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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 *
7 * Copyright 2003-2004 Red Hat Inc., Durham, North Carolina.
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
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>
Andi Kleen88172102006-01-17 07:03:38 +010032
Jiri Kosinacc503c12008-01-30 13:31:07 +010033/*
34 * Top of mmap area (just below the process stack).
35 *
36 * Leave an at least ~128 MB hole.
37 */
38#define MIN_GAP (128*1024*1024)
39#define MAX_GAP (TASK_SIZE/6*5)
Andi Kleen88172102006-01-17 07:03:38 +010040
Harvey Harrison675a0812008-01-30 13:31:10 +010041/*
42 * True on X86_32 or when emulating IA32 on X86_64
43 */
44static int mmap_is_ia32(void)
Andi Kleen88172102006-01-17 07:03:38 +010045{
Harvey Harrison675a0812008-01-30 13:31:10 +010046#ifdef CONFIG_X86_32
47 return 1;
48#endif
Jiri Kosinacc503c12008-01-30 13:31:07 +010049#ifdef CONFIG_IA32_EMULATION
50 if (test_thread_flag(TIF_IA32))
51 return 1;
52#endif
53 return 0;
54}
55
Andrew Morton954683a2008-01-30 13:31:07 +010056static int mmap_is_legacy(void)
Jiri Kosinacc503c12008-01-30 13:31:07 +010057{
58 if (current->personality & ADDR_COMPAT_LAYOUT)
59 return 1;
60
61 if (current->signal->rlim[RLIMIT_STACK].rlim_cur == RLIM_INFINITY)
62 return 1;
63
64 return sysctl_legacy_va_layout;
65}
66
Harvey Harrison675a0812008-01-30 13:31:10 +010067static unsigned long mmap_rnd(void)
68{
69 unsigned long rnd = 0;
70
71 /*
72 * 8 bits of randomness in 32bit mmaps, 20 address space bits
73 * 28 bits of randomness in 64bit mmaps, 40 address space bits
74 */
75 if (current->flags & PF_RANDOMIZE) {
76 if (mmap_is_ia32())
77 rnd = (long)get_random_int() % (1<<8);
78 else
79 rnd = (long)(get_random_int() % (1<<28));
80 }
81 return rnd << PAGE_SHIFT;
82}
83
84static unsigned long mmap_base(void)
85{
86 unsigned long gap = current->signal->rlim[RLIMIT_STACK].rlim_cur;
87
88 if (gap < MIN_GAP)
89 gap = MIN_GAP;
90 else if (gap > MAX_GAP)
91 gap = MAX_GAP;
92
93 return PAGE_ALIGN(TASK_SIZE - gap - mmap_rnd());
94}
95
96/*
97 * Bottom-up (legacy) layout on X86_32 did not support randomization, X86_64
98 * does, but not when emulating X86_32
99 */
100static unsigned long mmap_legacy_base(void)
101{
102 if (mmap_is_ia32())
103 return TASK_UNMAPPED_BASE;
104 else
105 return TASK_UNMAPPED_BASE + mmap_rnd();
106}
107
Jiri Kosinacc503c12008-01-30 13:31:07 +0100108/*
109 * This function, called very early during the creation of a new
110 * process VM image, sets up which VM layout function to use:
111 */
112void arch_pick_mmap_layout(struct mm_struct *mm)
113{
Harvey Harrison675a0812008-01-30 13:31:10 +0100114 if (mmap_is_legacy()) {
115 mm->mmap_base = mmap_legacy_base();
Jiri Kosinacc503c12008-01-30 13:31:07 +0100116 mm->get_unmapped_area = arch_get_unmapped_area;
117 mm->unmap_area = arch_unmap_area;
118 } else {
119 mm->mmap_base = mmap_base();
120 mm->get_unmapped_area = arch_get_unmapped_area_topdown;
121 mm->unmap_area = arch_unmap_area_topdown;
Jiri Kosinacc503c12008-01-30 13:31:07 +0100122 }
Jiri Kosinacc503c12008-01-30 13:31:07 +0100123}