From patchwork Thu Apr 6 19:00:30 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Allen Webb X-Patchwork-Id: 13203863 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E3946C76196 for ; Thu, 6 Apr 2023 19:02:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240552AbjDFTCB (ORCPT ); Thu, 6 Apr 2023 15:02:01 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56974 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240448AbjDFTBc (ORCPT ); Thu, 6 Apr 2023 15:01:32 -0400 Received: from mail-io1-xd4a.google.com (mail-io1-xd4a.google.com [IPv6:2607:f8b0:4864:20::d4a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8AD7CAD38 for ; Thu, 6 Apr 2023 12:01:09 -0700 (PDT) Received: by mail-io1-xd4a.google.com with SMTP id p128-20020a6b8d86000000b007583ebb18fdso24450053iod.19 for ; Thu, 06 Apr 2023 12:01:09 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; t=1680807668; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=lXaHngygoOShOtLfr1dWwTlpzanuSNfDsA9/IVCyMM4=; b=A1qC/ZvuARpF4aifJXh0p0le494sYKU2NUrJtNd2o8ZvihCjDaf3+R7KzU/ysrpbl6 l4vRFYVToK0UOMs0pZfZJ7KBI+Rl41ceZohihh9yw628OH8pKSweYgOGEyjX53rN+MH3 u2r5VzZepyIuhRLZEHGDRHYR4Yryg2rfMG46aAd7Jca5I7jedUgP1ewH8NgnLcVyakEp F4H5kVYuwj8RvLh0MhgIVykT7rtStfd74mo/DgYwCZTwVY2UqPmjoOLrZ57Eg7pCyh03 BpB549iKmEZJpj+E0ENtaR6aAv1+3vU3S/3z9qiLV4svNL23ganVPoSrhWkMrbQjfGbE QLFg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1680807668; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=lXaHngygoOShOtLfr1dWwTlpzanuSNfDsA9/IVCyMM4=; b=uhgLxK4CSE66wupwVrAxHBRdYwWc8BY5UPfzZJ6PwMzsrPpv5N8PLrVrUDpZZ5qpeU RqEw0y/bDnhnabClNNXTA/WMzaAXojSH+VCD3S/R0JqPcshh0FZUFbumkd0fxV+dnjCC YXUCsKKo1b1IOVR9rO5ZR2vz2KC3sZO2Eq4JM2QjtTP3ezJk06FMha36WxRWX+ISQM91 DPxxtiDBNGJvEt75MBzplxn7KPjqyQGxveCRe5kgaLPi922PucyUiL88hpbyF9aJKZoh /H+EIxKpnAzzQLyw4D7AaZmaKYALIPw0khVUT9CBgr6NzJIunYaxZFeNVuP3negmHPG5 cUZw== X-Gm-Message-State: AAQBX9cmB7k+Aw8HuGBDN4EVj76omldXBBP3343t+Nr0jZEmiv//70ea GUg18JOUVIktELi0a8X9nwpLhx4nbjdC2atU5gLm80a4JN6xV2Z/6c7ltjfsn2lzoOfbKvIXIvB gPjKQCd8hv6GNlS8ifkIjZx+a/zx7j7JcZ0lMxvEjQ8teWp4bxk8beDokpQ4BN1cBrSea8P6386 GEEVg= X-Google-Smtp-Source: AKy350Y3vePEPTjTofpsZaUJlnNunFT2KZcMeGuMTuCI/IqR0X3Td2aohNhIvplwI6YzX9YZIveMg5tfNSLS/1k= X-Received: from allenwebb.c.googlers.com ([fda3:e722:ac3:cc00:2b:ff92:c0a8:12e8]) (user=allenwebb job=sendgmr) by 2002:a05:6e02:d44:b0:326:315:f3d with SMTP id h4-20020a056e020d4400b0032603150f3dmr6023365ilj.1.1680807668678; Thu, 06 Apr 2023 12:01:08 -0700 (PDT) Date: Thu, 6 Apr 2023 14:00:30 -0500 In-Reply-To: <20230406190030.968972-1-allenwebb@google.com> Mime-Version: 1.0 References: <20221219204619.2205248-1-allenwebb@google.com> <20230406190030.968972-1-allenwebb@google.com> X-Mailer: git-send-email 2.40.0.577.gac1e443424-goog Message-ID: <20230406190030.968972-12-allenwebb@google.com> Subject: [PATCH v10 11/11] Documentation: add USB authorization document to driver-api From: Allen Webb To: "linux-modules@vger.kernel.org" , "linux-usb@vger.kernel.org" , "linux-kernel@vger.kernel.org" Cc: gregkh@linuxfoundation.org, mcgrof@kernel.org, christophe.leroy@csgroup.eu, nick.alcock@oracle.com, Allen Webb Precedence: bulk List-ID: There is a user-facing USB authorization document, but it is midding details a driver should have developer, so add them in a new document. Signed-off-by: Allen Webb --- .../driver-api/usb/authorization.rst | 71 +++++++++++++++++++ Documentation/driver-api/usb/index.rst | 1 + 2 files changed, 72 insertions(+) create mode 100644 Documentation/driver-api/usb/authorization.rst diff --git a/Documentation/driver-api/usb/authorization.rst b/Documentation/driver-api/usb/authorization.rst new file mode 100644 index 000000000000..383dcc037a15 --- /dev/null +++ b/Documentation/driver-api/usb/authorization.rst @@ -0,0 +1,71 @@ +.. SPDX-License-Identifier: GPL-2.0 + +==================== +Device Authorization +==================== + +This document is intended for driver developers. See +Documentation/usb/authorization.rst if you are looking for how to use +USB authorization. + +Authorization provides userspace a way to allow or block configuring +devices early during enumeration before any modules are probed for the +device. While it is possible to block a device by not loading the +required modules, this also prevents other devices from using the +module as well. For example someone might have an unattended computer +downloading installation media to a USB drive. Presumably this computer +would be locked to make it more difficult for a bad actor to access the +computer. Since USB storage devices are not needed to interact with the +lock screen, the authorized_default sysfs attribute can be set to not +authorize new USB devices by default. A userspace tool like USBGuard +can then vet the devices. Mice, keyboards, etc can be allowed by +writing to their authorized sysfs attribute so that the lock screen can +still be used (this important in cases like suspend+resume or docks) +while other devices can be blocked as long as the lock screen is shown. + +Sysfs Attributes +================ + +Userspace can control USB device authorization through the +authorized_default and authorized sysfs attributes. + +authorized_default +------------------ + +Defined in ``drivers/usb/core/hcd.c`` + +The authorized_default sysfs attribute is only present for host +controllers. It determines the initial state of the authorized sysfs +attribute of USB devices newly connected to the corresponding host +controller. It can take on the following values: + ++---------------------------------------------------+ +| Value | Behavior | ++=======+===========================================+ +| -1 | Authorize all devices except wireless USB | ++-------+-------------------------------------------+ +| 0 | Do not authorize new devices | ++-------+-------------------------------------------+ +| 1 | Authorize new devices | ++-------+-------------------------------------------+ +| 2 | Authorize new internal devices only | ++---------------------------------------------------+ + +Note that firmware platform code determines if a device is internal or +not and this is reported as the connect_type sysfs attribute of the USB +port. This is currently supported by ACPI, but device tree still needs +an implementation. Authorizing new internal devices only can be useful +to work around issues with devices that misbehave if there are delays +in probing their module. + +authorized +---------- + +Defined in ``drivers/usb/core/sysfs.c`` + +Every USB device has an authorized sysfs attribute which can take the +values 0 and 1. When authorized is 0, the device still is present in +sysfs, but none of its interfaces can be associated with drivers and +modules will not be probed. When authorized is 1 (or set to one) a +configuration is chosen for the device and its interfaces are +registered allowing drivers to bind to them. diff --git a/Documentation/driver-api/usb/index.rst b/Documentation/driver-api/usb/index.rst index cfa8797ea614..ffe37916f99f 100644 --- a/Documentation/driver-api/usb/index.rst +++ b/Documentation/driver-api/usb/index.rst @@ -7,6 +7,7 @@ Linux USB API usb gadget anchors + authorization bulk-streams callbacks dma