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=-6.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 98991C2BA19 for ; Mon, 13 Apr 2020 17:03:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 75C93206E9 for ; Mon, 13 Apr 2020 17:03:28 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=chromium.org header.i=@chromium.org header.b="KYGbZbMQ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732337AbgDMRD1 (ORCPT ); Mon, 13 Apr 2020 13:03:27 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50810 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1732285AbgDMRD0 (ORCPT ); Mon, 13 Apr 2020 13:03:26 -0400 Received: from mail-pg1-x542.google.com (mail-pg1-x542.google.com [IPv6:2607:f8b0:4864:20::542]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DE611C0A3BDC for ; Mon, 13 Apr 2020 10:03:25 -0700 (PDT) Received: by mail-pg1-x542.google.com with SMTP id i3so679006pgk.1 for ; Mon, 13 Apr 2020 10:03:25 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=date:from:to:cc:subject:message-id:mime-version:content-disposition; bh=x3mFfnqIPOP4ncfNP0YhubiozqQilUbpwFxKlgs4RG0=; b=KYGbZbMQIm+29jnu0eBWep2Qpj7EUvj5OxD18/BoGKgdOz1l2iQ4m2+w31Kngvf+IH GcdjexN1wyYzyEXPR/VDhTZqH4PPZ9aO5A0EhO34o1qIGUcUdSrX3tTNDE92i1Q4l3b2 VkukPsfy99O9hYBOYWhWV8FNhH0NyJVlseFP4= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:mime-version :content-disposition; bh=x3mFfnqIPOP4ncfNP0YhubiozqQilUbpwFxKlgs4RG0=; b=IMCpLwH8Zg45iEF32SuRtWLpHySnnvgGEst2Bp6ZxvW7ve1LMMXzguH1PZ+oCiA5o7 a7rJbC8MpYUovRYTYFpJYGDQ9LBlH6kACDigAmOMy9WQQKzGtQJwn8pfntuVrbxNnddq nk8SrI7yuRafI3EOFb1+qU9Z6Uc6EmMW2ry8vlDfyrXQOkV/4OK/VzabyRDXTwUsWV19 2TOb6dOHne9c/sfcqWZl0JMeJqbXZWCL3wOZJPIkw47Y1miiHzQ2UH6dyredXjvEBCve caU4N0PHburEACLq9KqVlK3ykD6gdpkkorLlH6gAOfSphXFbhrdGpCR7IDfYol+Tzq5R u3Gg== X-Gm-Message-State: AGi0PubAVVxmgsRtXzMS2p+ZCnr/udgdI0JL4KHuSk+mSkt82p7n7qL7 SnfsH5nWFO0du+cnIPTfn3AFDw== X-Google-Smtp-Source: APiQypK+y+cSTgULVptvqPAEXP1nOjIP7Z7QJApT2P8bmIcUgUTc1PHRqR/55e1rGZXJ8M5bffdmzg== X-Received: by 2002:a63:dd0c:: with SMTP id t12mr16114334pgg.429.1586797405295; Mon, 13 Apr 2020 10:03:25 -0700 (PDT) Received: from www.outflux.net (smtp.outflux.net. [198.145.64.163]) by smtp.gmail.com with ESMTPSA id d5sm9088113pfa.59.2020.04.13.10.03.23 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 13 Apr 2020 10:03:24 -0700 (PDT) Date: Mon, 13 Apr 2020 10:03:23 -0700 From: Kees Cook To: gregkh@linuxfoundation.org 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: [PATCH][v4.19][v4.14] slub: improve bit diffusion for freelist ptr obfuscation Message-ID: <202004131001.20346EB0E7@keescook> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org 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 -- Kees Cook