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_u32() & 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 ~128 MB hole. 62 */ 63 gap_min = SZ_128M; 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 static int get_align_mask(struct file *filp, unsigned long flags) 75 { 76 if (!(current->flags & PF_RANDOMIZE)) 77 return 0; 78 if (filp || (flags & MAP_SHARED)) 79 return MMAP_ALIGN_MASK << PAGE_SHIFT; 80 return 0; 81 } 82 83 unsigned long arch_get_unmapped_area(struct file *filp, unsigned long addr, 84 unsigned long len, unsigned long pgoff, 85 unsigned long flags) 86 { 87 struct mm_struct *mm = current->mm; 88 struct vm_area_struct *vma; 89 struct vm_unmapped_area_info info = {}; 90 91 if (len > TASK_SIZE - mmap_min_addr) 92 return -ENOMEM; 93 94 if (flags & MAP_FIXED) 95 goto check_asce_limit; 96 97 if (addr) { 98 addr = PAGE_ALIGN(addr); 99 vma = find_vma(mm, addr); 100 if (TASK_SIZE - len >= addr && addr >= mmap_min_addr && 101 (!vma || addr + len <= vm_start_gap(vma))) 102 goto check_asce_limit; 103 } 104 105 info.length = len; 106 info.low_limit = mm->mmap_base; 107 info.high_limit = TASK_SIZE; 108 info.align_mask = get_align_mask(filp, flags); 109 info.align_offset = pgoff << PAGE_SHIFT; 110 addr = vm_unmapped_area(&info); 111 if (offset_in_page(addr)) 112 return addr; 113 114 check_asce_limit: 115 return check_asce_limit(mm, addr, len); 116 } 117 118 unsigned long arch_get_unmapped_area_topdown(struct file *filp, unsigned long addr, 119 unsigned long len, unsigned long pgoff, 120 unsigned long flags) 121 { 122 struct vm_area_struct *vma; 123 struct mm_struct *mm = current->mm; 124 struct vm_unmapped_area_info info = {}; 125 126 /* requested length too big for entire address space */ 127 if (len > TASK_SIZE - mmap_min_addr) 128 return -ENOMEM; 129 130 if (flags & MAP_FIXED) 131 goto check_asce_limit; 132 133 /* requesting a specific address */ 134 if (addr) { 135 addr = PAGE_ALIGN(addr); 136 vma = find_vma(mm, addr); 137 if (TASK_SIZE - len >= addr && addr >= mmap_min_addr && 138 (!vma || addr + len <= vm_start_gap(vma))) 139 goto check_asce_limit; 140 } 141 142 info.flags = VM_UNMAPPED_AREA_TOPDOWN; 143 info.length = len; 144 info.low_limit = PAGE_SIZE; 145 info.high_limit = mm->mmap_base; 146 info.align_mask = get_align_mask(filp, flags); 147 info.align_offset = pgoff << PAGE_SHIFT; 148 addr = vm_unmapped_area(&info); 149 150 /* 151 * A failed mmap() very likely causes application failure, 152 * so fall back to the bottom-up function here. This scenario 153 * can happen with large stack limits and large mmap() 154 * allocations. 155 */ 156 if (offset_in_page(addr)) { 157 VM_BUG_ON(addr != -ENOMEM); 158 info.flags = 0; 159 info.low_limit = TASK_UNMAPPED_BASE; 160 info.high_limit = TASK_SIZE; 161 addr = vm_unmapped_area(&info); 162 if (offset_in_page(addr)) 163 return addr; 164 } 165 166 check_asce_limit: 167 return check_asce_limit(mm, addr, len); 168 } 169 170 /* 171 * This function, called very early during the creation of a new 172 * process VM image, sets up which VM layout function to use: 173 */ 174 void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack) 175 { 176 unsigned long random_factor = 0UL; 177 178 if (current->flags & PF_RANDOMIZE) 179 random_factor = arch_mmap_rnd(); 180 181 /* 182 * Fall back to the standard layout if the personality 183 * bit is set, or if the expected stack growth is unlimited: 184 */ 185 if (mmap_is_legacy(rlim_stack)) { 186 mm->mmap_base = mmap_base_legacy(random_factor); 187 clear_bit(MMF_TOPDOWN, &mm->flags); 188 } else { 189 mm->mmap_base = mmap_base(random_factor, rlim_stack); 190 set_bit(MMF_TOPDOWN, &mm->flags); 191 } 192 } 193 194 static const pgprot_t protection_map[16] = { 195 [VM_NONE] = PAGE_NONE, 196 [VM_READ] = PAGE_RO, 197 [VM_WRITE] = PAGE_RO, 198 [VM_WRITE | VM_READ] = PAGE_RO, 199 [VM_EXEC] = PAGE_RX, 200 [VM_EXEC | VM_READ] = PAGE_RX, 201 [VM_EXEC | VM_WRITE] = PAGE_RX, 202 [VM_EXEC | VM_WRITE | VM_READ] = PAGE_RX, 203 [VM_SHARED] = PAGE_NONE, 204 [VM_SHARED | VM_READ] = PAGE_RO, 205 [VM_SHARED | VM_WRITE] = PAGE_RW, 206 [VM_SHARED | VM_WRITE | VM_READ] = PAGE_RW, 207 [VM_SHARED | VM_EXEC] = PAGE_RX, 208 [VM_SHARED | VM_EXEC | VM_READ] = PAGE_RX, 209 [VM_SHARED | VM_EXEC | VM_WRITE] = PAGE_RWX, 210 [VM_SHARED | VM_EXEC | VM_WRITE | VM_READ] = PAGE_RWX 211 }; 212 DECLARE_VM_GET_PAGE_PROT 213