fault.c

来自「linux2.6.16版本」· C语言 代码 · 共 580 行 · 第 1/2 页

		BUG();
	return 0;
}

int page_fault_trace = 0;
int exception_trace = 1;

/*
 * This routine handles page faults.  It determines the address,
 * and the problem, and then passes it off to one of the appropriate
 * routines.
 */
asmlinkage void __kprobes do_page_fault(struct pt_regs *regs,
					unsigned long error_code)
{
	struct task_struct *tsk;
	struct mm_struct *mm;
	struct vm_area_struct * vma;
	unsigned long address;
	const struct exception_table_entry *fixup;
	int write;
	unsigned long flags;
	siginfo_t info;

	/* get the address */
	__asm__("movq %%cr2,%0":"=r" (address));
	if (notify_die(DIE_PAGE_FAULT, "page fault", regs, error_code, 14,
					SIGSEGV) == NOTIFY_STOP)
		return;

	if (likely(regs->eflags & X86_EFLAGS_IF))
		local_irq_enable();

	if (unlikely(page_fault_trace))
		printk("pagefault rip:%lx rsp:%lx cs:%lu ss:%lu address %lx error %lx\n",
		       regs->rip,regs->rsp,regs->cs,regs->ss,address,error_code); 

	tsk = current;
	mm = tsk->mm;
	info.si_code = SEGV_MAPERR;


	/*
	 * We fault-in kernel-space virtual memory on-demand. The
	 * 'reference' page table is init_mm.pgd.
	 *
	 * NOTE! We MUST NOT take any locks for this case. We may
	 * be in an interrupt or a critical region, and should
	 * only copy the information from the master page table,
	 * nothing more.
	 *
	 * This verifies that the fault happens in kernel space
	 * (error_code & 4) == 0, and that the fault was not a
	 * protection error (error_code & 9) == 0.
	 */
	if (unlikely(address >= TASK_SIZE64)) {
		/*
		 * Don't check for the module range here: its PML4
		 * is always initialized because it's shared with the main
		 * kernel text. Only vmalloc may need PML4 syncups.
		 */
		if (!(error_code & (PF_RSVD|PF_USER|PF_PROT)) &&
		      ((address >= VMALLOC_START && address < VMALLOC_END))) {
			if (vmalloc_fault(address) < 0)
				goto bad_area_nosemaphore;
			return;
		}
		/*
		 * Don't take the mm semaphore here. If we fixup a prefetch
		 * fault we could otherwise deadlock.
		 */
		goto bad_area_nosemaphore;
	}

	if (unlikely(error_code & PF_RSVD))
		pgtable_bad(address, regs, error_code);

	/*
	 * If we're in an interrupt or have no user
	 * context, we must not take the fault..
	 */
	if (unlikely(in_atomic() || !mm))
		goto bad_area_nosemaphore;

 again:
	/* When running in the kernel we expect faults to occur only to
	 * addresses in user space.  All other faults represent errors in the
	 * kernel and should generate an OOPS.  Unfortunatly, in the case of an
	 * erroneous fault occuring in a code path which already holds mmap_sem
	 * we will deadlock attempting to validate the fault against the
	 * address space.  Luckily the kernel only validly references user
	 * space from well defined areas of code, which are listed in the
	 * exceptions table.
	 *
	 * As the vast majority of faults will be valid we will only perform
	 * the source reference check when there is a possibilty of a deadlock.
	 * Attempt to lock the address space, if we cannot we then validate the
	 * source.  If this is invalid we can skip the address space check,
	 * thus avoiding the deadlock.
	 */
	if (!down_read_trylock(&mm->mmap_sem)) {
		if ((error_code & PF_USER) == 0 &&
		    !search_exception_tables(regs->rip))
			goto bad_area_nosemaphore;
		down_read(&mm->mmap_sem);
	}

	vma = find_vma(mm, address);
	if (!vma)
		goto bad_area;
	if (likely(vma->vm_start <= address))
		goto good_area;
	if (!(vma->vm_flags & VM_GROWSDOWN))
		goto bad_area;
	if (error_code & 4) {
		// XXX: align red zone size with ABI 
		if (address + 128 < regs->rsp)
			goto bad_area;
	}
	if (expand_stack(vma, address))
		goto bad_area;
/*
 * Ok, we have a good vm_area for this memory access, so
 * we can handle it..
 */
good_area:
	info.si_code = SEGV_ACCERR;
	write = 0;
	switch (error_code & (PF_PROT|PF_WRITE)) {
		default:	/* 3: write, present */
			/* fall through */
		case PF_WRITE:		/* write, not present */
			if (!(vma->vm_flags & VM_WRITE))
				goto bad_area;
			write++;
			break;
		case PF_PROT:		/* read, present */
			goto bad_area;
		case 0:			/* read, not present */
			if (!(vma->vm_flags & (VM_READ | VM_EXEC)))
				goto bad_area;
	}

	/*
	 * If for any reason at all we couldn't handle the fault,
	 * make sure we exit gracefully rather than endlessly redo
	 * the fault.
	 */
	switch (handle_mm_fault(mm, vma, address, write)) {
	case VM_FAULT_MINOR:
		tsk->min_flt++;
		break;
	case VM_FAULT_MAJOR:
		tsk->maj_flt++;
		break;
	case VM_FAULT_SIGBUS:
		goto do_sigbus;
	default:
		goto out_of_memory;
	}

	up_read(&mm->mmap_sem);
	return;

/*
 * Something tried to access memory that isn't in our memory map..
 * Fix it, but check if it's kernel or user first..
 */
bad_area:
	up_read(&mm->mmap_sem);

bad_area_nosemaphore:
	/* User mode accesses just cause a SIGSEGV */
	if (error_code & PF_USER) {
		if (is_prefetch(regs, address, error_code))
			return;

		/* Work around K8 erratum #100 K8 in compat mode
		   occasionally jumps to illegal addresses >4GB.  We
		   catch this here in the page fault handler because
		   these addresses are not reachable. Just detect this
		   case and return.  Any code segment in LDT is
		   compatibility mode. */
		if ((regs->cs == __USER32_CS || (regs->cs & (1<<2))) &&
		    (address >> 32))
			return;

		if (exception_trace && unhandled_signal(tsk, SIGSEGV)) {
			printk(
		       "%s%s[%d]: segfault at %016lx rip %016lx rsp %016lx error %lx\n",
					tsk->pid > 1 ? KERN_INFO : KERN_EMERG,
					tsk->comm, tsk->pid, address, regs->rip,
					regs->rsp, error_code);
		}
       
		tsk->thread.cr2 = address;
		/* Kernel addresses are always protection faults */
		tsk->thread.error_code = error_code | (address >= TASK_SIZE);
		tsk->thread.trap_no = 14;
		info.si_signo = SIGSEGV;
		info.si_errno = 0;
		/* info.si_code has been set above */
		info.si_addr = (void __user *)address;
		force_sig_info(SIGSEGV, &info, tsk);
		return;
	}

no_context:
	
	/* Are we prepared to handle this kernel fault?  */
	fixup = search_exception_tables(regs->rip);
	if (fixup) {
		regs->rip = fixup->fixup;
		return;
	}

	/* 
	 * Hall of shame of CPU/BIOS bugs.
	 */

 	if (is_prefetch(regs, address, error_code))
 		return;

	if (is_errata93(regs, address))
		return; 

/*
 * Oops. The kernel tried to access some bad page. We'll have to
 * terminate things with extreme prejudice.
 */

	flags = oops_begin();

	if (address < PAGE_SIZE)
		printk(KERN_ALERT "Unable to handle kernel NULL pointer dereference");
	else
		printk(KERN_ALERT "Unable to handle kernel paging request");
	printk(" at %016lx RIP: \n" KERN_ALERT,address);
	printk_address(regs->rip);
	printk("\n");
	dump_pagetable(address);
	tsk->thread.cr2 = address;
	tsk->thread.trap_no = 14;
	tsk->thread.error_code = error_code;
	__die("Oops", regs, error_code);
	/* Executive summary in case the body of the oops scrolled away */
	printk(KERN_EMERG "CR2: %016lx\n", address);
	oops_end(flags);
	do_exit(SIGKILL);

/*
 * We ran out of memory, or some other thing happened to us that made
 * us unable to handle the page fault gracefully.
 */
out_of_memory:
	up_read(&mm->mmap_sem);
	if (current->pid == 1) { 
		yield();
		goto again;
	}
	printk("VM: killing process %s\n", tsk->comm);
	if (error_code & 4)
		do_exit(SIGKILL);
	goto no_context;

do_sigbus:
	up_read(&mm->mmap_sem);

	/* Kernel mode? Handle exceptions or die */
	if (!(error_code & PF_USER))
		goto no_context;

	tsk->thread.cr2 = address;
	tsk->thread.error_code = error_code;
	tsk->thread.trap_no = 14;
	info.si_signo = SIGBUS;
	info.si_errno = 0;
	info.si_code = BUS_ADRERR;
	info.si_addr = (void __user *)address;
	force_sig_info(SIGBUS, &info, tsk);
	return;
}

static int __init enable_pagefaulttrace(char *str)
{
	page_fault_trace = 1;
	return 0;
}
__setup("pagefaulttrace", enable_pagefaulttrace);