4) + *name++; g = h & 0xf0000000; h ^= g; h ^= g >> 24; } return h; } static Elf32_Sym * soinfo_do_lookup(soinfo *si, const char *name, Elf32_Addr *offset, soinfo *needed[], bool ignore_local) { unsigned elf_hash = elfhash(name); Elf32_Sym *s = NULL; soinfo *lsi = si; int i; if (!ignore_local) { /* Look for symbols in the local scope (the object who is * searching). This happens with C++ templates on i386 for some * reason. * * Notes on weak symbols: * The ELF specs are ambiguous about treatment of weak definitions in * dynamic linking. Some systems return the first definition found * and some the first non-weak definition. This is system dependent. * Here we return the first definition found for simplicity. */ s = soinfo_elf_lookup(si, elf_hash, name); if(s != NULL) goto done; } /* Next, look for it in the preloads list */ for(i = 0; preloads[i] != NULL; i++) { lsi = preloads[i]; s = soinfo_elf_lookup(lsi, elf_hash, name); if(s != NULL) goto done; } for(i = 0; needed[i] != NULL; i++) { lsi = needed[i]; DEBUG("%5d %s: looking up %s in %s\n", pid, si->name, name, lsi->name); s = soinfo_elf_lookup(lsi, elf_hash, name); if (s != NULL) goto done; } #if ALLOW_SYMBOLS_FROM_MAIN /* If we are resolving relocations while dlopen()ing a library, it's OK for * the library to resolve a symbol that's defined in the executable itself, * although this is rare and is generally a bad idea. */ if (somain) { lsi = somain; DEBUG("%5d %s: looking up %s in executable %s\n", pid, si->name, name, lsi->name); s = soinfo_elf_lookup(lsi, elf_hash, name); } #endif done: if(s != NULL) { TRACE_TYPE(LOOKUP, "%5d si %s sym %s s->st_value = 0x%08x, " "found in %s, base = 0x%08x, load bias = 0x%08x\n", pid, si->name, name, s->st_value, lsi->name, lsi->base, lsi->load_bias); *offset = lsi->load_bias; return s; } return NULL; } /* This is used by dl_sym(). It performs symbol lookup only within the specified soinfo object and not in any of its dependencies. */ Elf32_Sym *soinfo_lookup(soinfo *si, const char *name) { return soinfo_elf_lookup(si, elfhash(name), name); } /* This is used by dl_sym(). It performs a global symbol lookup. */ Elf32_Sym *lookup(const char *name, soinfo **found, soinfo *start) { unsigned elf_hash = elfhash(name); Elf32_Sym *s = NULL; soinfo *si; if(start == NULL) { start = solist; } for(si = start; (s == NULL) && (si != NULL); si = si->next) { if(si->flags & FLAG_ERROR) continue; s = soinfo_elf_lookup(si, elf_hash, name); if (s != NULL) { *found = si; break; } } if(s != NULL) { TRACE_TYPE(LOOKUP, "%5d %s s->st_value = 0x%08x, " "si->base = 0x%08x\n", pid, name, s->st_value, si->base); return s; } return NULL; } soinfo *find_containing_library(const void *addr) { soinfo *si; for(si = solist; si != NULL; si = si->next) { if((unsigned)addr >= si->base && (unsigned)addr - si->base < si->size) { return si; } } return NULL; } Elf32_Sym *soinfo_find_symbol(soinfo* si, const void *addr) { unsigned int i; unsigned soaddr = (unsigned)addr - si->base; /* Search the library's symbol table for any defined symbol which * contains this address */ for(i=0; inchain; i++) { Elf32_Sym *sym = &si->symtab[i]; if(sym->st_shndx != SHN_UNDEF && soaddr >= sym->st_value && soaddr < sym->st_value + sym->st_size) { return sym; } } return NULL; } #if 0 static void dump(soinfo *si) { Elf32_Sym *s = si->symtab; unsigned n; for(n = 0; n < si->nchain; n++) { TRACE("%5d %04d> %08x: %02x %04x %08x %08x %s\n", pid, n, s, s->st_info, s->st_shndx, s->st_value, s->st_size, si->strtab + s->st_name); s++; } } #endif static const char * const sopaths[] = { "/vendor/lib", "/system/lib", 0 }; static int _open_lib(const char* name) { // TODO: why not just call open? struct stat sb; if (stat(name, &sb) == -1 || !S_ISREG(sb.st_mode)) { return -1; } return TEMP_FAILURE_RETRY(open(name, O_RDONLY)); } static int open_library(const char *name) { int fd; char buf[512]; const char * const*path; int n; TRACE("[ %5d opening %s ]\n", pid, name); if(name == 0) return -1; if(strlen(name) > 256) return -1; if ((name[0] == '/') && ((fd = _open_lib(name)) >= 0)) return fd; for (path = ldpaths; *path; path++) { n = format_buffer(buf, sizeof(buf), "%s/%s", *path, name); if (n < 0 || n >= (int)sizeof(buf)) { WARN("Ignoring very long library path: %s/%s\n", *path, name); continue; } if ((fd = _open_lib(buf)) >= 0) return fd; } for (path = sopaths; *path; path++) { n = format_buffer(buf, sizeof(buf), "%s/%s", *path, name); if (n < 0 || n >= (int)sizeof(buf)) { WARN("Ignoring very long library path: %s/%s\n", *path, name); continue; } if ((fd = _open_lib(buf)) >= 0) return fd; } return -1; } // Returns 'true' if the library is prelinked or on failure so we error out // either way. We no longer support prelinking. static bool is_prelinked(int fd, const char* name) { struct prelink_info_t { long mmap_addr; char tag[4]; // "PRE ". }; off_t sz = lseek(fd, -sizeof(prelink_info_t), SEEK_END); if (sz < 0) { DL_ERR("lseek failed: %s", strerror(errno)); return true; } prelink_info_t info; int rc = TEMP_FAILURE_RETRY(read(fd, &info, sizeof(info))); if (rc != sizeof(info)) { DL_ERR("could not read prelink_info_t structure for \"%s\":", name, strerror(errno)); return true; } if (memcmp(info.tag, "PRE ", 4) == 0) { DL_ERR("prelinked libraries no longer supported: %s", name); return true; } return false; } /* verify_elf_header * Verifies the content of an ELF header. * * Args: * * Returns: * 0 on success * -1 if no valid ELF object is found @ base. */ static int verify_elf_header(const Elf32_Ehdr* hdr) { if (hdr->e_ident[EI_MAG0] != ELFMAG0) return -1; if (hdr->e_ident[EI_MAG1] != ELFMAG1) return -1; if (hdr->e_ident[EI_MAG2] != ELFMAG2) return -1; if (hdr->e_ident[EI_MAG3] != ELFMAG3) return -1; if (hdr->e_type != ET_DYN) return -1; /* TODO: Should we verify anything else in the header? */ #ifdef ANDROID_ARM_LINKER if (hdr->e_machine != EM_ARM) return -1; #elif defined(ANDROID_X86_LINKER) if (hdr->e_machine != EM_386) return -1; #elif defined(ANDROID_MIPS_LINKER) if (hdr->e_machine != EM_MIPS) return -1; #endif return 0; } struct scoped_fd { ~scoped_fd() { if (fd != -1) { close(fd); } } int fd; }; struct soinfo_ptr { soinfo_ptr(const char* name) { const char* bname = strrchr(name, '/'); ptr = soinfo_alloc(bname ? bname + 1 : name); } ~soinfo_ptr() { soinfo_free(ptr); } soinfo* release() { soinfo* result = ptr; ptr = NULL; return result; } soinfo* ptr; }; // TODO: rewrite linker_phdr.h to use a class, then lose this. struct phdr_ptr { phdr_ptr() : phdr_mmap(NULL) {} ~phdr_ptr() { if (phdr_mmap != NULL) { phdr_table_unload(phdr_mmap, phdr_size); } } void* phdr_mmap; Elf32_Addr phdr_size; }; static soinfo* load_library(const char* name) { // Open the file. scoped_fd fd; fd.fd = open_library(name); if (fd.fd == -1) { DL_ERR("library \"%s\" not found", name); return NULL; } // Read the ELF header. Elf32_Ehdr header[1]; int ret = TEMP_FAILURE_RETRY(read(fd.fd, (void*)header, sizeof(header))); if (ret < 0) { DL_ERR("can't read file \"%s\": %s", name, strerror(errno)); return NULL; } if (ret != (int)sizeof(header)) { DL_ERR("too small to be an ELF executable: %s", name); return NULL; } if (verify_elf_header(header) < 0) { DL_ERR("not a valid ELF executable: %s", name); return NULL; } // Read the program header table. const Elf32_Phdr* phdr_table; phdr_ptr phdr_holder; ret = phdr_table_load(fd.fd, header->e_phoff, header->e_phnum, &phdr_holder.phdr_mmap, &phdr_holder.phdr_size, &phdr_table); if (ret < 0) { DL_ERR("can't load program header table: %s: %s", name, strerror(errno)); return NULL; } size_t phdr_count = header->e_phnum; // Get the load extents. Elf32_Addr ext_sz = phdr_table_get_load_size(phdr_table, phdr_count); TRACE("[ %5d - '%s' wants sz=0x%08x ]\n", pid, name, ext_sz); if (ext_sz == 0) { DL_ERR("no loadable segments in file: %s", name); return NULL; } // We no longer support pre-linked libraries. if (is_prelinked(fd.fd, name)) { return NULL; } // Reserve address space for all loadable segments. void* load_start = NULL; Elf32_Addr load_size = 0; Elf32_Addr load_bias = 0; ret = phdr_table_reserve_memory(phdr_table, phdr_count, &load_start, &load_size, &load_bias); if (ret < 0) { DL_ERR("can't reserve %d bytes in address space for \"%s\": %s", ext_sz, name, strerror(errno)); return NULL; } TRACE("[ %5d allocated memory for %s @ %p (0x%08x) ]\n", pid, name, load_start, load_size); /* Map all the segments in our address space with default protections */ ret = phdr_table_load_segments(phdr_table, phdr_count, load_bias, fd.fd); if (ret < 0) { DL_ERR("can't map loadable segments for \"%s\": %s", name, strerror(errno)); return NULL; } soinfo_ptr si(name); if (si.ptr == NULL) { return NULL; } si.ptr->base = (Elf32_Addr) load_start; si.ptr->size = load_size; si.ptr->load_bias = load_bias; si.ptr->flags = 0; si.ptr->entry = 0; si.ptr->dynamic = (unsigned *)-1; si.ptr->phnum = phdr_count; si.ptr->phdr = phdr_table_get_loaded_phdr(phdr_table, phdr_count, load_bias); if (si.ptr->phdr == NULL) { DL_ERR("can't find loaded PHDR for \"%s\"", name); return NULL; } return si.release(); } static soinfo * init_library(soinfo *si) { /* At this point we know that whatever is loaded @ base is a valid ELF * shared library whose segments are properly mapped in. */ TRACE("[ %5d init_library base=0x%08x sz=0x%08x name='%s') ]\n", pid, si->base, si->size, si->name); if(soinfo_link_image(si)) { munmap((void *)si->base, si->size); return NULL; } return si; } static soinfo *find_loaded_library(const char *name) { soinfo *si; const char *bname; // TODO: don't use basename only for determining libraries // http://code.google.com/p/android/issues/detail?id=6670 bname = strrchr(name, '/'); bname = bname ? bname + 1 : name; for(si = solist; si != NULL; si = si->next){ if(!strcmp(bname, si->name)) { return si; } } return NULL; } soinfo *find_library(const char *name) { soinfo *si; #if ALLOW_SYMBOLS_FROM_MAIN if (name == NULL) return somain; #else if (name == NULL) return NULL; #endif si = find_loaded_library(name); if (si != NULL) { if(si->flags & FLAG_ERROR) { DL_ERR("\"%s\" failed to load previously", name); return NULL; } if(si->flags & FLAG_LINKED) return si; DL_ERR("OOPS: recursive link to \"%s\"", si->name); return NULL; } TRACE("[ %5d '%s' has not been loaded yet. Locating...]\n", pid, name); si = load_library(name); if(si == NULL) return NULL; return init_library(si); } static void call_destructors(soinfo *si); int soinfo_unload(soinfo* si) { if (si->refcount == 1) { TRACE("%5d unloading '%s'\n", pid, si->name); call_destructors(si); for (unsigned* d = si->dynamic; *d; d += 2) { if(d[0] == DT_NEEDED){ soinfo *lsi = find_loaded_library(si->strtab + d[1]); if (lsi) { TRACE("%5d %s needs to unload %s\n", pid, si->name, lsi->name); soinfo_unload(lsi); } else { // TODO: should we return -1 in this case? DL_ERR("\"%s\": could not unload dependent library", si->name); } } } munmap((char *)si->base, si->size); notify_gdb_of_unload(si); soinfo_free(si); si->refcount = 0; } else { si->refcount--; PRINT("%5d not unloading '%s', decrementing refcount to %d\n", pid, si->name, si->refcount); } return 0; } /* TODO: don't use unsigned for addrs below. It works, but is not * ideal. They should probably be either uint32_t, Elf32_Addr, or unsigned * long. */ static int soinfo_relocate(soinfo *si, Elf32_Rel *rel, unsigned count, soinfo *needed[]) { Elf32_Sym *symtab = si->symtab; const char *strtab = si->strtab; Elf32_Sym *s; Elf32_Addr offset; Elf32_Rel *start = rel; for (size_t idx = 0; idx < count; ++idx, ++rel) { unsigned type = ELF32_R_TYPE(rel->r_info); unsigned sym = ELF32_R_SYM(rel->r_info); unsigned reloc = (unsigned)(rel->r_offset + si->load_bias); unsigned sym_addr = 0; char *sym_name = NULL; DEBUG("%5d Processing '%s' relocation at index %d\n", pid, si->name, idx); if (type == 0) { // R_*_NONE continue; } if(sym != 0) { sym_name = (char *)(strtab + symtab[sym].st_name); bool ignore_local = false; #if defined(ANDROID_ARM_LINKER) ignore_local = (type == R_ARM_COPY); #endif s = soinfo_do_lookup(si, sym_name, &offset, needed, ignore_local); if(s == NULL) { /* We only allow an undefined symbol if this is a weak reference.. */ s = &symtab[sym]; if (ELF32_ST_BIND(s->st_info) != STB_WEAK) { DL_ERR("cannot locate symbol \"%s\" referenced by \"%s\"...", sym_name, si->name); return -1; } /* IHI0044C AAELF 4.5.1.1: Libraries are not searched to resolve weak references. It is not an error for a weak reference to remain unsatisfied. During linking, the value of an undefined weak reference is: - Zero if the relocation type is absolute - The address of the place if the relocation is pc-relative - The address of nominal base address if the relocation type is base-relative. */ switch (type) { #if defined(ANDROID_ARM_LINKER) case R_ARM_JUMP_SLOT: case R_ARM_GLOB_DAT: case R_ARM_ABS32: case R_ARM_RELATIVE: /* Don't care. */ #elif defined(ANDROID_X86_LINKER) case R_386_JMP_SLOT: case R_386_GLOB_DAT: case R_386_32: case R_386_RELATIVE: /* Dont' care. */ #endif /* ANDROID_*_LINKER */ /* sym_addr was initialized to be zero above or relocation code below does not care about value of sym_addr. No need to do anything. */ break; #if defined(ANDROID_X86_LINKER) case R_386_PC32: sym_addr = reloc; break; #endif /* ANDROID_X86_LINKER */ #if defined(ANDROID_ARM_LINKER) case R_ARM_COPY: /* Fall through. Can't really copy if weak symbol is not found in run-time. */ #endif /* ANDROID_ARM_LINKER */ default: DL_ERR("unknown weak reloc type %d @ %p (%d)", type, rel, (int) (rel - start)); return -1; } } else { /* We got a definition. */ #if 0 if((base == 0) && (si->base != 0)){ /* linking from libraries to main image is bad */ DL_ERR("cannot locate \"%s\"...", strtab + symtab[sym].st_name); return -1; } #endif sym_addr = (unsigned)(s->st_value + offset); } count_relocation(kRelocSymbol); } else { s = NULL; } /* TODO: This is ugly. Split up the relocations by arch into * different files. */ switch(type){ #if defined(ANDROID_ARM_LINKER) case R_ARM_JUMP_SLOT: count_relocation(kRelocAbsolute); MARK(rel->r_offset); TRACE_TYPE(RELO, "%5d RELO JMP_SLOT %08x <- %08x %s\n", pid, reloc, sym_addr, sym_name); *((unsigned*)reloc) = sym_addr; break; case R_ARM_GLOB_DAT: count_relocation(kRelocAbsolute); MARK(rel->r_offset); TRACE_TYPE(RELO, "%5d RELO GLOB_DAT %08x <- %08x %s\n", pid, reloc, sym_addr, sym_name); *((unsigned*)reloc) = sym_addr; break; case R_ARM_ABS32: count_relocation(kRelocAbsolute); MARK(rel->r_offset); TRACE_TYPE(RELO, "%5d RELO ABS %08x <- %08x %s\n", pid, reloc, sym_addr, sym_name); *((unsigned*)reloc) += sym_addr; break; case R_ARM_REL32: count_relocation(kRelocRelative); MARK(rel->r_offset); TRACE_TYPE(RELO, "%5d RELO REL32 %08x <- %08x - %08x %s\n", pid, reloc, sym_addr, rel->r_offset, sym_name); *((unsigned*)reloc) += sym_addr - rel->r_offset; break; #elif defined(ANDROID_X86_LINKER) case R_386_JMP_SLOT: count_relocation(kRelocAbsolute); MARK(rel->r_offset); TRACE_TYPE(RELO, "%5d RELO JMP_SLOT %08x <- %08x %s\n", pid, reloc, sym_addr, sym_name); *((unsigned*)reloc) = sym_addr; break; case R_386_GLOB_DAT: count_relocation(kRelocAbsolute); MARK(rel->r_offset); TRACE_TYPE(RELO, "%5d RELO GLOB_DAT %08x <- %08x %s\n", pid, reloc, sym_addr, sym_name); *((unsigned*)reloc) = sym_addr; break; #elif defined(ANDROID_MIPS_LINKER) case R_MIPS_JUMP_SLOT: count_relocation(kRelocAbsolute); MARK(rel->r_offset); TRACE_TYPE(RELO, "%5d RELO JMP_SLOT %08x <- %08x %s\n", pid, reloc, sym_addr, sym_name); *((unsigned*)reloc) = sym_addr; break; case R_MIPS_REL32: count_relocation(kRelocAbsolute); MARK(rel->r_offset); TRACE_TYPE(RELO, "%5d RELO REL32 %08x <- %08x %s\n", pid, reloc, sym_addr, (sym_name) ? sym_name : "*SECTIONHDR*"); if (s) { *((unsigned*)reloc) += sym_addr; } else { *((unsigned*)reloc) += si->base; } break; #endif /* ANDROID_*_LINKER */ #if defined(ANDROID_ARM_LINKER) case R_ARM_RELATIVE: #elif defined(ANDROID_X86_LINKER) case R_386_RELATIVE: #endif /* ANDROID_*_LINKER */ count_relocation(kRelocRelative); MARK(rel->r_offset); if (sym) { DL_ERR("odd RELATIVE form...", pid); return -1; } TRACE_TYPE(RELO, "%5d RELO RELATIVE %08x <- +%08x\n", pid, reloc, si->base); *((unsigned*)reloc) += si->base; break; #if defined(ANDROID_X86_LINKER) case R_386_32: count_relocation(kRelocRelative); MARK(rel->r_offset); TRACE_TYPE(RELO, "%5d RELO R_386_32 %08x <- +%08x %s\n", pid, reloc, sym_addr, sym_name); *((unsigned *)reloc) += (unsigned)sym_addr; break; case R_386_PC32: count_relocation(kRelocRelative); MARK(rel->r_offset); TRACE_TYPE(RELO, "%5d RELO R_386_PC32 %08x <- " "+%08x (%08x - %08x) %s\n", pid, reloc, (sym_addr - reloc), sym_addr, reloc, sym_name); *((unsigned *)reloc) += (unsigned)(sym_addr - reloc); break; #endif /* ANDROID_X86_LINKER */ #ifdef ANDROID_ARM_LINKER case R_ARM_COPY: if ((si->flags & FLAG_EXE) == 0) { /* * http://infocenter.arm.com/help/topic/com.arm.doc.ihi0044d/IHI0044D_aaelf.pdf * * Section 4.7.1.10 "Dynamic relocations" * R_ARM_COPY may only appear in executable objects where e_type is * set to ET_EXEC. * * TODO: FLAG_EXE is set for both ET_DYN and ET_EXEC executables. * We should explicitly disallow ET_DYN executables from having * R_ARM_COPY relocations. */ DL_ERR("%s R_ARM_COPY relocations only supported for ET_EXEC", si->name); return -1; } count_relocation(kRelocCopy); MARK(rel->r_offset); TRACE_TYPE(RELO, "%5d RELO %08x <- %d @ %08x %s\n", pid, reloc, s->st_size, sym_addr, sym_name); if (reloc == sym_addr) { DL_ERR("Internal linker error detected. reloc == symaddr"); return -1; } memcpy((void*)reloc, (void*)sym_addr, s->st_size); break; #endif /* ANDROID_ARM_LINKER */ default: DL_ERR("unknown reloc type %d @ %p (%d)", type, rel, (int) (rel - start)); return -1; } } return 0; } #ifdef ANDROID_MIPS_LINKER static int mips_relocate_got(soinfo* si, soinfo* needed[]) { unsigned *got; unsigned local_gotno, gotsym, symtabno; Elf32_Sym *symtab, *sym; unsigned g; got = si->plt_got; local_gotno = si->mips_local_gotno; gotsym = si->mips_gotsym; symtabno = si->mips_symtabno; symtab = si->symtab; /* * got[0] is address of lazy resolver function * got[1] may be used for a GNU extension * set it to a recognizable address in case someone calls it * (should be _rtld_bind_start) * FIXME: maybe this should be in a separate routine */ if ((si->flags & FLAG_LINKER) == 0) { g = 0; got[g++] = 0xdeadbeef; if (got[g] & 0x80000000) { got[g++] = 0xdeadfeed; } /* * Relocate the local GOT entries need to be relocated */ for (; g < local_gotno; g++) { got[g] += si->load_bias; } } /* Now for the global GOT entries */ sym = symtab + gotsym; got = si->plt_got + local_gotno; for (g = gotsym; g < symtabno; g++, sym++, got++) { const char *sym_name; unsigned base; Elf32_Sym *s; /* This is an undefined reference... try to locate it */ sym_name = si->strtab + sym->st_name; s = soinfo_do_lookup(si, sym_name, &base, needed, false); if (s == NULL) { /* We only allow an undefined symbol if this is a weak reference.. */ s = &symtab[g]; if (ELF32_ST_BIND(s->st_info) != STB_WEAK) { DL_ERR("cannot locate \"%s\"...", sym_name); return -1; } *got = 0; } else { /* FIXME: is this sufficient? * For reference see NetBSD link loader * http://cvsweb.netbsd.org/bsdweb.cgi/src/libexec/ld.elf_so/arch/mips/mips_reloc.c?rev=1.53&content-type=text/x-cvsweb-markup */ *got = base + s->st_value; } } return 0; } #endif /* Please read the "Initialization and Termination functions" functions. * of the linker design note in bionic/linker/README.TXT to understand * what the following code is doing. * * The important things to remember are: * * DT_PREINIT_ARRAY must be called first for executables, and should * not appear in shared libraries. * * DT_INIT should be called before DT_INIT_ARRAY if both are present * * DT_FINI should be called after DT_FINI_ARRAY if both are present * * DT_FINI_ARRAY must be parsed in reverse order. */ static void call_array(unsigned *ctor, int count, int reverse) { int n, inc = 1; if (reverse) { ctor += (count-1); inc = -1; } for(n = count; n > 0; n--) { TRACE("[ %5d Looking at %s *0x%08x == 0x%08x ]\n", pid, reverse ? "dtor" : "ctor", (unsigned)ctor, (unsigned)*ctor); void (*func)() = (void (*)()) *ctor; ctor += inc; if(((int) func == 0) || ((int) func == -1)) continue; TRACE("[ %5d Calling func @ 0x%08x ]\n", pid, (unsigned)func); func(); } } static void soinfo_call_preinit_constructors(soinfo *si) { TRACE("[ %5d Calling preinit_array @ 0x%08x [%d] for '%s' ]\n", pid, (unsigned)si->preinit_array, si->preinit_array_count, si->name); call_array(si->preinit_array, si->preinit_array_count, 0); TRACE("[ %5d Done calling preinit_array for '%s' ]\n", pid, si->name); } void soinfo_call_constructors(soinfo *si) { if (si->constructors_called) return; // Set this before actually calling the constructors, otherwise it doesn't // protect against recursive constructor calls. One simple example of // constructor recursion is the libc debug malloc, which is implemented in // libc_malloc_debug_leak.so: // 1. The program depends on libc, so libc's constructor is called here. // 2. The libc constructor calls dlopen() to load libc_malloc_debug_leak.so. // 3. dlopen() calls soinfo_call_constructors() with the newly created // soinfo for libc_malloc_debug_leak.so. // 4. The debug so depends on libc, so soinfo_call_constructors() is // called again with the libc soinfo. If it doesn't trigger the early- // out above, the libc constructor will be called again (recursively!). si->constructors_called = 1; if (!(si->flags & FLAG_EXE) && si->preinit_array) { DL_ERR("shared library \"%s\" has a preinit_array table @ 0x%08x. " "This is INVALID.", si->name, (unsigned) si->preinit_array); } if (si->dynamic) { unsigned *d; for(d = si->dynamic; *d; d += 2) { if(d[0] == DT_NEEDED){ soinfo* lsi = find_loaded_library(si->strtab + d[1]); if (!lsi) { DL_ERR("\"%s\": could not initialize dependent library", si->name); } else { soinfo_call_constructors(lsi); } } } } if (si->init_func) { TRACE("[ %5d Calling init_func @ 0x%08x for '%s' ]\n", pid, (unsigned)si->init_func, si->name); si->init_func(); TRACE("[ %5d Done calling init_func for '%s' ]\n", pid, si->name); } if (si->init_array) { TRACE("[ %5d Calling init_array @ 0x%08x [%d] for '%s' ]\n", pid, (unsigned)si->init_array, si->init_array_count, si->name); call_array(si->init_array, si->init_array_count, 0); TRACE("[ %5d Done calling init_array for '%s' ]\n", pid, si->name); } } static void call_destructors(soinfo *si) { if (si->fini_array) { TRACE("[ %5d Calling fini_array @ 0x%08x [%d] for '%s' ]\n", pid, (unsigned)si->fini_array, si->fini_array_count, si->name); call_array(si->fini_array, si->fini_array_count, 1); TRACE("[ %5d Done calling fini_array for '%s' ]\n", pid, si->name); } if (si->fini_func) { TRACE("[ %5d Calling fini_func @ 0x%08x for '%s' ]\n", pid, (unsigned)si->fini_func, si->name); si->fini_func(); TRACE("[ %5d Done calling fini_func for '%s' ]\n", pid, si->name); } } /* Force any of the closed stdin, stdout and stderr to be associated with /dev/null. */ static int nullify_closed_stdio (void) { int dev_null, i, status; int return_value = 0; dev_null = TEMP_FAILURE_RETRY(open("/dev/null", O_RDWR)); if (dev_null < 0) { DL_ERR("cannot open /dev/null: %s", strerror(errno)); return -1; } TRACE("[ %5d Opened /dev/null file-descriptor=%d]\n", pid, dev_null); /* If any of the stdio file descriptors is valid and not associated with /dev/null, dup /dev/null to it. */ for (i = 0; i < 3; i++) { /* If it is /dev/null already, we are done. */ if (i == dev_null) { continue; } TRACE("[ %5d Nullifying stdio file descriptor %d]\n", pid, i); status = TEMP_FAILURE_RETRY(fcntl(i, F_GETFL)); /* If file is opened, we are good. */ if (status != -1) { continue; } /* The only error we allow is that the file descriptor does not exist, in which case we dup /dev/null to it. */ if (errno != EBADF) { DL_ERR("fcntl failed: %s", strerror(errno)); return_value = -1; continue; } /* Try dupping /dev/null to this stdio file descriptor and repeat if there is a signal. Note that any errors in closing the stdio descriptor are lost. */ status = TEMP_FAILURE_RETRY(dup2(dev_null, i)); if (status < 0) { DL_ERR("dup2 failed: %s", strerror(errno)); return_value = -1; continue; } } /* If /dev/null is not one of the stdio file descriptors, close it. */ if (dev_null > 2) { TRACE("[ %5d Closing /dev/null file-descriptor=%d]\n", pid, dev_null); status = TEMP_FAILURE_RETRY(close(dev_null)); if (status == -1) { DL_ERR("close failed: %s", strerror(errno)); return_value = -1; } } return return_value; } static int soinfo_link_image(soinfo *si) { unsigned *d; /* "base" might wrap around UINT32_MAX. */ Elf32_Addr base = si->load_bias; const Elf32_Phdr *phdr = si->phdr; int phnum = si->phnum; int relocating_linker = (si->flags & FLAG_LINKER) != 0; soinfo **needed, **pneeded; size_t dynamic_count; /* We can't debug anything until the linker is relocated */ if (!relocating_linker) { INFO("[ %5d linking %s ]\n", pid, si->name); DEBUG("%5d si->base = 0x%08x si->flags = 0x%08x\n", pid, si->base, si->flags); } /* Extract dynamic section */ phdr_table_get_dynamic_section(phdr, phnum, base, &si->dynamic, &dynamic_count); if (si->dynamic == NULL) { if (!relocating_linker) { DL_ERR("missing PT_DYNAMIC?!"); } goto fail; } else { if (!relocating_linker) { DEBUG("%5d dynamic = %p\n", pid, si->dynamic); } } #ifdef ANDROID_ARM_LINKER (void) phdr_table_get_arm_exidx(phdr, phnum, base, &si->ARM_exidx, &si->ARM_exidx_count); #endif /* extract useful information from dynamic section */ for(d = si->dynamic; *d; d++){ DEBUG("%5d d = %p, d[0] = 0x%08x d[1] = 0x%08x\n", pid, d, d[0], d[1]); switch(*d++){ case DT_HASH: si->nbucket = ((unsigned *) (base + *d))[0]; si->nchain = ((unsigned *) (base + *d))[1]; si->bucket = (unsigned *) (base + *d + 8); si->chain = (unsigned *) (base + *d + 8 + si->nbucket * 4); break; case DT_STRTAB: si->strtab = (const char *) (base + *d); break; case DT_SYMTAB: si->symtab = (Elf32_Sym *) (base + *d); break; case DT_PLTREL: if(*d != DT_REL) { DL_ERR("DT_RELA not supported"); goto fail; } break; case DT_JMPREL: si->plt_rel = (Elf32_Rel*) (base + *d); break; case DT_PLTRELSZ: si->plt_rel_count = *d / 8; break; case DT_REL: si->rel = (Elf32_Rel*) (base + *d); break; case DT_RELSZ: si->rel_count = *d / 8; break; case DT_PLTGOT: /* Save this in case we decide to do lazy binding. We don't yet. */ si->plt_got = (unsigned *)(base + *d); break; case DT_DEBUG: #if !defined(ANDROID_MIPS_LINKER) // Set the DT_DEBUG entry to the address of _r_debug for GDB *d = (int) &_r_debug; #endif break; case DT_RELA: DL_ERR("DT_RELA not supported"); goto fail; case DT_INIT: si->init_func = (void (*)(void))(base + *d); DEBUG("%5d %s constructors (init func) found at %p\n", pid, si->name, si->init_func); break; case DT_FINI: si->fini_func = (void (*)(void))(base + *d); DEBUG("%5d %s destructors (fini func) found at %p\n", pid, si->name, si->fini_func); break; case DT_INIT_ARRAY: si->init_array = (unsigned *)(base + *d); DEBUG("%5d %s constructors (init_array) found at %p\n", pid, si->name, si->init_array); break; case DT_INIT_ARRAYSZ: si->init_array_count = ((unsigned)*d) / sizeof(Elf32_Addr); break; case DT_FINI_ARRAY: si->fini_array = (unsigned *)(base + *d); DEBUG("%5d %s destructors (fini_array) found at %p\n", pid, si->name, si->fini_array); break; case DT_FINI_ARRAYSZ: si->fini_array_count = ((unsigned)*d) / sizeof(Elf32_Addr); break; case DT_PREINIT_ARRAY: si->preinit_array = (unsigned *)(base + *d); DEBUG("%5d %s constructors (preinit_array) found at %p\n", pid, si->name, si->preinit_array); break; case DT_PREINIT_ARRAYSZ: si->preinit_array_count = ((unsigned)*d) / sizeof(Elf32_Addr); break; case DT_TEXTREL: si->has_text_relocations = true; break; #if defined(ANDROID_MIPS_LINKER) case DT_NEEDED: case DT_STRSZ: case DT_SYMENT: case DT_RELENT: break; case DT_MIPS_RLD_MAP: // Set the DT_MIPS_RLD_MAP entry to the address of _r_debug for GDB. { r_debug** dp = (r_debug**) *d; *dp = &_r_debug; } break; case DT_MIPS_RLD_VERSION: case DT_MIPS_FLAGS: case DT_MIPS_BASE_ADDRESS: case DT_MIPS_UNREFEXTNO: case DT_MIPS_RWPLT: break; case DT_MIPS_PLTGOT: #if 0 /* not yet... */ si->mips_pltgot = (unsigned *)(si->base + *d); #endif break; case DT_MIPS_SYMTABNO: si->mips_symtabno = *d; break; case DT_MIPS_LOCAL_GOTNO: si->mips_local_gotno = *d; break; case DT_MIPS_GOTSYM: si->mips_gotsym = *d; break; default: DEBUG("%5d Unused DT entry: type 0x%08x arg 0x%08x\n", pid, d[-1], d[0]); break; #endif } } DEBUG("%5d si->base = 0x%08x, si->strtab = %p, si->symtab = %p\n", pid, si->base, si->strtab, si->symtab); if((si->strtab == 0) || (si->symtab == 0)) { DL_ERR("missing essential tables"); goto fail; } /* if this is the main executable, then load all of the preloads now */ if(si->flags & FLAG_EXE) { int i; memset(preloads, 0, sizeof(preloads)); for(i = 0; ldpreload_names[i] != NULL; i++) { soinfo *lsi = find_library(ldpreload_names[i]); if(lsi == 0) { strlcpy(tmp_err_buf, linker_get_error(), sizeof(tmp_err_buf)); DL_ERR("could not load library \"%s\" needed by \"%s\"; caused by %s", ldpreload_names[i], si->name, tmp_err_buf); goto fail; } lsi->refcount++; preloads[i] = lsi; } } /* dynamic_count is an upper bound for the number of needed libs */ pneeded = needed = (soinfo**) alloca((1 + dynamic_count) * sizeof(soinfo*)); for(d = si->dynamic; *d; d += 2) { if(d[0] == DT_NEEDED){ DEBUG("%5d %s needs %s\n", pid, si->name, si->strtab + d[1]); soinfo *lsi = find_library(si->strtab + d[1]); if(lsi == 0) { strlcpy(tmp_err_buf, linker_get_error(), sizeof(tmp_err_buf)); DL_ERR("could not load library \"%s\" needed by \"%s\"; caused by %s", si->strtab + d[1], si->name, tmp_err_buf); goto fail; } *pneeded++ = lsi; lsi->refcount++; } } *pneeded = NULL; if (si->has_text_relocations) { /* Unprotect the segments, i.e. make them writable, to allow * text relocations to work properly. We will later call * phdr_table_protect_segments() after all of them are applied * and all constructors are run. */ if (phdr_table_unprotect_segments(si->phdr, si->phnum, si->load_bias) < 0) { DL_ERR("can't unprotect loadable segments for \"%s\": %s", si->name, strerror(errno)); goto fail; } } if(si->plt_rel) { DEBUG("[ %5d relocating %s plt ]\n", pid, si->name ); if(soinfo_relocate(si, si->plt_rel, si->plt_rel_count, needed)) goto fail; } if(si->rel) { DEBUG("[ %5d relocating %s ]\n", pid, si->name ); if(soinfo_relocate(si, si->rel, si->rel_count, needed)) goto fail; } #ifdef ANDROID_MIPS_LINKER if(mips_relocate_got(si, needed)) { goto fail; } #endif si->flags |= FLAG_LINKED; DEBUG("[ %5d finished linking %s ]\n", pid, si->name); if (si->has_text_relocations) { /* All relocations are done, we can protect our segments back to * read-only. */ if (phdr_table_protect_segments(si->phdr, si->phnum, si->load_bias) < 0) { DL_ERR("can't protect segments for \"%s\": %s", si->name, strerror(errno)); goto fail; } } /* We can also turn on GNU RELRO protection */ if (phdr_table_protect_gnu_relro(si->phdr, si->phnum, si->load_bias) < 0) { DL_ERR("can't enable GNU RELRO protection for \"%s\": %s", si->name, strerror(errno)); goto fail; } /* If this is a SET?ID program, dup /dev/null to opened stdin, stdout and stderr to close a security hole described in: ftp://ftp.freebsd.org/pub/FreeBSD/CERT/advisories/FreeBSD-SA-02:23.stdio.asc */ if (program_is_setuid) { nullify_closed_stdio(); } notify_gdb_of_load(si); return 0; fail: ERROR("failed to link %s\n", si->name); si->flags |= FLAG_ERROR; return -1; } static void parse_path(const char* path, const char* delimiters, const char** array, char* buf, size_t buf_size, size_t max_count) { if (path == NULL) { return; } size_t len = strlcpy(buf, path, buf_size); size_t i = 0; char* buf_p = buf; while (i < max_count && (array[i] = strsep(&buf_p, delimiters))) { if (*array[i] != '\0') { ++i; } } // Forget the last path if we had to truncate; this occurs if the 2nd to // last char isn't '\0' (i.e. wasn't originally a delimiter). if (i > 0 && len >= buf_size && buf[buf_size - 2] != '\0') { array[i - 1] = NULL; } else { array[i] = NULL; } } static void parse_LD_LIBRARY_PATH(const char* path) { parse_path(path, ":", ldpaths, ldpaths_buf, sizeof(ldpaths_buf), LDPATH_MAX); } static void parse_LD_PRELOAD(const char* path) { // We have historically supported ':' as well as ' ' in LD_PRELOAD. parse_path(path, " :", ldpreload_names, ldpreloads_buf, sizeof(ldpreloads_buf), LDPRELOAD_MAX); } /* * This code is called after the linker has linked itself and * fixed it's own GOT. It is safe to make references to externs * and other non-local data at this point. */ static unsigned __linker_init_post_relocation(unsigned **elfdata, unsigned linker_base) { static soinfo linker_soinfo; int argc = (int) *elfdata; char **argv = (char**) (elfdata + 1); unsigned *vecs = (unsigned*) (argv + argc + 1); unsigned *v; soinfo *si; int i; const char *ldpath_env = NULL; const char *ldpreload_env = NULL; /* NOTE: we store the elfdata pointer on a special location * of the temporary TLS area in order to pass it to * the C Library's runtime initializer. * * The initializer must clear the slot and reset the TLS * to point to a different location to ensure that no other * shared library constructor can access it. */ __libc_init_tls(elfdata); pid = getpid(); #if TIMING struct timeval t0, t1; gettimeofday(&t0, 0); #endif /* Initialize environment functions, and get to the ELF aux vectors table */ vecs = linker_env_init(vecs); /* Check auxv for AT_SECURE first to see if program is setuid, setgid, has file caps, or caused a SELinux/AppArmor domain transition. */ for (v = vecs; v[0]; v += 2) { if (v[0] == AT_SECURE) { /* kernel told us whether to enable secure mode */ program_is_setuid = v[1]; goto sanitize; } } /* Kernel did not provide AT_SECURE - fall back on legacy test. */ program_is_setuid = (getuid() != geteuid()) || (getgid() != getegid()); sanitize: /* Sanitize environment if we're loading a setuid program */ if (program_is_setuid) { linker_env_secure(); } debugger_init(); /* Get a few environment variables */ { #if LINKER_DEBUG const char* env; env = linker_env_get("DEBUG"); /* XXX: TODO: Change to LD_DEBUG */ if (env) debug_verbosity = atoi(env); #endif /* Normally, these are cleaned by linker_env_secure, but the test * against program_is_setuid doesn't cost us anything */ if (!program_is_setuid) { ldpath_env = linker_env_get("LD_LIBRARY_PATH"); ldpreload_env = linker_env_get("LD_PRELOAD"); } } INFO("[ android linker & debugger ]\n"); DEBUG("%5d elfdata @ 0x%08x\n", pid, (unsigned)elfdata); si = soinfo_alloc(argv[0]); if(si == 0) { exit(-1); } /* bootstrap the link map, the main exe always needs to be first */ si->flags |= FLAG_EXE; link_map* map = &(si->linkmap); map->l_addr = 0; map->l_name = argv[0]; map->l_prev = NULL; map->l_next = NULL; _r_debug.r_map = map; r_debug_tail = map; /* gdb expects the linker to be in the debug shared object list. * Without this, gdb has trouble locating the linker's ".text" * and ".plt" sections. Gdb could also potentially use this to * relocate the offset of our exported 'rtld_db_dlactivity' symbol. * Don't use soinfo_alloc(), because the linker shouldn't * be on the soinfo list. */ strlcpy((char*) linker_soinfo.name, "/system/bin/linker", sizeof linker_soinfo.name); linker_soinfo.flags = 0; linker_soinfo.base = linker_base; /* * Set the dynamic field in the link map otherwise gdb will complain with * the following: * warning: .dynamic section for "/system/bin/linker" is not at the * expected address (wrong library or version mismatch?) */ Elf32_Ehdr *elf_hdr = (Elf32_Ehdr *) linker_base; Elf32_Phdr *phdr = (Elf32_Phdr *)((unsigned char *) linker_base + elf_hdr->e_phoff); phdr_table_get_dynamic_section(phdr, elf_hdr->e_phnum, linker_base, &linker_soinfo.dynamic, NULL); insert_soinfo_into_debug_map(&linker_soinfo); /* extract information passed from the kernel */ while(vecs[0] != 0){ switch(vecs[0]){ case AT_PHDR: si->phdr = (Elf32_Phdr*) vecs[1]; break; case AT_PHNUM: si->phnum = (int) vecs[1]; break; case AT_ENTRY: si->entry = vecs[1]; break; } vecs += 2; } /* Compute the value of si->base. We can't rely on the fact that * the first entry is the PHDR because this will not be true * for certain executables (e.g. some in the NDK unit test suite) */ int nn; si->base = 0; si->size = phdr_table_get_load_size(si->phdr, si->phnum); si->load_bias = 0; for ( nn = 0; nn < si->phnum; nn++ ) { if (si->phdr[nn].p_type == PT_PHDR) { si->load_bias = (Elf32_Addr)si->phdr - si->phdr[nn].p_vaddr; si->base = (Elf32_Addr) si->phdr - si->phdr[nn].p_offset; break; } } si->dynamic = (unsigned *)-1; si->refcount = 1; // Use LD_LIBRARY_PATH and LD_PRELOAD (but only if we aren't setuid/setgid). parse_LD_LIBRARY_PATH(ldpath_env); parse_LD_PRELOAD(ldpreload_env); if(soinfo_link_image(si)) { char errmsg[] = "CANNOT LINK EXECUTABLE\n"; write(2, __linker_dl_err_buf, strlen(__linker_dl_err_buf)); write(2, errmsg, sizeof(errmsg)); exit(-1); } soinfo_call_preinit_constructors(si); for(i = 0; preloads[i] != NULL; i++) { soinfo_call_constructors(preloads[i]); } /*After the link_image, the si->base is initialized. *For so lib, the map->l_addr will be updated in notify_gdb_of_load. *We need to update this value for so exe here. So Unwind_Backtrace *for some arch like x86 could work correctly within so exe. */ map->l_addr = si->base; soinfo_call_constructors(si); #if ALLOW_SYMBOLS_FROM_MAIN /* Set somain after we've loaded all the libraries in order to prevent * linking of symbols back to the main image, which is not set up at that * point yet. */ somain = si; #endif #if TIMING gettimeofday(&t1,NULL); PRINT("LINKER TIME: %s: %d microseconds\n", argv[0], (int) ( (((long long)t1.tv_sec * 1000000LL) + (long long)t1.tv_usec) - (((long long)t0.tv_sec * 1000000LL) + (long long)t0.tv_usec) )); #endif #if STATS PRINT("RELO STATS: %s: %d abs, %d rel, %d copy, %d symbol\n", argv[0], linker_stats.count[kRelocAbsolute], linker_stats.count[kRelocRelative], linker_stats.count[kRelocCopy], linker_stats.count[kRelocSymbol]); #endif #if COUNT_PAGES { unsigned n; unsigned i; unsigned count = 0; for(n = 0; n < 4096; n++){ if(bitmask[n]){ unsigned x = bitmask[n]; for(i = 0; i < 8; i++){ if(x & 1) count++; x >>= 1; } } } PRINT("PAGES MODIFIED: %s: %d (%dKB)\n", argv[0], count, count * 4); } #endif #if TIMING || STATS || COUNT_PAGES fflush(stdout); #endif TRACE("[ %5d Ready to execute '%s' @ 0x%08x ]\n", pid, si->name, si->entry); return si->entry; } /* * Find the value of AT_BASE passed to us by the kernel. This is the load * location of the linker. */ static unsigned find_linker_base(unsigned **elfdata) { int argc = (int) *elfdata; char **argv = (char**) (elfdata + 1); unsigned *vecs = (unsigned*) (argv + argc + 1); while (vecs[0] != 0) { vecs++; } /* The end of the environment block is marked by two NULL pointers */ vecs++; while(vecs[0]) { if (vecs[0] == AT_BASE) { return vecs[1]; } vecs += 2; } return 0; // should never happen } /* Compute the load-bias of an existing executable. This shall only * be used to compute the load bias of an executable or shared library * that was loaded by the kernel itself. * * Input: * elf -> address of ELF header, assumed to be at the start of the file. * Return: * load bias, i.e. add the value of any p_vaddr in the file to get * the corresponding address in memory. */ static Elf32_Addr get_elf_exec_load_bias(const Elf32_Ehdr* elf) { Elf32_Addr offset = elf->e_phoff; const Elf32_Phdr* phdr_table = (const Elf32_Phdr*)((char*)elf + offset); const Elf32_Phdr* phdr_end = phdr_table + elf->e_phnum; const Elf32_Phdr* phdr; for (phdr = phdr_table; phdr < phdr_end; phdr++) { if (phdr->p_type == PT_LOAD) { return (Elf32_Addr)elf + phdr->p_offset - phdr->p_vaddr; } } return 0; } /* * This is the entry point for the linker, called from begin.S. This * method is responsible for fixing the linker's own relocations, and * then calling __linker_init_post_relocation(). * * Because this method is called before the linker has fixed it's own * relocations, any attempt to reference an extern variable, extern * function, or other GOT reference will generate a segfault. */ extern "C" unsigned __linker_init(unsigned **elfdata) { unsigned linker_addr = find_linker_base(elfdata); Elf32_Ehdr *elf_hdr = (Elf32_Ehdr *) linker_addr; Elf32_Phdr *phdr = (Elf32_Phdr *)((unsigned char *) linker_addr + elf_hdr->e_phoff); soinfo linker_so; memset(&linker_so, 0, sizeof(soinfo)); linker_so.base = linker_addr; linker_so.size = phdr_table_get_load_size(phdr, elf_hdr->e_phnum); linker_so.load_bias = get_elf_exec_load_bias(elf_hdr); linker_so.dynamic = (unsigned *) -1; linker_so.phdr = phdr; linker_so.phnum = elf_hdr->e_phnum; linker_so.flags |= FLAG_LINKER; if (soinfo_link_image(&linker_so)) { // It would be nice to print an error message, but if the linker // can't link itself, there's no guarantee that we'll be able to // call write() (because it involves a GOT reference). // // This situation should never occur unless the linker itself // is corrupt. exit(-1); } // We have successfully fixed our own relocations. It's safe to run // the main part of the linker now. return __linker_init_post_relocation(elfdata, linker_addr); }