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/mm.h>
  22 #include <linux/mman.h>
  23 #include <linux/export.h>
  24 #include <linux/shm.h>
  25 #include <linux/sched.h>
  26 #include <linux/io.h>
  27 #include <linux/personality.h>
  28 #include <linux/random.h>
  29
  30 #include <asm/cputype.h>
  31
  32 /*
  33  * Leave enough space between the mmap area and the stack to honour ulimit in
  34  * the face of randomisation.
  35  */
  36 #define MIN_GAP (SZ_128M + ((STACK_RND_MASK << PAGE_SHIFT) + 1))
  37 #define MAX_GAP (STACK_TOP/6*5)
  38
  39 static int mmap_is_legacy(void)
  40 {
  41         if (current->personality & ADDR_COMPAT_LAYOUT)
  42                 return 1;
  43
  44         if (rlimit(RLIMIT_STACK) == RLIM_INFINITY)
  45                 return 1;
  46
  47         return sysctl_legacy_va_layout;
  48 }
  49
  50 /*
  51  * Since get_random_int() returns the same value within a 1 jiffy window, we
  52  * will almost always get the same randomisation for the stack and mmap
  53  * region. This will mean the relative distance between stack and mmap will be
  54  * the same.
  55  *
  56  * To avoid this we can shift the randomness by 1 bit.
  57  */
  58 static unsigned long mmap_rnd(void)
  59 {
  60         unsigned long rnd = 0;
  61
  62         if (current->flags & PF_RANDOMIZE)
  63                 rnd = (long)get_random_int() & (STACK_RND_MASK >> 1);
  64
  65         return rnd << (PAGE_SHIFT + 1);
  66 }
  67
  68 static unsigned long mmap_base(void)
  69 {
  70         unsigned long gap = rlimit(RLIMIT_STACK);
  71
  72         if (gap < MIN_GAP)
  73                 gap = MIN_GAP;
  74         else if (gap > MAX_GAP)
  75                 gap = MAX_GAP;
  76
  77         return PAGE_ALIGN(STACK_TOP - gap - mmap_rnd());
  78 }
  79
  80 /*
  81  * This function, called very early during the creation of a new process VM
  82  * image, sets up which VM layout function to use:
  83  */
  84 void arch_pick_mmap_layout(struct mm_struct *mm)
  85 {
  86         /*
  87          * Fall back to the standard layout if the personality bit is set, or
  88          * if the expected stack growth is unlimited:
  89          */
  90         if (mmap_is_legacy()) {
  91                 mm->mmap_base = TASK_UNMAPPED_BASE;
  92                 mm->get_unmapped_area = arch_get_unmapped_area;
  93                 mm->unmap_area = arch_unmap_area;
  94         } else {
  95                 mm->mmap_base = mmap_base();
  96                 mm->get_unmapped_area = arch_get_unmapped_area_topdown;
  97                 mm->unmap_area = arch_unmap_area_topdown;
  98         }
  99 }
 100 EXPORT_SYMBOL_GPL(arch_pick_mmap_layout);
 101
 102
 103 /*
 104  * You really shouldn't be using read() or write() on /dev/mem.  This might go
 105  * away in the future.
 106  */
 107 int valid_phys_addr_range(unsigned long addr, size_t size)
 108 {
 109         if (addr < PHYS_OFFSET)
 110                 return 0;
 111         if (addr + size > __pa(high_memory - 1) + 1)
 112                 return 0;
 113
 114         return 1;
 115 }
 116
 117 /*
 118  * Do not allow /dev/mem mappings beyond the supported physical range.
 119  */
 120 int valid_mmap_phys_addr_range(unsigned long pfn, size_t size)
 121 {
 122         return !(((pfn << PAGE_SHIFT) + size) & ~PHYS_MASK);
 123 }
 124
 125 #ifdef CONFIG_STRICT_DEVMEM
 126
 127 #include <linux/ioport.h>
 128
 129 /*
 130  * devmem_is_allowed() checks to see if /dev/mem access to a certain address
 131  * is valid. The argument is a physical page number.  We mimic x86 here by
 132  * disallowing access to system RAM as well as device-exclusive MMIO regions.
 133  * This effectively disable read()/write() on /dev/mem.
 134  */
 135 int devmem_is_allowed(unsigned long pfn)
 136 {
 137         if (iomem_is_exclusive(pfn << PAGE_SHIFT))
 138                 return 0;
 139         if (!page_is_ram(pfn))
 140                 return 1;
 141         return 0;
 142 }
 143
 144 #endif