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/*
* flexible mmap layout support
*
* Copyright 2003-2004 Red Hat Inc., Durham, North Carolina.
* All Rights Reserved.
*
* 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
*
*
* Started by Ingo Molnar <mingo@elte.hu>
*/
#include <linux/personality.h>
#include <linux/mm.h>
#include <linux/random.h>
#include <linux/sched.h>
/*
* Top of mmap area (just below the process stack).
*
* Leave at least a ~128 MB hole on 32bit applications.
*
* On 64bit applications we randomise the stack by 1GB so we need to
* space our mmap start address by a further 1GB, otherwise there is a
* chance the mmap area will end up closer to the stack than our ulimit
* requires.
*/
#define MIN_GAP32 (128*1024*1024)
#define MIN_GAP64 ((128 + 1024)*1024*1024UL)
#define MIN_GAP ((is_32bit_task()) ? MIN_GAP32 : MIN_GAP64)
#define MAX_GAP (TASK_SIZE/6*5)
static inline 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;
}
/*
* Since get_random_int() returns the same value within a 1 jiffy window,
* we will almost always get the same randomisation for the stack and mmap
* region. This will mean the relative distance between stack and mmap will
* be the same.
*
* To avoid this we can shift the randomness by 1 bit.
*/
static unsigned long mmap_rnd(void)
{
unsigned long rnd = 0;
if (current->flags & PF_RANDOMIZE) {
/* 8MB for 32bit, 1GB for 64bit */
if (is_32bit_task())
rnd = (long)(get_random_int() % (1<<(22-PAGE_SHIFT)));
else
rnd = (long)(get_random_int() % (1<<(29-PAGE_SHIFT)));
}
return (rnd << PAGE_SHIFT) * 2;
}
static inline 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 PAGE_ALIGN(TASK_SIZE - gap - 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)
{
/*
* Fall back to the standard layout if the personality
* bit is set, or if the expected stack growth is unlimited:
*/
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;
}
}
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