2 * Flexible mmap layout support
4 * Based on code by Ingo Molnar and Andi Kleen, copyrighted
7 * Copyright 2003-2009 Red Hat Inc.
9 * Copyright 2005 Andi Kleen, SUSE Labs.
10 * Copyright 2007 Jiri Kosina, SUSE Labs.
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.
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.
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
27 #include <linux/personality.h>
29 #include <linux/random.h>
30 #include <linux/limits.h>
31 #include <linux/sched.h>
34 struct __read_mostly va_alignment va_align = {
38 static unsigned int stack_maxrandom_size(void)
41 if ((current->flags & PF_RANDOMIZE) &&
42 !(current->personality & ADDR_NO_RANDOMIZE)) {
43 max = ((-1U) & STACK_RND_MASK) << PAGE_SHIFT;
50 * Top of mmap area (just below the process stack).
52 * Leave an at least ~128 MB hole with possible stack randomization.
54 #define MIN_GAP (128*1024*1024UL + stack_maxrandom_size())
55 #define MAX_GAP (TASK_SIZE/6*5)
57 static int mmap_is_legacy(void)
59 if (current->personality & ADDR_COMPAT_LAYOUT)
62 if (rlimit(RLIMIT_STACK) == RLIM_INFINITY)
65 return sysctl_legacy_va_layout;
68 static unsigned long mmap_rnd(void)
70 unsigned long rnd = 0;
73 * 8 bits of randomness in 32bit mmaps, 20 address space bits
74 * 28 bits of randomness in 64bit mmaps, 40 address space bits
76 if (current->flags & PF_RANDOMIZE) {
78 rnd = get_random_int() % (1<<8);
80 rnd = get_random_int() % (1<<28);
82 return rnd << PAGE_SHIFT;
85 static unsigned long mmap_base(void)
87 unsigned long gap = rlimit(RLIMIT_STACK);
91 else if (gap > MAX_GAP)
94 return PAGE_ALIGN(TASK_SIZE - gap - mmap_rnd());
98 * Bottom-up (legacy) layout on X86_32 did not support randomization, X86_64
99 * does, but not when emulating X86_32
101 static unsigned long mmap_legacy_base(void)
104 return TASK_UNMAPPED_BASE;
106 return TASK_UNMAPPED_BASE + mmap_rnd();
110 * This function, called very early during the creation of a new
111 * process VM image, sets up which VM layout function to use:
113 void arch_pick_mmap_layout(struct mm_struct *mm)
115 mm->mmap_legacy_base = mmap_legacy_base();
116 mm->mmap_base = mmap_base();
118 if (mmap_is_legacy()) {
119 mm->mmap_base = mm->mmap_legacy_base;
120 mm->get_unmapped_area = arch_get_unmapped_area;
122 mm->get_unmapped_area = arch_get_unmapped_area_topdown;