From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Hildenbrand Subject: Re: [PATCH RFC 1/2] s390x: mm: allow mixed page table types (2k and 4k) Date: Thu, 1 Jun 2017 14:44:52 +0200 Message-ID: References: <20170529163202.13077-1-david@redhat.com> <20170529163202.13077-2-david@redhat.com> <2a3d5383-cab4-6882-4050-c69404bda347@de.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Cc: linux-kernel@vger.kernel.org, Martin Schwidefsky , Heiko Carstens , Thomas Huth To: Christian Borntraeger , kvm@vger.kernel.org Return-path: Received: from mx1.redhat.com ([209.132.183.28]:57410 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750952AbdFAMo4 (ORCPT ); Thu, 1 Jun 2017 08:44:56 -0400 In-Reply-To: <2a3d5383-cab4-6882-4050-c69404bda347@de.ibm.com> Content-Language: en-US Sender: kvm-owner@vger.kernel.org List-ID: On 01.06.2017 13:39, Christian Borntraeger wrote: > On 05/29/2017 06:32 PM, David Hildenbrand wrote: > >> new = old = pgste_get_lock(ptep); >> pgste_val(new) &= ~(PGSTE_GR_BIT | PGSTE_GC_BIT | >> @@ -748,6 +764,11 @@ int reset_guest_reference_bit(struct mm_struct *mm, unsigned long addr) >> ptep = get_locked_pte(mm, addr, &ptl); >> if (unlikely(!ptep)) >> return -EFAULT; >> + if (!pgtable_has_pgste(mm, __pa(ptep))) { >> + pte_unmap_unlock(ptep, ptl); >> + WARN_ONCE(true, "Guest address on page table without pgste"); > > All these WARN_ONCE. Is there a way how a malicious user can trigger this or is this checked > everywhere and triggered would be indeed a bug? Very good question I added these for testing purposes, but leaving the WARN_ONCE here is wrong. The user can create memslots with "wrong" memory. Whenever such memory is linked into the gmap, we return -EFAULT. So we will only have page table with "pgstes" in our GMAP at any time. However, all these functions here go via memslots: test_and_clear_guest_dirty -> via memslot from memslot list set_guest_storage_key reset_guest_reference_bit get_guest_storage_key pgste_perform_essa set_pgste_bits get_pgste -> come via gfn_to_hva() -> gfn_to_memslot() -> search_memslots -> via memslot list And then use the calculated host address to just walk the ordinary process page tables (get_locked_pte) and not the pgste. So simply returning -EFAULT here is the right thing to, dropping the WARN_ONCE. Thanks! -- Thanks, David