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 
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 
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