1/*
2 * Based on arch/arm/mm/mmap.c
3 *
4 * Copyright (C) 2012 ARM Ltd.
5 *
6 * This program is free software; you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License version 2 as
8 * published by the Free Software Foundation.
9 *
10 * This program is distributed in the hope that it will be useful,
11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
13 * GNU General Public License for more details.
14 *
15 * You should have received a copy of the GNU General Public License
16 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
17 */
18
19#include <linux/elf.h>
20#include <linux/fs.h>
21#include <linux/mm.h>
22#include <linux/mman.h>
23#include <linux/export.h>
24#include <linux/shm.h>
25#include <linux/sched.h>
26#include <linux/io.h>
27#include <linux/personality.h>
28#include <linux/random.h>
29
30#include <asm/cputype.h>
31
32/*
33 * Leave enough space between the mmap area and the stack to honour ulimit in
34 * the face of randomisation.
35 */
36#define MIN_GAP (SZ_128M + ((STACK_RND_MASK << PAGE_SHIFT) + 1))
37#define MAX_GAP	(STACK_TOP/6*5)
38
39static int mmap_is_legacy(void)
40{
41	if (current->personality & ADDR_COMPAT_LAYOUT)
42		return 1;
43
44	if (rlimit(RLIMIT_STACK) == RLIM_INFINITY)
45		return 1;
46
47	return sysctl_legacy_va_layout;
48}
49
50unsigned long arch_mmap_rnd(void)
51{
52	unsigned long rnd;
53
54	rnd = (unsigned long)get_random_int() & STACK_RND_MASK;
55
56	return rnd << PAGE_SHIFT;
57}
58
59static unsigned long mmap_base(unsigned long rnd)
60{
61	unsigned long gap = rlimit(RLIMIT_STACK);
62
63	if (gap < MIN_GAP)
64		gap = MIN_GAP;
65	else if (gap > MAX_GAP)
66		gap = MAX_GAP;
67
68	return PAGE_ALIGN(STACK_TOP - gap - rnd);
69}
70
71/*
72 * This function, called very early during the creation of a new process VM
73 * image, sets up which VM layout function to use:
74 */
75void arch_pick_mmap_layout(struct mm_struct *mm)
76{
77	unsigned long random_factor = 0UL;
78
79	if (current->flags & PF_RANDOMIZE)
80		random_factor = arch_mmap_rnd();
81
82	/*
83	 * Fall back to the standard layout if the personality bit is set, or
84	 * if the expected stack growth is unlimited:
85	 */
86	if (mmap_is_legacy()) {
87		mm->mmap_base = TASK_UNMAPPED_BASE + random_factor;
88		mm->get_unmapped_area = arch_get_unmapped_area;
89	} else {
90		mm->mmap_base = mmap_base(random_factor);
91		mm->get_unmapped_area = arch_get_unmapped_area_topdown;
92	}
93}
94EXPORT_SYMBOL_GPL(arch_pick_mmap_layout);
95
96
97/*
98 * You really shouldn't be using read() or write() on /dev/mem.  This might go
99 * away in the future.
100 */
101int valid_phys_addr_range(phys_addr_t addr, size_t size)
102{
103	if (addr < PHYS_OFFSET)
104		return 0;
105	if (addr + size > __pa(high_memory - 1) + 1)
106		return 0;
107
108	return 1;
109}
110
111/*
112 * Do not allow /dev/mem mappings beyond the supported physical range.
113 */
114int valid_mmap_phys_addr_range(unsigned long pfn, size_t size)
115{
116	return !(((pfn << PAGE_SHIFT) + size) & ~PHYS_MASK);
117}
118
119#ifdef CONFIG_STRICT_DEVMEM
120
121#include <linux/ioport.h>
122
123/*
124 * devmem_is_allowed() checks to see if /dev/mem access to a certain address
125 * is valid. The argument is a physical page number.  We mimic x86 here by
126 * disallowing access to system RAM as well as device-exclusive MMIO regions.
127 * This effectively disable read()/write() on /dev/mem.
128 */
129int devmem_is_allowed(unsigned long pfn)
130{
131	if (iomem_is_exclusive(pfn << PAGE_SHIFT))
132		return 0;
133	if (!page_is_ram(pfn))
134		return 1;
135	return 0;
136}
137
138#endif
139