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/elf.h>
  21
  22 static unsigned long stack_maxrandom_size(void)
  23 {
  24         if (!(current->flags & PF_RANDOMIZE))
  25                 return 0;
  26         return STACK_RND_MASK << PAGE_SHIFT;
  27 }
  28
  29 static inline int mmap_is_legacy(struct rlimit *rlim_stack)
  30 {
  31         if (current->personality & ADDR_COMPAT_LAYOUT)
  32                 return 1;
  33         if (rlim_stack->rlim_cur == RLIM_INFINITY)
  34                 return 1;
  35         return sysctl_legacy_va_layout;
  36 }
  37
  38 unsigned long arch_mmap_rnd(void)
  39 {
  40         return (get_random_int() & MMAP_RND_MASK) << PAGE_SHIFT;
  41 }
  42
  43 static unsigned long mmap_base_legacy(unsigned long rnd)
  44 {
  45         return TASK_UNMAPPED_BASE + rnd;
  46 }
  47
  48 static inline unsigned long mmap_base(unsigned long rnd,
  49                                       struct rlimit *rlim_stack)
  50 {
  51         unsigned long gap = rlim_stack->rlim_cur;
  52         unsigned long pad = stack_maxrandom_size() + stack_guard_gap;
  53         unsigned long gap_min, gap_max;
  54
  55         /* Values close to RLIM_INFINITY can overflow. */
  56         if (gap + pad > gap)
  57                 gap += pad;
  58
  59         /*
  60          * Top of mmap area (just below the process stack).
  61          * Leave at least a ~32 MB hole.
  62          */
  63         gap_min = 32 * 1024 * 1024UL;
  64         gap_max = (STACK_TOP / 6) * 5;
  65
  66         if (gap < gap_min)
  67                 gap = gap_min;
  68         else if (gap > gap_max)
  69                 gap = gap_max;
  70
  71         return PAGE_ALIGN(STACK_TOP - gap - rnd);
  72 }
  73
  74 unsigned long arch_get_unmapped_area(struct file *filp, unsigned long addr,
  75                                      unsigned long len, unsigned long pgoff,
  76                                      unsigned long flags)
  77 {
  78         struct mm_struct *mm = current->mm;
  79         struct vm_area_struct *vma;
  80         struct vm_unmapped_area_info info;
  81
  82         if (len > TASK_SIZE - mmap_min_addr)
  83                 return -ENOMEM;
  84
  85         if (flags & MAP_FIXED)
  86                 goto check_asce_limit;
  87
  88         if (addr) {
  89                 addr = PAGE_ALIGN(addr);
  90                 vma = find_vma(mm, addr);
  91                 if (TASK_SIZE - len >= addr && addr >= mmap_min_addr &&
  92                     (!vma || addr + len <= vm_start_gap(vma)))
  93                         goto check_asce_limit;
  94         }
  95
  96         info.flags = 0;
  97         info.length = len;
  98         info.low_limit = mm->mmap_base;
  99         info.high_limit = TASK_SIZE;
 100         if (filp || (flags & MAP_SHARED))
 101                 info.align_mask = MMAP_ALIGN_MASK << PAGE_SHIFT;
 102         else
 103                 info.align_mask = 0;
 104         info.align_offset = pgoff << PAGE_SHIFT;
 105         addr = vm_unmapped_area(&info);
 106         if (offset_in_page(addr))
 107                 return addr;
 108
 109 check_asce_limit:
 110         return check_asce_limit(mm, addr, len);
 111 }
 112
 113 unsigned long arch_get_unmapped_area_topdown(struct file *filp, unsigned long addr,
 114                                              unsigned long len, unsigned long pgoff,
 115                                              unsigned long flags)
 116 {
 117         struct vm_area_struct *vma;
 118         struct mm_struct *mm = current->mm;
 119         struct vm_unmapped_area_info info;
 120
 121         /* requested length too big for entire address space */
 122         if (len > TASK_SIZE - mmap_min_addr)
 123                 return -ENOMEM;
 124
 125         if (flags & MAP_FIXED)
 126                 goto check_asce_limit;
 127
 128         /* requesting a specific address */
 129         if (addr) {
 130                 addr = PAGE_ALIGN(addr);
 131                 vma = find_vma(mm, addr);
 132                 if (TASK_SIZE - len >= addr && addr >= mmap_min_addr &&
 133                                 (!vma || addr + len <= vm_start_gap(vma)))
 134                         goto check_asce_limit;
 135         }
 136
 137         info.flags = VM_UNMAPPED_AREA_TOPDOWN;
 138         info.length = len;
 139         info.low_limit = max(PAGE_SIZE, mmap_min_addr);
 140         info.high_limit = mm->mmap_base;
 141         if (filp || (flags & MAP_SHARED))
 142                 info.align_mask = MMAP_ALIGN_MASK << PAGE_SHIFT;
 143         else
 144                 info.align_mask = 0;
 145         info.align_offset = pgoff << PAGE_SHIFT;
 146         addr = vm_unmapped_area(&info);
 147
 148         /*
 149          * A failed mmap() very likely causes application failure,
 150          * so fall back to the bottom-up function here. This scenario
 151          * can happen with large stack limits and large mmap()
 152          * allocations.
 153          */
 154         if (offset_in_page(addr)) {
 155                 VM_BUG_ON(addr != -ENOMEM);
 156                 info.flags = 0;
 157                 info.low_limit = TASK_UNMAPPED_BASE;
 158                 info.high_limit = TASK_SIZE;
 159                 addr = vm_unmapped_area(&info);
 160                 if (offset_in_page(addr))
 161                         return addr;
 162         }
 163
 164 check_asce_limit:
 165         return check_asce_limit(mm, addr, len);
 166 }
 167
 168 /*
 169  * This function, called very early during the creation of a new
 170  * process VM image, sets up which VM layout function to use:
 171  */
 172 void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
 173 {
 174         unsigned long random_factor = 0UL;
 175
 176         if (current->flags & PF_RANDOMIZE)
 177                 random_factor = arch_mmap_rnd();
 178
 179         /*
 180          * Fall back to the standard layout if the personality
 181          * bit is set, or if the expected stack growth is unlimited:
 182          */
 183         if (mmap_is_legacy(rlim_stack)) {
 184                 mm->mmap_base = mmap_base_legacy(random_factor);
 185                 mm->get_unmapped_area = arch_get_unmapped_area;
 186         } else {
 187                 mm->mmap_base = mmap_base(random_factor, rlim_stack);
 188                 mm->get_unmapped_area = arch_get_unmapped_area_topdown;
 189         }
 190 }