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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/pgtable.h>
39#include <asm/mmu.h>
40#include <asm/mmu_context.h>
41#include <asm/siginfo.h>
42#include <asm/debug.h>
43#include <asm/kup.h>
44
45/*
46 * Check whether the instruction inst is a store using
47 * an update addressing form which will update r1.
48 */
49static bool store_updates_sp(unsigned int inst)
50{
51 /* check for 1 in the rA field */
52 if (((inst >> 16) & 0x1f) != 1)
53 return false;
54 /* check major opcode */
55 switch (inst >> 26) {
56 case OP_STWU:
57 case OP_STBU:
58 case OP_STHU:
59 case OP_STFSU:
60 case OP_STFDU:
61 return true;
62 case OP_STD: /* std or stdu */
63 return (inst & 3) == 1;
64 case OP_31:
65 /* check minor opcode */
66 switch ((inst >> 1) & 0x3ff) {
67 case OP_31_XOP_STDUX:
68 case OP_31_XOP_STWUX:
69 case OP_31_XOP_STBUX:
70 case OP_31_XOP_STHUX:
71 case OP_31_XOP_STFSUX:
72 case OP_31_XOP_STFDUX:
73 return true;
74 }
75 }
76 return false;
77}
78/*
79 * do_page_fault error handling helpers
80 */
81
82static int
83__bad_area_nosemaphore(struct pt_regs *regs, unsigned long address, int si_code)
84{
85 /*
86 * If we are in kernel mode, bail out with a SEGV, this will
87 * be caught by the assembly which will restore the non-volatile
88 * registers before calling bad_page_fault()
89 */
90 if (!user_mode(regs))
91 return SIGSEGV;
92
93 _exception(SIGSEGV, regs, si_code, address);
94
95 return 0;
96}
97
98static noinline int bad_area_nosemaphore(struct pt_regs *regs, unsigned long address)
99{
100 return __bad_area_nosemaphore(regs, address, SEGV_MAPERR);
101}
102
103static int __bad_area(struct pt_regs *regs, unsigned long address, int si_code)
104{
105 struct mm_struct *mm = current->mm;
106
107 /*
108 * Something tried to access memory that isn't in our memory map..
109 * Fix it, but check if it's kernel or user first..
110 */
111 up_read(&mm->mmap_sem);
112
113 return __bad_area_nosemaphore(regs, address, si_code);
114}
115
116static noinline int bad_area(struct pt_regs *regs, unsigned long address)
117{
118 return __bad_area(regs, address, SEGV_MAPERR);
119}
120
121static int bad_key_fault_exception(struct pt_regs *regs, unsigned long address,
122 int pkey)
123{
124 /*
125 * If we are in kernel mode, bail out with a SEGV, this will
126 * be caught by the assembly which will restore the non-volatile
127 * registers before calling bad_page_fault()
128 */
129 if (!user_mode(regs))
130 return SIGSEGV;
131
132 _exception_pkey(regs, address, pkey);
133
134 return 0;
135}
136
137static noinline int bad_access(struct pt_regs *regs, unsigned long address)
138{
139 return __bad_area(regs, address, SEGV_ACCERR);
140}
141
142static int do_sigbus(struct pt_regs *regs, unsigned long address,
143 vm_fault_t fault)
144{
145 if (!user_mode(regs))
146 return SIGBUS;
147
148 current->thread.trap_nr = BUS_ADRERR;
149#ifdef CONFIG_MEMORY_FAILURE
150 if (fault & (VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE)) {
151 unsigned int lsb = 0; /* shutup gcc */
152
153 pr_err("MCE: Killing %s:%d due to hardware memory corruption fault at %lx\n",
154 current->comm, current->pid, address);
155
156 if (fault & VM_FAULT_HWPOISON_LARGE)
157 lsb = hstate_index_to_shift(VM_FAULT_GET_HINDEX(fault));
158 if (fault & VM_FAULT_HWPOISON)
159 lsb = PAGE_SHIFT;
160
161 force_sig_mceerr(BUS_MCEERR_AR, (void __user *)address, lsb);
162 return 0;
163 }
164
165#endif
166 force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address);
167 return 0;
168}
169
170static int mm_fault_error(struct pt_regs *regs, unsigned long addr,
171 vm_fault_t fault)
172{
173 /*
174 * Kernel page fault interrupted by SIGKILL. We have no reason to
175 * continue processing.
176 */
177 if (fatal_signal_pending(current) && !user_mode(regs))
178 return SIGKILL;
179
180 /* Out of memory */
181 if (fault & VM_FAULT_OOM) {
182 /*
183 * We ran out of memory, or some other thing happened to us that
184 * made us unable to handle the page fault gracefully.
185 */
186 if (!user_mode(regs))
187 return SIGSEGV;
188 pagefault_out_of_memory();
189 } else {
190 if (fault & (VM_FAULT_SIGBUS|VM_FAULT_HWPOISON|
191 VM_FAULT_HWPOISON_LARGE))
192 return do_sigbus(regs, addr, fault);
193 else if (fault & VM_FAULT_SIGSEGV)
194 return bad_area_nosemaphore(regs, addr);
195 else
196 BUG();
197 }
198 return 0;
199}
200
201/* Is this a bad kernel fault ? */
202static bool bad_kernel_fault(struct pt_regs *regs, unsigned long error_code,
203 unsigned long address, bool is_write)
204{
205 int is_exec = TRAP(regs) == 0x400;
206
207 /* NX faults set DSISR_PROTFAULT on the 8xx, DSISR_NOEXEC_OR_G on others */
208 if (is_exec && (error_code & (DSISR_NOEXEC_OR_G | DSISR_KEYFAULT |
209 DSISR_PROTFAULT))) {
210 pr_crit_ratelimited("kernel tried to execute %s page (%lx) - exploit attempt? (uid: %d)\n",
211 address >= TASK_SIZE ? "exec-protected" : "user",
212 address,
213 from_kuid(&init_user_ns, current_uid()));
214
215 // Kernel exec fault is always bad
216 return true;
217 }
218
219 if (!is_exec && address < TASK_SIZE && (error_code & DSISR_PROTFAULT) &&
220 !search_exception_tables(regs->nip)) {
221 pr_crit_ratelimited("Kernel attempted to access user page (%lx) - exploit attempt? (uid: %d)\n",
222 address,
223 from_kuid(&init_user_ns, current_uid()));
224 }
225
226 // Kernel fault on kernel address is bad
227 if (address >= TASK_SIZE)
228 return true;
229
230 // Fault on user outside of certain regions (eg. copy_tofrom_user()) is bad
231 if (!search_exception_tables(regs->nip))
232 return true;
233
234 // Read/write fault in a valid region (the exception table search passed
235 // above), but blocked by KUAP is bad, it can never succeed.
236 if (bad_kuap_fault(regs, is_write))
237 return true;
238
239 // What's left? Kernel fault on user in well defined regions (extable
240 // matched), and allowed by KUAP in the faulting context.
241 return false;
242}
243
244static bool bad_stack_expansion(struct pt_regs *regs, unsigned long address,
245 struct vm_area_struct *vma, unsigned int flags,
246 bool *must_retry)
247{
248 /*
249 * N.B. The POWER/Open ABI allows programs to access up to
250 * 288 bytes below the stack pointer.
251 * The kernel signal delivery code writes up to about 1.5kB
252 * below the stack pointer (r1) before decrementing it.
253 * The exec code can write slightly over 640kB to the stack
254 * before setting the user r1. Thus we allow the stack to
255 * expand to 1MB without further checks.
256 */
257 if (address + 0x100000 < vma->vm_end) {
258 unsigned int __user *nip = (unsigned int __user *)regs->nip;
259 /* get user regs even if this fault is in kernel mode */
260 struct pt_regs *uregs = current->thread.regs;
261 if (uregs == NULL)
262 return true;
263
264 /*
265 * A user-mode access to an address a long way below
266 * the stack pointer is only valid if the instruction
267 * is one which would update the stack pointer to the
268 * address accessed if the instruction completed,
269 * i.e. either stwu rs,n(r1) or stwux rs,r1,rb
270 * (or the byte, halfword, float or double forms).
271 *
272 * If we don't check this then any write to the area
273 * between the last mapped region and the stack will
274 * expand the stack rather than segfaulting.
275 */
276 if (address + 2048 >= uregs->gpr[1])
277 return false;
278
279 if ((flags & FAULT_FLAG_WRITE) && (flags & FAULT_FLAG_USER) &&
280 access_ok(nip, sizeof(*nip))) {
281 unsigned int inst;
282 int res;
283
284 pagefault_disable();
285 res = __get_user_inatomic(inst, nip);
286 pagefault_enable();
287 if (!res)
288 return !store_updates_sp(inst);
289 *must_retry = true;
290 }
291 return true;
292 }
293 return false;
294}
295
296static bool access_error(bool is_write, bool is_exec,
297 struct vm_area_struct *vma)
298{
299 /*
300 * Allow execution from readable areas if the MMU does not
301 * provide separate controls over reading and executing.
302 *
303 * Note: That code used to not be enabled for 4xx/BookE.
304 * It is now as I/D cache coherency for these is done at
305 * set_pte_at() time and I see no reason why the test
306 * below wouldn't be valid on those processors. This -may-
307 * break programs compiled with a really old ABI though.
308 */
309 if (is_exec) {
310 return !(vma->vm_flags & VM_EXEC) &&
311 (cpu_has_feature(CPU_FTR_NOEXECUTE) ||
312 !(vma->vm_flags & (VM_READ | VM_WRITE)));
313 }
314
315 if (is_write) {
316 if (unlikely(!(vma->vm_flags & VM_WRITE)))
317 return true;
318 return false;
319 }
320
321 if (unlikely(!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE))))
322 return true;
323 /*
324 * We should ideally do the vma pkey access check here. But in the
325 * fault path, handle_mm_fault() also does the same check. To avoid
326 * these multiple checks, we skip it here and handle access error due
327 * to pkeys later.
328 */
329 return false;
330}
331
332#ifdef CONFIG_PPC_SMLPAR
333static inline void cmo_account_page_fault(void)
334{
335 if (firmware_has_feature(FW_FEATURE_CMO)) {
336 u32 page_ins;
337
338 preempt_disable();
339 page_ins = be32_to_cpu(get_lppaca()->page_ins);
340 page_ins += 1 << PAGE_FACTOR;
341 get_lppaca()->page_ins = cpu_to_be32(page_ins);
342 preempt_enable();
343 }
344}
345#else
346static inline void cmo_account_page_fault(void) { }
347#endif /* CONFIG_PPC_SMLPAR */
348
349#ifdef CONFIG_PPC_BOOK3S
350static void sanity_check_fault(bool is_write, bool is_user,
351 unsigned long error_code, unsigned long address)
352{
353 /*
354 * Userspace trying to access kernel address, we get PROTFAULT for that.
355 */
356 if (is_user && address >= TASK_SIZE) {
357 pr_crit_ratelimited("%s[%d]: User access of kernel address (%lx) - exploit attempt? (uid: %d)\n",
358 current->comm, current->pid, address,
359 from_kuid(&init_user_ns, current_uid()));
360 return;
361 }
362
363 /*
364 * For hash translation mode, we should never get a
365 * PROTFAULT. Any update to pte to reduce access will result in us
366 * removing the hash page table entry, thus resulting in a DSISR_NOHPTE
367 * fault instead of DSISR_PROTFAULT.
368 *
369 * A pte update to relax the access will not result in a hash page table
370 * entry invalidate and hence can result in DSISR_PROTFAULT.
371 * ptep_set_access_flags() doesn't do a hpte flush. This is why we have
372 * the special !is_write in the below conditional.
373 *
374 * For platforms that doesn't supports coherent icache and do support
375 * per page noexec bit, we do setup things such that we do the
376 * sync between D/I cache via fault. But that is handled via low level
377 * hash fault code (hash_page_do_lazy_icache()) and we should not reach
378 * here in such case.
379 *
380 * For wrong access that can result in PROTFAULT, the above vma->vm_flags
381 * check should handle those and hence we should fall to the bad_area
382 * handling correctly.
383 *
384 * For embedded with per page exec support that doesn't support coherent
385 * icache we do get PROTFAULT and we handle that D/I cache sync in
386 * set_pte_at while taking the noexec/prot fault. Hence this is WARN_ON
387 * is conditional for server MMU.
388 *
389 * For radix, we can get prot fault for autonuma case, because radix
390 * page table will have them marked noaccess for user.
391 */
392 if (radix_enabled() || is_write)
393 return;
394
395 WARN_ON_ONCE(error_code & DSISR_PROTFAULT);
396}
397#else
398static void sanity_check_fault(bool is_write, bool is_user,
399 unsigned long error_code, unsigned long address) { }
400#endif /* CONFIG_PPC_BOOK3S */
401
402/*
403 * Define the correct "is_write" bit in error_code based
404 * on the processor family
405 */
406#if (defined(CONFIG_4xx) || defined(CONFIG_BOOKE))
407#define page_fault_is_write(__err) ((__err) & ESR_DST)
408#define page_fault_is_bad(__err) (0)
409#else
410#define page_fault_is_write(__err) ((__err) & DSISR_ISSTORE)
411#if defined(CONFIG_PPC_8xx)
412#define page_fault_is_bad(__err) ((__err) & DSISR_NOEXEC_OR_G)
413#elif defined(CONFIG_PPC64)
414#define page_fault_is_bad(__err) ((__err) & DSISR_BAD_FAULT_64S)
415#else
416#define page_fault_is_bad(__err) ((__err) & DSISR_BAD_FAULT_32S)
417#endif
418#endif
419
420/*
421 * For 600- and 800-family processors, the error_code parameter is DSISR
422 * for a data fault, SRR1 for an instruction fault. For 400-family processors
423 * the error_code parameter is ESR for a data fault, 0 for an instruction
424 * fault.
425 * For 64-bit processors, the error_code parameter is
426 * - DSISR for a non-SLB data access fault,
427 * - SRR1 & 0x08000000 for a non-SLB instruction access fault
428 * - 0 any SLB fault.
429 *
430 * The return value is 0 if the fault was handled, or the signal
431 * number if this is a kernel fault that can't be handled here.
432 */
433static int __do_page_fault(struct pt_regs *regs, unsigned long address,
434 unsigned long error_code)
435{
436 struct vm_area_struct * vma;
437 struct mm_struct *mm = current->mm;
438 unsigned int flags = FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_KILLABLE;
439 int is_exec = TRAP(regs) == 0x400;
440 int is_user = user_mode(regs);
441 int is_write = page_fault_is_write(error_code);
442 vm_fault_t fault, major = 0;
443 bool must_retry = false;
444 bool kprobe_fault = kprobe_page_fault(regs, 11);
445
446 if (unlikely(debugger_fault_handler(regs) || kprobe_fault))
447 return 0;
448
449 if (unlikely(page_fault_is_bad(error_code))) {
450 if (is_user) {
451 _exception(SIGBUS, regs, BUS_OBJERR, address);
452 return 0;
453 }
454 return SIGBUS;
455 }
456
457 /* Additional sanity check(s) */
458 sanity_check_fault(is_write, is_user, error_code, address);
459
460 /*
461 * The kernel should never take an execute fault nor should it
462 * take a page fault to a kernel address or a page fault to a user
463 * address outside of dedicated places
464 */
465 if (unlikely(!is_user && bad_kernel_fault(regs, error_code, address, is_write)))
466 return SIGSEGV;
467
468 /*
469 * If we're in an interrupt, have no user context or are running
470 * in a region with pagefaults disabled then we must not take the fault
471 */
472 if (unlikely(faulthandler_disabled() || !mm)) {
473 if (is_user)
474 printk_ratelimited(KERN_ERR "Page fault in user mode"
475 " with faulthandler_disabled()=%d"
476 " mm=%p\n",
477 faulthandler_disabled(), mm);
478 return bad_area_nosemaphore(regs, address);
479 }
480
481 /* We restore the interrupt state now */
482 if (!arch_irq_disabled_regs(regs))
483 local_irq_enable();
484
485 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
486
487 if (error_code & DSISR_KEYFAULT)
488 return bad_key_fault_exception(regs, address,
489 get_mm_addr_key(mm, address));
490
491 /*
492 * We want to do this outside mmap_sem, because reading code around nip
493 * can result in fault, which will cause a deadlock when called with
494 * mmap_sem held
495 */
496 if (is_user)
497 flags |= FAULT_FLAG_USER;
498 if (is_write)
499 flags |= FAULT_FLAG_WRITE;
500 if (is_exec)
501 flags |= FAULT_FLAG_INSTRUCTION;
502
503 /* When running in the kernel we expect faults to occur only to
504 * addresses in user space. All other faults represent errors in the
505 * kernel and should generate an OOPS. Unfortunately, in the case of an
506 * erroneous fault occurring in a code path which already holds mmap_sem
507 * we will deadlock attempting to validate the fault against the
508 * address space. Luckily the kernel only validly references user
509 * space from well defined areas of code, which are listed in the
510 * exceptions table.
511 *
512 * As the vast majority of faults will be valid we will only perform
513 * the source reference check when there is a possibility of a deadlock.
514 * Attempt to lock the address space, if we cannot we then validate the
515 * source. If this is invalid we can skip the address space check,
516 * thus avoiding the deadlock.
517 */
518 if (unlikely(!down_read_trylock(&mm->mmap_sem))) {
519 if (!is_user && !search_exception_tables(regs->nip))
520 return bad_area_nosemaphore(regs, address);
521
522retry:
523 down_read(&mm->mmap_sem);
524 } else {
525 /*
526 * The above down_read_trylock() might have succeeded in
527 * which case we'll have missed the might_sleep() from
528 * down_read():
529 */
530 might_sleep();
531 }
532
533 vma = find_vma(mm, address);
534 if (unlikely(!vma))
535 return bad_area(regs, address);
536 if (likely(vma->vm_start <= address))
537 goto good_area;
538 if (unlikely(!(vma->vm_flags & VM_GROWSDOWN)))
539 return bad_area(regs, address);
540
541 /* The stack is being expanded, check if it's valid */
542 if (unlikely(bad_stack_expansion(regs, address, vma, flags,
543 &must_retry))) {
544 if (!must_retry)
545 return bad_area(regs, address);
546
547 up_read(&mm->mmap_sem);
548 if (fault_in_pages_readable((const char __user *)regs->nip,
549 sizeof(unsigned int)))
550 return bad_area_nosemaphore(regs, address);
551 goto retry;
552 }
553
554 /* Try to expand it */
555 if (unlikely(expand_stack(vma, address)))
556 return bad_area(regs, address);
557
558good_area:
559 if (unlikely(access_error(is_write, is_exec, vma)))
560 return bad_access(regs, address);
561
562 /*
563 * If for any reason at all we couldn't handle the fault,
564 * make sure we exit gracefully rather than endlessly redo
565 * the fault.
566 */
567 fault = handle_mm_fault(vma, address, flags);
568
569#ifdef CONFIG_PPC_MEM_KEYS
570 /*
571 * we skipped checking for access error due to key earlier.
572 * Check that using handle_mm_fault error return.
573 */
574 if (unlikely(fault & VM_FAULT_SIGSEGV) &&
575 !arch_vma_access_permitted(vma, is_write, is_exec, 0)) {
576
577 int pkey = vma_pkey(vma);
578
579 up_read(&mm->mmap_sem);
580 return bad_key_fault_exception(regs, address, pkey);
581 }
582#endif /* CONFIG_PPC_MEM_KEYS */
583
584 major |= fault & VM_FAULT_MAJOR;
585
586 /*
587 * Handle the retry right now, the mmap_sem has been released in that
588 * case.
589 */
590 if (unlikely(fault & VM_FAULT_RETRY)) {
591 /* We retry only once */
592 if (flags & FAULT_FLAG_ALLOW_RETRY) {
593 /*
594 * Clear FAULT_FLAG_ALLOW_RETRY to avoid any risk
595 * of starvation.
596 */
597 flags &= ~FAULT_FLAG_ALLOW_RETRY;
598 flags |= FAULT_FLAG_TRIED;
599 if (!fatal_signal_pending(current))
600 goto retry;
601 }
602
603 /*
604 * User mode? Just return to handle the fatal exception otherwise
605 * return to bad_page_fault
606 */
607 return is_user ? 0 : SIGBUS;
608 }
609
610 up_read(¤t->mm->mmap_sem);
611
612 if (unlikely(fault & VM_FAULT_ERROR))
613 return mm_fault_error(regs, address, fault);
614
615 /*
616 * Major/minor page fault accounting.
617 */
618 if (major) {
619 current->maj_flt++;
620 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MAJ, 1, regs, address);
621 cmo_account_page_fault();
622 } else {
623 current->min_flt++;
624 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS_MIN, 1, regs, address);
625 }
626 return 0;
627}
628NOKPROBE_SYMBOL(__do_page_fault);
629
630int do_page_fault(struct pt_regs *regs, unsigned long address,
631 unsigned long error_code)
632{
633 enum ctx_state prev_state = exception_enter();
634 int rc = __do_page_fault(regs, address, error_code);
635 exception_exit(prev_state);
636 return rc;
637}
638NOKPROBE_SYMBOL(do_page_fault);
639
640/*
641 * bad_page_fault is called when we have a bad access from the kernel.
642 * It is called from the DSI and ISI handlers in head.S and from some
643 * of the procedures in traps.c.
644 */
645void bad_page_fault(struct pt_regs *regs, unsigned long address, int sig)
646{
647 const struct exception_table_entry *entry;
648
649 /* Are we prepared to handle this fault? */
650 if ((entry = search_exception_tables(regs->nip)) != NULL) {
651 regs->nip = extable_fixup(entry);
652 return;
653 }
654
655 /* kernel has accessed a bad area */
656
657 switch (TRAP(regs)) {
658 case 0x300:
659 case 0x380:
660 case 0xe00:
661 pr_alert("BUG: %s at 0x%08lx\n",
662 regs->dar < PAGE_SIZE ? "Kernel NULL pointer dereference" :
663 "Unable to handle kernel data access", regs->dar);
664 break;
665 case 0x400:
666 case 0x480:
667 pr_alert("BUG: Unable to handle kernel instruction fetch%s",
668 regs->nip < PAGE_SIZE ? " (NULL pointer?)\n" : "\n");
669 break;
670 case 0x600:
671 pr_alert("BUG: Unable to handle kernel unaligned access at 0x%08lx\n",
672 regs->dar);
673 break;
674 default:
675 pr_alert("BUG: Unable to handle unknown paging fault at 0x%08lx\n",
676 regs->dar);
677 break;
678 }
679 printk(KERN_ALERT "Faulting instruction address: 0x%08lx\n",
680 regs->nip);
681
682 if (task_stack_end_corrupted(current))
683 printk(KERN_ALERT "Thread overran stack, or stack corrupted\n");
684
685 die("Kernel access of bad area", regs, sig);
686}
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#include <linux/kfence.h>
36#include <linux/pkeys.h>
37
38#include <asm/firmware.h>
39#include <asm/interrupt.h>
40#include <asm/page.h>
41#include <asm/mmu.h>
42#include <asm/mmu_context.h>
43#include <asm/siginfo.h>
44#include <asm/debug.h>
45#include <asm/kup.h>
46#include <asm/inst.h>
47
48
49/*
50 * do_page_fault error handling helpers
51 */
52
53static int
54__bad_area_nosemaphore(struct pt_regs *regs, unsigned long address, int si_code)
55{
56 /*
57 * If we are in kernel mode, bail out with a SEGV, this will
58 * be caught by the assembly which will restore the non-volatile
59 * registers before calling bad_page_fault()
60 */
61 if (!user_mode(regs))
62 return SIGSEGV;
63
64 _exception(SIGSEGV, regs, si_code, address);
65
66 return 0;
67}
68
69static noinline int bad_area_nosemaphore(struct pt_regs *regs, unsigned long address)
70{
71 return __bad_area_nosemaphore(regs, address, SEGV_MAPERR);
72}
73
74static int __bad_area(struct pt_regs *regs, unsigned long address, int si_code)
75{
76 struct mm_struct *mm = current->mm;
77
78 /*
79 * Something tried to access memory that isn't in our memory map..
80 * Fix it, but check if it's kernel or user first..
81 */
82 mmap_read_unlock(mm);
83
84 return __bad_area_nosemaphore(regs, address, si_code);
85}
86
87static noinline int bad_area(struct pt_regs *regs, unsigned long address)
88{
89 return __bad_area(regs, address, SEGV_MAPERR);
90}
91
92static noinline int bad_access_pkey(struct pt_regs *regs, unsigned long address,
93 struct vm_area_struct *vma)
94{
95 struct mm_struct *mm = current->mm;
96 int pkey;
97
98 /*
99 * We don't try to fetch the pkey from page table because reading
100 * page table without locking doesn't guarantee stable pte value.
101 * Hence the pkey value that we return to userspace can be different
102 * from the pkey that actually caused access error.
103 *
104 * It does *not* guarantee that the VMA we find here
105 * was the one that we faulted on.
106 *
107 * 1. T1 : mprotect_key(foo, PAGE_SIZE, pkey=4);
108 * 2. T1 : set AMR to deny access to pkey=4, touches, page
109 * 3. T1 : faults...
110 * 4. T2: mprotect_key(foo, PAGE_SIZE, pkey=5);
111 * 5. T1 : enters fault handler, takes mmap_lock, etc...
112 * 6. T1 : reaches here, sees vma_pkey(vma)=5, when we really
113 * faulted on a pte with its pkey=4.
114 */
115 pkey = vma_pkey(vma);
116
117 mmap_read_unlock(mm);
118
119 /*
120 * If we are in kernel mode, bail out with a SEGV, this will
121 * be caught by the assembly which will restore the non-volatile
122 * registers before calling bad_page_fault()
123 */
124 if (!user_mode(regs))
125 return SIGSEGV;
126
127 _exception_pkey(regs, address, pkey);
128
129 return 0;
130}
131
132static noinline int bad_access(struct pt_regs *regs, unsigned long address)
133{
134 return __bad_area(regs, address, SEGV_ACCERR);
135}
136
137static int do_sigbus(struct pt_regs *regs, unsigned long address,
138 vm_fault_t fault)
139{
140 if (!user_mode(regs))
141 return SIGBUS;
142
143 current->thread.trap_nr = BUS_ADRERR;
144#ifdef CONFIG_MEMORY_FAILURE
145 if (fault & (VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE)) {
146 unsigned int lsb = 0; /* shutup gcc */
147
148 pr_err("MCE: Killing %s:%d due to hardware memory corruption fault at %lx\n",
149 current->comm, current->pid, address);
150
151 if (fault & VM_FAULT_HWPOISON_LARGE)
152 lsb = hstate_index_to_shift(VM_FAULT_GET_HINDEX(fault));
153 if (fault & VM_FAULT_HWPOISON)
154 lsb = PAGE_SHIFT;
155
156 force_sig_mceerr(BUS_MCEERR_AR, (void __user *)address, lsb);
157 return 0;
158 }
159
160#endif
161 force_sig_fault(SIGBUS, BUS_ADRERR, (void __user *)address);
162 return 0;
163}
164
165static int mm_fault_error(struct pt_regs *regs, unsigned long addr,
166 vm_fault_t fault)
167{
168 /*
169 * Kernel page fault interrupted by SIGKILL. We have no reason to
170 * continue processing.
171 */
172 if (fatal_signal_pending(current) && !user_mode(regs))
173 return SIGKILL;
174
175 /* Out of memory */
176 if (fault & VM_FAULT_OOM) {
177 /*
178 * We ran out of memory, or some other thing happened to us that
179 * made us unable to handle the page fault gracefully.
180 */
181 if (!user_mode(regs))
182 return SIGSEGV;
183 pagefault_out_of_memory();
184 } else {
185 if (fault & (VM_FAULT_SIGBUS|VM_FAULT_HWPOISON|
186 VM_FAULT_HWPOISON_LARGE))
187 return do_sigbus(regs, addr, fault);
188 else if (fault & VM_FAULT_SIGSEGV)
189 return bad_area_nosemaphore(regs, addr);
190 else
191 BUG();
192 }
193 return 0;
194}
195
196/* Is this a bad kernel fault ? */
197static bool bad_kernel_fault(struct pt_regs *regs, unsigned long error_code,
198 unsigned long address, bool is_write)
199{
200 int is_exec = TRAP(regs) == INTERRUPT_INST_STORAGE;
201
202 if (is_exec) {
203 pr_crit_ratelimited("kernel tried to execute %s page (%lx) - exploit attempt? (uid: %d)\n",
204 address >= TASK_SIZE ? "exec-protected" : "user",
205 address,
206 from_kuid(&init_user_ns, current_uid()));
207
208 // Kernel exec fault is always bad
209 return true;
210 }
211
212 // Kernel fault on kernel address is bad
213 if (address >= TASK_SIZE)
214 return true;
215
216 // Read/write fault blocked by KUAP is bad, it can never succeed.
217 if (bad_kuap_fault(regs, address, is_write)) {
218 pr_crit_ratelimited("Kernel attempted to %s user page (%lx) - exploit attempt? (uid: %d)\n",
219 is_write ? "write" : "read", address,
220 from_kuid(&init_user_ns, current_uid()));
221
222 // Fault on user outside of certain regions (eg. copy_tofrom_user()) is bad
223 if (!search_exception_tables(regs->nip))
224 return true;
225
226 // Read/write fault in a valid region (the exception table search passed
227 // above), but blocked by KUAP is bad, it can never succeed.
228 return WARN(true, "Bug: %s fault blocked by KUAP!", is_write ? "Write" : "Read");
229 }
230
231 // What's left? Kernel fault on user and allowed by KUAP in the faulting context.
232 return false;
233}
234
235static bool access_pkey_error(bool is_write, bool is_exec, bool is_pkey,
236 struct vm_area_struct *vma)
237{
238 /*
239 * Make sure to check the VMA so that we do not perform
240 * faults just to hit a pkey fault as soon as we fill in a
241 * page. Only called for current mm, hence foreign == 0
242 */
243 if (!arch_vma_access_permitted(vma, is_write, is_exec, 0))
244 return true;
245
246 return false;
247}
248
249static bool access_error(bool is_write, bool is_exec, struct vm_area_struct *vma)
250{
251 /*
252 * Allow execution from readable areas if the MMU does not
253 * provide separate controls over reading and executing.
254 *
255 * Note: That code used to not be enabled for 4xx/BookE.
256 * It is now as I/D cache coherency for these is done at
257 * set_pte_at() time and I see no reason why the test
258 * below wouldn't be valid on those processors. This -may-
259 * break programs compiled with a really old ABI though.
260 */
261 if (is_exec) {
262 return !(vma->vm_flags & VM_EXEC) &&
263 (cpu_has_feature(CPU_FTR_NOEXECUTE) ||
264 !(vma->vm_flags & (VM_READ | VM_WRITE)));
265 }
266
267 if (is_write) {
268 if (unlikely(!(vma->vm_flags & VM_WRITE)))
269 return true;
270 return false;
271 }
272
273 if (unlikely(!vma_is_accessible(vma)))
274 return true;
275 /*
276 * We should ideally do the vma pkey access check here. But in the
277 * fault path, handle_mm_fault() also does the same check. To avoid
278 * these multiple checks, we skip it here and handle access error due
279 * to pkeys later.
280 */
281 return false;
282}
283
284#ifdef CONFIG_PPC_SMLPAR
285static inline void cmo_account_page_fault(void)
286{
287 if (firmware_has_feature(FW_FEATURE_CMO)) {
288 u32 page_ins;
289
290 preempt_disable();
291 page_ins = be32_to_cpu(get_lppaca()->page_ins);
292 page_ins += 1 << PAGE_FACTOR;
293 get_lppaca()->page_ins = cpu_to_be32(page_ins);
294 preempt_enable();
295 }
296}
297#else
298static inline void cmo_account_page_fault(void) { }
299#endif /* CONFIG_PPC_SMLPAR */
300
301static void sanity_check_fault(bool is_write, bool is_user,
302 unsigned long error_code, unsigned long address)
303{
304 /*
305 * Userspace trying to access kernel address, we get PROTFAULT for that.
306 */
307 if (is_user && address >= TASK_SIZE) {
308 if ((long)address == -1)
309 return;
310
311 pr_crit_ratelimited("%s[%d]: User access of kernel address (%lx) - exploit attempt? (uid: %d)\n",
312 current->comm, current->pid, address,
313 from_kuid(&init_user_ns, current_uid()));
314 return;
315 }
316
317 if (!IS_ENABLED(CONFIG_PPC_BOOK3S))
318 return;
319
320 /*
321 * For hash translation mode, we should never get a
322 * PROTFAULT. Any update to pte to reduce access will result in us
323 * removing the hash page table entry, thus resulting in a DSISR_NOHPTE
324 * fault instead of DSISR_PROTFAULT.
325 *
326 * A pte update to relax the access will not result in a hash page table
327 * entry invalidate and hence can result in DSISR_PROTFAULT.
328 * ptep_set_access_flags() doesn't do a hpte flush. This is why we have
329 * the special !is_write in the below conditional.
330 *
331 * For platforms that doesn't supports coherent icache and do support
332 * per page noexec bit, we do setup things such that we do the
333 * sync between D/I cache via fault. But that is handled via low level
334 * hash fault code (hash_page_do_lazy_icache()) and we should not reach
335 * here in such case.
336 *
337 * For wrong access that can result in PROTFAULT, the above vma->vm_flags
338 * check should handle those and hence we should fall to the bad_area
339 * handling correctly.
340 *
341 * For embedded with per page exec support that doesn't support coherent
342 * icache we do get PROTFAULT and we handle that D/I cache sync in
343 * set_pte_at while taking the noexec/prot fault. Hence this is WARN_ON
344 * is conditional for server MMU.
345 *
346 * For radix, we can get prot fault for autonuma case, because radix
347 * page table will have them marked noaccess for user.
348 */
349 if (radix_enabled() || is_write)
350 return;
351
352 WARN_ON_ONCE(error_code & DSISR_PROTFAULT);
353}
354
355/*
356 * Define the correct "is_write" bit in error_code based
357 * on the processor family
358 */
359#if (defined(CONFIG_4xx) || defined(CONFIG_BOOKE))
360#define page_fault_is_write(__err) ((__err) & ESR_DST)
361#else
362#define page_fault_is_write(__err) ((__err) & DSISR_ISSTORE)
363#endif
364
365#if defined(CONFIG_4xx) || defined(CONFIG_BOOKE)
366#define page_fault_is_bad(__err) (0)
367#elif defined(CONFIG_PPC_8xx)
368#define page_fault_is_bad(__err) ((__err) & DSISR_NOEXEC_OR_G)
369#elif defined(CONFIG_PPC64)
370#define page_fault_is_bad(__err) ((__err) & DSISR_BAD_FAULT_64S)
371#else
372#define page_fault_is_bad(__err) ((__err) & DSISR_BAD_FAULT_32S)
373#endif
374
375/*
376 * For 600- and 800-family processors, the error_code parameter is DSISR
377 * for a data fault, SRR1 for an instruction fault.
378 * For 400-family processors the error_code parameter is ESR for a data fault,
379 * 0 for an instruction fault.
380 * For 64-bit processors, the error_code parameter is DSISR for a data access
381 * fault, SRR1 & 0x08000000 for an instruction access fault.
382 *
383 * The return value is 0 if the fault was handled, or the signal
384 * number if this is a kernel fault that can't be handled here.
385 */
386static int ___do_page_fault(struct pt_regs *regs, unsigned long address,
387 unsigned long error_code)
388{
389 struct vm_area_struct * vma;
390 struct mm_struct *mm = current->mm;
391 unsigned int flags = FAULT_FLAG_DEFAULT;
392 int is_exec = TRAP(regs) == INTERRUPT_INST_STORAGE;
393 int is_user = user_mode(regs);
394 int is_write = page_fault_is_write(error_code);
395 vm_fault_t fault, major = 0;
396 bool kprobe_fault = kprobe_page_fault(regs, 11);
397
398 if (unlikely(debugger_fault_handler(regs) || kprobe_fault))
399 return 0;
400
401 if (unlikely(page_fault_is_bad(error_code))) {
402 if (is_user) {
403 _exception(SIGBUS, regs, BUS_OBJERR, address);
404 return 0;
405 }
406 return SIGBUS;
407 }
408
409 /* Additional sanity check(s) */
410 sanity_check_fault(is_write, is_user, error_code, address);
411
412 /*
413 * The kernel should never take an execute fault nor should it
414 * take a page fault to a kernel address or a page fault to a user
415 * address outside of dedicated places
416 */
417 if (unlikely(!is_user && bad_kernel_fault(regs, error_code, address, is_write))) {
418 if (kfence_handle_page_fault(address, is_write, regs))
419 return 0;
420
421 return SIGSEGV;
422 }
423
424 /*
425 * If we're in an interrupt, have no user context or are running
426 * in a region with pagefaults disabled then we must not take the fault
427 */
428 if (unlikely(faulthandler_disabled() || !mm)) {
429 if (is_user)
430 printk_ratelimited(KERN_ERR "Page fault in user mode"
431 " with faulthandler_disabled()=%d"
432 " mm=%p\n",
433 faulthandler_disabled(), mm);
434 return bad_area_nosemaphore(regs, address);
435 }
436
437 interrupt_cond_local_irq_enable(regs);
438
439 perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);
440
441 /*
442 * We want to do this outside mmap_lock, because reading code around nip
443 * can result in fault, which will cause a deadlock when called with
444 * mmap_lock held
445 */
446 if (is_user)
447 flags |= FAULT_FLAG_USER;
448 if (is_write)
449 flags |= FAULT_FLAG_WRITE;
450 if (is_exec)
451 flags |= FAULT_FLAG_INSTRUCTION;
452
453 /* When running in the kernel we expect faults to occur only to
454 * addresses in user space. All other faults represent errors in the
455 * kernel and should generate an OOPS. Unfortunately, in the case of an
456 * erroneous fault occurring in a code path which already holds mmap_lock
457 * we will deadlock attempting to validate the fault against the
458 * address space. Luckily the kernel only validly references user
459 * space from well defined areas of code, which are listed in the
460 * exceptions table.
461 *
462 * As the vast majority of faults will be valid we will only perform
463 * the source reference check when there is a possibility of a deadlock.
464 * Attempt to lock the address space, if we cannot we then validate the
465 * source. If this is invalid we can skip the address space check,
466 * thus avoiding the deadlock.
467 */
468 if (unlikely(!mmap_read_trylock(mm))) {
469 if (!is_user && !search_exception_tables(regs->nip))
470 return bad_area_nosemaphore(regs, address);
471
472retry:
473 mmap_read_lock(mm);
474 } else {
475 /*
476 * The above down_read_trylock() might have succeeded in
477 * which case we'll have missed the might_sleep() from
478 * down_read():
479 */
480 might_sleep();
481 }
482
483 vma = find_vma(mm, address);
484 if (unlikely(!vma))
485 return bad_area(regs, address);
486
487 if (unlikely(vma->vm_start > address)) {
488 if (unlikely(!(vma->vm_flags & VM_GROWSDOWN)))
489 return bad_area(regs, address);
490
491 if (unlikely(expand_stack(vma, address)))
492 return bad_area(regs, address);
493 }
494
495 if (unlikely(access_pkey_error(is_write, is_exec,
496 (error_code & DSISR_KEYFAULT), vma)))
497 return bad_access_pkey(regs, address, vma);
498
499 if (unlikely(access_error(is_write, is_exec, vma)))
500 return bad_access(regs, address);
501
502 /*
503 * If for any reason at all we couldn't handle the fault,
504 * make sure we exit gracefully rather than endlessly redo
505 * the fault.
506 */
507 fault = handle_mm_fault(vma, address, flags, regs);
508
509 major |= fault & VM_FAULT_MAJOR;
510
511 if (fault_signal_pending(fault, regs))
512 return user_mode(regs) ? 0 : SIGBUS;
513
514 /*
515 * Handle the retry right now, the mmap_lock has been released in that
516 * case.
517 */
518 if (unlikely(fault & VM_FAULT_RETRY)) {
519 if (flags & FAULT_FLAG_ALLOW_RETRY) {
520 flags |= FAULT_FLAG_TRIED;
521 goto retry;
522 }
523 }
524
525 mmap_read_unlock(current->mm);
526
527 if (unlikely(fault & VM_FAULT_ERROR))
528 return mm_fault_error(regs, address, fault);
529
530 /*
531 * Major/minor page fault accounting.
532 */
533 if (major)
534 cmo_account_page_fault();
535
536 return 0;
537}
538NOKPROBE_SYMBOL(___do_page_fault);
539
540static __always_inline void __do_page_fault(struct pt_regs *regs)
541{
542 long err;
543
544 err = ___do_page_fault(regs, regs->dar, regs->dsisr);
545 if (unlikely(err))
546 bad_page_fault(regs, err);
547}
548
549DEFINE_INTERRUPT_HANDLER(do_page_fault)
550{
551 __do_page_fault(regs);
552}
553
554#ifdef CONFIG_PPC_BOOK3S_64
555/* Same as do_page_fault but interrupt entry has already run in do_hash_fault */
556void hash__do_page_fault(struct pt_regs *regs)
557{
558 __do_page_fault(regs);
559}
560NOKPROBE_SYMBOL(hash__do_page_fault);
561#endif
562
563/*
564 * bad_page_fault is called when we have a bad access from the kernel.
565 * It is called from the DSI and ISI handlers in head.S and from some
566 * of the procedures in traps.c.
567 */
568static void __bad_page_fault(struct pt_regs *regs, int sig)
569{
570 int is_write = page_fault_is_write(regs->dsisr);
571
572 /* kernel has accessed a bad area */
573
574 switch (TRAP(regs)) {
575 case INTERRUPT_DATA_STORAGE:
576 case INTERRUPT_DATA_SEGMENT:
577 case INTERRUPT_H_DATA_STORAGE:
578 pr_alert("BUG: %s on %s at 0x%08lx\n",
579 regs->dar < PAGE_SIZE ? "Kernel NULL pointer dereference" :
580 "Unable to handle kernel data access",
581 is_write ? "write" : "read", regs->dar);
582 break;
583 case INTERRUPT_INST_STORAGE:
584 case INTERRUPT_INST_SEGMENT:
585 pr_alert("BUG: Unable to handle kernel instruction fetch%s",
586 regs->nip < PAGE_SIZE ? " (NULL pointer?)\n" : "\n");
587 break;
588 case INTERRUPT_ALIGNMENT:
589 pr_alert("BUG: Unable to handle kernel unaligned access at 0x%08lx\n",
590 regs->dar);
591 break;
592 default:
593 pr_alert("BUG: Unable to handle unknown paging fault at 0x%08lx\n",
594 regs->dar);
595 break;
596 }
597 printk(KERN_ALERT "Faulting instruction address: 0x%08lx\n",
598 regs->nip);
599
600 if (task_stack_end_corrupted(current))
601 printk(KERN_ALERT "Thread overran stack, or stack corrupted\n");
602
603 die("Kernel access of bad area", regs, sig);
604}
605
606void bad_page_fault(struct pt_regs *regs, int sig)
607{
608 const struct exception_table_entry *entry;
609
610 /* Are we prepared to handle this fault? */
611 entry = search_exception_tables(instruction_pointer(regs));
612 if (entry)
613 instruction_pointer_set(regs, extable_fixup(entry));
614 else
615 __bad_page_fault(regs, sig);
616}
617
618#ifdef CONFIG_PPC_BOOK3S_64
619DEFINE_INTERRUPT_HANDLER(do_bad_page_fault_segv)
620{
621 bad_page_fault(regs, SIGSEGV);
622}
623#endif