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mm: expose arch_mmap_rnd when available
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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
39 static 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
50 unsigned 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
59 static 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 */
75 void 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 }
94 EXPORT_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 */
101 int 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 */
114 int 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 */
129 int 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