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
42 static 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
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
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
79 static 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 */
103 static unsigned long
104 radix__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
144 static unsigned long
145 radix__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
199 static 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 */
213 extern 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 */
221 void 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 }
243
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