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 unsigned long arch_mmap_rnd(void)
  51 {
  52         unsigned long rnd;
  53
  54         rnd = (unsigned long)get_random_int() & STACK_RND_MASK;
  55
  56         return rnd << PAGE_SHIFT;
  57 }
  58
  59 static unsigned long mmap_base(unsigned long rnd)
  60 {
  61         unsigned long gap = rlimit(RLIMIT_STACK);
  62
  63         if (gap < MIN_GAP)
  64                 gap = MIN_GAP;
  65         else if (gap > MAX_GAP)
  66                 gap = MAX_GAP;
  67
  68         return PAGE_ALIGN(STACK_TOP - gap - rnd);
  69 }
  70
  71 /*
  72  * This function, called very early during the creation of a new process VM
  73  * image, sets up which VM layout function to use:
  74  */
  75 void arch_pick_mmap_layout(struct mm_struct *mm)
  76 {
  77         unsigned long random_factor = 0UL;
  78
  79         if (current->flags & PF_RANDOMIZE)
  80                 random_factor = arch_mmap_rnd();
  81
  82         /*
  83          * Fall back to the standard layout if the personality bit is set, or
  84          * if the expected stack growth is unlimited:
  85          */
  86         if (mmap_is_legacy()) {
  87                 mm->mmap_base = TASK_UNMAPPED_BASE + random_factor;
  88                 mm->get_unmapped_area = arch_get_unmapped_area;
  89         } else {
  90                 mm->mmap_base = mmap_base(random_factor);
  91                 mm->get_unmapped_area = arch_get_unmapped_area_topdown;
  92         }
  93 }
  94 EXPORT_SYMBOL_GPL(arch_pick_mmap_layout);
  95
  96
  97 /*
  98  * You really shouldn't be using read() or write() on /dev/mem.  This might go
  99  * away in the future.
 100  */
 101 int valid_phys_addr_range(phys_addr_t addr, size_t size)
 102 {
 103         if (addr < PHYS_OFFSET)
 104                 return 0;
 105         if (addr + size > __pa(high_memory - 1) + 1)
 106                 return 0;
 107
 108         return 1;
 109 }
 110
 111 /*
 112  * Do not allow /dev/mem mappings beyond the supported physical range.
 113  */
 114 int valid_mmap_phys_addr_range(unsigned long pfn, size_t size)
 115 {
 116         return !(((pfn << PAGE_SHIFT) + size) & ~PHYS_MASK);
 117 }
 118
 119 #ifdef CONFIG_STRICT_DEVMEM
 120
 121 #include <linux/ioport.h>
 122
 123 /*
 124  * devmem_is_allowed() checks to see if /dev/mem access to a certain address
 125  * is valid. The argument is a physical page number.  We mimic x86 here by
 126  * disallowing access to system RAM as well as device-exclusive MMIO regions.
 127  * This effectively disable read()/write() on /dev/mem.
 128  */
 129 int devmem_is_allowed(unsigned long pfn)
 130 {
 131         if (iomem_is_exclusive(pfn << PAGE_SHIFT))
 132                 return 0;
 133         if (!page_is_ram(pfn))
 134                 return 1;
 135         return 0;
 136 }
 137
 138 #endif