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1 /*
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>
27 #include <linux/random.h>
28 #include <linux/sched.h>
29
30 /*
31 * Top of mmap area (just below the process stack).
32 *
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.
39 */
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)
43 #define MAX_GAP (TASK_SIZE/6*5)
44
45 static inline int mmap_is_legacy(void)
46 {
47 if (current->personality & ADDR_COMPAT_LAYOUT)
48 return 1;
49
50 if (rlimit(RLIMIT_STACK) == RLIM_INFINITY)
51 return 1;
52
53 return sysctl_legacy_va_layout;
54 }
55
56 unsigned long arch_mmap_rnd(void)
57 {
58 unsigned long rnd;
59
60 /* 8MB for 32bit, 1GB for 64bit */
61 if (is_32bit_task())
62 rnd = (unsigned long)get_random_int() % (1<<(23-PAGE_SHIFT));
63 else
64 rnd = (unsigned long)get_random_int() % (1<<(30-PAGE_SHIFT));
65
66 return rnd << PAGE_SHIFT;
67 }
68
69 static inline unsigned long mmap_base(unsigned long rnd)
70 {
71 unsigned long gap = rlimit(RLIMIT_STACK);
72
73 if (gap < MIN_GAP)
74 gap = MIN_GAP;
75 else if (gap > MAX_GAP)
76 gap = MAX_GAP;
77
78 return PAGE_ALIGN(TASK_SIZE - gap - rnd);
79 }
80
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 */
85 void arch_pick_mmap_layout(struct mm_struct *mm)
86 {
87 unsigned long random_factor = 0UL;
88
89 if (current->flags & PF_RANDOMIZE)
90 random_factor = arch_mmap_rnd();
91
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;
99 } else {
100 mm->mmap_base = mmap_base(random_factor);
101 mm->get_unmapped_area = arch_get_unmapped_area_topdown;
102 }
103 }