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 <linux/elf-randomize.h> 22 #include <asm/elf.h> 23 #include <asm/io.h> 24 25 #include "physaddr.h" 26 27 struct va_alignment __read_mostly va_align = { 28 .flags = -1, 29 }; 30 31 unsigned long task_size_32bit(void) 32 { 33 return IA32_PAGE_OFFSET; 34 } 35 36 unsigned long task_size_64bit(int full_addr_space) 37 { 38 return full_addr_space ? TASK_SIZE_MAX : DEFAULT_MAP_WINDOW; 39 } 40 41 static unsigned long stack_maxrandom_size(unsigned long task_size) 42 { 43 unsigned long max = 0; 44 if (current->flags & PF_RANDOMIZE) { 45 max = (-1UL) & __STACK_RND_MASK(task_size == task_size_32bit()); 46 max <<= PAGE_SHIFT; 47 } 48 49 return max; 50 } 51 52 #ifdef CONFIG_COMPAT 53 # define mmap32_rnd_bits mmap_rnd_compat_bits 54 # define mmap64_rnd_bits mmap_rnd_bits 55 #else 56 # define mmap32_rnd_bits mmap_rnd_bits 57 # define mmap64_rnd_bits mmap_rnd_bits 58 #endif 59 60 #define SIZE_128M (128 * 1024 * 1024UL) 61 62 static int mmap_is_legacy(void) 63 { 64 if (current->personality & ADDR_COMPAT_LAYOUT) 65 return 1; 66 67 return sysctl_legacy_va_layout; 68 } 69 70 static unsigned long arch_rnd(unsigned int rndbits) 71 { 72 if (!(current->flags & PF_RANDOMIZE)) 73 return 0; 74 return (get_random_long() & ((1UL << rndbits) - 1)) << PAGE_SHIFT; 75 } 76 77 unsigned long arch_mmap_rnd(void) 78 { 79 return arch_rnd(mmap_is_ia32() ? mmap32_rnd_bits : mmap64_rnd_bits); 80 } 81 82 static unsigned long mmap_base(unsigned long rnd, unsigned long task_size, 83 struct rlimit *rlim_stack) 84 { 85 unsigned long gap = rlim_stack->rlim_cur; 86 unsigned long pad = stack_maxrandom_size(task_size) + stack_guard_gap; 87 unsigned long gap_min, gap_max; 88 89 /* Values close to RLIM_INFINITY can overflow. */ 90 if (gap + pad > gap) 91 gap += pad; 92 93 /* 94 * Top of mmap area (just below the process stack). 95 * Leave an at least ~128 MB hole with possible stack randomization. 96 */ 97 gap_min = SIZE_128M; 98 gap_max = (task_size / 6) * 5; 99 100 if (gap < gap_min) 101 gap = gap_min; 102 else if (gap > gap_max) 103 gap = gap_max; 104 105 return PAGE_ALIGN(task_size - gap - rnd); 106 } 107 108 static unsigned long mmap_legacy_base(unsigned long rnd, 109 unsigned long task_size) 110 { 111 return __TASK_UNMAPPED_BASE(task_size) + rnd; 112 } 113 114 /* 115 * This function, called very early during the creation of a new 116 * process VM image, sets up which VM layout function to use: 117 */ 118 static void arch_pick_mmap_base(unsigned long *base, unsigned long *legacy_base, 119 unsigned long random_factor, unsigned long task_size, 120 struct rlimit *rlim_stack) 121 { 122 *legacy_base = mmap_legacy_base(random_factor, task_size); 123 if (mmap_is_legacy()) 124 *base = *legacy_base; 125 else 126 *base = mmap_base(random_factor, task_size, rlim_stack); 127 } 128 129 void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack) 130 { 131 if (mmap_is_legacy()) 132 clear_bit(MMF_TOPDOWN, &mm->flags); 133 else 134 set_bit(MMF_TOPDOWN, &mm->flags); 135 136 arch_pick_mmap_base(&mm->mmap_base, &mm->mmap_legacy_base, 137 arch_rnd(mmap64_rnd_bits), task_size_64bit(0), 138 rlim_stack); 139 140 #ifdef CONFIG_HAVE_ARCH_COMPAT_MMAP_BASES 141 /* 142 * The mmap syscall mapping base decision depends solely on the 143 * syscall type (64-bit or compat). This applies for 64bit 144 * applications and 32bit applications. The 64bit syscall uses 145 * mmap_base, the compat syscall uses mmap_compat_base. 146 */ 147 arch_pick_mmap_base(&mm->mmap_compat_base, &mm->mmap_compat_legacy_base, 148 arch_rnd(mmap32_rnd_bits), task_size_32bit(), 149 rlim_stack); 150 #endif 151 } 152 153 unsigned long get_mmap_base(int is_legacy) 154 { 155 struct mm_struct *mm = current->mm; 156 157 #ifdef CONFIG_HAVE_ARCH_COMPAT_MMAP_BASES 158 if (in_32bit_syscall()) { 159 return is_legacy ? mm->mmap_compat_legacy_base 160 : mm->mmap_compat_base; 161 } 162 #endif 163 return is_legacy ? mm->mmap_legacy_base : mm->mmap_base; 164 } 165 166 const char *arch_vma_name(struct vm_area_struct *vma) 167 { 168 return NULL; 169 } 170 171 /** 172 * mmap_address_hint_valid - Validate the address hint of mmap 173 * @addr: Address hint 174 * @len: Mapping length 175 * 176 * Check whether @addr and @addr + @len result in a valid mapping. 177 * 178 * On 32bit this only checks whether @addr + @len is <= TASK_SIZE. 179 * 180 * On 64bit with 5-level page tables another sanity check is required 181 * because mappings requested by mmap(@addr, 0) which cross the 47-bit 182 * virtual address boundary can cause the following theoretical issue: 183 * 184 * An application calls mmap(addr, 0), i.e. without MAP_FIXED, where @addr 185 * is below the border of the 47-bit address space and @addr + @len is 186 * above the border. 187 * 188 * With 4-level paging this request succeeds, but the resulting mapping 189 * address will always be within the 47-bit virtual address space, because 190 * the hint address does not result in a valid mapping and is 191 * ignored. Hence applications which are not prepared to handle virtual 192 * addresses above 47-bit work correctly. 193 * 194 * With 5-level paging this request would be granted and result in a 195 * mapping which crosses the border of the 47-bit virtual address 196 * space. If the application cannot handle addresses above 47-bit this 197 * will lead to misbehaviour and hard to diagnose failures. 198 * 199 * Therefore ignore address hints which would result in a mapping crossing 200 * the 47-bit virtual address boundary. 201 * 202 * Note, that in the same scenario with MAP_FIXED the behaviour is 203 * different. The request with @addr < 47-bit and @addr + @len > 47-bit 204 * fails on a 4-level paging machine but succeeds on a 5-level paging 205 * machine. It is reasonable to expect that an application does not rely on 206 * the failure of such a fixed mapping request, so the restriction is not 207 * applied. 208 */ 209 bool mmap_address_hint_valid(unsigned long addr, unsigned long len) 210 { 211 if (TASK_SIZE - len < addr) 212 return false; 213 214 return (addr > DEFAULT_MAP_WINDOW) == (addr + len > DEFAULT_MAP_WINDOW); 215 } 216 217 /* Can we access it for direct reading/writing? Must be RAM: */ 218 int valid_phys_addr_range(phys_addr_t addr, size_t count) 219 { 220 return addr + count - 1 <= __pa(high_memory - 1); 221 } 222 223 /* Can we access it through mmap? Must be a valid physical address: */ 224 int valid_mmap_phys_addr_range(unsigned long pfn, size_t count) 225 { 226 phys_addr_t addr = (phys_addr_t)pfn << PAGE_SHIFT; 227 228 return phys_addr_valid(addr + count - 1); 229 } 230 231 /* 232 * Only allow root to set high MMIO mappings to PROT_NONE. 233 * This prevents an unpriv. user to set them to PROT_NONE and invert 234 * them, then pointing to valid memory for L1TF speculation. 235 * 236 * Note: for locked down kernels may want to disable the root override. 237 */ 238 bool pfn_modify_allowed(unsigned long pfn, pgprot_t prot) 239 { 240 if (!boot_cpu_has_bug(X86_BUG_L1TF)) 241 return true; 242 if (!__pte_needs_invert(pgprot_val(prot))) 243 return true; 244 /* If it's real memory always allow */ 245 if (pfn_valid(pfn)) 246 return true; 247 if (pfn >= l1tf_pfn_limit() && !capable(CAP_SYS_ADMIN)) 248 return false; 249 return true; 250 } 251