1 /* Linux kernel image support for libdwfl.
2 Copyright (C) 2009-2011 Red Hat, Inc.
3 Copyright (C) 2022 Mark J. Wielaard <mark@klomp.org>
4 This file is part of elfutils.
5
6 This file is free software; you can redistribute it and/or modify
7 it under the terms of either
8
9 * the GNU Lesser General Public License as published by the Free
10 Software Foundation; either version 3 of the License, or (at
11 your option) any later version
12
13 or
14
15 * the GNU General Public License as published by the Free
16 Software Foundation; either version 2 of the License, or (at
17 your option) any later version
18
19 or both in parallel, as here.
20
21 elfutils is distributed in the hope that it will be useful, but
22 WITHOUT ANY WARRANTY; without even the implied warranty of
23 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
24 General Public License for more details.
25
26 You should have received copies of the GNU General Public License and
27 the GNU Lesser General Public License along with this program. If
28 not, see <http://www.gnu.org/licenses/>. */
29
30 #ifdef HAVE_CONFIG_H
31 # include <config.h>
32 #endif
33
34 #include "libdwflP.h"
35
36 #if BYTE_ORDER == LITTLE_ENDIAN
37 # define LE16(x) (x)
38 #else
39 # define LE16(x) bswap_16 (x)
40 #endif
41
42 /* See Documentation/x86/boot.txt in Linux kernel sources
43 for an explanation of these format details. */
44
45 #define MAGIC1 0xaa55
46 #define MAGIC2 0x53726448 /* "HdrS" little-endian */
47 #define MIN_VERSION 0x0208
48
49 #define H_START (H_SETUP_SECTS & -4)
50 #define H_SETUP_SECTS 0x1f1
51 #define H_MAGIC1 0x1fe
52 #define H_MAGIC2 0x202
53 #define H_VERSION 0x206
54 #define H_PAYLOAD_OFFSET 0x248
55 #define H_PAYLOAD_LENGTH 0x24c
56 #define H_END 0x250
57 #define H_READ_SIZE (H_END - H_START)
58
59 Dwfl_Error
60 internal_function
__libdw_image_header(int fd,off_t * start_offset,void * mapped,size_t mapped_size)61 __libdw_image_header (int fd, off_t *start_offset,
62 void *mapped, size_t mapped_size)
63 {
64 if (likely (mapped_size > H_END))
65 {
66 const void *header = mapped;
67 char header_buffer[H_READ_SIZE];
68 if (header == NULL)
69 {
70 ssize_t n = pread_retry (fd, header_buffer, H_READ_SIZE,
71 *start_offset + H_START);
72 if (n < 0)
73 return DWFL_E_ERRNO;
74 if (n < H_READ_SIZE)
75 return DWFL_E_BADELF;
76
77 header = header_buffer - H_START;
78 }
79
80 uint16_t magic1;
81 uint32_t magic2;
82 uint16_t version;
83 memcpy (&magic1, header + H_MAGIC1, sizeof (uint16_t));
84 memcpy (&magic2, header + H_MAGIC2, sizeof (uint32_t));
85 memcpy (&version, header + H_VERSION, sizeof (uint16_t));
86 if (magic1 == LE16 (MAGIC1) && magic2 == LE32 (MAGIC2)
87 && LE16 (version) >= MIN_VERSION)
88 {
89 /* The magic numbers match and the version field is sufficient.
90 Extract the payload bounds. */
91
92 uint32_t offset;
93 uint32_t length;
94 uint8_t sects;
95 memcpy (&offset, header + H_PAYLOAD_OFFSET, sizeof (uint32_t));
96 memcpy (&length, header + H_PAYLOAD_LENGTH, sizeof (uint32_t));
97 memcpy (§s, header + H_SETUP_SECTS, sizeof (uint8_t));
98 offset = LE32 (offset);
99 length = LE32 (length);
100
101 offset += ((sects ?: 4) + 1) * 512;
102
103 if (offset > H_END && offset < mapped_size
104 && mapped_size - offset >= length)
105 {
106 /* It looks kosher. Use it! */
107 *start_offset += offset;
108 return DWFL_E_NOERROR;
109 }
110 }
111 }
112 return DWFL_E_BADELF;
113 }
114