1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * Flexible mmap layout support
4 *
5 * Based on code by Ingo Molnar and Andi Kleen, copyrighted
6 * as follows:
7 *
8 * Copyright 2003-2009 Red Hat Inc.
9 * All Rights Reserved.
10 * Copyright 2005 Andi Kleen, SUSE Labs.
11 * Copyright 2007 Jiri Kosina, SUSE Labs.
12 */
13
14#include <linux/personality.h>
15#include <linux/mm.h>
16#include <linux/random.h>
17#include <linux/limits.h>
18#include <linux/sched/signal.h>
19#include <linux/sched/mm.h>
20#include <linux/compat.h>
21#include <linux/elf-randomize.h>
22#include <asm/elf.h>
23#include <asm/io.h>
24
25#include "physaddr.h"
26
27struct va_alignment __read_mostly va_align = {
28 .flags = -1,
29};
30
31unsigned long task_size_32bit(void)
32{
33 return IA32_PAGE_OFFSET;
34}
35
36unsigned long task_size_64bit(int full_addr_space)
37{
38 return full_addr_space ? TASK_SIZE_MAX : DEFAULT_MAP_WINDOW;
39}
40
41static unsigned long stack_maxrandom_size(unsigned long task_size)
42{
43 unsigned long max = 0;
44 if (current->flags & PF_RANDOMIZE) {
45 max = (-1UL) & __STACK_RND_MASK(task_size == task_size_32bit());
46 max <<= PAGE_SHIFT;
47 }
48
49 return max;
50}
51
52#ifdef CONFIG_COMPAT
53# define mmap32_rnd_bits mmap_rnd_compat_bits
54# define mmap64_rnd_bits mmap_rnd_bits
55#else
56# define mmap32_rnd_bits mmap_rnd_bits
57# define mmap64_rnd_bits mmap_rnd_bits
58#endif
59
60#define SIZE_128M (128 * 1024 * 1024UL)
61
62static int mmap_is_legacy(void)
63{
64 if (current->personality & ADDR_COMPAT_LAYOUT)
65 return 1;
66
67 return sysctl_legacy_va_layout;
68}
69
70static unsigned long arch_rnd(unsigned int rndbits)
71{
72 if (!(current->flags & PF_RANDOMIZE))
73 return 0;
74 return (get_random_long() & ((1UL << rndbits) - 1)) << PAGE_SHIFT;
75}
76
77unsigned long arch_mmap_rnd(void)
78{
79 return arch_rnd(rndbits: mmap_is_ia32() ? mmap32_rnd_bits : mmap64_rnd_bits);
80}
81
82static unsigned long mmap_base(unsigned long rnd, unsigned long task_size,
83 const struct rlimit *rlim_stack)
84{
85 unsigned long gap = rlim_stack->rlim_cur;
86 unsigned long pad = stack_maxrandom_size(task_size) + stack_guard_gap;
87
88 /* Values close to RLIM_INFINITY can overflow. */
89 if (gap + pad > gap)
90 gap += pad;
91
92 /*
93 * Top of mmap area (just below the process stack).
94 * Leave an at least ~128 MB hole with possible stack randomization.
95 */
96 gap = clamp(gap, SIZE_128M, (task_size / 6) * 5);
97
98 return PAGE_ALIGN(task_size - gap - rnd);
99}
100
101static unsigned long mmap_legacy_base(unsigned long rnd,
102 unsigned long task_size)
103{
104 return __TASK_UNMAPPED_BASE(task_size) + rnd;
105}
106
107/*
108 * This function, called very early during the creation of a new
109 * process VM image, sets up which VM layout function to use:
110 */
111static void arch_pick_mmap_base(unsigned long *base, unsigned long *legacy_base,
112 unsigned long random_factor, unsigned long task_size,
113 const struct rlimit *rlim_stack)
114{
115 *legacy_base = mmap_legacy_base(rnd: random_factor, task_size);
116 if (mmap_is_legacy())
117 *base = *legacy_base;
118 else
119 *base = mmap_base(rnd: random_factor, task_size, rlim_stack);
120}
121
122void arch_pick_mmap_layout(struct mm_struct *mm, const struct rlimit *rlim_stack)
123{
124 if (mmap_is_legacy())
125 mm_flags_clear(MMF_TOPDOWN, mm);
126 else
127 mm_flags_set(MMF_TOPDOWN, mm);
128
129 arch_pick_mmap_base(base: &mm->mmap_base, legacy_base: &mm->mmap_legacy_base,
130 random_factor: arch_rnd(mmap64_rnd_bits), task_size: task_size_64bit(full_addr_space: 0),
131 rlim_stack);
132
133#ifdef CONFIG_HAVE_ARCH_COMPAT_MMAP_BASES
134 /*
135 * The mmap syscall mapping base decision depends solely on the
136 * syscall type (64-bit or compat). This applies for 64bit
137 * applications and 32bit applications. The 64bit syscall uses
138 * mmap_base, the compat syscall uses mmap_compat_base.
139 */
140 arch_pick_mmap_base(base: &mm->mmap_compat_base, legacy_base: &mm->mmap_compat_legacy_base,
141 random_factor: arch_rnd(mmap32_rnd_bits), task_size: task_size_32bit(),
142 rlim_stack);
143#endif
144}
145
146unsigned long get_mmap_base(int is_legacy)
147{
148 struct mm_struct *mm = current->mm;
149
150#ifdef CONFIG_HAVE_ARCH_COMPAT_MMAP_BASES
151 if (in_32bit_syscall()) {
152 return is_legacy ? mm->mmap_compat_legacy_base
153 : mm->mmap_compat_base;
154 }
155#endif
156 return is_legacy ? mm->mmap_legacy_base : mm->mmap_base;
157}
158
159/**
160 * mmap_address_hint_valid - Validate the address hint of mmap
161 * @addr: Address hint
162 * @len: Mapping length
163 *
164 * Check whether @addr and @addr + @len result in a valid mapping.
165 *
166 * On 32bit this only checks whether @addr + @len is <= TASK_SIZE.
167 *
168 * On 64bit with 5-level page tables another sanity check is required
169 * because mappings requested by mmap(@addr, 0) which cross the 47-bit
170 * virtual address boundary can cause the following theoretical issue:
171 *
172 * An application calls mmap(addr, 0), i.e. without MAP_FIXED, where @addr
173 * is below the border of the 47-bit address space and @addr + @len is
174 * above the border.
175 *
176 * With 4-level paging this request succeeds, but the resulting mapping
177 * address will always be within the 47-bit virtual address space, because
178 * the hint address does not result in a valid mapping and is
179 * ignored. Hence applications which are not prepared to handle virtual
180 * addresses above 47-bit work correctly.
181 *
182 * With 5-level paging this request would be granted and result in a
183 * mapping which crosses the border of the 47-bit virtual address
184 * space. If the application cannot handle addresses above 47-bit this
185 * will lead to misbehaviour and hard to diagnose failures.
186 *
187 * Therefore ignore address hints which would result in a mapping crossing
188 * the 47-bit virtual address boundary.
189 *
190 * Note, that in the same scenario with MAP_FIXED the behaviour is
191 * different. The request with @addr < 47-bit and @addr + @len > 47-bit
192 * fails on a 4-level paging machine but succeeds on a 5-level paging
193 * machine. It is reasonable to expect that an application does not rely on
194 * the failure of such a fixed mapping request, so the restriction is not
195 * applied.
196 */
197bool mmap_address_hint_valid(unsigned long addr, unsigned long len)
198{
199 if (TASK_SIZE - len < addr)
200 return false;
201
202 return (addr > DEFAULT_MAP_WINDOW) == (addr + len > DEFAULT_MAP_WINDOW);
203}
204
205/* Can we access it for direct reading/writing? Must be RAM: */
206int valid_phys_addr_range(phys_addr_t addr, size_t count)
207{
208 return addr + count - 1 <= __pa(high_memory - 1);
209}
210
211/* Can we access it through mmap? Must be a valid physical address: */
212int valid_mmap_phys_addr_range(unsigned long pfn, size_t count)
213{
214 phys_addr_t addr = (phys_addr_t)pfn << PAGE_SHIFT;
215
216 return phys_addr_valid(addr: addr + count - 1);
217}
218
219/*
220 * Only allow root to set high MMIO mappings to PROT_NONE.
221 * This prevents an unpriv. user to set them to PROT_NONE and invert
222 * them, then pointing to valid memory for L1TF speculation.
223 *
224 * Note: for locked down kernels may want to disable the root override.
225 */
226bool pfn_modify_allowed(unsigned long pfn, pgprot_t prot)
227{
228 if (!boot_cpu_has_bug(X86_BUG_L1TF))
229 return true;
230 if (!__pte_needs_invert(pgprot_val(prot)))
231 return true;
232 /* If it's real memory always allow */
233 if (pfn_valid(pfn))
234 return true;
235 if (pfn >= l1tf_pfn_limit() && !capable(CAP_SYS_ADMIN))
236 return false;
237 return true;
238}
239