1 /*
2 * vdso2c - A vdso image preparation tool
3 * Copyright (c) 2014 Andy Lutomirski and others
4 * Licensed under the GPL v2
5 *
6 * vdso2c requires stripped and unstripped input. It would be trivial
7 * to fully strip the input in here, but, for reasons described below,
8 * we need to write a section table. Doing this is more or less
9 * equivalent to dropping all non-allocatable sections, but it's
10 * easier to let objcopy handle that instead of doing it ourselves.
11 * If we ever need to do something fancier than what objcopy provides,
12 * it would be straightforward to add here.
13 *
14 * We keep a section table for a few reasons:
15 *
16 * Binutils has issues debugging the vDSO: it reads the section table to
17 * find SHT_NOTE; it won't look at PT_NOTE for the in-memory vDSO, which
18 * would break build-id if we removed the section table. Binutils
19 * also requires that shstrndx != 0. See:
20 * https://sourceware.org/bugzilla/show_bug.cgi?id=17064
21 *
22 * elfutils might not look for PT_NOTE if there is a section table at
23 * all. I don't know whether this matters for any practical purpose.
24 *
25 * For simplicity, rather than hacking up a partial section table, we
26 * just write a mostly complete one. We omit non-dynamic symbols,
27 * though, since they're rather large.
28 *
29 * Once binutils gets fixed, we might be able to drop this for all but
30 * the 64-bit vdso, since build-id only works in kernel RPMs, and
31 * systems that update to new enough kernel RPMs will likely update
32 * binutils in sync. build-id has never worked for home-built kernel
33 * RPMs without manual symlinking, and I suspect that no one ever does
34 * that.
35 */
36
37 /*
38 * Copyright (c) 2017 Oracle and/or its affiliates. All rights reserved.
39 */
40
41 #include <inttypes.h>
42 #include <stdint.h>
43 #include <unistd.h>
44 #include <stdarg.h>
45 #include <stdlib.h>
46 #include <stdio.h>
47 #include <string.h>
48 #include <fcntl.h>
49 #include <err.h>
50
51 #include <sys/mman.h>
52 #include <sys/types.h>
53 #include <tools/be_byteshift.h>
54
55 #include <linux/elf.h>
56 #include <linux/types.h>
57 #include <linux/kernel.h>
58
59 const char *outfilename;
60
61 /* Symbols that we need in vdso2c. */
62 enum {
63 sym_vvar_start,
64 sym_VDSO_FAKE_SECTION_TABLE_START,
65 sym_VDSO_FAKE_SECTION_TABLE_END,
66 };
67
68 struct vdso_sym {
69 const char *name;
70 int export;
71 };
72
73 struct vdso_sym required_syms[] = {
74 [sym_vvar_start] = {"vvar_start", 1},
75 [sym_VDSO_FAKE_SECTION_TABLE_START] = {
76 "VDSO_FAKE_SECTION_TABLE_START", 0
77 },
78 [sym_VDSO_FAKE_SECTION_TABLE_END] = {
79 "VDSO_FAKE_SECTION_TABLE_END", 0
80 },
81 };
82
83 __attribute__((format(printf, 1, 2))) __attribute__((noreturn))
fail(const char * format,...)84 static void fail(const char *format, ...)
85 {
86 va_list ap;
87
88 va_start(ap, format);
89 fprintf(stderr, "Error: ");
90 vfprintf(stderr, format, ap);
91 if (outfilename)
92 unlink(outfilename);
93 exit(1);
94 va_end(ap);
95 }
96
97 /*
98 * Evil macros for big-endian reads and writes
99 */
100 #define GBE(x, bits, ifnot) \
101 __builtin_choose_expr( \
102 (sizeof(*(x)) == bits/8), \
103 (__typeof__(*(x)))get_unaligned_be##bits(x), ifnot)
104
105 #define LAST_GBE(x) \
106 __builtin_choose_expr(sizeof(*(x)) == 1, *(x), (void)(0))
107
108 #define GET_BE(x) \
109 GBE(x, 64, GBE(x, 32, GBE(x, 16, LAST_GBE(x))))
110
111 #define PBE(x, val, bits, ifnot) \
112 __builtin_choose_expr( \
113 (sizeof(*(x)) == bits/8), \
114 put_unaligned_be##bits((val), (x)), ifnot)
115
116 #define LAST_PBE(x, val) \
117 __builtin_choose_expr(sizeof(*(x)) == 1, *(x) = (val), (void)(0))
118
119 #define PUT_BE(x, val) \
120 PBE(x, val, 64, PBE(x, val, 32, PBE(x, val, 16, LAST_PBE(x, val))))
121
122 #define NSYMS ARRAY_SIZE(required_syms)
123
124 #define BITSFUNC3(name, bits, suffix) name##bits##suffix
125 #define BITSFUNC2(name, bits, suffix) BITSFUNC3(name, bits, suffix)
126 #define BITSFUNC(name) BITSFUNC2(name, ELF_BITS, )
127
128 #define INT_BITS BITSFUNC2(int, ELF_BITS, _t)
129
130 #define ELF_BITS_XFORM2(bits, x) Elf##bits##_##x
131 #define ELF_BITS_XFORM(bits, x) ELF_BITS_XFORM2(bits, x)
132 #define ELF(x) ELF_BITS_XFORM(ELF_BITS, x)
133
134 #define ELF_BITS 64
135 #include "vdso2c.h"
136 #undef ELF_BITS
137
138 #define ELF_BITS 32
139 #include "vdso2c.h"
140 #undef ELF_BITS
141
go(void * raw_addr,size_t raw_len,void * stripped_addr,size_t stripped_len,FILE * outfile,const char * name)142 static void go(void *raw_addr, size_t raw_len,
143 void *stripped_addr, size_t stripped_len,
144 FILE *outfile, const char *name)
145 {
146 Elf64_Ehdr *hdr = (Elf64_Ehdr *)raw_addr;
147
148 if (hdr->e_ident[EI_CLASS] == ELFCLASS64) {
149 go64(raw_addr, raw_len, stripped_addr, stripped_len,
150 outfile, name);
151 } else if (hdr->e_ident[EI_CLASS] == ELFCLASS32) {
152 go32(raw_addr, raw_len, stripped_addr, stripped_len,
153 outfile, name);
154 } else {
155 fail("unknown ELF class\n");
156 }
157 }
158
map_input(const char * name,void ** addr,size_t * len,int prot)159 static void map_input(const char *name, void **addr, size_t *len, int prot)
160 {
161 off_t tmp_len;
162
163 int fd = open(name, O_RDONLY);
164
165 if (fd == -1)
166 err(1, "%s", name);
167
168 tmp_len = lseek(fd, 0, SEEK_END);
169 if (tmp_len == (off_t)-1)
170 err(1, "lseek");
171 *len = (size_t)tmp_len;
172
173 *addr = mmap(NULL, tmp_len, prot, MAP_PRIVATE, fd, 0);
174 if (*addr == MAP_FAILED)
175 err(1, "mmap");
176
177 close(fd);
178 }
179
main(int argc,char ** argv)180 int main(int argc, char **argv)
181 {
182 size_t raw_len, stripped_len;
183 void *raw_addr, *stripped_addr;
184 FILE *outfile;
185 char *name, *tmp;
186 int namelen;
187
188 if (argc != 4) {
189 printf("Usage: vdso2c RAW_INPUT STRIPPED_INPUT OUTPUT\n");
190 return 1;
191 }
192
193 /*
194 * Figure out the struct name. If we're writing to a .so file,
195 * generate raw output insted.
196 */
197 name = strdup(argv[3]);
198 namelen = strlen(name);
199 if (namelen >= 3 && !strcmp(name + namelen - 3, ".so")) {
200 name = NULL;
201 } else {
202 tmp = strrchr(name, '/');
203 if (tmp)
204 name = tmp + 1;
205 tmp = strchr(name, '.');
206 if (tmp)
207 *tmp = '\0';
208 for (tmp = name; *tmp; tmp++)
209 if (*tmp == '-')
210 *tmp = '_';
211 }
212
213 map_input(argv[1], &raw_addr, &raw_len, PROT_READ);
214 map_input(argv[2], &stripped_addr, &stripped_len, PROT_READ);
215
216 outfilename = argv[3];
217 outfile = fopen(outfilename, "w");
218 if (!outfile)
219 err(1, "%s", argv[2]);
220
221 go(raw_addr, raw_len, stripped_addr, stripped_len, outfile, name);
222
223 munmap(raw_addr, raw_len);
224 munmap(stripped_addr, stripped_len);
225 fclose(outfile);
226
227 return 0;
228 }
229