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 if (rlimit(RLIMIT_STACK) == RLIM_INFINITY) 78 return 1; 79 80 return sysctl_legacy_va_layout; 81 } 82 83 static unsigned long arch_rnd(unsigned int rndbits) 84 { 85 return (get_random_long() & ((1UL << rndbits) - 1)) << PAGE_SHIFT; 86 } 87 88 unsigned long arch_mmap_rnd(void) 89 { 90 if (!(current->flags & PF_RANDOMIZE)) 91 return 0; 92 return arch_rnd(mmap_is_ia32() ? mmap32_rnd_bits : mmap64_rnd_bits); 93 } 94 95 static unsigned long mmap_base(unsigned long rnd, unsigned long task_size) 96 { 97 unsigned long gap = rlimit(RLIMIT_STACK); 98 unsigned long gap_min, gap_max; 99 100 /* 101 * Top of mmap area (just below the process stack). 102 * Leave an at least ~128 MB hole with possible stack randomization. 103 */ 104 gap_min = SIZE_128M + stack_maxrandom_size(task_size); 105 gap_max = (task_size / 6) * 5; 106 107 if (gap < gap_min) 108 gap = gap_min; 109 else if (gap > gap_max) 110 gap = gap_max; 111 112 return PAGE_ALIGN(task_size - gap - rnd); 113 } 114 115 static unsigned long mmap_legacy_base(unsigned long rnd, 116 unsigned long task_size) 117 { 118 return __TASK_UNMAPPED_BASE(task_size) + 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 static void arch_pick_mmap_base(unsigned long *base, unsigned long *legacy_base, 126 unsigned long random_factor, unsigned long task_size) 127 { 128 *legacy_base = mmap_legacy_base(random_factor, task_size); 129 if (mmap_is_legacy()) 130 *base = *legacy_base; 131 else 132 *base = mmap_base(random_factor, task_size); 133 } 134 135 void arch_pick_mmap_layout(struct mm_struct *mm) 136 { 137 if (mmap_is_legacy()) 138 mm->get_unmapped_area = arch_get_unmapped_area; 139 else 140 mm->get_unmapped_area = arch_get_unmapped_area_topdown; 141 142 arch_pick_mmap_base(&mm->mmap_base, &mm->mmap_legacy_base, 143 arch_rnd(mmap64_rnd_bits), tasksize_64bit()); 144 145 #ifdef CONFIG_HAVE_ARCH_COMPAT_MMAP_BASES 146 /* 147 * The mmap syscall mapping base decision depends solely on the 148 * syscall type (64-bit or compat). This applies for 64bit 149 * applications and 32bit applications. The 64bit syscall uses 150 * mmap_base, the compat syscall uses mmap_compat_base. 151 */ 152 arch_pick_mmap_base(&mm->mmap_compat_base, &mm->mmap_compat_legacy_base, 153 arch_rnd(mmap32_rnd_bits), tasksize_32bit()); 154 #endif 155 } 156 157 unsigned long get_mmap_base(int is_legacy) 158 { 159 struct mm_struct *mm = current->mm; 160 161 #ifdef CONFIG_HAVE_ARCH_COMPAT_MMAP_BASES 162 if (in_compat_syscall()) { 163 return is_legacy ? mm->mmap_compat_legacy_base 164 : mm->mmap_compat_base; 165 } 166 #endif 167 return is_legacy ? mm->mmap_legacy_base : mm->mmap_base; 168 } 169 170 const char *arch_vma_name(struct vm_area_struct *vma) 171 { 172 if (vma->vm_flags & VM_MPX) 173 return "[mpx]"; 174 return NULL; 175 } 176