1 /* Compress or decompress a section.
2 Copyright (C) 2015 Red Hat, Inc.
3 This file is part of elfutils.
4
5 This file is free software; you can redistribute it and/or modify
6 it under the terms of either
7
8 * the GNU Lesser General Public License as published by the Free
9 Software Foundation; either version 3 of the License, or (at
10 your option) any later version
11
12 or
13
14 * the GNU General Public License as published by the Free
15 Software Foundation; either version 2 of the License, or (at
16 your option) any later version
17
18 or both in parallel, as here.
19
20 elfutils is distributed in the hope that it will be useful, but
21 WITHOUT ANY WARRANTY; without even the implied warranty of
22 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
23 General Public License for more details.
24
25 You should have received copies of the GNU General Public License and
26 the GNU Lesser General Public License along with this program. If
27 not, see <http://www.gnu.org/licenses/>. */
28
29 #ifdef HAVE_CONFIG_H
30 # include <config.h>
31 #endif
32
33 #include <libelf.h>
34 #include "libelfP.h"
35 #include "common.h"
36
37 int
elf_compress_gnu(Elf_Scn * scn,int inflate,unsigned int flags)38 elf_compress_gnu (Elf_Scn *scn, int inflate, unsigned int flags)
39 {
40 if (scn == NULL)
41 return -1;
42
43 if ((flags & ~ELF_CHF_FORCE) != 0)
44 {
45 __libelf_seterrno (ELF_E_INVALID_OPERAND);
46 return -1;
47 }
48
49 bool force = (flags & ELF_CHF_FORCE) != 0;
50
51 Elf *elf = scn->elf;
52 GElf_Ehdr ehdr;
53 if (gelf_getehdr (elf, &ehdr) == NULL)
54 return -1;
55
56 int elfclass = elf->class;
57 int elfdata = ehdr.e_ident[EI_DATA];
58
59 Elf64_Xword sh_flags;
60 Elf64_Word sh_type;
61 Elf64_Xword sh_addralign;
62 if (elfclass == ELFCLASS32)
63 {
64 Elf32_Shdr *shdr = elf32_getshdr (scn);
65 if (shdr == NULL)
66 return -1;
67
68 sh_flags = shdr->sh_flags;
69 sh_type = shdr->sh_type;
70 sh_addralign = shdr->sh_addralign;
71 }
72 else
73 {
74 Elf64_Shdr *shdr = elf64_getshdr (scn);
75 if (shdr == NULL)
76 return -1;
77
78 sh_flags = shdr->sh_flags;
79 sh_type = shdr->sh_type;
80 sh_addralign = shdr->sh_addralign;
81 }
82
83 /* Allocated sections, or sections that are already are compressed
84 cannot (also) be GNU compressed. */
85 if ((sh_flags & SHF_ALLOC) != 0 || (sh_flags & SHF_COMPRESSED))
86 {
87 __libelf_seterrno (ELF_E_INVALID_SECTION_FLAGS);
88 return -1;
89 }
90
91 if (sh_type == SHT_NULL || sh_type == SHT_NOBITS)
92 {
93 __libelf_seterrno (ELF_E_INVALID_SECTION_TYPE);
94 return -1;
95 }
96
97 /* For GNU compression we cannot really know whether the section is
98 already compressed or not. Just try and see what happens... */
99 // int compressed = (sh_flags & SHF_COMPRESSED);
100 if (inflate == 1)
101 {
102 size_t hsize = 4 + 8; /* GNU "ZLIB" + 8 byte size. */
103 size_t orig_size, new_size, orig_addralign;
104 void *out_buf = __libelf_compress (scn, hsize, elfdata,
105 &orig_size, &orig_addralign,
106 &new_size, force,
107 /* use_zstd */ false);
108
109 /* Compression would make section larger, don't change anything. */
110 if (out_buf == (void *) -1)
111 return 0;
112
113 /* Compression failed, return error. */
114 if (out_buf == NULL)
115 return -1;
116
117 uint64_t be64_size = htobe64 (orig_size);
118 memmove (out_buf, "ZLIB", 4);
119 memmove (out_buf + 4, &be64_size, sizeof (be64_size));
120
121 /* We don't know anything about sh_entsize, sh_addralign and
122 sh_flags won't have a SHF_COMPRESSED hint in the GNU format.
123 Just adjust the sh_size. */
124 if (elfclass == ELFCLASS32)
125 {
126 Elf32_Shdr *shdr = elf32_getshdr (scn);
127 shdr->sh_size = new_size;
128 }
129 else
130 {
131 Elf64_Shdr *shdr = elf64_getshdr (scn);
132 shdr->sh_size = new_size;
133 }
134
135 __libelf_reset_rawdata (scn, out_buf, new_size, 1, ELF_T_BYTE);
136
137 /* The section is now compressed, we could keep the uncompressed
138 data around, but since that might have been multiple Elf_Data
139 buffers let the user uncompress it explicitly again if they
140 want it to simplify bookkeeping. */
141 scn->zdata_base = NULL;
142
143 return 1;
144 }
145 else if (inflate == 0)
146 {
147 /* In theory the user could have constructed a compressed section
148 by hand. And in practice they do. For example when copying
149 a section from one file to another using elf_newdata. So we
150 have to use elf_getdata (not elf_rawdata). */
151 Elf_Data *data = elf_getdata (scn, NULL);
152 if (data == NULL)
153 return -1;
154
155 size_t hsize = 4 + 8; /* GNU "ZLIB" + 8 byte size. */
156 if (data->d_size < hsize || memcmp (data->d_buf, "ZLIB", 4) != 0)
157 {
158 __libelf_seterrno (ELF_E_NOT_COMPRESSED);
159 return -1;
160 }
161
162 /* There is a 12-byte header of "ZLIB" followed by
163 an 8-byte big-endian size. There is only one type and
164 Alignment isn't preserved separately. */
165 uint64_t gsize;
166 memcpy (&gsize, data->d_buf + 4, sizeof gsize);
167 gsize = be64toh (gsize);
168
169 /* One more sanity check, size should be bigger than original
170 data size plus some overhead (4 chars ZLIB + 8 bytes size + 6
171 bytes zlib stream overhead + 5 bytes overhead max for one 16K
172 block) and should fit into a size_t. */
173 if (gsize + 4 + 8 + 6 + 5 < data->d_size || gsize > SIZE_MAX)
174 {
175 __libelf_seterrno (ELF_E_NOT_COMPRESSED);
176 return -1;
177 }
178
179 size_t size = gsize;
180 size_t size_in = data->d_size - hsize;
181 void *buf_in = data->d_buf + hsize;
182 void *buf_out = __libelf_decompress (ELFCOMPRESS_ZLIB, buf_in, size_in, size);
183 if (buf_out == NULL)
184 return -1;
185
186 /* We don't know anything about sh_entsize, sh_addralign and
187 sh_flags won't have a SHF_COMPRESSED hint in the GNU format.
188 Just adjust the sh_size. */
189 if (elfclass == ELFCLASS32)
190 {
191 Elf32_Shdr *shdr = elf32_getshdr (scn);
192 shdr->sh_size = size;
193 }
194 else
195 {
196 Elf64_Shdr *shdr = elf64_getshdr (scn);
197 shdr->sh_size = size;
198 }
199
200 __libelf_reset_rawdata (scn, buf_out, size, sh_addralign,
201 __libelf_data_type (&ehdr, sh_type,
202 sh_addralign));
203
204 scn->zdata_base = buf_out;
205
206 return 1;
207 }
208 else
209 {
210 __libelf_seterrno (ELF_E_UNKNOWN_COMPRESSION_TYPE);
211 return -1;
212 }
213 }
214