From nobody Tue Feb 10 05:09:37 2026 Delivered-To: importer@patchew.org Received-SPF: pass (zohomail.com: domain of lists.xenproject.org designates 192.237.175.120 as permitted sender) client-ip=192.237.175.120; envelope-from=xen-devel-bounces@lists.xenproject.org; helo=lists.xenproject.org; Authentication-Results: mx.zohomail.com; dkim=pass; spf=pass (zohomail.com: domain of lists.xenproject.org designates 192.237.175.120 as permitted sender) smtp.mailfrom=xen-devel-bounces@lists.xenproject.org ARC-Seal: i=1; a=rsa-sha256; t=1608651848; cv=none; d=zohomail.com; s=zohoarc; b=AgW59vCu/3t+b4pXxyaO+vhRHVL/4IV3gnSAk4cXlVLLR1vaMyPY6HYGIFU8+0GRw0eX3d34yvFINyfizwWo1QOcVFADcYAdGYN/ssnfK0hXvqxBzM7oWwqwkBqOKZjwAywWJPsRz1QNzehCXFnWhHbZmm2Ntbjmru6u3FIpatc= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zohomail.com; s=zohoarc; t=1608651848; h=Cc:Date:From:In-Reply-To:List-Subscribe:List-Post:List-Id:List-Help:List-Unsubscribe:Message-ID:References:Sender:Subject:To; bh=kSPSsNxqjRsah0K2F/khe3S48PU9Vn+ea2ql+1qJVow=; b=Grqb9wu6/oJXZdM3IIf9ow+sH5AO9J/AnA5g+Qb/+ADmS1r5u2IAVpjPy1zC2e0dMHt9I7S4/srakPve7NFeiE2QFK+naYJHjd9ZPOmwiKwrN1aKQRvLXH1xci7ey8qUTmIXek2AkKIJDPhXt/mo0f1dYs9Ub65Zet43/fK+JX8= ARC-Authentication-Results: i=1; mx.zohomail.com; dkim=pass; spf=pass (zohomail.com: domain of lists.xenproject.org designates 192.237.175.120 as permitted sender) smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Return-Path: Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) by mx.zohomail.com with SMTPS id 16086518481321002.7207224052804; Tue, 22 Dec 2020 07:44:08 -0800 (PST) Received: from list by lists.xenproject.org with outflank-mailman.57962.101662 (Exim 4.92) (envelope-from ) id 1krjpD-0006es-5j; Tue, 22 Dec 2020 15:43:47 +0000 Received: by outflank-mailman (output) from mailman id 57962.101662; Tue, 22 Dec 2020 15:43:47 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1krjpD-0006ed-27; Tue, 22 Dec 2020 15:43:47 +0000 Received: by outflank-mailman (input) for mailman id 57962; Tue, 22 Dec 2020 15:43:45 +0000 Received: from mail.xenproject.org ([104.130.215.37]) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1krjpB-0006cH-8H for xen-devel@lists.xenproject.org; Tue, 22 Dec 2020 15:43:45 +0000 Received: from xenbits.xenproject.org ([104.239.192.120]) by mail.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1krjpA-0001pv-Q2; Tue, 22 Dec 2020 15:43:44 +0000 Received: from 54-240-197-235.amazon.com ([54.240.197.235] helo=ufe34d9ed68d054.ant.amazon.com) by xenbits.xenproject.org with esmtpsa (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1krjpA-0002Vd-Gp; Tue, 22 Dec 2020 15:43:44 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=xen.org; s=20200302mail; h=References:In-Reply-To:Message-Id:Date:Subject:Cc:To:From; bh=kSPSsNxqjRsah0K2F/khe3S48PU9Vn+ea2ql+1qJVow=; b=u7zwD9TpUghLdk5/4t796dN7R OOEKsJTI9epORlTXPMuVoXxnmmbIjmRfUdkldFMZAy9GA+ZhknOA4hcvMVw4n4cUV2qqawv7dMhOd Of74k7GR4v8G7Rb07S7LfRq8ISeZ5tbsc5hBO8WlTOoK7umNxl8HSn0bLLoh193yGWF7c=; From: Julien Grall To: xen-devel@lists.xenproject.org Cc: hongyxia@amazon.co.uk, Julien Grall , Jan Beulich , Paul Durrant Subject: [PATCH for-4.15 3/4] [RFC] xen/iommu: x86: Clear the root page-table before freeing the page-tables Date: Tue, 22 Dec 2020 15:43:37 +0000 Message-Id: <20201222154338.9459-4-julien@xen.org> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20201222154338.9459-1-julien@xen.org> References: <20201222154338.9459-1-julien@xen.org> X-ZohoMail-DKIM: pass (identity @xen.org) Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" From: Julien Grall The new per-domain IOMMU page-table allocator will now free the page-tables when domain's resources are relinquished. However, the root page-table (i.e. hd->arch.pg_maddr) will not be cleared. Xen may access the IOMMU page-tables afterwards at least in the case of PV domain: (XEN) Xen call trace: (XEN) [] R iommu.c#addr_to_dma_page_maddr+0x12e/0x1d8 (XEN) [] F iommu.c#intel_iommu_unmap_page+0x5d/0xf8 (XEN) [] F iommu_unmap+0x9c/0x129 (XEN) [] F iommu_legacy_unmap+0x26/0x63 (XEN) [] F mm.c#cleanup_page_mappings+0x139/0x144 (XEN) [] F put_page+0x4b/0xb3 (XEN) [] F put_page_from_l1e+0x136/0x13b (XEN) [] F devalidate_page+0x256/0x8dc (XEN) [] F mm.c#_put_page_type+0x236/0x47e (XEN) [] F mm.c#put_pt_page+0x6f/0x80 (XEN) [] F mm.c#put_page_from_l2e+0x8a/0xcf (XEN) [] F devalidate_page+0x3a3/0x8dc (XEN) [] F mm.c#_put_page_type+0x236/0x47e (XEN) [] F mm.c#put_pt_page+0x6f/0x80 (XEN) [] F mm.c#put_page_from_l3e+0x8a/0xcf (XEN) [] F devalidate_page+0x56c/0x8dc (XEN) [] F mm.c#_put_page_type+0x236/0x47e (XEN) [] F mm.c#put_pt_page+0x6f/0x80 (XEN) [] F mm.c#put_page_from_l4e+0x69/0x6d (XEN) [] F devalidate_page+0x6a0/0x8dc (XEN) [] F mm.c#_put_page_type+0x236/0x47e (XEN) [] F put_page_type_preemptible+0x13/0x15 (XEN) [] F domain.c#relinquish_memory+0x1ff/0x4e9 (XEN) [] F domain_relinquish_resources+0x2b6/0x36a (XEN) [] F domain_kill+0xb8/0x141 (XEN) [] F do_domctl+0xb6f/0x18e5 (XEN) [] F pv_hypercall+0x2f0/0x55f (XEN) [] F lstar_enter+0x112/0x120 This will result to a use after-free and possibly an host crash or memory corruption. Freeing the page-tables further down in domain_relinquish_resources() would not work because pages may not be released until later if another domain hold a reference on them. Once all the PCI devices have been de-assigned, it is actually pointless to access modify the IOMMU page-tables. So we can simply clear the root page-table address. Fixes: 3eef6d07d722 ("x86/iommu: convert VT-d code to use new page table al= locator") Signed-off-by: Julien Grall --- This is an RFC because it would break AMD IOMMU driver. One option would be to move the call to the teardown callback earlier on. Any opinions? --- xen/drivers/passthrough/x86/iommu.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/xen/drivers/passthrough/x86/iommu.c b/xen/drivers/passthrough/= x86/iommu.c index 779dbb5b98ba..99a23177b3d2 100644 --- a/xen/drivers/passthrough/x86/iommu.c +++ b/xen/drivers/passthrough/x86/iommu.c @@ -267,6 +267,16 @@ int iommu_free_pgtables(struct domain *d) struct page_info *pg; unsigned int done =3D 0; =20 + /* + * Pages will be moved to the free list in a bit. So we want to + * clear the root page-table to avoid any potential use after-free. + * + * XXX: This only code works for Intel vT-D. + */ + spin_lock(&hd->arch.mapping_lock); + hd->arch.vtd.pgd_maddr =3D 0; + spin_unlock(&hd->arch.mapping_lock); + spin_lock(&hd->arch.pgtables.lock); while ( (pg =3D page_list_remove_head(&hd->arch.pgtables.list)) ) { --=20 2.17.1