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=-11.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 2E2F6C43461 for ; Thu, 13 May 2021 20:05:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 04372613CD for ; Thu, 13 May 2021 20:05:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232412AbhEMUHE (ORCPT ); Thu, 13 May 2021 16:07:04 -0400 Received: from mail.kernel.org ([198.145.29.99]:39456 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232389AbhEMUHC (ORCPT ); Thu, 13 May 2021 16:07:02 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id B307161421; Thu, 13 May 2021 20:05:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1620936352; bh=8T+J3wCXI/e4i0Nq0qkxzfPcgMyR9DsieXzCu8AyHN4=; h=Date:From:To:Cc:Subject:In-Reply-To:From; b=S8aZH569dpHyPV1WO9KYLvi5aeA4T/Bi2TDTlr76AqbK7Lss5y8R7nzoaJvXSoh8v AlAi/al1uKP6LoN6pTwS+Dbd6rny3YwO5cDVtK1DC74Fqv/ejJqOwgF/af3d4oE08o QT5DjPJ4GXOAagBrMiKykL58ii3A2EuFPFGuP2FPjdcq83lgS/0Km5N2cUzZDp8x4B Wj/GXNjZ41PLmuXelRojpihdaXt+o7+yWC2ioTg6vHAOdFxv15DcQ8SCFDXt4veoBE 1EbsXRaHuYonUI6rnefgLjRpu8TUsLMKo32FB/NTxKi1JdqUbijoRwEHgkljkpOZw5 5M9uuGP7jhqrg== Date: Thu, 13 May 2021 15:05:50 -0500 From: Bjorn Helgaas To: Rajat Jain Cc: Greg Kroah-Hartman , "Rafael J. Wysocki" , Bjorn Helgaas , Alan Stern , Linux Kernel Mailing List , linux-pci , "open list:ULTRA-WIDEBAND (UWB) SUBSYSTEM:" , Oliver Neukum , David Laight , Krzysztof =?utf-8?Q?Wilczy=C5=84ski?= , Rajat Jain , Jesse Barnes , Dmitry Torokhov Subject: Re: [PATCH v3 2/2] PCI: Add sysfs "removable" attribute Message-ID: <20210513200550.GA2604592@bjorn-Precision-5520> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 13, 2021 at 11:02:10AM -0700, Rajat Jain wrote: > On Wed, May 12, 2021 at 2:35 PM Rajat Jain wrote: > > > > A PCI device is "external_facing" if it's a Root Port with the ACPI > > "ExternalFacingPort" property or if it has the DT "external-facing" > > property. We consider everything downstream from such a device to > > be removable by user. > > > > We're mainly concerned with consumer platforms with user accessible > > thunderbolt ports that are vulnerable to DMA attacks, and we expect those > > ports to be identified as "ExternalFacingPort". Devices in traditional > > hotplug slots can technically be removed, but the expectation is that > > unless the port is marked with "ExternalFacingPort", such devices are less > > accessible to user / may not be removed by end user, and thus not exposed > > as "removable" to userspace. s/thunderbolt/Thunderbolt/ since I think it's a trademark s/identified as/identified by firmware as/ > > Set pci_dev_type.supports_removable so the device core exposes the > > "removable" file in sysfs, and tell the device core about removable > > devices. > > > > This can be used by userspace to implment any policies it wants to, > > tailored specifically for user removable devices. Eg usage: > > https://chromium-review.googlesource.com/c/chromiumos/platform2/+/2591812 > > https://chromium-review.googlesource.com/c/chromiumos/platform2/+/2795038 > > (code uses such an attribute to remove external PCI devicces or disable > > features on them as needed by the policy desired) s/implment/implement/ s/devicces/devices/ Or maybe something like: This can be used to implement userspace policies tailored for user-removable devices. Not sure exactly what "remove external PCI devices" means. You're talking about the *code* doing something, so I don't think it means physically unplugging the device from the system. Maybe preventing a driver from binding to it or something similar? I hesitate slightly to rely on URLs like googlesource.com in commit logs because we don't know how long they will remain valid. But I guess there's no real alternative here, since this code probably hasn't been posted to any public mailing lists like the ones archived at https://lore.kernel.org/lists.html, right? > > Signed-off-by: Rajat Jain > > +static void pci_set_removable(struct pci_dev *dev) > > +{ > > + struct pci_dev *parent = pci_upstream_bridge(dev); > > + if (parent && > > + (parent->external_facing || dev_is_removable(&parent->dev))) > > + dev_set_removable(&dev->dev, DEVICE_REMOVABLE); > > + else > > + dev_set_removable(&dev->dev, DEVICE_FIXED); > > +} > > Copying comments from Krzysztof from another thread: > > [Krzysztof] We were also wondering if we should only set DEVICE_REMOVABLE for > devices known to be behind an external-facing port, and let everything > else be set to "unknown" (or whatever the default would be). > > [Rajat]: I think I'm fine with this proposal if Bjorn & PCI community > also sees this as a better idea. Essentially the question here is, > would it be better for the non-removable PCI devices to be shown as > "fixed" or "unknown"? I think I would rather see this as: struct pci_dev *parent = pci_upstream_bridge(dev); if (parent && (parent->external_facing || dev_is_removable(&parent->dev))) dev_set_removable(&dev->dev, DEVICE_REMOVABLE); In other words, assume only that everything below an "external-facing" device is removable. In the absence of an "external-facing" property, we don't know anything about the connection, and I'd rather use the default (probably "unknown") instead of assuming "fixed." I don't think we have anything that depends on "fixed," so I don't think there's value in setting it. (Note the blank line between local variables and the "if"; maybe that's what Greg hinted at?) Bjorn