1/*
  2 *  flexible mmap layout support
  3 *
  4 * Copyright 2003-2004 Red Hat Inc., Durham, North Carolina.
  5 * All Rights Reserved.
  6 *
  7 * This program is free software; you can redistribute it and/or modify
  8 * it under the terms of the GNU General Public License as published by
  9 * the Free Software Foundation; either version 2 of the License, or
 10 * (at your option) any later version.
 11 *
 12 * This program is distributed in the hope that it will be useful,
 13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 15 * GNU General Public License for more details.
 16 *
 17 * You should have received a copy of the GNU General Public License
 18 * along with this program; if not, write to the Free Software
 19 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 20 *
 21 *
 22 * Started by Ingo Molnar <mingo@elte.hu>
 23 */
 24
 25#include <linux/personality.h>
 26#include <linux/mm.h>
 27#include <linux/random.h>
 28#include <linux/sched/signal.h>
 29#include <linux/sched/mm.h>
 30#include <linux/elf-randomize.h>
 31#include <linux/security.h>
 32#include <linux/mman.h>
 33
 34/*
 35 * Top of mmap area (just below the process stack).
 36 *
 37 * Leave at least a ~128 MB hole.
 38 */
 39#define MIN_GAP (128*1024*1024)
 40#define MAX_GAP (TASK_SIZE/6*5)
 41
 42static inline int mmap_is_legacy(struct rlimit *rlim_stack)
 43{
 44	if (current->personality & ADDR_COMPAT_LAYOUT)
 45		return 1;
 46
 47	if (rlim_stack->rlim_cur == RLIM_INFINITY)
 48		return 1;
 49
 50	return sysctl_legacy_va_layout;
 51}
 52
 53unsigned long arch_mmap_rnd(void)
 54{
 55	unsigned long shift, rnd;
 56
 57	shift = mmap_rnd_bits;
 58#ifdef CONFIG_COMPAT
 59	if (is_32bit_task())
 60		shift = mmap_rnd_compat_bits;
 61#endif
 62	rnd = get_random_long() % (1ul << shift);
 63
 64	return rnd << PAGE_SHIFT;
 65}
 66
 67static inline unsigned long stack_maxrandom_size(void)
 68{
 69	if (!(current->flags & PF_RANDOMIZE))
 70		return 0;
 71
 72	/* 8MB for 32bit, 1GB for 64bit */
 73	if (is_32bit_task())
 74		return (1<<23);
 75	else
 76		return (1<<30);
 77}
 78
 79static inline unsigned long mmap_base(unsigned long rnd,
 80				      struct rlimit *rlim_stack)
 81{
 82	unsigned long gap = rlim_stack->rlim_cur;
 83	unsigned long pad = stack_maxrandom_size() + stack_guard_gap;
 84
 85	/* Values close to RLIM_INFINITY can overflow. */
 86	if (gap + pad > gap)
 87		gap += pad;
 88
 89	if (gap < MIN_GAP)
 90		gap = MIN_GAP;
 91	else if (gap > MAX_GAP)
 92		gap = MAX_GAP;
 93
 94	return PAGE_ALIGN(DEFAULT_MAP_WINDOW - gap - rnd);
 95}
 96
 97#ifdef CONFIG_PPC_RADIX_MMU
 98/*
 99 * Same function as generic code used only for radix, because we don't need to overload
100 * the generic one. But we will have to duplicate, because hash select
101 * HAVE_ARCH_UNMAPPED_AREA
102 */
103static unsigned long
104radix__arch_get_unmapped_area(struct file *filp, unsigned long addr,
105			     unsigned long len, unsigned long pgoff,
106			     unsigned long flags)
107{
108	struct mm_struct *mm = current->mm;
109	struct vm_area_struct *vma;
110	int fixed = (flags & MAP_FIXED);
111	unsigned long high_limit;
112	struct vm_unmapped_area_info info;
113
114	high_limit = DEFAULT_MAP_WINDOW;
115	if (addr >= high_limit || (fixed && (addr + len > high_limit)))
116		high_limit = TASK_SIZE;
117
118	if (len > high_limit)
119		return -ENOMEM;
120
121	if (fixed) {
122		if (addr > high_limit - len)
123			return -ENOMEM;
124		return addr;
125	}
126
127	if (addr) {
128		addr = PAGE_ALIGN(addr);
129		vma = find_vma(mm, addr);
130		if (high_limit - len >= addr && addr >= mmap_min_addr &&
131		    (!vma || addr + len <= vm_start_gap(vma)))
132			return addr;
133	}
134
135	info.flags = 0;
136	info.length = len;
137	info.low_limit = mm->mmap_base;
138	info.high_limit = high_limit;
139	info.align_mask = 0;
140
141	return vm_unmapped_area(&info);
142}
143
144static unsigned long
145radix__arch_get_unmapped_area_topdown(struct file *filp,
146				     const unsigned long addr0,
147				     const unsigned long len,
148				     const unsigned long pgoff,
149				     const unsigned long flags)
150{
151	struct vm_area_struct *vma;
152	struct mm_struct *mm = current->mm;
153	unsigned long addr = addr0;
154	int fixed = (flags & MAP_FIXED);
155	unsigned long high_limit;
156	struct vm_unmapped_area_info info;
157
158	high_limit = DEFAULT_MAP_WINDOW;
159	if (addr >= high_limit || (fixed && (addr + len > high_limit)))
160		high_limit = TASK_SIZE;
161
162	if (len > high_limit)
163		return -ENOMEM;
164
165	if (fixed) {
166		if (addr > high_limit - len)
167			return -ENOMEM;
168		return addr;
169	}
170
171	if (addr) {
172		addr = PAGE_ALIGN(addr);
173		vma = find_vma(mm, addr);
174		if (high_limit - len >= addr && addr >= mmap_min_addr &&
175		    (!vma || addr + len <= vm_start_gap(vma)))
176			return addr;
177	}
178
179	info.flags = VM_UNMAPPED_AREA_TOPDOWN;
180	info.length = len;
181	info.low_limit = max(PAGE_SIZE, mmap_min_addr);
182	info.high_limit = mm->mmap_base + (high_limit - DEFAULT_MAP_WINDOW);
183	info.align_mask = 0;
184
185	addr = vm_unmapped_area(&info);
186	if (!(addr & ~PAGE_MASK))
187		return addr;
188	VM_BUG_ON(addr != -ENOMEM);
189
190	/*
191	 * A failed mmap() very likely causes application failure,
192	 * so fall back to the bottom-up function here. This scenario
193	 * can happen with large stack limits and large mmap()
194	 * allocations.
195	 */
196	return radix__arch_get_unmapped_area(filp, addr0, len, pgoff, flags);
197}
198
199static void radix__arch_pick_mmap_layout(struct mm_struct *mm,
200					unsigned long random_factor,
201					struct rlimit *rlim_stack)
202{
203	if (mmap_is_legacy(rlim_stack)) {
204		mm->mmap_base = TASK_UNMAPPED_BASE;
205		mm->get_unmapped_area = radix__arch_get_unmapped_area;
206	} else {
207		mm->mmap_base = mmap_base(random_factor, rlim_stack);
208		mm->get_unmapped_area = radix__arch_get_unmapped_area_topdown;
209	}
210}
211#else
212/* dummy */
213extern void radix__arch_pick_mmap_layout(struct mm_struct *mm,
214					unsigned long random_factor,
215					struct rlimit *rlim_stack);
216#endif
217/*
218 * This function, called very early during the creation of a new
219 * process VM image, sets up which VM layout function to use:
220 */
221void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
222{
223	unsigned long random_factor = 0UL;
224
225	if (current->flags & PF_RANDOMIZE)
226		random_factor = arch_mmap_rnd();
227
228	if (radix_enabled())
229		return radix__arch_pick_mmap_layout(mm, random_factor,
230						    rlim_stack);
231	/*
232	 * Fall back to the standard layout if the personality
233	 * bit is set, or if the expected stack growth is unlimited:
234	 */
235	if (mmap_is_legacy(rlim_stack)) {
236		mm->mmap_base = TASK_UNMAPPED_BASE;
237		mm->get_unmapped_area = arch_get_unmapped_area;
238	} else {
239		mm->mmap_base = mmap_base(random_factor, rlim_stack);
240		mm->get_unmapped_area = arch_get_unmapped_area_topdown;
241	}
242}