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=-5.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_2 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 8AD2DC4363D for ; Fri, 9 Oct 2020 12:39:57 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 10976222E7 for ; Fri, 9 Oct 2020 12:39:56 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="ebPwE13h" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 10976222E7 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 377636B0062; Fri, 9 Oct 2020 08:39:56 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 3019E6B0068; Fri, 9 Oct 2020 08:39:56 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1C7416B006C; Fri, 9 Oct 2020 08:39:56 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0083.hostedemail.com [216.40.44.83]) by kanga.kvack.org (Postfix) with ESMTP id DB48F6B0062 for ; Fri, 9 Oct 2020 08:39:55 -0400 (EDT) Received: from smtpin15.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 7C7FB8249980 for ; Fri, 9 Oct 2020 12:39:55 +0000 (UTC) X-FDA: 77352343950.15.skate04_5f116b5271e0 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin15.hostedemail.com (Postfix) with ESMTP id 58EB21814B0C1 for ; Fri, 9 Oct 2020 12:39:55 +0000 (UTC) X-HE-Tag: skate04_5f116b5271e0 X-Filterd-Recvd-Size: 5758 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf27.hostedemail.com (Postfix) with ESMTP for ; Fri, 9 Oct 2020 12:39:54 +0000 (UTC) Received: from coco.lan (ip5f5ad5d0.dynamic.kabel-deutschland.de [95.90.213.208]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 85AD3222B8; Fri, 9 Oct 2020 12:39:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1602247193; bh=ruA15GjB/fFH2gJQRaoGIXfNQO5QPyDiPzMmJhWfrxQ=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=ebPwE13hJTyu7GU7hqGujNTcQ3SJtz+JCoKsDWHQbhtRGSTdSLTjnjECptwHYqY3q MKQ41Y6J0y7haidc1ZWrDQLUW0A2sUpIAG5O9TanLsaA0fGLcNuObliZM9g/MbS7s+ gKoB0ZuFxhI8SXftz7+Nxh4xSbD62xyIpNDeilOA= Date: Fri, 9 Oct 2020 14:39:47 +0200 From: Mauro Carvalho Chehab To: Jason Gunthorpe Cc: Daniel Vetter , DRI Development , LKML , kvm@vger.kernel.org, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linux-samsung-soc@vger.kernel.org, linux-media@vger.kernel.org, linux-s390@vger.kernel.org, Daniel Vetter , Kees Cook , Dan Williams , Andrew Morton , John Hubbard , =?UTF-8?B?SsOpcsO0bWU=?= Glisse , Jan Kara , Linus Torvalds Subject: Re: [PATCH v2 09/17] mm: Add unsafe_follow_pfn Message-ID: <20201009143947.751c5eb1@coco.lan> In-Reply-To: <20201009143723.45609bfb@coco.lan> References: <20201009075934.3509076-1-daniel.vetter@ffwll.ch> <20201009075934.3509076-10-daniel.vetter@ffwll.ch> <20201009123421.67a80d72@coco.lan> <20201009122111.GN5177@ziepe.ca> <20201009143723.45609bfb@coco.lan> X-Mailer: Claws Mail 3.17.6 (GTK+ 2.24.32; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit 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: Em Fri, 9 Oct 2020 14:37:23 +0200 Mauro Carvalho Chehab escreveu: > Em Fri, 9 Oct 2020 09:21:11 -0300 > Jason Gunthorpe escreveu: > > > On Fri, Oct 09, 2020 at 12:34:21PM +0200, Mauro Carvalho Chehab wrote: > > > Hi, > > > > > > Em Fri, 9 Oct 2020 09:59:26 +0200 > > > Daniel Vetter escreveu: > > > > > > > Way back it was a reasonable assumptions that iomem mappings never > > > > change the pfn range they point at. But this has changed: > > > > > > > > - gpu drivers dynamically manage their memory nowadays, invalidating > > > > ptes with unmap_mapping_range when buffers get moved > > > > > > > > - contiguous dma allocations have moved from dedicated carvetouts to > > > > cma regions. This means if we miss the unmap the pfn might contain > > > > pagecache or anon memory (well anything allocated with GFP_MOVEABLE) > > > > > > > > - even /dev/mem now invalidates mappings when the kernel requests that > > > > iomem region when CONFIG_IO_STRICT_DEVMEM is set, see 3234ac664a87 > > > > ("/dev/mem: Revoke mappings when a driver claims the region") > > > > > > > > Accessing pfns obtained from ptes without holding all the locks is > > > > therefore no longer a good idea. > > > > > > > > Unfortunately there's some users where this is not fixable (like v4l > > > > userptr of iomem mappings) or involves a pile of work (vfio type1 > > > > iommu). For now annotate these as unsafe and splat appropriately. > > > > > > > > This patch adds an unsafe_follow_pfn, which later patches will then > > > > roll out to all appropriate places. > > > > > > NACK, as this breaks an existing userspace API on media. > > > > It doesn't break it. You get a big warning the thing is broken and it > > keeps working. > > > > We can't leave such a huge security hole open - it impacts other > > subsystems, distros need to be able to run in a secure mode. > > Well, if distros disable it, then apps will break. > > > > While I agree that using the userptr on media is something that > > > new drivers may not support, as DMABUF is a better way of > > > handling it, changing this for existing ones is a big no, > > > as it may break usersapace. > > > > media community needs to work to fix this, not pretend it is OK to > > keep going as-is. > > > Dealing with security issues is the one case where an uABI break might > > be acceptable. > > > > If you want to NAK it then you need to come up with the work to do > > something here correctly that will support the old drivers without the > > kernel taint. > > > > Unfortunately making things uncomfortable for the subsystem is the big > > hammer the core kernel needs to use to actually get this security work > > done by those responsible. > > > I'm not pretending that this is ok. Just pointing that the approach > taken is NOT OK. > > I'm not a mm/ expert, but, from what I understood from Daniel's patch > description is that this is unsafe *only if* __GFP_MOVABLE is used. > > Well, no drivers inside the media subsystem uses such flag, although > they may rely on some infrastructure that could be using it behind > the bars. > > If this is the case, the proper fix seems to have a GFP_NOT_MOVABLE > flag that it would be denying the core mm code to set __GFP_MOVABLE. > > Please let address the issue on this way, instead of broken an > userspace API that it is there since 1991. In time: I meant to say 1998. Thanks, Mauro