min_addr.c

 1// SPDX-License-Identifier: GPL-2.0
 2#include <linux/init.h>
 3#include <linux/mm.h>
 4#include <linux/security.h>
 5#include <linux/sysctl.h>
 6#include <linux/minmax.h>
 7
 8/* amount of vm to protect from userspace access by both DAC and the LSM*/
 9unsigned long mmap_min_addr;
10/* amount of vm to protect from userspace using CAP_SYS_RAWIO (DAC) */
11unsigned long dac_mmap_min_addr = CONFIG_DEFAULT_MMAP_MIN_ADDR;
12/* amount of vm to protect from userspace using the LSM = CONFIG_LSM_MMAP_MIN_ADDR */
13
14/*
15 * Update mmap_min_addr = max(dac_mmap_min_addr, CONFIG_LSM_MMAP_MIN_ADDR)
16 */
17static void update_mmap_min_addr(void)
18{
19#ifdef CONFIG_LSM_MMAP_MIN_ADDR
20	mmap_min_addr = umax(dac_mmap_min_addr, CONFIG_LSM_MMAP_MIN_ADDR);
21#else
22	mmap_min_addr = dac_mmap_min_addr;
23#endif
24}
25
26/*
27 * sysctl handler which just sets dac_mmap_min_addr = the new value and then
28 * calls update_mmap_min_addr() so non MAP_FIXED hints get rounded properly
29 */
30int mmap_min_addr_handler(const struct ctl_table *table, int write,
31			  void *buffer, size_t *lenp, loff_t *ppos)
32{
33	int ret;
34
35	if (write && !capable(CAP_SYS_RAWIO))
36		return -EPERM;
37
38	ret = proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
39
40	update_mmap_min_addr();
41
42	return ret;
43}
44
45static const struct ctl_table min_addr_sysctl_table[] = {
46	{
47		.procname	= "mmap_min_addr",
48		.data		= &dac_mmap_min_addr,
49		.maxlen		= sizeof(unsigned long),
50		.mode		= 0644,
51		.proc_handler	= mmap_min_addr_handler,
52	},
53};
54
55static int __init mmap_min_addr_init(void)
56{
57	register_sysctl_init("vm", min_addr_sysctl_table);
58	update_mmap_min_addr();
59
60	return 0;
61}
62pure_initcall(mmap_min_addr_init);