netdev - Re: [PATCH 5/7] slub: support for bulk free with SLUB freelists

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Mon, 28 Sep 2015 11:30:00 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Jesper Dangaard Brouer <brouer@...hat.com>
cc:	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	netdev@...r.kernel.org,
	Alexander Duyck <alexander.duyck@...il.com>,
	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH 5/7] slub: support for bulk free with SLUB freelists

On Mon, 28 Sep 2015, Jesper Dangaard Brouer wrote:

> Not knowing SLUB as well as you, it took me several hours to realize
> init_object() didn't overwrite the freepointer in the object.  Thus, I
> think these comments make the reader aware of not-so-obvious
> side-effects of SLAB_POISON and SLAB_RED_ZONE.

>From the source:

/*
 * Object layout:
 *
 * object address
 *      Bytes of the object to be managed.
 *      If the freepointer may overlay the object then the free
 *      pointer is the first word of the object.
 *
 *      Poisoning uses 0x6b (POISON_FREE) and the last byte is
 *      0xa5 (POISON_END)
 *
 * object + s->object_size
 *      Padding to reach word boundary. This is also used for Redzoning.
 *      Padding is extended by another word if Redzoning is enabled and
 *      object_size == inuse.
 *
 *      We fill with 0xbb (RED_INACTIVE) for inactive objects and with
 *      0xcc (RED_ACTIVE) for objects in use.
 *
 * object + s->inuse
 *      Meta data starts here.
 *
 *      A. Free pointer (if we cannot overwrite object on free)
 *      B. Tracking data for SLAB_STORE_USER
 *      C. Padding to reach required alignment boundary or at mininum
 *              one word if debugging is on to be able to detect writes
 *              before the word boundary.
 *
 *      Padding is done using 0x5a (POISON_INUSE)
 *
 * object + s->size
 *      Nothing is used beyond s->size.
 *
 * If slabcaches are merged then the object_size and inuse boundaries are
mostly
 * ignored. And therefore no slab options that rely on these boundaries
 * may be used with merged slabcaches.
 */

--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html