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/*
* Copyright 2010 Tilera Corporation. 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, version 2.
*
* 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, GOOD TITLE or
* NON INFRINGEMENT. See the GNU General Public License for
* more details.
*
* Taken from the i386 architecture and simplified.
*/
#include <linux/mm.h>
#include <linux/random.h>
#include <linux/limits.h>
#include <linux/sched/signal.h>
#include <linux/sched/mm.h>
#include <linux/mman.h>
#include <linux/compat.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 inline unsigned long mmap_base(struct mm_struct *mm)
{
unsigned long gap = rlimit(RLIMIT_STACK);
unsigned long random_factor = 0;
if (current->flags & PF_RANDOMIZE)
random_factor = get_random_int() % (1024*1024);
if (gap < MIN_GAP)
gap = MIN_GAP;
else if (gap > MAX_GAP)
gap = MAX_GAP;
return PAGE_ALIGN(TASK_SIZE - gap - random_factor);
}
/*
* 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)
{
#if !defined(__tilegx__)
int is_32bit = 1;
#elif defined(CONFIG_COMPAT)
int is_32bit = is_compat_task();
#else
int is_32bit = 0;
#endif
unsigned long random_factor = 0UL;
/*
* 8 bits of randomness in 32bit mmaps, 24 address space bits
* 12 bits of randomness in 64bit mmaps, 28 address space bits
*/
if (current->flags & PF_RANDOMIZE) {
if (is_32bit)
random_factor = get_random_int() % (1<<8);
else
random_factor = get_random_int() % (1<<12);
random_factor <<= PAGE_SHIFT;
}
/*
* Use standard layout if the expected stack growth is unlimited
* or we are running native 64 bits.
*/
if (rlimit(RLIMIT_STACK) == RLIM_INFINITY) {
mm->mmap_base = TASK_UNMAPPED_BASE + random_factor;
mm->get_unmapped_area = arch_get_unmapped_area;
} else {
mm->mmap_base = mmap_base(mm);
mm->get_unmapped_area = arch_get_unmapped_area_topdown;
}
}
unsigned long arch_randomize_brk(struct mm_struct *mm)
{
return randomize_page(mm->brk, 0x02000000);
}
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