xref: /linux/arch/x86/mm/mmap.c (revision 37744feebc086908fd89760650f458ab19071750)
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 
25 struct va_alignment __read_mostly va_align = {
26 	.flags = -1,
27 };
28 
29 unsigned long task_size_32bit(void)
30 {
31 	return IA32_PAGE_OFFSET;
32 }
33 
34 unsigned long task_size_64bit(int full_addr_space)
35 {
36 	return full_addr_space ? TASK_SIZE_MAX : DEFAULT_MAP_WINDOW;
37 }
38 
39 static 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 
60 static 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 
68 static 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 
75 unsigned long arch_mmap_rnd(void)
76 {
77 	return arch_rnd(mmap_is_ia32() ? mmap32_rnd_bits : mmap64_rnd_bits);
78 }
79 
80 static 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 
106 static 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  */
116 static 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 
127 void 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 
151 unsigned 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 
164 const char *arch_vma_name(struct vm_area_struct *vma)
165 {
166 	return NULL;
167 }
168 
169 /**
170  * mmap_address_hint_valid - Validate the address hint of mmap
171  * @addr:	Address hint
172  * @len:	Mapping length
173  *
174  * Check whether @addr and @addr + @len result in a valid mapping.
175  *
176  * On 32bit this only checks whether @addr + @len is <= TASK_SIZE.
177  *
178  * On 64bit with 5-level page tables another sanity check is required
179  * because mappings requested by mmap(@addr, 0) which cross the 47-bit
180  * virtual address boundary can cause the following theoretical issue:
181  *
182  *  An application calls mmap(addr, 0), i.e. without MAP_FIXED, where @addr
183  *  is below the border of the 47-bit address space and @addr + @len is
184  *  above the border.
185  *
186  *  With 4-level paging this request succeeds, but the resulting mapping
187  *  address will always be within the 47-bit virtual address space, because
188  *  the hint address does not result in a valid mapping and is
189  *  ignored. Hence applications which are not prepared to handle virtual
190  *  addresses above 47-bit work correctly.
191  *
192  *  With 5-level paging this request would be granted and result in a
193  *  mapping which crosses the border of the 47-bit virtual address
194  *  space. If the application cannot handle addresses above 47-bit this
195  *  will lead to misbehaviour and hard to diagnose failures.
196  *
197  * Therefore ignore address hints which would result in a mapping crossing
198  * the 47-bit virtual address boundary.
199  *
200  * Note, that in the same scenario with MAP_FIXED the behaviour is
201  * different. The request with @addr < 47-bit and @addr + @len > 47-bit
202  * fails on a 4-level paging machine but succeeds on a 5-level paging
203  * machine. It is reasonable to expect that an application does not rely on
204  * the failure of such a fixed mapping request, so the restriction is not
205  * applied.
206  */
207 bool mmap_address_hint_valid(unsigned long addr, unsigned long len)
208 {
209 	if (TASK_SIZE - len < addr)
210 		return false;
211 
212 	return (addr > DEFAULT_MAP_WINDOW) == (addr + len > DEFAULT_MAP_WINDOW);
213 }
214 
215 /* Can we access it for direct reading/writing? Must be RAM: */
216 int valid_phys_addr_range(phys_addr_t addr, size_t count)
217 {
218 	return addr + count - 1 <= __pa(high_memory - 1);
219 }
220 
221 /* Can we access it through mmap? Must be a valid physical address: */
222 int valid_mmap_phys_addr_range(unsigned long pfn, size_t count)
223 {
224 	phys_addr_t addr = (phys_addr_t)pfn << PAGE_SHIFT;
225 
226 	return phys_addr_valid(addr + count - 1);
227 }
228 
229 /*
230  * Only allow root to set high MMIO mappings to PROT_NONE.
231  * This prevents an unpriv. user to set them to PROT_NONE and invert
232  * them, then pointing to valid memory for L1TF speculation.
233  *
234  * Note: for locked down kernels may want to disable the root override.
235  */
236 bool pfn_modify_allowed(unsigned long pfn, pgprot_t prot)
237 {
238 	if (!boot_cpu_has_bug(X86_BUG_L1TF))
239 		return true;
240 	if (!__pte_needs_invert(pgprot_val(prot)))
241 		return true;
242 	/* If it's real memory always allow */
243 	if (pfn_valid(pfn))
244 		return true;
245 	if (pfn >= l1tf_pfn_limit() && !capable(CAP_SYS_ADMIN))
246 		return false;
247 	return true;
248 }
249