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)
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.flags = 0;
106	info.length = len;
107	info.low_limit = mm->mmap_base;
108	info.high_limit = TASK_SIZE;
109	info.align_mask = get_align_mask(filp, flags);
110	info.align_offset = pgoff << PAGE_SHIFT;
111	addr = vm_unmapped_area(&info);
112	if (offset_in_page(addr))
113		return addr;
114
115check_asce_limit:
116	return check_asce_limit(mm, addr, len);
117}
118
119unsigned long arch_get_unmapped_area_topdown(struct file *filp, unsigned long addr,
120					     unsigned long len, unsigned long pgoff,
121					     unsigned long flags)
122{
123	struct vm_area_struct *vma;
124	struct mm_struct *mm = current->mm;
125	struct vm_unmapped_area_info info;
126
127	/* requested length too big for entire address space */
128	if (len > TASK_SIZE - mmap_min_addr)
129		return -ENOMEM;
130
131	if (flags & MAP_FIXED)
132		goto check_asce_limit;
133
134	/* requesting a specific address */
135	if (addr) {
136		addr = PAGE_ALIGN(addr);
137		vma = find_vma(mm, addr);
138		if (TASK_SIZE - len >= addr && addr >= mmap_min_addr &&
139				(!vma || addr + len <= vm_start_gap(vma)))
140			goto check_asce_limit;
141	}
142
143	info.flags = VM_UNMAPPED_AREA_TOPDOWN;
144	info.length = len;
145	info.low_limit = PAGE_SIZE;
146	info.high_limit = mm->mmap_base;
147	info.align_mask = get_align_mask(filp, flags);
148	info.align_offset = pgoff << PAGE_SHIFT;
149	addr = vm_unmapped_area(&info);
150
151	/*
152	 * A failed mmap() very likely causes application failure,
153	 * so fall back to the bottom-up function here. This scenario
154	 * can happen with large stack limits and large mmap()
155	 * allocations.
156	 */
157	if (offset_in_page(addr)) {
158		VM_BUG_ON(addr != -ENOMEM);
159		info.flags = 0;
160		info.low_limit = TASK_UNMAPPED_BASE;
161		info.high_limit = TASK_SIZE;
162		addr = vm_unmapped_area(&info);
163		if (offset_in_page(addr))
164			return addr;
165	}
166
167check_asce_limit:
168	return check_asce_limit(mm, addr, len);
169}
170
171/*
172 * This function, called very early during the creation of a new
173 * process VM image, sets up which VM layout function to use:
174 */
175void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
176{
177	unsigned long random_factor = 0UL;
178
179	if (current->flags & PF_RANDOMIZE)
180		random_factor = arch_mmap_rnd();
181
182	/*
183	 * Fall back to the standard layout if the personality
184	 * bit is set, or if the expected stack growth is unlimited:
185	 */
186	if (mmap_is_legacy(rlim_stack)) {
187		mm->mmap_base = mmap_base_legacy(random_factor);
188		mm->get_unmapped_area = arch_get_unmapped_area;
189	} else {
190		mm->mmap_base = mmap_base(random_factor, rlim_stack);
191		mm->get_unmapped_area = arch_get_unmapped_area_topdown;
192	}
193}
194
195static const pgprot_t protection_map[16] = {
196	[VM_NONE]					= PAGE_NONE,
197	[VM_READ]					= PAGE_RO,
198	[VM_WRITE]					= PAGE_RO,
199	[VM_WRITE | VM_READ]				= PAGE_RO,
200	[VM_EXEC]					= PAGE_RX,
201	[VM_EXEC | VM_READ]				= PAGE_RX,
202	[VM_EXEC | VM_WRITE]				= PAGE_RX,
203	[VM_EXEC | VM_WRITE | VM_READ]			= PAGE_RX,
204	[VM_SHARED]					= PAGE_NONE,
205	[VM_SHARED | VM_READ]				= PAGE_RO,
206	[VM_SHARED | VM_WRITE]				= PAGE_RW,
207	[VM_SHARED | VM_WRITE | VM_READ]		= PAGE_RW,
208	[VM_SHARED | VM_EXEC]				= PAGE_RX,
209	[VM_SHARED | VM_EXEC | VM_READ]			= PAGE_RX,
210	[VM_SHARED | VM_EXEC | VM_WRITE]		= PAGE_RWX,
211	[VM_SHARED | VM_EXEC | VM_WRITE | VM_READ]	= PAGE_RWX
212};
213DECLARE_VM_GET_PAGE_PROT
214