1 /*- 2 * Copyright (c) 2006,2008 Joseph Koshy 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 AND CONTRIBUTORS ``AS IS'' AND 15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 17 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 24 * SUCH DAMAGE. 25 */ 26 27 #include <assert.h> 28 #include <gelf.h> 29 30 #include "_libelf.h" 31 32 ELFTC_VCSID("$Id: elf_strptr.c,v 1.2 2021/09/02 21:12:25 deraadt Exp $"); 33 34 /* 35 * Convert an ELF section#,offset pair to a string pointer. 36 */ 37 38 char * 39 elf_strptr(Elf *e, size_t scndx, size_t offset) 40 { 41 Elf_Scn *s; 42 Elf_Data *d; 43 GElf_Shdr shdr; 44 uint64_t alignment, count; 45 46 if (e == NULL || e->e_kind != ELF_K_ELF) { 47 LIBELF_SET_ERROR(ARGUMENT, 0); 48 return (NULL); 49 } 50 51 if ((s = elf_getscn(e, scndx)) == NULL || 52 gelf_getshdr(s, &shdr) == NULL) 53 return (NULL); 54 55 if (shdr.sh_type != SHT_STRTAB || 56 offset >= shdr.sh_size) { 57 LIBELF_SET_ERROR(ARGUMENT, 0); 58 return (NULL); 59 } 60 61 d = NULL; 62 if (e->e_flags & ELF_F_LAYOUT) { 63 64 /* 65 * The application is taking responsibility for the 66 * ELF object's layout, so we can directly translate 67 * an offset to a `char *' address using the `d_off' 68 * members of Elf_Data descriptors. 69 */ 70 while ((d = elf_getdata(s, d)) != NULL) { 71 72 if (d->d_buf == 0 || d->d_size == 0) 73 continue; 74 75 if (d->d_type != ELF_T_BYTE) { 76 LIBELF_SET_ERROR(DATA, 0); 77 return (NULL); 78 } 79 80 if (offset >= d->d_off && 81 offset < d->d_off + d->d_size) 82 return ((char *) d->d_buf + offset - d->d_off); 83 } 84 } else { 85 /* 86 * Otherwise, the `d_off' members are not useable and 87 * we need to compute offsets ourselves, taking into 88 * account 'holes' in coverage of the section introduced 89 * by alignment requirements. 90 */ 91 count = (uint64_t) 0; /* cumulative count of bytes seen */ 92 while ((d = elf_getdata(s, d)) != NULL && count <= offset) { 93 94 if (d->d_buf == NULL || d->d_size == 0) 95 continue; 96 97 if (d->d_type != ELF_T_BYTE) { 98 LIBELF_SET_ERROR(DATA, 0); 99 return (NULL); 100 } 101 102 if ((alignment = d->d_align) > 1) { 103 if ((alignment & (alignment - 1)) != 0) { 104 LIBELF_SET_ERROR(DATA, 0); 105 return (NULL); 106 } 107 count = roundup2(count, alignment); 108 } 109 110 if (offset < count) { 111 /* offset starts in the 'hole' */ 112 LIBELF_SET_ERROR(ARGUMENT, 0); 113 return (NULL); 114 } 115 116 if (offset < count + d->d_size) { 117 if (d->d_buf != NULL) 118 return ((char *) d->d_buf + 119 offset - count); 120 LIBELF_SET_ERROR(DATA, 0); 121 return (NULL); 122 } 123 124 count += d->d_size; 125 } 126 } 127 128 LIBELF_SET_ERROR(ARGUMENT, 0); 129 return (NULL); 130 } 131