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
25static 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
57int 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