1 /* SPDX-License-Identifier: GPL-2.0 */ 2 #ifndef _ASM_X86_MMU_CONTEXT_H 3 #define _ASM_X86_MMU_CONTEXT_H 4 5 #include <asm/desc.h> 6 #include <linux/atomic.h> 7 #include <linux/mm_types.h> 8 #include <linux/pkeys.h> 9 10 #include <trace/events/tlb.h> 11 12 #include <asm/pgalloc.h> 13 #include <asm/tlbflush.h> 14 #include <asm/paravirt.h> 15 #include <asm/mpx.h> 16 #include <asm/debugreg.h> 17 18 extern atomic64_t last_mm_ctx_id; 19 20 #ifndef CONFIG_PARAVIRT_XXL 21 static inline void paravirt_activate_mm(struct mm_struct *prev, 22 struct mm_struct *next) 23 { 24 } 25 #endif /* !CONFIG_PARAVIRT_XXL */ 26 27 #ifdef CONFIG_PERF_EVENTS 28 29 DECLARE_STATIC_KEY_FALSE(rdpmc_always_available_key); 30 31 static inline void load_mm_cr4_irqsoff(struct mm_struct *mm) 32 { 33 if (static_branch_unlikely(&rdpmc_always_available_key) || 34 atomic_read(&mm->context.perf_rdpmc_allowed)) 35 cr4_set_bits_irqsoff(X86_CR4_PCE); 36 else 37 cr4_clear_bits_irqsoff(X86_CR4_PCE); 38 } 39 #else 40 static inline void load_mm_cr4_irqsoff(struct mm_struct *mm) {} 41 #endif 42 43 #ifdef CONFIG_MODIFY_LDT_SYSCALL 44 /* 45 * ldt_structs can be allocated, used, and freed, but they are never 46 * modified while live. 47 */ 48 struct ldt_struct { 49 /* 50 * Xen requires page-aligned LDTs with special permissions. This is 51 * needed to prevent us from installing evil descriptors such as 52 * call gates. On native, we could merge the ldt_struct and LDT 53 * allocations, but it's not worth trying to optimize. 54 */ 55 struct desc_struct *entries; 56 unsigned int nr_entries; 57 58 /* 59 * If PTI is in use, then the entries array is not mapped while we're 60 * in user mode. The whole array will be aliased at the addressed 61 * given by ldt_slot_va(slot). We use two slots so that we can allocate 62 * and map, and enable a new LDT without invalidating the mapping 63 * of an older, still-in-use LDT. 64 * 65 * slot will be -1 if this LDT doesn't have an alias mapping. 66 */ 67 int slot; 68 }; 69 70 /* This is a multiple of PAGE_SIZE. */ 71 #define LDT_SLOT_STRIDE (LDT_ENTRIES * LDT_ENTRY_SIZE) 72 73 static inline void *ldt_slot_va(int slot) 74 { 75 return (void *)(LDT_BASE_ADDR + LDT_SLOT_STRIDE * slot); 76 } 77 78 /* 79 * Used for LDT copy/destruction. 80 */ 81 static inline void init_new_context_ldt(struct mm_struct *mm) 82 { 83 mm->context.ldt = NULL; 84 init_rwsem(&mm->context.ldt_usr_sem); 85 } 86 int ldt_dup_context(struct mm_struct *oldmm, struct mm_struct *mm); 87 void destroy_context_ldt(struct mm_struct *mm); 88 void ldt_arch_exit_mmap(struct mm_struct *mm); 89 #else /* CONFIG_MODIFY_LDT_SYSCALL */ 90 static inline void init_new_context_ldt(struct mm_struct *mm) { } 91 static inline int ldt_dup_context(struct mm_struct *oldmm, 92 struct mm_struct *mm) 93 { 94 return 0; 95 } 96 static inline void destroy_context_ldt(struct mm_struct *mm) { } 97 static inline void ldt_arch_exit_mmap(struct mm_struct *mm) { } 98 #endif 99 100 static inline void load_mm_ldt(struct mm_struct *mm) 101 { 102 #ifdef CONFIG_MODIFY_LDT_SYSCALL 103 struct ldt_struct *ldt; 104 105 /* READ_ONCE synchronizes with smp_store_release */ 106 ldt = READ_ONCE(mm->context.ldt); 107 108 /* 109 * Any change to mm->context.ldt is followed by an IPI to all 110 * CPUs with the mm active. The LDT will not be freed until 111 * after the IPI is handled by all such CPUs. This means that, 112 * if the ldt_struct changes before we return, the values we see 113 * will be safe, and the new values will be loaded before we run 114 * any user code. 115 * 116 * NB: don't try to convert this to use RCU without extreme care. 117 * We would still need IRQs off, because we don't want to change 118 * the local LDT after an IPI loaded a newer value than the one 119 * that we can see. 120 */ 121 122 if (unlikely(ldt)) { 123 if (static_cpu_has(X86_FEATURE_PTI)) { 124 if (WARN_ON_ONCE((unsigned long)ldt->slot > 1)) { 125 /* 126 * Whoops -- either the new LDT isn't mapped 127 * (if slot == -1) or is mapped into a bogus 128 * slot (if slot > 1). 129 */ 130 clear_LDT(); 131 return; 132 } 133 134 /* 135 * If page table isolation is enabled, ldt->entries 136 * will not be mapped in the userspace pagetables. 137 * Tell the CPU to access the LDT through the alias 138 * at ldt_slot_va(ldt->slot). 139 */ 140 set_ldt(ldt_slot_va(ldt->slot), ldt->nr_entries); 141 } else { 142 set_ldt(ldt->entries, ldt->nr_entries); 143 } 144 } else { 145 clear_LDT(); 146 } 147 #else 148 clear_LDT(); 149 #endif 150 } 151 152 static inline void switch_ldt(struct mm_struct *prev, struct mm_struct *next) 153 { 154 #ifdef CONFIG_MODIFY_LDT_SYSCALL 155 /* 156 * Load the LDT if either the old or new mm had an LDT. 157 * 158 * An mm will never go from having an LDT to not having an LDT. Two 159 * mms never share an LDT, so we don't gain anything by checking to 160 * see whether the LDT changed. There's also no guarantee that 161 * prev->context.ldt actually matches LDTR, but, if LDTR is non-NULL, 162 * then prev->context.ldt will also be non-NULL. 163 * 164 * If we really cared, we could optimize the case where prev == next 165 * and we're exiting lazy mode. Most of the time, if this happens, 166 * we don't actually need to reload LDTR, but modify_ldt() is mostly 167 * used by legacy code and emulators where we don't need this level of 168 * performance. 169 * 170 * This uses | instead of || because it generates better code. 171 */ 172 if (unlikely((unsigned long)prev->context.ldt | 173 (unsigned long)next->context.ldt)) 174 load_mm_ldt(next); 175 #endif 176 177 DEBUG_LOCKS_WARN_ON(preemptible()); 178 } 179 180 void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk); 181 182 /* 183 * Init a new mm. Used on mm copies, like at fork() 184 * and on mm's that are brand-new, like at execve(). 185 */ 186 static inline int init_new_context(struct task_struct *tsk, 187 struct mm_struct *mm) 188 { 189 mutex_init(&mm->context.lock); 190 191 mm->context.ctx_id = atomic64_inc_return(&last_mm_ctx_id); 192 atomic64_set(&mm->context.tlb_gen, 0); 193 194 #ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS 195 if (cpu_feature_enabled(X86_FEATURE_OSPKE)) { 196 /* pkey 0 is the default and allocated implicitly */ 197 mm->context.pkey_allocation_map = 0x1; 198 /* -1 means unallocated or invalid */ 199 mm->context.execute_only_pkey = -1; 200 } 201 #endif 202 init_new_context_ldt(mm); 203 return 0; 204 } 205 static inline void destroy_context(struct mm_struct *mm) 206 { 207 destroy_context_ldt(mm); 208 } 209 210 extern void switch_mm(struct mm_struct *prev, struct mm_struct *next, 211 struct task_struct *tsk); 212 213 extern void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next, 214 struct task_struct *tsk); 215 #define switch_mm_irqs_off switch_mm_irqs_off 216 217 #define activate_mm(prev, next) \ 218 do { \ 219 paravirt_activate_mm((prev), (next)); \ 220 switch_mm((prev), (next), NULL); \ 221 } while (0); 222 223 #ifdef CONFIG_X86_32 224 #define deactivate_mm(tsk, mm) \ 225 do { \ 226 lazy_load_gs(0); \ 227 } while (0) 228 #else 229 #define deactivate_mm(tsk, mm) \ 230 do { \ 231 load_gs_index(0); \ 232 loadsegment(fs, 0); \ 233 } while (0) 234 #endif 235 236 static inline void arch_dup_pkeys(struct mm_struct *oldmm, 237 struct mm_struct *mm) 238 { 239 #ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS 240 if (!cpu_feature_enabled(X86_FEATURE_OSPKE)) 241 return; 242 243 /* Duplicate the oldmm pkey state in mm: */ 244 mm->context.pkey_allocation_map = oldmm->context.pkey_allocation_map; 245 mm->context.execute_only_pkey = oldmm->context.execute_only_pkey; 246 #endif 247 } 248 249 static inline int arch_dup_mmap(struct mm_struct *oldmm, struct mm_struct *mm) 250 { 251 arch_dup_pkeys(oldmm, mm); 252 paravirt_arch_dup_mmap(oldmm, mm); 253 return ldt_dup_context(oldmm, mm); 254 } 255 256 static inline void arch_exit_mmap(struct mm_struct *mm) 257 { 258 paravirt_arch_exit_mmap(mm); 259 ldt_arch_exit_mmap(mm); 260 } 261 262 #ifdef CONFIG_X86_64 263 static inline bool is_64bit_mm(struct mm_struct *mm) 264 { 265 return !IS_ENABLED(CONFIG_IA32_EMULATION) || 266 !(mm->context.ia32_compat == TIF_IA32); 267 } 268 #else 269 static inline bool is_64bit_mm(struct mm_struct *mm) 270 { 271 return false; 272 } 273 #endif 274 275 static inline void arch_bprm_mm_init(struct mm_struct *mm, 276 struct vm_area_struct *vma) 277 { 278 mpx_mm_init(mm); 279 } 280 281 static inline void arch_unmap(struct mm_struct *mm, unsigned long start, 282 unsigned long end) 283 { 284 /* 285 * mpx_notify_unmap() goes and reads a rarely-hot 286 * cacheline in the mm_struct. That can be expensive 287 * enough to be seen in profiles. 288 * 289 * The mpx_notify_unmap() call and its contents have been 290 * observed to affect munmap() performance on hardware 291 * where MPX is not present. 292 * 293 * The unlikely() optimizes for the fast case: no MPX 294 * in the CPU, or no MPX use in the process. Even if 295 * we get this wrong (in the unlikely event that MPX 296 * is widely enabled on some system) the overhead of 297 * MPX itself (reading bounds tables) is expected to 298 * overwhelm the overhead of getting this unlikely() 299 * consistently wrong. 300 */ 301 if (unlikely(cpu_feature_enabled(X86_FEATURE_MPX))) 302 mpx_notify_unmap(mm, start, end); 303 } 304 305 /* 306 * We only want to enforce protection keys on the current process 307 * because we effectively have no access to PKRU for other 308 * processes or any way to tell *which * PKRU in a threaded 309 * process we could use. 310 * 311 * So do not enforce things if the VMA is not from the current 312 * mm, or if we are in a kernel thread. 313 */ 314 static inline bool vma_is_foreign(struct vm_area_struct *vma) 315 { 316 if (!current->mm) 317 return true; 318 /* 319 * Should PKRU be enforced on the access to this VMA? If 320 * the VMA is from another process, then PKRU has no 321 * relevance and should not be enforced. 322 */ 323 if (current->mm != vma->vm_mm) 324 return true; 325 326 return false; 327 } 328 329 static inline bool arch_vma_access_permitted(struct vm_area_struct *vma, 330 bool write, bool execute, bool foreign) 331 { 332 /* pkeys never affect instruction fetches */ 333 if (execute) 334 return true; 335 /* allow access if the VMA is not one from this process */ 336 if (foreign || vma_is_foreign(vma)) 337 return true; 338 return __pkru_allows_pkey(vma_pkey(vma), write); 339 } 340 341 /* 342 * This can be used from process context to figure out what the value of 343 * CR3 is without needing to do a (slow) __read_cr3(). 344 * 345 * It's intended to be used for code like KVM that sneakily changes CR3 346 * and needs to restore it. It needs to be used very carefully. 347 */ 348 static inline unsigned long __get_current_cr3_fast(void) 349 { 350 unsigned long cr3 = build_cr3(this_cpu_read(cpu_tlbstate.loaded_mm)->pgd, 351 this_cpu_read(cpu_tlbstate.loaded_mm_asid)); 352 353 /* For now, be very restrictive about when this can be called. */ 354 VM_WARN_ON(in_nmi() || preemptible()); 355 356 VM_BUG_ON(cr3 != __read_cr3()); 357 return cr3; 358 } 359 360 typedef struct { 361 struct mm_struct *mm; 362 } temp_mm_state_t; 363 364 /* 365 * Using a temporary mm allows to set temporary mappings that are not accessible 366 * by other CPUs. Such mappings are needed to perform sensitive memory writes 367 * that override the kernel memory protections (e.g., W^X), without exposing the 368 * temporary page-table mappings that are required for these write operations to 369 * other CPUs. Using a temporary mm also allows to avoid TLB shootdowns when the 370 * mapping is torn down. 371 * 372 * Context: The temporary mm needs to be used exclusively by a single core. To 373 * harden security IRQs must be disabled while the temporary mm is 374 * loaded, thereby preventing interrupt handler bugs from overriding 375 * the kernel memory protection. 376 */ 377 static inline temp_mm_state_t use_temporary_mm(struct mm_struct *mm) 378 { 379 temp_mm_state_t temp_state; 380 381 lockdep_assert_irqs_disabled(); 382 temp_state.mm = this_cpu_read(cpu_tlbstate.loaded_mm); 383 switch_mm_irqs_off(NULL, mm, current); 384 385 /* 386 * If breakpoints are enabled, disable them while the temporary mm is 387 * used. Userspace might set up watchpoints on addresses that are used 388 * in the temporary mm, which would lead to wrong signals being sent or 389 * crashes. 390 * 391 * Note that breakpoints are not disabled selectively, which also causes 392 * kernel breakpoints (e.g., perf's) to be disabled. This might be 393 * undesirable, but still seems reasonable as the code that runs in the 394 * temporary mm should be short. 395 */ 396 if (hw_breakpoint_active()) 397 hw_breakpoint_disable(); 398 399 return temp_state; 400 } 401 402 static inline void unuse_temporary_mm(temp_mm_state_t prev_state) 403 { 404 lockdep_assert_irqs_disabled(); 405 switch_mm_irqs_off(NULL, prev_state.mm, current); 406 407 /* 408 * Restore the breakpoints if they were disabled before the temporary mm 409 * was loaded. 410 */ 411 if (hw_breakpoint_active()) 412 hw_breakpoint_restore(); 413 } 414 415 #endif /* _ASM_X86_MMU_CONTEXT_H */ 416