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=-3.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED 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 5CB5FC433DF for ; Sat, 10 Oct 2020 21:12:01 +0000 (UTC) Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 32188207CD for ; Sat, 10 Oct 2020 21:12:00 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=ideasonboard.com header.i=@ideasonboard.com header.b="rHwYSWi2" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 32188207CD Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ideasonboard.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=dri-devel-bounces@lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 05D656E02D; Sat, 10 Oct 2020 21:11:59 +0000 (UTC) Received: from perceval.ideasonboard.com (perceval.ideasonboard.com [IPv6:2001:4b98:dc2:55:216:3eff:fef7:d647]) by gabe.freedesktop.org (Postfix) with ESMTPS id 5DC686E02D for ; Sat, 10 Oct 2020 21:11:58 +0000 (UTC) Received: from pendragon.ideasonboard.com (62-78-145-57.bb.dnainternet.fi [62.78.145.57]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id D2859528; Sat, 10 Oct 2020 23:11:55 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1602364316; bh=fpHhn5rM48GkcDX4bL4eRbG5dZr4i+sFRkbewEJH1Dg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=rHwYSWi2XUI2y1Ti8u+N8R/KTpRgkW0TVn4LDZpKlDrbVLcAqDJGAnhyonxoldFRN psEGjrkDGp3K4p9i8ooaZhsYuS95RR6PuHIrw4PwyU90aSj/y97JR/y7rgRiYg/Ar0 8MefjhVZFKvV0sPG+/srQf9fVVfiV4dR3+khqARU= Date: Sun, 11 Oct 2020 00:11:11 +0300 From: Laurent Pinchart To: Daniel Vetter Subject: Re: [PATCH v2 09/17] mm: Add unsafe_follow_pfn Message-ID: <20201010211111.GA3939@pendragon.ideasonboard.com> 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> <20201009124850.GP5177@ziepe.ca> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-s390 , linux-samsung-soc , Jan Kara , Kees Cook , KVM list , Linux MM , Mauro Carvalho Chehab , John Hubbard , LKML , DRI Development , Jason Gunthorpe , =?utf-8?B?SsOpcsO0bWU=?= Glisse , Daniel Vetter , Dan Williams , Linus Torvalds , Andrew Morton , Linux ARM , "open list:DMA BUFFER SHARING FRAMEWORK" Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" Hi Daniel, On Fri, Oct 09, 2020 at 07:52:05PM +0200, Daniel Vetter wrote: > On Fri, Oct 9, 2020 at 2:48 PM Jason Gunthorpe wrote: > > On Fri, Oct 09, 2020 at 02:37:23PM +0200, Mauro Carvalho Chehab wrote: > > > > > 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. > > > > No, it is unconditionally unsafe. The CMA movable mappings are > > specific VMAs that will have bad issues here, but there are other > > types too. > > > > The only way to do something at a VMA level is to have a list of OK > > VMAs, eg because they were creatd via a special mmap helper from the > > media subsystem. > > > > > 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. > > > > It doesn't matter, nothing prevents the user from calling media APIs > > on mmaps it gets from other subsystems. > > I think a good first step would be to disable userptr of non struct > page backed storage going forward for any new hw support. Even on > existing drivers. dma-buf sharing has been around for long enough now > that this shouldn't be a problem. Unfortunately right now this doesn't > seem to exist, so the entire problem keeps getting perpetuated. On the V4L2 side, I think we should disable USERPTR for any new driver, period. That's what I've been recommended when reviewing patches for several years already. It's a deprecated API, it should be phased out, which starts by not allowing any new use case. > > > 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. > > > > We can't tell from the VMA these kinds of details.. > > > > It has to go the other direction, evey mmap that might be used as a > > userptr here has to be found and the VMA specially created to allow > > its use. At least that is a kernel only change, but will need people > > with the HW to do this work. > > I think the only reasonable way to keep this working is: > - add a struct dma_buf *vma_tryget_dma_buf(struct vm_area_struct *vma); > - add dma-buf export support to fbdev and v4l > - roll this out everywhere we still need it. > > Realistically this just isn't going to happen. And anything else just > reimplements half of dma-buf, which is kinda pointless (you need > minimally refcounting and some way to get at a promise of a permanent > sg list for dma. Plus probably the vmap for kernel cpu access. > > > > Please let address the issue on this way, instead of broken an > > > userspace API that it is there since 1991. > > > > It has happened before :( It took 4 years for RDMA to undo the uAPI > > breakage caused by a security fix for something that was a 15 years > > old bug. > > Yeah we have a bunch of these on the drm side too. Some of them are > really just "you have to upgrade userspace", and there's no real fix > for the security nightmare without that. -- Regards, Laurent Pinchart _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel