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         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 }