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1da177e4 1/*
1da177e4
LT
2 * 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>
9f14c42d 27#include <linux/random.h>
e8edc6e0 28#include <linux/sched.h>
1da177e4
LT
29
30/*
31 * Top of mmap area (just below the process stack).
32 *
002b0ec7
AB
33 * 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.
1da177e4 39 */
002b0ec7
AB
40#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)
1da177e4
LT
43#define MAX_GAP (TASK_SIZE/6*5)
44
13a2cb36
AB
45static inline int mmap_is_legacy(void)
46{
47 if (current->personality & ADDR_COMPAT_LAYOUT)
48 return 1;
49
4bf936b9 50 if (rlimit(RLIMIT_STACK) == RLIM_INFINITY)
13a2cb36
AB
51 return 1;
52
53 return sysctl_legacy_va_layout;
54}
55
2b68f6ca 56unsigned long arch_mmap_rnd(void)
9f14c42d 57{
ed632274
KC
58 unsigned long rnd;
59
60 /* 8MB for 32bit, 1GB for 64bit */
61 if (is_32bit_task())
5ef11c35 62 rnd = get_random_long() % (1<<(23-PAGE_SHIFT));
ed632274 63 else
5ef11c35 64 rnd = get_random_long() % (1UL<<(30-PAGE_SHIFT));
9f14c42d 65
fa8cbaaf 66 return rnd << PAGE_SHIFT;
9f14c42d
AB
67}
68
ed632274 69static inline unsigned long mmap_base(unsigned long rnd)
1da177e4 70{
4bf936b9 71 unsigned long gap = rlimit(RLIMIT_STACK);
1da177e4
LT
72
73 if (gap < MIN_GAP)
74 gap = MIN_GAP;
75 else if (gap > MAX_GAP)
76 gap = MAX_GAP;
77
ed632274 78 return PAGE_ALIGN(TASK_SIZE - gap - rnd);
1da177e4
LT
79}
80
1da177e4
LT
81/*
82 * This function, called very early during the creation of a new
83 * process VM image, sets up which VM layout function to use:
84 */
85void arch_pick_mmap_layout(struct mm_struct *mm)
86{
ed632274
KC
87 unsigned long random_factor = 0UL;
88
89 if (current->flags & PF_RANDOMIZE)
2b68f6ca 90 random_factor = arch_mmap_rnd();
ed632274 91
1da177e4
LT
92 /*
93 * Fall back to the standard layout if the personality
94 * bit is set, or if the expected stack growth is unlimited:
95 */
96 if (mmap_is_legacy()) {
97 mm->mmap_base = TASK_UNMAPPED_BASE;
98 mm->get_unmapped_area = arch_get_unmapped_area;
1da177e4 99 } else {
ed632274 100 mm->mmap_base = mmap_base(random_factor);
1da177e4 101 mm->get_unmapped_area = arch_get_unmapped_area_topdown;
1da177e4
LT
102 }
103}