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)
  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         unsigned long pad = (STACK_RND_MASK << PAGE_SHIFT) + stack_guard_gap;
  69
  70         /* Values close to RLIM_INFINITY can overflow. */
  71         if (gap + pad > gap)
  72                 gap += pad;
  73
  74         if (gap < MIN_GAP)
  75                 gap = MIN_GAP;
  76         else if (gap > MAX_GAP)
  77                 gap = MAX_GAP;
  78
  79         return PAGE_ALIGN(STACK_TOP - gap - rnd);
  80 }
  81
  82 /*
  83  * This function, called very early during the creation of a new process VM
  84  * image, sets up which VM layout function to use:
  85  */
  86 void arch_pick_mmap_layout(struct mm_struct *mm)
  87 {
  88         unsigned long random_factor = 0UL;
  89
  90         if (current->flags & PF_RANDOMIZE)
  91                 random_factor = arch_mmap_rnd();
  92
  93         /*
  94          * Fall back to the standard layout if the personality bit is set, or
  95          * if the expected stack growth is unlimited:
  96          */
  97         if (mmap_is_legacy()) {
  98                 mm->mmap_base = TASK_UNMAPPED_BASE + random_factor;
  99                 mm->get_unmapped_area = arch_get_unmapped_area;
 100         } else {
 101                 mm->mmap_base = mmap_base(random_factor);
 102                 mm->get_unmapped_area = arch_get_unmapped_area_topdown;
 103         }
 104 }
 105
 106 /*
 107  * You really shouldn't be using read() or write() on /dev/mem.  This might go
 108  * away in the future.
 109  */
 110 int valid_phys_addr_range(phys_addr_t addr, size_t size)
 111 {
 112         /*
 113          * Check whether addr is covered by a memory region without the
 114          * MEMBLOCK_NOMAP attribute, and whether that region covers the
 115          * entire range. In theory, this could lead to false negatives
 116          * if the range is covered by distinct but adjacent memory regions
 117          * that only differ in other attributes. However, few of such
 118          * attributes have been defined, and it is debatable whether it
 119          * follows that /dev/mem read() calls should be able traverse
 120          * such boundaries.
 121          */
 122         return memblock_is_region_memory(addr, size) &&
 123                memblock_is_map_memory(addr);
 124 }
 125
 126 /*
 127  * Do not allow /dev/mem mappings beyond the supported physical range.
 128  */
 129 int valid_mmap_phys_addr_range(unsigned long pfn, size_t size)
 130 {
 131         return !(((pfn << PAGE_SHIFT) + size) & ~PHYS_MASK);
 132 }
 133
 134 #ifdef CONFIG_STRICT_DEVMEM
 135
 136 #include <linux/ioport.h>
 137
 138 /*
 139  * devmem_is_allowed() checks to see if /dev/mem access to a certain address
 140  * is valid. The argument is a physical page number.  We mimic x86 here by
 141  * disallowing access to system RAM as well as device-exclusive MMIO regions.
 142  * This effectively disable read()/write() on /dev/mem.
 143  */
 144 int devmem_is_allowed(unsigned long pfn)
 145 {
 146         if (iomem_is_exclusive(pfn << PAGE_SHIFT))
 147                 return 0;
 148         if (!page_is_ram(pfn))
 149                 return 1;
 150         return 0;
 151 }
 152
 153 #endif