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
mmap_is_legacy(void)42 static inline int mmap_is_legacy(void)
43 {
44 if (current->personality & ADDR_COMPAT_LAYOUT)
45 return 1;
46
47 if (rlimit(RLIMIT_STACK) == RLIM_INFINITY)
48 return 1;
49
50 return sysctl_legacy_va_layout;
51 }
52
arch_mmap_rnd(void)53 unsigned 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
stack_maxrandom_size(void)67 static 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
mmap_base(unsigned long rnd)79 static inline unsigned long mmap_base(unsigned long rnd)
80 {
81 unsigned long gap = rlimit(RLIMIT_STACK);
82 unsigned long pad = stack_maxrandom_size() + stack_guard_gap;
83
84 /* Values close to RLIM_INFINITY can overflow. */
85 if (gap + pad > gap)
86 gap += pad;
87
88 if (gap < MIN_GAP)
89 gap = MIN_GAP;
90 else if (gap > MAX_GAP)
91 gap = MAX_GAP;
92
93 return PAGE_ALIGN(DEFAULT_MAP_WINDOW - gap - rnd);
94 }
95
96 #ifdef CONFIG_PPC_RADIX_MMU
97 /*
98 * Same function as generic code used only for radix, because we don't need to overload
99 * the generic one. But we will have to duplicate, because hash select
100 * HAVE_ARCH_UNMAPPED_AREA
101 */
102 static unsigned long
radix__arch_get_unmapped_area(struct file * filp,unsigned long addr,unsigned long len,unsigned long pgoff,unsigned long flags)103 radix__arch_get_unmapped_area(struct file *filp, unsigned long addr,
104 unsigned long len, unsigned long pgoff,
105 unsigned long flags)
106 {
107 struct mm_struct *mm = current->mm;
108 struct vm_area_struct *vma;
109 int fixed = (flags & MAP_FIXED);
110 unsigned long high_limit;
111 struct vm_unmapped_area_info info;
112
113 high_limit = DEFAULT_MAP_WINDOW;
114 if (addr >= high_limit || (fixed && (addr + len > high_limit)))
115 high_limit = TASK_SIZE;
116
117 if (len > high_limit)
118 return -ENOMEM;
119 if (fixed) {
120 if (addr > high_limit - len)
121 return -ENOMEM;
122 }
123
124 if (unlikely(addr > mm->context.addr_limit &&
125 mm->context.addr_limit != TASK_SIZE))
126 mm->context.addr_limit = TASK_SIZE;
127
128 if (fixed)
129 return addr;
130
131 if (addr) {
132 addr = PAGE_ALIGN(addr);
133 vma = find_vma(mm, addr);
134 if (high_limit - len >= addr && addr >= mmap_min_addr &&
135 (!vma || addr + len <= vm_start_gap(vma)))
136 return addr;
137 }
138
139 info.flags = 0;
140 info.length = len;
141 info.low_limit = mm->mmap_base;
142 info.high_limit = high_limit;
143 info.align_mask = 0;
144
145 return vm_unmapped_area(&info);
146 }
147
148 static unsigned long
radix__arch_get_unmapped_area_topdown(struct file * filp,const unsigned long addr0,const unsigned long len,const unsigned long pgoff,const unsigned long flags)149 radix__arch_get_unmapped_area_topdown(struct file *filp,
150 const unsigned long addr0,
151 const unsigned long len,
152 const unsigned long pgoff,
153 const unsigned long flags)
154 {
155 struct vm_area_struct *vma;
156 struct mm_struct *mm = current->mm;
157 unsigned long addr = addr0;
158 int fixed = (flags & MAP_FIXED);
159 unsigned long high_limit;
160 struct vm_unmapped_area_info info;
161
162 high_limit = DEFAULT_MAP_WINDOW;
163 if (addr >= high_limit || (fixed && (addr + len > high_limit)))
164 high_limit = TASK_SIZE;
165
166 if (len > high_limit)
167 return -ENOMEM;
168 if (fixed) {
169 if (addr > high_limit - len)
170 return -ENOMEM;
171 }
172
173 if (unlikely(addr > mm->context.addr_limit &&
174 mm->context.addr_limit != TASK_SIZE))
175 mm->context.addr_limit = TASK_SIZE;
176
177 if (fixed)
178 return addr;
179
180 if (addr) {
181 addr = PAGE_ALIGN(addr);
182 vma = find_vma(mm, addr);
183 if (high_limit - len >= addr && addr >= mmap_min_addr &&
184 (!vma || addr + len <= vm_start_gap(vma)))
185 return addr;
186 }
187
188 info.flags = VM_UNMAPPED_AREA_TOPDOWN;
189 info.length = len;
190 info.low_limit = max(PAGE_SIZE, mmap_min_addr);
191 info.high_limit = mm->mmap_base + (high_limit - DEFAULT_MAP_WINDOW);
192 info.align_mask = 0;
193
194 addr = vm_unmapped_area(&info);
195 if (!(addr & ~PAGE_MASK))
196 return addr;
197 VM_BUG_ON(addr != -ENOMEM);
198
199 /*
200 * A failed mmap() very likely causes application failure,
201 * so fall back to the bottom-up function here. This scenario
202 * can happen with large stack limits and large mmap()
203 * allocations.
204 */
205 return radix__arch_get_unmapped_area(filp, addr0, len, pgoff, flags);
206 }
207
radix__arch_pick_mmap_layout(struct mm_struct * mm,unsigned long random_factor)208 static void radix__arch_pick_mmap_layout(struct mm_struct *mm,
209 unsigned long random_factor)
210 {
211 if (mmap_is_legacy()) {
212 mm->mmap_base = TASK_UNMAPPED_BASE;
213 mm->get_unmapped_area = radix__arch_get_unmapped_area;
214 } else {
215 mm->mmap_base = mmap_base(random_factor);
216 mm->get_unmapped_area = radix__arch_get_unmapped_area_topdown;
217 }
218 }
219 #else
220 /* dummy */
221 extern void radix__arch_pick_mmap_layout(struct mm_struct *mm,
222 unsigned long random_factor);
223 #endif
224 /*
225 * This function, called very early during the creation of a new
226 * process VM image, sets up which VM layout function to use:
227 */
arch_pick_mmap_layout(struct mm_struct * mm)228 void arch_pick_mmap_layout(struct mm_struct *mm)
229 {
230 unsigned long random_factor = 0UL;
231
232 if (current->flags & PF_RANDOMIZE)
233 random_factor = arch_mmap_rnd();
234
235 if (radix_enabled())
236 return radix__arch_pick_mmap_layout(mm, random_factor);
237 /*
238 * Fall back to the standard layout if the personality
239 * bit is set, or if the expected stack growth is unlimited:
240 */
241 if (mmap_is_legacy()) {
242 mm->mmap_base = TASK_UNMAPPED_BASE;
243 mm->get_unmapped_area = arch_get_unmapped_area;
244 } else {
245 mm->mmap_base = mmap_base(random_factor);
246 mm->get_unmapped_area = arch_get_unmapped_area_topdown;
247 }
248 }
249