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
  50unsigned long arch_mmap_rnd(void)
  51{
  52        unsigned long rnd;
  53
  54#ifdef CONFIG_COMPAT
  55        if (test_thread_flag(TIF_32BIT))
  56                rnd = get_random_long() & ((1UL << mmap_rnd_compat_bits) - 1);
  57        else
  58#endif
  59                rnd = get_random_long() & ((1UL << mmap_rnd_bits) - 1);
  60        return rnd << PAGE_SHIFT;
  61}
  62
  63static unsigned long mmap_base(unsigned long rnd)
  64{
  65        unsigned long gap = rlimit(RLIMIT_STACK);
  66
  67        if (gap < MIN_GAP)
  68                gap = MIN_GAP;
  69        else if (gap > MAX_GAP)
  70                gap = MAX_GAP;
  71
  72        return PAGE_ALIGN(STACK_TOP - gap - rnd);
  73}
  74
  75/*
  76 * This function, called very early during the creation of a new process VM
  77 * image, sets up which VM layout function to use:
  78 */
  79void arch_pick_mmap_layout(struct mm_struct *mm)
  80{
  81        unsigned long random_factor = 0UL;
  82
  83        if (current->flags & PF_RANDOMIZE)
  84                random_factor = arch_mmap_rnd();
  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 + random_factor;
  92                mm->get_unmapped_area = arch_get_unmapped_area;
  93        } else {
  94                mm->mmap_base = mmap_base(random_factor);
  95                mm->get_unmapped_area = arch_get_unmapped_area_topdown;
  96        }
  97}
  98
  99/*
 100 * You really shouldn't be using read() or write() on /dev/mem.  This might go
 101 * away in the future.
 102 */
 103int valid_phys_addr_range(phys_addr_t addr, size_t size)
 104{
 105        if (addr < PHYS_OFFSET)
 106                return 0;
 107        if (addr + size > __pa(high_memory - 1) + 1)
 108                return 0;
 109
 110        return 1;
 111}
 112
 113/*
 114 * Do not allow /dev/mem mappings beyond the supported physical range.
 115 */
 116int valid_mmap_phys_addr_range(unsigned long pfn, size_t size)
 117{
 118        return !(((pfn << PAGE_SHIFT) + size) & ~PHYS_MASK);
 119}
 120
 121#ifdef CONFIG_STRICT_DEVMEM
 122
 123#include <linux/ioport.h>
 124
 125/*
 126 * devmem_is_allowed() checks to see if /dev/mem access to a certain address
 127 * is valid. The argument is a physical page number.  We mimic x86 here by
 128 * disallowing access to system RAM as well as device-exclusive MMIO regions.
 129 * This effectively disable read()/write() on /dev/mem.
 130 */
 131int devmem_is_allowed(unsigned long pfn)
 132{
 133        if (iomem_is_exclusive(pfn << PAGE_SHIFT))
 134                return 0;
 135        if (!page_is_ram(pfn))
 136                return 1;
 137        return 0;
 138}
 139
 140#endif
 141