init.c

 1// SPDX-License-Identifier: GPL-2.0
 2
 3#include <stdio.h>
 4#include <unistd.h>
 5#include <fcntl.h>
 6#include <sys/syscall.h>
 7#include <sys/mount.h>
 8#include <sys/reboot.h>
 9#include <linux/kexec.h>
10
11/* from arch/x86/include/asm/setup.h */
12#define COMMAND_LINE_SIZE	2048
13
14#define KHO_FINALIZE "/debugfs/kho/out/finalize"
15#define KERNEL_IMAGE "/kernel"
16
17static int mount_filesystems(void)
18{
19	if (mount("debugfs", "/debugfs", "debugfs", 0, NULL) < 0)
20		return -1;
21
22	return mount("proc", "/proc", "proc", 0, NULL);
23}
24
25static int kho_enable(void)
26{
27	const char enable[] = "1";
28	int fd;
29
30	fd = open(KHO_FINALIZE, O_RDWR);
31	if (fd < 0)
32		return -1;
33
34	if (write(fd, enable, sizeof(enable)) != sizeof(enable))
35		return 1;
36
37	close(fd);
38	return 0;
39}
40
41static long kexec_file_load(int kernel_fd, int initrd_fd,
42			    unsigned long cmdline_len, const char *cmdline,
43			    unsigned long flags)
44{
45	return syscall(__NR_kexec_file_load, kernel_fd, initrd_fd, cmdline_len,
46		       cmdline, flags);
47}
48
49static int kexec_load(void)
50{
51	char cmdline[COMMAND_LINE_SIZE];
52	ssize_t len;
53	int fd, err;
54
55	fd = open("/proc/cmdline", O_RDONLY);
56	if (fd < 0)
57		return -1;
58
59	len = read(fd, cmdline, sizeof(cmdline));
60	close(fd);
61	if (len < 0)
62		return -1;
63
64	/* replace \n with \0 */
65	cmdline[len - 1] = 0;
66	fd = open(KERNEL_IMAGE, O_RDONLY);
67	if (fd < 0)
68		return -1;
69
70	err = kexec_file_load(fd, -1, len, cmdline, KEXEC_FILE_NO_INITRAMFS);
71	close(fd);
72
73	return err ? : 0;
74}
75
76int main(int argc, char *argv[])
77{
78	if (mount_filesystems())
79		goto err_reboot;
80
81	if (kho_enable())
82		goto err_reboot;
83
84	if (kexec_load())
85		goto err_reboot;
86
87	if (reboot(RB_KEXEC))
88		goto err_reboot;
89
90	return 0;
91
92err_reboot:
93	reboot(RB_AUTOBOOT);
94	return -1;
95}