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Linux/arch/x86/mm/mmap.c

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  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/signal.h>
 32 #include <linux/sched/mm.h>
 33 #include <linux/compat.h>
 34 #include <asm/elf.h>
 35 
 36 #include "physaddr.h"
 37 
 38 struct va_alignment __read_mostly va_align = {
 39         .flags = -1,
 40 };
 41 
 42 unsigned long task_size_32bit(void)
 43 {
 44         return IA32_PAGE_OFFSET;
 45 }
 46 
 47 unsigned long task_size_64bit(int full_addr_space)
 48 {
 49         return full_addr_space ? TASK_SIZE_MAX : DEFAULT_MAP_WINDOW;
 50 }
 51 
 52 static unsigned long stack_maxrandom_size(unsigned long task_size)
 53 {
 54         unsigned long max = 0;
 55         if (current->flags & PF_RANDOMIZE) {
 56                 max = (-1UL) & __STACK_RND_MASK(task_size == task_size_32bit());
 57                 max <<= PAGE_SHIFT;
 58         }
 59 
 60         return max;
 61 }
 62 
 63 #ifdef CONFIG_COMPAT
 64 # define mmap32_rnd_bits  mmap_rnd_compat_bits
 65 # define mmap64_rnd_bits  mmap_rnd_bits
 66 #else
 67 # define mmap32_rnd_bits  mmap_rnd_bits
 68 # define mmap64_rnd_bits  mmap_rnd_bits
 69 #endif
 70 
 71 #define SIZE_128M    (128 * 1024 * 1024UL)
 72 
 73 static int mmap_is_legacy(void)
 74 {
 75         if (current->personality & ADDR_COMPAT_LAYOUT)
 76                 return 1;
 77 
 78         return sysctl_legacy_va_layout;
 79 }
 80 
 81 static unsigned long arch_rnd(unsigned int rndbits)
 82 {
 83         if (!(current->flags & PF_RANDOMIZE))
 84                 return 0;
 85         return (get_random_long() & ((1UL << rndbits) - 1)) << PAGE_SHIFT;
 86 }
 87 
 88 unsigned long arch_mmap_rnd(void)
 89 {
 90         return arch_rnd(mmap_is_ia32() ? mmap32_rnd_bits : mmap64_rnd_bits);
 91 }
 92 
 93 static unsigned long mmap_base(unsigned long rnd, unsigned long task_size)
 94 {
 95         unsigned long gap = rlimit(RLIMIT_STACK);
 96         unsigned long pad = stack_maxrandom_size(task_size) + stack_guard_gap;
 97         unsigned long gap_min, gap_max;
 98 
 99         /* Values close to RLIM_INFINITY can overflow. */
100         if (gap + pad > gap)
101                 gap += pad;
102 
103         /*
104          * Top of mmap area (just below the process stack).
105          * Leave an at least ~128 MB hole with possible stack randomization.
106          */
107         gap_min = SIZE_128M;
108         gap_max = (task_size / 6) * 5;
109 
110         if (gap < gap_min)
111                 gap = gap_min;
112         else if (gap > gap_max)
113                 gap = gap_max;
114 
115         return PAGE_ALIGN(task_size - gap - rnd);
116 }
117 
118 static unsigned long mmap_legacy_base(unsigned long rnd,
119                                       unsigned long task_size)
120 {
121         return __TASK_UNMAPPED_BASE(task_size) + rnd;
122 }
123 
124 /*
125  * This function, called very early during the creation of a new
126  * process VM image, sets up which VM layout function to use:
127  */
128 static void arch_pick_mmap_base(unsigned long *base, unsigned long *legacy_base,
129                 unsigned long random_factor, unsigned long task_size)
130 {
131         *legacy_base = mmap_legacy_base(random_factor, task_size);
132         if (mmap_is_legacy())
133                 *base = *legacy_base;
134         else
135                 *base = mmap_base(random_factor, task_size);
136 }
137 
138 void arch_pick_mmap_layout(struct mm_struct *mm)
139 {
140         if (mmap_is_legacy())
141                 mm->get_unmapped_area = arch_get_unmapped_area;
142         else
143                 mm->get_unmapped_area = arch_get_unmapped_area_topdown;
144 
145         arch_pick_mmap_base(&mm->mmap_base, &mm->mmap_legacy_base,
146                         arch_rnd(mmap64_rnd_bits), task_size_64bit(0));
147 
148 #ifdef CONFIG_HAVE_ARCH_COMPAT_MMAP_BASES
149         /*
150          * The mmap syscall mapping base decision depends solely on the
151          * syscall type (64-bit or compat). This applies for 64bit
152          * applications and 32bit applications. The 64bit syscall uses
153          * mmap_base, the compat syscall uses mmap_compat_base.
154          */
155         arch_pick_mmap_base(&mm->mmap_compat_base, &mm->mmap_compat_legacy_base,
156                         arch_rnd(mmap32_rnd_bits), task_size_32bit());
157 #endif
158 }
159 
160 unsigned long get_mmap_base(int is_legacy)
161 {
162         struct mm_struct *mm = current->mm;
163 
164 #ifdef CONFIG_HAVE_ARCH_COMPAT_MMAP_BASES
165         if (in_compat_syscall()) {
166                 return is_legacy ? mm->mmap_compat_legacy_base
167                                  : mm->mmap_compat_base;
168         }
169 #endif
170         return is_legacy ? mm->mmap_legacy_base : mm->mmap_base;
171 }
172 
173 const char *arch_vma_name(struct vm_area_struct *vma)
174 {
175         if (vma->vm_flags & VM_MPX)
176                 return "[mpx]";
177         return NULL;
178 }
179 
180 /**
181  * mmap_address_hint_valid - Validate the address hint of mmap
182  * @addr:       Address hint
183  * @len:        Mapping length
184  *
185  * Check whether @addr and @addr + @len result in a valid mapping.
186  *
187  * On 32bit this only checks whether @addr + @len is <= TASK_SIZE.
188  *
189  * On 64bit with 5-level page tables another sanity check is required
190  * because mappings requested by mmap(@addr, 0) which cross the 47-bit
191  * virtual address boundary can cause the following theoretical issue:
192  *
193  *  An application calls mmap(addr, 0), i.e. without MAP_FIXED, where @addr
194  *  is below the border of the 47-bit address space and @addr + @len is
195  *  above the border.
196  *
197  *  With 4-level paging this request succeeds, but the resulting mapping
198  *  address will always be within the 47-bit virtual address space, because
199  *  the hint address does not result in a valid mapping and is
200  *  ignored. Hence applications which are not prepared to handle virtual
201  *  addresses above 47-bit work correctly.
202  *
203  *  With 5-level paging this request would be granted and result in a
204  *  mapping which crosses the border of the 47-bit virtual address
205  *  space. If the application cannot handle addresses above 47-bit this
206  *  will lead to misbehaviour and hard to diagnose failures.
207  *
208  * Therefore ignore address hints which would result in a mapping crossing
209  * the 47-bit virtual address boundary.
210  *
211  * Note, that in the same scenario with MAP_FIXED the behaviour is
212  * different. The request with @addr < 47-bit and @addr + @len > 47-bit
213  * fails on a 4-level paging machine but succeeds on a 5-level paging
214  * machine. It is reasonable to expect that an application does not rely on
215  * the failure of such a fixed mapping request, so the restriction is not
216  * applied.
217  */
218 bool mmap_address_hint_valid(unsigned long addr, unsigned long len)
219 {
220         if (TASK_SIZE - len < addr)
221                 return false;
222 
223         return (addr > DEFAULT_MAP_WINDOW) == (addr + len > DEFAULT_MAP_WINDOW);
224 }
225 
226 /* Can we access it for direct reading/writing? Must be RAM: */
227 int valid_phys_addr_range(phys_addr_t addr, size_t count)
228 {
229         return addr + count <= __pa(high_memory);
230 }
231 
232 /* Can we access it through mmap? Must be a valid physical address: */
233 int valid_mmap_phys_addr_range(unsigned long pfn, size_t count)
234 {
235         phys_addr_t addr = (phys_addr_t)pfn << PAGE_SHIFT;
236 
237         return phys_addr_valid(addr + count - 1);
238 }
239 

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