1 /* 2 * Flexible mmap layout support 3 * 4 * Based on code by Ingo Molnar and Andi Kleen, copyrighted 5 * as follows: 6 * 7 * Copyright 2003-2004 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 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 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) 40 41 /* 42 * True on X86_32 or when emulating IA32 on X86_64 43 */ 44 static int mmap_is_ia32(void) 45 { 46 #ifdef CONFIG_X86_32 47 return 1; 48 #endif 49 #ifdef CONFIG_IA32_EMULATION 50 if (test_thread_flag(TIF_IA32)) 51 return 1; 52 #endif 53 return 0; 54 } 55 56 static int mmap_is_legacy(void) 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 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 } 107 108 /* 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 { 114 if (mmap_is_legacy()) { 115 mm->mmap_base = mmap_legacy_base(); 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; 122 } 123 } 124