/*
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* Copyright 2010 Tilera Corporation. All Rights Reserved.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation, version 2.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
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* NON INFRINGEMENT. See the GNU General Public License for
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* more details.
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*
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* Taken from the i386 architecture and simplified.
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*/
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#include <linux/mm.h>
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#include <linux/random.h>
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#include <linux/limits.h>
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#include <linux/sched.h>
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#include <linux/mman.h>
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#include <linux/compat.h>
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/*
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* Top of mmap area (just below the process stack).
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*
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* Leave an at least ~128 MB hole.
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*/
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#define MIN_GAP (128*1024*1024)
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#define MAX_GAP (TASK_SIZE/6*5)
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static inline unsigned long mmap_base(struct mm_struct *mm)
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{
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unsigned long gap = rlimit(RLIMIT_STACK);
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unsigned long random_factor = 0;
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if (current->flags & PF_RANDOMIZE)
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random_factor = get_random_int() % (1024*1024);
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if (gap < MIN_GAP)
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gap = MIN_GAP;
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else if (gap > MAX_GAP)
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gap = MAX_GAP;
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return PAGE_ALIGN(TASK_SIZE - gap - random_factor);
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}
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/*
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* This function, called very early during the creation of a new
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* process VM image, sets up which VM layout function to use:
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*/
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void arch_pick_mmap_layout(struct mm_struct *mm)
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{
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#if !defined(__tilegx__)
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int is_32bit = 1;
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#elif defined(CONFIG_COMPAT)
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int is_32bit = is_compat_task();
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#else
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int is_32bit = 0;
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#endif
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unsigned long random_factor = 0UL;
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/*
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* 8 bits of randomness in 32bit mmaps, 24 address space bits
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* 12 bits of randomness in 64bit mmaps, 28 address space bits
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*/
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if (current->flags & PF_RANDOMIZE) {
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if (is_32bit)
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random_factor = get_random_int() % (1<<8);
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else
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random_factor = get_random_int() % (1<<12);
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random_factor <<= PAGE_SHIFT;
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}
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/*
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* Use standard layout if the expected stack growth is unlimited
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* or we are running native 64 bits.
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*/
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if (rlimit(RLIMIT_STACK) == RLIM_INFINITY) {
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mm->mmap_base = TASK_UNMAPPED_BASE + random_factor;
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mm->get_unmapped_area = arch_get_unmapped_area;
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} else {
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mm->mmap_base = mmap_base(mm);
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mm->get_unmapped_area = arch_get_unmapped_area_topdown;
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}
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}
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unsigned long arch_randomize_brk(struct mm_struct *mm)
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{
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return randomize_page(mm->brk, 0x02000000);
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}
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