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/arch/i386/mm/fault.c

https://bitbucket.org/evzijst/gittest
C | 552 lines | 328 code | 58 blank | 166 comment | 79 complexity | 611fecc6963c4261abf9049c3944a01f MD5 | raw file
  1/*
  2 *  linux/arch/i386/mm/fault.c
  3 *
  4 *  Copyright (C) 1995  Linus Torvalds
  5 */
  6
  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>
 15#include <linux/mm.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/module.h>
 24
 25#include <asm/system.h>
 26#include <asm/uaccess.h>
 27#include <asm/desc.h>
 28#include <asm/kdebug.h>
 29
 30extern void die(const char *,struct pt_regs *,long);
 31
 32/*
 33 * Unlock any spinlocks which will prevent us from getting the
 34 * message out 
 35 */
 36void bust_spinlocks(int yes)
 37{
 38	int loglevel_save = console_loglevel;
 39
 40	if (yes) {
 41		oops_in_progress = 1;
 42		return;
 43	}
 44#ifdef CONFIG_VT
 45	unblank_screen();
 46#endif
 47	oops_in_progress = 0;
 48	/*
 49	 * OK, the message is on the console.  Now we call printk()
 50	 * without oops_in_progress set so that printk will give klogd
 51	 * a poke.  Hold onto your hats...
 52	 */
 53	console_loglevel = 15;		/* NMI oopser may have shut the console up */
 54	printk(" ");
 55	console_loglevel = loglevel_save;
 56}
 57
 58/*
 59 * Return EIP plus the CS segment base.  The segment limit is also
 60 * adjusted, clamped to the kernel/user address space (whichever is
 61 * appropriate), and returned in *eip_limit.
 62 *
 63 * The segment is checked, because it might have been changed by another
 64 * task between the original faulting instruction and here.
 65 *
 66 * If CS is no longer a valid code segment, or if EIP is beyond the
 67 * limit, or if it is a kernel address when CS is not a kernel segment,
 68 * then the returned value will be greater than *eip_limit.
 69 * 
 70 * This is slow, but is very rarely executed.
 71 */
 72static inline unsigned long get_segment_eip(struct pt_regs *regs,
 73					    unsigned long *eip_limit)
 74{
 75	unsigned long eip = regs->eip;
 76	unsigned seg = regs->xcs & 0xffff;
 77	u32 seg_ar, seg_limit, base, *desc;
 78
 79	/* The standard kernel/user address space limit. */
 80	*eip_limit = (seg & 3) ? USER_DS.seg : KERNEL_DS.seg;
 81
 82	/* Unlikely, but must come before segment checks. */
 83	if (unlikely((regs->eflags & VM_MASK) != 0))
 84		return eip + (seg << 4);
 85	
 86	/* By far the most common cases. */
 87	if (likely(seg == __USER_CS || seg == __KERNEL_CS))
 88		return eip;
 89
 90	/* Check the segment exists, is within the current LDT/GDT size,
 91	   that kernel/user (ring 0..3) has the appropriate privilege,
 92	   that it's a code segment, and get the limit. */
 93	__asm__ ("larl %3,%0; lsll %3,%1"
 94		 : "=&r" (seg_ar), "=r" (seg_limit) : "0" (0), "rm" (seg));
 95	if ((~seg_ar & 0x9800) || eip > seg_limit) {
 96		*eip_limit = 0;
 97		return 1;	 /* So that returned eip > *eip_limit. */
 98	}
 99
100	/* Get the GDT/LDT descriptor base. 
101	   When you look for races in this code remember that
102	   LDT and other horrors are only used in user space. */
103	if (seg & (1<<2)) {
104		/* Must lock the LDT while reading it. */
105		down(&current->mm->context.sem);
106		desc = current->mm->context.ldt;
107		desc = (void *)desc + (seg & ~7);
108	} else {
109		/* Must disable preemption while reading the GDT. */
110		desc = (u32 *)&per_cpu(cpu_gdt_table, get_cpu());
111		desc = (void *)desc + (seg & ~7);
112	}
113
114	/* Decode the code segment base from the descriptor */
115	base = get_desc_base((unsigned long *)desc);
116
117	if (seg & (1<<2)) { 
118		up(&current->mm->context.sem);
119	} else
120		put_cpu();
121
122	/* Adjust EIP and segment limit, and clamp at the kernel limit.
123	   It's legitimate for segments to wrap at 0xffffffff. */
124	seg_limit += base;
125	if (seg_limit < *eip_limit && seg_limit >= base)
126		*eip_limit = seg_limit;
127	return eip + base;
128}
129
130/* 
131 * Sometimes AMD Athlon/Opteron CPUs report invalid exceptions on prefetch.
132 * Check that here and ignore it.
133 */
134static int __is_prefetch(struct pt_regs *regs, unsigned long addr)
135{ 
136	unsigned long limit;
137	unsigned long instr = get_segment_eip (regs, &limit);
138	int scan_more = 1;
139	int prefetch = 0; 
140	int i;
141
142	for (i = 0; scan_more && i < 15; i++) { 
143		unsigned char opcode;
144		unsigned char instr_hi;
145		unsigned char instr_lo;
146
147		if (instr > limit)
148			break;
149		if (__get_user(opcode, (unsigned char *) instr))
150			break; 
151
152		instr_hi = opcode & 0xf0; 
153		instr_lo = opcode & 0x0f; 
154		instr++;
155
156		switch (instr_hi) { 
157		case 0x20:
158		case 0x30:
159			/* Values 0x26,0x2E,0x36,0x3E are valid x86 prefixes. */
160			scan_more = ((instr_lo & 7) == 0x6);
161			break;
162			
163		case 0x60:
164			/* 0x64 thru 0x67 are valid prefixes in all modes. */
165			scan_more = (instr_lo & 0xC) == 0x4;
166			break;		
167		case 0xF0:
168			/* 0xF0, 0xF2, and 0xF3 are valid prefixes */
169			scan_more = !instr_lo || (instr_lo>>1) == 1;
170			break;			
171		case 0x00:
172			/* Prefetch instruction is 0x0F0D or 0x0F18 */
173			scan_more = 0;
174			if (instr > limit)
175				break;
176			if (__get_user(opcode, (unsigned char *) instr)) 
177				break;
178			prefetch = (instr_lo == 0xF) &&
179				(opcode == 0x0D || opcode == 0x18);
180			break;			
181		default:
182			scan_more = 0;
183			break;
184		} 
185	}
186	return prefetch;
187}
188
189static inline int is_prefetch(struct pt_regs *regs, unsigned long addr,
190			      unsigned long error_code)
191{
192	if (unlikely(boot_cpu_data.x86_vendor == X86_VENDOR_AMD &&
193		     boot_cpu_data.x86 >= 6)) {
194		/* Catch an obscure case of prefetch inside an NX page. */
195		if (nx_enabled && (error_code & 16))
196			return 0;
197		return __is_prefetch(regs, addr);
198	}
199	return 0;
200} 
201
202fastcall void do_invalid_op(struct pt_regs *, unsigned long);
203
204/*
205 * This routine handles page faults.  It determines the address,
206 * and the problem, and then passes it off to one of the appropriate
207 * routines.
208 *
209 * error_code:
210 *	bit 0 == 0 means no page found, 1 means protection fault
211 *	bit 1 == 0 means read, 1 means write
212 *	bit 2 == 0 means kernel, 1 means user-mode
213 */
214fastcall void do_page_fault(struct pt_regs *regs, unsigned long error_code)
215{
216	struct task_struct *tsk;
217	struct mm_struct *mm;
218	struct vm_area_struct * vma;
219	unsigned long address;
220	unsigned long page;
221	int write;
222	siginfo_t info;
223
224	/* get the address */
225	__asm__("movl %%cr2,%0":"=r" (address));
226
227	if (notify_die(DIE_PAGE_FAULT, "page fault", regs, error_code, 14,
228					SIGSEGV) == NOTIFY_STOP)
229		return;
230	/* It's safe to allow irq's after cr2 has been saved */
231	if (regs->eflags & (X86_EFLAGS_IF|VM_MASK))
232		local_irq_enable();
233
234	tsk = current;
235
236	info.si_code = SEGV_MAPERR;
237
238	/*
239	 * We fault-in kernel-space virtual memory on-demand. The
240	 * 'reference' page table is init_mm.pgd.
241	 *
242	 * NOTE! We MUST NOT take any locks for this case. We may
243	 * be in an interrupt or a critical region, and should
244	 * only copy the information from the master page table,
245	 * nothing more.
246	 *
247	 * This verifies that the fault happens in kernel space
248	 * (error_code & 4) == 0, and that the fault was not a
249	 * protection error (error_code & 1) == 0.
250	 */
251	if (unlikely(address >= TASK_SIZE)) { 
252		if (!(error_code & 5))
253			goto vmalloc_fault;
254		/* 
255		 * Don't take the mm semaphore here. If we fixup a prefetch
256		 * fault we could otherwise deadlock.
257		 */
258		goto bad_area_nosemaphore;
259	} 
260
261	mm = tsk->mm;
262
263	/*
264	 * If we're in an interrupt, have no user context or are running in an
265	 * atomic region then we must not take the fault..
266	 */
267	if (in_atomic() || !mm)
268		goto bad_area_nosemaphore;
269
270	/* When running in the kernel we expect faults to occur only to
271	 * addresses in user space.  All other faults represent errors in the
272	 * kernel and should generate an OOPS.  Unfortunatly, in the case of an
273	 * erroneous fault occuring in a code path which already holds mmap_sem
274	 * we will deadlock attempting to validate the fault against the
275	 * address space.  Luckily the kernel only validly references user
276	 * space from well defined areas of code, which are listed in the
277	 * exceptions table.
278	 *
279	 * As the vast majority of faults will be valid we will only perform
280	 * the source reference check when there is a possibilty of a deadlock.
281	 * Attempt to lock the address space, if we cannot we then validate the
282	 * source.  If this is invalid we can skip the address space check,
283	 * thus avoiding the deadlock.
284	 */
285	if (!down_read_trylock(&mm->mmap_sem)) {
286		if ((error_code & 4) == 0 &&
287		    !search_exception_tables(regs->eip))
288			goto bad_area_nosemaphore;
289		down_read(&mm->mmap_sem);
290	}
291
292	vma = find_vma(mm, address);
293	if (!vma)
294		goto bad_area;
295	if (vma->vm_start <= address)
296		goto good_area;
297	if (!(vma->vm_flags & VM_GROWSDOWN))
298		goto bad_area;
299	if (error_code & 4) {
300		/*
301		 * accessing the stack below %esp is always a bug.
302		 * The "+ 32" is there due to some instructions (like
303		 * pusha) doing post-decrement on the stack and that
304		 * doesn't show up until later..
305		 */
306		if (address + 32 < regs->esp)
307			goto bad_area;
308	}
309	if (expand_stack(vma, address))
310		goto bad_area;
311/*
312 * Ok, we have a good vm_area for this memory access, so
313 * we can handle it..
314 */
315good_area:
316	info.si_code = SEGV_ACCERR;
317	write = 0;
318	switch (error_code & 3) {
319		default:	/* 3: write, present */
320#ifdef TEST_VERIFY_AREA
321			if (regs->cs == KERNEL_CS)
322				printk("WP fault at %08lx\n", regs->eip);
323#endif
324			/* fall through */
325		case 2:		/* write, not present */
326			if (!(vma->vm_flags & VM_WRITE))
327				goto bad_area;
328			write++;
329			break;
330		case 1:		/* read, present */
331			goto bad_area;
332		case 0:		/* read, not present */
333			if (!(vma->vm_flags & (VM_READ | VM_EXEC)))
334				goto bad_area;
335	}
336
337 survive:
338	/*
339	 * If for any reason at all we couldn't handle the fault,
340	 * make sure we exit gracefully rather than endlessly redo
341	 * the fault.
342	 */
343	switch (handle_mm_fault(mm, vma, address, write)) {
344		case VM_FAULT_MINOR:
345			tsk->min_flt++;
346			break;
347		case VM_FAULT_MAJOR:
348			tsk->maj_flt++;
349			break;
350		case VM_FAULT_SIGBUS:
351			goto do_sigbus;
352		case VM_FAULT_OOM:
353			goto out_of_memory;
354		default:
355			BUG();
356	}
357
358	/*
359	 * Did it hit the DOS screen memory VA from vm86 mode?
360	 */
361	if (regs->eflags & VM_MASK) {
362		unsigned long bit = (address - 0xA0000) >> PAGE_SHIFT;
363		if (bit < 32)
364			tsk->thread.screen_bitmap |= 1 << bit;
365	}
366	up_read(&mm->mmap_sem);
367	return;
368
369/*
370 * Something tried to access memory that isn't in our memory map..
371 * Fix it, but check if it's kernel or user first..
372 */
373bad_area:
374	up_read(&mm->mmap_sem);
375
376bad_area_nosemaphore:
377	/* User mode accesses just cause a SIGSEGV */
378	if (error_code & 4) {
379		/* 
380		 * Valid to do another page fault here because this one came 
381		 * from user space.
382		 */
383		if (is_prefetch(regs, address, error_code))
384			return;
385
386		tsk->thread.cr2 = address;
387		/* Kernel addresses are always protection faults */
388		tsk->thread.error_code = error_code | (address >= TASK_SIZE);
389		tsk->thread.trap_no = 14;
390		info.si_signo = SIGSEGV;
391		info.si_errno = 0;
392		/* info.si_code has been set above */
393		info.si_addr = (void __user *)address;
394		force_sig_info(SIGSEGV, &info, tsk);
395		return;
396	}
397
398#ifdef CONFIG_X86_F00F_BUG
399	/*
400	 * Pentium F0 0F C7 C8 bug workaround.
401	 */
402	if (boot_cpu_data.f00f_bug) {
403		unsigned long nr;
404		
405		nr = (address - idt_descr.address) >> 3;
406
407		if (nr == 6) {
408			do_invalid_op(regs, 0);
409			return;
410		}
411	}
412#endif
413
414no_context:
415	/* Are we prepared to handle this kernel fault?  */
416	if (fixup_exception(regs))
417		return;
418
419	/* 
420	 * Valid to do another page fault here, because if this fault
421	 * had been triggered by is_prefetch fixup_exception would have 
422	 * handled it.
423	 */
424 	if (is_prefetch(regs, address, error_code))
425 		return;
426
427/*
428 * Oops. The kernel tried to access some bad page. We'll have to
429 * terminate things with extreme prejudice.
430 */
431
432	bust_spinlocks(1);
433
434#ifdef CONFIG_X86_PAE
435	if (error_code & 16) {
436		pte_t *pte = lookup_address(address);
437
438		if (pte && pte_present(*pte) && !pte_exec_kernel(*pte))
439			printk(KERN_CRIT "kernel tried to execute NX-protected page - exploit attempt? (uid: %d)\n", current->uid);
440	}
441#endif
442	if (address < PAGE_SIZE)
443		printk(KERN_ALERT "Unable to handle kernel NULL pointer dereference");
444	else
445		printk(KERN_ALERT "Unable to handle kernel paging request");
446	printk(" at virtual address %08lx\n",address);
447	printk(KERN_ALERT " printing eip:\n");
448	printk("%08lx\n", regs->eip);
449	asm("movl %%cr3,%0":"=r" (page));
450	page = ((unsigned long *) __va(page))[address >> 22];
451	printk(KERN_ALERT "*pde = %08lx\n", page);
452	/*
453	 * We must not directly access the pte in the highpte
454	 * case, the page table might be allocated in highmem.
455	 * And lets rather not kmap-atomic the pte, just in case
456	 * it's allocated already.
457	 */
458#ifndef CONFIG_HIGHPTE
459	if (page & 1) {
460		page &= PAGE_MASK;
461		address &= 0x003ff000;
462		page = ((unsigned long *) __va(page))[address >> PAGE_SHIFT];
463		printk(KERN_ALERT "*pte = %08lx\n", page);
464	}
465#endif
466	die("Oops", regs, error_code);
467	bust_spinlocks(0);
468	do_exit(SIGKILL);
469
470/*
471 * We ran out of memory, or some other thing happened to us that made
472 * us unable to handle the page fault gracefully.
473 */
474out_of_memory:
475	up_read(&mm->mmap_sem);
476	if (tsk->pid == 1) {
477		yield();
478		down_read(&mm->mmap_sem);
479		goto survive;
480	}
481	printk("VM: killing process %s\n", tsk->comm);
482	if (error_code & 4)
483		do_exit(SIGKILL);
484	goto no_context;
485
486do_sigbus:
487	up_read(&mm->mmap_sem);
488
489	/* Kernel mode? Handle exceptions or die */
490	if (!(error_code & 4))
491		goto no_context;
492
493	/* User space => ok to do another page fault */
494	if (is_prefetch(regs, address, error_code))
495		return;
496
497	tsk->thread.cr2 = address;
498	tsk->thread.error_code = error_code;
499	tsk->thread.trap_no = 14;
500	info.si_signo = SIGBUS;
501	info.si_errno = 0;
502	info.si_code = BUS_ADRERR;
503	info.si_addr = (void __user *)address;
504	force_sig_info(SIGBUS, &info, tsk);
505	return;
506
507vmalloc_fault:
508	{
509		/*
510		 * Synchronize this task's top level page-table
511		 * with the 'reference' page table.
512		 *
513		 * Do _not_ use "tsk" here. We might be inside
514		 * an interrupt in the middle of a task switch..
515		 */
516		int index = pgd_index(address);
517		unsigned long pgd_paddr;
518		pgd_t *pgd, *pgd_k;
519		pud_t *pud, *pud_k;
520		pmd_t *pmd, *pmd_k;
521		pte_t *pte_k;
522
523		asm("movl %%cr3,%0":"=r" (pgd_paddr));
524		pgd = index + (pgd_t *)__va(pgd_paddr);
525		pgd_k = init_mm.pgd + index;
526
527		if (!pgd_present(*pgd_k))
528			goto no_context;
529
530		/*
531		 * set_pgd(pgd, *pgd_k); here would be useless on PAE
532		 * and redundant with the set_pmd() on non-PAE. As would
533		 * set_pud.
534		 */
535
536		pud = pud_offset(pgd, address);
537		pud_k = pud_offset(pgd_k, address);
538		if (!pud_present(*pud_k))
539			goto no_context;
540		
541		pmd = pmd_offset(pud, address);
542		pmd_k = pmd_offset(pud_k, address);
543		if (!pmd_present(*pmd_k))
544			goto no_context;
545		set_pmd(pmd, *pmd_k);
546
547		pte_k = pte_offset_kernel(pmd_k, address);
548		if (!pte_present(*pte_k))
549			goto no_context;
550		return;
551	}
552}