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Commit | Line | Data |
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cc503c1b | 1 | /* |
675a0813 | 2 | * Flexible mmap layout support |
cc503c1b JK |
3 | * |
4 | * Based on code by Ingo Molnar and Andi Kleen, copyrighted | |
5 | * as follows: | |
6 | * | |
8f47e163 | 7 | * Copyright 2003-2009 Red Hat Inc. |
cc503c1b JK |
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 | |
8817210d | 25 | */ |
cc503c1b JK |
26 | |
27 | #include <linux/personality.h> | |
8817210d | 28 | #include <linux/mm.h> |
8817210d | 29 | #include <linux/random.h> |
cc503c1b JK |
30 | #include <linux/limits.h> |
31 | #include <linux/sched.h> | |
80938332 MH |
32 | #include <asm/elf.h> |
33 | ||
34 | static unsigned int stack_maxrandom_size(void) | |
35 | { | |
36 | unsigned int max = 0; | |
37 | if ((current->flags & PF_RANDOMIZE) && | |
38 | !(current->personality & ADDR_NO_RANDOMIZE)) { | |
39 | max = ((-1U) & STACK_RND_MASK) << PAGE_SHIFT; | |
40 | } | |
41 | ||
42 | return max; | |
43 | } | |
44 | ||
8817210d | 45 | |
cc503c1b JK |
46 | /* |
47 | * Top of mmap area (just below the process stack). | |
48 | * | |
80938332 | 49 | * Leave an at least ~128 MB hole with possible stack randomization. |
cc503c1b | 50 | */ |
80938332 | 51 | #define MIN_GAP (128*1024*1024UL + stack_maxrandom_size()) |
cc503c1b | 52 | #define MAX_GAP (TASK_SIZE/6*5) |
8817210d | 53 | |
954683a2 | 54 | static int mmap_is_legacy(void) |
cc503c1b JK |
55 | { |
56 | if (current->personality & ADDR_COMPAT_LAYOUT) | |
57 | return 1; | |
58 | ||
2854e72b | 59 | if (rlimit(RLIMIT_STACK) == RLIM_INFINITY) |
cc503c1b JK |
60 | return 1; |
61 | ||
62 | return sysctl_legacy_va_layout; | |
63 | } | |
64 | ||
675a0813 HH |
65 | static unsigned long mmap_rnd(void) |
66 | { | |
67 | unsigned long rnd = 0; | |
68 | ||
69 | /* | |
70 | * 8 bits of randomness in 32bit mmaps, 20 address space bits | |
71 | * 28 bits of randomness in 64bit mmaps, 40 address space bits | |
72 | */ | |
73 | if (current->flags & PF_RANDOMIZE) { | |
74 | if (mmap_is_ia32()) | |
75 | rnd = (long)get_random_int() % (1<<8); | |
76 | else | |
77 | rnd = (long)(get_random_int() % (1<<28)); | |
78 | } | |
79 | return rnd << PAGE_SHIFT; | |
80 | } | |
81 | ||
82 | static unsigned long mmap_base(void) | |
83 | { | |
2854e72b | 84 | unsigned long gap = rlimit(RLIMIT_STACK); |
675a0813 HH |
85 | |
86 | if (gap < MIN_GAP) | |
87 | gap = MIN_GAP; | |
88 | else if (gap > MAX_GAP) | |
89 | gap = MAX_GAP; | |
90 | ||
91 | return PAGE_ALIGN(TASK_SIZE - gap - mmap_rnd()); | |
92 | } | |
93 | ||
94 | /* | |
95 | * Bottom-up (legacy) layout on X86_32 did not support randomization, X86_64 | |
96 | * does, but not when emulating X86_32 | |
97 | */ | |
98 | static unsigned long mmap_legacy_base(void) | |
99 | { | |
100 | if (mmap_is_ia32()) | |
101 | return TASK_UNMAPPED_BASE; | |
102 | else | |
103 | return TASK_UNMAPPED_BASE + mmap_rnd(); | |
104 | } | |
105 | ||
cc503c1b JK |
106 | /* |
107 | * This function, called very early during the creation of a new | |
108 | * process VM image, sets up which VM layout function to use: | |
109 | */ | |
110 | void arch_pick_mmap_layout(struct mm_struct *mm) | |
111 | { | |
675a0813 HH |
112 | if (mmap_is_legacy()) { |
113 | mm->mmap_base = mmap_legacy_base(); | |
cc503c1b JK |
114 | mm->get_unmapped_area = arch_get_unmapped_area; |
115 | mm->unmap_area = arch_unmap_area; | |
116 | } else { | |
117 | mm->mmap_base = mmap_base(); | |
118 | mm->get_unmapped_area = arch_get_unmapped_area_topdown; | |
119 | mm->unmap_area = arch_unmap_area_topdown; | |
cc503c1b | 120 | } |
8817210d | 121 | } |