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
stack_maxrandom_size(void)22 static 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
mmap_is_legacy(struct rlimit * rlim_stack)29 static 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
arch_mmap_rnd(void)38 unsigned long arch_mmap_rnd(void)
39 {
40 return (get_random_u32() & MMAP_RND_MASK) << PAGE_SHIFT;
41 }
42
mmap_base_legacy(unsigned long rnd)43 static unsigned long mmap_base_legacy(unsigned long rnd)
44 {
45 return TASK_UNMAPPED_BASE + rnd;
46 }
47
mmap_base(unsigned long rnd,struct rlimit * rlim_stack)48 static 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
arch_get_unmapped_area(struct file * filp,unsigned long addr,unsigned long len,unsigned long pgoff,unsigned long flags)74 unsigned long arch_get_unmapped_area(struct file *filp, unsigned long addr,
75 unsigned long len, unsigned long pgoff,
76 unsigned long flags)
77 {
78 struct mm_struct *mm = current->mm;
79 struct vm_area_struct *vma;
80 struct vm_unmapped_area_info info;
81
82 if (len > TASK_SIZE - mmap_min_addr)
83 return -ENOMEM;
84
85 if (flags & MAP_FIXED)
86 goto check_asce_limit;
87
88 if (addr) {
89 addr = PAGE_ALIGN(addr);
90 vma = find_vma(mm, addr);
91 if (TASK_SIZE - len >= addr && addr >= mmap_min_addr &&
92 (!vma || addr + len <= vm_start_gap(vma)))
93 goto check_asce_limit;
94 }
95
96 info.flags = 0;
97 info.length = len;
98 info.low_limit = mm->mmap_base;
99 info.high_limit = TASK_SIZE;
100 if (filp || (flags & MAP_SHARED))
101 info.align_mask = MMAP_ALIGN_MASK << PAGE_SHIFT;
102 else
103 info.align_mask = 0;
104 info.align_offset = pgoff << PAGE_SHIFT;
105 addr = vm_unmapped_area(&info);
106 if (offset_in_page(addr))
107 return addr;
108
109 check_asce_limit:
110 return check_asce_limit(mm, addr, len);
111 }
112
arch_get_unmapped_area_topdown(struct file * filp,unsigned long addr,unsigned long len,unsigned long pgoff,unsigned long flags)113 unsigned long arch_get_unmapped_area_topdown(struct file *filp, unsigned long addr,
114 unsigned long len, unsigned long pgoff,
115 unsigned long flags)
116 {
117 struct vm_area_struct *vma;
118 struct mm_struct *mm = current->mm;
119 struct vm_unmapped_area_info info;
120
121 /* requested length too big for entire address space */
122 if (len > TASK_SIZE - mmap_min_addr)
123 return -ENOMEM;
124
125 if (flags & MAP_FIXED)
126 goto check_asce_limit;
127
128 /* requesting a specific address */
129 if (addr) {
130 addr = PAGE_ALIGN(addr);
131 vma = find_vma(mm, addr);
132 if (TASK_SIZE - len >= addr && addr >= mmap_min_addr &&
133 (!vma || addr + len <= vm_start_gap(vma)))
134 goto check_asce_limit;
135 }
136
137 info.flags = VM_UNMAPPED_AREA_TOPDOWN;
138 info.length = len;
139 info.low_limit = PAGE_SIZE;
140 info.high_limit = mm->mmap_base;
141 if (filp || (flags & MAP_SHARED))
142 info.align_mask = MMAP_ALIGN_MASK << PAGE_SHIFT;
143 else
144 info.align_mask = 0;
145 info.align_offset = pgoff << PAGE_SHIFT;
146 addr = vm_unmapped_area(&info);
147
148 /*
149 * A failed mmap() very likely causes application failure,
150 * so fall back to the bottom-up function here. This scenario
151 * can happen with large stack limits and large mmap()
152 * allocations.
153 */
154 if (offset_in_page(addr)) {
155 VM_BUG_ON(addr != -ENOMEM);
156 info.flags = 0;
157 info.low_limit = TASK_UNMAPPED_BASE;
158 info.high_limit = TASK_SIZE;
159 addr = vm_unmapped_area(&info);
160 if (offset_in_page(addr))
161 return addr;
162 }
163
164 check_asce_limit:
165 return check_asce_limit(mm, addr, len);
166 }
167
168 /*
169 * This function, called very early during the creation of a new
170 * process VM image, sets up which VM layout function to use:
171 */
arch_pick_mmap_layout(struct mm_struct * mm,struct rlimit * rlim_stack)172 void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
173 {
174 unsigned long random_factor = 0UL;
175
176 if (current->flags & PF_RANDOMIZE)
177 random_factor = arch_mmap_rnd();
178
179 /*
180 * Fall back to the standard layout if the personality
181 * bit is set, or if the expected stack growth is unlimited:
182 */
183 if (mmap_is_legacy(rlim_stack)) {
184 mm->mmap_base = mmap_base_legacy(random_factor);
185 mm->get_unmapped_area = arch_get_unmapped_area;
186 } else {
187 mm->mmap_base = mmap_base(random_factor, rlim_stack);
188 mm->get_unmapped_area = arch_get_unmapped_area_topdown;
189 }
190 }
191
192 static const pgprot_t protection_map[16] = {
193 [VM_NONE] = PAGE_NONE,
194 [VM_READ] = PAGE_RO,
195 [VM_WRITE] = PAGE_RO,
196 [VM_WRITE | VM_READ] = PAGE_RO,
197 [VM_EXEC] = PAGE_RX,
198 [VM_EXEC | VM_READ] = PAGE_RX,
199 [VM_EXEC | VM_WRITE] = PAGE_RX,
200 [VM_EXEC | VM_WRITE | VM_READ] = PAGE_RX,
201 [VM_SHARED] = PAGE_NONE,
202 [VM_SHARED | VM_READ] = PAGE_RO,
203 [VM_SHARED | VM_WRITE] = PAGE_RW,
204 [VM_SHARED | VM_WRITE | VM_READ] = PAGE_RW,
205 [VM_SHARED | VM_EXEC] = PAGE_RX,
206 [VM_SHARED | VM_EXEC | VM_READ] = PAGE_RX,
207 [VM_SHARED | VM_EXEC | VM_WRITE] = PAGE_RWX,
208 [VM_SHARED | VM_EXEC | VM_WRITE | VM_READ] = PAGE_RWX
209 };
210 DECLARE_VM_GET_PAGE_PROT
211