/* * 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 /* special private C library header - see Android.mk */ #include #include "linker.h" #include "linker_debug.h" #include "linker_environ.h" #include "linker_format.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 (64) */ static int link_image(soinfo *si, unsigned wr_offset); 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 inline int validate_soinfo(soinfo *si) { return (si >= sopool && si < sopool + SO_MAX) || si == &libdl_info; } 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 int program_is_setuid; #if STATS struct _link_stats linker_stats; #endif #if COUNT_PAGES unsigned bitmask[4096]; #endif #ifndef PT_ARM_EXIDX #define PT_ARM_EXIDX 0x70000001 /* .ARM.exidx segment */ #endif #define HOODLUM(name, ret, ...) \ ret name __VA_ARGS__ \ { \ char errstr[] = "ERROR: " #name " called from the dynamic linker!\n"; \ write(2, errstr, sizeof(errstr)); \ abort(); \ } HOODLUM(malloc, void *, (size_t size)); HOODLUM(free, void, (void *ptr)); HOODLUM(realloc, void *, (void *ptr, size_t size)); HOODLUM(calloc, void *, (size_t cnt, size_t size)); static char tmp_err_buf[768]; static char __linker_dl_err_buf[768]; #define DL_ERR(fmt, x...) \ do { \ format_buffer(__linker_dl_err_buf, sizeof(__linker_dl_err_buf), \ "%s[%d]: " fmt, __func__, __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 void __attribute__((noinline)) rtld_db_dlactivity(void); static struct r_debug _r_debug = {1, NULL, &rtld_db_dlactivity, RT_CONSISTENT, 0}; static struct 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) { struct link_map * map; /* Copy the necessary fields into the debug structure. */ 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) { struct 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; } 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); } 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); } 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 *alloc_info(const char *name) { soinfo *si; if(strlen(name) >= SOINFO_NAME_LEN) { DL_ERR("%5d library name %s too long", pid, name); return NULL; } /* The freelist is populated when we call free_info(), which in turn is done only by dlclose(), which is not likely to be used. */ if (!freelist) { if(socount == SO_MAX) { DL_ERR("%5d too many libraries when loading %s", pid, name); return NULL; } freelist = sopool + socount++; freelist->next = NULL; } 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 free_info(soinfo *si) { 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("%5d name %s is not in solist!", pid, 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; } const char *addr_to_name(unsigned addr) { soinfo *si; for(si = solist; si != 0; si = si->next){ if((addr >= si->base) && (addr < (si->base + si->size))) { return si->name; } } return ""; } /* 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. */ #ifdef ANDROID_ARM_LINKER _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->base + (unsigned long)si->ARM_exidx); } } *pcount = 0; return NULL; } #elif defined(ANDROID_X86_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)(struct dl_phdr_info *info, size_t size, void *data), void *data) { soinfo *si; struct dl_phdr_info dl_info; int rv = 0; for (si = solist; si != NULL; si = si->next) { 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 (struct dl_phdr_info), data); if (rv != 0) break; } return rv; } #endif static Elf32_Sym *_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: /* no section == undefined */ if(s->st_shndx == 0) 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 * _do_lookup(soinfo *si, const char *name, unsigned *base) { unsigned elf_hash = elfhash(name); Elf32_Sym *s; unsigned *d; soinfo *lsi = si; int i; /* 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 ambigious 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 = _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 = _elf_lookup(lsi, elf_hash, name); if(s != NULL) goto done; } for(d = si->dynamic; *d; d += 2) { if(d[0] == DT_NEEDED){ lsi = (soinfo *)d[1]; if (!validate_soinfo(lsi)) { DL_ERR("%5d bad DT_NEEDED pointer in %s", pid, si->name); return NULL; } DEBUG("%5d %s: looking up %s in %s\n", pid, si->name, name, lsi->name); s = _elf_lookup(lsi, elf_hash, name); if ((s != NULL) && (s->st_shndx != SHN_UNDEF)) 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 = _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\n", pid, si->name, name, s->st_value, lsi->name, lsi->base); *base = lsi->base; 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 *lookup_in_library(soinfo *si, const char *name) { return _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 = _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 *find_containing_symbol(const void *addr, soinfo *si) { 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 *sopaths[] = { "/vendor/lib", "/system/lib", 0 }; static int _open_lib(const char *name) { int fd; struct stat filestat; if ((stat(name, &filestat) >= 0) && S_ISREG(filestat.st_mode)) { if ((fd = open(name, O_RDONLY)) >= 0) return fd; } return -1; } static int open_library(const char *name) { int fd; char buf[512]; const char **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; } /* temporary space for holding the first page of the shared lib * which contains the elf header (with the pht). */ static unsigned char __header[PAGE_SIZE]; typedef struct { long mmap_addr; char tag[4]; /* 'P', 'R', 'E', ' ' */ } prelink_info_t; /* Returns the requested base address if the library is prelinked, * and 0 otherwise. */ static unsigned long is_prelinked(int fd, const char *name) { off_t sz; prelink_info_t info; sz = lseek(fd, -sizeof(prelink_info_t), SEEK_END); if (sz < 0) { DL_ERR("lseek() failed!"); return 0; } if (read(fd, &info, sizeof(info)) != sizeof(info)) { WARN("Could not read prelink_info_t structure for `%s`\n", name); return 0; } if (strncmp(info.tag, "PRE ", 4)) { WARN("`%s` is not a prelinked library\n", name); return 0; } return (unsigned long)info.mmap_addr; } /* verify_elf_object * Verifies if the object @ base is a valid ELF object * * Args: * * Returns: * 0 on success * -1 if no valid ELF object is found @ base. */ static int verify_elf_object(void *base, const char *name) { Elf32_Ehdr *hdr = (Elf32_Ehdr *) base; 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; /* 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; #endif return 0; } /* get_lib_extents * Retrieves the base (*base) address where the ELF object should be * mapped and its overall memory size (*total_sz). * * Args: * fd: Opened file descriptor for the library * name: The name of the library * _hdr: Pointer to the header page of the library * total_sz: Total size of the memory that should be allocated for * this library * * Returns: * -1 if there was an error while trying to get the lib extents. * The possible reasons are: * - Could not determine if the library was prelinked. * - The library provided is not a valid ELF object * 0 if the library did not request a specific base offset (normal * for non-prelinked libs) * > 0 if the library requests a specific address to be mapped to. * This indicates a pre-linked library. */ static unsigned get_lib_extents(int fd, const char *name, void *__hdr, unsigned *total_sz) { unsigned req_base; unsigned min_vaddr = 0xffffffff; unsigned max_vaddr = 0; unsigned char *_hdr = (unsigned char *)__hdr; Elf32_Ehdr *ehdr = (Elf32_Ehdr *)_hdr; Elf32_Phdr *phdr; int cnt; TRACE("[ %5d Computing extents for '%s'. ]\n", pid, name); if (verify_elf_object(_hdr, name) < 0) { DL_ERR("%5d - %s is not a valid ELF object", pid, name); return (unsigned)-1; } req_base = (unsigned) is_prelinked(fd, name); if (req_base == (unsigned)-1) return -1; else if (req_base != 0) { TRACE("[ %5d - Prelinked library '%s' requesting base @ 0x%08x ]\n", pid, name, req_base); } else { TRACE("[ %5d - Non-prelinked library '%s' found. ]\n", pid, name); } phdr = (Elf32_Phdr *)(_hdr + ehdr->e_phoff); /* find the min/max p_vaddrs from all the PT_LOAD segments so we can * get the range. */ for (cnt = 0; cnt < ehdr->e_phnum; ++cnt, ++phdr) { if (phdr->p_type == PT_LOAD) { if ((phdr->p_vaddr + phdr->p_memsz) > max_vaddr) max_vaddr = phdr->p_vaddr + phdr->p_memsz; if (phdr->p_vaddr < min_vaddr) min_vaddr = phdr->p_vaddr; } } if ((min_vaddr == 0xffffffff) && (max_vaddr == 0)) { DL_ERR("%5d - No loadable segments found in %s.", pid, name); return (unsigned)-1; } /* truncate min_vaddr down to page boundary */ min_vaddr &= ~PAGE_MASK; /* round max_vaddr up to the next page */ max_vaddr = (max_vaddr + PAGE_SIZE - 1) & ~PAGE_MASK; *total_sz = (max_vaddr - min_vaddr); return (unsigned)req_base; } /* reserve_mem_region * * This function reserves a chunk of memory to be used for mapping in * a prelinked shared library. We reserve the entire memory region here, and * then the rest of the linker will relocate the individual loadable * segments into the correct locations within this memory range. * * Args: * si->base: The requested base of the allocation. * si->size: The size of the allocation. * * Returns: * -1 on failure, and 0 on success. On success, si->base will contain * the virtual address at which the library will be mapped. */ static int reserve_mem_region(soinfo *si) { void *base = mmap((void *)si->base, si->size, PROT_NONE, MAP_FIXED | MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); if (base == MAP_FAILED) { DL_ERR("%5d can NOT map (%sprelinked) library '%s' at 0x%08x " "as requested, will try general pool: %d (%s)", pid, (si->base ? "" : "non-"), si->name, si->base, errno, strerror(errno)); return -1; } else if (base != (void *)si->base) { DL_ERR("OOPS: %5d %sprelinked library '%s' mapped at 0x%08x, " "not at 0x%08x", pid, (si->base ? "" : "non-"), si->name, (unsigned)base, si->base); munmap(base, si->size); return -1; } return 0; } static int alloc_mem_region(soinfo *si) { if (si->base) { /* Attempt to mmap a prelinked library. */ return reserve_mem_region(si); } /* This is not a prelinked library, so we use the kernel's default allocator. */ void *base = mmap(NULL, si->size, PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); if (base == MAP_FAILED) { DL_ERR("%5d mmap of library '%s' failed: %d (%s)\n", pid, si->name, errno, strerror(errno)); goto err; } si->base = (unsigned) base; PRINT("%5d mapped library '%s' to %08x via kernel allocator.\n", pid, si->name, si->base); return 0; err: DL_ERR("OOPS: %5d cannot map library '%s'. no vspace available.", pid, si->name); return -1; } #define MAYBE_MAP_FLAG(x,from,to) (((x) & (from)) ? (to) : 0) #define PFLAGS_TO_PROT(x) (MAYBE_MAP_FLAG((x), PF_X, PROT_EXEC) | \ MAYBE_MAP_FLAG((x), PF_R, PROT_READ) | \ MAYBE_MAP_FLAG((x), PF_W, PROT_WRITE)) /* load_segments * * This function loads all the loadable (PT_LOAD) segments into memory * at their appropriate memory offsets off the base address. * * Args: * fd: Open file descriptor to the library to load. * header: Pointer to a header page that contains the ELF header. * This is needed since we haven't mapped in the real file yet. * si: ptr to soinfo struct describing the shared object. * * Returns: * 0 on success, -1 on failure. */ static int load_segments(int fd, void *header, soinfo *si) { Elf32_Ehdr *ehdr = (Elf32_Ehdr *)header; Elf32_Phdr *phdr = (Elf32_Phdr *)((unsigned char *)header + ehdr->e_phoff); Elf32_Addr base = (Elf32_Addr) si->base; int cnt; unsigned len; Elf32_Addr tmp; unsigned char *pbase; unsigned char *extra_base; unsigned extra_len; unsigned total_sz = 0; si->wrprotect_start = 0xffffffff; si->wrprotect_end = 0; TRACE("[ %5d - Begin loading segments for '%s' @ 0x%08x ]\n", pid, si->name, (unsigned)si->base); /* Now go through all the PT_LOAD segments and map them into memory * at the appropriate locations. */ for (cnt = 0; cnt < ehdr->e_phnum; ++cnt, ++phdr) { if (phdr->p_type == PT_LOAD) { DEBUG_DUMP_PHDR(phdr, "PT_LOAD", pid); /* we want to map in the segment on a page boundary */ tmp = base + (phdr->p_vaddr & (~PAGE_MASK)); /* add the # of bytes we masked off above to the total length. */ len = phdr->p_filesz + (phdr->p_vaddr & PAGE_MASK); TRACE("[ %d - Trying to load segment from '%s' @ 0x%08x " "(0x%08x). p_vaddr=0x%08x p_offset=0x%08x ]\n", pid, si->name, (unsigned)tmp, len, phdr->p_vaddr, phdr->p_offset); pbase = mmap((void *)tmp, len, PFLAGS_TO_PROT(phdr->p_flags), MAP_PRIVATE | MAP_FIXED, fd, phdr->p_offset & (~PAGE_MASK)); if (pbase == MAP_FAILED) { DL_ERR("%d failed to map segment from '%s' @ 0x%08x (0x%08x). " "p_vaddr=0x%08x p_offset=0x%08x", pid, si->name, (unsigned)tmp, len, phdr->p_vaddr, phdr->p_offset); goto fail; } /* If 'len' didn't end on page boundary, and it's a writable * segment, zero-fill the rest. */ if ((len & PAGE_MASK) && (phdr->p_flags & PF_W)) memset((void *)(pbase + len), 0, PAGE_SIZE - (len & PAGE_MASK)); /* Check to see if we need to extend the map for this segment to * cover the diff between filesz and memsz (i.e. for bss). * * base _+---------------------+ page boundary * . . * | | * . . * pbase _+---------------------+ page boundary * | | * . . * base + p_vaddr _| | * . \ \ . * . | filesz | . * pbase + len _| / | | * <0 pad> . . . * extra_base _+------------|--------+ page boundary * / . . . * | . . . * | +------------|--------+ page boundary * extra_len-> | | | | * | . | memsz . * | . | . * \ _| / | * . . * | | * _+---------------------+ page boundary */ tmp = (Elf32_Addr)(((unsigned)pbase + len + PAGE_SIZE - 1) & (~PAGE_MASK)); if (tmp < (base + phdr->p_vaddr + phdr->p_memsz)) { extra_len = base + phdr->p_vaddr + phdr->p_memsz - tmp; TRACE("[ %5d - Need to extend segment from '%s' @ 0x%08x " "(0x%08x) ]\n", pid, si->name, (unsigned)tmp, extra_len); /* map in the extra page(s) as anonymous into the range. * This is probably not necessary as we already mapped in * the entire region previously, but we just want to be * sure. This will also set the right flags on the region * (though we can probably accomplish the same thing with * mprotect). */ extra_base = mmap((void *)tmp, extra_len, PFLAGS_TO_PROT(phdr->p_flags), MAP_PRIVATE | MAP_FIXED | MAP_ANONYMOUS, -1, 0); if (extra_base == MAP_FAILED) { DL_ERR("[ %5d - failed to extend segment from '%s' @ 0x%08x" " (0x%08x) ]", pid, si->name, (unsigned)tmp, extra_len); goto fail; } /* TODO: Check if we need to memset-0 this region. * Anonymous mappings are zero-filled copy-on-writes, so we * shouldn't need to. */ TRACE("[ %5d - Segment from '%s' extended @ 0x%08x " "(0x%08x)\n", pid, si->name, (unsigned)extra_base, extra_len); } /* set the len here to show the full extent of the segment we * just loaded, mostly for debugging */ len = (((unsigned)base + phdr->p_vaddr + phdr->p_memsz + PAGE_SIZE - 1) & (~PAGE_MASK)) - (unsigned)pbase; TRACE("[ %5d - Successfully loaded segment from '%s' @ 0x%08x " "(0x%08x). p_vaddr=0x%08x p_offset=0x%08x\n", pid, si->name, (unsigned)pbase, len, phdr->p_vaddr, phdr->p_offset); total_sz += len; /* Make the section writable just in case we'll have to write to * it during relocation (i.e. text segment). However, we will * remember what range of addresses should be write protected. * */ if (!(phdr->p_flags & PF_W)) { if ((unsigned)pbase < si->wrprotect_start) si->wrprotect_start = (unsigned)pbase; if (((unsigned)pbase + len) > si->wrprotect_end) si->wrprotect_end = (unsigned)pbase + len; mprotect(pbase, len, PFLAGS_TO_PROT(phdr->p_flags) | PROT_WRITE); } } else if (phdr->p_type == PT_DYNAMIC) { DEBUG_DUMP_PHDR(phdr, "PT_DYNAMIC", pid); /* this segment contains the dynamic linking information */ si->dynamic = (unsigned *)(base + phdr->p_vaddr); } else if (phdr->p_type == PT_GNU_RELRO) { if ((phdr->p_vaddr >= si->size) || ((phdr->p_vaddr + phdr->p_memsz) > si->size) || ((base + phdr->p_vaddr + phdr->p_memsz) < base)) { DL_ERR("%d invalid GNU_RELRO in '%s' " "p_vaddr=0x%08x p_memsz=0x%08x", pid, si->name, phdr->p_vaddr, phdr->p_memsz); goto fail; } si->gnu_relro_start = (Elf32_Addr) (base + phdr->p_vaddr); si->gnu_relro_len = (unsigned) phdr->p_memsz; } else { #ifdef ANDROID_ARM_LINKER if (phdr->p_type == PT_ARM_EXIDX) { DEBUG_DUMP_PHDR(phdr, "PT_ARM_EXIDX", pid); /* exidx entries (used for stack unwinding) are 8 bytes each. */ si->ARM_exidx = (unsigned *)phdr->p_vaddr; si->ARM_exidx_count = phdr->p_memsz / 8; } #endif } } /* Sanity check */ if (total_sz > si->size) { DL_ERR("%5d - Total length (0x%08x) of mapped segments from '%s' is " "greater than what was allocated (0x%08x). THIS IS BAD!", pid, total_sz, si->name, si->size); goto fail; } TRACE("[ %5d - Finish loading segments for '%s' @ 0x%08x. " "Total memory footprint: 0x%08x bytes ]\n", pid, si->name, (unsigned)si->base, si->size); return 0; fail: /* We can just blindly unmap the entire region even though some things * were mapped in originally with anonymous and others could have been * been mapped in from the file before we failed. The kernel will unmap * all the pages in the range, irrespective of how they got there. */ munmap((void *)si->base, si->size); si->flags |= FLAG_ERROR; return -1; } /* TODO: Implement this to take care of the fact that Android ARM * ELF objects shove everything into a single loadable segment that has the * write bit set. wr_offset is then used to set non-(data|bss) pages to be * non-writable. */ #if 0 static unsigned get_wr_offset(int fd, const char *name, Elf32_Ehdr *ehdr) { Elf32_Shdr *shdr_start; Elf32_Shdr *shdr; int shdr_sz = ehdr->e_shnum * sizeof(Elf32_Shdr); int cnt; unsigned wr_offset = 0xffffffff; shdr_start = mmap(0, shdr_sz, PROT_READ, MAP_PRIVATE, fd, ehdr->e_shoff & (~PAGE_MASK)); if (shdr_start == MAP_FAILED) { WARN("%5d - Could not read section header info from '%s'. Will not " "not be able to determine write-protect offset.\n", pid, name); return (unsigned)-1; } for(cnt = 0, shdr = shdr_start; cnt < ehdr->e_shnum; ++cnt, ++shdr) { if ((shdr->sh_type != SHT_NULL) && (shdr->sh_flags & SHF_WRITE) && (shdr->sh_addr < wr_offset)) { wr_offset = shdr->sh_addr; } } munmap(shdr_start, shdr_sz); return wr_offset; } #endif static soinfo * load_library(const char *name) { int fd = open_library(name); int cnt; unsigned ext_sz; unsigned req_base; const char *bname; soinfo *si = NULL; Elf32_Ehdr *hdr; if(fd == -1) { DL_ERR("Library '%s' not found", name); return NULL; } /* We have to read the ELF header to figure out what to do with this image */ if (lseek(fd, 0, SEEK_SET) < 0) { DL_ERR("lseek() failed!"); goto fail; } if ((cnt = read(fd, &__header[0], PAGE_SIZE)) < 0) { DL_ERR("read() failed!"); goto fail; } /* Parse the ELF header and get the size of the memory footprint for * the library */ req_base = get_lib_extents(fd, name, &__header[0], &ext_sz); if (req_base == (unsigned)-1) goto fail; TRACE("[ %5d - '%s' (%s) wants base=0x%08x sz=0x%08x ]\n", pid, name, (req_base ? "prelinked" : "not pre-linked"), req_base, ext_sz); /* Now configure the soinfo struct where we'll store all of our data * for the ELF object. If the loading fails, we waste the entry, but * same thing would happen if we failed during linking. Configuring the * soinfo struct here is a lot more convenient. */ bname = strrchr(name, '/'); si = alloc_info(bname ? bname + 1 : name); if (si == NULL) goto fail; /* Carve out a chunk of memory where we will map in the individual * segments */ si->base = req_base; si->size = ext_sz; si->flags = 0; si->entry = 0; si->dynamic = (unsigned *)-1; if (alloc_mem_region(si) < 0) goto fail; TRACE("[ %5d allocated memory for %s @ %p (0x%08x) ]\n", pid, name, (void *)si->base, (unsigned) ext_sz); /* Now actually load the library's segments into right places in memory */ if (load_segments(fd, &__header[0], si) < 0) { goto fail; } /* this might not be right. Technically, we don't even need this info * once we go through 'load_segments'. */ hdr = (Elf32_Ehdr *)si->base; si->phdr = (Elf32_Phdr *)((unsigned char *)si->base + hdr->e_phoff); si->phnum = hdr->e_phnum; /**/ close(fd); return si; fail: if (si) free_info(si); close(fd); return NULL; } static soinfo * init_library(soinfo *si) { unsigned wr_offset = 0xffffffff; /* 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(link_image(si, wr_offset)) { /* We failed to link. However, we can only restore libbase ** if no additional libraries have moved it since we updated it. */ munmap((void *)si->base, si->size); return NULL; } return si; } soinfo *find_library(const char *name) { soinfo *si; const char *bname; #if ALLOW_SYMBOLS_FROM_MAIN if (name == NULL) return somain; #else if (name == NULL) return NULL; #endif bname = strrchr(name, '/'); bname = bname ? bname + 1 : name; for(si = solist; si != 0; si = si->next){ if(!strcmp(bname, si->name)) { if(si->flags & FLAG_ERROR) { DL_ERR("%5d '%s' failed to load previously", pid, bname); return NULL; } if(si->flags & FLAG_LINKED) return si; DL_ERR("OOPS: %5d recursive link to '%s'", pid, 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); } /* TODO: * notify gdb of unload * for non-prelinked libraries, find a way to decrement libbase */ static void call_destructors(soinfo *si); unsigned unload_library(soinfo *si) { unsigned *d; if (si->refcount == 1) { TRACE("%5d unloading '%s'\n", pid, si->name); call_destructors(si); /* * Make sure that we undo the PT_GNU_RELRO protections we added * in link_image. This is needed to undo the DT_NEEDED hack below. */ if ((si->gnu_relro_start != 0) && (si->gnu_relro_len != 0)) { Elf32_Addr start = (si->gnu_relro_start & ~PAGE_MASK); unsigned len = (si->gnu_relro_start - start) + si->gnu_relro_len; if (mprotect((void *) start, len, PROT_READ | PROT_WRITE) < 0) DL_ERR("%5d %s: could not undo GNU_RELRO protections. " "Expect a crash soon. errno=%d (%s)", pid, si->name, errno, strerror(errno)); } for(d = si->dynamic; *d; d += 2) { if(d[0] == DT_NEEDED){ soinfo *lsi = (soinfo *)d[1]; // The next line will segfault if the we don't undo the // PT_GNU_RELRO protections (see comments above and in // link_image(). d[1] = 0; if (validate_soinfo(lsi)) { TRACE("%5d %s needs to unload %s\n", pid, si->name, lsi->name); unload_library(lsi); } else DL_ERR("%5d %s: could not unload dependent library", pid, si->name); } } munmap((char *)si->base, si->size); notify_gdb_of_unload(si); free_info(si); si->refcount = 0; } else { si->refcount--; PRINT("%5d not unloading '%s', decrementing refcount to %d\n", pid, si->name, si->refcount); } return si->refcount; } /* 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 reloc_library(soinfo *si, Elf32_Rel *rel, unsigned count) { Elf32_Sym *symtab = si->symtab; const char *strtab = si->strtab; Elf32_Sym *s; unsigned base; Elf32_Rel *start = rel; unsigned idx; for (idx = 0; idx < count; ++idx) { unsigned type = ELF32_R_TYPE(rel->r_info); unsigned sym = ELF32_R_SYM(rel->r_info); unsigned reloc = (unsigned)(rel->r_offset + si->base); unsigned sym_addr = 0; char *sym_name = NULL; DEBUG("%5d Processing '%s' relocation at index %d\n", pid, si->name, idx); if(sym != 0) { sym_name = (char *)(strtab + symtab[sym].st_name); s = _do_lookup(si, sym_name, &base); 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("%5d cannot locate '%s'...\n", pid, sym_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 nominial 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. */ case R_ARM_NONE: /* Don't care. */ #elif defined(ANDROID_X86_LINKER) case R_386_JUMP_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("%5d unknown weak reloc type %d @ %p (%d)\n", pid, 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("%5d cannot locate '%s'...", pid, strtab + symtab[sym].st_name); return -1; } #endif sym_addr = (unsigned)(s->st_value + base); } COUNT_RELOC(RELOC_SYMBOL); } 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_RELOC(RELOC_ABSOLUTE); 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_RELOC(RELOC_ABSOLUTE); 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_RELOC(RELOC_ABSOLUTE); 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_RELOC(RELOC_RELATIVE); 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_JUMP_SLOT: COUNT_RELOC(RELOC_ABSOLUTE); 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_RELOC(RELOC_ABSOLUTE); 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; #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_RELOC(RELOC_RELATIVE); MARK(rel->r_offset); if(sym){ DL_ERR("%5d 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_RELOC(RELOC_RELATIVE); 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_RELOC(RELOC_RELATIVE); 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: COUNT_RELOC(RELOC_COPY); MARK(rel->r_offset); TRACE_TYPE(RELO, "%5d RELO %08x <- %d @ %08x %s\n", pid, reloc, s->st_size, sym_addr, sym_name); memcpy((void*)reloc, (void*)sym_addr, s->st_size); break; case R_ARM_NONE: break; #endif /* ANDROID_ARM_LINKER */ default: DL_ERR("%5d unknown reloc type %d @ %p (%d)", pid, type, rel, (int) (rel - start)); return -1; } rel++; } return 0; } /* 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(); } } void call_constructors_recursive(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 call_constructors_recursive() with the newly created // soinfo for libc_malloc_debug_leak.so. // 4. The debug so depends on libc, so call_constructors_recursive() 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) { 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); } else { if (si->preinit_array) { DL_ERR("%5d Shared library '%s' has a preinit_array table @ 0x%08x." " This is INVALID.", pid, 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 = (soinfo *)d[1]; if (!validate_soinfo(lsi)) { DL_ERR("%5d bad DT_NEEDED pointer in %s", pid, si->name); } else { call_constructors_recursive(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 = open("/dev/null", O_RDWR); if (dev_null < 0) { DL_ERR("Cannot open /dev/null."); 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); /* The man page of fcntl does not say that fcntl(..,F_GETFL) can be interrupted but we do this just to be safe. */ do { status = fcntl(i, F_GETFL); } while (status < 0 && errno == EINTR); /* If file is openned, we are good. */ if (status >= 0) 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("nullify_stdio: unhandled error %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. */ do { status = dup2(dev_null, i); } while (status < 0 && errno == EINTR); if (status < 0) { DL_ERR("nullify_stdio: dup2 error %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); do { status = close(dev_null); } while (status < 0 && errno == EINTR); if (status < 0) { DL_ERR("nullify_stdio: close error %s", strerror(errno)); return_value = -1; } } return return_value; } static int link_image(soinfo *si, unsigned wr_offset) { unsigned *d; Elf32_Phdr *phdr = si->phdr; int phnum = si->phnum; INFO("[ %5d linking %s ]\n", pid, si->name); DEBUG("%5d si->base = 0x%08x si->flags = 0x%08x\n", pid, si->base, si->flags); if (si->flags & (FLAG_EXE | FLAG_LINKER)) { /* Locate the needed program segments (DYNAMIC/ARM_EXIDX) for * linkage info if this is the executable or the linker itself. * If this was a dynamic lib, that would have been done at load time. * * TODO: It's unfortunate that small pieces of this are * repeated from the load_library routine. Refactor this just * slightly to reuse these bits. */ si->size = 0; for(; phnum > 0; --phnum, ++phdr) { #ifdef ANDROID_ARM_LINKER if(phdr->p_type == PT_ARM_EXIDX) { /* exidx entries (used for stack unwinding) are 8 bytes each. */ si->ARM_exidx = (unsigned *)phdr->p_vaddr; si->ARM_exidx_count = phdr->p_memsz / 8; } #endif if (phdr->p_type == PT_LOAD) { /* For the executable, we use the si->size field only in dl_unwind_find_exidx(), so the meaning of si->size is not the size of the executable; it is the distance between the load location of the executable and the last address of the loadable part of the executable. We use the range [si->base, si->base + si->size) to determine whether a PC value falls within the executable section. Of course, if a value is between si->base and (si->base + phdr->p_vaddr), it's not in the executable section, but a) we shouldn't be asking for such a value anyway, and b) if we have to provide an EXIDX for such a value, then the executable's EXIDX is probably the better choice. */ DEBUG_DUMP_PHDR(phdr, "PT_LOAD", pid); if (phdr->p_vaddr + phdr->p_memsz > si->size) si->size = phdr->p_vaddr + phdr->p_memsz; /* try to remember what range of addresses should be write * protected */ if (!(phdr->p_flags & PF_W)) { unsigned _end; if (si->base + phdr->p_vaddr < si->wrprotect_start) si->wrprotect_start = si->base + phdr->p_vaddr; _end = (((si->base + phdr->p_vaddr + phdr->p_memsz + PAGE_SIZE - 1) & (~PAGE_MASK))); if (_end > si->wrprotect_end) si->wrprotect_end = _end; /* Make the section writable just in case we'll have to * write to it during relocation (i.e. text segment). * However, we will remember what range of addresses * should be write protected. */ mprotect((void *) (si->base + phdr->p_vaddr), phdr->p_memsz, PFLAGS_TO_PROT(phdr->p_flags) | PROT_WRITE); } } else if (phdr->p_type == PT_DYNAMIC) { if (si->dynamic != (unsigned *)-1) { DL_ERR("%5d multiple PT_DYNAMIC segments found in '%s'. " "Segment at 0x%08x, previously one found at 0x%08x", pid, si->name, si->base + phdr->p_vaddr, (unsigned)si->dynamic); goto fail; } DEBUG_DUMP_PHDR(phdr, "PT_DYNAMIC", pid); si->dynamic = (unsigned *) (si->base + phdr->p_vaddr); } else if (phdr->p_type == PT_GNU_RELRO) { if ((phdr->p_vaddr >= si->size) || ((phdr->p_vaddr + phdr->p_memsz) > si->size) || ((si->base + phdr->p_vaddr + phdr->p_memsz) < si->base)) { DL_ERR("%d invalid GNU_RELRO in '%s' " "p_vaddr=0x%08x p_memsz=0x%08x", pid, si->name, phdr->p_vaddr, phdr->p_memsz); goto fail; } si->gnu_relro_start = (Elf32_Addr) (si->base + phdr->p_vaddr); si->gnu_relro_len = (unsigned) phdr->p_memsz; } } } if (si->dynamic == (unsigned *)-1) { DL_ERR("%5d missing PT_DYNAMIC?!", pid); goto fail; } DEBUG("%5d dynamic = %p\n", pid, si->dynamic); /* 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 *) (si->base + *d))[0]; si->nchain = ((unsigned *) (si->base + *d))[1]; si->bucket = (unsigned *) (si->base + *d + 8); si->chain = (unsigned *) (si->base + *d + 8 + si->nbucket * 4); break; case DT_STRTAB: si->strtab = (const char *) (si->base + *d); break; case DT_SYMTAB: si->symtab = (Elf32_Sym *) (si->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*) (si->base + *d); break; case DT_PLTRELSZ: si->plt_rel_count = *d / 8; break; case DT_REL: si->rel = (Elf32_Rel*) (si->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 *)(si->base + *d); break; case DT_DEBUG: // Set the DT_DEBUG entry to the addres of _r_debug for GDB *d = (int) &_r_debug; break; case DT_RELA: DL_ERR("%5d DT_RELA not supported", pid); goto fail; case DT_INIT: si->init_func = (void (*)(void))(si->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))(si->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 *)(si->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 *)(si->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 *)(si->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: /* TODO: make use of this. */ /* this means that we might have to write into where the text * segment was loaded during relocation... Do something with * it. */ DEBUG("%5d Text segment should be writable during relocation.\n", pid); break; } } 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("%5d missing essential tables", pid); 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("%5d could not load needed library '%s' for '%s' (%s)", pid, ldpreload_names[i], si->name, tmp_err_buf); goto fail; } lsi->refcount++; preloads[i] = lsi; } } 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("%5d could not load needed library '%s' for '%s' (%s)", pid, si->strtab + d[1], si->name, tmp_err_buf); goto fail; } /* Save the soinfo of the loaded DT_NEEDED library in the payload of the DT_NEEDED entry itself, so that we can retrieve the soinfo directly later from the dynamic segment. This is a hack, but it allows us to map from DT_NEEDED to soinfo efficiently later on when we resolve relocations, trying to look up a symbol with dlsym(). */ d[1] = (unsigned)lsi; lsi->refcount++; } } if(si->plt_rel) { DEBUG("[ %5d relocating %s plt ]\n", pid, si->name ); if(reloc_library(si, si->plt_rel, si->plt_rel_count)) goto fail; } if(si->rel) { DEBUG("[ %5d relocating %s ]\n", pid, si->name ); if(reloc_library(si, si->rel, si->rel_count)) goto fail; } si->flags |= FLAG_LINKED; DEBUG("[ %5d finished linking %s ]\n", pid, si->name); #if 0 /* This is the way that the old dynamic linker did protection of * non-writable areas. It would scan section headers and find where * .text ended (rather where .data/.bss began) and assume that this is * the upper range of the non-writable area. This is too coarse, * and is kept here for reference until we fully move away from single * segment elf objects. See the code in get_wr_offset (also #if'd 0) * that made this possible. */ if(wr_offset < 0xffffffff){ mprotect((void*) si->base, wr_offset, PROT_READ | PROT_EXEC); } #else /* TODO: Verify that this does the right thing in all cases, as it * presently probably does not. It is possible that an ELF image will * come with multiple read-only segments. What we ought to do is scan * the program headers again and mprotect all the read-only segments. * To prevent re-scanning the program header, we would have to build a * list of loadable segments in si, and then scan that instead. */ if (si->wrprotect_start != 0xffffffff && si->wrprotect_end != 0) { mprotect((void *)si->wrprotect_start, si->wrprotect_end - si->wrprotect_start, PROT_READ | PROT_EXEC); } #endif if (si->gnu_relro_start != 0 && si->gnu_relro_len != 0) { Elf32_Addr start = (si->gnu_relro_start & ~PAGE_MASK); unsigned len = (si->gnu_relro_start - start) + si->gnu_relro_len; if (mprotect((void *) start, len, PROT_READ) < 0) { DL_ERR("%5d GNU_RELRO mprotect of library '%s' failed: %d (%s)\n", pid, si->name, errno, 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_library_path(const char *path, char *delim) { size_t len; char *ldpaths_bufp = ldpaths_buf; int i = 0; len = strlcpy(ldpaths_buf, path, sizeof(ldpaths_buf)); while (i < LDPATH_MAX && (ldpaths[i] = strsep(&ldpaths_bufp, delim))) { if (*ldpaths[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. not originally a delim). */ if (i > 0 && len >= sizeof(ldpaths_buf) && ldpaths_buf[sizeof(ldpaths_buf) - 2] != '\0') { ldpaths[i - 1] = NULL; } else { ldpaths[i] = NULL; } } static void parse_preloads(const char *path, char *delim) { size_t len; char *ldpreloads_bufp = ldpreloads_buf; int i = 0; len = strlcpy(ldpreloads_buf, path, sizeof(ldpreloads_buf)); while (i < LDPRELOAD_MAX && (ldpreload_names[i] = strsep(&ldpreloads_bufp, delim))) { if (*ldpreload_names[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. not originally a delim). */ if (i > 0 && len >= sizeof(ldpreloads_buf) && ldpreloads_buf[sizeof(ldpreloads_buf) - 2] != '\0') { ldpreload_names[i - 1] = NULL; } else { ldpreload_names[i] = NULL; } } /* * 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) { static soinfo linker_soinfo; int argc = (int) *elfdata; char **argv = (char**) (elfdata + 1); unsigned *vecs = (unsigned*) (argv + argc + 1); unsigned *v; soinfo *si; struct link_map * map; 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 = alloc_info(argv[0]); if(si == 0) { exit(-1); } /* bootstrap the link map, the main exe always needs to be first */ si->flags |= FLAG_EXE; 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, * and we need to make sure that the reported load address is zero. * Without this, gdb gets the wrong idea of where rtld_db_dlactivity() * is. Don't use alloc_info(), 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 = 0; // This is the important part; must be zero. 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; for ( nn = 0; nn < si->phnum; nn++ ) { if (si->phdr[nn].p_type == PT_PHDR) { si->base = (Elf32_Addr) si->phdr - si->phdr[nn].p_vaddr; break; } } si->dynamic = (unsigned *)-1; si->wrprotect_start = 0xffffffff; si->wrprotect_end = 0; si->refcount = 1; si->gnu_relro_start = 0; si->gnu_relro_len = 0; /* Use LD_LIBRARY_PATH if we aren't setuid/setgid */ if (ldpath_env) parse_library_path(ldpath_env, ":"); if (ldpreload_env) { parse_preloads(ldpreload_env, " :"); } if(link_image(si, 0)) { char errmsg[] = "CANNOT LINK EXECUTABLE\n"; write(2, __linker_dl_err_buf, strlen(__linker_dl_err_buf)); write(2, errmsg, sizeof(errmsg)); exit(-1); } call_constructors_recursive(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.reloc[RELOC_ABSOLUTE], linker_stats.reloc[RELOC_RELATIVE], linker_stats.reloc[RELOC_COPY], linker_stats.reloc[RELOC_SYMBOL]); #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 } /* * 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. */ 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.dynamic = (unsigned *) -1; linker_so.phdr = phdr; linker_so.phnum = elf_hdr->e_phnum; linker_so.flags |= FLAG_LINKER; linker_so.wrprotect_start = 0xffffffff; linker_so.wrprotect_end = 0; linker_so.gnu_relro_start = 0; linker_so.gnu_relro_len = 0; if (link_image(&linker_so, 0)) { // 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); }