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/*
* linux/arch/x86-64/mm/mmap.c
*
* flexible mmap layout support
*
* Based on code by Ingo Molnar and Andi Kleen, copyrighted
* as follows:
*
* Copyright 2003-2004 Red Hat Inc., Durham, North Carolina.
* 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/ia32.h>
/*
* Top of mmap area (just below the process stack).
*
* Leave an at least ~128 MB hole.
*/
#define MIN_GAP (128*1024*1024)
#define MAX_GAP (TASK_SIZE/6*5)
static unsigned long mmap_base(void)
{
unsigned long gap = current->signal->rlim[RLIMIT_STACK].rlim_cur;
if (gap < MIN_GAP)
gap = MIN_GAP;
else if (gap > MAX_GAP)
gap = MAX_GAP;
return TASK_SIZE - (gap & PAGE_MASK);
}
static int mmap_is_32(void)
{
#ifdef CONFIG_IA32_EMULATION
if (test_thread_flag(TIF_IA32))
return 1;
#endif
return 0;
}
static int mmap_is_legacy(void)
{
if (current->personality & ADDR_COMPAT_LAYOUT)
return 1;
if (current->signal->rlim[RLIMIT_STACK].rlim_cur == RLIM_INFINITY)
return 1;
return sysctl_legacy_va_layout;
}
/*
* 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)
{
int rnd = 0;
if (current->flags & PF_RANDOMIZE) {
/*
* Add 28bit randomness which is about 40bits of address space
* because mmap base has to be page aligned.
* or ~1/128 of the total user VM
* (total user address space is 47bits)
*/
rnd = get_random_int() & 0xfffffff;
}
/*
* Fall back to the standard layout if the personality
* bit is set, or if the expected stack growth is unlimited:
*/
if (mmap_is_32()) {
#ifdef CONFIG_IA32_EMULATION
/* ia32_pick_mmap_layout has its own. */
return ia32_pick_mmap_layout(mm);
#endif
} else if (mmap_is_legacy()) {
mm->mmap_base = TASK_UNMAPPED_BASE;
mm->get_unmapped_area = arch_get_unmapped_area;
mm->unmap_area = arch_unmap_area;
} else {
mm->mmap_base = mmap_base();
mm->get_unmapped_area = arch_get_unmapped_area_topdown;
mm->unmap_area = arch_unmap_area_topdown;
if (current->flags & PF_RANDOMIZE)
rnd = -rnd;
}
if (current->flags & PF_RANDOMIZE)
mm->mmap_base += ((long)rnd) << PAGE_SHIFT;
}
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