arch/x86/mm/mmap.c

   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                                struct rlimit *rlim_stack)
  95 {
  96         unsigned long gap = rlim_stack->rlim_cur;
  97         unsigned long pad = stack_maxrandom_size(task_size) + stack_guard_gap;
  98         unsigned long gap_min, gap_max;
  99
 100         /* Values close to RLIM_INFINITY can overflow. */
 101         if (gap + pad > gap)
 102                 gap += pad;
 103
 104         /*
 105          * Top of mmap area (just below the process stack).
 106          * Leave an at least ~128 MB hole with possible stack randomization.
 107          */
 108         gap_min = SIZE_128M;
 109         gap_max = (task_size / 6) * 5;
 110
 111         if (gap < gap_min)
 112                 gap = gap_min;
 113         else if (gap > gap_max)
 114                 gap = gap_max;
 115
 116         return PAGE_ALIGN(task_size - gap - rnd);
 117 }
 118
 119 static unsigned long mmap_legacy_base(unsigned long rnd,
 120                                       unsigned long task_size)
 121 {
 122         return __TASK_UNMAPPED_BASE(task_size) + rnd;
 123 }
 124
 125 /*
 126  * This function, called very early during the creation of a new
 127  * process VM image, sets up which VM layout function to use:
 128  */
 129 static void arch_pick_mmap_base(unsigned long *base, unsigned long *legacy_base,
 130                 unsigned long random_factor, unsigned long task_size,
 131                 struct rlimit *rlim_stack)
 132 {
 133         *legacy_base = mmap_legacy_base(random_factor, task_size);
 134         if (mmap_is_legacy())
 135                 *base = *legacy_base;
 136         else
 137                 *base = mmap_base(random_factor, task_size, rlim_stack);
 138 }
 139
 140 void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
 141 {
 142         if (mmap_is_legacy())
 143                 mm->get_unmapped_area = arch_get_unmapped_area;
 144         else
 145                 mm->get_unmapped_area = arch_get_unmapped_area_topdown;
 146
 147         arch_pick_mmap_base(&mm->mmap_base, &mm->mmap_legacy_base,
 148                         arch_rnd(mmap64_rnd_bits), task_size_64bit(0),
 149                         rlim_stack);
 150
 151 #ifdef CONFIG_HAVE_ARCH_COMPAT_MMAP_BASES
 152         /*
 153          * The mmap syscall mapping base decision depends solely on the
 154          * syscall type (64-bit or compat). This applies for 64bit
 155          * applications and 32bit applications. The 64bit syscall uses
 156          * mmap_base, the compat syscall uses mmap_compat_base.
 157          */
 158         arch_pick_mmap_base(&mm->mmap_compat_base, &mm->mmap_compat_legacy_base,
 159                         arch_rnd(mmap32_rnd_bits), task_size_32bit(),
 160                         rlim_stack);
 161 #endif
 162 }
 163
 164 unsigned long get_mmap_base(int is_legacy)
 165 {
 166         struct mm_struct *mm = current->mm;
 167
 168 #ifdef CONFIG_HAVE_ARCH_COMPAT_MMAP_BASES
 169         if (in_32bit_syscall()) {
 170                 return is_legacy ? mm->mmap_compat_legacy_base
 171                                  : mm->mmap_compat_base;
 172         }
 173 #endif
 174         return is_legacy ? mm->mmap_legacy_base : mm->mmap_base;
 175 }
 176
 177 const char *arch_vma_name(struct vm_area_struct *vma)
 178 {
 179         if (vma->vm_flags & VM_MPX)
 180                 return "[mpx]";
 181         return NULL;
 182 }
 183
 184 /**
 185  * mmap_address_hint_valid - Validate the address hint of mmap
 186  * @addr:       Address hint
 187  * @len:        Mapping length
 188  *
 189  * Check whether @addr and @addr + @len result in a valid mapping.
 190  *
 191  * On 32bit this only checks whether @addr + @len is <= TASK_SIZE.
 192  *
 193  * On 64bit with 5-level page tables another sanity check is required
 194  * because mappings requested by mmap(@addr, 0) which cross the 47-bit
 195  * virtual address boundary can cause the following theoretical issue:
 196  *
 197  *  An application calls mmap(addr, 0), i.e. without MAP_FIXED, where @addr
 198  *  is below the border of the 47-bit address space and @addr + @len is
 199  *  above the border.
 200  *
 201  *  With 4-level paging this request succeeds, but the resulting mapping
 202  *  address will always be within the 47-bit virtual address space, because
 203  *  the hint address does not result in a valid mapping and is
 204  *  ignored. Hence applications which are not prepared to handle virtual
 205  *  addresses above 47-bit work correctly.
 206  *
 207  *  With 5-level paging this request would be granted and result in a
 208  *  mapping which crosses the border of the 47-bit virtual address
 209  *  space. If the application cannot handle addresses above 47-bit this
 210  *  will lead to misbehaviour and hard to diagnose failures.
 211  *
 212  * Therefore ignore address hints which would result in a mapping crossing
 213  * the 47-bit virtual address boundary.
 214  *
 215  * Note, that in the same scenario with MAP_FIXED the behaviour is
 216  * different. The request with @addr < 47-bit and @addr + @len > 47-bit
 217  * fails on a 4-level paging machine but succeeds on a 5-level paging
 218  * machine. It is reasonable to expect that an application does not rely on
 219  * the failure of such a fixed mapping request, so the restriction is not
 220  * applied.
 221  */
 222 bool mmap_address_hint_valid(unsigned long addr, unsigned long len)
 223 {
 224         if (TASK_SIZE - len < addr)
 225                 return false;
 226
 227         return (addr > DEFAULT_MAP_WINDOW) == (addr + len > DEFAULT_MAP_WINDOW);
 228 }
 229
 230 /* Can we access it for direct reading/writing? Must be RAM: */
 231 int valid_phys_addr_range(phys_addr_t addr, size_t count)
 232 {
 233         return addr + count <= __pa(high_memory);
 234 }
 235
 236 /* Can we access it through mmap? Must be a valid physical address: */
 237 int valid_mmap_phys_addr_range(unsigned long pfn, size_t count)
 238 {
 239         phys_addr_t addr = (phys_addr_t)pfn << PAGE_SHIFT;
 240
 241         return phys_addr_valid(addr + count - 1);
 242 }
 243
 244 /*
 245  * Only allow root to set high MMIO mappings to PROT_NONE.
 246  * This prevents an unpriv. user to set them to PROT_NONE and invert
 247  * them, then pointing to valid memory for L1TF speculation.
 248  *
 249  * Note: for locked down kernels may want to disable the root override.
 250  */
 251 bool pfn_modify_allowed(unsigned long pfn, pgprot_t prot)
 252 {
 253         if (!boot_cpu_has_bug(X86_BUG_L1TF))
 254                 return true;
 255         if (!__pte_needs_invert(pgprot_val(prot)))
 256                 return true;
 257         /* If it's real memory always allow */
 258         if (pfn_valid(pfn))
 259                 return true;
 260         if (pfn >= l1tf_pfn_limit() && !capable(CAP_SYS_ADMIN))
 261                 return false;
 262         return true;
 263 }