1 // SPDX-License-Identifier: GPL-2.0-or-later 2 /* 3 * PowerPC version 4 * Copyright (C) 1995-1996 Gary Thomas (gdt@linuxppc.org) 5 * 6 * Derived from "arch/i386/mm/fault.c" 7 * Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds 8 * 9 * Modified by Cort Dougan and Paul Mackerras. 10 * 11 * Modified for PPC64 by Dave Engebretsen (engebret@ibm.com) 12 */ 13 14 #include <linux/signal.h> 15 #include <linux/sched.h> 16 #include <linux/sched/task_stack.h> 17 #include <linux/kernel.h> 18 #include <linux/errno.h> 19 #include <linux/string.h> 20 #include <linux/types.h> 21 #include <linux/pagemap.h> 22 #include <linux/ptrace.h> 23 #include <linux/mman.h> 24 #include <linux/mm.h> 25 #include <linux/interrupt.h> 26 #include <linux/highmem.h> 27 #include <linux/extable.h> 28 #include <linux/kprobes.h> 29 #include <linux/kdebug.h> 30 #include <linux/perf_event.h> 31 #include <linux/ratelimit.h> 32 #include <linux/context_tracking.h> 33 #include <linux/hugetlb.h> 34 #include <linux/uaccess.h> 35 36 #include <asm/firmware.h> 37 #include <asm/page.h> 38 #include <asm/mmu.h> 39 #include <asm/mmu_context.h> 40 #include <asm/siginfo.h> 41 #include <asm/debug.h> 42 #include <asm/kup.h> 43 #include <asm/inst.h> 44 45 46 /* 47 * do_page_fault error handling helpers 48 */ 49 50 static int 51 __bad_area_nosemaphore(struct pt_regs *regs, unsigned long address, int si_code) 52 { 53 /* 54 * If we are in kernel mode, bail out with a SEGV, this will 55 * be caught by the assembly which will restore the non-volatile 56 * registers before calling bad_page_fault() 57 */ 58 if (!user_mode(regs)) 59 return SIGSEGV; 60 61 _exception(SIGSEGV, regs, si_code, address); 62 63 return 0; 64 } 65 66 static noinline int bad_area_nosemaphore(struct pt_regs *regs, unsigned long address) 67 { 68 return __bad_area_nosemaphore(regs, address, SEGV_MAPERR); 69 } 70 71 static int __bad_area(struct pt_regs *regs, unsigned long address, int si_code) 72 { 73 struct mm_struct *mm = current->mm; 74 75 /* 76 * Something tried to access memory that isn't in our memory map.. 77 * Fix it, but check if it's kernel or user first.. 78 */ 79 mmap_read_unlock(mm); 80 81 return __bad_area_nosemaphore(regs, address, si_code); 82 } 83 84 static noinline int bad_area(struct pt_regs *regs, unsigned long address) 85 { 86 return __bad_area(regs, address, SEGV_MAPERR); 87 } 88 89 #ifdef CONFIG_PPC_MEM_KEYS 90 static noinline int bad_access_pkey(struct pt_regs *regs, unsigned long address, 91 struct vm_area_struct *vma) 92 { 93 struct mm_struct *mm = current->mm; 94 int pkey; 95 96 /* 97 * We don't try to fetch the pkey from page table because reading 98 * page table without locking doesn't guarantee stable pte value. 99 * Hence the pkey value that we return to userspace can be different 100 * from the pkey that actually caused access error. 101 * 102 * It does *not* guarantee that the VMA we find here 103 * was the one that we faulted on. 104 * 105 * 1. T1 : mprotect_key(foo, PAGE_SIZE, pkey=4); 106 * 2. T1 : set AMR to deny access to pkey=4, touches, page 107 * 3. T1 : faults... 108 * 4. T2: mprotect_key(foo, PAGE_SIZE, pkey=5); 109 * 5. T1 : enters fault handler, takes mmap_lock, etc... 110 * 6. T1 : reaches here, sees vma_pkey(vma)=5, when we really 111 * faulted on a pte with its pkey=4. 112 */ 113 pkey = vma_pkey(vma); 114 115 mmap_read_unlock(mm); 116 117 /* 118 * If we are in kernel mode, bail out with a SEGV, this will 119 * be caught by the assembly which will restore the non-volatile 120 * registers before calling bad_page_fault() 121 */ 122 if (!user_mode(regs)) 123 return SIGSEGV; 124 125 _exception_pkey(regs, address, pkey); 126 127 return 0; 128 } 129 #endif 130 131 static noinline int bad_access(struct pt_regs *regs, unsigned long address) 132 { 133 return __bad_area(regs, address, SEGV_ACCERR); 134 } 135 136 static int do_sigbus(struct pt_regs *regs, unsigned long address, 137 vm_fault_t fault) 138 { 139 if (!user_mode(regs)) 140 return SIGBUS; 141 142 current->thread.trap_nr = BUS_ADRERR; 143 #ifdef CONFIG_MEMORY_FAILURE 144 if (fault & (VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE)) { 145 unsigned int lsb = 0; /* shutup gcc */ 146 147 pr_err("MCE: Killing %s:%d due to hardware memory corruption fault at %lx\n", 148 current->comm, current->pid, address); 149 150 if (fault & VM_FAULT_HWPOISON_LARGE) 151 lsb = hstate_index_to_shift(VM_FAULT_GET_HINDEX(fault)); 152 if (fault & VM_FAULT_HWPOISON) 153 lsb = PAGE_SHIFT; 154 155 force_sig_mceerr(BUS_MCEERR_AR, (void __user *)address, lsb); 156 return 0; 157 } 158 159 #endif 160 force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address); 161 return 0; 162 } 163 164 static int mm_fault_error(struct pt_regs *regs, unsigned long addr, 165 vm_fault_t fault) 166 { 167 /* 168 * Kernel page fault interrupted by SIGKILL. We have no reason to 169 * continue processing. 170 */ 171 if (fatal_signal_pending(current) && !user_mode(regs)) 172 return SIGKILL; 173 174 /* Out of memory */ 175 if (fault & VM_FAULT_OOM) { 176 /* 177 * We ran out of memory, or some other thing happened to us that 178 * made us unable to handle the page fault gracefully. 179 */ 180 if (!user_mode(regs)) 181 return SIGSEGV; 182 pagefault_out_of_memory(); 183 } else { 184 if (fault & (VM_FAULT_SIGBUS|VM_FAULT_HWPOISON| 185 VM_FAULT_HWPOISON_LARGE)) 186 return do_sigbus(regs, addr, fault); 187 else if (fault & VM_FAULT_SIGSEGV) 188 return bad_area_nosemaphore(regs, addr); 189 else 190 BUG(); 191 } 192 return 0; 193 } 194 195 /* Is this a bad kernel fault ? */ 196 static bool bad_kernel_fault(struct pt_regs *regs, unsigned long error_code, 197 unsigned long address, bool is_write) 198 { 199 int is_exec = TRAP(regs) == 0x400; 200 201 /* NX faults set DSISR_PROTFAULT on the 8xx, DSISR_NOEXEC_OR_G on others */ 202 if (is_exec && (error_code & (DSISR_NOEXEC_OR_G | DSISR_KEYFAULT | 203 DSISR_PROTFAULT))) { 204 pr_crit_ratelimited("kernel tried to execute %s page (%lx) - exploit attempt? (uid: %d)\n", 205 address >= TASK_SIZE ? "exec-protected" : "user", 206 address, 207 from_kuid(&init_user_ns, current_uid())); 208 209 // Kernel exec fault is always bad 210 return true; 211 } 212 213 if (!is_exec && address < TASK_SIZE && (error_code & (DSISR_PROTFAULT | DSISR_KEYFAULT)) && 214 !search_exception_tables(regs->nip)) { 215 pr_crit_ratelimited("Kernel attempted to access user page (%lx) - exploit attempt? (uid: %d)\n", 216 address, 217 from_kuid(&init_user_ns, current_uid())); 218 } 219 220 // Kernel fault on kernel address is bad 221 if (address >= TASK_SIZE) 222 return true; 223 224 // Fault on user outside of certain regions (eg. copy_tofrom_user()) is bad 225 if (!search_exception_tables(regs->nip)) 226 return true; 227 228 // Read/write fault in a valid region (the exception table search passed 229 // above), but blocked by KUAP is bad, it can never succeed. 230 if (bad_kuap_fault(regs, address, is_write)) 231 return WARN(true, "Bug: %s fault blocked by KUAP!", is_write ? "Write" : "Read"); 232 233 // What's left? Kernel fault on user in well defined regions (extable 234 // matched), and allowed by KUAP in the faulting context. 235 return false; 236 } 237 238 #ifdef CONFIG_PPC_MEM_KEYS 239 static bool access_pkey_error(bool is_write, bool is_exec, bool is_pkey, 240 struct vm_area_struct *vma) 241 { 242 /* 243 * Make sure to check the VMA so that we do not perform 244 * faults just to hit a pkey fault as soon as we fill in a 245 * page. Only called for current mm, hence foreign == 0 246 */ 247 if (!arch_vma_access_permitted(vma, is_write, is_exec, 0)) 248 return true; 249 250 return false; 251 } 252 #endif 253 254 static bool access_error(bool is_write, bool is_exec, struct vm_area_struct *vma) 255 { 256 /* 257 * Allow execution from readable areas if the MMU does not 258 * provide separate controls over reading and executing. 259 * 260 * Note: That code used to not be enabled for 4xx/BookE. 261 * It is now as I/D cache coherency for these is done at 262 * set_pte_at() time and I see no reason why the test 263 * below wouldn't be valid on those processors. This -may- 264 * break programs compiled with a really old ABI though. 265 */ 266 if (is_exec) { 267 return !(vma->vm_flags & VM_EXEC) && 268 (cpu_has_feature(CPU_FTR_NOEXECUTE) || 269 !(vma->vm_flags & (VM_READ | VM_WRITE))); 270 } 271 272 if (is_write) { 273 if (unlikely(!(vma->vm_flags & VM_WRITE))) 274 return true; 275 return false; 276 } 277 278 if (unlikely(!vma_is_accessible(vma))) 279 return true; 280 /* 281 * We should ideally do the vma pkey access check here. But in the 282 * fault path, handle_mm_fault() also does the same check. To avoid 283 * these multiple checks, we skip it here and handle access error due 284 * to pkeys later. 285 */ 286 return false; 287 } 288 289 #ifdef CONFIG_PPC_SMLPAR 290 static inline void cmo_account_page_fault(void) 291 { 292 if (firmware_has_feature(FW_FEATURE_CMO)) { 293 u32 page_ins; 294 295 preempt_disable(); 296 page_ins = be32_to_cpu(get_lppaca()->page_ins); 297 page_ins += 1 << PAGE_FACTOR; 298 get_lppaca()->page_ins = cpu_to_be32(page_ins); 299 preempt_enable(); 300 } 301 } 302 #else 303 static inline void cmo_account_page_fault(void) { } 304 #endif /* CONFIG_PPC_SMLPAR */ 305 306 static void sanity_check_fault(bool is_write, bool is_user, 307 unsigned long error_code, unsigned long address) 308 { 309 /* 310 * Userspace trying to access kernel address, we get PROTFAULT for that. 311 */ 312 if (is_user && address >= TASK_SIZE) { 313 if ((long)address == -1) 314 return; 315 316 pr_crit_ratelimited("%s[%d]: User access of kernel address (%lx) - exploit attempt? (uid: %d)\n", 317 current->comm, current->pid, address, 318 from_kuid(&init_user_ns, current_uid())); 319 return; 320 } 321 322 if (!IS_ENABLED(CONFIG_PPC_BOOK3S)) 323 return; 324 325 /* 326 * For hash translation mode, we should never get a 327 * PROTFAULT. Any update to pte to reduce access will result in us 328 * removing the hash page table entry, thus resulting in a DSISR_NOHPTE 329 * fault instead of DSISR_PROTFAULT. 330 * 331 * A pte update to relax the access will not result in a hash page table 332 * entry invalidate and hence can result in DSISR_PROTFAULT. 333 * ptep_set_access_flags() doesn't do a hpte flush. This is why we have 334 * the special !is_write in the below conditional. 335 * 336 * For platforms that doesn't supports coherent icache and do support 337 * per page noexec bit, we do setup things such that we do the 338 * sync between D/I cache via fault. But that is handled via low level 339 * hash fault code (hash_page_do_lazy_icache()) and we should not reach 340 * here in such case. 341 * 342 * For wrong access that can result in PROTFAULT, the above vma->vm_flags 343 * check should handle those and hence we should fall to the bad_area 344 * handling correctly. 345 * 346 * For embedded with per page exec support that doesn't support coherent 347 * icache we do get PROTFAULT and we handle that D/I cache sync in 348 * set_pte_at while taking the noexec/prot fault. Hence this is WARN_ON 349 * is conditional for server MMU. 350 * 351 * For radix, we can get prot fault for autonuma case, because radix 352 * page table will have them marked noaccess for user. 353 */ 354 if (radix_enabled() || is_write) 355 return; 356 357 WARN_ON_ONCE(error_code & DSISR_PROTFAULT); 358 } 359 360 /* 361 * Define the correct "is_write" bit in error_code based 362 * on the processor family 363 */ 364 #if (defined(CONFIG_4xx) || defined(CONFIG_BOOKE)) 365 #define page_fault_is_write(__err) ((__err) & ESR_DST) 366 #else 367 #define page_fault_is_write(__err) ((__err) & DSISR_ISSTORE) 368 #endif 369 370 #if defined(CONFIG_4xx) || defined(CONFIG_BOOKE) 371 #define page_fault_is_bad(__err) (0) 372 #elif defined(CONFIG_PPC_8xx) 373 #define page_fault_is_bad(__err) ((__err) & DSISR_NOEXEC_OR_G) 374 #elif defined(CONFIG_PPC64) 375 #define page_fault_is_bad(__err) ((__err) & DSISR_BAD_FAULT_64S) 376 #else 377 #define page_fault_is_bad(__err) ((__err) & DSISR_BAD_FAULT_32S) 378 #endif 379 380 /* 381 * For 600- and 800-family processors, the error_code parameter is DSISR 382 * for a data fault, SRR1 for an instruction fault. For 400-family processors 383 * the error_code parameter is ESR for a data fault, 0 for an instruction 384 * fault. 385 * For 64-bit processors, the error_code parameter is 386 * - DSISR for a non-SLB data access fault, 387 * - SRR1 & 0x08000000 for a non-SLB instruction access fault 388 * - 0 any SLB fault. 389 * 390 * The return value is 0 if the fault was handled, or the signal 391 * number if this is a kernel fault that can't be handled here. 392 */ 393 static int __do_page_fault(struct pt_regs *regs, unsigned long address, 394 unsigned long error_code) 395 { 396 struct vm_area_struct * vma; 397 struct mm_struct *mm = current->mm; 398 unsigned int flags = FAULT_FLAG_DEFAULT; 399 int is_exec = TRAP(regs) == 0x400; 400 int is_user = user_mode(regs); 401 int is_write = page_fault_is_write(error_code); 402 vm_fault_t fault, major = 0; 403 bool kprobe_fault = kprobe_page_fault(regs, 11); 404 405 if (unlikely(debugger_fault_handler(regs) || kprobe_fault)) 406 return 0; 407 408 if (unlikely(page_fault_is_bad(error_code))) { 409 if (is_user) { 410 _exception(SIGBUS, regs, BUS_OBJERR, address); 411 return 0; 412 } 413 return SIGBUS; 414 } 415 416 /* Additional sanity check(s) */ 417 sanity_check_fault(is_write, is_user, error_code, address); 418 419 /* 420 * The kernel should never take an execute fault nor should it 421 * take a page fault to a kernel address or a page fault to a user 422 * address outside of dedicated places 423 */ 424 if (unlikely(!is_user && bad_kernel_fault(regs, error_code, address, is_write))) 425 return SIGSEGV; 426 427 /* 428 * If we're in an interrupt, have no user context or are running 429 * in a region with pagefaults disabled then we must not take the fault 430 */ 431 if (unlikely(faulthandler_disabled() || !mm)) { 432 if (is_user) 433 printk_ratelimited(KERN_ERR "Page fault in user mode" 434 " with faulthandler_disabled()=%d" 435 " mm=%p\n", 436 faulthandler_disabled(), mm); 437 return bad_area_nosemaphore(regs, address); 438 } 439 440 /* We restore the interrupt state now */ 441 if (!arch_irq_disabled_regs(regs)) 442 local_irq_enable(); 443 444 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address); 445 446 /* 447 * We want to do this outside mmap_lock, because reading code around nip 448 * can result in fault, which will cause a deadlock when called with 449 * mmap_lock held 450 */ 451 if (is_user) 452 flags |= FAULT_FLAG_USER; 453 if (is_write) 454 flags |= FAULT_FLAG_WRITE; 455 if (is_exec) 456 flags |= FAULT_FLAG_INSTRUCTION; 457 458 /* When running in the kernel we expect faults to occur only to 459 * addresses in user space. All other faults represent errors in the 460 * kernel and should generate an OOPS. Unfortunately, in the case of an 461 * erroneous fault occurring in a code path which already holds mmap_lock 462 * we will deadlock attempting to validate the fault against the 463 * address space. Luckily the kernel only validly references user 464 * space from well defined areas of code, which are listed in the 465 * exceptions table. 466 * 467 * As the vast majority of faults will be valid we will only perform 468 * the source reference check when there is a possibility of a deadlock. 469 * Attempt to lock the address space, if we cannot we then validate the 470 * source. If this is invalid we can skip the address space check, 471 * thus avoiding the deadlock. 472 */ 473 if (unlikely(!mmap_read_trylock(mm))) { 474 if (!is_user && !search_exception_tables(regs->nip)) 475 return bad_area_nosemaphore(regs, address); 476 477 retry: 478 mmap_read_lock(mm); 479 } else { 480 /* 481 * The above down_read_trylock() might have succeeded in 482 * which case we'll have missed the might_sleep() from 483 * down_read(): 484 */ 485 might_sleep(); 486 } 487 488 vma = find_vma(mm, address); 489 if (unlikely(!vma)) 490 return bad_area(regs, address); 491 492 if (unlikely(vma->vm_start > address)) { 493 if (unlikely(!(vma->vm_flags & VM_GROWSDOWN))) 494 return bad_area(regs, address); 495 496 if (unlikely(expand_stack(vma, address))) 497 return bad_area(regs, address); 498 } 499 500 #ifdef CONFIG_PPC_MEM_KEYS 501 if (unlikely(access_pkey_error(is_write, is_exec, 502 (error_code & DSISR_KEYFAULT), vma))) 503 return bad_access_pkey(regs, address, vma); 504 #endif /* CONFIG_PPC_MEM_KEYS */ 505 506 if (unlikely(access_error(is_write, is_exec, vma))) 507 return bad_access(regs, address); 508 509 /* 510 * If for any reason at all we couldn't handle the fault, 511 * make sure we exit gracefully rather than endlessly redo 512 * the fault. 513 */ 514 fault = handle_mm_fault(vma, address, flags, regs); 515 516 major |= fault & VM_FAULT_MAJOR; 517 518 if (fault_signal_pending(fault, regs)) 519 return user_mode(regs) ? 0 : SIGBUS; 520 521 /* 522 * Handle the retry right now, the mmap_lock has been released in that 523 * case. 524 */ 525 if (unlikely(fault & VM_FAULT_RETRY)) { 526 if (flags & FAULT_FLAG_ALLOW_RETRY) { 527 flags |= FAULT_FLAG_TRIED; 528 goto retry; 529 } 530 } 531 532 mmap_read_unlock(current->mm); 533 534 if (unlikely(fault & VM_FAULT_ERROR)) 535 return mm_fault_error(regs, address, fault); 536 537 /* 538 * Major/minor page fault accounting. 539 */ 540 if (major) 541 cmo_account_page_fault(); 542 543 return 0; 544 } 545 NOKPROBE_SYMBOL(__do_page_fault); 546 547 int do_page_fault(struct pt_regs *regs, unsigned long address, 548 unsigned long error_code) 549 { 550 enum ctx_state prev_state = exception_enter(); 551 int rc = __do_page_fault(regs, address, error_code); 552 exception_exit(prev_state); 553 return rc; 554 } 555 NOKPROBE_SYMBOL(do_page_fault); 556 557 /* 558 * bad_page_fault is called when we have a bad access from the kernel. 559 * It is called from the DSI and ISI handlers in head.S and from some 560 * of the procedures in traps.c. 561 */ 562 void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig) 563 { 564 const struct exception_table_entry *entry; 565 int is_write = page_fault_is_write(regs->dsisr); 566 567 /* Are we prepared to handle this fault? */ 568 if ((entry = search_exception_tables(regs->nip)) != NULL) { 569 regs->nip = extable_fixup(entry); 570 return; 571 } 572 573 /* kernel has accessed a bad area */ 574 575 switch (TRAP(regs)) { 576 case 0x300: 577 case 0x380: 578 case 0xe00: 579 pr_alert("BUG: %s on %s at 0x%08lx\n", 580 regs->dar < PAGE_SIZE ? "Kernel NULL pointer dereference" : 581 "Unable to handle kernel data access", 582 is_write ? "write" : "read", regs->dar); 583 break; 584 case 0x400: 585 case 0x480: 586 pr_alert("BUG: Unable to handle kernel instruction fetch%s", 587 regs->nip < PAGE_SIZE ? " (NULL pointer?)\n" : "\n"); 588 break; 589 case 0x600: 590 pr_alert("BUG: Unable to handle kernel unaligned access at 0x%08lx\n", 591 regs->dar); 592 break; 593 default: 594 pr_alert("BUG: Unable to handle unknown paging fault at 0x%08lx\n", 595 regs->dar); 596 break; 597 } 598 printk(KERN_ALERT "Faulting instruction address: 0x%08lx\n", 599 regs->nip); 600 601 if (task_stack_end_corrupted(current)) 602 printk(KERN_ALERT "Thread overran stack, or stack corrupted\n"); 603 604 die("Kernel access of bad area", regs, sig); 605 } 606