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=-7.9 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 9850CC433E9 for ; Thu, 3 Sep 2020 18:10:06 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 43F9D20716 for ; Thu, 3 Sep 2020 18:10:06 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 43F9D20716 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id D4723900003; Thu, 3 Sep 2020 14:10:05 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id CF7906B0073; Thu, 3 Sep 2020 14:10:05 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id BE75C900003; Thu, 3 Sep 2020 14:10:05 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0237.hostedemail.com [216.40.44.237]) by kanga.kvack.org (Postfix) with ESMTP id A86506B0072 for ; Thu, 3 Sep 2020 14:10:05 -0400 (EDT) Received: from smtpin28.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 6807A181AC9CC for ; Thu, 3 Sep 2020 18:10:05 +0000 (UTC) X-FDA: 77222539170.28.team91_2c03635270ab Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin28.hostedemail.com (Postfix) with ESMTP id 37CD56C05 for ; Thu, 3 Sep 2020 18:10:05 +0000 (UTC) X-HE-Tag: team91_2c03635270ab X-Filterd-Recvd-Size: 8105 Received: from mga01.intel.com (mga01.intel.com [192.55.52.88]) by imf20.hostedemail.com (Postfix) with ESMTP for ; Thu, 3 Sep 2020 18:10:03 +0000 (UTC) IronPort-SDR: QiItIAvhXbG0BVaZs8Wbil/bDpL28p7EHhD1TJaI3TBAo+0/+CtTk6ZpJ5iva7Bfb9RRJdIKMk zAtHd55lDweg== X-IronPort-AV: E=McAfee;i="6000,8403,9733"; a="175688112" X-IronPort-AV: E=Sophos;i="5.76,387,1592895600"; d="scan'208";a="175688112" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga005.jf.intel.com ([10.7.209.41]) by fmsmga101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 03 Sep 2020 11:09:21 -0700 IronPort-SDR: AQ4vUnaPo2MJc7jw7BU7YE4JMcdXVq5T9e/4111m6XcZWo/Rkt+UXghBqMByRSHqLfZbG6xeLF ITBUzB1OR5Og== X-IronPort-AV: E=Sophos;i="5.76,387,1592895600"; d="scan'208";a="478146066" Received: from viveksh1-mobl.amr.corp.intel.com (HELO [10.212.108.191]) ([10.212.108.191]) by orsmga005-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 03 Sep 2020 11:09:17 -0700 Subject: Re: [PATCH v7 3/3] mm: add a field to store names for private anonymous memory To: Kees Cook , Sumit Semwal Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Alexey Dobriyan , Jonathan Corbet , Mauro Carvalho Chehab , Michal Hocko , Colin Cross , Alexey Gladkov , Matthew Wilcox , Jason Gunthorpe , "Kirill A . Shutemov" , Michel Lespinasse , =?UTF-8?Q?Michal_Koutn=c3=bd?= , Song Liu , Huang Ying , Vlastimil Babka , Yang Shi , chenqiwu , Mathieu Desnoyers , John Hubbard , Mike Christie , Bart Van Assche , Amit Pundir , Thomas Gleixner , Christian Brauner , Daniel Jordan , Adrian Reber , Nicolas Viennot , Al Viro , linux-fsdevel@vger.kernel.org, John Stultz , Pekka Enberg , Peter Zijlstra , Ingo Molnar , Oleg Nesterov , "Eric W. Biederman" , Jan Glauber , Rob Landley , Cyrill Gorcunov , "Serge E. Hallyn" , David Rientjes , Hugh Dickins , Rik van Riel , Mel Gorman , Tang Chen , Robin Holt , Shaohua Li , Sasha Levin , Johannes Weiner , Minchan Kim References: <20200901161459.11772-1-sumit.semwal@linaro.org> <20200901161459.11772-4-sumit.semwal@linaro.org> <202009031031.D32EF57ED@keescook> From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; keydata= xsFNBE6HMP0BEADIMA3XYkQfF3dwHlj58Yjsc4E5y5G67cfbt8dvaUq2fx1lR0K9h1bOI6fC oAiUXvGAOxPDsB/P6UEOISPpLl5IuYsSwAeZGkdQ5g6m1xq7AlDJQZddhr/1DC/nMVa/2BoY 2UnKuZuSBu7lgOE193+7Uks3416N2hTkyKUSNkduyoZ9F5twiBhxPJwPtn/wnch6n5RsoXsb ygOEDxLEsSk/7eyFycjE+btUtAWZtx+HseyaGfqkZK0Z9bT1lsaHecmB203xShwCPT49Blxz VOab8668QpaEOdLGhtvrVYVK7x4skyT3nGWcgDCl5/Vp3TWA4K+IofwvXzX2ON/Mj7aQwf5W iC+3nWC7q0uxKwwsddJ0Nu+dpA/UORQWa1NiAftEoSpk5+nUUi0WE+5DRm0H+TXKBWMGNCFn c6+EKg5zQaa8KqymHcOrSXNPmzJuXvDQ8uj2J8XuzCZfK4uy1+YdIr0yyEMI7mdh4KX50LO1 pmowEqDh7dLShTOif/7UtQYrzYq9cPnjU2ZW4qd5Qz2joSGTG9eCXLz5PRe5SqHxv6ljk8mb ApNuY7bOXO/A7T2j5RwXIlcmssqIjBcxsRRoIbpCwWWGjkYjzYCjgsNFL6rt4OL11OUF37wL QcTl7fbCGv53KfKPdYD5hcbguLKi/aCccJK18ZwNjFhqr4MliQARAQABzShEYXZpZCBDaHJp c3RvcGhlciBIYW5zZW4gPGRhdmVAc3I3MS5uZXQ+wsF7BBMBAgAlAhsDBgsJCAcDAgYVCAIJ CgsEFgIDAQIeAQIXgAUCTo3k0QIZAQAKCRBoNZUwcMmSsMO2D/421Xg8pimb9mPzM5N7khT0 2MCnaGssU1T59YPE25kYdx2HntwdO0JA27Wn9xx5zYijOe6B21ufrvsyv42auCO85+oFJWfE K2R/IpLle09GDx5tcEmMAHX6KSxpHmGuJmUPibHVbfep2aCh9lKaDqQR07gXXWK5/yU1Dx0r VVFRaHTasp9fZ9AmY4K9/BSA3VkQ8v3OrxNty3OdsrmTTzO91YszpdbjjEFZK53zXy6tUD2d e1i0kBBS6NLAAsqEtneplz88T/v7MpLmpY30N9gQU3QyRC50jJ7LU9RazMjUQY1WohVsR56d ORqFxS8ChhyJs7BI34vQusYHDTp6PnZHUppb9WIzjeWlC7Jc8lSBDlEWodmqQQgp5+6AfhTD kDv1a+W5+ncq+Uo63WHRiCPuyt4di4/0zo28RVcjtzlGBZtmz2EIC3vUfmoZbO/Gn6EKbYAn rzz3iU/JWV8DwQ+sZSGu0HmvYMt6t5SmqWQo/hyHtA7uF5Wxtu1lCgolSQw4t49ZuOyOnQi5 f8R3nE7lpVCSF1TT+h8kMvFPv3VG7KunyjHr3sEptYxQs4VRxqeirSuyBv1TyxT+LdTm6j4a mulOWf+YtFRAgIYyyN5YOepDEBv4LUM8Tz98lZiNMlFyRMNrsLV6Pv6SxhrMxbT6TNVS5D+6 UorTLotDZKp5+M7BTQRUY85qARAAsgMW71BIXRgxjYNCYQ3Xs8k3TfAvQRbHccky50h99TUY sqdULbsb3KhmY29raw1bgmyM0a4DGS1YKN7qazCDsdQlxIJp9t2YYdBKXVRzPCCsfWe1dK/q 66UVhRPP8EGZ4CmFYuPTxqGY+dGRInxCeap/xzbKdvmPm01Iw3YFjAE4PQ4hTMr/H76KoDbD cq62U50oKC83ca/PRRh2QqEqACvIH4BR7jueAZSPEDnzwxvVgzyeuhwqHY05QRK/wsKuhq7s UuYtmN92Fasbxbw2tbVLZfoidklikvZAmotg0dwcFTjSRGEg0Gr3p/xBzJWNavFZZ95Rj7Et db0lCt0HDSY5q4GMR+SrFbH+jzUY/ZqfGdZCBqo0cdPPp58krVgtIGR+ja2Mkva6ah94/oQN lnCOw3udS+Eb/aRcM6detZr7XOngvxsWolBrhwTQFT9D2NH6ryAuvKd6yyAFt3/e7r+HHtkU kOy27D7IpjngqP+b4EumELI/NxPgIqT69PQmo9IZaI/oRaKorYnDaZrMXViqDrFdD37XELwQ gmLoSm2VfbOYY7fap/AhPOgOYOSqg3/Nxcapv71yoBzRRxOc4FxmZ65mn+q3rEM27yRztBW9 AnCKIc66T2i92HqXCw6AgoBJRjBkI3QnEkPgohQkZdAb8o9WGVKpfmZKbYBo4pEAEQEAAcLB XwQYAQIACQUCVGPOagIbDAAKCRBoNZUwcMmSsJeCEACCh7P/aaOLKWQxcnw47p4phIVR6pVL e4IEdR7Jf7ZL00s3vKSNT+nRqdl1ugJx9Ymsp8kXKMk9GSfmZpuMQB9c6io1qZc6nW/3TtvK pNGz7KPPtaDzvKA4S5tfrWPnDr7n15AU5vsIZvgMjU42gkbemkjJwP0B1RkifIK60yQqAAlT YZ14P0dIPdIPIlfEPiAWcg5BtLQU4Wg3cNQdpWrCJ1E3m/RIlXy/2Y3YOVVohfSy+4kvvYU3 lXUdPb04UPw4VWwjcVZPg7cgR7Izion61bGHqVqURgSALt2yvHl7cr68NYoFkzbNsGsye9ft M9ozM23JSgMkRylPSXTeh5JIK9pz2+etco3AfLCKtaRVysjvpysukmWMTrx8QnI5Nn5MOlJj 1Ov4/50JY9pXzgIDVSrgy6LYSMc4vKZ3QfCY7ipLRORyalFDF3j5AGCMRENJjHPD6O7bl3Xo 4DzMID+8eucbXxKiNEbs21IqBZbbKdY1GkcEGTE7AnkA3Y6YB7I/j9mQ3hCgm5muJuhM/2Fr OPsw5tV/LmQ5GXH0JQ/TZXWygyRFyyI2FqNTx4WHqUn3yFj8rwTAU1tluRUYyeLy0ayUlKBH ybj0N71vWO936MqP6haFERzuPAIpxj2ezwu0xb1GjTk4ynna6h5GjnKgdfOWoRtoWndMZxbA z5cecg== Message-ID: <393be893-6379-8adb-217c-4064f5052702@intel.com> Date: Thu, 3 Sep 2020 11:09:16 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <202009031031.D32EF57ED@keescook> Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-Rspamd-Queue-Id: 37CD56C05 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam04 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 9/3/20 11:00 AM, Kees Cook wrote: > Why is a kernel-copied string insufficient for this? I don't think VMA > merging is a fast-path operation, so doing a strcmp isn't going to wrec= k > anything... >=20 > Let me try to find the earlier thread with Dave Hansen... okay, found i= t: > https://lore.kernel.org/linux-mm/51DDF071.5000309@intel.com/ >=20 > Right, so, this idea predates userfaultfd. :) >=20 > More notes below, but I *really* think this should not be a userspace > pointer. And since a separate union has been found, let's just do a > strndup_user() for the name, validate it as containing only printable > characters without \n \r \v \f and move the merging logic into a > separate patch. FWIW, I don't have any objections to this. Refcounting strings was what I think I had the strongest reaction to back in the good old days of 2013. strdup() on split plus strcmp() on merge doesn't sound afwul to me, and it is darn straightforward. The biggest downside is probably kernel memory consumption. We should probably just think through whether having so many duplicates changes things materially. For instance, should/could we penalize a task's vm.max_map_count when it's using this mechanism?