From patchwork Tue Jun 18 09:47:13 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Arnd Bergmann X-Patchwork-Id: 11001335 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 443286C5 for ; Tue, 18 Jun 2019 09:47:52 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 321BE288A0 for ; Tue, 18 Jun 2019 09:47:52 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 2570128A26; Tue, 18 Jun 2019 09:47:52 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=2.0 tests=BAYES_00,RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id A2253288A0 for ; Tue, 18 Jun 2019 09:47:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729325AbfFRJrv (ORCPT ); Tue, 18 Jun 2019 05:47:51 -0400 Received: from mout.kundenserver.de ([212.227.126.135]:34129 "EHLO mout.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729113AbfFRJrv (ORCPT ); Tue, 18 Jun 2019 05:47:51 -0400 Received: from threadripper.lan ([149.172.19.189]) by mrelayeu.kundenserver.de (mreue011 [212.227.15.129]) with ESMTPA (Nemesis) id 1MvazO-1iVYJd1CNC-00sfaV; Tue, 18 Jun 2019 11:47:35 +0200 From: Arnd Bergmann To: Kees Cook Cc: Andrey Ryabinin , Alexander Potapenko , Dmitry Vyukov , kasan-dev@googlegroups.com, Alexander Popov , Arnd Bergmann , Ard Biesheuvel , James Morris , "Serge E. Hallyn" , Masahiro Yamada , linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] structleak: disable BYREF_ALL in combination with KASAN_STACK Date: Tue, 18 Jun 2019 11:47:13 +0200 Message-Id: <20190618094731.3677294-1-arnd@arndb.de> X-Mailer: git-send-email 2.20.0 MIME-Version: 1.0 X-Provags-ID: V03:K1:peaZfmlkgECAGz9riypsIjV4ic/JP7FXX72Osd9/Mq+xyvBdsCS QBR6nMT1ohGbRCit/XsDuRwE9m62UtxQb8P0hVuaqx/phcvYootks744nTD7mnuahBKuDRd nlFPtsir0LRT4s7DskzMEeyJxjArgwMxWUyRsgRPXJRek+d2c5rWM1qoz78m39pnj+BpCM6 +yskDQBig2i7wcwA6yOBg== X-UI-Out-Filterresults: notjunk:1;V03:K0:mt0pBl9Irk8=:bYl9+u5Pgnw4rI3NpDMYHT i53Q/NuCg7Ndw7pN9sP3ZPFD5oeob8tWcVRjg+sNsM7RJ5b9tSeQixOT4O5MYt/D3k3OxKKFR CsMMgCj6iveTYDoMsmni/ibnZEv82LWgLycDF/VppP+KZDUEtaLbGUL1zO2KSr9QbWPN8aFc+ lRLUI9FmI141/v+985lLmm3oOfEgVbmyl/+U0etuXukfVHrJ2YAISq96Nax93pejvbGmN/R6E gMxHU1tztk8Bz8A9z+LMq1SuiZ+fCaWyUv7cz//JBCwF0A7R3amDs1oofWWmGIhZ2woS7knzk s2PUnpiym4S4dWsQXv4Nm1q7zRzXDtGcHuwqhdfls7EcfffVnoBSejJk958zKoe9Usl3xWCK1 /VC9gy9fE8Lu+nU5LxlteBelIwC5h1mcq3slnIylUnNW+FfZ01OCbNerLhuiMZrsRfuOG3j9R oySFqVKdqDDE77EVHlxUtZAKaY7H5C/Y74EzN7nfv/c3E2mHSdN7IZHpEbZztPDEqa72lY1Ko 8jW/nWO+ZzsizP7A//X5ToG2yMsjuCd3Bx4XEbTmCGpgAREI2JI637qz53t4QPAkoNsjSDSKs GVIY8zbeF2JUvFkqt5Xx1omS8tFFZKlzcdalZOoMjwUo0ntoXLnDbOtPirWOLhizc1pqZri7Z ZnGvPtxhuCnVqCQk9ESm64GpMnDxt0gfXVzKqAu1fYwaMqXdZQAOAw2Jq18zIJuTgzkyl+5Vm qNG0l247NeNjdJmxBsYCKJm7kUZFWaEYg7MCEg== Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: X-Virus-Scanned: ClamAV using ClamSMTP The combination of KASAN_STACK and GCC_PLUGIN_STRUCTLEAK_BYREF_ALL leads to much larger kernel stack usage, as seen from the warnings about functions that now exceed the 2048 byte limit: drivers/media/i2c/tvp5150.c:253:1: error: the frame size of 3936 bytes is larger than 2048 bytes fs/ocfs2/dlm/dlmrecovery.c:737:1: error: the frame size of 2088 bytes is larger than 2048 bytes fs/ocfs2/aops.c:1892:1: error: the frame size of 2088 bytes is larger than 2048 bytes fs/ocfs2/namei.c:1677:1: error: the frame size of 2584 bytes is larger than 2048 bytes fs/ocfs2/super.c:1186:1: error: the frame size of 2640 bytes is larger than 2048 bytes fs/ocfs2/xattr.c:3678:1: error: the frame size of 2176 bytes is larger than 2048 bytes net/bridge/br_netlink.c:1505:1: error: the frame size of 2448 bytes is larger than 2048 bytes net/ieee802154/nl802154.c:548:1: error: the frame size of 2232 bytes is larger than 2048 bytes net/wireless/nl80211.c:1726:1: error: the frame size of 2224 bytes is larger than 2048 bytes net/wireless/nl80211.c:6472:1: error: the frame size of 2112 bytes is larger than 2048 bytes net/wireless/nl80211.c:2357:1: error: the frame size of 4584 bytes is larger than 2048 bytes net/wireless/nl80211.c:5108:1: error: the frame size of 2760 bytes is larger than 2048 bytes drivers/media/tuners/r820t.c:1327:1: error: the frame size of 2816 bytes is larger than 2048 bytes The warnings are distracting, and risking a kernel stack overflow is generally not beneficial to performance, so it may be best to disallow that particular combination. This can be done by turning off either one. I picked the dependency in GCC_PLUGIN_STRUCTLEAK_BYREF_ALL, as this option is designed to make uninitialized stack usage less harmful when enabled on its own, but it also prevents KASAN from detecting those cases in which it was in fact needed. KASAN_STACK is currently implied by KASAN on gcc, but could be made a user selectable option if we want to allow combining (non-stack) KASAN wtih GCC_PLUGIN_STRUCTLEAK_BYREF_ALL. Note that it woult be possible to specifically address the files that print the warning, but presumably the overall stack usage is still significantly higher than in other configurations, so this would not address the full problem. I could not test this with CONFIG_INIT_STACK_ALL, which may or may not suffer from a similar problem. Fixes: 81a56f6dcd20 ("gcc-plugins: structleak: Generalize to all variable types") Signed-off-by: Arnd Bergmann --- security/Kconfig.hardening | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/security/Kconfig.hardening b/security/Kconfig.hardening index c6cb2d9b2905..e742d1006a4b 100644 --- a/security/Kconfig.hardening +++ b/security/Kconfig.hardening @@ -73,6 +73,7 @@ choice config GCC_PLUGIN_STRUCTLEAK_BYREF_ALL bool "zero-init anything passed by reference (very strong)" depends on GCC_PLUGINS + depends on !(KASAN && KASAN_STACK=1) select GCC_PLUGIN_STRUCTLEAK help Zero-initialize any stack variables that may be passed @@ -80,6 +81,10 @@ choice initialized. This is intended to eliminate all classes of uninitialized stack variable exploits and information exposures. + As a side-effect, this keeps a lot of variables on the + stack that can otherwise be optimized out, so combining + this with CONFIG_KASAN_STACK can lead to a stack overflow + and is disallowed. config INIT_STACK_ALL bool "0xAA-init everything on the stack (strongest)"