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 
task_size_32bit(void)31 unsigned long task_size_32bit(void)
32 {
33 	return IA32_PAGE_OFFSET;
34 }
35 
task_size_64bit(int full_addr_space)36 unsigned long task_size_64bit(int full_addr_space)
37 {
38 	return full_addr_space ? TASK_SIZE_MAX : DEFAULT_MAP_WINDOW;
39 }
40 
stack_maxrandom_size(unsigned long task_size)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 
mmap_is_legacy(void)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 
arch_rnd(unsigned int rndbits)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 
arch_mmap_rnd(void)77 unsigned long arch_mmap_rnd(void)
78 {
79 	return arch_rnd(mmap_is_ia32() ? mmap32_rnd_bits : mmap64_rnd_bits);
80 }
81 
mmap_base(unsigned long rnd,unsigned long task_size,struct rlimit * rlim_stack)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 
mmap_legacy_base(unsigned long rnd,unsigned long task_size)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  */
arch_pick_mmap_base(unsigned long * base,unsigned long * legacy_base,unsigned long random_factor,unsigned long task_size,struct rlimit * rlim_stack)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 
arch_pick_mmap_layout(struct mm_struct * mm,struct rlimit * rlim_stack)129 void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
130 {
131 	if (mmap_is_legacy())
132 		mm->get_unmapped_area = arch_get_unmapped_area;
133 	else
134 		mm->get_unmapped_area = arch_get_unmapped_area_topdown;
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 
get_mmap_base(int is_legacy)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 
arch_vma_name(struct vm_area_struct * vma)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  */
mmap_address_hint_valid(unsigned long addr,unsigned long len)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: */
valid_phys_addr_range(phys_addr_t addr,size_t count)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: */
valid_mmap_phys_addr_range(unsigned long pfn,size_t count)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  */
pfn_modify_allowed(unsigned long pfn,pgprot_t prot)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