1 /* Copyright (c) 2014 The Chromium OS Authors. All rights reserved.
2 * Use of this source code is governed by a BSD-style license that can be
3 * found in the LICENSE file.
4 */
5
6 #include "elfparse.h"
7
is_elf_magic(const uint8_t * buf)8 int is_elf_magic (const uint8_t *buf)
9 {
10 return (buf[EI_MAG0] == ELFMAG0) &&
11 (buf[EI_MAG1] == ELFMAG1) &&
12 (buf[EI_MAG2] == ELFMAG2) &&
13 (buf[EI_MAG3] == ELFMAG3);
14 }
15
16 #define parseElftemplate(bit) \
17 ElfType parseElf ## bit(FILE *elf_file, uint8_t *pHead, int little_endian) \
18 { \
19 ElfType ret = ELFSTATIC; \
20 Minijail_Elf ## bit ## _Ehdr *pHeader = NULL; \
21 Minijail_Elf ## bit ## _Phdr pheader = { 0 }; \
22 uint32_t i = 0; \
23 \
24 if (!elf_file || !pHead) \
25 return ELFERROR; \
26 \
27 pHeader = (Minijail_Elf ## bit ## _Ehdr *)pHead; \
28 if (little_endian) { \
29 pHeader->e_phoff = le ## bit ## toh(pHeader->e_phoff); \
30 pHeader->e_phentsize = le16toh(pHeader->e_phentsize); \
31 pHeader->e_phnum = le16toh(pHeader->e_phnum); \
32 } else { \
33 pHeader->e_phoff = be ## bit ## toh(pHeader->e_phoff); \
34 pHeader->e_phentsize = be16toh(pHeader->e_phentsize); \
35 pHeader->e_phnum = be16toh(pHeader->e_phnum); \
36 } \
37 if (pHeader->e_phentsize != sizeof(Minijail_Elf ## bit ## _Phdr)) \
38 return ELFERROR; \
39 \
40 if (fseek(elf_file, pHeader->e_phoff, SEEK_SET) != 0) \
41 return ELFERROR; \
42 \
43 for (i = 0; i < pHeader->e_phnum; i++) { \
44 if (fread(&pheader, sizeof(pheader), 1, elf_file) == 1) { \
45 if (pheader.p_type == PT_INTERP) { \
46 ret = ELFDYNAMIC; \
47 break; \
48 } \
49 } else { \
50 ret = ELFERROR; \
51 break; \
52 } \
53 } \
54 return ret; \
55 }
56 parseElftemplate(64)
57 parseElftemplate(32)
58
59 /* Public function to determine the linkage of an ELF. */
get_elf_linkage(const char * path)60 ElfType get_elf_linkage(const char *path)
61 {
62 ElfType ret = ELFERROR;
63 FILE *elf_file = NULL;
64 uint8_t pHeader[HEADERSIZE] = "";
65
66 elf_file = fopen(path, "r");
67 if (elf_file) {
68 if (fread(pHeader, 1, HEADERSIZE, elf_file) == HEADERSIZE) {
69 if (is_elf_magic(pHeader)) {
70 if ((pHeader[EI_DATA] == ELFDATA2LSB) &&
71 (pHeader[EI_CLASS] == ELFCLASS64)) {
72 /* 64-bit little endian. */
73 ret = parseElf64(elf_file, pHeader, 1);
74 } else if ((pHeader[EI_DATA] == ELFDATA2MSB) &&
75 (pHeader[EI_CLASS] == ELFCLASS64)) {
76 /* 64-bit big endian. */
77 ret = parseElf64(elf_file, pHeader, 0);
78 } else if ((pHeader[EI_DATA] == ELFDATA2LSB) &&
79 (pHeader[EI_CLASS] == ELFCLASS32)) {
80 /* 32-bit little endian. */
81 ret = parseElf32(elf_file, pHeader, 1);
82 } else if ((pHeader[EI_DATA] == ELFDATA2MSB) &&
83 (pHeader[EI_CLASS] == ELFCLASS32)) {
84 /* 32-bit big endian. */
85 ret = parseElf32(elf_file, pHeader, 0);
86 }
87 } else {
88 /*
89 * The binary is not an ELF. We assume it's a
90 * script. We should parse the #! line and
91 * check the interpreter to guard against
92 * static interpreters escaping the sandbox.
93 * As Minijail is only called from the rootfs
94 * it was deemed not necessary to check this.
95 * So we will just let execve(2) decide if this
96 * is valid.
97 */
98 ret = ELFDYNAMIC;
99 }
100 } else {
101 /*
102 * The file is smaller than |HEADERSIZE| bytes.
103 * We assume it's a short script. See above for
104 * reasoning on scripts.
105 */
106 ret = ELFDYNAMIC;
107 }
108 fclose(elf_file);
109 }
110 return ret;
111 }
112