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 <linux/compat.h> 34 #include <asm/elf.h> 35 36 struct va_alignment __read_mostly va_align = { 37 .flags = -1, 38 }; 39 40 unsigned long tasksize_32bit(void) 41 { 42 return IA32_PAGE_OFFSET; 43 } 44 45 unsigned long tasksize_64bit(void) 46 { 47 return TASK_SIZE_MAX; 48 } 49 50 static unsigned long stack_maxrandom_size(unsigned long task_size) 51 { 52 unsigned long max = 0; 53 if ((current->flags & PF_RANDOMIZE) && 54 !(current->personality & ADDR_NO_RANDOMIZE)) { 55 max = (-1UL) & __STACK_RND_MASK(task_size == tasksize_32bit()); 56 max <<= PAGE_SHIFT; 57 } 58 59 return max; 60 } 61 62 #ifdef CONFIG_COMPAT 63 # define mmap32_rnd_bits mmap_rnd_compat_bits 64 # define mmap64_rnd_bits mmap_rnd_bits 65 #else 66 # define mmap32_rnd_bits mmap_rnd_bits 67 # define mmap64_rnd_bits mmap_rnd_bits 68 #endif 69 70 #define SIZE_128M (128 * 1024 * 1024UL) 71 72 static int mmap_is_legacy(void) 73 { 74 if (current->personality & ADDR_COMPAT_LAYOUT) 75 return 1; 76 77 return sysctl_legacy_va_layout; 78 } 79 80 static unsigned long arch_rnd(unsigned int rndbits) 81 { 82 return (get_random_long() & ((1UL << rndbits) - 1)) << PAGE_SHIFT; 83 } 84 85 unsigned long arch_mmap_rnd(void) 86 { 87 if (!(current->flags & PF_RANDOMIZE)) 88 return 0; 89 return arch_rnd(mmap_is_ia32() ? mmap32_rnd_bits : mmap64_rnd_bits); 90 } 91 92 static unsigned long mmap_base(unsigned long rnd, unsigned long task_size) 93 { 94 unsigned long gap = rlimit(RLIMIT_STACK); 95 unsigned long gap_min, gap_max; 96 97 /* 98 * Top of mmap area (just below the process stack). 99 * Leave an at least ~128 MB hole with possible stack randomization. 100 */ 101 gap_min = SIZE_128M + stack_maxrandom_size(task_size); 102 gap_max = (task_size / 6) * 5; 103 104 if (gap < gap_min) 105 gap = gap_min; 106 else if (gap > gap_max) 107 gap = gap_max; 108 109 return PAGE_ALIGN(task_size - gap - rnd); 110 } 111 112 static unsigned long mmap_legacy_base(unsigned long rnd, 113 unsigned long task_size) 114 { 115 return __TASK_UNMAPPED_BASE(task_size) + rnd; 116 } 117 118 /* 119 * This function, called very early during the creation of a new 120 * process VM image, sets up which VM layout function to use: 121 */ 122 static void arch_pick_mmap_base(unsigned long *base, unsigned long *legacy_base, 123 unsigned long random_factor, unsigned long task_size) 124 { 125 *legacy_base = mmap_legacy_base(random_factor, task_size); 126 if (mmap_is_legacy()) 127 *base = *legacy_base; 128 else 129 *base = mmap_base(random_factor, task_size); 130 } 131 132 void arch_pick_mmap_layout(struct mm_struct *mm) 133 { 134 if (mmap_is_legacy()) 135 mm->get_unmapped_area = arch_get_unmapped_area; 136 else 137 mm->get_unmapped_area = arch_get_unmapped_area_topdown; 138 139 arch_pick_mmap_base(&mm->mmap_base, &mm->mmap_legacy_base, 140 arch_rnd(mmap64_rnd_bits), tasksize_64bit()); 141 142 #ifdef CONFIG_HAVE_ARCH_COMPAT_MMAP_BASES 143 /* 144 * The mmap syscall mapping base decision depends solely on the 145 * syscall type (64-bit or compat). This applies for 64bit 146 * applications and 32bit applications. The 64bit syscall uses 147 * mmap_base, the compat syscall uses mmap_compat_base. 148 */ 149 arch_pick_mmap_base(&mm->mmap_compat_base, &mm->mmap_compat_legacy_base, 150 arch_rnd(mmap32_rnd_bits), tasksize_32bit()); 151 #endif 152 } 153 154 unsigned long get_mmap_base(int is_legacy) 155 { 156 struct mm_struct *mm = current->mm; 157 158 #ifdef CONFIG_HAVE_ARCH_COMPAT_MMAP_BASES 159 if (in_compat_syscall()) { 160 return is_legacy ? mm->mmap_compat_legacy_base 161 : mm->mmap_compat_base; 162 } 163 #endif 164 return is_legacy ? mm->mmap_legacy_base : mm->mmap_base; 165 } 166 167 const char *arch_vma_name(struct vm_area_struct *vma) 168 { 169 if (vma->vm_flags & VM_MPX) 170 return "[mpx]"; 171 return NULL; 172 } 173