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/memblock.h>
22 #include <linux/mm.h>
23 #include <linux/mman.h>
24 #include <linux/export.h>
25 #include <linux/shm.h>
26 #include <linux/sched/signal.h>
27 #include <linux/sched/mm.h>
28 #include <linux/io.h>
29 #include <linux/personality.h>
30 #include <linux/random.h>
31
32 #include <asm/cputype.h>
33
34 /*
35 * Leave enough space between the mmap area and the stack to honour ulimit in
36 * the face of randomisation.
37 */
38 #define MIN_GAP (SZ_128M)
39 #define MAX_GAP (STACK_TOP/6*5)
40
41 static int mmap_is_legacy(void)
42 {
43 if (current->personality & ADDR_COMPAT_LAYOUT)
44 return 1;
45
46 if (rlimit(RLIMIT_STACK) == RLIM_INFINITY)
47 return 1;
48
49 return sysctl_legacy_va_layout;
50 }
51
52 unsigned long arch_mmap_rnd(void)
53 {
54 unsigned long rnd;
55
56 #ifdef CONFIG_COMPAT
57 if (test_thread_flag(TIF_32BIT))
58 rnd = get_random_long() & ((1UL << mmap_rnd_compat_bits) - 1);
59 else
60 #endif
61 rnd = get_random_long() & ((1UL << mmap_rnd_bits) - 1);
62 return rnd << PAGE_SHIFT;
63 }
64
65 static unsigned long mmap_base(unsigned long rnd)
66 {
67 unsigned long gap = rlimit(RLIMIT_STACK);
68 unsigned long pad = (STACK_RND_MASK << PAGE_SHIFT) + stack_guard_gap;
69
70 /* Values close to RLIM_INFINITY can overflow. */
71 if (gap + pad > gap)
72 gap += pad;
73
74 if (gap < MIN_GAP)
75 gap = MIN_GAP;
76 else if (gap > MAX_GAP)
77 gap = MAX_GAP;
78
79 return PAGE_ALIGN(STACK_TOP - gap - rnd);
80 }
81
82 /*
83 * This function, called very early during the creation of a new process VM
84 * image, sets up which VM layout function to use:
85 */
86 void arch_pick_mmap_layout(struct mm_struct *mm)
87 {
88 unsigned long random_factor = 0UL;
89
90 if (current->flags & PF_RANDOMIZE)
91 random_factor = arch_mmap_rnd();
92
93 /*
94 * Fall back to the standard layout if the personality bit is set, or
95 * if the expected stack growth is unlimited:
96 */
97 if (mmap_is_legacy()) {
98 mm->mmap_base = TASK_UNMAPPED_BASE + random_factor;
99 mm->get_unmapped_area = arch_get_unmapped_area;
100 } else {
101 mm->mmap_base = mmap_base(random_factor);
102 mm->get_unmapped_area = arch_get_unmapped_area_topdown;
103 }
104 }
105
106 /*
107 * You really shouldn't be using read() or write() on /dev/mem. This might go
108 * away in the future.
109 */
110 int valid_phys_addr_range(phys_addr_t addr, size_t size)
111 {
112 /*
113 * Check whether addr is covered by a memory region without the
114 * MEMBLOCK_NOMAP attribute, and whether that region covers the
115 * entire range. In theory, this could lead to false negatives
116 * if the range is covered by distinct but adjacent memory regions
117 * that only differ in other attributes. However, few of such
118 * attributes have been defined, and it is debatable whether it
119 * follows that /dev/mem read() calls should be able traverse
120 * such boundaries.
121 */
122 return memblock_is_region_memory(addr, size) &&
123 memblock_is_map_memory(addr);
124 }
125
126 /*
127 * Do not allow /dev/mem mappings beyond the supported physical range.
128 */
129 int valid_mmap_phys_addr_range(unsigned long pfn, size_t size)
130 {
131 return !(((pfn << PAGE_SHIFT) + size) & ~PHYS_MASK);
132 }
133
134 #ifdef CONFIG_STRICT_DEVMEM
135
136 #include <linux/ioport.h>
137
138 /*
139 * devmem_is_allowed() checks to see if /dev/mem access to a certain address
140 * is valid. The argument is a physical page number. We mimic x86 here by
141 * disallowing access to system RAM as well as device-exclusive MMIO regions.
142 * This effectively disable read()/write() on /dev/mem.
143 */
144 int devmem_is_allowed(unsigned long pfn)
145 {
146 if (iomem_is_exclusive(pfn << PAGE_SHIFT))
147 return 0;
148 if (!page_is_ram(pfn))
149 return 1;
150 return 0;
151 }
152
153 #endif
154
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