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                 max = (-1UL) & __STACK_RND_MASK(task_size == tasksize_32bit());
  55                 max <<= PAGE_SHIFT;
  56         }
  57
  58         return max;
  59 }
  60
  61 #ifdef CONFIG_COMPAT
  62 # define mmap32_rnd_bits  mmap_rnd_compat_bits
  63 # define mmap64_rnd_bits  mmap_rnd_bits
  64 #else
  65 # define mmap32_rnd_bits  mmap_rnd_bits
  66 # define mmap64_rnd_bits  mmap_rnd_bits
  67 #endif
  68
  69 #define SIZE_128M    (128 * 1024 * 1024UL)
  70
  71 static int mmap_is_legacy(void)
  72 {
  73         if (current->personality & ADDR_COMPAT_LAYOUT)
  74                 return 1;
  75
  76         return sysctl_legacy_va_layout;
  77 }
  78
  79 static unsigned long arch_rnd(unsigned int rndbits)
  80 {
  81         if (!(current->flags & PF_RANDOMIZE))
  82                 return 0;
  83         return (get_random_long() & ((1UL << rndbits) - 1)) << PAGE_SHIFT;
  84 }
  85
  86 unsigned long arch_mmap_rnd(void)
  87 {
  88         return arch_rnd(mmap_is_ia32() ? mmap32_rnd_bits : mmap64_rnd_bits);
  89 }
  90
  91 static unsigned long mmap_base(unsigned long rnd, unsigned long task_size)
  92 {
  93         unsigned long gap = rlimit(RLIMIT_STACK);
  94         unsigned long pad = stack_maxrandom_size(task_size) + stack_guard_gap;
  95         unsigned long gap_min, gap_max;
  96
  97         /* Values close to RLIM_INFINITY can overflow. */
  98         if (gap + pad > gap)
  99                 gap += pad;
 100
 101         /*
 102          * Top of mmap area (just below the process stack).
 103          * Leave an at least ~128 MB hole with possible stack randomization.
 104          */
 105         gap_min = SIZE_128M;
 106         gap_max = (task_size / 6) * 5;
 107
 108         if (gap < gap_min)
 109                 gap = gap_min;
 110         else if (gap > gap_max)
 111                 gap = gap_max;
 112
 113         return PAGE_ALIGN(task_size - gap - rnd);
 114 }
 115
 116 static unsigned long mmap_legacy_base(unsigned long rnd,
 117                                       unsigned long task_size)
 118 {
 119         return __TASK_UNMAPPED_BASE(task_size) + rnd;
 120 }
 121
 122 /*
 123  * This function, called very early during the creation of a new
 124  * process VM image, sets up which VM layout function to use:
 125  */
 126 static void arch_pick_mmap_base(unsigned long *base, unsigned long *legacy_base,
 127                 unsigned long random_factor, unsigned long task_size)
 128 {
 129         *legacy_base = mmap_legacy_base(random_factor, task_size);
 130         if (mmap_is_legacy())
 131                 *base = *legacy_base;
 132         else
 133                 *base = mmap_base(random_factor, task_size);
 134 }
 135
 136 void arch_pick_mmap_layout(struct mm_struct *mm)
 137 {
 138         if (mmap_is_legacy())
 139                 mm->get_unmapped_area = arch_get_unmapped_area;
 140         else
 141                 mm->get_unmapped_area = arch_get_unmapped_area_topdown;
 142
 143         arch_pick_mmap_base(&mm->mmap_base, &mm->mmap_legacy_base,
 144                         arch_rnd(mmap64_rnd_bits), tasksize_64bit());
 145
 146 #ifdef CONFIG_HAVE_ARCH_COMPAT_MMAP_BASES
 147         /*
 148          * The mmap syscall mapping base decision depends solely on the
 149          * syscall type (64-bit or compat). This applies for 64bit
 150          * applications and 32bit applications. The 64bit syscall uses
 151          * mmap_base, the compat syscall uses mmap_compat_base.
 152          */
 153         arch_pick_mmap_base(&mm->mmap_compat_base, &mm->mmap_compat_legacy_base,
 154                         arch_rnd(mmap32_rnd_bits), tasksize_32bit());
 155 #endif
 156 }
 157
 158 unsigned long get_mmap_base(int is_legacy)
 159 {
 160         struct mm_struct *mm = current->mm;
 161
 162 #ifdef CONFIG_HAVE_ARCH_COMPAT_MMAP_BASES
 163         if (in_compat_syscall()) {
 164                 return is_legacy ? mm->mmap_compat_legacy_base
 165                                  : mm->mmap_compat_base;
 166         }
 167 #endif
 168         return is_legacy ? mm->mmap_legacy_base : mm->mmap_base;
 169 }
 170
 171 const char *arch_vma_name(struct vm_area_struct *vma)
 172 {
 173         if (vma->vm_flags & VM_MPX)
 174                 return "[mpx]";
 175         return NULL;
 176 }