1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * 32-bit test to check vDSO mremap.
4 *
5 * Copyright (c) 2016 Dmitry Safonov
6 * Suggested-by: Andrew Lutomirski
7 */
8 /*
9 * Can be built statically:
10 * gcc -Os -Wall -static -m32 test_mremap_vdso.c
11 */
12 #define _GNU_SOURCE
13 #include <stdio.h>
14 #include <errno.h>
15 #include <unistd.h>
16 #include <string.h>
17
18 #include <sys/mman.h>
19 #include <sys/auxv.h>
20 #include <sys/syscall.h>
21 #include <sys/wait.h>
22
23 #define PAGE_SIZE 4096
24
try_to_remap(void * vdso_addr,unsigned long size)25 static int try_to_remap(void *vdso_addr, unsigned long size)
26 {
27 void *dest_addr, *new_addr;
28
29 /* Searching for memory location where to remap */
30 dest_addr = mmap(0, size, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
31 if (dest_addr == MAP_FAILED) {
32 printf("[WARN]\tmmap failed (%d): %m\n", errno);
33 return 0;
34 }
35
36 printf("[NOTE]\tMoving vDSO: [%p, %#lx] -> [%p, %#lx]\n",
37 vdso_addr, (unsigned long)vdso_addr + size,
38 dest_addr, (unsigned long)dest_addr + size);
39 fflush(stdout);
40
41 new_addr = mremap(vdso_addr, size, size,
42 MREMAP_FIXED|MREMAP_MAYMOVE, dest_addr);
43 if ((unsigned long)new_addr == (unsigned long)-1) {
44 munmap(dest_addr, size);
45 if (errno == EINVAL) {
46 printf("[NOTE]\tvDSO partial move failed, will try with bigger size\n");
47 return -1; /* Retry with larger */
48 }
49 printf("[FAIL]\tmremap failed (%d): %m\n", errno);
50 return 1;
51 }
52
53 return 0;
54
55 }
56
main(int argc,char ** argv,char ** envp)57 int main(int argc, char **argv, char **envp)
58 {
59 pid_t child;
60
61 child = fork();
62 if (child == -1) {
63 printf("[WARN]\tfailed to fork (%d): %m\n", errno);
64 return 1;
65 }
66
67 if (child == 0) {
68 unsigned long vdso_size = PAGE_SIZE;
69 unsigned long auxval;
70 int ret = -1;
71
72 auxval = getauxval(AT_SYSINFO_EHDR);
73 printf("\tAT_SYSINFO_EHDR is %#lx\n", auxval);
74 if (!auxval || auxval == -ENOENT) {
75 printf("[WARN]\tgetauxval failed\n");
76 return 0;
77 }
78
79 /* Simpler than parsing ELF header */
80 while (ret < 0) {
81 ret = try_to_remap((void *)auxval, vdso_size);
82 vdso_size += PAGE_SIZE;
83 }
84
85 #ifdef __i386__
86 /* Glibc is likely to explode now - exit with raw syscall */
87 asm volatile ("int $0x80" : : "a" (__NR_exit), "b" (!!ret));
88 #else /* __x86_64__ */
89 syscall(SYS_exit, ret);
90 #endif
91 } else {
92 int status;
93
94 if (waitpid(child, &status, 0) != child ||
95 !WIFEXITED(status)) {
96 printf("[FAIL]\tmremap() of the vDSO does not work on this kernel!\n");
97 return 1;
98 } else if (WEXITSTATUS(status) != 0) {
99 printf("[FAIL]\tChild failed with %d\n",
100 WEXITSTATUS(status));
101 return 1;
102 }
103 printf("[OK]\n");
104 }
105
106 return 0;
107 }
108