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
27 struct va_alignment __read_mostly va_align = {
28 .flags = -1,
29 };
30
31 unsigned long task_size_32bit(void)
32 {
33 return IA32_PAGE_OFFSET;
34 }
35
36 unsigned long task_size_64bit(int full_addr_space)
37 {
38 return full_addr_space ? TASK_SIZE_MAX : DEFAULT_MAP_WINDOW;
39 }
40
41 static 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
62 static 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
70 static 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
77 unsigned long arch_mmap_rnd(void)
78 {
79 return arch_rnd(mmap_is_ia32() ? mmap32_rnd_bits : mmap64_rnd_bits);
80 }
81
82 static unsigned long mmap_base(unsigned long rnd, unsigned long task_size,
83 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 unsigned long gap_min, gap_max;
88
89 /* Values close to RLIM_INFINITY can overflow. */
90 if (gap + pad > gap)
91 gap += pad;
92
93 /*
94 * Top of mmap area (just below the process stack).
95 * Leave an at least ~128 MB hole with possible stack randomization.
96 */
97 gap_min = SIZE_128M;
98 gap_max = (task_size / 6) * 5;
99
100 if (gap < gap_min)
101 gap = gap_min;
102 else if (gap > gap_max)
103 gap = gap_max;
104
105 return PAGE_ALIGN(task_size - gap - rnd);
106 }
107
108 static unsigned long mmap_legacy_base(unsigned long rnd,
109 unsigned long task_size)
110 {
111 return __TASK_UNMAPPED_BASE(task_size) + rnd;
112 }
113
114 /*
115 * This function, called very early during the creation of a new
116 * process VM image, sets up which VM layout function to use:
117 */
118 static void arch_pick_mmap_base(unsigned long *base, unsigned long *legacy_base,
119 unsigned long random_factor, unsigned long task_size,
120 struct rlimit *rlim_stack)
121 {
122 *legacy_base = mmap_legacy_base(random_factor, task_size);
123 if (mmap_is_legacy())
124 *base = *legacy_base;
125 else
126 *base = mmap_base(random_factor, task_size, rlim_stack);
127 }
128
129 void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
130 {
131 if (mmap_is_legacy())
132 clear_bit(MMF_TOPDOWN, &mm->flags);
133 else
134 set_bit(MMF_TOPDOWN, &mm->flags);
135
136 arch_pick_mmap_base(&mm->mmap_base, &mm->mmap_legacy_base,
137 arch_rnd(mmap64_rnd_bits), task_size_64bit(0),
138 rlim_stack);
139
140 #ifdef CONFIG_HAVE_ARCH_COMPAT_MMAP_BASES
141 /*
142 * The mmap syscall mapping base decision depends solely on the
143 * syscall type (64-bit or compat). This applies for 64bit
144 * applications and 32bit applications. The 64bit syscall uses
145 * mmap_base, the compat syscall uses mmap_compat_base.
146 */
147 arch_pick_mmap_base(&mm->mmap_compat_base, &mm->mmap_compat_legacy_base,
148 arch_rnd(mmap32_rnd_bits), task_size_32bit(),
149 rlim_stack);
150 #endif
151 }
152
153 unsigned long get_mmap_base(int is_legacy)
154 {
155 struct mm_struct *mm = current->mm;
156
157 #ifdef CONFIG_HAVE_ARCH_COMPAT_MMAP_BASES
158 if (in_32bit_syscall()) {
159 return is_legacy ? mm->mmap_compat_legacy_base
160 : mm->mmap_compat_base;
161 }
162 #endif
163 return is_legacy ? mm->mmap_legacy_base : mm->mmap_base;
164 }
165
166 const char *arch_vma_name(struct vm_area_struct *vma)
167 {
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 */
209 bool 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: */
218 int 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: */
224 int 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 */
238 bool 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 }
251
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