asmlinkage void __kprobes do_page_fault()

in mm/fault.c [389:500]

• 67 lines of code
• 18 McCabe index (conditional complexity)

asmlinkage void __kprobes do_page_fault(struct pt_regs *regs,
					unsigned long error_code,
					unsigned long address)
{
	unsigned long vec;
	struct task_struct *tsk;
	struct mm_struct *mm;
	struct vm_area_struct * vma;
	vm_fault_t fault;
	unsigned int flags = FAULT_FLAG_DEFAULT;

	tsk = current;
	mm = tsk->mm;
	vec = lookup_exception_vector();

	/*
	 * 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.
	 */
	if (unlikely(fault_in_kernel_space(address))) {
		if (vmalloc_fault(address) >= 0)
			return;
		if (kprobe_page_fault(regs, vec))
			return;

		bad_area_nosemaphore(regs, error_code, address);
		return;
	}

	if (unlikely(kprobe_page_fault(regs, vec)))
		return;

	/* Only enable interrupts if they were on before the fault */
	if ((regs->sr & SR_IMASK) != SR_IMASK)
		local_irq_enable();

	perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address);

	/*
	 * If we're in an interrupt, have no user context or are running
	 * with pagefaults disabled then we must not take the fault:
	 */
	if (unlikely(faulthandler_disabled() || !mm)) {
		bad_area_nosemaphore(regs, error_code, address);
		return;
	}

retry:
	mmap_read_lock(mm);

	vma = find_vma(mm, address);
	if (unlikely(!vma)) {
		bad_area(regs, error_code, address);
		return;
	}
	if (likely(vma->vm_start <= address))
		goto good_area;
	if (unlikely(!(vma->vm_flags & VM_GROWSDOWN))) {
		bad_area(regs, error_code, address);
		return;
	}
	if (unlikely(expand_stack(vma, address))) {
		bad_area(regs, error_code, address);
		return;
	}

	/*
	 * Ok, we have a good vm_area for this memory access, so
	 * we can handle it..
	 */
good_area:
	if (unlikely(access_error(error_code, vma))) {
		bad_area_access_error(regs, error_code, address);
		return;
	}

	set_thread_fault_code(error_code);

	if (user_mode(regs))
		flags |= FAULT_FLAG_USER;
	if (error_code & FAULT_CODE_WRITE)
		flags |= FAULT_FLAG_WRITE;

	/*
	 * If for any reason at all we couldn't handle the fault,
	 * make sure we exit gracefully rather than endlessly redo
	 * the fault.
	 */
	fault = handle_mm_fault(vma, address, flags, regs);

	if (unlikely(fault & (VM_FAULT_RETRY | VM_FAULT_ERROR)))
		if (mm_fault_error(regs, error_code, address, fault))
			return;

	if (fault & VM_FAULT_RETRY) {
		flags |= FAULT_FLAG_TRIED;

		/*
		 * No need to mmap_read_unlock(mm) as we would
		 * have already released it in __lock_page_or_retry
		 * in mm/filemap.c.
		 */
		goto retry;
	}

	mmap_read_unlock(mm);
}