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[23.128.96.18]) by mx.google.com with ESMTP id v5si4414770edi.582.2021.05.13.15.42.55; Thu, 13 May 2021 15:43:19 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; dkim=pass header.i=@linuxfoundation.org header.s=korg header.b=b0vVVuwx; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=linuxfoundation.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230501AbhEMRnR (ORCPT + 99 others); Thu, 13 May 2021 13:43:17 -0400 Received: from mail.kernel.org ([198.145.29.99]:38492 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229964AbhEMRnM (ORCPT ); Thu, 13 May 2021 13:43:12 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id AA0E161352; Thu, 13 May 2021 17:42:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1620927722; bh=ALM+zyZ7ii+SEw0cD5Jf+wDVvb/5CGSOX1wX3nCR53w=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=b0vVVuwxQ0YaglllLHuSAoLMXXoR8EjxMet4x9wSmDQ/GBeOVtHi3ACNJcCc1I1NM PlFGXIHudIIjJ30ajp8gWLEgo5ZukZcryfwM0jroPpcSGAhD9loDkH7OVSMJTkrTcc u6vqjUbRU5zvWr3xT4XiGfVvBSW4ZRfGCoJvTEos= Date: Thu, 13 May 2021 19:41:59 +0200 From: Greg Kroah-Hartman To: Rajat Jain Cc: "Rafael J. Wysocki" , Bjorn Helgaas , Alan Stern , Linux Kernel Mailing List , linux-pci , "open list:ULTRA-WIDEBAND (UWB) SUBSYSTEM:" , Bjorn Helgaas , 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: References: <20210512213457.1310774-1-rajatja@google.com> <20210512213457.1310774-2-rajatja@google.com> 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 09:39:58AM -0700, Rajat Jain wrote: > Hello, > > On Thu, May 13, 2021 at 6:58 AM Greg Kroah-Hartman > wrote: > > > > On Wed, May 12, 2021 at 02:34:57PM -0700, 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. > > > > > > 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) > > > > > > Signed-off-by: Rajat Jain > > > --- > > > v3: - commit log updated > > > - Rename set_pci_dev_removable() -> pci_set_removable() > > > - Call it after applying early PCI quirks. > > > v2: Add documentation > > > > > > Documentation/ABI/testing/sysfs-devices-removable | 3 ++- > > > drivers/pci/pci-sysfs.c | 1 + > > > drivers/pci/probe.c | 12 ++++++++++++ > > > 3 files changed, 15 insertions(+), 1 deletion(-) > > > > > > diff --git a/Documentation/ABI/testing/sysfs-devices-removable b/Documentation/ABI/testing/sysfs-devices-removable > > > index 9dabcad7cdcd..ec0b243f5db4 100644 > > > --- a/Documentation/ABI/testing/sysfs-devices-removable > > > +++ b/Documentation/ABI/testing/sysfs-devices-removable > > > @@ -14,4 +14,5 @@ Description: > > > > > > Currently this is only supported by USB (which infers the > > > information from a combination of hub descriptor bits and > > > - platform-specific data such as ACPI). > > > + platform-specific data such as ACPI) and PCI (which gets this > > > + from ACPI / device tree). > > > diff --git a/drivers/pci/pci-sysfs.c b/drivers/pci/pci-sysfs.c > > > index beb8d1f4fafe..38b3259ba333 100644 > > > --- a/drivers/pci/pci-sysfs.c > > > +++ b/drivers/pci/pci-sysfs.c > > > @@ -1541,4 +1541,5 @@ static const struct attribute_group *pci_dev_attr_groups[] = { > > > > > > const struct device_type pci_dev_type = { > > > .groups = pci_dev_attr_groups, > > > + .supports_removable = true, > > > }; > > > diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c > > > index 3a62d09b8869..3515afeeaba8 100644 > > > --- a/drivers/pci/probe.c > > > +++ b/drivers/pci/probe.c > > > @@ -1575,6 +1575,16 @@ static void set_pcie_untrusted(struct pci_dev *dev) > > > dev->untrusted = true; > > > } > > > > > > +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); > > > +} > > > > Always run checkpatch.pl so you don't get grumpy maintainers telling you > > to run checkpatch.pl :( > > Yes, I did (it gave me 0 errors and 0 warnings). Please let me know if > I need to fix something and I'll be happy to fix that. > > > > > And why does external_facing come into play here? I know you say it > > above, but you should also put it here into the code for when we need to > > look at it in a few months and wonder what in the world this is doing. > > Ack, will do. > > > > > Also, are you SURE this is correct and will handle the hotpluggable PCI > > devices in things like drawers and the like? > > Yes, me and Bjorn discussed this in the v2 of this patch > (https://patchwork.kernel.org/project/linux-usb/patch/20210424021631.1972022-2-rajatja@google.com/), > and yes, this can take care of the hot-pluggable trays if the firmware > marks the slots external-facing. Ok, I'll trust you two :) > > What is the goal here in exposing this information to userspace, who is > > going to use it and what is it going to be used for? > > The goal here is to implement policies regarding usage of external PCI > devices, in userspace. ChromeOS is using it for things like: > - Remove external PCI devices when a user logs out. remove them how? disconnect the device from the system through what method? > - Don't allow new external PCI devices while the screen is locked. Don't allow how? Don't allow the binding of a driver to a device, or the device to be discovered at all? What controls this? > - collect metrics about usage of external PCI devices (how many users > actually use it etc). > - disable certain features (that are deemed to be dangerous) for > external PCI network cards. What is a "dangerous" network feature, RDMA? thanks, greg k-h