[{"id":1775814,"web_url":"http://patchwork.ozlabs.org/comment/1775814/","msgid":"","list_archive_url":null,"date":"2017-09-26T19:36:38","subject":"Re: [PATCH v4 9/9] kasan: rework Kconfig settings","submitter":{"id":67796,"url":"http://patchwork.ozlabs.org/api/people/67796/","name":"Andrey Ryabinin","email":"aryabinin@virtuozzo.com"},"content":"On 09/23/2017 12:29 AM, Arnd Bergmann wrote:\n> We get a lot of very large stack frames using gcc-7.0.1 with the default\n> -fsanitize-address-use-after-scope --param asan-stack=1 options, which\n> can easily cause an overflow of the kernel stack, e.g.\n> \n> drivers/gpu/drm/i915/gvt/handlers.c:2407:1: error: the frame size of 31216 bytes is larger than 2048 bytes\n> drivers/net/wireless/ralink/rt2x00/rt2800lib.c:5650:1: error: the frame size of 23632 bytes is larger than 2048 bytes\n> drivers/scsi/fnic/fnic_trace.c:451:1: error: the frame size of 5152 bytes is larger than 2048 bytes\n> fs/btrfs/relocation.c:1202:1: error: the frame size of 4256 bytes is larger than 2048 bytes\n> fs/fscache/stats.c:287:1: error: the frame size of 6552 bytes is larger than 2048 bytes\n> lib/atomic64_test.c:250:1: error: the frame size of 12616 bytes is larger than 2048 bytes\n> mm/vmscan.c:1367:1: error: the frame size of 5080 bytes is larger than 2048 bytes\n> net/wireless/nl80211.c:1905:1: error: the frame size of 4232 bytes is larger than 2048 bytes\n> \n> To reduce this risk, -fsanitize-address-use-after-scope is now split\n> out into a separate CONFIG_KASAN_EXTRA Kconfig option, leading to stack\n> frames that are smaller than 2 kilobytes most of the time on x86_64. An\n> earlier version of this patch also prevented combining KASAN_EXTRA with\n> KASAN_INLINE, but that is no longer necessary with gcc-7.0.1.\n> \n> A lot of warnings with KASAN_EXTRA go away if we disable KMEMCHECK,\n> as -fsanitize-address-use-after-scope seems to understand the builtin\n> memcpy, but adds checking code around an extern memcpy call. I had to work\n> around a circular dependency, as DEBUG_SLAB/SLUB depended on !KMEMCHECK,\n> while KASAN did it the other way round. Now we handle both the same way\n> and make KASAN and KMEMCHECK mutually exclusive.\n> \n> All patches to get the frame size below 2048 bytes with CONFIG_KASAN=y\n> and CONFIG_KASAN_EXTRA=n have been submitted along with this patch, so\n> we can bring back that default now. KASAN_EXTRA=y still causes lots of\n> warnings but now defaults to !COMPILE_TEST to disable it in allmodconfig,\n> and it remains disabled in all other defconfigs since it is a new option.\n> I arbitrarily raise the warning limit for KASAN_EXTRA to 3072 to reduce\n> the noise, but an allmodconfig kernel still has around 50 warnings\n> on gcc-7.\n> \n> I experimented a bit more with smaller stack frames and have another\n> follow-up series that reduces the warning limit for 64-bit architectures\n> to 1280 bytes (without CONFIG_KASAN).\n> \n> With earlier versions of this patch series, I also had patches to\n> address the warnings we get with KASAN and/or KASAN_EXTRA, using a\n> \"noinline_if_stackbloat\" annotation. That annotation now got replaced with\n> a gcc-8 bugfix (see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81715)\n> and a workaround for older compilers, which means that KASAN_EXTRA is\n> now just as bad as before and will lead to an instant stack overflow in\n> a few extreme cases.\n> \n> This reverts parts of commit commit 3f181b4 (\"lib/Kconfig.debug: disable\n> -Wframe-larger-than warnings with KASAN=y\").\n> \n> Signed-off-by: Arnd Bergmann \n\nAcked-by: Andrey Ryabinin ","headers":{"Return-Path":"","X-Original-To":"patchwork-incoming@ozlabs.org","Delivered-To":"patchwork-incoming@ozlabs.org","Authentication-Results":["ozlabs.org;\n\tspf=none (mailfrom) smtp.mailfrom=vger.kernel.org\n\t(client-ip=209.132.180.67; helo=vger.kernel.org;\n\tenvelope-from=netdev-owner@vger.kernel.org;\n\treceiver=)","ozlabs.org; dkim=pass (1024-bit key;\n\tunprotected) header.d=virtuozzo.com header.i=@virtuozzo.com\n\theader.b=\"CyF7Wbg9\"; dkim-atps=neutral","spf=none (sender IP is )\n\tsmtp.mailfrom=aryabinin@virtuozzo.com; "],"Received":["from vger.kernel.org (vger.kernel.org [209.132.180.67])\n\tby ozlabs.org (Postfix) with ESMTP id 3y1rpQ3wvpz9t3F\n\tfor ;\n\tWed, 27 Sep 2017 05:38:06 +1000 (AEST)","(majordomo@vger.kernel.org) by vger.kernel.org via listexpand\n\tid S1031934AbdIZTh4 (ORCPT );\n\tTue, 26 Sep 2017 15:37:56 -0400","from mail-he1eur01on0127.outbound.protection.outlook.com\n\t([104.47.0.127]:54965\n\t\"EHLO EUR01-HE1-obe.outbound.protection.outlook.com\"\n\trhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP\n\tid S935225AbdIZThv (ORCPT );\n\tTue, 26 Sep 2017 15:37:51 -0400","from [10.52.82.105] (84.47.128.244) by\n\tVI1PR08MB2832.eurprd08.prod.outlook.com (2603:10a6:802:25::31) with\n\tMicrosoft SMTP Server (version=TLS1_2,\n\tcipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384_P256) id 15.20.35.12;\n\tTue, 26 Sep 2017 19:37:46 +0000"],"DKIM-Signature":"v=1; a=rsa-sha256; c=relaxed/relaxed; d=virtuozzo.com;\n\ts=selector1; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version;\n\tbh=hN/dNv6xzOE+VGZkD9bZue7mgy5ULt7AMs+5GXu7BoA=;\n\tb=CyF7Wbg95laub/g9n8t8Xtw0VR9uQSxAZcE0cqB1poSBKDocHVvTyjmEVU8NlpSdhufJ+mKSP2irbqDgOY2Ver1rYbwv1NRCdY8TTJC6KsiTSptnFvzJsgxKpdf6L4CeBrnMt0V9bH3iWPocLu6sgy3Ge4i4mNIg0OmCW17Ak3g=","Subject":"Re: [PATCH v4 9/9] kasan: rework Kconfig settings","To":"Arnd Bergmann ,\n\tMasahiro Yamada ,\n\tMichal Marek , Andrew Morton ","Cc":"Mauro Carvalho Chehab ,\n\tJiri Pirko , Arend van Spriel\n\t, Kalle Valo ,\n\t\"David S. Miller\" , \n\tAlexander Potapenko , Dmitry Vyukov\n\t, Kees Cook ,\n\tGeert Uytterhoeven , \n\tGreg Kroah-Hartman , \n\tlinux-media@vger.kernel.org, linux-kernel@vger.kernel.org, \n\tnetdev@vger.kernel.org, linux-wireless@vger.kernel.org, \n\tbrcm80211-dev-list.pdl@broadcom.com, brcm80211-dev-list@cypress.com,\n\tkasan-dev@googlegroups.com, linux-kbuild@vger.kernel.org,\n\tJakub Jelinek , =?utf-8?q?Martin_Li=C5=A1ka?=\n\t","References":"<20170922212930.620249-1-arnd@arndb.de>\n\t<20170922212930.620249-10-arnd@arndb.de>","From":"Andrey Ryabinin ","Message-ID":"","Date":"Tue, 26 Sep 2017 22:36:38 +0300","User-Agent":"Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101\n\tThunderbird/52.3.0","MIME-Version":"1.0","In-Reply-To":"<20170922212930.620249-10-arnd@arndb.de>","Content-Type":"text/plain; charset=utf-8","Content-Language":"en-US","Content-Transfer-Encoding":"7bit","X-Originating-IP":"[84.47.128.244]","X-ClientProxiedBy":"VI1PR0102CA0005.eurprd01.prod.exchangelabs.com\n\t(2603:10a6:802::18) To VI1PR08MB2832.eurprd08.prod.outlook.com\n\t(2603:10a6:802:25::31)","X-MS-PublicTrafficType":"Email","X-MS-Office365-Filtering-Correlation-Id":"2fad0bee-a937-48ab-4ba7-08d505161119","X-Microsoft-Antispam":"UriScan:; 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