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,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 6BF33C55189 for ; Wed, 22 Apr 2020 10:53:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 48EFF2073A for ; Wed, 22 Apr 2020 10:53:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1587552789; bh=SNp5Cfh7breCq57LI8vZEAzmEX05Q+IiYdGzMs2VsjE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=T4AxbYFeK6GcM2Md4aAk+6NRJrRl9XF0B1zIw6ePDho5THfcW6ncyGjuk2EWoZu/a stZV3zWzeqOMbqWmSDqiYWIfT1BGEbjus2m57T/ackZfN4N6qtcOfjL/1t57faqkXS uHzQfxcMK26dSkDvlgOLzvvhzndPvSA+xZFN0fEY= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732246AbgDVKxH (ORCPT ); Wed, 22 Apr 2020 06:53:07 -0400 Received: from mail.kernel.org ([198.145.29.99]:35818 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728842AbgDVKJQ (ORCPT ); Wed, 22 Apr 2020 06:09:16 -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 E12CE2166E; Wed, 22 Apr 2020 10:09:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1587550155; bh=SNp5Cfh7breCq57LI8vZEAzmEX05Q+IiYdGzMs2VsjE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ozs3bRKde9n5OJRtvrzGbgY9kgLkYcF8QUYEmGSdh7g45LTxcE0GOdI4l/OZb24I6 vM1umhgW7PzAZbYWdqBUeiM2G0owM4KeFnSBEMdf9PUs0g0pW3dHNP45NzSIt3Txww sjOrhXC1T/5/EQcXP3mAKxgrxrtDfO2JwETWdMcE= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Silvio Cesare , Kees Cook , Andrew Morton , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Linus Torvalds Subject: [PATCH 4.14 031/199] slub: improve bit diffusion for freelist ptr obfuscation Date: Wed, 22 Apr 2020 11:55:57 +0200 Message-Id: <20200422095101.178110516@linuxfoundation.org> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20200422095057.806111593@linuxfoundation.org> References: <20200422095057.806111593@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Kees Cook 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 Signed-off-by: Greg Kroah-Hartman --- mm/slub.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/mm/slub.c +++ b/mm/slub.c @@ -248,7 +248,7 @@ static inline void *freelist_ptr(const s 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