arch/s390/mm/mmap.c

   1 // SPDX-License-Identifier: GPL-2.0+
   2 /*
   3  *  flexible mmap layout support
   4  *
   5  * Copyright 2003-2004 Red Hat Inc., Durham, North Carolina.
   6  * All Rights Reserved.
   7  *
   8  * Started by Ingo Molnar <mingo@elte.hu>
   9  */
  10
  11 #include <linux/elf-randomize.h>
  12 #include <linux/personality.h>
  13 #include <linux/mm.h>
  14 #include <linux/mman.h>
  15 #include <linux/sched/signal.h>
  16 #include <linux/sched/mm.h>
  17 #include <linux/random.h>
  18 #include <linux/compat.h>
  19 #include <linux/security.h>
  20 #include <asm/pgalloc.h>
  21 #include <asm/elf.h>
  22
  23 static unsigned long stack_maxrandom_size(void)
  24 {
  25         if (!(current->flags & PF_RANDOMIZE))
  26                 return 0;
  27         if (current->personality & ADDR_NO_RANDOMIZE)
  28                 return 0;
  29         return STACK_RND_MASK << PAGE_SHIFT;
  30 }
  31
  32 static inline int mmap_is_legacy(struct rlimit *rlim_stack)
  33 {
  34         if (current->personality & ADDR_COMPAT_LAYOUT)
  35                 return 1;
  36         if (rlim_stack->rlim_cur == RLIM_INFINITY)
  37                 return 1;
  38         return sysctl_legacy_va_layout;
  39 }
  40
  41 unsigned long arch_mmap_rnd(void)
  42 {
  43         return (get_random_int() & MMAP_RND_MASK) << PAGE_SHIFT;
  44 }
  45
  46 static unsigned long mmap_base_legacy(unsigned long rnd)
  47 {
  48         return TASK_UNMAPPED_BASE + rnd;
  49 }
  50
  51 static inline unsigned long mmap_base(unsigned long rnd,
  52                                       struct rlimit *rlim_stack)
  53 {
  54         unsigned long gap = rlim_stack->rlim_cur;
  55         unsigned long pad = stack_maxrandom_size() + stack_guard_gap;
  56         unsigned long gap_min, gap_max;
  57
  58         /* Values close to RLIM_INFINITY can overflow. */
  59         if (gap + pad > gap)
  60                 gap += pad;
  61
  62         /*
  63          * Top of mmap area (just below the process stack).
  64          * Leave at least a ~32 MB hole.
  65          */
  66         gap_min = 32 * 1024 * 1024UL;
  67         gap_max = (STACK_TOP / 6) * 5;
  68
  69         if (gap < gap_min)
  70                 gap = gap_min;
  71         else if (gap > gap_max)
  72                 gap = gap_max;
  73
  74         return PAGE_ALIGN(STACK_TOP - gap - rnd);
  75 }
  76
  77 unsigned long
  78 arch_get_unmapped_area(struct file *filp, unsigned long addr,
  79                 unsigned long len, unsigned long pgoff, unsigned long flags)
  80 {
  81         struct mm_struct *mm = current->mm;
  82         struct vm_area_struct *vma;
  83         struct vm_unmapped_area_info info;
  84         int rc;
  85
  86         if (len > TASK_SIZE - mmap_min_addr)
  87                 return -ENOMEM;
  88
  89         if (flags & MAP_FIXED)
  90                 goto check_asce_limit;
  91
  92         if (addr) {
  93                 addr = PAGE_ALIGN(addr);
  94                 vma = find_vma(mm, addr);
  95                 if (TASK_SIZE - len >= addr && addr >= mmap_min_addr &&
  96                     (!vma || addr + len <= vm_start_gap(vma)))
  97                         goto check_asce_limit;
  98         }
  99
 100         info.flags = 0;
 101         info.length = len;
 102         info.low_limit = mm->mmap_base;
 103         info.high_limit = TASK_SIZE;
 104         if (filp || (flags & MAP_SHARED))
 105                 info.align_mask = MMAP_ALIGN_MASK << PAGE_SHIFT;
 106         else
 107                 info.align_mask = 0;
 108         info.align_offset = pgoff << PAGE_SHIFT;
 109         addr = vm_unmapped_area(&info);
 110         if (addr & ~PAGE_MASK)
 111                 return addr;
 112
 113 check_asce_limit:
 114         if (addr + len > current->mm->context.asce_limit &&
 115             addr + len <= TASK_SIZE) {
 116                 rc = crst_table_upgrade(mm, addr + len);
 117                 if (rc)
 118                         return (unsigned long) rc;
 119         }
 120
 121         return addr;
 122 }
 123
 124 unsigned long
 125 arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
 126                           const unsigned long len, const unsigned long pgoff,
 127                           const unsigned long flags)
 128 {
 129         struct vm_area_struct *vma;
 130         struct mm_struct *mm = current->mm;
 131         unsigned long addr = addr0;
 132         struct vm_unmapped_area_info info;
 133         int rc;
 134
 135         /* requested length too big for entire address space */
 136         if (len > TASK_SIZE - mmap_min_addr)
 137                 return -ENOMEM;
 138
 139         if (flags & MAP_FIXED)
 140                 goto check_asce_limit;
 141
 142         /* requesting a specific address */
 143         if (addr) {
 144                 addr = PAGE_ALIGN(addr);
 145                 vma = find_vma(mm, addr);
 146                 if (TASK_SIZE - len >= addr && addr >= mmap_min_addr &&
 147                                 (!vma || addr + len <= vm_start_gap(vma)))
 148                         goto check_asce_limit;
 149         }
 150
 151         info.flags = VM_UNMAPPED_AREA_TOPDOWN;
 152         info.length = len;
 153         info.low_limit = max(PAGE_SIZE, mmap_min_addr);
 154         info.high_limit = mm->mmap_base;
 155         if (filp || (flags & MAP_SHARED))
 156                 info.align_mask = MMAP_ALIGN_MASK << PAGE_SHIFT;
 157         else
 158                 info.align_mask = 0;
 159         info.align_offset = pgoff << PAGE_SHIFT;
 160         addr = vm_unmapped_area(&info);
 161
 162         /*
 163          * A failed mmap() very likely causes application failure,
 164          * so fall back to the bottom-up function here. This scenario
 165          * can happen with large stack limits and large mmap()
 166          * allocations.
 167          */
 168         if (addr & ~PAGE_MASK) {
 169                 VM_BUG_ON(addr != -ENOMEM);
 170                 info.flags = 0;
 171                 info.low_limit = TASK_UNMAPPED_BASE;
 172                 info.high_limit = TASK_SIZE;
 173                 addr = vm_unmapped_area(&info);
 174                 if (addr & ~PAGE_MASK)
 175                         return addr;
 176         }
 177
 178 check_asce_limit:
 179         if (addr + len > current->mm->context.asce_limit &&
 180             addr + len <= TASK_SIZE) {
 181                 rc = crst_table_upgrade(mm, addr + len);
 182                 if (rc)
 183                         return (unsigned long) rc;
 184         }
 185
 186         return addr;
 187 }
 188
 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, struct rlimit *rlim_stack)
 194 {
 195         unsigned long random_factor = 0UL;
 196
 197         if (current->flags & PF_RANDOMIZE)
 198                 random_factor = arch_mmap_rnd();
 199
 200         /*
 201          * Fall back to the standard layout if the personality
 202          * bit is set, or if the expected stack growth is unlimited:
 203          */
 204         if (mmap_is_legacy(rlim_stack)) {
 205                 mm->mmap_base = mmap_base_legacy(random_factor);
 206                 mm->get_unmapped_area = arch_get_unmapped_area;
 207         } else {
 208                 mm->mmap_base = mmap_base(random_factor, rlim_stack);
 209                 mm->get_unmapped_area = arch_get_unmapped_area_topdown;
 210         }
 211 }