1/*
2 * Copyright 2010 Tilera Corporation. All Rights Reserved.
3 *
4 *   This program is free software; you can redistribute it and/or
5 *   modify it under the terms of the GNU General Public License
6 *   as published by the Free Software Foundation, version 2.
7 *
8 *   This program is distributed in the hope that it will be useful, but
9 *   WITHOUT ANY WARRANTY; without even the implied warranty of
10 *   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
11 *   NON INFRINGEMENT.  See the GNU General Public License for
12 *   more details.
13 *
14 * Taken from the i386 architecture and simplified.
15 */
16
17#include <linux/mm.h>
18#include <linux/random.h>
19#include <linux/limits.h>
20#include <linux/sched.h>
21#include <linux/mman.h>
22#include <linux/compat.h>
23
24/*
25 * Top of mmap area (just below the process stack).
26 *
27 * Leave an at least ~128 MB hole.
28 */
29#define MIN_GAP (128*1024*1024)
30#define MAX_GAP (TASK_SIZE/6*5)
31
32static inline unsigned long mmap_base(struct mm_struct *mm)
33{
34	unsigned long gap = rlimit(RLIMIT_STACK);
35	unsigned long random_factor = 0;
36
37	if (current->flags & PF_RANDOMIZE)
38		random_factor = get_random_int() % (1024*1024);
39
40	if (gap < MIN_GAP)
41		gap = MIN_GAP;
42	else if (gap > MAX_GAP)
43		gap = MAX_GAP;
44
45	return PAGE_ALIGN(TASK_SIZE - gap - random_factor);
46}
47
48/*
49 * This function, called very early during the creation of a new
50 * process VM image, sets up which VM layout function to use:
51 */
52void arch_pick_mmap_layout(struct mm_struct *mm)
53{
54#if !defined(__tilegx__)
55	int is_32bit = 1;
56#elif defined(CONFIG_COMPAT)
57	int is_32bit = is_compat_task();
58#else
59	int is_32bit = 0;
60#endif
61	unsigned long random_factor = 0UL;
62
63	/*
64	 *  8 bits of randomness in 32bit mmaps, 24 address space bits
65	 * 12 bits of randomness in 64bit mmaps, 28 address space bits
66	 */
67	if (current->flags & PF_RANDOMIZE) {
68		if (is_32bit)
69			random_factor = get_random_int() % (1<<8);
70		else
71			random_factor = get_random_int() % (1<<12);
72
73		random_factor <<= PAGE_SHIFT;
74	}
75
76	/*
77	 * Use standard layout if the expected stack growth is unlimited
78	 * or we are running native 64 bits.
79	 */
80	if (rlimit(RLIMIT_STACK) == RLIM_INFINITY) {
81		mm->mmap_base = TASK_UNMAPPED_BASE + random_factor;
82		mm->get_unmapped_area = arch_get_unmapped_area;
83	} else {
84		mm->mmap_base = mmap_base(mm);
85		mm->get_unmapped_area = arch_get_unmapped_area_topdown;
86	}
87}
88
89unsigned long arch_randomize_brk(struct mm_struct *mm)
90{
91	unsigned long range_end = mm->brk + 0x02000000;
92	return randomize_range(mm->brk, range_end, 0) ? : mm->brk;
93}
94