projects / linux-2.6 / blame
| Commit | Line | Data |
|---|---|---|
| 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 | * | |
| 002b0ec7 AB |
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. | |
| 1da177e4 | 39 | */ |
| 002b0ec7 AB |
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) | |
| 1da177e4 LT |
43 | #define MAX_GAP (TASK_SIZE/6*5) |
| 44 | ||
| 13a2cb36 AB |
45 | static inline int mmap_is_legacy(void) |
| 46 | { | |
| 47 | if (current->personality & ADDR_COMPAT_LAYOUT) | |
| 48 | return 1; | |
| 49 | ||
| 50 | if (current->signal->rlim[RLIMIT_STACK].rlim_cur == RLIM_INFINITY) | |
| 51 | return 1; | |
| 52 | ||
| 53 | return sysctl_legacy_va_layout; | |
| 54 | } | |
| 55 | ||
| a5adc91a AB |
56 | /* |
| 57 | * Since get_random_int() returns the same value within a 1 jiffy window, | |
| 58 | * we will almost always get the same randomisation for the stack and mmap | |
| 59 | * region. This will mean the relative distance between stack and mmap will | |
| 60 | * be the same. | |
| 61 | * | |
| 62 | * To avoid this we can shift the randomness by 1 bit. | |
| 63 | */ | |
| 9f14c42d AB |
64 | static unsigned long mmap_rnd(void) |
| 65 | { | |
| 66 | unsigned long rnd = 0; | |
| 67 | ||
| 68 | if (current->flags & PF_RANDOMIZE) { | |
| 69 | /* 8MB for 32bit, 1GB for 64bit */ | |
| 70 | if (is_32bit_task()) | |
| a5adc91a | 71 | rnd = (long)(get_random_int() % (1<<(22-PAGE_SHIFT))); |
| 9f14c42d | 72 | else |
| a5adc91a | 73 | rnd = (long)(get_random_int() % (1<<(29-PAGE_SHIFT))); |
| 9f14c42d | 74 | } |
| a5adc91a | 75 | return (rnd << PAGE_SHIFT) * 2; |
| 9f14c42d AB |
76 | } |
| 77 | ||
| 1da177e4 LT |
78 | static inline unsigned long mmap_base(void) |
| 79 | { | |
| 80 | unsigned long gap = current->signal->rlim[RLIMIT_STACK].rlim_cur; | |
| 81 | ||
| 82 | if (gap < MIN_GAP) | |
| 83 | gap = MIN_GAP; | |
| 84 | else if (gap > MAX_GAP) | |
| 85 | gap = MAX_GAP; | |
| 86 | ||
| 9f14c42d | 87 | return PAGE_ALIGN(TASK_SIZE - gap - mmap_rnd()); |
| 1da177e4 LT |
88 | } |
| 89 | ||
| 1da177e4 LT |
90 | /* |
| 91 | * This function, called very early during the creation of a new | |
| 92 | * process VM image, sets up which VM layout function to use: | |
| 93 | */ | |
| 94 | void arch_pick_mmap_layout(struct mm_struct *mm) | |
| 95 | { | |
| 96 | /* | |
| 97 | * Fall back to the standard layout if the personality | |
| 98 | * bit is set, or if the expected stack growth is unlimited: | |
| 99 | */ | |
| 100 | if (mmap_is_legacy()) { | |
| 101 | mm->mmap_base = TASK_UNMAPPED_BASE; | |
| 102 | mm->get_unmapped_area = arch_get_unmapped_area; | |
| 103 | mm->unmap_area = arch_unmap_area; | |
| 104 | } else { | |
| 105 | mm->mmap_base = mmap_base(); | |
| 106 | mm->get_unmapped_area = arch_get_unmapped_area_topdown; | |
| 107 | mm->unmap_area = arch_unmap_area_topdown; | |
| 108 | } | |
| 109 | } |