2 * Copyright (C) 1995 Linus Torvalds
5 #include <linux/signal.h>
6 #include <linux/sched.h>
7 #include <linux/kernel.h>
8 #include <linux/errno.h>
9 #include <linux/string.h>
10 #include <linux/types.h>
11 #include <linux/ptrace.h>
12 #include <linux/mman.h>
14 #include <linux/smp.h>
15 #include <linux/interrupt.h>
16 #include <linux/init.h>
17 #include <linux/tty.h>
18 #include <linux/vt_kern.h> /* For unblank_screen() */
19 #include <linux/highmem.h>
20 #include <linux/bootmem.h> /* for max_low_pfn */
21 #include <linux/vmalloc.h>
22 #include <linux/module.h>
23 #include <linux/kprobes.h>
24 #include <linux/uaccess.h>
25 #include <linux/kdebug.h>
27 #include <asm/system.h>
29 #include <asm/segment.h>
32 * Page fault error code bits
33 * bit 0 == 0 means no page found, 1 means protection fault
34 * bit 1 == 0 means read, 1 means write
35 * bit 2 == 0 means kernel, 1 means user-mode
36 * bit 3 == 1 means use of reserved bit detected
37 * bit 4 == 1 means fault was an instruction fetch
39 #define PF_PROT (1<<0)
40 #define PF_WRITE (1<<1)
41 #define PF_USER (1<<2)
42 #define PF_RSVD (1<<3)
43 #define PF_INSTR (1<<4)
45 static inline int notify_page_fault(struct pt_regs *regs)
50 /* kprobe_running() needs smp_processor_id() */
51 if (!user_mode_vm(regs)) {
53 if (kprobe_running() && kprobe_fault_handler(regs, 14))
66 * Sometimes AMD Athlon/Opteron CPUs report invalid exceptions on prefetch.
67 * Check that here and ignore it.
70 * Sometimes the CPU reports invalid exceptions on prefetch.
71 * Check that here and ignore it.
73 * Opcode checker based on code by Richard Brunner
75 static int is_prefetch(struct pt_regs *regs, unsigned long addr,
76 unsigned long error_code)
81 unsigned char *max_instr;
84 if (unlikely(boot_cpu_data.x86_vendor == X86_VENDOR_AMD &&
85 boot_cpu_data.x86 >= 6)) {
86 /* Catch an obscure case of prefetch inside an NX page. */
87 if (nx_enabled && (error_code & PF_INSTR))
93 /* If it was a exec fault ignore */
94 if (error_code & PF_INSTR)
98 instr = (unsigned char *)convert_ip_to_linear(current, regs);
99 max_instr = instr + 15;
101 if (user_mode(regs) && instr >= (unsigned char *)TASK_SIZE)
104 while (scan_more && instr < max_instr) {
105 unsigned char opcode;
106 unsigned char instr_hi;
107 unsigned char instr_lo;
109 if (probe_kernel_address(instr, opcode))
112 instr_hi = opcode & 0xf0;
113 instr_lo = opcode & 0x0f;
120 * Values 0x26,0x2E,0x36,0x3E are valid x86 prefixes.
121 * In X86_64 long mode, the CPU will signal invalid
122 * opcode if some of these prefixes are present so
123 * X86_64 will never get here anyway
125 scan_more = ((instr_lo & 7) == 0x6);
130 * In AMD64 long mode 0x40..0x4F are valid REX prefixes
131 * Need to figure out under what instruction mode the
132 * instruction was issued. Could check the LDT for lm,
133 * but for now it's good enough to assume that long
134 * mode only uses well known segments or kernel.
136 scan_more = (!user_mode(regs)) || (regs->cs == __USER_CS);
140 /* 0x64 thru 0x67 are valid prefixes in all modes. */
141 scan_more = (instr_lo & 0xC) == 0x4;
144 /* 0xF0, 0xF2, 0xF3 are valid prefixes in all modes. */
145 scan_more = !instr_lo || (instr_lo>>1) == 1;
148 /* Prefetch instruction is 0x0F0D or 0x0F18 */
151 if (probe_kernel_address(instr, opcode))
153 prefetch = (instr_lo == 0xF) &&
154 (opcode == 0x0D || opcode == 0x18);
164 static void force_sig_info_fault(int si_signo, int si_code,
165 unsigned long address, struct task_struct *tsk)
169 info.si_signo = si_signo;
171 info.si_code = si_code;
172 info.si_addr = (void __user *)address;
173 force_sig_info(si_signo, &info, tsk);
176 void dump_pagetable(unsigned long address)
178 __typeof__(pte_val(__pte(0))) page;
181 page = ((__typeof__(page) *) __va(page))[address >> PGDIR_SHIFT];
182 #ifdef CONFIG_X86_PAE
183 printk("*pdpt = %016Lx ", page);
184 if ((page >> PAGE_SHIFT) < max_low_pfn
185 && page & _PAGE_PRESENT) {
187 page = ((__typeof__(page) *) __va(page))[(address >> PMD_SHIFT)
188 & (PTRS_PER_PMD - 1)];
189 printk(KERN_CONT "*pde = %016Lx ", page);
193 printk("*pde = %08lx ", page);
197 * We must not directly access the pte in the highpte
198 * case if the page table is located in highmem.
199 * And let's rather not kmap-atomic the pte, just in case
200 * it's allocated already.
202 if ((page >> PAGE_SHIFT) < max_low_pfn
203 && (page & _PAGE_PRESENT)
204 && !(page & _PAGE_PSE)) {
206 page = ((__typeof__(page) *) __va(page))[(address >> PAGE_SHIFT)
207 & (PTRS_PER_PTE - 1)];
208 printk("*pte = %0*Lx ", sizeof(page)*2, (u64)page);
214 static inline pmd_t *vmalloc_sync_one(pgd_t *pgd, unsigned long address)
216 unsigned index = pgd_index(address);
222 pgd_k = init_mm.pgd + index;
224 if (!pgd_present(*pgd_k))
228 * set_pgd(pgd, *pgd_k); here would be useless on PAE
229 * and redundant with the set_pmd() on non-PAE. As would
233 pud = pud_offset(pgd, address);
234 pud_k = pud_offset(pgd_k, address);
235 if (!pud_present(*pud_k))
238 pmd = pmd_offset(pud, address);
239 pmd_k = pmd_offset(pud_k, address);
240 if (!pmd_present(*pmd_k))
242 if (!pmd_present(*pmd)) {
243 set_pmd(pmd, *pmd_k);
244 arch_flush_lazy_mmu_mode();
246 BUG_ON(pmd_page(*pmd) != pmd_page(*pmd_k));
251 static const char errata93_warning[] =
252 KERN_ERR "******* Your BIOS seems to not contain a fix for K8 errata #93\n"
253 KERN_ERR "******* Working around it, but it may cause SEGVs or burn power.\n"
254 KERN_ERR "******* Please consider a BIOS update.\n"
255 KERN_ERR "******* Disabling USB legacy in the BIOS may also help.\n";
258 /* Workaround for K8 erratum #93 & buggy BIOS.
259 BIOS SMM functions are required to use a specific workaround
260 to avoid corruption of the 64bit RIP register on C stepping K8.
261 A lot of BIOS that didn't get tested properly miss this.
262 The OS sees this as a page fault with the upper 32bits of RIP cleared.
263 Try to work around it here.
264 Note we only handle faults in kernel here.
265 Does nothing for X86_32
267 static int is_errata93(struct pt_regs *regs, unsigned long address)
271 if (address != regs->ip)
273 if ((address >> 32) != 0)
275 address |= 0xffffffffUL << 32;
276 if ((address >= (u64)_stext && address <= (u64)_etext) ||
277 (address >= MODULES_VADDR && address <= MODULES_END)) {
279 printk(errata93_warning);
290 * Work around K8 erratum #100 K8 in compat mode occasionally jumps to illegal
291 * addresses >4GB. We catch this in the page fault handler because these
292 * addresses are not reachable. Just detect this case and return. Any code
293 * segment in LDT is compatibility mode.
295 static int is_errata100(struct pt_regs *regs, unsigned long address)
298 if ((regs->cs == __USER32_CS || (regs->cs & (1<<2))) &&
305 void do_invalid_op(struct pt_regs *, unsigned long);
307 static int is_f00f_bug(struct pt_regs *regs, unsigned long address)
309 #ifdef CONFIG_X86_F00F_BUG
312 * Pentium F0 0F C7 C8 bug workaround.
314 if (boot_cpu_data.f00f_bug) {
315 nr = (address - idt_descr.address) >> 3;
318 do_invalid_op(regs, 0);
327 * Handle a fault on the vmalloc or module mapping area
329 * This assumes no large pages in there.
331 static inline int vmalloc_fault(unsigned long address)
334 unsigned long pgd_paddr;
338 * Synchronize this task's top level page-table
339 * with the 'reference' page table.
341 * Do _not_ use "current" here. We might be inside
342 * an interrupt in the middle of a task switch..
344 pgd_paddr = read_cr3();
345 pmd_k = vmalloc_sync_one(__va(pgd_paddr), address);
348 pte_k = pte_offset_kernel(pmd_k, address);
349 if (!pte_present(*pte_k))
353 pgd_t *pgd, *pgd_ref;
354 pud_t *pud, *pud_ref;
355 pmd_t *pmd, *pmd_ref;
356 pte_t *pte, *pte_ref;
358 /* Copy kernel mappings over when needed. This can also
359 happen within a race in page table update. In the later
362 pgd = pgd_offset(current->mm ?: &init_mm, address);
363 pgd_ref = pgd_offset_k(address);
364 if (pgd_none(*pgd_ref))
367 set_pgd(pgd, *pgd_ref);
369 BUG_ON(pgd_page_vaddr(*pgd) != pgd_page_vaddr(*pgd_ref));
371 /* Below here mismatches are bugs because these lower tables
374 pud = pud_offset(pgd, address);
375 pud_ref = pud_offset(pgd_ref, address);
376 if (pud_none(*pud_ref))
378 if (pud_none(*pud) || pud_page_vaddr(*pud) != pud_page_vaddr(*pud_ref))
380 pmd = pmd_offset(pud, address);
381 pmd_ref = pmd_offset(pud_ref, address);
382 if (pmd_none(*pmd_ref))
384 if (pmd_none(*pmd) || pmd_page(*pmd) != pmd_page(*pmd_ref))
386 pte_ref = pte_offset_kernel(pmd_ref, address);
387 if (!pte_present(*pte_ref))
389 pte = pte_offset_kernel(pmd, address);
390 /* Don't use pte_page here, because the mappings can point
391 outside mem_map, and the NUMA hash lookup cannot handle
393 if (!pte_present(*pte) || pte_pfn(*pte) != pte_pfn(*pte_ref))
399 int show_unhandled_signals = 1;
402 * This routine handles page faults. It determines the address,
403 * and the problem, and then passes it off to one of the appropriate
406 void __kprobes do_page_fault(struct pt_regs *regs, unsigned long error_code)
408 struct task_struct *tsk;
409 struct mm_struct *mm;
410 struct vm_area_struct *vma;
411 unsigned long address;
416 * We can fault from pretty much anywhere, with unknown IRQ state.
418 trace_hardirqs_fixup();
422 prefetchw(&mm->mmap_sem);
424 /* get the address */
425 address = read_cr2();
427 si_code = SEGV_MAPERR;
429 if (notify_page_fault(regs))
433 * We fault-in kernel-space virtual memory on-demand. The
434 * 'reference' page table is init_mm.pgd.
436 * NOTE! We MUST NOT take any locks for this case. We may
437 * be in an interrupt or a critical region, and should
438 * only copy the information from the master page table,
441 * This verifies that the fault happens in kernel space
442 * (error_code & 4) == 0, and that the fault was not a
443 * protection error (error_code & 9) == 0.
445 if (unlikely(address >= TASK_SIZE)) {
446 if (!(error_code & (PF_RSVD|PF_USER|PF_PROT)) &&
447 vmalloc_fault(address) >= 0)
450 * Don't take the mm semaphore here. If we fixup a prefetch
451 * fault we could otherwise deadlock.
453 goto bad_area_nosemaphore;
456 /* It's safe to allow irq's after cr2 has been saved and the vmalloc
457 fault has been handled. */
458 if (regs->flags & (X86_EFLAGS_IF|VM_MASK))
462 * If we're in an interrupt, have no user context or are running in an
463 * atomic region then we must not take the fault.
465 if (in_atomic() || !mm)
466 goto bad_area_nosemaphore;
468 /* When running in the kernel we expect faults to occur only to
469 * addresses in user space. All other faults represent errors in the
470 * kernel and should generate an OOPS. Unfortunately, in the case of an
471 * erroneous fault occurring in a code path which already holds mmap_sem
472 * we will deadlock attempting to validate the fault against the
473 * address space. Luckily the kernel only validly references user
474 * space from well defined areas of code, which are listed in the
477 * As the vast majority of faults will be valid we will only perform
478 * the source reference check when there is a possibility of a deadlock.
479 * Attempt to lock the address space, if we cannot we then validate the
480 * source. If this is invalid we can skip the address space check,
481 * thus avoiding the deadlock.
483 if (!down_read_trylock(&mm->mmap_sem)) {
484 if ((error_code & PF_USER) == 0 &&
485 !search_exception_tables(regs->ip))
486 goto bad_area_nosemaphore;
487 down_read(&mm->mmap_sem);
490 vma = find_vma(mm, address);
493 if (vma->vm_start <= address)
495 if (!(vma->vm_flags & VM_GROWSDOWN))
497 if (error_code & PF_USER) {
499 * Accessing the stack below %sp is always a bug.
500 * The large cushion allows instructions like enter
501 * and pusha to work. ("enter $65535,$31" pushes
502 * 32 pointers and then decrements %sp by 65535.)
504 if (address + 65536 + 32 * sizeof(unsigned long) < regs->sp)
507 if (expand_stack(vma, address))
510 * Ok, we have a good vm_area for this memory access, so
514 si_code = SEGV_ACCERR;
516 switch (error_code & (PF_PROT|PF_WRITE)) {
517 default: /* 3: write, present */
519 case PF_WRITE: /* write, not present */
520 if (!(vma->vm_flags & VM_WRITE))
524 case PF_PROT: /* read, present */
526 case 0: /* read, not present */
527 if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))
533 * If for any reason at all we couldn't handle the fault,
534 * make sure we exit gracefully rather than endlessly redo
537 fault = handle_mm_fault(mm, vma, address, write);
538 if (unlikely(fault & VM_FAULT_ERROR)) {
539 if (fault & VM_FAULT_OOM)
541 else if (fault & VM_FAULT_SIGBUS)
545 if (fault & VM_FAULT_MAJOR)
552 * Did it hit the DOS screen memory VA from vm86 mode?
554 if (v8086_mode(regs)) {
555 unsigned long bit = (address - 0xA0000) >> PAGE_SHIFT;
557 tsk->thread.screen_bitmap |= 1 << bit;
560 up_read(&mm->mmap_sem);
564 * Something tried to access memory that isn't in our memory map..
565 * Fix it, but check if it's kernel or user first..
568 up_read(&mm->mmap_sem);
570 bad_area_nosemaphore:
571 /* User mode accesses just cause a SIGSEGV */
572 if (error_code & PF_USER) {
574 * It's possible to have interrupts off here.
579 * Valid to do another page fault here because this one came
582 if (is_prefetch(regs, address, error_code))
585 if (is_errata100(regs, address))
588 if (show_unhandled_signals && unhandled_signal(tsk, SIGSEGV) &&
589 printk_ratelimit()) {
592 "%s%s[%d]: segfault at %lx ip %08lx sp %08lx error %lx",
594 "%s%s[%d]: segfault at %lx ip %lx sp %lx error %lx",
596 task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG,
597 tsk->comm, task_pid_nr(tsk), address, regs->ip,
598 regs->sp, error_code);
599 print_vma_addr(" in ", regs->ip);
602 tsk->thread.cr2 = address;
603 /* Kernel addresses are always protection faults */
604 tsk->thread.error_code = error_code | (address >= TASK_SIZE);
605 tsk->thread.trap_no = 14;
606 force_sig_info_fault(SIGSEGV, si_code, address, tsk);
610 if (is_f00f_bug(regs, address))
614 /* Are we prepared to handle this kernel fault? */
615 if (fixup_exception(regs))
619 * Valid to do another page fault here, because if this fault
620 * had been triggered by is_prefetch fixup_exception would have
623 if (is_prefetch(regs, address, error_code))
626 if (is_errata93(regs, address))
630 * Oops. The kernel tried to access some bad page. We'll have to
631 * terminate things with extreme prejudice.
636 if (oops_may_print()) {
638 #ifdef CONFIG_X86_PAE
639 if (error_code & PF_INSTR) {
641 pte_t *pte = lookup_address(address, &level);
643 if (pte && pte_present(*pte) && !pte_exec(*pte))
644 printk(KERN_CRIT "kernel tried to execute "
645 "NX-protected page - exploit attempt? "
646 "(uid: %d)\n", current->uid);
649 if (address < PAGE_SIZE)
650 printk(KERN_ALERT "BUG: unable to handle kernel NULL "
651 "pointer dereference");
653 printk(KERN_ALERT "BUG: unable to handle kernel paging"
655 printk(" at virtual address %08lx\n", address);
656 printk(KERN_ALERT "printing ip: %08lx ", regs->ip);
658 dump_pagetable(address);
661 tsk->thread.cr2 = address;
662 tsk->thread.trap_no = 14;
663 tsk->thread.error_code = error_code;
664 die("Oops", regs, error_code);
669 * We ran out of memory, or some other thing happened to us that made
670 * us unable to handle the page fault gracefully.
673 up_read(&mm->mmap_sem);
674 if (is_global_init(tsk)) {
676 down_read(&mm->mmap_sem);
679 printk("VM: killing process %s\n", tsk->comm);
680 if (error_code & PF_USER)
681 do_group_exit(SIGKILL);
685 up_read(&mm->mmap_sem);
687 /* Kernel mode? Handle exceptions or die */
688 if (!(error_code & PF_USER))
691 /* User space => ok to do another page fault */
692 if (is_prefetch(regs, address, error_code))
695 tsk->thread.cr2 = address;
696 tsk->thread.error_code = error_code;
697 tsk->thread.trap_no = 14;
698 force_sig_info_fault(SIGBUS, BUS_ADRERR, address, tsk);
701 void vmalloc_sync_all(void)
704 * Note that races in the updates of insync and start aren't
705 * problematic: insync can only get set bits added, and updates to
706 * start are only improving performance (without affecting correctness
709 static DECLARE_BITMAP(insync, PTRS_PER_PGD);
710 static unsigned long start = TASK_SIZE;
711 unsigned long address;
713 if (SHARED_KERNEL_PMD)
716 BUILD_BUG_ON(TASK_SIZE & ~PGDIR_MASK);
717 for (address = start; address >= TASK_SIZE; address += PGDIR_SIZE) {
718 if (!test_bit(pgd_index(address), insync)) {
722 spin_lock_irqsave(&pgd_lock, flags);
723 for (page = pgd_list; page; page =
724 (struct page *)page->index)
725 if (!vmalloc_sync_one(page_address(page),
727 BUG_ON(page != pgd_list);
730 spin_unlock_irqrestore(&pgd_lock, flags);
732 set_bit(pgd_index(address), insync);
734 if (address == start && test_bit(pgd_index(address), insync))
735 start = address + PGDIR_SIZE;