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Linus Torvalds1da177e2005-04-16 15:20:36 -07001/*
Linus Torvalds1da177e2005-04-16 15:20:36 -07002 * flexible mmap layout support
3 *
4 * Copyright 2003-2004 Red Hat Inc., Durham, North Carolina.
5 * All Rights Reserved.
6 *
7 * This program is free software; you can redistribute it and/or modify
8 * it under the terms of the GNU General Public License as published by
9 * the Free Software Foundation; either version 2 of the License, or
10 * (at your option) any later version.
11 *
12 * This program is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 * GNU General Public License for more details.
16 *
17 * You should have received a copy of the GNU General Public License
18 * along with this program; if not, write to the Free Software
19 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
20 *
21 *
22 * Started by Ingo Molnar <mingo@elte.hu>
23 */
24
25#include <linux/personality.h>
26#include <linux/mm.h>
Anton Blanchard9f14c422009-02-22 01:50:01 +000027#include <linux/random.h>
Alexey Dobriyane8edc6e2007-05-21 01:22:52 +040028#include <linux/sched.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070029
30/*
31 * Top of mmap area (just below the process stack).
32 *
Anton Blanchard002b0ec2009-02-22 01:50:06 +000033 * Leave at least a ~128 MB hole on 32bit applications.
34 *
35 * On 64bit applications we randomise the stack by 1GB so we need to
36 * space our mmap start address by a further 1GB, otherwise there is a
37 * chance the mmap area will end up closer to the stack than our ulimit
38 * requires.
Linus Torvalds1da177e2005-04-16 15:20:36 -070039 */
Anton Blanchard002b0ec2009-02-22 01:50:06 +000040#define MIN_GAP32 (128*1024*1024)
41#define MIN_GAP64 ((128 + 1024)*1024*1024UL)
42#define MIN_GAP ((is_32bit_task()) ? MIN_GAP32 : MIN_GAP64)
Linus Torvalds1da177e2005-04-16 15:20:36 -070043#define MAX_GAP (TASK_SIZE/6*5)
44
Anton Blanchard13a2cb32009-02-22 01:50:00 +000045static inline int mmap_is_legacy(void)
46{
47 if (current->personality & ADDR_COMPAT_LAYOUT)
48 return 1;
49
Jiri Slaby4bf936b2010-01-06 05:24:31 +000050 if (rlimit(RLIMIT_STACK) == RLIM_INFINITY)
Anton Blanchard13a2cb32009-02-22 01:50:00 +000051 return 1;
52
53 return sysctl_legacy_va_layout;
54}
55
Anton Blancharda5adc912009-02-22 01:50:05 +000056/*
57 * Since get_random_int() returns the same value within a 1 jiffy window,
58 * we will almost always get the same randomisation for the stack and mmap
59 * region. This will mean the relative distance between stack and mmap will
60 * be the same.
61 *
62 * To avoid this we can shift the randomness by 1 bit.
63 */
Anton Blanchard9f14c422009-02-22 01:50:01 +000064static unsigned long mmap_rnd(void)
65{
66 unsigned long rnd = 0;
67
68 if (current->flags & PF_RANDOMIZE) {
69 /* 8MB for 32bit, 1GB for 64bit */
70 if (is_32bit_task())
Anton Blancharda5adc912009-02-22 01:50:05 +000071 rnd = (long)(get_random_int() % (1<<(22-PAGE_SHIFT)));
Anton Blanchard9f14c422009-02-22 01:50:01 +000072 else
Anton Blancharda5adc912009-02-22 01:50:05 +000073 rnd = (long)(get_random_int() % (1<<(29-PAGE_SHIFT)));
Anton Blanchard9f14c422009-02-22 01:50:01 +000074 }
Anton Blancharda5adc912009-02-22 01:50:05 +000075 return (rnd << PAGE_SHIFT) * 2;
Anton Blanchard9f14c422009-02-22 01:50:01 +000076}
77
Linus Torvalds1da177e2005-04-16 15:20:36 -070078static inline unsigned long mmap_base(void)
79{
Jiri Slaby4bf936b2010-01-06 05:24:31 +000080 unsigned long gap = rlimit(RLIMIT_STACK);
Linus Torvalds1da177e2005-04-16 15:20:36 -070081
82 if (gap < MIN_GAP)
83 gap = MIN_GAP;
84 else if (gap > MAX_GAP)
85 gap = MAX_GAP;
86
Anton Blanchard9f14c422009-02-22 01:50:01 +000087 return PAGE_ALIGN(TASK_SIZE - gap - mmap_rnd());
Linus Torvalds1da177e2005-04-16 15:20:36 -070088}
89
Linus Torvalds1da177e2005-04-16 15:20:36 -070090/*
91 * This function, called very early during the creation of a new
92 * process VM image, sets up which VM layout function to use:
93 */
94void arch_pick_mmap_layout(struct mm_struct *mm)
95{
96 /*
97 * Fall back to the standard layout if the personality
98 * bit is set, or if the expected stack growth is unlimited:
99 */
100 if (mmap_is_legacy()) {
101 mm->mmap_base = TASK_UNMAPPED_BASE;
102 mm->get_unmapped_area = arch_get_unmapped_area;
103 mm->unmap_area = arch_unmap_area;
104 } else {
105 mm->mmap_base = mmap_base();
106 mm->get_unmapped_area = arch_get_unmapped_area_topdown;
107 mm->unmap_area = arch_unmap_area_topdown;
108 }
109}