1 /*
2 * Flexible mmap layout support
3 *
4 * Based on code by Ingo Molnar and Andi Kleen, copyrighted
5 * as follows:
6 *
7 * Copyright 2003-2009 Red Hat Inc.
8 * All Rights Reserved.
9 * Copyright 2005 Andi Kleen, SUSE Labs.
10 * Copyright 2007 Jiri Kosina, SUSE Labs.
11 *
12 * This program is free software; you can redistribute it and/or modify
13 * it under the terms of the GNU General Public License as published by
14 * the Free Software Foundation; either version 2 of the License, or
15 * (at your option) any later version.
16 *
17 * This program is distributed in the hope that it will be useful,
18 * but WITHOUT ANY WARRANTY; without even the implied warranty of
19 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
20 * GNU General Public License for more details.
21 *
22 * You should have received a copy of the GNU General Public License
23 * along with this program; if not, write to the Free Software
24 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
25 */
26
27 #include <linux/personality.h>
28 #include <linux/mm.h>
29 #include <linux/random.h>
30 #include <linux/limits.h>
31 #include <linux/sched.h>
32 #include <asm/elf.h>
33
34 struct va_alignment __read_mostly va_align = {
35 .flags = -1,
36 };
37
stack_maxrandom_size(void)38 static unsigned long stack_maxrandom_size(void)
39 {
40 unsigned long max = 0;
41 if ((current->flags & PF_RANDOMIZE) &&
42 !(current->personality & ADDR_NO_RANDOMIZE)) {
43 max = ((-1UL) & STACK_RND_MASK) << PAGE_SHIFT;
44 }
45
46 return max;
47 }
48
49 /*
50 * Top of mmap area (just below the process stack).
51 *
52 * Leave an at least ~128 MB hole with possible stack randomization.
53 */
54 #define MIN_GAP (128*1024*1024UL + stack_maxrandom_size())
55 #define MAX_GAP (TASK_SIZE/6*5)
56
mmap_is_legacy(void)57 static int mmap_is_legacy(void)
58 {
59 if (current->personality & ADDR_COMPAT_LAYOUT)
60 return 1;
61
62 if (rlimit(RLIMIT_STACK) == RLIM_INFINITY)
63 return 1;
64
65 return sysctl_legacy_va_layout;
66 }
67
mmap_rnd(void)68 static unsigned long mmap_rnd(void)
69 {
70 unsigned long rnd = 0;
71
72 if (current->flags & PF_RANDOMIZE) {
73 if (mmap_is_ia32())
74 #ifdef CONFIG_COMPAT
75 rnd = get_random_long() & ((1UL << mmap_rnd_compat_bits) - 1);
76 #else
77 rnd = get_random_long() & ((1UL << mmap_rnd_bits) - 1);
78 #endif
79 else
80 rnd = get_random_long() & ((1UL << mmap_rnd_bits) - 1);
81 }
82 return rnd << PAGE_SHIFT;
83 }
84
mmap_base(void)85 static unsigned long mmap_base(void)
86 {
87 unsigned long gap = rlimit(RLIMIT_STACK);
88
89 if (gap < MIN_GAP)
90 gap = MIN_GAP;
91 else if (gap > MAX_GAP)
92 gap = MAX_GAP;
93
94 return PAGE_ALIGN(TASK_SIZE - gap - mmap_rnd());
95 }
96
97 /*
98 * This function, called very early during the creation of a new
99 * process VM image, sets up which VM layout function to use:
100 */
arch_pick_mmap_layout(struct mm_struct * mm)101 void arch_pick_mmap_layout(struct mm_struct *mm)
102 {
103 unsigned long random_factor = 0UL;
104
105 if (current->flags & PF_RANDOMIZE)
106 random_factor = mmap_rnd();
107
108 mm->mmap_legacy_base = TASK_UNMAPPED_BASE + random_factor;
109
110 if (mmap_is_legacy()) {
111 mm->mmap_base = mm->mmap_legacy_base;
112 mm->get_unmapped_area = arch_get_unmapped_area;
113 } else {
114 mm->mmap_base = mmap_base();
115 mm->get_unmapped_area = arch_get_unmapped_area_topdown;
116 }
117 }
118