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=-1.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,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 C662CC43387 for ; Thu, 17 Jan 2019 22:29:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 895FA20851 for ; Thu, 17 Jan 2019 22:29:41 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="JHdAQc93" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727434AbfAQW3l (ORCPT ); Thu, 17 Jan 2019 17:29:41 -0500 Received: from mail-pl1-f196.google.com ([209.85.214.196]:42146 "EHLO mail-pl1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727346AbfAQW3l (ORCPT ); Thu, 17 Jan 2019 17:29:41 -0500 Received: by mail-pl1-f196.google.com with SMTP id y1so5378427plp.9; Thu, 17 Jan 2019 14:29:40 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:subject:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to; bh=8fuEgNkk8T1WJ/UHEMWutP1XUoE1BoPWupQNbWBmkdk=; b=JHdAQc93+ID0LwKz7qTSCs/xLJtLJ6/H4Jb1895LciW26CEbMyIEXMoDqApzwUHSG+ nY7n0XiZvB/uNijfmCxk7WcqkMygdoMZTg2TzzIAM5GmPUaR3UutTUaeX4UCdgjaDVyi ugYVoMCcyNLEtDHdKO6HpbovnHuYeGo39FwDfmII3VYAMNo7jNaks8U6gutXTz245Ash R7iUKsrrv5RSrW0KlAM5rYDk6TxgAiB5m6V41WkEARlA71sRfVsws1mLt5v0r1cIDORw 4B23uNB7tVKKUj+hOV/6gc2ncdpjITiQ+enlleUuuVlD9rYemJU2JOYjm1cLALKQYKTs LnlQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:subject:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to; bh=8fuEgNkk8T1WJ/UHEMWutP1XUoE1BoPWupQNbWBmkdk=; b=i33yYF08ohiiIVz5OONhxtg0CdUxdJsQo1F5+xENUqHIIHX5fuHsG8Bzhp6weReU3z 202NHsohwq3z+kvyDK1ql4giLlFpoesJBt8ftz56bkmVROGWvOYk2pAfjEWMzTrftnyb vezO2tdjosVLyyJpnPHquRW5SwYMkJAeU1N0EuaZJs+Q5f0U3eRonAPI9ADLym1nCGRF VGx71vcd5aUZb2AMxBE0v/ge6VA3jOshv+jK4TSym9SS26nHMRAJ05xByz6FbdmD3IMb Ntrfm6cO+TSmgtiQxx3TFu+D78KyR3myDT2Kgbg5VQRWThNPYL9pG5WneWoY7wOmOAJj Kfcg== X-Gm-Message-State: AJcUukeK9bokjxKReNjh/KHwqG8y1lubMO8XkCnEOgHGYD8zGJOqLRqv Fk006stFU2GSGBcCJexd6Bc= X-Google-Smtp-Source: ALg8bN4Y+37YAJRaLEFv+LRu5H/rIjwl1kaTrNnvfK/eu2C6XAoCkkj+RSfVNd9hxKUWd+tSix/C2w== X-Received: by 2002:a17:902:2ac3:: with SMTP id j61mr16746843plb.185.1547764179149; Thu, 17 Jan 2019 14:29:39 -0800 (PST) Received: from [10.33.115.182] ([66.170.99.1]) by smtp.gmail.com with ESMTPSA id n21sm4171802pfg.84.2019.01.17.14.29.37 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 17 Jan 2019 14:29:38 -0800 (PST) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 12.2 \(3445.102.3\)) Subject: Re: [PATCH 06/17] x86/alternative: use temporary mm for text poking From: Nadav Amit In-Reply-To: Date: Thu, 17 Jan 2019 14:29:36 -0800 Cc: Rick Edgecombe , Ingo Molnar , LKML , X86 ML , "H. Peter Anvin" , Thomas Gleixner , Borislav Petkov , Dave Hansen , Peter Zijlstra , Damian Tometzki , linux-integrity , LSM List , Andrew Morton , Kernel Hardening , Linux-MM , Will Deacon , Ard Biesheuvel , Kristen Carlson Accardi , "Dock, Deneen T" , Kees Cook , Dave Hansen , Masami Hiramatsu Content-Transfer-Encoding: quoted-printable Message-Id: <32219CAE-7D49-4848-9497-A17E0D809B3E@gmail.com> References: <20190117003259.23141-1-rick.p.edgecombe@intel.com> <20190117003259.23141-7-rick.p.edgecombe@intel.com> To: Andy Lutomirski X-Mailer: Apple Mail (2.3445.102.3) Sender: linux-integrity-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-integrity@vger.kernel.org > On Jan 17, 2019, at 1:43 PM, Nadav Amit wrote: >=20 >> On Jan 17, 2019, at 12:47 PM, Andy Lutomirski = wrote: >>=20 >> On Thu, Jan 17, 2019 at 12:27 PM Andy Lutomirski = wrote: >>> On Wed, Jan 16, 2019 at 4:33 PM Rick Edgecombe >>> wrote: >>>> From: Nadav Amit >>>>=20 >>>> text_poke() can potentially compromise the security as it sets = temporary >>>> PTEs in the fixmap. These PTEs might be used to rewrite the kernel = code >>>> from other cores accidentally or maliciously, if an attacker gains = the >>>> ability to write onto kernel memory. >>>=20 >>> i think this may be sufficient, but barely. >>>=20 >>>> + pte_clear(poking_mm, poking_addr, ptep); >>>> + >>>> + /* >>>> + * __flush_tlb_one_user() performs a redundant TLB flush = when PTI is on, >>>> + * as it also flushes the corresponding "user" address = spaces, which >>>> + * does not exist. >>>> + * >>>> + * Poking, however, is already very inefficient since it = does not try to >>>> + * batch updates, so we ignore this problem for the time = being. >>>> + * >>>> + * Since the PTEs do not exist in other kernel = address-spaces, we do >>>> + * not use __flush_tlb_one_kernel(), which when PTI is on = would cause >>>> + * more unwarranted TLB flushes. >>>> + * >>>> + * There is a slight anomaly here: the PTE is a = supervisor-only and >>>> + * (potentially) global and we use __flush_tlb_one_user() = but this >>>> + * should be fine. >>>> + */ >>>> + __flush_tlb_one_user(poking_addr); >>>> + if (cross_page_boundary) { >>>> + pte_clear(poking_mm, poking_addr + PAGE_SIZE, ptep = + 1); >>>> + __flush_tlb_one_user(poking_addr + PAGE_SIZE); >>>> + } >>>=20 >>> In principle, another CPU could still have the old translation. = Your >>> mutex probably makes this impossible, but it makes me nervous. >>> Ideally you'd use flush_tlb_mm_range(), but I guess you can't do = that >>> with IRQs off. Hmm. I think you should add an inc_mm_tlb_gen() = here. >>> Arguably, if you did that, you could omit the flushes, but maybe >>> that's silly. >>>=20 >>> If we start getting new users of use_temporary_mm(), we should give >>> some serious thought to the SMP semantics. >>>=20 >>> Also, you're using PAGE_KERNEL. Please tell me that the global bit >>> isn't set in there. >>=20 >> Much better solution: do unuse_temporary_mm() and *then* >> flush_tlb_mm_range(). This is entirely non-sketchy and should be = just >> about optimal, too. >=20 > This solution sounds nice and clean. The fact the global-bit was set = didn=E2=80=99t > matter before (since __flush_tlb_one_user would get rid of it no = matter > what), but would matter now, so I=E2=80=99ll change it too. Err.. so actually text_poke() might be called with disabled IRQs (by = kgdb). flush_tlb_mm_range() should still work fine even with disabled IRQs = since no core would use poking_mm at this point. I can add a comment to flush_tlb_mm_range(), but all in all it is actually not very pretty.