LXR linux/arch/powerpc/mm/mmap.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
  45static 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
  56unsigned long arch_mmap_rnd(void)
  57{
  58        unsigned long rnd;
  59
  60        /* 8MB for 32bit, 1GB for 64bit */
  61        if (is_32bit_task())
  62                rnd = (unsigned long)get_random_int() % (1<<(23-PAGE_SHIFT));
  63        else
  64                rnd = (unsigned long)get_random_int() % (1<<(30-PAGE_SHIFT));
  65
  66        return rnd << PAGE_SHIFT;
  67}
  68
  69static inline unsigned long mmap_base(unsigned long rnd)
  70{
  71        unsigned long gap = rlimit(RLIMIT_STACK);
  72
  73        if (gap < MIN_GAP)
  74                gap = MIN_GAP;
  75        else if (gap > MAX_GAP)
  76                gap = MAX_GAP;
  77
  78        return PAGE_ALIGN(TASK_SIZE - gap - rnd);
  79}
  80
  81/*
  82 * This function, called very early during the creation of a new
  83 * process VM image, sets up which VM layout function to use:
  84 */
  85void arch_pick_mmap_layout(struct mm_struct *mm)
  86{
  87        unsigned long random_factor = 0UL;
  88
  89        if (current->flags & PF_RANDOMIZE)
  90                random_factor = arch_mmap_rnd();
  91
  92        /*
  93         * Fall back to the standard layout if the personality
  94         * bit is set, or if the expected stack growth is unlimited:
  95         */
  96        if (mmap_is_legacy()) {
  97                mm->mmap_base = TASK_UNMAPPED_BASE;
  98                mm->get_unmapped_area = arch_get_unmapped_area;
  99        } else {
 100                mm->mmap_base = mmap_base(random_factor);
 101                mm->get_unmapped_area = arch_get_unmapped_area_topdown;
 102        }
 103}
 104