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 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 45 46 /* 47 * Top of mmap area (just below the process stack). 48 * 49 * Leave an at least ~128 MB hole with possible stack randomization. 50 */ 51 #define MIN_GAP (128*1024*1024UL + stack_maxrandom_size()) 52 #define MAX_GAP (TASK_SIZE/6*5) 53 54 /* 55 * True on X86_32 or when emulating IA32 on X86_64 56 */ 57 static int mmap_is_ia32(void) 58 { 59 #ifdef CONFIG_X86_32 60 return 1; 61 #endif 62 #ifdef CONFIG_IA32_EMULATION 63 if (test_thread_flag(TIF_IA32)) 64 return 1; 65 #endif 66 return 0; 67 } 68 69 static int mmap_is_legacy(void) 70 { 71 if (current->personality & ADDR_COMPAT_LAYOUT) 72 return 1; 73 74 if (rlimit(RLIMIT_STACK) == RLIM_INFINITY) 75 return 1; 76 77 return sysctl_legacy_va_layout; 78 } 79 80 static unsigned long mmap_rnd(void) 81 { 82 unsigned long rnd = 0; 83 84 /* 85 * 8 bits of randomness in 32bit mmaps, 20 address space bits 86 * 28 bits of randomness in 64bit mmaps, 40 address space bits 87 */ 88 if (current->flags & PF_RANDOMIZE) { 89 if (mmap_is_ia32()) 90 rnd = (long)get_random_int() % (1<<8); 91 else 92 rnd = (long)(get_random_int() % (1<<28)); 93 } 94 return rnd << PAGE_SHIFT; 95 } 96 97 static unsigned long mmap_base(void) 98 { 99 unsigned long gap = rlimit(RLIMIT_STACK); 100 101 if (gap < MIN_GAP) 102 gap = MIN_GAP; 103 else if (gap > MAX_GAP) 104 gap = MAX_GAP; 105 106 return PAGE_ALIGN(TASK_SIZE - gap - mmap_rnd()); 107 } 108 109 /* 110 * Bottom-up (legacy) layout on X86_32 did not support randomization, X86_64 111 * does, but not when emulating X86_32 112 */ 113 static unsigned long mmap_legacy_base(void) 114 { 115 if (mmap_is_ia32()) 116 return TASK_UNMAPPED_BASE; 117 else 118 return TASK_UNMAPPED_BASE + mmap_rnd(); 119 } 120 121 /* 122 * This function, called very early during the creation of a new 123 * process VM image, sets up which VM layout function to use: 124 */ 125 void arch_pick_mmap_layout(struct mm_struct *mm) 126 { 127 if (mmap_is_legacy()) { 128 mm->mmap_base = mmap_legacy_base(); 129 mm->get_unmapped_area = arch_get_unmapped_area; 130 mm->unmap_area = arch_unmap_area; 131 } else { 132 mm->mmap_base = mmap_base(); 133 mm->get_unmapped_area = arch_get_unmapped_area_topdown; 134 mm->unmap_area = arch_unmap_area_topdown; 135 } 136 } 137