arch/tile/mm/mmap.c

   1 /*
   2  * Copyright 2010 Tilera Corporation. All Rights Reserved.
   3  *
   4  *   This program is free software; you can redistribute it and/or
   5  *   modify it under the terms of the GNU General Public License
   6  *   as published by the Free Software Foundation, version 2.
   7  *
   8  *   This program is distributed in the hope that it will be useful, but
   9  *   WITHOUT ANY WARRANTY; without even the implied warranty of
  10  *   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
  11  *   NON INFRINGEMENT.  See the GNU General Public License for
  12  *   more details.
  13  *
  14  * Taken from the i386 architecture and simplified.
  15  */
  16
  17 #include <linux/mm.h>
  18 #include <linux/random.h>
  19 #include <linux/limits.h>
  20 #include <linux/sched.h>
  21 #include <linux/mman.h>
  22 #include <linux/compat.h>
  23
  24 /*
  25  * Top of mmap area (just below the process stack).
  26  *
  27  * Leave an at least ~128 MB hole.
  28  */
  29 #define MIN_GAP (128*1024*1024)
  30 #define MAX_GAP (TASK_SIZE/6*5)
  31
  32 static inline unsigned long mmap_base(struct mm_struct *mm)
  33 {
  34         unsigned long gap = rlimit(RLIMIT_STACK);
  35         unsigned long random_factor = 0;
  36
  37         if (current->flags & PF_RANDOMIZE)
  38                 random_factor = get_random_int() % (1024*1024);
  39
  40         if (gap < MIN_GAP)
  41                 gap = MIN_GAP;
  42         else if (gap > MAX_GAP)
  43                 gap = MAX_GAP;
  44
  45         return PAGE_ALIGN(TASK_SIZE - gap - random_factor);
  46 }
  47
  48 /*
  49  * This function, called very early during the creation of a new
  50  * process VM image, sets up which VM layout function to use:
  51  */
  52 void arch_pick_mmap_layout(struct mm_struct *mm)
  53 {
  54 #if !defined(__tilegx__)
  55         int is_32bit = 1;
  56 #elif defined(CONFIG_COMPAT)
  57         int is_32bit = is_compat_task();
  58 #else
  59         int is_32bit = 0;
  60 #endif
  61         unsigned long random_factor = 0UL;
  62
  63         /*
  64          *  8 bits of randomness in 32bit mmaps, 24 address space bits
  65          * 12 bits of randomness in 64bit mmaps, 28 address space bits
  66          */
  67         if (current->flags & PF_RANDOMIZE) {
  68                 if (is_32bit)
  69                         random_factor = get_random_int() % (1<<8);
  70                 else
  71                         random_factor = get_random_int() % (1<<12);
  72
  73                 random_factor <<= PAGE_SHIFT;
  74         }
  75
  76         /*
  77          * Use standard layout if the expected stack growth is unlimited
  78          * or we are running native 64 bits.
  79          */
  80         if (rlimit(RLIMIT_STACK) == RLIM_INFINITY) {
  81                 mm->mmap_base = TASK_UNMAPPED_BASE + random_factor;
  82                 mm->get_unmapped_area = arch_get_unmapped_area;
  83         } else {
  84                 mm->mmap_base = mmap_base(mm);
  85                 mm->get_unmapped_area = arch_get_unmapped_area_topdown;
  86         }
  87 }
  88
  89 unsigned long arch_randomize_brk(struct mm_struct *mm)
  90 {
  91         return randomize_page(mm->brk, 0x02000000);
  92 }