Loading...
1/*
2 * Flexible mmap layout support
3 *
4 * Based on code by Ingo Molnar and Andi Kleen, copyrighted
5 * as follows:
6 *
7 * Copyright 2003-2009 Red Hat Inc.
8 * All Rights Reserved.
9 * Copyright 2005 Andi Kleen, SUSE Labs.
10 * Copyright 2007 Jiri Kosina, SUSE Labs.
11 *
12 * This program is free software; you can redistribute it and/or modify
13 * it under the terms of the GNU General Public License as published by
14 * the Free Software Foundation; either version 2 of the License, or
15 * (at your option) any later version.
16 *
17 * This program is distributed in the hope that it will be useful,
18 * but WITHOUT ANY WARRANTY; without even the implied warranty of
19 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
20 * GNU General Public License for more details.
21 *
22 * You should have received a copy of the GNU General Public License
23 * along with this program; if not, write to the Free Software
24 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
25 */
26
27#include <linux/personality.h>
28#include <linux/mm.h>
29#include <linux/random.h>
30#include <linux/limits.h>
31#include <linux/sched.h>
32#include <asm/elf.h>
33
34static unsigned int stack_maxrandom_size(void)
35{
36 unsigned int max = 0;
37 if ((current->flags & PF_RANDOMIZE) &&
38 !(current->personality & ADDR_NO_RANDOMIZE)) {
39 max = ((-1U) & STACK_RND_MASK) << PAGE_SHIFT;
40 }
41
42 return max;
43}
44
45
46/*
47 * Top of mmap area (just below the process stack).
48 *
49 * Leave an at least ~128 MB hole with possible stack randomization.
50 */
51#define MIN_GAP (128*1024*1024UL + stack_maxrandom_size())
52#define MAX_GAP (TASK_SIZE/6*5)
53
54/*
55 * True on X86_32 or when emulating IA32 on X86_64
56 */
57static int mmap_is_ia32(void)
58{
59#ifdef CONFIG_X86_32
60 return 1;
61#endif
62#ifdef CONFIG_IA32_EMULATION
63 if (test_thread_flag(TIF_IA32))
64 return 1;
65#endif
66 return 0;
67}
68
69static int mmap_is_legacy(void)
70{
71 if (current->personality & ADDR_COMPAT_LAYOUT)
72 return 1;
73
74 if (rlimit(RLIMIT_STACK) == RLIM_INFINITY)
75 return 1;
76
77 return sysctl_legacy_va_layout;
78}
79
80static unsigned long mmap_rnd(void)
81{
82 unsigned long rnd = 0;
83
84 /*
85 * 8 bits of randomness in 32bit mmaps, 20 address space bits
86 * 28 bits of randomness in 64bit mmaps, 40 address space bits
87 */
88 if (current->flags & PF_RANDOMIZE) {
89 if (mmap_is_ia32())
90 rnd = (long)get_random_int() % (1<<8);
91 else
92 rnd = (long)(get_random_int() % (1<<28));
93 }
94 return rnd << PAGE_SHIFT;
95}
96
97static unsigned long mmap_base(void)
98{
99 unsigned long gap = rlimit(RLIMIT_STACK);
100
101 if (gap < MIN_GAP)
102 gap = MIN_GAP;
103 else if (gap > MAX_GAP)
104 gap = MAX_GAP;
105
106 return PAGE_ALIGN(TASK_SIZE - gap - mmap_rnd());
107}
108
109/*
110 * Bottom-up (legacy) layout on X86_32 did not support randomization, X86_64
111 * does, but not when emulating X86_32
112 */
113static unsigned long mmap_legacy_base(void)
114{
115 if (mmap_is_ia32())
116 return TASK_UNMAPPED_BASE;
117 else
118 return TASK_UNMAPPED_BASE + mmap_rnd();
119}
120
121/*
122 * This function, called very early during the creation of a new
123 * process VM image, sets up which VM layout function to use:
124 */
125void arch_pick_mmap_layout(struct mm_struct *mm)
126{
127 if (mmap_is_legacy()) {
128 mm->mmap_base = mmap_legacy_base();
129 mm->get_unmapped_area = arch_get_unmapped_area;
130 mm->unmap_area = arch_unmap_area;
131 } else {
132 mm->mmap_base = mmap_base();
133 mm->get_unmapped_area = arch_get_unmapped_area_topdown;
134 mm->unmap_area = arch_unmap_area_topdown;
135 }
136}
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 <asm/elf.h>
22
23#include "physaddr.h"
24
25struct va_alignment __read_mostly va_align = {
26 .flags = -1,
27};
28
29unsigned long task_size_32bit(void)
30{
31 return IA32_PAGE_OFFSET;
32}
33
34unsigned long task_size_64bit(int full_addr_space)
35{
36 return full_addr_space ? TASK_SIZE_MAX : DEFAULT_MAP_WINDOW;
37}
38
39static unsigned long stack_maxrandom_size(unsigned long task_size)
40{
41 unsigned long max = 0;
42 if (current->flags & PF_RANDOMIZE) {
43 max = (-1UL) & __STACK_RND_MASK(task_size == task_size_32bit());
44 max <<= PAGE_SHIFT;
45 }
46
47 return max;
48}
49
50#ifdef CONFIG_COMPAT
51# define mmap32_rnd_bits mmap_rnd_compat_bits
52# define mmap64_rnd_bits mmap_rnd_bits
53#else
54# define mmap32_rnd_bits mmap_rnd_bits
55# define mmap64_rnd_bits mmap_rnd_bits
56#endif
57
58#define SIZE_128M (128 * 1024 * 1024UL)
59
60static int mmap_is_legacy(void)
61{
62 if (current->personality & ADDR_COMPAT_LAYOUT)
63 return 1;
64
65 return sysctl_legacy_va_layout;
66}
67
68static unsigned long arch_rnd(unsigned int rndbits)
69{
70 if (!(current->flags & PF_RANDOMIZE))
71 return 0;
72 return (get_random_long() & ((1UL << rndbits) - 1)) << PAGE_SHIFT;
73}
74
75unsigned long arch_mmap_rnd(void)
76{
77 return arch_rnd(mmap_is_ia32() ? mmap32_rnd_bits : mmap64_rnd_bits);
78}
79
80static unsigned long mmap_base(unsigned long rnd, unsigned long task_size,
81 struct rlimit *rlim_stack)
82{
83 unsigned long gap = rlim_stack->rlim_cur;
84 unsigned long pad = stack_maxrandom_size(task_size) + stack_guard_gap;
85 unsigned long gap_min, gap_max;
86
87 /* Values close to RLIM_INFINITY can overflow. */
88 if (gap + pad > gap)
89 gap += pad;
90
91 /*
92 * Top of mmap area (just below the process stack).
93 * Leave an at least ~128 MB hole with possible stack randomization.
94 */
95 gap_min = SIZE_128M;
96 gap_max = (task_size / 6) * 5;
97
98 if (gap < gap_min)
99 gap = gap_min;
100 else if (gap > gap_max)
101 gap = gap_max;
102
103 return PAGE_ALIGN(task_size - gap - rnd);
104}
105
106static unsigned long mmap_legacy_base(unsigned long rnd,
107 unsigned long task_size)
108{
109 return __TASK_UNMAPPED_BASE(task_size) + rnd;
110}
111
112/*
113 * This function, called very early during the creation of a new
114 * process VM image, sets up which VM layout function to use:
115 */
116static void arch_pick_mmap_base(unsigned long *base, unsigned long *legacy_base,
117 unsigned long random_factor, unsigned long task_size,
118 struct rlimit *rlim_stack)
119{
120 *legacy_base = mmap_legacy_base(random_factor, task_size);
121 if (mmap_is_legacy())
122 *base = *legacy_base;
123 else
124 *base = mmap_base(random_factor, task_size, rlim_stack);
125}
126
127void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
128{
129 if (mmap_is_legacy())
130 mm->get_unmapped_area = arch_get_unmapped_area;
131 else
132 mm->get_unmapped_area = arch_get_unmapped_area_topdown;
133
134 arch_pick_mmap_base(&mm->mmap_base, &mm->mmap_legacy_base,
135 arch_rnd(mmap64_rnd_bits), task_size_64bit(0),
136 rlim_stack);
137
138#ifdef CONFIG_HAVE_ARCH_COMPAT_MMAP_BASES
139 /*
140 * The mmap syscall mapping base decision depends solely on the
141 * syscall type (64-bit or compat). This applies for 64bit
142 * applications and 32bit applications. The 64bit syscall uses
143 * mmap_base, the compat syscall uses mmap_compat_base.
144 */
145 arch_pick_mmap_base(&mm->mmap_compat_base, &mm->mmap_compat_legacy_base,
146 arch_rnd(mmap32_rnd_bits), task_size_32bit(),
147 rlim_stack);
148#endif
149}
150
151unsigned long get_mmap_base(int is_legacy)
152{
153 struct mm_struct *mm = current->mm;
154
155#ifdef CONFIG_HAVE_ARCH_COMPAT_MMAP_BASES
156 if (in_32bit_syscall()) {
157 return is_legacy ? mm->mmap_compat_legacy_base
158 : mm->mmap_compat_base;
159 }
160#endif
161 return is_legacy ? mm->mmap_legacy_base : mm->mmap_base;
162}
163
164const char *arch_vma_name(struct vm_area_struct *vma)
165{
166 if (vma->vm_flags & VM_MPX)
167 return "[mpx]";
168 return NULL;
169}
170
171/**
172 * mmap_address_hint_valid - Validate the address hint of mmap
173 * @addr: Address hint
174 * @len: Mapping length
175 *
176 * Check whether @addr and @addr + @len result in a valid mapping.
177 *
178 * On 32bit this only checks whether @addr + @len is <= TASK_SIZE.
179 *
180 * On 64bit with 5-level page tables another sanity check is required
181 * because mappings requested by mmap(@addr, 0) which cross the 47-bit
182 * virtual address boundary can cause the following theoretical issue:
183 *
184 * An application calls mmap(addr, 0), i.e. without MAP_FIXED, where @addr
185 * is below the border of the 47-bit address space and @addr + @len is
186 * above the border.
187 *
188 * With 4-level paging this request succeeds, but the resulting mapping
189 * address will always be within the 47-bit virtual address space, because
190 * the hint address does not result in a valid mapping and is
191 * ignored. Hence applications which are not prepared to handle virtual
192 * addresses above 47-bit work correctly.
193 *
194 * With 5-level paging this request would be granted and result in a
195 * mapping which crosses the border of the 47-bit virtual address
196 * space. If the application cannot handle addresses above 47-bit this
197 * will lead to misbehaviour and hard to diagnose failures.
198 *
199 * Therefore ignore address hints which would result in a mapping crossing
200 * the 47-bit virtual address boundary.
201 *
202 * Note, that in the same scenario with MAP_FIXED the behaviour is
203 * different. The request with @addr < 47-bit and @addr + @len > 47-bit
204 * fails on a 4-level paging machine but succeeds on a 5-level paging
205 * machine. It is reasonable to expect that an application does not rely on
206 * the failure of such a fixed mapping request, so the restriction is not
207 * applied.
208 */
209bool mmap_address_hint_valid(unsigned long addr, unsigned long len)
210{
211 if (TASK_SIZE - len < addr)
212 return false;
213
214 return (addr > DEFAULT_MAP_WINDOW) == (addr + len > DEFAULT_MAP_WINDOW);
215}
216
217/* Can we access it for direct reading/writing? Must be RAM: */
218int valid_phys_addr_range(phys_addr_t addr, size_t count)
219{
220 return addr + count - 1 <= __pa(high_memory - 1);
221}
222
223/* Can we access it through mmap? Must be a valid physical address: */
224int valid_mmap_phys_addr_range(unsigned long pfn, size_t count)
225{
226 phys_addr_t addr = (phys_addr_t)pfn << PAGE_SHIFT;
227
228 return phys_addr_valid(addr + count - 1);
229}
230
231/*
232 * Only allow root to set high MMIO mappings to PROT_NONE.
233 * This prevents an unpriv. user to set them to PROT_NONE and invert
234 * them, then pointing to valid memory for L1TF speculation.
235 *
236 * Note: for locked down kernels may want to disable the root override.
237 */
238bool pfn_modify_allowed(unsigned long pfn, pgprot_t prot)
239{
240 if (!boot_cpu_has_bug(X86_BUG_L1TF))
241 return true;
242 if (!__pte_needs_invert(pgprot_val(prot)))
243 return true;
244 /* If it's real memory always allow */
245 if (pfn_valid(pfn))
246 return true;
247 if (pfn >= l1tf_pfn_limit() && !capable(CAP_SYS_ADMIN))
248 return false;
249 return true;
250}