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 
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 
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 		/* Glibc is likely to explode now - exit with raw syscall */
94 		asm volatile ("int $0x80" : : "a" (__NR_exit), "b" (!!ret));
95 	} else {
96 		int status;
97 
98 		if (waitpid(child, &status, 0) != child ||
99 			!WIFEXITED(status)) {
100 			printf("[FAIL]\tmremap() of the vDSO does not work on this kernel!\n");
101 			return 1;
102 		} else if (WEXITSTATUS(status) != 0) {
103 			printf("[FAIL]\tChild failed with %d\n",
104 					WEXITSTATUS(status));
105 			return 1;
106 		}
107 		printf("[OK]\n");
108 	}
109 
110 	return 0;
111 }
112