/*
   * Flexible mmap layout support
   *
   * Based on code by Ingo Molnar and Andi Kleen, copyrighted
   * as follows:
   *
   * Copyright 2003-2009 Red Hat Inc.
   * All Rights Reserved.
   * Copyright 2005 Andi Kleen, SUSE Labs.
   * Copyright 2007 Jiri Kosina, SUSE Labs.
   *
   * This program is free software; you can redistribute it and/or modify
   * it under the terms of the GNU General Public License as published by
   * the Free Software Foundation; either version 2 of the License, or
   * (at your option) any later version.
   *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with this program; if not, write to the Free Software
   * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
   */
  
  #include <linux/personality.h>
  #include <linux/mm.h>
  #include <linux/random.h>
  #include <linux/limits.h>
  #include <linux/sched.h>
  #include <asm/elf.h>
  
  struct __read_mostly va_alignment va_align = {
  	.flags = -1,
  };
  
  static unsigned int stack_maxrandom_size(void)
  {
  	unsigned int max = 0;
  	if ((current->flags & PF_RANDOMIZE) &&
  		!(current->personality & ADDR_NO_RANDOMIZE)) {
  		max = ((-1U) & STACK_RND_MASK) << PAGE_SHIFT;
  	}
  
  	return max;
  }
  
  /*
   * Top of mmap area (just below the process stack).
   *
   * Leave an at least ~128 MB hole with possible stack randomization.
   */
  #define MIN_GAP (128*1024*1024UL + stack_maxrandom_size())
  #define MAX_GAP (TASK_SIZE/6*5)
  
  static int mmap_is_legacy(void)
  {
  	if (current->personality & ADDR_COMPAT_LAYOUT)
  		return 1;
  
  	if (rlimit(RLIMIT_STACK) == RLIM_INFINITY)
  		return 1;
  
  	return sysctl_legacy_va_layout;
  }
  
  static unsigned long mmap_rnd(void)
  {
  	unsigned long rnd = 0;
  
  	/*
  	*  8 bits of randomness in 32bit mmaps, 20 address space bits
  	* 28 bits of randomness in 64bit mmaps, 40 address space bits
  	*/
  	if (current->flags & PF_RANDOMIZE) {
  		if (mmap_is_ia32())
  			rnd = get_random_int() % (1<<8);
  		else
  			rnd = get_random_int() % (1<<28);
  	}
  	return rnd << PAGE_SHIFT;
  }
  
  static unsigned long mmap_base(void)
  {
  	unsigned long gap = rlimit(RLIMIT_STACK);
  
  	if (gap < MIN_GAP)
  		gap = MIN_GAP;
  	else if (gap > MAX_GAP)
  		gap = MAX_GAP;
  
  	return PAGE_ALIGN(TASK_SIZE - gap - mmap_rnd());
  }
  
  /*
   * Bottom-up (legacy) layout on X86_32 did not support randomization, X86_64
   * does, but not when emulating X86_32
   */
  static unsigned long mmap_legacy_base(void)
  {
  	if (mmap_is_ia32())
  		return TASK_UNMAPPED_BASE;
  	else
  		return TASK_UNMAPPED_BASE + mmap_rnd();
  }
  
  /*
   * This function, called very early during the creation of a new
   * process VM image, sets up which VM layout function to use:
   */
  void arch_pick_mmap_layout(struct mm_struct *mm)
  {
  	mm->mmap_legacy_base = mmap_legacy_base();
  	mm->mmap_base = mmap_base();
  
  	if (mmap_is_legacy()) {
  		mm->mmap_base = mm->mmap_legacy_base;
  		mm->get_unmapped_area = arch_get_unmapped_area;
  	} else {
  		mm->get_unmapped_area = arch_get_unmapped_area_topdown;
  	}
  }