arch/x86/mm/mmap.c

   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 }