2 * linux/arch/i386/mm/fault.c
4 * Copyright (C) 1995 Linus Torvalds
7 #include <linux/signal.h>
8 #include <linux/sched.h>
9 #include <linux/kernel.h>
10 #include <linux/errno.h>
11 #include <linux/string.h>
12 #include <linux/types.h>
13 #include <linux/ptrace.h>
14 #include <linux/mman.h>
16 #include <linux/smp.h>
17 #include <linux/smp_lock.h>
18 #include <linux/interrupt.h>
19 #include <linux/init.h>
20 #include <linux/tty.h>
21 #include <linux/vt_kern.h> /* For unblank_screen() */
22 #include <linux/highmem.h>
23 #include <linux/bootmem.h> /* for max_low_pfn */
24 #include <linux/vmalloc.h>
25 #include <linux/module.h>
26 #include <linux/kprobes.h>
27 #include <linux/uaccess.h>
28 #include <linux/kdebug.h>
30 #include <asm/system.h>
32 #include <asm/segment.h>
34 extern void die(const char *,struct pt_regs *,long);
36 static ATOMIC_NOTIFIER_HEAD(notify_page_fault_chain);
38 int register_page_fault_notifier(struct notifier_block *nb)
41 return atomic_notifier_chain_register(¬ify_page_fault_chain, nb);
43 EXPORT_SYMBOL_GPL(register_page_fault_notifier);
45 int unregister_page_fault_notifier(struct notifier_block *nb)
47 return atomic_notifier_chain_unregister(¬ify_page_fault_chain, nb);
49 EXPORT_SYMBOL_GPL(unregister_page_fault_notifier);
51 static inline int notify_page_fault(struct pt_regs *regs, long err)
53 struct die_args args = {
60 return atomic_notifier_call_chain(¬ify_page_fault_chain,
61 DIE_PAGE_FAULT, &args);
65 * Return EIP plus the CS segment base. The segment limit is also
66 * adjusted, clamped to the kernel/user address space (whichever is
67 * appropriate), and returned in *eip_limit.
69 * The segment is checked, because it might have been changed by another
70 * task between the original faulting instruction and here.
72 * If CS is no longer a valid code segment, or if EIP is beyond the
73 * limit, or if it is a kernel address when CS is not a kernel segment,
74 * then the returned value will be greater than *eip_limit.
76 * This is slow, but is very rarely executed.
78 static inline unsigned long get_segment_eip(struct pt_regs *regs,
79 unsigned long *eip_limit)
81 unsigned long eip = regs->eip;
82 unsigned seg = regs->xcs & 0xffff;
83 u32 seg_ar, seg_limit, base, *desc;
85 /* Unlikely, but must come before segment checks. */
86 if (unlikely(regs->eflags & VM_MASK)) {
88 *eip_limit = base + 0xffff;
89 return base + (eip & 0xffff);
92 /* The standard kernel/user address space limit. */
93 *eip_limit = user_mode(regs) ? USER_DS.seg : KERNEL_DS.seg;
95 /* By far the most common cases. */
96 if (likely(SEGMENT_IS_FLAT_CODE(seg)))
99 /* Check the segment exists, is within the current LDT/GDT size,
100 that kernel/user (ring 0..3) has the appropriate privilege,
101 that it's a code segment, and get the limit. */
102 __asm__ ("larl %3,%0; lsll %3,%1"
103 : "=&r" (seg_ar), "=r" (seg_limit) : "0" (0), "rm" (seg));
104 if ((~seg_ar & 0x9800) || eip > seg_limit) {
106 return 1; /* So that returned eip > *eip_limit. */
109 /* Get the GDT/LDT descriptor base.
110 When you look for races in this code remember that
111 LDT and other horrors are only used in user space. */
113 /* Must lock the LDT while reading it. */
114 down(¤t->mm->context.sem);
115 desc = current->mm->context.ldt;
116 desc = (void *)desc + (seg & ~7);
118 /* Must disable preemption while reading the GDT. */
119 desc = (u32 *)get_cpu_gdt_table(get_cpu());
120 desc = (void *)desc + (seg & ~7);
123 /* Decode the code segment base from the descriptor */
124 base = get_desc_base((unsigned long *)desc);
127 up(¤t->mm->context.sem);
131 /* Adjust EIP and segment limit, and clamp at the kernel limit.
132 It's legitimate for segments to wrap at 0xffffffff. */
134 if (seg_limit < *eip_limit && seg_limit >= base)
135 *eip_limit = seg_limit;
140 * Sometimes AMD Athlon/Opteron CPUs report invalid exceptions on prefetch.
141 * Check that here and ignore it.
143 static int __is_prefetch(struct pt_regs *regs, unsigned long addr)
146 unsigned char *instr = (unsigned char *)get_segment_eip (regs, &limit);
151 for (i = 0; scan_more && i < 15; i++) {
152 unsigned char opcode;
153 unsigned char instr_hi;
154 unsigned char instr_lo;
156 if (instr > (unsigned char *)limit)
158 if (probe_kernel_address(instr, opcode))
161 instr_hi = opcode & 0xf0;
162 instr_lo = opcode & 0x0f;
168 /* Values 0x26,0x2E,0x36,0x3E are valid x86 prefixes. */
169 scan_more = ((instr_lo & 7) == 0x6);
173 /* 0x64 thru 0x67 are valid prefixes in all modes. */
174 scan_more = (instr_lo & 0xC) == 0x4;
177 /* 0xF0, 0xF2, and 0xF3 are valid prefixes */
178 scan_more = !instr_lo || (instr_lo>>1) == 1;
181 /* Prefetch instruction is 0x0F0D or 0x0F18 */
183 if (instr > (unsigned char *)limit)
185 if (probe_kernel_address(instr, opcode))
187 prefetch = (instr_lo == 0xF) &&
188 (opcode == 0x0D || opcode == 0x18);
198 static inline int is_prefetch(struct pt_regs *regs, unsigned long addr,
199 unsigned long error_code)
201 if (unlikely(boot_cpu_data.x86_vendor == X86_VENDOR_AMD &&
202 boot_cpu_data.x86 >= 6)) {
203 /* Catch an obscure case of prefetch inside an NX page. */
204 if (nx_enabled && (error_code & 16))
206 return __is_prefetch(regs, addr);
211 static noinline void force_sig_info_fault(int si_signo, int si_code,
212 unsigned long address, struct task_struct *tsk)
216 info.si_signo = si_signo;
218 info.si_code = si_code;
219 info.si_addr = (void __user *)address;
220 force_sig_info(si_signo, &info, tsk);
223 fastcall void do_invalid_op(struct pt_regs *, unsigned long);
225 static inline pmd_t *vmalloc_sync_one(pgd_t *pgd, unsigned long address)
227 unsigned index = pgd_index(address);
233 pgd_k = init_mm.pgd + index;
235 if (!pgd_present(*pgd_k))
239 * set_pgd(pgd, *pgd_k); here would be useless on PAE
240 * and redundant with the set_pmd() on non-PAE. As would
244 pud = pud_offset(pgd, address);
245 pud_k = pud_offset(pgd_k, address);
246 if (!pud_present(*pud_k))
249 pmd = pmd_offset(pud, address);
250 pmd_k = pmd_offset(pud_k, address);
251 if (!pmd_present(*pmd_k))
253 if (!pmd_present(*pmd))
254 set_pmd(pmd, *pmd_k);
256 BUG_ON(pmd_page(*pmd) != pmd_page(*pmd_k));
261 * Handle a fault on the vmalloc or module mapping area
263 * This assumes no large pages in there.
265 static inline int vmalloc_fault(unsigned long address)
267 unsigned long pgd_paddr;
271 * Synchronize this task's top level page-table
272 * with the 'reference' page table.
274 * Do _not_ use "current" here. We might be inside
275 * an interrupt in the middle of a task switch..
277 pgd_paddr = read_cr3();
278 pmd_k = vmalloc_sync_one(__va(pgd_paddr), address);
281 pte_k = pte_offset_kernel(pmd_k, address);
282 if (!pte_present(*pte_k))
288 * This routine handles page faults. It determines the address,
289 * and the problem, and then passes it off to one of the appropriate
293 * bit 0 == 0 means no page found, 1 means protection fault
294 * bit 1 == 0 means read, 1 means write
295 * bit 2 == 0 means kernel, 1 means user-mode
296 * bit 3 == 1 means use of reserved bit detected
297 * bit 4 == 1 means fault was an instruction fetch
299 fastcall void __kprobes do_page_fault(struct pt_regs *regs,
300 unsigned long error_code)
302 struct task_struct *tsk;
303 struct mm_struct *mm;
304 struct vm_area_struct * vma;
305 unsigned long address;
308 /* get the address */
309 address = read_cr2();
313 si_code = SEGV_MAPERR;
316 * We fault-in kernel-space virtual memory on-demand. The
317 * 'reference' page table is init_mm.pgd.
319 * NOTE! We MUST NOT take any locks for this case. We may
320 * be in an interrupt or a critical region, and should
321 * only copy the information from the master page table,
324 * This verifies that the fault happens in kernel space
325 * (error_code & 4) == 0, and that the fault was not a
326 * protection error (error_code & 9) == 0.
328 if (unlikely(address >= TASK_SIZE)) {
329 if (!(error_code & 0x0000000d) && vmalloc_fault(address) >= 0)
331 if (notify_page_fault(regs, error_code) == NOTIFY_STOP)
334 * Don't take the mm semaphore here. If we fixup a prefetch
335 * fault we could otherwise deadlock.
337 goto bad_area_nosemaphore;
340 if (notify_page_fault(regs, error_code) == NOTIFY_STOP)
343 /* It's safe to allow irq's after cr2 has been saved and the vmalloc
344 fault has been handled. */
345 if (regs->eflags & (X86_EFLAGS_IF|VM_MASK))
351 * If we're in an interrupt, have no user context or are running in an
352 * atomic region then we must not take the fault..
354 if (in_atomic() || !mm)
355 goto bad_area_nosemaphore;
357 /* When running in the kernel we expect faults to occur only to
358 * addresses in user space. All other faults represent errors in the
359 * kernel and should generate an OOPS. Unfortunatly, in the case of an
360 * erroneous fault occurring in a code path which already holds mmap_sem
361 * we will deadlock attempting to validate the fault against the
362 * address space. Luckily the kernel only validly references user
363 * space from well defined areas of code, which are listed in the
366 * As the vast majority of faults will be valid we will only perform
367 * the source reference check when there is a possibilty of a deadlock.
368 * Attempt to lock the address space, if we cannot we then validate the
369 * source. If this is invalid we can skip the address space check,
370 * thus avoiding the deadlock.
372 if (!down_read_trylock(&mm->mmap_sem)) {
373 if ((error_code & 4) == 0 &&
374 !search_exception_tables(regs->eip))
375 goto bad_area_nosemaphore;
376 down_read(&mm->mmap_sem);
379 vma = find_vma(mm, address);
382 if (vma->vm_start <= address)
384 if (!(vma->vm_flags & VM_GROWSDOWN))
386 if (error_code & 4) {
388 * Accessing the stack below %esp is always a bug.
389 * The large cushion allows instructions like enter
390 * and pusha to work. ("enter $65535,$31" pushes
391 * 32 pointers and then decrements %esp by 65535.)
393 if (address + 65536 + 32 * sizeof(unsigned long) < regs->esp)
396 if (expand_stack(vma, address))
399 * Ok, we have a good vm_area for this memory access, so
403 si_code = SEGV_ACCERR;
405 switch (error_code & 3) {
406 default: /* 3: write, present */
408 case 2: /* write, not present */
409 if (!(vma->vm_flags & VM_WRITE))
413 case 1: /* read, present */
415 case 0: /* read, not present */
416 if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))
422 * If for any reason at all we couldn't handle the fault,
423 * make sure we exit gracefully rather than endlessly redo
426 switch (handle_mm_fault(mm, vma, address, write)) {
433 case VM_FAULT_SIGBUS:
442 * Did it hit the DOS screen memory VA from vm86 mode?
444 if (regs->eflags & VM_MASK) {
445 unsigned long bit = (address - 0xA0000) >> PAGE_SHIFT;
447 tsk->thread.screen_bitmap |= 1 << bit;
449 up_read(&mm->mmap_sem);
453 * Something tried to access memory that isn't in our memory map..
454 * Fix it, but check if it's kernel or user first..
457 up_read(&mm->mmap_sem);
459 bad_area_nosemaphore:
460 /* User mode accesses just cause a SIGSEGV */
461 if (error_code & 4) {
463 * Valid to do another page fault here because this one came
466 if (is_prefetch(regs, address, error_code))
469 tsk->thread.cr2 = address;
470 /* Kernel addresses are always protection faults */
471 tsk->thread.error_code = error_code | (address >= TASK_SIZE);
472 tsk->thread.trap_no = 14;
473 force_sig_info_fault(SIGSEGV, si_code, address, tsk);
477 #ifdef CONFIG_X86_F00F_BUG
479 * Pentium F0 0F C7 C8 bug workaround.
481 if (boot_cpu_data.f00f_bug) {
484 nr = (address - idt_descr.address) >> 3;
487 do_invalid_op(regs, 0);
494 /* Are we prepared to handle this kernel fault? */
495 if (fixup_exception(regs))
499 * Valid to do another page fault here, because if this fault
500 * had been triggered by is_prefetch fixup_exception would have
503 if (is_prefetch(regs, address, error_code))
507 * Oops. The kernel tried to access some bad page. We'll have to
508 * terminate things with extreme prejudice.
513 if (oops_may_print()) {
514 __typeof__(pte_val(__pte(0))) page;
516 #ifdef CONFIG_X86_PAE
517 if (error_code & 16) {
518 pte_t *pte = lookup_address(address);
520 if (pte && pte_present(*pte) && !pte_exec_kernel(*pte))
521 printk(KERN_CRIT "kernel tried to execute "
522 "NX-protected page - exploit attempt? "
523 "(uid: %d)\n", current->uid);
526 if (address < PAGE_SIZE)
527 printk(KERN_ALERT "BUG: unable to handle kernel NULL "
528 "pointer dereference");
530 printk(KERN_ALERT "BUG: unable to handle kernel paging"
532 printk(" at virtual address %08lx\n",address);
533 printk(KERN_ALERT " printing eip:\n");
534 printk("%08lx\n", regs->eip);
537 page = ((__typeof__(page) *) __va(page))[address >> PGDIR_SHIFT];
538 #ifdef CONFIG_X86_PAE
539 printk(KERN_ALERT "*pdpt = %016Lx\n", page);
540 if ((page >> PAGE_SHIFT) < max_low_pfn
541 && page & _PAGE_PRESENT) {
543 page = ((__typeof__(page) *) __va(page))[(address >> PMD_SHIFT)
544 & (PTRS_PER_PMD - 1)];
545 printk(KERN_ALERT "*pde = %016Lx\n", page);
549 printk(KERN_ALERT "*pde = %08lx\n", page);
553 * We must not directly access the pte in the highpte
554 * case if the page table is located in highmem.
555 * And let's rather not kmap-atomic the pte, just in case
556 * it's allocated already.
558 if ((page >> PAGE_SHIFT) < max_low_pfn
559 && (page & _PAGE_PRESENT)) {
561 page = ((__typeof__(page) *) __va(page))[(address >> PAGE_SHIFT)
562 & (PTRS_PER_PTE - 1)];
563 printk(KERN_ALERT "*pte = %0*Lx\n", sizeof(page)*2, (u64)page);
567 tsk->thread.cr2 = address;
568 tsk->thread.trap_no = 14;
569 tsk->thread.error_code = error_code;
570 die("Oops", regs, error_code);
575 * We ran out of memory, or some other thing happened to us that made
576 * us unable to handle the page fault gracefully.
579 up_read(&mm->mmap_sem);
582 down_read(&mm->mmap_sem);
585 printk("VM: killing process %s\n", tsk->comm);
591 up_read(&mm->mmap_sem);
593 /* Kernel mode? Handle exceptions or die */
594 if (!(error_code & 4))
597 /* User space => ok to do another page fault */
598 if (is_prefetch(regs, address, error_code))
601 tsk->thread.cr2 = address;
602 tsk->thread.error_code = error_code;
603 tsk->thread.trap_no = 14;
604 force_sig_info_fault(SIGBUS, BUS_ADRERR, address, tsk);
607 void vmalloc_sync_all(void)
610 * Note that races in the updates of insync and start aren't
611 * problematic: insync can only get set bits added, and updates to
612 * start are only improving performance (without affecting correctness
615 static DECLARE_BITMAP(insync, PTRS_PER_PGD);
616 static unsigned long start = TASK_SIZE;
617 unsigned long address;
619 if (SHARED_KERNEL_PMD)
622 BUILD_BUG_ON(TASK_SIZE & ~PGDIR_MASK);
623 for (address = start; address >= TASK_SIZE; address += PGDIR_SIZE) {
624 if (!test_bit(pgd_index(address), insync)) {
628 spin_lock_irqsave(&pgd_lock, flags);
629 for (page = pgd_list; page; page =
630 (struct page *)page->index)
631 if (!vmalloc_sync_one(page_address(page),
633 BUG_ON(page != pgd_list);
636 spin_unlock_irqrestore(&pgd_lock, flags);
638 set_bit(pgd_index(address), insync);
640 if (address == start && test_bit(pgd_index(address), insync))
641 start = address + PGDIR_SIZE;