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/signal.h>
  29 #include <linux/sched/mm.h>
  30 #include <linux/elf-randomize.h>
  31 #include <linux/security.h>
  32 #include <linux/mman.h>
  33
  34 /*
  35  * Top of mmap area (just below the process stack).
  36  *
  37  * Leave at least a ~128 MB hole on 32bit applications.
  38  *
  39  * On 64bit applications we randomise the stack by 1GB so we need to
  40  * space our mmap start address by a further 1GB, otherwise there is a
  41  * chance the mmap area will end up closer to the stack than our ulimit
  42  * requires.
  43  */
  44 #define MIN_GAP32 (128*1024*1024)
  45 #define MIN_GAP64 ((128 + 1024)*1024*1024UL)
  46 #define MIN_GAP ((is_32bit_task()) ? MIN_GAP32 : MIN_GAP64)
  47 #define MAX_GAP (TASK_SIZE/6*5)
  48
  49 static inline int mmap_is_legacy(void)
  50 {
  51         if (current->personality & ADDR_COMPAT_LAYOUT)
  52                 return 1;
  53
  54         if (rlimit(RLIMIT_STACK) == RLIM_INFINITY)
  55                 return 1;
  56
  57         return sysctl_legacy_va_layout;
  58 }
  59
  60 unsigned long arch_mmap_rnd(void)
  61 {
  62         unsigned long shift, rnd;
  63
  64         shift = mmap_rnd_bits;
  65 #ifdef CONFIG_COMPAT
  66         if (is_32bit_task())
  67                 shift = mmap_rnd_compat_bits;
  68 #endif
  69         rnd = get_random_long() % (1ul << shift);
  70
  71         return rnd << PAGE_SHIFT;
  72 }
  73
  74 static inline unsigned long mmap_base(unsigned long rnd)
  75 {
  76         unsigned long gap = rlimit(RLIMIT_STACK);
  77
  78         if (gap < MIN_GAP)
  79                 gap = MIN_GAP;
  80         else if (gap > MAX_GAP)
  81                 gap = MAX_GAP;
  82
  83         return PAGE_ALIGN(DEFAULT_MAP_WINDOW - gap - rnd);
  84 }
  85
  86 #ifdef CONFIG_PPC_RADIX_MMU
  87 /*
  88  * Same function as generic code used only for radix, because we don't need to overload
  89  * the generic one. But we will have to duplicate, because hash select
  90  * HAVE_ARCH_UNMAPPED_AREA
  91  */
  92 static unsigned long
  93 radix__arch_get_unmapped_area(struct file *filp, unsigned long addr,
  94                              unsigned long len, unsigned long pgoff,
  95                              unsigned long flags)
  96 {
  97         struct mm_struct *mm = current->mm;
  98         struct vm_area_struct *vma;
  99         struct vm_unmapped_area_info info;
 100
 101         if (unlikely(addr > mm->context.addr_limit &&
 102                      mm->context.addr_limit != TASK_SIZE))
 103                 mm->context.addr_limit = TASK_SIZE;
 104
 105         if (len > mm->task_size - mmap_min_addr)
 106                 return -ENOMEM;
 107
 108         if (flags & MAP_FIXED)
 109                 return addr;
 110
 111         if (addr) {
 112                 addr = PAGE_ALIGN(addr);
 113                 vma = find_vma(mm, addr);
 114                 if (mm->task_size - len >= addr && addr >= mmap_min_addr &&
 115                     (!vma || addr + len <= vm_start_gap(vma)))
 116                         return addr;
 117         }
 118
 119         info.flags = 0;
 120         info.length = len;
 121         info.low_limit = mm->mmap_base;
 122         info.align_mask = 0;
 123
 124         if (unlikely(addr > DEFAULT_MAP_WINDOW))
 125                 info.high_limit = mm->context.addr_limit;
 126         else
 127                 info.high_limit = DEFAULT_MAP_WINDOW;
 128
 129         return vm_unmapped_area(&info);
 130 }
 131
 132 static unsigned long
 133 radix__arch_get_unmapped_area_topdown(struct file *filp,
 134                                      const unsigned long addr0,
 135                                      const unsigned long len,
 136                                      const unsigned long pgoff,
 137                                      const unsigned long flags)
 138 {
 139         struct vm_area_struct *vma;
 140         struct mm_struct *mm = current->mm;
 141         unsigned long addr = addr0;
 142         struct vm_unmapped_area_info info;
 143
 144         if (unlikely(addr > mm->context.addr_limit &&
 145                      mm->context.addr_limit != TASK_SIZE))
 146                 mm->context.addr_limit = TASK_SIZE;
 147
 148         /* requested length too big for entire address space */
 149         if (len > mm->task_size - mmap_min_addr)
 150                 return -ENOMEM;
 151
 152         if (flags & MAP_FIXED)
 153                 return addr;
 154
 155         /* requesting a specific address */
 156         if (addr) {
 157                 addr = PAGE_ALIGN(addr);
 158                 vma = find_vma(mm, addr);
 159                 if (mm->task_size - len >= addr && addr >= mmap_min_addr &&
 160                                 (!vma || addr + len <= vm_start_gap(vma)))
 161                         return addr;
 162         }
 163
 164         info.flags = VM_UNMAPPED_AREA_TOPDOWN;
 165         info.length = len;
 166         info.low_limit = max(PAGE_SIZE, mmap_min_addr);
 167         info.high_limit = mm->mmap_base;
 168         info.align_mask = 0;
 169
 170         if (addr > DEFAULT_MAP_WINDOW)
 171                 info.high_limit += mm->context.addr_limit - DEFAULT_MAP_WINDOW;
 172
 173         addr = vm_unmapped_area(&info);
 174         if (!(addr & ~PAGE_MASK))
 175                 return addr;
 176         VM_BUG_ON(addr != -ENOMEM);
 177
 178         /*
 179          * A failed mmap() very likely causes application failure,
 180          * so fall back to the bottom-up function here. This scenario
 181          * can happen with large stack limits and large mmap()
 182          * allocations.
 183          */
 184         return radix__arch_get_unmapped_area(filp, addr0, len, pgoff, flags);
 185 }
 186
 187 static void radix__arch_pick_mmap_layout(struct mm_struct *mm,
 188                                         unsigned long random_factor)
 189 {
 190         if (mmap_is_legacy()) {
 191                 mm->mmap_base = TASK_UNMAPPED_BASE;
 192                 mm->get_unmapped_area = radix__arch_get_unmapped_area;
 193         } else {
 194                 mm->mmap_base = mmap_base(random_factor);
 195                 mm->get_unmapped_area = radix__arch_get_unmapped_area_topdown;
 196         }
 197 }
 198 #else
 199 /* dummy */
 200 extern void radix__arch_pick_mmap_layout(struct mm_struct *mm,
 201                                         unsigned long random_factor);
 202 #endif
 203 /*
 204  * This function, called very early during the creation of a new
 205  * process VM image, sets up which VM layout function to use:
 206  */
 207 void arch_pick_mmap_layout(struct mm_struct *mm)
 208 {
 209         unsigned long random_factor = 0UL;
 210
 211         if (current->flags & PF_RANDOMIZE)
 212                 random_factor = arch_mmap_rnd();
 213
 214         if (radix_enabled())
 215                 return radix__arch_pick_mmap_layout(mm, random_factor);
 216         /*
 217          * Fall back to the standard layout if the personality
 218          * bit is set, or if the expected stack growth is unlimited:
 219          */
 220         if (mmap_is_legacy()) {
 221                 mm->mmap_base = TASK_UNMAPPED_BASE;
 222                 mm->get_unmapped_area = arch_get_unmapped_area;
 223         } else {
 224                 mm->mmap_base = mmap_base(random_factor);
 225                 mm->get_unmapped_area = arch_get_unmapped_area_topdown;
 226         }
 227 }