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Message-ID: <cdd42a1b-ce15-df8c-6bd1-b0943275986f@linux.com> Date: Tue, 25 Jul 2017 00:17:11 +0300 From: Alexander Popov <alex.popov@...ux.com> To: Kees Cook <keescook@...omium.org> Cc: Andrew Morton <akpm@...ux-foundation.org>, Christoph Lameter <cl@...ux.com>, Pekka Enberg <penberg@...nel.org>, David Rientjes <rientjes@...gle.com>, Joonsoo Kim <iamjoonsoo.kim@....com>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, Ingo Molnar <mingo@...nel.org>, Josh Triplett <josh@...htriplett.org>, Andy Lutomirski <luto@...nel.org>, Nicolas Pitre <nicolas.pitre@...aro.org>, Tejun Heo <tj@...nel.org>, Daniel Mack <daniel@...que.org>, Sebastian Andrzej Siewior <bigeasy@...utronix.de>, Sergey Senozhatsky <sergey.senozhatsky@...il.com>, Helge Deller <deller@....de>, Rik van Riel <riel@...hat.com>, linux-mm@...ck.org, Tycho Andersen <tycho@...ker.com>, linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com Subject: Re: [v3] mm: Add SLUB free list pointer obfuscation >From 86f4f1f6deb76849e00c761fa30eeb479f789c35 Mon Sep 17 00:00:00 2001 From: Alexander Popov <alex.popov@...ux.com> Date: Mon, 24 Jul 2017 23:16:28 +0300 Subject: [PATCH 2/2] mm/slub.c: add a naive detection of double free or corruption On 06.07.2017 03:27, Kees Cook wrote: > This SLUB free list pointer obfuscation code is modified from Brad > Spengler/PaX Team's code in the last public patch of grsecurity/PaX based > on my understanding of the code. Changes or omissions from the original > code are mine and don't reflect the original grsecurity/PaX code. > > This adds a per-cache random value to SLUB caches that is XORed with > their freelist pointer address and value. This adds nearly zero overhead > and frustrates the very common heap overflow exploitation method of > overwriting freelist pointers. A recent example of the attack is written > up here: http://cyseclabs.com/blog/cve-2016-6187-heap-off-by-one-exploit > > This is based on patches by Daniel Micay, and refactored to minimize the > use of #ifdef. Hello! This is an addition to the SLAB_FREELIST_HARDENED feature. I'm sending it according the discussion here: http://www.openwall.com/lists/kernel-hardening/2017/07/17/9 -- >8 -- Add an assertion similar to "fasttop" check in GNU C Library allocator as a part of SLAB_FREELIST_HARDENED feature. An object added to a singly linked freelist should not point to itself. That helps to detect some double free errors (e.g. CVE-2017-2636) without slub_debug and KASAN. Signed-off-by: Alexander Popov <alex.popov@...ux.com> --- mm/slub.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/mm/slub.c b/mm/slub.c index c92d636..f39d06e 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -290,6 +290,10 @@ static inline void set_freepointer(struct kmem_cache *s, void *object, void *fp) { unsigned long freeptr_addr = (unsigned long)object + s->offset; +#ifdef CONFIG_SLAB_FREELIST_HARDENED + BUG_ON(object == fp); /* naive detection of double free or corruption */ +#endif + *(void **)freeptr_addr = freelist_ptr(s, fp, freeptr_addr); } -- 2.7.4
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