LXR linux/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
  39static 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
  50static unsigned long mmap_rnd(void)
  51{
  52        unsigned long rnd = 0;
  53
  54        if (current->flags & PF_RANDOMIZE)
  55                rnd = (long)get_random_int() & STACK_RND_MASK;
  56
  57        return rnd << PAGE_SHIFT;
  58}
  59
  60static unsigned long mmap_base(void)
  61{
  62        unsigned long gap = rlimit(RLIMIT_STACK);
  63
  64        if (gap < MIN_GAP)
  65                gap = MIN_GAP;
  66        else if (gap > MAX_GAP)
  67                gap = MAX_GAP;
  68
  69        return PAGE_ALIGN(STACK_TOP - gap - mmap_rnd());
  70}
  71
  72/*
  73 * This function, called very early during the creation of a new process VM
  74 * image, sets up which VM layout function to use:
  75 */
  76void arch_pick_mmap_layout(struct mm_struct *mm)
  77{
  78        /*
  79         * Fall back to the standard layout if the personality bit is set, or
  80         * if the expected stack growth is unlimited:
  81         */
  82        if (mmap_is_legacy()) {
  83                mm->mmap_base = TASK_UNMAPPED_BASE;
  84                mm->get_unmapped_area = arch_get_unmapped_area;
  85        } else {
  86                mm->mmap_base = mmap_base();
  87                mm->get_unmapped_area = arch_get_unmapped_area_topdown;
  88        }
  89}
  90EXPORT_SYMBOL_GPL(arch_pick_mmap_layout);
  91
  92
  93/*
  94 * You really shouldn't be using read() or write() on /dev/mem.  This might go
  95 * away in the future.
  96 */
  97int valid_phys_addr_range(phys_addr_t addr, size_t size)
  98{
  99        if (addr < PHYS_OFFSET)
 100                return 0;
 101        if (addr + size > __pa(high_memory - 1) + 1)
 102                return 0;
 103
 104        return 1;
 105}
 106
 107/*
 108 * Do not allow /dev/mem mappings beyond the supported physical range.
 109 */
 110int valid_mmap_phys_addr_range(unsigned long pfn, size_t size)
 111{
 112        return !(((pfn << PAGE_SHIFT) + size) & ~PHYS_MASK);
 113}
 114
 115#ifdef CONFIG_STRICT_DEVMEM
 116
 117#include <linux/ioport.h>
 118
 119/*
 120 * devmem_is_allowed() checks to see if /dev/mem access to a certain address
 121 * is valid. The argument is a physical page number.  We mimic x86 here by
 122 * disallowing access to system RAM as well as device-exclusive MMIO regions.
 123 * This effectively disable read()/write() on /dev/mem.
 124 */
 125int devmem_is_allowed(unsigned long pfn)
 126{
 127        if (iomem_is_exclusive(pfn << PAGE_SHIFT))
 128                return 0;
 129        if (!page_is_ram(pfn))
 130                return 1;
 131        return 0;
 132}
 133
 134#endif
 135