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linux
1// SPDX-License-Identifier: GPL-2.0+
2/*
3 * flexible mmap layout support
4 *
5 * Copyright 2003-2004 Red Hat Inc., Durham, North Carolina.
6 * All Rights Reserved.
7 *
8 * Started by Ingo Molnar <mingo@elte.hu>
9 */
10
11#include <linux/elf-randomize.h>
12#include <linux/personality.h>
13#include <linux/mm.h>
14#include <linux/mman.h>
15#include <linux/sched/signal.h>
16#include <linux/sched/mm.h>
17#include <linux/random.h>
18#include <linux/compat.h>
19#include <linux/security.h>
20#include <asm/elf.h>
21
22static unsigned long stack_maxrandom_size(void)
23{
24 if (!(current->flags & PF_RANDOMIZE))
25 return 0;
26 return STACK_RND_MASK << PAGE_SHIFT;
27}
28
29static inline int mmap_is_legacy(struct rlimit *rlim_stack)
30{
31 if (current->personality & ADDR_COMPAT_LAYOUT)
32 return 1;
33 if (rlim_stack->rlim_cur == RLIM_INFINITY)
34 return 1;
35 return sysctl_legacy_va_layout;
36}
37
38unsigned long arch_mmap_rnd(void)
39{
40 return (get_random_u32() & MMAP_RND_MASK) << PAGE_SHIFT;
41}
42
43static unsigned long mmap_base_legacy(unsigned long rnd)
44{
45 return TASK_UNMAPPED_BASE + rnd;
46}
47
48static inline unsigned long mmap_base(unsigned long rnd,
49 struct rlimit *rlim_stack)
50{
51 unsigned long gap = rlim_stack->rlim_cur;
52 unsigned long pad = stack_maxrandom_size() + stack_guard_gap;
53 unsigned long gap_min, gap_max;
54
55 /* Values close to RLIM_INFINITY can overflow. */
56 if (gap + pad > gap)
57 gap += pad;
58
59 /*
60 * Top of mmap area (just below the process stack).
61 * Leave at least a ~128 MB hole.
62 */
63 gap_min = SZ_128M;
64 gap_max = (STACK_TOP / 6) * 5;
65
66 if (gap < gap_min)
67 gap = gap_min;
68 else if (gap > gap_max)
69 gap = gap_max;
70
71 return PAGE_ALIGN(STACK_TOP - gap - rnd);
72}
73
74static int get_align_mask(struct file *filp, unsigned long flags)
75{
76 if (!(current->flags & PF_RANDOMIZE))
77 return 0;
78 if (filp || (flags & MAP_SHARED))
79 return MMAP_ALIGN_MASK << PAGE_SHIFT;
80 return 0;
81}
82
83unsigned long arch_get_unmapped_area(struct file *filp, unsigned long addr,
84 unsigned long len, unsigned long pgoff,
85 unsigned long flags, vm_flags_t vm_flags)
86{
87 struct mm_struct *mm = current->mm;
88 struct vm_area_struct *vma;
89 struct vm_unmapped_area_info info = {};
90
91 if (len > TASK_SIZE - mmap_min_addr)
92 return -ENOMEM;
93
94 if (flags & MAP_FIXED)
95 goto check_asce_limit;
96
97 if (addr) {
98 addr = PAGE_ALIGN(addr);
99 vma = find_vma(mm, addr);
100 if (TASK_SIZE - len >= addr && addr >= mmap_min_addr &&
101 (!vma || addr + len <= vm_start_gap(vma)))
102 goto check_asce_limit;
103 }
104
105 info.length = len;
106 info.low_limit = mm->mmap_base;
107 info.high_limit = TASK_SIZE;
108 info.align_mask = get_align_mask(filp, flags);
109 info.align_offset = pgoff << PAGE_SHIFT;
110 addr = vm_unmapped_area(&info);
111 if (offset_in_page(addr))
112 return addr;
113
114check_asce_limit:
115 return check_asce_limit(mm, addr, len);
116}
117
118unsigned long arch_get_unmapped_area_topdown(struct file *filp, unsigned long addr,
119 unsigned long len, unsigned long pgoff,
120 unsigned long flags, vm_flags_t vm_flags)
121{
122 struct vm_area_struct *vma;
123 struct mm_struct *mm = current->mm;
124 struct vm_unmapped_area_info info = {};
125
126 /* requested length too big for entire address space */
127 if (len > TASK_SIZE - mmap_min_addr)
128 return -ENOMEM;
129
130 if (flags & MAP_FIXED)
131 goto check_asce_limit;
132
133 /* requesting a specific address */
134 if (addr) {
135 addr = PAGE_ALIGN(addr);
136 vma = find_vma(mm, addr);
137 if (TASK_SIZE - len >= addr && addr >= mmap_min_addr &&
138 (!vma || addr + len <= vm_start_gap(vma)))
139 goto check_asce_limit;
140 }
141
142 info.flags = VM_UNMAPPED_AREA_TOPDOWN;
143 info.length = len;
144 info.low_limit = PAGE_SIZE;
145 info.high_limit = mm->mmap_base;
146 info.align_mask = get_align_mask(filp, flags);
147 info.align_offset = pgoff << PAGE_SHIFT;
148 addr = vm_unmapped_area(&info);
149
150 /*
151 * A failed mmap() very likely causes application failure,
152 * so fall back to the bottom-up function here. This scenario
153 * can happen with large stack limits and large mmap()
154 * allocations.
155 */
156 if (offset_in_page(addr)) {
157 VM_BUG_ON(addr != -ENOMEM);
158 info.flags = 0;
159 info.low_limit = TASK_UNMAPPED_BASE;
160 info.high_limit = TASK_SIZE;
161 addr = vm_unmapped_area(&info);
162 if (offset_in_page(addr))
163 return addr;
164 }
165
166check_asce_limit:
167 return check_asce_limit(mm, addr, len);
168}
169
170/*
171 * This function, called very early during the creation of a new
172 * process VM image, sets up which VM layout function to use:
173 */
174void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
175{
176 unsigned long random_factor = 0UL;
177
178 if (current->flags & PF_RANDOMIZE)
179 random_factor = arch_mmap_rnd();
180
181 /*
182 * Fall back to the standard layout if the personality
183 * bit is set, or if the expected stack growth is unlimited:
184 */
185 if (mmap_is_legacy(rlim_stack)) {
186 mm->mmap_base = mmap_base_legacy(random_factor);
187 clear_bit(MMF_TOPDOWN, &mm->flags);
188 } else {
189 mm->mmap_base = mmap_base(random_factor, rlim_stack);
190 set_bit(MMF_TOPDOWN, &mm->flags);
191 }
192}
193
194static const pgprot_t protection_map[16] = {
195 [VM_NONE] = PAGE_NONE,
196 [VM_READ] = PAGE_RO,
197 [VM_WRITE] = PAGE_RO,
198 [VM_WRITE | VM_READ] = PAGE_RO,
199 [VM_EXEC] = PAGE_RX,
200 [VM_EXEC | VM_READ] = PAGE_RX,
201 [VM_EXEC | VM_WRITE] = PAGE_RX,
202 [VM_EXEC | VM_WRITE | VM_READ] = PAGE_RX,
203 [VM_SHARED] = PAGE_NONE,
204 [VM_SHARED | VM_READ] = PAGE_RO,
205 [VM_SHARED | VM_WRITE] = PAGE_RW,
206 [VM_SHARED | VM_WRITE | VM_READ] = PAGE_RW,
207 [VM_SHARED | VM_EXEC] = PAGE_RX,
208 [VM_SHARED | VM_EXEC | VM_READ] = PAGE_RX,
209 [VM_SHARED | VM_EXEC | VM_WRITE] = PAGE_RWX,
210 [VM_SHARED | VM_EXEC | VM_WRITE | VM_READ] = PAGE_RWX
211};
212DECLARE_VM_GET_PAGE_PROT