/* * Copyright (C) 2016 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 "linker_main.h" #include "linker_debug.h" #include "linker_cfi.h" #include "linker_gdb_support.h" #include "linker_globals.h" #include "linker_phdr.h" #include "linker_utils.h" #include "private/bionic_auxv.h" #include "private/bionic_globals.h" #include "private/bionic_tls.h" #include "private/KernelArgumentBlock.h" #include "android-base/unique_fd.h" #include "android-base/strings.h" #include "android-base/stringprintf.h" #ifdef __ANDROID__ #include "debuggerd/handler.h" #endif #include #include extern void __libc_init_globals(KernelArgumentBlock&); extern void __libc_init_AT_SECURE(KernelArgumentBlock&); __LIBC_HIDDEN__ extern "C" void _start(); static ElfW(Addr) get_elf_exec_load_bias(const ElfW(Ehdr)* elf); static void get_elf_base_from_phdr(const ElfW(Phdr)* phdr_table, size_t phdr_count, ElfW(Addr)* base, ElfW(Addr)* load_bias); // These should be preserved static to avoid emitting // RELATIVE relocations for the part of the code running // before linker links itself. // TODO (dimtiry): remove somain, rename solist to solist_head static soinfo* solist; static soinfo* sonext; static soinfo* somain; // main process, always the one after libdl_info static soinfo* solinker; static soinfo* vdso; // vdso if present void solist_add_soinfo(soinfo* si) { sonext->next = si; sonext = si; } bool solist_remove_soinfo(soinfo* si) { soinfo *prev = nullptr, *trav; for (trav = solist; trav != nullptr; trav = trav->next) { if (trav == si) { break; } prev = trav; } if (trav == nullptr) { // si was not in solist PRINT("name \"%s\"@%p is not in solist!", si->get_realpath(), si); return false; } // prev will never be null, because the first entry in solist is // always the static libdl_info. CHECK(prev != nullptr); prev->next = si->next; if (si == sonext) { sonext = prev; } return true; } soinfo* solist_get_head() { return solist; } soinfo* solist_get_somain() { return somain; } soinfo* solist_get_vdso() { return vdso; } int g_ld_debug_verbosity; abort_msg_t* g_abort_message = nullptr; // For debuggerd. static std::vector g_ld_preload_names; static std::vector g_ld_preloads; static void parse_path(const char* path, const char* delimiters, std::vector* resolved_paths) { std::vector paths; split_path(path, delimiters, &paths); resolve_paths(paths, resolved_paths); } static void parse_LD_LIBRARY_PATH(const char* path) { std::vector ld_libary_paths; parse_path(path, ":", &ld_libary_paths); g_default_namespace.set_ld_library_paths(std::move(ld_libary_paths)); } static void parse_LD_PRELOAD(const char* path) { g_ld_preload_names.clear(); if (path != nullptr) { // We have historically supported ':' as well as ' ' in LD_PRELOAD. g_ld_preload_names = android::base::Split(path, " :"); g_ld_preload_names.erase(std::remove_if(g_ld_preload_names.begin(), g_ld_preload_names.end(), [](const std::string& s) { return s.empty(); }), g_ld_preload_names.end()); } } // An empty list of soinfos static soinfo_list_t g_empty_list; static void add_vdso(KernelArgumentBlock& args) { ElfW(Ehdr)* ehdr_vdso = reinterpret_cast(args.getauxval(AT_SYSINFO_EHDR)); if (ehdr_vdso == nullptr) { return; } soinfo* si = soinfo_alloc(&g_default_namespace, "[vdso]", nullptr, 0, 0); si->phdr = reinterpret_cast(reinterpret_cast(ehdr_vdso) + ehdr_vdso->e_phoff); si->phnum = ehdr_vdso->e_phnum; si->base = reinterpret_cast(ehdr_vdso); si->size = phdr_table_get_load_size(si->phdr, si->phnum); si->load_bias = get_elf_exec_load_bias(ehdr_vdso); si->prelink_image(); si->link_image(g_empty_list, soinfo_list_t::make_list(si), nullptr); // prevents accidental unloads... si->set_dt_flags_1(si->get_dt_flags_1() | DF_1_NODELETE); si->set_linked(); si->call_constructors(); vdso = si; } // Initializes an soinfo's link_map_head field using other fields from the // soinfo (phdr, phnum, load_bias). static void init_link_map_head(soinfo& info, const char* linker_path) { auto& map = info.link_map_head; map.l_addr = info.load_bias; map.l_name = const_cast(linker_path); phdr_table_get_dynamic_section(info.phdr, info.phnum, info.load_bias, &map.l_ld, nullptr); } extern "C" int __system_properties_init(void); struct ExecutableInfo { std::string path; struct stat file_stat; const ElfW(Phdr)* phdr; size_t phdr_count; ElfW(Addr) entry_point; }; static ExecutableInfo get_executable_info(KernelArgumentBlock& args) { ExecutableInfo result = {}; if (is_init()) { // /proc fs is not mounted when init starts. Therefore we can't use // /proc/self/exe for init. stat("/init", &result.file_stat); result.path = "/init"; } else { // Stat "/proc/self/exe" instead of executable_path because // the executable could be unlinked by this point and it should // not cause a crash (see http://b/31084669) if (TEMP_FAILURE_RETRY(stat("/proc/self/exe", &result.file_stat)) != 0) { async_safe_fatal("unable to stat \"/proc/self/exe\": %s", strerror(errno)); } char path[PATH_MAX]; ssize_t path_len = readlink("/proc/self/exe", path, sizeof(path)); if (path_len == -1 || path_len >= static_cast(sizeof(path))) { async_safe_fatal("readlink('/proc/self/exe') failed: %s", strerror(errno)); } result.path = std::string(path, path_len); } result.phdr = reinterpret_cast(args.getauxval(AT_PHDR)); result.phdr_count = args.getauxval(AT_PHNUM); result.entry_point = args.getauxval(AT_ENTRY); return result; } #if defined(__LP64__) static char kLinkerPath[] = "/system/bin/linker64"; #else static char kLinkerPath[] = "/system/bin/linker"; #endif __printflike(1, 2) static void __linker_error(const char* fmt, ...) { va_list ap; va_start(ap, fmt); async_safe_format_fd_va_list(STDERR_FILENO, fmt, ap); va_end(ap); va_start(ap, fmt); async_safe_format_log_va_list(ANDROID_LOG_FATAL, "linker", fmt, ap); va_end(ap); _exit(EXIT_FAILURE); } static void __linker_cannot_link(const char* argv0) { __linker_error("CANNOT LINK EXECUTABLE \"%s\": %s\n", argv0, linker_get_error_buffer()); } // Load an executable. Normally the kernel has already loaded the executable when the linker // starts. The linker can be invoked directly on an executable, though, and then the linker must // load it. This function doesn't load dependencies or resolve relocations. static ExecutableInfo load_executable(const char* orig_path) { ExecutableInfo result = {}; if (orig_path[0] != '/') { __linker_error("error: expected absolute path: \"%s\"\n", orig_path); } off64_t file_offset; android::base::unique_fd fd(open_executable(orig_path, &file_offset, &result.path)); if (fd.get() == -1) { __linker_error("error: unable to open file \"%s\"\n", orig_path); } if (TEMP_FAILURE_RETRY(fstat(fd.get(), &result.file_stat)) == -1) { __linker_error("error: unable to stat \"%s\": %s\n", result.path.c_str(), strerror(errno)); } ElfReader elf_reader; if (!elf_reader.Read(result.path.c_str(), fd.get(), file_offset, result.file_stat.st_size)) { __linker_error("error: %s\n", linker_get_error_buffer()); } if (!elf_reader.Load(nullptr)) { __linker_error("error: %s\n", linker_get_error_buffer()); } result.phdr = elf_reader.loaded_phdr(); result.phdr_count = elf_reader.phdr_count(); result.entry_point = elf_reader.entry_point(); return result; } static ElfW(Addr) linker_main(KernelArgumentBlock& args, const char* exe_to_load) { ProtectedDataGuard guard; #if TIMING struct timeval t0, t1; gettimeofday(&t0, 0); #endif // Sanitize the environment. __libc_init_AT_SECURE(args); // Initialize system properties __system_properties_init(); // may use 'environ' // Register the debuggerd signal handler. #ifdef __ANDROID__ debuggerd_callbacks_t callbacks = { .get_abort_message = []() { return g_abort_message; }, .post_dump = ¬ify_gdb_of_libraries, }; debuggerd_init(&callbacks); #endif g_linker_logger.ResetState(); // Get a few environment variables. const char* LD_DEBUG = getenv("LD_DEBUG"); if (LD_DEBUG != nullptr) { g_ld_debug_verbosity = atoi(LD_DEBUG); } #if defined(__LP64__) INFO("[ Android dynamic linker (64-bit) ]"); #else INFO("[ Android dynamic linker (32-bit) ]"); #endif // These should have been sanitized by __libc_init_AT_SECURE, but the test // doesn't cost us anything. const char* ldpath_env = nullptr; const char* ldpreload_env = nullptr; if (!getauxval(AT_SECURE)) { ldpath_env = getenv("LD_LIBRARY_PATH"); if (ldpath_env != nullptr) { INFO("[ LD_LIBRARY_PATH set to \"%s\" ]", ldpath_env); } ldpreload_env = getenv("LD_PRELOAD"); if (ldpreload_env != nullptr) { INFO("[ LD_PRELOAD set to \"%s\" ]", ldpreload_env); } } const ExecutableInfo exe_info = exe_to_load ? load_executable(exe_to_load) : get_executable_info(args); // Assign to a static variable for the sake of the debug map, which needs // a C-style string to last until the program exits. static std::string exe_path = exe_info.path; // Initialize the main exe's soinfo. soinfo* si = soinfo_alloc(&g_default_namespace, exe_path.c_str(), &exe_info.file_stat, 0, RTLD_GLOBAL); somain = si; si->phdr = exe_info.phdr; si->phnum = exe_info.phdr_count; get_elf_base_from_phdr(si->phdr, si->phnum, &si->base, &si->load_bias); si->size = phdr_table_get_load_size(si->phdr, si->phnum); si->dynamic = nullptr; si->set_main_executable(); init_link_map_head(*si, exe_path.c_str()); // Register the main executable and the linker upfront to have // gdb aware of them before loading the rest of the dependency // tree. // // 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. // insert_link_map_into_debug_map(&si->link_map_head); insert_link_map_into_debug_map(&solinker->link_map_head); add_vdso(args); ElfW(Ehdr)* elf_hdr = reinterpret_cast(si->base); // We haven't supported non-PIE since Lollipop for security reasons. if (elf_hdr->e_type != ET_DYN) { // We don't use async_safe_fatal here because we don't want a tombstone: // even after several years we still find ourselves on app compatibility // investigations because some app's trying to launch an executable that // hasn't worked in at least three years, and we've "helpfully" dropped a // tombstone for them. The tombstone never provided any detail relevant to // fixing the problem anyway, and the utility of drawing extra attention // to the problem is non-existent at this late date. async_safe_format_fd(STDERR_FILENO, "\"%s\": error: Android 5.0 and later only support " "position-independent executables (-fPIE).\n", g_argv[0]); exit(EXIT_FAILURE); } // 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); std::vector namespaces = init_default_namespaces(exe_path.c_str()); if (!si->prelink_image()) __linker_cannot_link(g_argv[0]); // add somain to global group si->set_dt_flags_1(si->get_dt_flags_1() | DF_1_GLOBAL); // ... and add it to all other linked namespaces for (auto linked_ns : namespaces) { if (linked_ns != &g_default_namespace) { linked_ns->add_soinfo(somain); somain->add_secondary_namespace(linked_ns); } } // Load ld_preloads and dependencies. std::vector needed_library_name_list; size_t ld_preloads_count = 0; for (const auto& ld_preload_name : g_ld_preload_names) { needed_library_name_list.push_back(ld_preload_name.c_str()); ++ld_preloads_count; } for_each_dt_needed(si, [&](const char* name) { needed_library_name_list.push_back(name); }); const char** needed_library_names = &needed_library_name_list[0]; size_t needed_libraries_count = needed_library_name_list.size(); if (needed_libraries_count > 0 && !find_libraries(&g_default_namespace, si, needed_library_names, needed_libraries_count, nullptr, &g_ld_preloads, ld_preloads_count, RTLD_GLOBAL, nullptr, true /* add_as_children */, true /* search_linked_namespaces */, &namespaces)) { __linker_cannot_link(g_argv[0]); } else if (needed_libraries_count == 0) { if (!si->link_image(g_empty_list, soinfo_list_t::make_list(si), nullptr)) { __linker_cannot_link(g_argv[0]); } si->increment_ref_count(); } if (!get_cfi_shadow()->InitialLinkDone(solist)) __linker_cannot_link(g_argv[0]); // Store a pointer to the kernel argument block in a TLS slot to be // picked up by the libc constructor. __get_tls()[TLS_SLOT_BIONIC_PREINIT] = &args; si->call_pre_init_constructors(); si->call_constructors(); #if TIMING gettimeofday(&t1, nullptr); PRINT("LINKER TIME: %s: %d microseconds", g_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", g_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]; #if defined(__LP64__) for (i = 0; i < 32; i++) { #else for (i = 0; i < 8; i++) { #endif if (x & 1) { count++; } x >>= 1; } } } PRINT("PAGES MODIFIED: %s: %d (%dKB)", g_argv[0], count, count * 4); } #endif #if TIMING || STATS || COUNT_PAGES fflush(stdout); #endif ElfW(Addr) entry = exe_info.entry_point; TRACE("[ Ready to execute \"%s\" @ %p ]", si->get_realpath(), reinterpret_cast(entry)); return entry; } /* 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 ElfW(Addr) get_elf_exec_load_bias(const ElfW(Ehdr)* elf) { ElfW(Addr) offset = elf->e_phoff; const ElfW(Phdr)* phdr_table = reinterpret_cast(reinterpret_cast(elf) + offset); const ElfW(Phdr)* phdr_end = phdr_table + elf->e_phnum; for (const ElfW(Phdr)* phdr = phdr_table; phdr < phdr_end; phdr++) { if (phdr->p_type == PT_LOAD) { return reinterpret_cast(elf) + phdr->p_offset - phdr->p_vaddr; } } return 0; } /* Find the load bias and base address of an executable or shared object loaded * by the kernel. The ELF file's PHDR table must have a PT_PHDR entry. * * A VDSO doesn't have a PT_PHDR entry in its PHDR table. */ static void get_elf_base_from_phdr(const ElfW(Phdr)* phdr_table, size_t phdr_count, ElfW(Addr)* base, ElfW(Addr)* load_bias) { for (size_t i = 0; i < phdr_count; ++i) { if (phdr_table[i].p_type == PT_PHDR) { *load_bias = reinterpret_cast(phdr_table) - phdr_table[i].p_vaddr; *base = reinterpret_cast(phdr_table) - phdr_table[i].p_offset; return; } } async_safe_fatal("Could not find a PHDR: broken executable?"); } static ElfW(Addr) __attribute__((noinline)) __linker_init_post_relocation(KernelArgumentBlock& args, soinfo& linker_so); /* * 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" ElfW(Addr) __linker_init(void* raw_args) { KernelArgumentBlock args(raw_args); #if defined(__i386__) __libc_init_sysinfo(args); #endif // When the linker is run by itself (rather than as an interpreter for // another program), AT_BASE is 0. ElfW(Addr) linker_addr = args.getauxval(AT_BASE); if (linker_addr == 0) { // Detect an attempt to run the linker on itself (e.g. // `linker64 /system/bin/linker64`). If the kernel loaded this instance of // the linker, then AT_ENTRY will refer to &_start. If it doesn't, then // something else must have loaded this instance of the linker. It's // simpler if we only allow one copy of the linker to be loaded at a time. if (args.getauxval(AT_ENTRY) != reinterpret_cast(&_start)) { // The first linker already relocated this one and set up TLS, so we don't // need further libc initialization. __linker_error("error: linker cannot load itself\n"); } // Otherwise, the AT_PHDR and AT_PHNUM aux values describe this linker // instance, so use the phdr to find the linker's base address. ElfW(Addr) load_bias; get_elf_base_from_phdr( reinterpret_cast(args.getauxval(AT_PHDR)), args.getauxval(AT_PHNUM), &linker_addr, &load_bias); } ElfW(Ehdr)* elf_hdr = reinterpret_cast(linker_addr); ElfW(Phdr)* phdr = reinterpret_cast(linker_addr + elf_hdr->e_phoff); soinfo tmp_linker_so(nullptr, nullptr, nullptr, 0, 0); tmp_linker_so.base = linker_addr; tmp_linker_so.size = phdr_table_get_load_size(phdr, elf_hdr->e_phnum); tmp_linker_so.load_bias = get_elf_exec_load_bias(elf_hdr); tmp_linker_so.dynamic = nullptr; tmp_linker_so.phdr = phdr; tmp_linker_so.phnum = elf_hdr->e_phnum; tmp_linker_so.set_linker_flag(); // Prelink the linker so we can access linker globals. if (!tmp_linker_so.prelink_image()) __linker_cannot_link(args.argv[0]); // This might not be obvious... The reasons why we pass g_empty_list // in place of local_group here are (1) we do not really need it, because // linker is built with DT_SYMBOLIC and therefore relocates its symbols against // itself without having to look into local_group and (2) allocators // are not yet initialized, and therefore we cannot use linked_list.push_* // functions at this point. if (!tmp_linker_so.link_image(g_empty_list, g_empty_list, nullptr)) __linker_cannot_link(args.argv[0]); return __linker_init_post_relocation(args, tmp_linker_so); } /* * This code is called after the linker has linked itself and fixed its own * GOT. It is safe to make references to externs and other non-local data at * this point. The compiler sometimes moves GOT references earlier in a * function, so avoid inlining this function (http://b/80503879). */ static ElfW(Addr) __attribute__((noinline)) __linker_init_post_relocation(KernelArgumentBlock& args, soinfo& tmp_linker_so) { // Initialize the main thread (including TLS, so system calls really work). __libc_init_main_thread(args); // We didn't protect the linker's RELRO pages in link_image because we // couldn't make system calls on x86 at that point, but we can now... if (!tmp_linker_so.protect_relro()) __linker_cannot_link(args.argv[0]); // Initialize the linker/libc.so shared global inside the linker. static libc_shared_globals shared_globals; __libc_shared_globals = &shared_globals; __libc_init_shared_globals(&shared_globals); args.shared_globals = __libc_shared_globals; // Initialize the linker's static libc's globals __libc_init_globals(args); // Initialize the linker's own global variables tmp_linker_so.call_constructors(); // When the linker is run directly rather than acting as PT_INTERP, parse // arguments and determine the executable to load. When it's instead acting // as PT_INTERP, AT_ENTRY will refer to the loaded executable rather than the // linker's _start. const char* exe_to_load = nullptr; if (args.getauxval(AT_ENTRY) == reinterpret_cast(&_start)) { if (args.argc <= 1 || !strcmp(args.argv[1], "--help")) { async_safe_format_fd(STDOUT_FILENO, "Usage: %s program [arguments...]\n" " %s path.zip!/program [arguments...]\n" "\n" "A helper program for linking dynamic executables. Typically, the kernel loads\n" "this program because it's the PT_INTERP of a dynamic executable.\n" "\n" "This program can also be run directly to load and run a dynamic executable. The\n" "executable can be inside a zip file if it's stored uncompressed and at a\n" "page-aligned offset.\n", args.argv[0], args.argv[0]); exit(0); } exe_to_load = args.argv[1]; __libc_shared_globals->initial_linker_arg_count = 1; } // store argc/argv/envp to use them for calling constructors g_argc = args.argc - __libc_shared_globals->initial_linker_arg_count; g_argv = args.argv + __libc_shared_globals->initial_linker_arg_count; g_envp = args.envp; // Initialize static variables. Note that in order to // get correct libdl_info we need to call constructors // before get_libdl_info(). sonext = solist = solinker = get_libdl_info(kLinkerPath, tmp_linker_so); g_default_namespace.add_soinfo(solinker); init_link_map_head(*solinker, kLinkerPath); args.abort_message_ptr = &g_abort_message; ElfW(Addr) start_address = linker_main(args, exe_to_load); INFO("[ Jumping to _start (%p)... ]", reinterpret_cast(start_address)); // Return the address that the calling assembly stub should jump to. return start_address; }