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/signal.h> 32 #include <linux/sched/mm.h> 33 #include <asm/elf.h> 34 35 struct va_alignment __read_mostly va_align = { 36 .flags = -1, 37 }; 38 39 static unsigned long stack_maxrandom_size(void) 40 { 41 unsigned long max = 0; 42 if ((current->flags & PF_RANDOMIZE) && 43 !(current->personality & ADDR_NO_RANDOMIZE)) { 44 max = ((-1UL) & STACK_RND_MASK) << PAGE_SHIFT; 45 } 46 47 return max; 48 } 49 50 /* 51 * Top of mmap area (just below the process stack). 52 * 53 * Leave an at least ~128 MB hole with possible stack randomization. 54 */ 55 #define MIN_GAP (128*1024*1024UL + stack_maxrandom_size()) 56 #define MAX_GAP (TASK_SIZE/6*5) 57 58 static int mmap_is_legacy(void) 59 { 60 if (current->personality & ADDR_COMPAT_LAYOUT) 61 return 1; 62 63 if (rlimit(RLIMIT_STACK) == RLIM_INFINITY) 64 return 1; 65 66 return sysctl_legacy_va_layout; 67 } 68 69 unsigned long arch_mmap_rnd(void) 70 { 71 unsigned long rnd; 72 73 if (mmap_is_ia32()) 74 #ifdef CONFIG_COMPAT 75 rnd = get_random_long() & ((1UL << mmap_rnd_compat_bits) - 1); 76 #else 77 rnd = get_random_long() & ((1UL << mmap_rnd_bits) - 1); 78 #endif 79 else 80 rnd = get_random_long() & ((1UL << mmap_rnd_bits) - 1); 81 82 return rnd << PAGE_SHIFT; 83 } 84 85 static unsigned long mmap_base(unsigned long rnd) 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 - rnd); 95 } 96 97 /* 98 * This function, called very early during the creation of a new 99 * process VM image, sets up which VM layout function to use: 100 */ 101 void arch_pick_mmap_layout(struct mm_struct *mm) 102 { 103 unsigned long random_factor = 0UL; 104 105 if (current->flags & PF_RANDOMIZE) 106 random_factor = arch_mmap_rnd(); 107 108 mm->mmap_legacy_base = TASK_UNMAPPED_BASE + random_factor; 109 110 if (mmap_is_legacy()) { 111 mm->mmap_base = mm->mmap_legacy_base; 112 mm->get_unmapped_area = arch_get_unmapped_area; 113 } else { 114 mm->mmap_base = mmap_base(random_factor); 115 mm->get_unmapped_area = arch_get_unmapped_area_topdown; 116 } 117 } 118 119 const char *arch_vma_name(struct vm_area_struct *vma) 120 { 121 if (vma->vm_flags & VM_MPX) 122 return "[mpx]"; 123 return NULL; 124 } 125