arch/arm64/mm/mmap.c

   1 /*
   2  * Based on arch/arm/mm/mmap.c
   3  *
   4  * Copyright (C) 2012 ARM Ltd.
   5  *
   6  * This program is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License version 2 as
   8  * published by the Free Software Foundation.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License
  16  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  17  */
  18
  19 #include <linux/elf.h>
  20 #include <linux/fs.h>
  21 #include <linux/memblock.h>
  22 #include <linux/mm.h>
  23 #include <linux/mman.h>
  24 #include <linux/export.h>
  25 #include <linux/shm.h>
  26 #include <linux/sched/signal.h>
  27 #include <linux/sched/mm.h>
  28 #include <linux/io.h>
  29 #include <linux/personality.h>
  30 #include <linux/random.h>
  31
  32 #include <asm/cputype.h>
  33
  34 /*
  35  * Leave enough space between the mmap area and the stack to honour ulimit in
  36  * the face of randomisation.
  37  */
  38 #define MIN_GAP (SZ_128M + ((STACK_RND_MASK << PAGE_SHIFT) + 1))
  39 #define MAX_GAP (STACK_TOP/6*5)
  40
  41 static int mmap_is_legacy(void)
  42 {
  43         if (current->personality & ADDR_COMPAT_LAYOUT)
  44                 return 1;
  45
  46         if (rlimit(RLIMIT_STACK) == RLIM_INFINITY)
  47                 return 1;
  48
  49         return sysctl_legacy_va_layout;
  50 }
  51
  52 unsigned long arch_mmap_rnd(void)
  53 {
  54         unsigned long rnd;
  55
  56 #ifdef CONFIG_COMPAT
  57         if (test_thread_flag(TIF_32BIT))
  58                 rnd = get_random_long() & ((1UL << mmap_rnd_compat_bits) - 1);
  59         else
  60 #endif
  61                 rnd = get_random_long() & ((1UL << mmap_rnd_bits) - 1);
  62         return rnd << PAGE_SHIFT;
  63 }
  64
  65 static unsigned long mmap_base(unsigned long rnd)
  66 {
  67         unsigned long gap = rlimit(RLIMIT_STACK);
  68
  69         if (gap < MIN_GAP)
  70                 gap = MIN_GAP;
  71         else if (gap > MAX_GAP)
  72                 gap = MAX_GAP;
  73
  74         return PAGE_ALIGN(STACK_TOP - gap - rnd);
  75 }
  76
  77 /*
  78  * This function, called very early during the creation of a new process VM
  79  * image, sets up which VM layout function to use:
  80  */
  81 void arch_pick_mmap_layout(struct mm_struct *mm)
  82 {
  83         unsigned long random_factor = 0UL;
  84
  85         if (current->flags & PF_RANDOMIZE)
  86                 random_factor = arch_mmap_rnd();
  87
  88         /*
  89          * Fall back to the standard layout if the personality bit is set, or
  90          * if the expected stack growth is unlimited:
  91          */
  92         if (mmap_is_legacy()) {
  93                 mm->mmap_base = TASK_UNMAPPED_BASE + random_factor;
  94                 mm->get_unmapped_area = arch_get_unmapped_area;
  95         } else {
  96                 mm->mmap_base = mmap_base(random_factor);
  97                 mm->get_unmapped_area = arch_get_unmapped_area_topdown;
  98         }
  99 }
 100
 101 /*
 102  * You really shouldn't be using read() or write() on /dev/mem.  This might go
 103  * away in the future.
 104  */
 105 int valid_phys_addr_range(phys_addr_t addr, size_t size)
 106 {
 107         /*
 108          * Check whether addr is covered by a memory region without the
 109          * MEMBLOCK_NOMAP attribute, and whether that region covers the
 110          * entire range. In theory, this could lead to false negatives
 111          * if the range is covered by distinct but adjacent memory regions
 112          * that only differ in other attributes. However, few of such
 113          * attributes have been defined, and it is debatable whether it
 114          * follows that /dev/mem read() calls should be able traverse
 115          * such boundaries.
 116          */
 117         return memblock_is_region_memory(addr, size) &&
 118                memblock_is_map_memory(addr);
 119 }
 120
 121 /*
 122  * Do not allow /dev/mem mappings beyond the supported physical range.
 123  */
 124 int valid_mmap_phys_addr_range(unsigned long pfn, size_t size)
 125 {
 126         return !(((pfn << PAGE_SHIFT) + size) & ~PHYS_MASK);
 127 }
 128
 129 #ifdef CONFIG_STRICT_DEVMEM
 130
 131 #include <linux/ioport.h>
 132
 133 /*
 134  * devmem_is_allowed() checks to see if /dev/mem access to a certain address
 135  * is valid. The argument is a physical page number.  We mimic x86 here by
 136  * disallowing access to system RAM as well as device-exclusive MMIO regions.
 137  * This effectively disable read()/write() on /dev/mem.
 138  */
 139 int devmem_is_allowed(unsigned long pfn)
 140 {
 141         if (iomem_is_exclusive(pfn << PAGE_SHIFT))
 142                 return 0;
 143         if (!page_is_ram(pfn))
 144                 return 1;
 145         return 0;
 146 }
 147
 148 #endif