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 <asm/elf.h>
  34
  35 struct va_alignment __read_mostly va_align = {
  36         .flags = -1,
  37 };
  38
  39 static unsigned long stack_maxrandom_size(void)
  40 {
  41         unsigned long max = 0;
  42         if ((current->flags & PF_RANDOMIZE) &&
  43                 !(current->personality & ADDR_NO_RANDOMIZE)) {
  44                 max = ((-1UL) & STACK_RND_MASK) << PAGE_SHIFT;
  45         }
  46
  47         return max;
  48 }
  49
  50 /*
  51  * Top of mmap area (just below the process stack).
  52  *
  53  * Leave an at least ~128 MB hole with possible stack randomization.
  54  */
  55 #define MIN_GAP (128*1024*1024UL + stack_maxrandom_size())
  56 #define MAX_GAP (TASK_SIZE/6*5)
  57
  58 static int mmap_is_legacy(void)
  59 {
  60         if (current->personality & ADDR_COMPAT_LAYOUT)
  61                 return 1;
  62
  63         if (rlimit(RLIMIT_STACK) == RLIM_INFINITY)
  64                 return 1;
  65
  66         return sysctl_legacy_va_layout;
  67 }
  68
  69 unsigned long arch_mmap_rnd(void)
  70 {
  71         unsigned long rnd;
  72
  73         if (mmap_is_ia32())
  74 #ifdef CONFIG_COMPAT
  75                 rnd = get_random_long() & ((1UL << mmap_rnd_compat_bits) - 1);
  76 #else
  77                 rnd = get_random_long() & ((1UL << mmap_rnd_bits) - 1);
  78 #endif
  79         else
  80                 rnd = get_random_long() & ((1UL << mmap_rnd_bits) - 1);
  81
  82         return rnd << PAGE_SHIFT;
  83 }
  84
  85 static unsigned long mmap_base(unsigned long rnd)
  86 {
  87         unsigned long gap = rlimit(RLIMIT_STACK);
  88
  89         if (gap < MIN_GAP)
  90                 gap = MIN_GAP;
  91         else if (gap > MAX_GAP)
  92                 gap = MAX_GAP;
  93
  94         return PAGE_ALIGN(TASK_SIZE - gap - rnd);
  95 }
  96
  97 /*
  98  * This function, called very early during the creation of a new
  99  * process VM image, sets up which VM layout function to use:
 100  */
 101 void arch_pick_mmap_layout(struct mm_struct *mm)
 102 {
 103         unsigned long random_factor = 0UL;
 104
 105         if (current->flags & PF_RANDOMIZE)
 106                 random_factor = arch_mmap_rnd();
 107
 108         mm->mmap_legacy_base = TASK_UNMAPPED_BASE + random_factor;
 109
 110         if (mmap_is_legacy()) {
 111                 mm->mmap_base = mm->mmap_legacy_base;
 112                 mm->get_unmapped_area = arch_get_unmapped_area;
 113         } else {
 114                 mm->mmap_base = mmap_base(random_factor);
 115                 mm->get_unmapped_area = arch_get_unmapped_area_topdown;
 116         }
 117 }
 118
 119 const char *arch_vma_name(struct vm_area_struct *vma)
 120 {
 121         if (vma->vm_flags & VM_MPX)
 122                 return "[mpx]";
 123         return NULL;
 124 }