From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6BA30C2BA19 for ; Tue, 14 Apr 2020 08:09:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 434042072D for ; Tue, 14 Apr 2020 08:09:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1586851798; bh=rd4UzSC7fqh1hR2kFovsbwQ9fnm18W2TFfNbB10bdhk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=dFr0nKyXXZ1eR/1626FFAWjWjkiKgldyA1SFYuKcqMWPNc+c98YwEDhCVQ6ugLxYM bfx6HSI9kccgxMj3fAF2FLyMPPwjLoaknS/JHD428jp/wirWKL/UZSB+tqlz4/xfUp m/X4naW2TYlnJrXClKhzP4gP+wCXfBPLRz81yESA= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2407010AbgDNIJz (ORCPT ); Tue, 14 Apr 2020 04:09:55 -0400 Received: from mail.kernel.org ([198.145.29.99]:51990 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2406988AbgDNIJL (ORCPT ); Tue, 14 Apr 2020 04:09:11 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 4AC0F2072D; Tue, 14 Apr 2020 08:09:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1586851750; bh=rd4UzSC7fqh1hR2kFovsbwQ9fnm18W2TFfNbB10bdhk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=O/ohGZdiAxJY+0+MlKK+EBO9YcS4C6z8tdbRz1b+aM9P9k1ADBlFElr7s+ZzQ39ys ILLjEYLe0jAgAt5IaXAZDCM7SXIQZH9f3eCGXoLvYQVDS+0JzTb0xG1eYKvgmSwXGj /5LrmqW1u6gYBL5acYu4Ft98UHJi+LOU/aiqFYz0= Date: Tue, 14 Apr 2020 10:09:08 +0200 From: Greg KH To: Kees Cook Cc: akpm@linux-foundation.org, cl@linux.com, iamjoonsoo.kim@lge.com, penberg@kernel.org, rientjes@google.com, silvio.cesare@gmail.com, stable@vger.kernel.org Subject: Re: [PATCH][v4.19][v4.14] slub: improve bit diffusion for freelist ptr obfuscation Message-ID: <20200414080908.GA4147420@kroah.com> References: <202004131001.20346EB0E7@keescook> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <202004131001.20346EB0E7@keescook> Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Mon, Apr 13, 2020 at 10:03:23AM -0700, Kees Cook wrote: > commit 1ad53d9fa3f6168ebcf48a50e08b170432da2257 upstream. > > Under CONFIG_SLAB_FREELIST_HARDENED=y, the obfuscation was relatively weak > in that the ptr and ptr address were usually so close that the first XOR > would result in an almost entirely 0-byte value[1], leaving most of the > "secret" number ultimately being stored after the third XOR. A single > blind memory content exposure of the freelist was generally sufficient to > learn the secret. > > Add a swab() call to mix bits a little more. This is a cheap way (1 > cycle) to make attacks need more than a single exposure to learn the > secret (or to know _where_ the exposure is in memory). > > kmalloc-32 freelist walk, before: > > ptr ptr_addr stored value secret > ffff90c22e019020@ffff90c22e019000 is 86528eb656b3b5bd (86528eb656b3b59d) > ffff90c22e019040@ffff90c22e019020 is 86528eb656b3b5fd (86528eb656b3b59d) > ffff90c22e019060@ffff90c22e019040 is 86528eb656b3b5bd (86528eb656b3b59d) > ffff90c22e019080@ffff90c22e019060 is 86528eb656b3b57d (86528eb656b3b59d) > ffff90c22e0190a0@ffff90c22e019080 is 86528eb656b3b5bd (86528eb656b3b59d) > ... > > after: > > ptr ptr_addr stored value secret > ffff9eed6e019020@ffff9eed6e019000 is 793d1135d52cda42 (86528eb656b3b59d) > ffff9eed6e019040@ffff9eed6e019020 is 593d1135d52cda22 (86528eb656b3b59d) > ffff9eed6e019060@ffff9eed6e019040 is 393d1135d52cda02 (86528eb656b3b59d) > ffff9eed6e019080@ffff9eed6e019060 is 193d1135d52cdae2 (86528eb656b3b59d) > ffff9eed6e0190a0@ffff9eed6e019080 is f93d1135d52cdac2 (86528eb656b3b59d) > > [1] https://blog.infosectcbr.com.au/2020/03/weaknesses-in-linux-kernel-heap.html > > Fixes: 2482ddec670f ("mm: add SLUB free list pointer obfuscation") > Reported-by: Silvio Cesare > Signed-off-by: Kees Cook > Signed-off-by: Andrew Morton > Cc: Christoph Lameter > Cc: Pekka Enberg > Cc: David Rientjes > Cc: Joonsoo Kim > Cc: > Link: http://lkml.kernel.org/r/202003051623.AF4F8CB@keescook > Signed-off-by: Linus Torvalds > [kees: Backport to v4.19 which doesn't call kasan_reset_untag()] > Signed-off-by: Kees Cook > --- > This requires that commit d5767057c9a76a29f073dad66b7fa12a90e8c748 is > also cherry-picked into -stable. > --- > mm/slub.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/slub.c b/mm/slub.c > index 9b7b989273d4..d8116a43a287 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -249,7 +249,7 @@ static inline void *freelist_ptr(const struct kmem_cache *s, void *ptr, > unsigned long ptr_addr) > { > #ifdef CONFIG_SLAB_FREELIST_HARDENED > - return (void *)((unsigned long)ptr ^ s->random ^ ptr_addr); > + return (void *)((unsigned long)ptr ^ s->random ^ swab(ptr_addr)); > #else > return ptr; > #endif > -- > 2.20.1 > > > -- Now queued up, thanks. greg k-h