Commit | Line | Data |
---|---|---|
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 | * | |
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 | |
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> | |
8817210d | 32 | |
cc503c1b JK |
33 | /* |
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) | |
8817210d | 40 | |
675a0813 HH |
41 | /* |
42 | * True on X86_32 or when emulating IA32 on X86_64 | |
43 | */ | |
44 | static int mmap_is_ia32(void) | |
8817210d | 45 | { |
675a0813 HH |
46 | #ifdef CONFIG_X86_32 |
47 | return 1; | |
48 | #endif | |
8817210d | 49 | #ifdef CONFIG_IA32_EMULATION |
cc503c1b JK |
50 | if (test_thread_flag(TIF_IA32)) |
51 | return 1; | |
8817210d | 52 | #endif |
cc503c1b JK |
53 | return 0; |
54 | } | |
55 | ||
954683a2 | 56 | static int mmap_is_legacy(void) |
cc503c1b JK |
57 | { |
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 | ||
675a0813 HH |
67 | static 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 | ||
84 | static 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 | */ | |
100 | static 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 | ||
cc503c1b JK |
108 | /* |
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 | */ | |
112 | void arch_pick_mmap_layout(struct mm_struct *mm) | |
113 | { | |
675a0813 HH |
114 | if (mmap_is_legacy()) { |
115 | mm->mmap_base = mmap_legacy_base(); | |
cc503c1b JK |
116 | 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; | |
cc503c1b | 122 | } |
8817210d | 123 | } |