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Commit | Line | Data |
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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 | * | |
33 | * Leave an at least ~128 MB hole. | |
34 | */ | |
35 | #define MIN_GAP (128*1024*1024) | |
36 | #define MAX_GAP (TASK_SIZE/6*5) | |
37 | ||
13a2cb36 AB |
38 | static inline int mmap_is_legacy(void) |
39 | { | |
40 | if (current->personality & ADDR_COMPAT_LAYOUT) | |
41 | return 1; | |
42 | ||
43 | if (current->signal->rlim[RLIMIT_STACK].rlim_cur == RLIM_INFINITY) | |
44 | return 1; | |
45 | ||
46 | return sysctl_legacy_va_layout; | |
47 | } | |
48 | ||
a5adc91a AB |
49 | /* |
50 | * Since get_random_int() returns the same value within a 1 jiffy window, | |
51 | * we will almost always get the same randomisation for the stack and mmap | |
52 | * region. This will mean the relative distance between stack and mmap will | |
53 | * be the same. | |
54 | * | |
55 | * To avoid this we can shift the randomness by 1 bit. | |
56 | */ | |
9f14c42d AB |
57 | static unsigned long mmap_rnd(void) |
58 | { | |
59 | unsigned long rnd = 0; | |
60 | ||
61 | if (current->flags & PF_RANDOMIZE) { | |
62 | /* 8MB for 32bit, 1GB for 64bit */ | |
63 | if (is_32bit_task()) | |
a5adc91a | 64 | rnd = (long)(get_random_int() % (1<<(22-PAGE_SHIFT))); |
9f14c42d | 65 | else |
a5adc91a | 66 | rnd = (long)(get_random_int() % (1<<(29-PAGE_SHIFT))); |
9f14c42d | 67 | } |
a5adc91a | 68 | return (rnd << PAGE_SHIFT) * 2; |
9f14c42d AB |
69 | } |
70 | ||
1da177e4 LT |
71 | static inline unsigned long mmap_base(void) |
72 | { | |
73 | unsigned long gap = current->signal->rlim[RLIMIT_STACK].rlim_cur; | |
74 | ||
75 | if (gap < MIN_GAP) | |
76 | gap = MIN_GAP; | |
77 | else if (gap > MAX_GAP) | |
78 | gap = MAX_GAP; | |
79 | ||
9f14c42d | 80 | return PAGE_ALIGN(TASK_SIZE - gap - mmap_rnd()); |
1da177e4 LT |
81 | } |
82 | ||
1da177e4 LT |
83 | /* |
84 | * This function, called very early during the creation of a new | |
85 | * process VM image, sets up which VM layout function to use: | |
86 | */ | |
87 | void arch_pick_mmap_layout(struct mm_struct *mm) | |
88 | { | |
89 | /* | |
90 | * Fall back to the standard layout if the personality | |
91 | * bit is set, or if the expected stack growth is unlimited: | |
92 | */ | |
93 | if (mmap_is_legacy()) { | |
94 | mm->mmap_base = TASK_UNMAPPED_BASE; | |
95 | mm->get_unmapped_area = arch_get_unmapped_area; | |
96 | mm->unmap_area = arch_unmap_area; | |
97 | } else { | |
98 | mm->mmap_base = mmap_base(); | |
99 | mm->get_unmapped_area = arch_get_unmapped_area_topdown; | |
100 | mm->unmap_area = arch_unmap_area_topdown; | |
101 | } | |
102 | } |