1 /* 2 * Copyright (c) 2003, 2020, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 * 23 */ 24 25 #include "salibelf.h" 26 #include <stdlib.h> 27 #include <unistd.h> 28 #include <string.h> 29 30 extern void print_debug(const char*,...); 31 32 // ELF file parsing helpers. Note that we do *not* use libelf here. 33 int read_elf_header(int fd, ELF_EHDR* ehdr) { 34 if (pread(fd, ehdr, sizeof (ELF_EHDR), 0) != sizeof (ELF_EHDR) || 35 memcmp(&ehdr->e_ident[EI_MAG0], ELFMAG, SELFMAG) != 0 || 36 ehdr->e_version != EV_CURRENT) { 37 return 0; 38 } 39 return 1; 40 } 41 42 bool is_elf_file(int fd) { 43 ELF_EHDR ehdr; 44 return read_elf_header(fd, &ehdr); 45 } 46 47 // read program header table of an ELF file 48 ELF_PHDR* read_program_header_table(int fd, ELF_EHDR* hdr) { 49 ELF_PHDR* phbuf = 0; 50 // allocate memory for program header table 51 size_t nbytes = hdr->e_phnum * hdr->e_phentsize; 52 53 if ((phbuf = (ELF_PHDR*) malloc(nbytes)) == NULL) { 54 print_debug("can't allocate memory for reading program header table\n"); 55 return NULL; 56 } 57 58 if (pread(fd, phbuf, nbytes, hdr->e_phoff) != nbytes) { 59 print_debug("ELF file is truncated! can't read program header table\n"); 60 free(phbuf); 61 return NULL; 62 } 63 64 return phbuf; 65 } 66 67 // read section header table of an ELF file 68 ELF_SHDR* read_section_header_table(int fd, ELF_EHDR* hdr) { 69 ELF_SHDR* shbuf = 0; 70 // allocate memory for section header table 71 size_t nbytes = hdr->e_shnum * hdr->e_shentsize; 72 73 if ((shbuf = (ELF_SHDR*) malloc(nbytes)) == NULL) { 74 print_debug("can't allocate memory for reading section header table\n"); 75 return NULL; 76 } 77 78 if (pread(fd, shbuf, nbytes, hdr->e_shoff) != nbytes) { 79 print_debug("ELF file is truncated! can't read section header table\n"); 80 free(shbuf); 81 return NULL; 82 } 83 84 return shbuf; 85 } 86 87 // read a particular section's data 88 void* read_section_data(int fd, ELF_EHDR* ehdr, ELF_SHDR* shdr) { 89 void *buf = NULL; 90 if (shdr->sh_type == SHT_NOBITS || shdr->sh_size == 0) { 91 return buf; 92 } 93 if ((buf = calloc(shdr->sh_size, 1)) == NULL) { 94 print_debug("can't allocate memory for reading section data\n"); 95 return NULL; 96 } 97 if (pread(fd, buf, shdr->sh_size, shdr->sh_offset) != shdr->sh_size) { 98 free(buf); 99 print_debug("section data read failed\n"); 100 return NULL; 101 } 102 return buf; 103 } 104 105 uintptr_t find_base_address(int fd, ELF_EHDR* ehdr) { 106 uintptr_t baseaddr = (uintptr_t)-1; 107 int cnt; 108 ELF_PHDR *phbuf, *phdr; 109 110 // read program header table 111 if ((phbuf = read_program_header_table(fd, ehdr)) == NULL) { 112 goto quit; 113 } 114 115 // the base address of a shared object is the lowest vaddr of 116 // its loadable segments (PT_LOAD) 117 for (phdr = phbuf, cnt = 0; cnt < ehdr->e_phnum; cnt++, phdr++) { 118 if (phdr->p_type == PT_LOAD && phdr->p_vaddr < baseaddr) { 119 baseaddr = phdr->p_vaddr; 120 } 121 } 122 123 quit: 124 if (phbuf) free(phbuf); 125 return baseaddr; 126 } 127 128 struct elf_section *find_section_by_name(char *name, 129 int fd, 130 ELF_EHDR *ehdr, 131 struct elf_section *scn_cache) { 132 char *strtab; 133 int cnt; 134 int strtab_size; 135 136 // Section cache have to already contain data for e_shstrndx section. 137 // If it's not true - elf file is broken, so just bail out 138 if (scn_cache[ehdr->e_shstrndx].c_data == NULL) { 139 return NULL; 140 } 141 142 strtab = scn_cache[ehdr->e_shstrndx].c_data; 143 strtab_size = scn_cache[ehdr->e_shstrndx].c_shdr->sh_size; 144 145 for (cnt = 0; cnt < ehdr->e_shnum; ++cnt) { 146 if (scn_cache[cnt].c_shdr->sh_name < strtab_size) { 147 if (strcmp(scn_cache[cnt].c_shdr->sh_name + strtab, name) == 0) { 148 scn_cache[cnt].c_data = read_section_data(fd, ehdr, scn_cache[cnt].c_shdr); 149 return &scn_cache[cnt]; 150 } 151 } 152 } 153 154 return NULL; 155 }