1 /*- 2 * Copyright 1996-1998 John D. Polstra. 3 * All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 1. Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in the 12 * documentation and/or other materials provided with the distribution. 13 * 14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 15 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 16 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 17 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 18 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 19 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 20 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 21 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 22 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 23 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 24 * 25 * $FreeBSD$ 26 */ 27 28 #include <sys/param.h> 29 #include <sys/mman.h> 30 31 #include <errno.h> 32 #include <stddef.h> 33 #include <string.h> 34 #include <unistd.h> 35 36 #include "rtld.h" 37 38 static int protflags(int); /* Elf flags -> mmap protection */ 39 40 /* 41 * Map a shared object into memory. The "fd" argument is a file descriptor, 42 * which must be open on the object and positioned at its beginning. 43 * The "path" argument is a pathname that is used only for error messages. 44 * 45 * The return value is a pointer to a newly-allocated Obj_Entry structure 46 * for the shared object. Returns NULL on failure. 47 */ 48 Obj_Entry * 49 map_object(int fd, const char *path) 50 { 51 Obj_Entry *obj; 52 union { 53 Elf_Ehdr hdr; 54 char buf[PAGE_SIZE]; 55 } u; 56 int nbytes; 57 Elf_Phdr *phdr; 58 Elf_Phdr *phlimit; 59 Elf_Phdr *segs[2]; 60 int nsegs; 61 Elf_Phdr *phdyn; 62 Elf_Phdr *phphdr; 63 caddr_t mapbase; 64 size_t mapsize; 65 Elf_Off base_offset; 66 Elf_Addr base_vaddr; 67 Elf_Addr base_vlimit; 68 caddr_t base_addr; 69 Elf_Off data_offset; 70 Elf_Addr data_vaddr; 71 Elf_Addr data_vlimit; 72 caddr_t data_addr; 73 Elf_Addr clear_vaddr; 74 caddr_t clear_addr; 75 size_t nclear; 76 Elf_Addr bss_vaddr; 77 Elf_Addr bss_vlimit; 78 caddr_t bss_addr; 79 80 if ((nbytes = read(fd, u.buf, PAGE_SIZE)) == -1) { 81 _rtld_error("%s: read error: %s", path, strerror(errno)); 82 return NULL; 83 } 84 85 /* Make sure the file is valid */ 86 if (nbytes < sizeof(Elf_Ehdr) 87 || u.hdr.e_ident[EI_MAG0] != ELFMAG0 88 || u.hdr.e_ident[EI_MAG1] != ELFMAG1 89 || u.hdr.e_ident[EI_MAG2] != ELFMAG2 90 || u.hdr.e_ident[EI_MAG3] != ELFMAG3) { 91 _rtld_error("%s: invalid file format", path); 92 return NULL; 93 } 94 if (u.hdr.e_ident[EI_CLASS] != ELF_TARG_CLASS 95 || u.hdr.e_ident[EI_DATA] != ELF_TARG_DATA) { 96 _rtld_error("%s: unsupported file layout", path); 97 return NULL; 98 } 99 if (u.hdr.e_ident[EI_VERSION] != EV_CURRENT 100 || u.hdr.e_version != EV_CURRENT) { 101 _rtld_error("%s: unsupported file version", path); 102 return NULL; 103 } 104 if (u.hdr.e_type != ET_EXEC && u.hdr.e_type != ET_DYN) { 105 _rtld_error("%s: unsupported file type", path); 106 return NULL; 107 } 108 if (u.hdr.e_machine != ELF_TARG_MACH) { 109 _rtld_error("%s: unsupported machine", path); 110 return NULL; 111 } 112 113 /* 114 * We rely on the program header being in the first page. This is 115 * not strictly required by the ABI specification, but it seems to 116 * always true in practice. And, it simplifies things considerably. 117 */ 118 if (u.hdr.e_phentsize != sizeof(Elf_Phdr)) { 119 _rtld_error( 120 "%s: invalid shared object: e_phentsize != sizeof(Elf_Phdr)", path); 121 return NULL; 122 } 123 if (u.hdr.e_phoff + u.hdr.e_phnum*sizeof(Elf_Phdr) > nbytes) { 124 _rtld_error("%s: program header too large", path); 125 return NULL; 126 } 127 128 /* 129 * Scan the program header entries, and save key information. 130 * 131 * We rely on there being exactly two load segments, text and data, 132 * in that order. 133 */ 134 phdr = (Elf_Phdr *) (u.buf + u.hdr.e_phoff); 135 phlimit = phdr + u.hdr.e_phnum; 136 nsegs = 0; 137 phdyn = NULL; 138 phphdr = NULL; 139 while (phdr < phlimit) { 140 switch (phdr->p_type) { 141 142 case PT_LOAD: 143 if (nsegs >= 2) { 144 _rtld_error("%s: too many PT_LOAD segments", path); 145 return NULL; 146 } 147 segs[nsegs] = phdr; 148 ++nsegs; 149 break; 150 151 case PT_PHDR: 152 phphdr = phdr; 153 break; 154 155 case PT_DYNAMIC: 156 phdyn = phdr; 157 break; 158 } 159 160 ++phdr; 161 } 162 if (phdyn == NULL) { 163 _rtld_error("%s: object is not dynamically-linked", path); 164 return NULL; 165 } 166 167 if (nsegs < 2) { 168 _rtld_error("%s: too few PT_LOAD segments", path); 169 return NULL; 170 } 171 if (segs[0]->p_align < PAGE_SIZE || segs[1]->p_align < PAGE_SIZE) { 172 _rtld_error("%s: PT_LOAD segments not page-aligned", path); 173 return NULL; 174 } 175 176 /* 177 * Map the entire address space of the object, to stake out our 178 * contiguous region, and to establish the base address for relocation. 179 */ 180 base_offset = trunc_page(segs[0]->p_offset); 181 base_vaddr = trunc_page(segs[0]->p_vaddr); 182 base_vlimit = round_page(segs[1]->p_vaddr + segs[1]->p_memsz); 183 mapsize = base_vlimit - base_vaddr; 184 base_addr = u.hdr.e_type == ET_EXEC ? (caddr_t) base_vaddr : NULL; 185 186 mapbase = mmap(base_addr, mapsize, protflags(segs[0]->p_flags), 187 MAP_PRIVATE, fd, base_offset); 188 if (mapbase == (caddr_t) -1) { 189 _rtld_error("%s: mmap of entire address space failed: %s", 190 path, strerror(errno)); 191 return NULL; 192 } 193 if (base_addr != NULL && mapbase != base_addr) { 194 _rtld_error("%s: mmap returned wrong address: wanted %p, got %p", 195 path, base_addr, mapbase); 196 munmap(mapbase, mapsize); 197 return NULL; 198 } 199 200 /* Overlay the data segment onto the proper region. */ 201 data_offset = trunc_page(segs[1]->p_offset); 202 data_vaddr = trunc_page(segs[1]->p_vaddr); 203 data_vlimit = round_page(segs[1]->p_vaddr + segs[1]->p_filesz); 204 data_addr = mapbase + (data_vaddr - base_vaddr); 205 if (mmap(data_addr, data_vlimit - data_vaddr, protflags(segs[1]->p_flags), 206 MAP_PRIVATE|MAP_FIXED, fd, data_offset) == (caddr_t) -1) { 207 _rtld_error("%s: mmap of data failed: %s", path, strerror(errno)); 208 return NULL; 209 } 210 211 /* Clear any BSS in the last page of the data segment. */ 212 clear_vaddr = segs[1]->p_vaddr + segs[1]->p_filesz; 213 clear_addr = mapbase + (clear_vaddr - base_vaddr); 214 if ((nclear = data_vlimit - clear_vaddr) > 0) 215 memset(clear_addr, 0, nclear); 216 217 /* Overlay the BSS segment onto the proper region. */ 218 bss_vaddr = data_vlimit; 219 bss_vlimit = round_page(segs[1]->p_vaddr + segs[1]->p_memsz); 220 bss_addr = mapbase + (bss_vaddr - base_vaddr); 221 if (bss_vlimit > bss_vaddr) { /* There is something to do */ 222 if (mmap(bss_addr, bss_vlimit - bss_vaddr, protflags(segs[1]->p_flags), 223 MAP_PRIVATE|MAP_FIXED|MAP_ANON, -1, 0) == (caddr_t) -1) { 224 _rtld_error("%s: mmap of bss failed: %s", path, strerror(errno)); 225 return NULL; 226 } 227 } 228 229 obj = CNEW(Obj_Entry); 230 obj->mapbase = mapbase; 231 obj->mapsize = mapsize; 232 obj->textsize = round_page(segs[0]->p_vaddr + segs[0]->p_memsz) - 233 base_vaddr; 234 obj->vaddrbase = base_vaddr; 235 obj->relocbase = mapbase - base_vaddr; 236 obj->dynamic = (const Elf_Dyn *) 237 (mapbase + (phdyn->p_vaddr - base_vaddr)); 238 if (u.hdr.e_entry != 0) 239 obj->entry = (caddr_t) (mapbase + (u.hdr.e_entry - base_vaddr)); 240 if (phphdr != NULL) { 241 obj->phdr = (const Elf_Phdr *) 242 (mapbase + (phphdr->p_vaddr - base_vaddr)); 243 obj->phsize = phphdr->p_memsz; 244 } 245 246 return obj; 247 } 248 249 /* 250 * Given a set of ELF protection flags, return the corresponding protection 251 * flags for MMAP. 252 */ 253 static int 254 protflags(int elfflags) 255 { 256 int prot = 0; 257 if (elfflags & PF_R) 258 prot |= PROT_READ; 259 if (elfflags & PF_W) 260 prot |= PROT_WRITE; 261 if (elfflags & PF_X) 262 prot |= PROT_EXEC; 263 return prot; 264 } 265