arch/powerpc/mm/mmap_64.c

   1 /*
   2  *  flexible mmap layout support
   3  *
   4  * Copyright 2003-2004 Red Hat Inc., Durham, North Carolina.
   5  * All Rights Reserved.
   6  *
   7  * This program is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License as published by
   9  * the Free Software Foundation; either version 2 of the License, or
  10  * (at your option) any later version.
  11  *
  12  * This program is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15  * GNU General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU General Public License
  18  * along with this program; if not, write to the Free Software
  19  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  20  *
  21  *
  22  * Started by Ingo Molnar <mingo@elte.hu>
  23  */
  24
  25 #include <linux/personality.h>
  26 #include <linux/mm.h>
  27 #include <linux/random.h>
  28 #include <linux/sched.h>
  29
  30 /*
  31  * Top of mmap area (just below the process stack).
  32  *
  33  * Leave at least a ~128 MB hole on 32bit applications.
  34  *
  35  * On 64bit applications we randomise the stack by 1GB so we need to
  36  * space our mmap start address by a further 1GB, otherwise there is a
  37  * chance the mmap area will end up closer to the stack than our ulimit
  38  * requires.
  39  */
  40 #define MIN_GAP32 (128*1024*1024)
  41 #define MIN_GAP64 ((128 + 1024)*1024*1024UL)
  42 #define MIN_GAP ((is_32bit_task()) ? MIN_GAP32 : MIN_GAP64)
  43 #define MAX_GAP (TASK_SIZE/6*5)
  44
  45 static inline int mmap_is_legacy(void)
  46 {
  47         if (current->personality & ADDR_COMPAT_LAYOUT)
  48                 return 1;
  49
  50         if (rlimit(RLIMIT_STACK) == RLIM_INFINITY)
  51                 return 1;
  52
  53         return sysctl_legacy_va_layout;
  54 }
  55
  56 /*
  57  * Since get_random_int() returns the same value within a 1 jiffy window,
  58  * we will almost always get the same randomisation for the stack and mmap
  59  * region. This will mean the relative distance between stack and mmap will
  60  * be the same.
  61  *
  62  * To avoid this we can shift the randomness by 1 bit.
  63  */
  64 static unsigned long mmap_rnd(void)
  65 {
  66         unsigned long rnd = 0;
  67
  68         if (current->flags & PF_RANDOMIZE) {
  69                 /* 8MB for 32bit, 1GB for 64bit */
  70                 if (is_32bit_task())
  71                         rnd = (long)(get_random_int() % (1<<(22-PAGE_SHIFT)));
  72                 else
  73                         rnd = (long)(get_random_int() % (1<<(29-PAGE_SHIFT)));
  74         }
  75         return (rnd << PAGE_SHIFT) * 2;
  76 }
  77
  78 static inline unsigned long mmap_base(void)
  79 {
  80         unsigned long gap = rlimit(RLIMIT_STACK);
  81
  82         if (gap < MIN_GAP)
  83                 gap = MIN_GAP;
  84         else if (gap > MAX_GAP)
  85                 gap = MAX_GAP;
  86
  87         return PAGE_ALIGN(TASK_SIZE - gap - mmap_rnd());
  88 }
  89
  90 /*
  91  * This function, called very early during the creation of a new
  92  * process VM image, sets up which VM layout function to use:
  93  */
  94 void arch_pick_mmap_layout(struct mm_struct *mm)
  95 {
  96         /*
  97          * Fall back to the standard layout if the personality
  98          * bit is set, or if the expected stack growth is unlimited:
  99          */
 100         if (mmap_is_legacy()) {
 101                 mm->mmap_base = TASK_UNMAPPED_BASE;
 102                 mm->get_unmapped_area = arch_get_unmapped_area;
 103                 mm->unmap_area = arch_unmap_area;
 104         } else {
 105                 mm->mmap_base = mmap_base();
 106                 mm->get_unmapped_area = arch_get_unmapped_area_topdown;
 107                 mm->unmap_area = arch_unmap_area_topdown;
 108         }
 109 }