1 /*
2 * 32-bit test to check vDSO mremap.
3 *
4 * Copyright (c) 2016 Dmitry Safonov
5 * Suggested-by: Andrew Lutomirski
6 *
7 * This program is free software; you can redistribute it and/or modify
8 * it under the terms and conditions of the GNU General Public License,
9 * version 2, as published by the Free Software Foundation.
10 *
11 * This program is distributed in the hope it will be useful, but
12 * WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 * General Public License for more details.
15 */
16 /*
17 * Can be built statically:
18 * gcc -Os -Wall -static -m32 test_mremap_vdso.c
19 */
20 #define _GNU_SOURCE
21 #include <stdio.h>
22 #include <errno.h>
23 #include <unistd.h>
24 #include <string.h>
25
26 #include <sys/mman.h>
27 #include <sys/auxv.h>
28 #include <sys/syscall.h>
29 #include <sys/wait.h>
30
31 #define PAGE_SIZE 4096
32
try_to_remap(void * vdso_addr,unsigned long size)33 static int try_to_remap(void *vdso_addr, unsigned long size)
34 {
35 void *dest_addr, *new_addr;
36
37 /* Searching for memory location where to remap */
38 dest_addr = mmap(0, size, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
39 if (dest_addr == MAP_FAILED) {
40 printf("[WARN]\tmmap failed (%d): %m\n", errno);
41 return 0;
42 }
43
44 printf("[NOTE]\tMoving vDSO: [%p, %#lx] -> [%p, %#lx]\n",
45 vdso_addr, (unsigned long)vdso_addr + size,
46 dest_addr, (unsigned long)dest_addr + size);
47 fflush(stdout);
48
49 new_addr = mremap(vdso_addr, size, size,
50 MREMAP_FIXED|MREMAP_MAYMOVE, dest_addr);
51 if ((unsigned long)new_addr == (unsigned long)-1) {
52 munmap(dest_addr, size);
53 if (errno == EINVAL) {
54 printf("[NOTE]\tvDSO partial move failed, will try with bigger size\n");
55 return -1; /* Retry with larger */
56 }
57 printf("[FAIL]\tmremap failed (%d): %m\n", errno);
58 return 1;
59 }
60
61 return 0;
62
63 }
64
main(int argc,char ** argv,char ** envp)65 int main(int argc, char **argv, char **envp)
66 {
67 pid_t child;
68
69 child = fork();
70 if (child == -1) {
71 printf("[WARN]\tfailed to fork (%d): %m\n", errno);
72 return 1;
73 }
74
75 if (child == 0) {
76 unsigned long vdso_size = PAGE_SIZE;
77 unsigned long auxval;
78 int ret = -1;
79
80 auxval = getauxval(AT_SYSINFO_EHDR);
81 printf("\tAT_SYSINFO_EHDR is %#lx\n", auxval);
82 if (!auxval || auxval == -ENOENT) {
83 printf("[WARN]\tgetauxval failed\n");
84 return 0;
85 }
86
87 /* Simpler than parsing ELF header */
88 while (ret < 0) {
89 ret = try_to_remap((void *)auxval, vdso_size);
90 vdso_size += PAGE_SIZE;
91 }
92
93 #ifdef __i386__
94 /* Glibc is likely to explode now - exit with raw syscall */
95 asm volatile ("int $0x80" : : "a" (__NR_exit), "b" (!!ret));
96 #else /* __x86_64__ */
97 syscall(SYS_exit, ret);
98 #endif
99 } else {
100 int status;
101
102 if (waitpid(child, &status, 0) != child ||
103 !WIFEXITED(status)) {
104 printf("[FAIL]\tmremap() of the vDSO does not work on this kernel!\n");
105 return 1;
106 } else if (WEXITSTATUS(status) != 0) {
107 printf("[FAIL]\tChild failed with %d\n",
108 WEXITSTATUS(status));
109 return 1;
110 }
111 printf("[OK]\n");
112 }
113
114 return 0;
115 }
116