From mboxrd@z Thu Jan 1 00:00:00 1970 Reply-To: kernel-hardening@lists.openwall.com References: <1450755641-7856-1-git-send-email-laura@labbott.name> <5679ACE9.70701@labbott.name> <568C8741.4040709@labbott.name> <568F0F75.4090101@labbott.name> From: Laura Abbott Message-ID: <56971AE1.1020706@labbott.name> Date: Wed, 13 Jan 2016 19:49:53 -0800 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Subject: [kernel-hardening] Re: [RFC][PATCH 0/7] Sanitization of slabs based on grsecurity/PaX To: Christoph Lameter Cc: Kees Cook , Pekka Enberg , David Rientjes , Joonsoo Kim , Andrew Morton , Linux-MM , LKML , "kernel-hardening@lists.openwall.com" List-ID: On 1/8/16 6:07 AM, Christoph Lameter wrote: > On Thu, 7 Jan 2016, Laura Abbott wrote: > >> The slub_debug=P not only poisons it enables other consistency checks on the >> slab as well, assuming my understanding of what check_object does is correct. >> My hope was to have the poison part only and none of the consistency checks in >> an attempt to mitigate performance issues. I misunderstood when the checks >> actually run and how SLUB_DEBUG was used. > > Ok I see that there pointer check is done without checking the > corresponding debug flag. Patch attached thar fixes it. > >> Another option would be to have a flag like SLAB_NO_SANITY_CHECK. >> sanitization enablement would just be that and SLAB_POISON >> in the debug options. The disadvantage to this approach would be losing >> the sanitization for ->ctor caches (the grsecurity version works around this >> by re-initializing with ->ctor, I haven't heard any feedback if this actually >> acceptable) and not having some of the fast paths enabled >> (assuming I'm understanding the code path correctly.) which would also >> be a performance penalty > > I think we simply need to fix the missing check there. There is already a > flag SLAB_DEBUG_FREE for the pointer checks. > > The patch improves performance but the overall performance of these full sanitization patches is still significantly better than slub_debug=P. I'll put some effort into seeing if I can figure out where the slow down is coming from. Thanks, Laura > > Subject: slub: Only perform pointer checks in check_object when SLAB_DEBUG_FREE is set > > Seems that check_object() always checks for pointer issues currently. > > Signed-off-by: Christoph Lameter > > Index: linux/mm/slub.c > =================================================================== > --- linux.orig/mm/slub.c > +++ linux/mm/slub.c > @@ -848,6 +848,9 @@ static int check_object(struct kmem_cach > */ > return 1; > > + if (!(s->flags & SLAB_DEBUG_FREE)) > + return 1; > + > /* Check free pointer validity */ > if (!check_valid_pointer(s, page, get_freepointer(s, p))) { > object_err(s, page, p, "Freepointer corrupt"); >