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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_2 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 381FCC433E1 for ; Wed, 8 Jul 2020 15:15:12 +0000 (UTC) Received: from hemlock.osuosl.org (smtp2.osuosl.org [140.211.166.133]) (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 139642078D for ; Wed, 8 Jul 2020 15:15:11 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 139642078D Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=iommu-bounces@lists.linux-foundation.org Received: from localhost (localhost [127.0.0.1]) by hemlock.osuosl.org (Postfix) with ESMTP id D73D78944E; Wed, 8 Jul 2020 15:15:11 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from hemlock.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id NeHIgfMRhXWV; Wed, 8 Jul 2020 15:15:10 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [140.211.9.56]) by hemlock.osuosl.org (Postfix) with ESMTP id 74A8589449; Wed, 8 Jul 2020 15:15:10 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id 616F2C077B; Wed, 8 Jul 2020 15:15:10 +0000 (UTC) Received: from whitealder.osuosl.org (smtp1.osuosl.org [140.211.166.138]) by lists.linuxfoundation.org (Postfix) with ESMTP id 1A152C077B for ; Wed, 8 Jul 2020 15:15:09 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by whitealder.osuosl.org (Postfix) with ESMTP id 01FAD86B04 for ; Wed, 8 Jul 2020 15:15:09 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from whitealder.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 8rhySL+H2S01 for ; Wed, 8 Jul 2020 15:15:06 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from mga03.intel.com (mga03.intel.com [134.134.136.65]) by whitealder.osuosl.org (Postfix) with ESMTPS id BF85988E89 for ; Wed, 8 Jul 2020 15:15:06 +0000 (UTC) IronPort-SDR: +dfK3Bx888+VuqbYob70GIvG6UNEwkuMrmz/9mamjPfVoQKVzpVBiNFl5JbLxHeDA/ArBVvf1D 4vwvj2bM7X9A== X-IronPort-AV: E=McAfee;i="6000,8403,9676"; a="147825145" X-IronPort-AV: E=Sophos;i="5.75,327,1589266800"; d="scan'208";a="147825145" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga005.jf.intel.com ([10.7.209.41]) by orsmga103.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 08 Jul 2020 08:15:06 -0700 IronPort-SDR: Sn8uiaMZ/RhlF97mg7zR3+EnFHRYzkT/OMKZnH6wpEWYeIen14LVgd8m6/QDC7tLeDYLIFspS3 JLFLqXmVlDLQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.75,327,1589266800"; d="scan'208";a="457536094" Received: from jacob-builder.jf.intel.com (HELO jacob-builder) ([10.7.199.155]) by orsmga005.jf.intel.com with ESMTP; 08 Jul 2020 08:15:06 -0700 Date: Wed, 8 Jul 2020 08:21:45 -0700 From: Jacob Pan To: Alex Williamson Subject: Re: [PATCH v3 1/5] docs: IOMMU user API Message-ID: <20200708082145.016d1f04@jacob-builder> In-Reply-To: <20200707154054.0893c30d@x1.home> References: <1592931837-58223-1-git-send-email-jacob.jun.pan@linux.intel.com> <1592931837-58223-2-git-send-email-jacob.jun.pan@linux.intel.com> <20200626161923.339e17a6@w520.home> <20200629160518.471159cf@jacob-builder> <20200707154054.0893c30d@x1.home> Organization: OTC X-Mailer: Claws Mail 3.13.2 (GTK+ 2.24.30; x86_64-pc-linux-gnu) MIME-Version: 1.0 Cc: "Tian, Kevin" , Raj Ashok , Jonathan Corbet , Jean-Philippe Brucker , LKML , Christoph Hellwig , iommu@lists.linux-foundation.org, David Woodhouse X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" Hi Alex, All points below are taken. I have sent out v4 that addresses these feedbacks. Thanks for the review. Jacob On Tue, 7 Jul 2020 15:40:54 -0600 Alex Williamson wrote: > On Mon, 29 Jun 2020 16:05:18 -0700 > Jacob Pan wrote: > > > On Fri, 26 Jun 2020 16:19:23 -0600 > > Alex Williamson wrote: > > > > > On Tue, 23 Jun 2020 10:03:53 -0700 > > > Jacob Pan wrote: > > > > > > > IOMMU UAPI is newly introduced to support communications between > > > > guest virtual IOMMU and host IOMMU. There has been lots of > > > > discussions on how it should work with VFIO UAPI and userspace > > > > in general. > > > > > > > > This document is indended to clarify the UAPI design and usage. > > > > The mechenics of how future extensions should be achieved are > > > > also covered in this documentation. > > > > > > > > Signed-off-by: Liu Yi L > > > > Signed-off-by: Jacob Pan > > > > --- > > > > Documentation/userspace-api/iommu.rst | 244 > > > > ++++++++++++++++++++++++++++++++++ 1 file changed, 244 > > > > insertions(+) create mode 100644 > > > > Documentation/userspace-api/iommu.rst > > > > > > > > diff --git a/Documentation/userspace-api/iommu.rst > > > > b/Documentation/userspace-api/iommu.rst new file mode 100644 > > > > index 000000000000..f9e4ed90a413 > > > > --- /dev/null > > > > +++ b/Documentation/userspace-api/iommu.rst > > > > @@ -0,0 +1,244 @@ > > > > +.. SPDX-License-Identifier: GPL-2.0 > > > > +.. iommu: > > > > + > > > > +===================================== > > > > +IOMMU Userspace API > > > > +===================================== > > > > + > > > > +IOMMU UAPI is used for virtualization cases where > > > > communications are +needed between physical and virtual IOMMU > > > > drivers. For native +usage, IOMMU is a system device which does > > > > not need to communicate +with user space directly. > > > > + > > > > +The primary use cases are guest Shared Virtual Address (SVA) > > > > and +guest IO virtual address (IOVA), wherein a virtual IOMMU > > > > (vIOMMU) is +required to communicate with the physical IOMMU in > > > > the host. + > > > > +.. contents:: :local: > > > > + > > > > +Functionalities > > > > +=============== > > > > +Communications of user and kernel involve both directions. The > > > > +supported user-kernel APIs are as follows: > > > > + > > > > +1. Alloc/Free PASID > > > > +2. Bind/unbind guest PASID (e.g. Intel VT-d) > > > > +3. Bind/unbind guest PASID table (e.g. ARM sMMU) > > > > +4. Invalidate IOMMU caches > > > > +5. Service page requests > > > > + > > > > +Requirements > > > > +============ > > > > +The IOMMU UAPIs are generic and extensible to meet the > > > > following +requirements: > > > > + > > > > +1. Emulated and para-virtualised vIOMMUs > > > > +2. Multiple vendors (Intel VT-d, ARM sMMU, etc.) > > > > +3. Extensions to the UAPI shall not break existing user space > > > > + > > > > +Interfaces > > > > +========== > > > > +Although the data structures defined in IOMMU UAPI are > > > > self-contained, +there is no user API functions introduced. > > > > Instead, IOMMU UAPI is +designed to work with existing user > > > > driver frameworks such as VFIO. + > > > > +Extension Rules & Precautions > > > > +----------------------------- > > > > +When IOMMU UAPI gets extended, the data structures can *only* > > > > be +modified in two ways: > > > > + > > > > +1. Adding new fields by re-purposing the padding[] field. No > > > > size change. +2. Adding new union members at the end. May > > > > increase in size. + > > > > +No new fields can be added *after* the variable sized union in > > > > that it +will break backward compatibility when offset moves. In > > > > both cases, a +new flag must be accompanied with a new field > > > > such that the IOMMU +driver can process the data based on the > > > > new flag. Version field is +only reserved for the unlikely > > > > event of UAPI upgrade at its entirety. + > > > > +It's *always* the caller's responsibility to indicate the size > > > > of the +structure passed by setting argsz appropriately. > > > > +Though at the same time, argsz is user provided data which is > > > > not +trusted. The argsz field allows the user to indicate how > > > > much data +they're providing, it's still the kernel's > > > > responsibility to validate +whether it's correct and sufficient > > > > for the requested operation. + > > > > +Compatibility Checking > > > > +---------------------- > > > > +When IOMMU UAPI extension results in size increase, user such > > > > as VFIO +has to handle the following cases: > > > > + > > > > +1. User and kernel has exact size match > > > > +2. An older user with older kernel header (smaller UAPI size) > > > > running on a > > > > + newer kernel (larger UAPI size) > > > > +3. A newer user with newer kernel header (larger UAPI size) > > > > running > > > > + on an older kernel. > > > > +4. A malicious/misbehaving user pass illegal/invalid size but > > > > within > > > > + range. The data may contain garbage. > > > > > > What exactly does vfio need to do to handle these? > > > > > VFIO does nothing other than returning the status from IOMMU driver. > > Based on the return status, users such as QEMU can cause fault > > conditions within the vIOMMU. > > > > > > + > > > > +Feature Checking > > > > +---------------- > > > > +While launching a guest with vIOMMU, it is important to ensure > > > > that host +can support the UAPI data structures to be used for > > > > vIOMMU-pIOMMU +communications. Without upfront compatibility > > > > checking, future faults +are difficult to report even in normal > > > > conditions. For example, TLB +invalidations should always > > > > succeed. There is no architectural way to +report back to the > > > > vIOMMU if the UAPI data is incompatible. If that +happens, in > > > > order to protect IOMMU iosolation guarantee, we have to +resort > > > > to not giving completion status in vIOMMU. This may result in > > > > +VM hang. + > > > > +For this reason the following IOMMU UAPIs cannot fail: > > > > + > > > > +1. Free PASID > > > > +2. Unbind guest PASID > > > > +3. Unbind guest PASID table (SMMU) > > > > +4. Cache invalidate > > > > + > > > > +User applications such as QEMU is expected to import kernel > > > > UAPI +headers. Backward compatibility is supported per feature > > > > flags. +For example, an older QEMU (with older kernel header) > > > > can run on newer +kernel. Newer QEMU (with new kernel header) > > > > may refuse to initialize +on an older kernel if new feature > > > > flags are not supported by older +kernel. Simply recompile > > > > existing code with newer kernel header should +not be an issue > > > > in that only existing flags are used. + > > > > +IOMMU vendor driver should report the below features to IOMMU > > > > UAPI +consumers (e.g. via VFIO). > > > > + > > > > +1. IOMMU_NESTING_FEAT_SYSWIDE_PASID > > > > +2. IOMMU_NESTING_FEAT_BIND_PGTBL > > > > +3. IOMMU_NESTING_FEAT_BIND_PASID_TABLE > > > > +4. IOMMU_NESTING_FEAT_CACHE_INVLD > > > > +5. IOMMU_NESTING_FEAT_PAGE_REQUEST > > > > + > > > > +Take VFIO as example, upon request from VFIO user space (e.g. > > > > QEMU), +VFIO kernel code shall query IOMMU vendor driver for the > > > > support of +the above features. Query result can then be > > > > reported back to the +user-space caller. Details can be found in > > > > +Documentation/driver-api/vfio.rst. > > > > + > > > > + > > > > +Data Passing Example with VFIO > > > > +------------------------------ > > > > +As the ubiquitous userspace driver framework, VFIO is already > > > > IOMMU +aware and share many key concepts such as device model, > > > > group, and +protection domain. Other user driver frameworks can > > > > also be extended +to support IOMMU UAPI but it is outside the > > > > scope of this document. + > > > > +In this tight-knit VFIO-IOMMU interface, the ultimate consumer > > > > of the +IOMMU UAPI data is the host IOMMU driver. VFIO > > > > facilitates user-kernel +transport, capability checking, > > > > security, and life cycle management of +process address space > > > > ID (PASID). + > > > > +Unlike normal user data passed via VFIO UAPI IOTCL, IOMMU > > > > driver is the +ultimate consumer of its UAPI data. At VFIO > > > > layer, the IOMMU UAPI data +is wrapped in a VFIO UAPI data. It > > > > follows the +pattern below:: > > > > + > > > > + struct { > > > > + __u32 argsz; > > > > + __u32 flags; > > > > + __u8 data[]; > > > > + }; > > > > + > > > > +Here data[] contains the IOMMU UAPI data structures. VFIO has > > > > the +freedom to bundle the data as well as parse data size > > > > based on its own flags. + > > > > +In order to determine the size and feature set of the user > > > > data, argsz +and flags are also embedded in the IOMMU UAPI data > > > > structures. +A "__u32 argsz" field is *always* at the beginning > > > > of each structure. + > > > > +For example: > > > > +:: > > > > + > > > > + struct iommu_cache_invalidate_info { > > > > + __u32 argsz; > > > > + #define IOMMU_CACHE_INVALIDATE_INFO_VERSION_1 1 > > > > + __u32 version; > > > > + /* IOMMU paging structure cache */ > > > > + #define IOMMU_CACHE_INV_TYPE_IOTLB (1 << 0) /* > > > > IOMMU IOTLB */ > > > > + #define IOMMU_CACHE_INV_TYPE_DEV_IOTLB (1 << > > > > 1) /* Device IOTLB */ > > > > + #define IOMMU_CACHE_INV_TYPE_PASID (1 << 2) /* > > > > PASID cache */ > > > > + #define IOMMU_CACHE_INV_TYPE_NR (3) > > > > + __u8 cache; > > > > + __u8 granularity; > > > > + __u8 padding[2]; > > > > + union { > > > > + struct iommu_inv_pasid_info pasid_info; > > > > + struct iommu_inv_addr_info addr_info; > > > > + } granu; > > > > + }; > > > > + > > > > +VFIO is responsible for checking its own argsz and flags then > > > > invokes +appropriate IOMMU UAPI functions. User pointer is > > > > passed to IOMMU +layer for further processing. The > > > > responsibilities are divided as +follows: > > > > + > > > > +- Generic IOMMU layer checks argsz range and override > > > > out-of-range > > > > + value. If the exact argsz is based on generic flags, they are > > > > checked > > > > + here as well. > > > > + > > > > +- Vendor IOMMU driver checks argsz based on vendor flags, UAPI > > > > data > > > > + is consumed based on flags > > > > + > > > > +Once again, use guest TLB invalidation as an example, argsz is > > > > based +on generic flags in the invalidation information. IOMMU > > > > generic code +shall process the UAPI data as the following: > > > > + > > > > +:: > > > > + > > > > + int iommu_cache_invalidate(struct iommu_domain *domain, struct > > > > device *dev, > > > > + void __user *uinfo) > > > > + { > > > > + /* Current kernel data size is the max to be copied > > > > from user */ > > > > + maxsz = sizeof(struct iommu_cache_invalidate_info); > > > > + memset((void *)&inv_info, 0, maxsz); > > > > + > > > > + /* > > > > + * No new spaces can be added before the variable sized > > > > union, the > > > > + * minimum size is the offset to the union. > > > > + */ > > > > + minsz = offsetof(struct iommu_cache_invalidate_info, > > > > granu); + > > > > + /* Copy minsz from user to get flags and argsz */ > > > > + if (copy_from_user(&inv_info, uinfo, minsz)) > > > > + return -EFAULT; > > > > + > > > > + /* Fields before variable size union is mandatory */ > > > > + if (inv_info.argsz < minsz) > > > > + return -EINVAL; > > > > + /* > > > > + * User might be using a newer UAPI header which has a > > > > larger data > > > > + * size, we shall support the existing flags within the > > > > current > > > > + * size. > > > > + */ > > > > + if (inv_info.argsz > maxsz) > > > > + inv_info.argsz = maxsz; > > > > + > > > > + /* Checking the exact argsz based on generic flags */ > > > > + if (inv_info.granularity == IOMMU_INV_GRANU_ADDR && > > > > + inv_info.argsz != offsetofend(struct > > > > iommu_cache_invalidate_info, > > > > + granu.addr_info)) > > > > > > Is it really reasonable to expect the user to specify argsz to the > > > exact union element for the callback? I'd certainly expect users > > > to simply use sizeof(struct iommu_cache_invalidate_info) and it > > > should therefore be sufficient to test >= here rather than jump > > > through hoops with an exact size. We're already changing > > > inv_info.argsz above to fit our known structure, it's > > > inconsistent to then expect it to be some exact value. > > > > > I was thinking argsz doesn't have to be the exact struct size. It > > should be whatever the sufficient & correct size used by the user > > for a given call. > > > > For example, current struct iommu_gpasid_bind_data {} only has VT-d > > data. If it gets extended with SMMU data in the union, VT-d vIOMMU > > emulation should only fill the union size of vt-d. > > But the user is simply going to have a struct iommu_gpasid_bind_data > and set argsz to sizeof that struct. The user is providing that > entire struct as the arg, so it doesn't really make sense to pinpoint > the last field of the union they chose to use. The fields of the > structure define which union is applicable. If you're following the > vfio interface as an example, sufficiently sized is all we require, > we don't ask for union member level granularity, which I think is > confusing and error prone for users. > > > > > + return -EINVAL; > > > > + > > > > + if (inv_info.granularity == IOMMU_INV_GRANU_PASID && > > > > + inv_info.argsz != offsetofend(struct > > > > iommu_cache_invalidate_info, > > > > + granu.pasid_info)) > > > > + return -EINVAL; > > > > + > > > > + /* Copy the remaining user data _after_ minsz */ > > > > + if (copy_from_user((void *)&inv_info + minsz, uinfo + > > > > minsz, > > > > + inv_info.argsz - minsz)) > > > > + return -EFAULT; > > > > + > > > > + return domain->ops->cache_invalidate(domain, dev, > > > > &inv_info); > > > > + } > > > > + Add a wrapper > > > > + __iommu_unbind_( kernel data, same user data, kernel copy) > > > > + > > This should be removed. Sorry about the confusion. The patch does > > not have two data pointers, just separate APIs for kernel and user. > > > > > > +Notice that in this example, since union size is determined by > > > > generic +flags, all checking to argsz is validated in the > > > > generic IOMMU layer, +vendor driver does not need to check > > > > argsz. However, if union size is +based on vendor data, such as > > > > iommu_sva_bind_gpasid(), it will be +vendor driver's > > > > responsibility to validate the exact argsz. > > > > > > struct iommu_cache_invalidate_info is a good example because it > > > explicitly states a table of type vs granularity validity. When > > > the cache_invalidate() callback is used by an internal user we can > > > consider it a bug in the caller if its usage falls outside of > > > these prescribed valid combinations, ie. iommu_ops callbacks may > > > assume a trusted caller that isn't trying to exploit any > > > loophole. > > Separate APIs are proposed in the patchset to address UAPIs > > with both kernel and user callers. Sorry about the last line in the > > example above. Currently, only unbind_gpasid() and page_response() > > have both kernel and userspace callers. e.g. > > > > /* userspace caller */ > > int iommu_sva_unbind_gpasid(struct iommu_domain *domain, struct > > device *dev, void __user *udata) > > > > /* in-kernel caller */ > > int __iommu_sva_unbind_gpasid(struct iommu_domain *domain, > > struct device *dev, struct iommu_gpasid_bind_data *data) > > > > We don;t expect in-kernel caller for cache invalidate in that it is > > implied in unmap, unbind operations. > > That specific function was only an example of an interface which has > invalid combinations where in-kernel it's the caller's responsibility > to abide by the rules, but a user interface needs further validation. > > > > But here > > > we've done nothing more than validated the supplied size to pass > > > it through to a non-user hardened callback. We didn't check the > > > version, > > Yes, I should move up the version check from vendor driver. > > > > > we didn't check that any of the undefined bits in cache or > > > granularity or padding were set, we don't know what flags might be > > > set in the union elements. > > You are right, we should sanitize reserved bits. > > > > > For example, if a user is able to set a > > > flag that gets ignored now, that means we can never use that flag > > > without potentially breaking that user in the future. > > Good point, all reserved/unused bits should be tested. > > > > > If a user can > > > pass in version 3141592654 now, then we can never use version for > > > validation. I see that intel_iommu_sva_invalidate() does test the > > > version, but has no obvious other hardening. I'm afraid we're > > > being far to lax about accepting a data structure provided by a > > > user, we should not assume good faith. Thanks, > > > > > Agreed. will add checks in the IOMMU generic layer for reserved > > bits. > > For VT-d vendor driver, we do check all bits in cache types, i.e. in > > intel/iommu.c > > for_each_set_bit(cache_type, > > (unsigned long *)&inv_info->cache, > > IOMMU_CACHE_INV_TYPE_NR) { > > > > > > one other hardening is to check vendor argsz. This is in the > > bind_gpasid call. > > > > if (data->argsz != offsetofend(struct > > iommu_gpasid_bind_data, vendor.vtd)) return -EINVAL; > > This is the same issue I raise above whether this is actually too > strict. The user is providing a full structure as the arg, the > structure defines the valid fields via its content, it shouldn't be > necessary to have field level granularity for argsz. Thanks, > > Alex > [Jacob Pan] _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu