arch/x86/mm/mmap.c

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