1 /* 2 * Flexible mmap layout support 3 * 4 * Based on code by Ingo Molnar and Andi Kleen, copyrighted 5 * as follows: 6 * 7 * Copyright 2003-2009 Red Hat Inc. 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 25 */ 26 27 #include <linux/personality.h> 28 #include <linux/mm.h> 29 #include <linux/random.h> 30 #include <linux/limits.h> 31 #include <linux/sched.h> 32 #include <asm/elf.h> 33 34 struct va_alignment __read_mostly va_align = { 35 .flags = -1, 36 }; 37 38 static unsigned int stack_maxrandom_size(void) 39 { 40 unsigned int max = 0; 41 if ((current->flags & PF_RANDOMIZE) && 42 !(current->personality & ADDR_NO_RANDOMIZE)) { 43 max = ((-1U) & STACK_RND_MASK) << PAGE_SHIFT; 44 } 45 46 return max; 47 } 48 49 /* 50 * Top of mmap area (just below the process stack). 51 * 52 * Leave an at least ~128 MB hole with possible stack randomization. 53 */ 54 #define MIN_GAP (128*1024*1024UL + stack_maxrandom_size()) 55 #define MAX_GAP (TASK_SIZE/6*5) 56 57 static int mmap_is_legacy(void) 58 { 59 if (current->personality & ADDR_COMPAT_LAYOUT) 60 return 1; 61 62 if (rlimit(RLIMIT_STACK) == RLIM_INFINITY) 63 return 1; 64 65 return sysctl_legacy_va_layout; 66 } 67 68 static unsigned long mmap_rnd(void) 69 { 70 unsigned long rnd = 0; 71 72 /* 73 * 8 bits of randomness in 32bit mmaps, 20 address space bits 74 * 28 bits of randomness in 64bit mmaps, 40 address space bits 75 */ 76 if (current->flags & PF_RANDOMIZE) { 77 if (mmap_is_ia32()) 78 rnd = get_random_int() % (1<<8); 79 else 80 rnd = get_random_int() % (1<<28); 81 } 82 return rnd << PAGE_SHIFT; 83 } 84 85 static unsigned long mmap_base(void) 86 { 87 unsigned long gap = rlimit(RLIMIT_STACK); 88 89 if (gap < MIN_GAP) 90 gap = MIN_GAP; 91 else if (gap > MAX_GAP) 92 gap = MAX_GAP; 93 94 return PAGE_ALIGN(TASK_SIZE - gap - mmap_rnd()); 95 } 96 97 /* 98 * Bottom-up (legacy) layout on X86_32 did not support randomization, X86_64 99 * does, but not when emulating X86_32 100 */ 101 static unsigned long mmap_legacy_base(void) 102 { 103 if (mmap_is_ia32()) 104 return TASK_UNMAPPED_BASE; 105 else 106 return TASK_UNMAPPED_BASE + mmap_rnd(); 107 } 108 109 /* 110 * This function, called very early during the creation of a new 111 * process VM image, sets up which VM layout function to use: 112 */ 113 void arch_pick_mmap_layout(struct mm_struct *mm) 114 { 115 mm->mmap_legacy_base = mmap_legacy_base(); 116 mm->mmap_base = mmap_base(); 117 118 if (mmap_is_legacy()) { 119 mm->mmap_base = mm->mmap_legacy_base; 120 mm->get_unmapped_area = arch_get_unmapped_area; 121 } else { 122 mm->get_unmapped_area = arch_get_unmapped_area_topdown; 123 } 124 } 125