1 // SPDX-License-Identifier: GPL-2.0+
3 * flexible mmap layout support
5 * Copyright 2003-2004 Red Hat Inc., Durham, North Carolina.
8 * Started by Ingo Molnar <mingo@elte.hu>
11 #include <linux/elf-randomize.h>
12 #include <linux/personality.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>
23 static unsigned long stack_maxrandom_size(void)
25 if (!(current->flags & PF_RANDOMIZE))
27 if (current->personality & ADDR_NO_RANDOMIZE)
29 return STACK_RND_MASK << PAGE_SHIFT;
32 static inline int mmap_is_legacy(struct rlimit *rlim_stack)
34 if (current->personality & ADDR_COMPAT_LAYOUT)
36 if (rlim_stack->rlim_cur == RLIM_INFINITY)
38 return sysctl_legacy_va_layout;
41 unsigned long arch_mmap_rnd(void)
43 return (get_random_int() & MMAP_RND_MASK) << PAGE_SHIFT;
46 static unsigned long mmap_base_legacy(unsigned long rnd)
48 return TASK_UNMAPPED_BASE + rnd;
51 static inline unsigned long mmap_base(unsigned long rnd,
52 struct rlimit *rlim_stack)
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;
58 /* Values close to RLIM_INFINITY can overflow. */
63 * Top of mmap area (just below the process stack).
64 * Leave at least a ~32 MB hole.
66 gap_min = 32 * 1024 * 1024UL;
67 gap_max = (STACK_TOP / 6) * 5;
71 else if (gap > gap_max)
74 return PAGE_ALIGN(STACK_TOP - gap - rnd);
78 arch_get_unmapped_area(struct file *filp, unsigned long addr,
79 unsigned long len, unsigned long pgoff, unsigned long flags)
81 struct mm_struct *mm = current->mm;
82 struct vm_area_struct *vma;
83 struct vm_unmapped_area_info info;
86 if (len > TASK_SIZE - mmap_min_addr)
89 if (flags & MAP_FIXED)
90 goto check_asce_limit;
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;
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;
108 info.align_offset = pgoff << PAGE_SHIFT;
109 addr = vm_unmapped_area(&info);
110 if (addr & ~PAGE_MASK)
114 if (addr + len > current->mm->context.asce_limit &&
115 addr + len <= TASK_SIZE) {
116 rc = crst_table_upgrade(mm, addr + len);
118 return (unsigned long) rc;
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)
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;
135 /* requested length too big for entire address space */
136 if (len > TASK_SIZE - mmap_min_addr)
139 if (flags & MAP_FIXED)
140 goto check_asce_limit;
142 /* requesting a specific address */
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;
151 info.flags = VM_UNMAPPED_AREA_TOPDOWN;
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;
159 info.align_offset = pgoff << PAGE_SHIFT;
160 addr = vm_unmapped_area(&info);
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()
168 if (addr & ~PAGE_MASK) {
169 VM_BUG_ON(addr != -ENOMEM);
171 info.low_limit = TASK_UNMAPPED_BASE;
172 info.high_limit = TASK_SIZE;
173 addr = vm_unmapped_area(&info);
174 if (addr & ~PAGE_MASK)
179 if (addr + len > current->mm->context.asce_limit &&
180 addr + len <= TASK_SIZE) {
181 rc = crst_table_upgrade(mm, addr + len);
183 return (unsigned long) rc;
190 * This function, called very early during the creation of a new
191 * process VM image, sets up which VM layout function to use:
193 void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
195 unsigned long random_factor = 0UL;
197 if (current->flags & PF_RANDOMIZE)
198 random_factor = arch_mmap_rnd();
201 * Fall back to the standard layout if the personality
202 * bit is set, or if the expected stack growth is unlimited:
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;
208 mm->mmap_base = mmap_base(random_factor, rlim_stack);
209 mm->get_unmapped_area = arch_get_unmapped_area_topdown;