1 // SPDX-License-Identifier: GPL-2.0-or-later 2 /* 3 * Flexible mmap layout support 4 * 5 * Based on code by Ingo Molnar and Andi Kleen, copyrighted 6 * as follows: 7 * 8 * Copyright 2003-2009 Red Hat Inc. 9 * All Rights Reserved. 10 * Copyright 2005 Andi Kleen, SUSE Labs. 11 * Copyright 2007 Jiri Kosina, SUSE Labs. 12 */ 13 14 #include <linux/personality.h> 15 #include <linux/mm.h> 16 #include <linux/random.h> 17 #include <linux/limits.h> 18 #include <linux/sched/signal.h> 19 #include <linux/sched/mm.h> 20 #include <linux/compat.h> 21 #include <asm/elf.h> 22 23 #include "physaddr.h" 24 25 struct va_alignment __read_mostly va_align = { 26 .flags = -1, 27 }; 28 29 unsigned long task_size_32bit(void) 30 { 31 return IA32_PAGE_OFFSET; 32 } 33 34 unsigned long task_size_64bit(int full_addr_space) 35 { 36 return full_addr_space ? TASK_SIZE_MAX : DEFAULT_MAP_WINDOW; 37 } 38 39 static unsigned long stack_maxrandom_size(unsigned long task_size) 40 { 41 unsigned long max = 0; 42 if (current->flags & PF_RANDOMIZE) { 43 max = (-1UL) & __STACK_RND_MASK(task_size == task_size_32bit()); 44 max <<= PAGE_SHIFT; 45 } 46 47 return max; 48 } 49 50 #ifdef CONFIG_COMPAT 51 # define mmap32_rnd_bits mmap_rnd_compat_bits 52 # define mmap64_rnd_bits mmap_rnd_bits 53 #else 54 # define mmap32_rnd_bits mmap_rnd_bits 55 # define mmap64_rnd_bits mmap_rnd_bits 56 #endif 57 58 #define SIZE_128M (128 * 1024 * 1024UL) 59 60 static int mmap_is_legacy(void) 61 { 62 if (current->personality & ADDR_COMPAT_LAYOUT) 63 return 1; 64 65 return sysctl_legacy_va_layout; 66 } 67 68 static unsigned long arch_rnd(unsigned int rndbits) 69 { 70 if (!(current->flags & PF_RANDOMIZE)) 71 return 0; 72 return (get_random_long() & ((1UL << rndbits) - 1)) << PAGE_SHIFT; 73 } 74 75 unsigned long arch_mmap_rnd(void) 76 { 77 return arch_rnd(mmap_is_ia32() ? mmap32_rnd_bits : mmap64_rnd_bits); 78 } 79 80 static unsigned long mmap_base(unsigned long rnd, unsigned long task_size, 81 struct rlimit *rlim_stack) 82 { 83 unsigned long gap = rlim_stack->rlim_cur; 84 unsigned long pad = stack_maxrandom_size(task_size) + stack_guard_gap; 85 unsigned long gap_min, gap_max; 86 87 /* Values close to RLIM_INFINITY can overflow. */ 88 if (gap + pad > gap) 89 gap += pad; 90 91 /* 92 * Top of mmap area (just below the process stack). 93 * Leave an at least ~128 MB hole with possible stack randomization. 94 */ 95 gap_min = SIZE_128M; 96 gap_max = (task_size / 6) * 5; 97 98 if (gap < gap_min) 99 gap = gap_min; 100 else if (gap > gap_max) 101 gap = gap_max; 102 103 return PAGE_ALIGN(task_size - gap - rnd); 104 } 105 106 static unsigned long mmap_legacy_base(unsigned long rnd, 107 unsigned long task_size) 108 { 109 return __TASK_UNMAPPED_BASE(task_size) + rnd; 110 } 111 112 /* 113 * This function, called very early during the creation of a new 114 * process VM image, sets up which VM layout function to use: 115 */ 116 static void arch_pick_mmap_base(unsigned long *base, unsigned long *legacy_base, 117 unsigned long random_factor, unsigned long task_size, 118 struct rlimit *rlim_stack) 119 { 120 *legacy_base = mmap_legacy_base(random_factor, task_size); 121 if (mmap_is_legacy()) 122 *base = *legacy_base; 123 else 124 *base = mmap_base(random_factor, task_size, rlim_stack); 125 } 126 127 void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack) 128 { 129 if (mmap_is_legacy()) 130 mm->get_unmapped_area = arch_get_unmapped_area; 131 else 132 mm->get_unmapped_area = arch_get_unmapped_area_topdown; 133 134 arch_pick_mmap_base(&mm->mmap_base, &mm->mmap_legacy_base, 135 arch_rnd(mmap64_rnd_bits), task_size_64bit(0), 136 rlim_stack); 137 138 #ifdef CONFIG_HAVE_ARCH_COMPAT_MMAP_BASES 139 /* 140 * The mmap syscall mapping base decision depends solely on the 141 * syscall type (64-bit or compat). This applies for 64bit 142 * applications and 32bit applications. The 64bit syscall uses 143 * mmap_base, the compat syscall uses mmap_compat_base. 144 */ 145 arch_pick_mmap_base(&mm->mmap_compat_base, &mm->mmap_compat_legacy_base, 146 arch_rnd(mmap32_rnd_bits), task_size_32bit(), 147 rlim_stack); 148 #endif 149 } 150 151 unsigned long get_mmap_base(int is_legacy) 152 { 153 struct mm_struct *mm = current->mm; 154 155 #ifdef CONFIG_HAVE_ARCH_COMPAT_MMAP_BASES 156 if (in_32bit_syscall()) { 157 return is_legacy ? mm->mmap_compat_legacy_base 158 : mm->mmap_compat_base; 159 } 160 #endif 161 return is_legacy ? mm->mmap_legacy_base : mm->mmap_base; 162 } 163 164 const char *arch_vma_name(struct vm_area_struct *vma) 165 { 166 return NULL; 167 } 168 169 /** 170 * mmap_address_hint_valid - Validate the address hint of mmap 171 * @addr: Address hint 172 * @len: Mapping length 173 * 174 * Check whether @addr and @addr + @len result in a valid mapping. 175 * 176 * On 32bit this only checks whether @addr + @len is <= TASK_SIZE. 177 * 178 * On 64bit with 5-level page tables another sanity check is required 179 * because mappings requested by mmap(@addr, 0) which cross the 47-bit 180 * virtual address boundary can cause the following theoretical issue: 181 * 182 * An application calls mmap(addr, 0), i.e. without MAP_FIXED, where @addr 183 * is below the border of the 47-bit address space and @addr + @len is 184 * above the border. 185 * 186 * With 4-level paging this request succeeds, but the resulting mapping 187 * address will always be within the 47-bit virtual address space, because 188 * the hint address does not result in a valid mapping and is 189 * ignored. Hence applications which are not prepared to handle virtual 190 * addresses above 47-bit work correctly. 191 * 192 * With 5-level paging this request would be granted and result in a 193 * mapping which crosses the border of the 47-bit virtual address 194 * space. If the application cannot handle addresses above 47-bit this 195 * will lead to misbehaviour and hard to diagnose failures. 196 * 197 * Therefore ignore address hints which would result in a mapping crossing 198 * the 47-bit virtual address boundary. 199 * 200 * Note, that in the same scenario with MAP_FIXED the behaviour is 201 * different. The request with @addr < 47-bit and @addr + @len > 47-bit 202 * fails on a 4-level paging machine but succeeds on a 5-level paging 203 * machine. It is reasonable to expect that an application does not rely on 204 * the failure of such a fixed mapping request, so the restriction is not 205 * applied. 206 */ 207 bool mmap_address_hint_valid(unsigned long addr, unsigned long len) 208 { 209 if (TASK_SIZE - len < addr) 210 return false; 211 212 return (addr > DEFAULT_MAP_WINDOW) == (addr + len > DEFAULT_MAP_WINDOW); 213 } 214 215 /* Can we access it for direct reading/writing? Must be RAM: */ 216 int valid_phys_addr_range(phys_addr_t addr, size_t count) 217 { 218 return addr + count - 1 <= __pa(high_memory - 1); 219 } 220 221 /* Can we access it through mmap? Must be a valid physical address: */ 222 int valid_mmap_phys_addr_range(unsigned long pfn, size_t count) 223 { 224 phys_addr_t addr = (phys_addr_t)pfn << PAGE_SHIFT; 225 226 return phys_addr_valid(addr + count - 1); 227 } 228 229 /* 230 * Only allow root to set high MMIO mappings to PROT_NONE. 231 * This prevents an unpriv. user to set them to PROT_NONE and invert 232 * them, then pointing to valid memory for L1TF speculation. 233 * 234 * Note: for locked down kernels may want to disable the root override. 235 */ 236 bool pfn_modify_allowed(unsigned long pfn, pgprot_t prot) 237 { 238 if (!boot_cpu_has_bug(X86_BUG_L1TF)) 239 return true; 240 if (!__pte_needs_invert(pgprot_val(prot))) 241 return true; 242 /* If it's real memory always allow */ 243 if (pfn_valid(pfn)) 244 return true; 245 if (pfn >= l1tf_pfn_limit() && !capable(CAP_SYS_ADMIN)) 246 return false; 247 return true; 248 } 249