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 * $Id: map_object.c,v 1.2 1998/03/06 22:14:53 jdp Exp $ 26 */ 27 28 #include <sys/param.h> 29 #include <sys/mman.h> 30 31 #include <assert.h> 32 #include <errno.h> 33 #include <stddef.h> 34 #include <string.h> 35 #include <unistd.h> 36 37 #include "rtld.h" 38 39 static int protflags(int); /* Elf flags -> mmap protection */ 40 41 /* 42 * Map a shared object into memory. The argument is a file descriptor, 43 * which must be open on the object and positioned at its beginning. 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) 50 { 51 Obj_Entry *obj; 52 union { 53 Elf32_Ehdr hdr; 54 char buf[PAGE_SIZE]; 55 } u; 56 int nbytes; 57 Elf32_Phdr *phdr; 58 Elf32_Phdr *phlimit; 59 Elf32_Phdr *segs[2]; 60 int nsegs; 61 Elf32_Phdr *phdyn; 62 Elf32_Phdr *phphdr; 63 caddr_t mapbase; 64 size_t mapsize; 65 Elf32_Off base_offset; 66 Elf32_Addr base_vaddr; 67 Elf32_Addr base_vlimit; 68 caddr_t base_addr; 69 Elf32_Off data_offset; 70 Elf32_Addr data_vaddr; 71 Elf32_Addr data_vlimit; 72 caddr_t data_addr; 73 Elf32_Addr clear_vaddr; 74 caddr_t clear_addr; 75 size_t nclear; 76 Elf32_Addr bss_vaddr; 77 Elf32_Addr bss_vlimit; 78 caddr_t bss_addr; 79 80 if ((nbytes = read(fd, u.buf, PAGE_SIZE)) == -1) { 81 _rtld_error("Read error: %s", strerror(errno)); 82 return NULL; 83 } 84 85 /* Make sure the file is valid */ 86 if (nbytes < sizeof(Elf32_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("Invalid file format"); 92 return NULL; 93 } 94 if (u.hdr.e_ident[EI_CLASS] != ELFCLASS32 95 || u.hdr.e_ident[EI_DATA] != ELFDATA2LSB) { 96 _rtld_error("Unsupported file layout"); 97 return NULL; 98 } 99 if (u.hdr.e_ident[EI_VERSION] != EV_CURRENT 100 || u.hdr.e_version != EV_CURRENT) { 101 _rtld_error("Unsupported file version"); 102 return NULL; 103 } 104 if (u.hdr.e_type != ET_EXEC && u.hdr.e_type != ET_DYN) { 105 _rtld_error("Unsupported file type"); 106 return NULL; 107 } 108 if (u.hdr.e_machine != EM_386) { 109 _rtld_error("Unsupported machine"); 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 assert(u.hdr.e_phentsize == sizeof(Elf32_Phdr)); 119 assert(u.hdr.e_phoff + u.hdr.e_phnum*sizeof(Elf32_Phdr) <= PAGE_SIZE); 120 assert(u.hdr.e_phoff + u.hdr.e_phnum*sizeof(Elf32_Phdr) <= nbytes); 121 122 /* 123 * Scan the program header entries, and save key information. 124 * 125 * We rely on there being exactly two load segments, text and data, 126 * in that order. 127 */ 128 phdr = (Elf32_Phdr *) (u.buf + u.hdr.e_phoff); 129 phlimit = phdr + u.hdr.e_phnum; 130 nsegs = 0; 131 phdyn = NULL; 132 phphdr = NULL; 133 while (phdr < phlimit) { 134 switch (phdr->p_type) { 135 136 case PT_LOAD: 137 assert(nsegs < 2); 138 segs[nsegs] = phdr; 139 ++nsegs; 140 break; 141 142 case PT_PHDR: 143 phphdr = phdr; 144 break; 145 146 case PT_DYNAMIC: 147 phdyn = phdr; 148 break; 149 } 150 151 ++phdr; 152 } 153 if (phdyn == NULL) { 154 _rtld_error("Object is not dynamically-linked"); 155 return NULL; 156 } 157 158 assert(nsegs == 2); 159 assert(segs[0]->p_align <= PAGE_SIZE); 160 assert(segs[1]->p_align <= PAGE_SIZE); 161 162 /* 163 * Map the entire address space of the object, to stake out our 164 * contiguous region, and to establish the base address for relocation. 165 */ 166 base_offset = trunc_page(segs[0]->p_offset); 167 base_vaddr = trunc_page(segs[0]->p_vaddr); 168 base_vlimit = round_page(segs[1]->p_vaddr + segs[1]->p_memsz); 169 mapsize = base_vlimit - base_vaddr; 170 base_addr = u.hdr.e_type == ET_EXEC ? (caddr_t) base_vaddr : NULL; 171 172 mapbase = mmap(base_addr, mapsize, protflags(segs[0]->p_flags), 173 MAP_PRIVATE, fd, base_offset); 174 if (mapbase == (caddr_t) -1) { 175 _rtld_error("mmap of entire address space failed: %s", 176 strerror(errno)); 177 return NULL; 178 } 179 if (base_addr != NULL && mapbase != base_addr) { 180 _rtld_error("mmap returned wrong address: wanted %p, got %p", 181 base_addr, mapbase); 182 munmap(mapbase, mapsize); 183 return NULL; 184 } 185 186 /* Overlay the data segment onto the proper region. */ 187 data_offset = trunc_page(segs[1]->p_offset); 188 data_vaddr = trunc_page(segs[1]->p_vaddr); 189 data_vlimit = round_page(segs[1]->p_vaddr + segs[1]->p_filesz); 190 data_addr = mapbase + (data_vaddr - base_vaddr); 191 if (mmap(data_addr, data_vlimit - data_vaddr, protflags(segs[1]->p_flags), 192 MAP_PRIVATE|MAP_FIXED, fd, data_offset) == (caddr_t) -1) { 193 _rtld_error("mmap of data failed: %s", strerror(errno)); 194 return NULL; 195 } 196 197 /* Clear any BSS in the last page of the data segment. */ 198 clear_vaddr = segs[1]->p_vaddr + segs[1]->p_filesz; 199 clear_addr = mapbase + (clear_vaddr - base_vaddr); 200 if ((nclear = data_vlimit - clear_vaddr) > 0) 201 memset(clear_addr, 0, nclear); 202 203 /* Overlay the BSS segment onto the proper region. */ 204 bss_vaddr = data_vlimit; 205 bss_vlimit = round_page(segs[1]->p_vaddr + segs[1]->p_memsz); 206 bss_addr = mapbase + (bss_vaddr - base_vaddr); 207 if (bss_vlimit > bss_vaddr) { /* There is something to do */ 208 if (mmap(bss_addr, bss_vlimit - bss_vaddr, protflags(segs[1]->p_flags), 209 MAP_PRIVATE|MAP_FIXED|MAP_ANON, -1, 0) == (caddr_t) -1) { 210 _rtld_error("mmap of bss failed: %s", strerror(errno)); 211 return NULL; 212 } 213 } 214 215 obj = CNEW(Obj_Entry); 216 obj->mapbase = mapbase; 217 obj->mapsize = mapsize; 218 obj->textsize = round_page(segs[0]->p_vaddr + segs[0]->p_memsz) - 219 base_vaddr; 220 obj->vaddrbase = base_vaddr; 221 obj->relocbase = mapbase - base_vaddr; 222 obj->dynamic = (const Elf32_Dyn *) 223 (mapbase + (phdyn->p_vaddr - base_vaddr)); 224 if (u.hdr.e_entry != 0) 225 obj->entry = (caddr_t) (mapbase + (u.hdr.e_entry - base_vaddr)); 226 if (phphdr != NULL) { 227 obj->phdr = (const Elf32_Phdr *) 228 (mapbase + (phphdr->p_vaddr - base_vaddr)); 229 obj->phsize = phphdr->p_memsz; 230 } 231 232 return obj; 233 } 234 235 /* 236 * Given a set of ELF protection flags, return the corresponding protection 237 * flags for MMAP. 238 */ 239 static int 240 protflags(int elfflags) 241 { 242 int prot = 0; 243 if (elfflags & PF_R) 244 prot |= PROT_READ; 245 if (elfflags & PF_W) 246 prot |= PROT_WRITE; 247 if (elfflags & PF_X) 248 prot |= PROT_EXEC; 249 return prot; 250 } 251