arch/powerpc/mm/mmap.c

   1 /*
   2  *  flexible mmap layout support
   3  *
   4  * Copyright 2003-2004 Red Hat Inc., Durham, North Carolina.
   5  * All Rights Reserved.
   6  *
   7  * This program is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License as published by
   9  * the Free Software Foundation; either version 2 of the License, or
  10  * (at your option) any later version.
  11  *
  12  * This program is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15  * GNU General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU General Public License
  18  * along with this program; if not, write to the Free Software
  19  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  20  *
  21  *
  22  * Started by Ingo Molnar <mingo@elte.hu>
  23  */
  24
  25 #include <linux/personality.h>
  26 #include <linux/mm.h>
  27 #include <linux/random.h>
  28 #include <linux/sched.h>
  29 #include <linux/elf-randomize.h>
  30 #include <linux/security.h>
  31 #include <linux/mman.h>
  32
  33 /*
  34  * Top of mmap area (just below the process stack).
  35  *
  36  * Leave at least a ~128 MB hole on 32bit applications.
  37  *
  38  * On 64bit applications we randomise the stack by 1GB so we need to
  39  * space our mmap start address by a further 1GB, otherwise there is a
  40  * chance the mmap area will end up closer to the stack than our ulimit
  41  * requires.
  42  */
  43 #define MIN_GAP32 (128*1024*1024)
  44 #define MIN_GAP64 ((128 + 1024)*1024*1024UL)
  45 #define MIN_GAP ((is_32bit_task()) ? MIN_GAP32 : MIN_GAP64)
  46 #define MAX_GAP (TASK_SIZE/6*5)
  47
  48 static inline int mmap_is_legacy(void)
  49 {
  50         if (current->personality & ADDR_COMPAT_LAYOUT)
  51                 return 1;
  52
  53         if (rlimit(RLIMIT_STACK) == RLIM_INFINITY)
  54                 return 1;
  55
  56         return sysctl_legacy_va_layout;
  57 }
  58
  59 unsigned long arch_mmap_rnd(void)
  60 {
  61         unsigned long rnd;
  62
  63         /* 8MB for 32bit, 1GB for 64bit */
  64         if (is_32bit_task())
  65                 rnd = get_random_long() % (1<<(23-PAGE_SHIFT));
  66         else
  67                 rnd = get_random_long() % (1UL<<(30-PAGE_SHIFT));
  68
  69         return rnd << PAGE_SHIFT;
  70 }
  71
  72 static inline unsigned long mmap_base(unsigned long rnd)
  73 {
  74         unsigned long gap = rlimit(RLIMIT_STACK);
  75
  76         if (gap < MIN_GAP)
  77                 gap = MIN_GAP;
  78         else if (gap > MAX_GAP)
  79                 gap = MAX_GAP;
  80
  81         return PAGE_ALIGN(TASK_SIZE - gap - rnd);
  82 }
  83
  84 #ifdef CONFIG_PPC_RADIX_MMU
  85 /*
  86  * Same function as generic code used only for radix, because we don't need to overload
  87  * the generic one. But we will have to duplicate, because hash select
  88  * HAVE_ARCH_UNMAPPED_AREA
  89  */
  90 static unsigned long
  91 radix__arch_get_unmapped_area(struct file *filp, unsigned long addr,
  92                              unsigned long len, unsigned long pgoff,
  93                              unsigned long flags)
  94 {
  95         struct mm_struct *mm = current->mm;
  96         struct vm_area_struct *vma;
  97         struct vm_unmapped_area_info info;
  98
  99         if (len > TASK_SIZE - mmap_min_addr)
 100                 return -ENOMEM;
 101
 102         if (flags & MAP_FIXED)
 103                 return addr;
 104
 105         if (addr) {
 106                 addr = PAGE_ALIGN(addr);
 107                 vma = find_vma(mm, addr);
 108                 if (TASK_SIZE - len >= addr && addr >= mmap_min_addr &&
 109                     (!vma || addr + len <= vm_start_gap(vma)))
 110                         return addr;
 111         }
 112
 113         info.flags = 0;
 114         info.length = len;
 115         info.low_limit = mm->mmap_base;
 116         info.high_limit = TASK_SIZE;
 117         info.align_mask = 0;
 118         return vm_unmapped_area(&info);
 119 }
 120
 121 static unsigned long
 122 radix__arch_get_unmapped_area_topdown(struct file *filp,
 123                                      const unsigned long addr0,
 124                                      const unsigned long len,
 125                                      const unsigned long pgoff,
 126                                      const unsigned long flags)
 127 {
 128         struct vm_area_struct *vma;
 129         struct mm_struct *mm = current->mm;
 130         unsigned long addr = addr0;
 131         struct vm_unmapped_area_info info;
 132
 133         /* requested length too big for entire address space */
 134         if (len > TASK_SIZE - mmap_min_addr)
 135                 return -ENOMEM;
 136
 137         if (flags & MAP_FIXED)
 138                 return addr;
 139
 140         /* requesting a specific address */
 141         if (addr) {
 142                 addr = PAGE_ALIGN(addr);
 143                 vma = find_vma(mm, addr);
 144                 if (TASK_SIZE - len >= addr && addr >= mmap_min_addr &&
 145                                 (!vma || addr + len <= vm_start_gap(vma)))
 146                         return addr;
 147         }
 148
 149         info.flags = VM_UNMAPPED_AREA_TOPDOWN;
 150         info.length = len;
 151         info.low_limit = max(PAGE_SIZE, mmap_min_addr);
 152         info.high_limit = mm->mmap_base;
 153         info.align_mask = 0;
 154         addr = vm_unmapped_area(&info);
 155
 156         /*
 157          * A failed mmap() very likely causes application failure,
 158          * so fall back to the bottom-up function here. This scenario
 159          * can happen with large stack limits and large mmap()
 160          * allocations.
 161          */
 162         if (addr & ~PAGE_MASK) {
 163                 VM_BUG_ON(addr != -ENOMEM);
 164                 info.flags = 0;
 165                 info.low_limit = TASK_UNMAPPED_BASE;
 166                 info.high_limit = TASK_SIZE;
 167                 addr = vm_unmapped_area(&info);
 168         }
 169
 170         return addr;
 171 }
 172
 173 static void radix__arch_pick_mmap_layout(struct mm_struct *mm,
 174                                         unsigned long random_factor)
 175 {
 176         if (mmap_is_legacy()) {
 177                 mm->mmap_base = TASK_UNMAPPED_BASE;
 178                 mm->get_unmapped_area = radix__arch_get_unmapped_area;
 179         } else {
 180                 mm->mmap_base = mmap_base(random_factor);
 181                 mm->get_unmapped_area = radix__arch_get_unmapped_area_topdown;
 182         }
 183 }
 184 #else
 185 /* dummy */
 186 extern void radix__arch_pick_mmap_layout(struct mm_struct *mm,
 187                                         unsigned long random_factor);
 188 #endif
 189 /*
 190  * This function, called very early during the creation of a new
 191  * process VM image, sets up which VM layout function to use:
 192  */
 193 void arch_pick_mmap_layout(struct mm_struct *mm)
 194 {
 195         unsigned long random_factor = 0UL;
 196
 197         if (current->flags & PF_RANDOMIZE)
 198                 random_factor = arch_mmap_rnd();
 199
 200         if (radix_enabled())
 201                 return radix__arch_pick_mmap_layout(mm, random_factor);
 202         /*
 203          * Fall back to the standard layout if the personality
 204          * bit is set, or if the expected stack growth is unlimited:
 205          */
 206         if (mmap_is_legacy()) {
 207                 mm->mmap_base = TASK_UNMAPPED_BASE;
 208                 mm->get_unmapped_area = arch_get_unmapped_area;
 209         } else {
 210                 mm->mmap_base = mmap_base(random_factor);
 211                 mm->get_unmapped_area = arch_get_unmapped_area_topdown;
 212         }
 213 }