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Jiri Kosinacc503c12008-01-30 13:31:07 +01001/*
Harvey Harrison675a0812008-01-30 13:31:10 +01002 * Flexible mmap layout support
Jiri Kosinacc503c12008-01-30 13:31:07 +01003 *
4 * Based on code by Ingo Molnar and Andi Kleen, copyrighted
5 * as follows:
6 *
Ingo Molnar8f47e162009-01-31 02:03:42 +01007 * Copyright 2003-2009 Red Hat Inc.
Jiri Kosinacc503c12008-01-30 13:31:07 +01008 * 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
Andi Kleen88172102006-01-17 07:03:38 +010025 */
Jiri Kosinacc503c12008-01-30 13:31:07 +010026
27#include <linux/personality.h>
Andi Kleen88172102006-01-17 07:03:38 +010028#include <linux/mm.h>
Andi Kleen88172102006-01-17 07:03:38 +010029#include <linux/random.h>
Jiri Kosinacc503c12008-01-30 13:31:07 +010030#include <linux/limits.h>
31#include <linux/sched.h>
Michal Hocko80938332009-09-08 11:01:55 +020032#include <asm/elf.h>
33
34static unsigned int stack_maxrandom_size(void)
35{
36 unsigned int max = 0;
37 if ((current->flags & PF_RANDOMIZE) &&
38 !(current->personality & ADDR_NO_RANDOMIZE)) {
39 max = ((-1U) & STACK_RND_MASK) << PAGE_SHIFT;
40 }
41
42 return max;
43}
44
Andi Kleen88172102006-01-17 07:03:38 +010045
Jiri Kosinacc503c12008-01-30 13:31:07 +010046/*
47 * Top of mmap area (just below the process stack).
48 *
Michal Hocko80938332009-09-08 11:01:55 +020049 * Leave an at least ~128 MB hole with possible stack randomization.
Jiri Kosinacc503c12008-01-30 13:31:07 +010050 */
Michal Hocko80938332009-09-08 11:01:55 +020051#define MIN_GAP (128*1024*1024UL + stack_maxrandom_size())
Jiri Kosinacc503c12008-01-30 13:31:07 +010052#define MAX_GAP (TASK_SIZE/6*5)
Andi Kleen88172102006-01-17 07:03:38 +010053
Harvey Harrison675a0812008-01-30 13:31:10 +010054/*
55 * True on X86_32 or when emulating IA32 on X86_64
56 */
57static int mmap_is_ia32(void)
Andi Kleen88172102006-01-17 07:03:38 +010058{
Harvey Harrison675a0812008-01-30 13:31:10 +010059#ifdef CONFIG_X86_32
60 return 1;
61#endif
Jiri Kosinacc503c12008-01-30 13:31:07 +010062#ifdef CONFIG_IA32_EMULATION
63 if (test_thread_flag(TIF_IA32))
64 return 1;
65#endif
66 return 0;
67}
68
Andrew Morton954683a2008-01-30 13:31:07 +010069static int mmap_is_legacy(void)
Jiri Kosinacc503c12008-01-30 13:31:07 +010070{
71 if (current->personality & ADDR_COMPAT_LAYOUT)
72 return 1;
73
Jiri Slaby2854e722010-01-27 17:32:22 +010074 if (rlimit(RLIMIT_STACK) == RLIM_INFINITY)
Jiri Kosinacc503c12008-01-30 13:31:07 +010075 return 1;
76
77 return sysctl_legacy_va_layout;
78}
79
Harvey Harrison675a0812008-01-30 13:31:10 +010080static unsigned long mmap_rnd(void)
81{
82 unsigned long rnd = 0;
83
84 /*
85 * 8 bits of randomness in 32bit mmaps, 20 address space bits
86 * 28 bits of randomness in 64bit mmaps, 40 address space bits
87 */
88 if (current->flags & PF_RANDOMIZE) {
89 if (mmap_is_ia32())
90 rnd = (long)get_random_int() % (1<<8);
91 else
92 rnd = (long)(get_random_int() % (1<<28));
93 }
94 return rnd << PAGE_SHIFT;
95}
96
97static unsigned long mmap_base(void)
98{
Jiri Slaby2854e722010-01-27 17:32:22 +010099 unsigned long gap = rlimit(RLIMIT_STACK);
Harvey Harrison675a0812008-01-30 13:31:10 +0100100
101 if (gap < MIN_GAP)
102 gap = MIN_GAP;
103 else if (gap > MAX_GAP)
104 gap = MAX_GAP;
105
106 return PAGE_ALIGN(TASK_SIZE - gap - mmap_rnd());
107}
108
109/*
110 * Bottom-up (legacy) layout on X86_32 did not support randomization, X86_64
111 * does, but not when emulating X86_32
112 */
113static unsigned long mmap_legacy_base(void)
114{
115 if (mmap_is_ia32())
116 return TASK_UNMAPPED_BASE;
117 else
118 return TASK_UNMAPPED_BASE + mmap_rnd();
119}
120
Jiri Kosinacc503c12008-01-30 13:31:07 +0100121/*
122 * This function, called very early during the creation of a new
123 * process VM image, sets up which VM layout function to use:
124 */
125void arch_pick_mmap_layout(struct mm_struct *mm)
126{
Harvey Harrison675a0812008-01-30 13:31:10 +0100127 if (mmap_is_legacy()) {
128 mm->mmap_base = mmap_legacy_base();
Jiri Kosinacc503c12008-01-30 13:31:07 +0100129 mm->get_unmapped_area = arch_get_unmapped_area;
130 mm->unmap_area = arch_unmap_area;
131 } else {
132 mm->mmap_base = mmap_base();
133 mm->get_unmapped_area = arch_get_unmapped_area_topdown;
134 mm->unmap_area = arch_unmap_area_topdown;
Jiri Kosinacc503c12008-01-30 13:31:07 +0100135 }
Jiri Kosinacc503c12008-01-30 13:31:07 +0100136}