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=-19.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_GIT 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 CE014C4338F for ; Mon, 26 Jul 2021 16:04:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B480C60F6F for ; Mon, 26 Jul 2021 16:04:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237646AbhGZPYA (ORCPT ); Mon, 26 Jul 2021 11:24:00 -0400 Received: from mail.kernel.org ([198.145.29.99]:54394 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237414AbhGZPPo (ORCPT ); Mon, 26 Jul 2021 11:15:44 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id E932460F38; Mon, 26 Jul 2021 15:54:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1627314882; bh=dCtGQNwzd3c0hMcer7DUisp5Ap121SIXtSkorzoUrhQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=EnjrFsu0Uy149SKzma0ttF1k7sV96MIkXmjvthlnU/6nH7dh90WHN8UIIk8GTPXsT stJdYURgpgo0i719dImaw1bbLDTIUYctICu1Vk5rJyCe37kpzxBVCq8mGQGScyU6tw 8CaJ57DC9Nvq69/mARqg1lP0msxyrLdRZNCutzEU= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, David Stevens , 3pvd@google.com, Jann Horn , Jason Gunthorpe , Paolo Bonzini , Ovidiu Panait Subject: [PATCH 4.19 111/120] KVM: do not assume PTE is writable after follow_pfn Date: Mon, 26 Jul 2021 17:39:23 +0200 Message-Id: <20210726153836.031515657@linuxfoundation.org> X-Mailer: git-send-email 2.32.0 In-Reply-To: <20210726153832.339431936@linuxfoundation.org> References: <20210726153832.339431936@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Paolo Bonzini commit bd2fae8da794b55bf2ac02632da3a151b10e664c upstream. In order to convert an HVA to a PFN, KVM usually tries to use the get_user_pages family of functinso. This however is not possible for VM_IO vmas; in that case, KVM instead uses follow_pfn. In doing this however KVM loses the information on whether the PFN is writable. That is usually not a problem because the main use of VM_IO vmas with KVM is for BARs in PCI device assignment, however it is a bug. To fix it, use follow_pte and check pte_write while under the protection of the PTE lock. The information can be used to fail hva_to_pfn_remapped or passed back to the caller via *writable. Usage of follow_pfn was introduced in commit add6a0cd1c5b ("KVM: MMU: try to fix up page faults before giving up", 2016-07-05); however, even older version have the same issue, all the way back to commit 2e2e3738af33 ("KVM: Handle vma regions with no backing page", 2008-07-20), as they also did not check whether the PFN was writable. Fixes: 2e2e3738af33 ("KVM: Handle vma regions with no backing page") Reported-by: David Stevens Cc: 3pvd@google.com Cc: Jann Horn Cc: Jason Gunthorpe Cc: stable@vger.kernel.org Signed-off-by: Paolo Bonzini [OP: backport to 4.19, adjust follow_pte() -> follow_pte_pmd()] Signed-off-by: Ovidiu Panait Signed-off-by: Greg Kroah-Hartman --- virt/kvm/kvm_main.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-) --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -1495,9 +1495,11 @@ static int hva_to_pfn_remapped(struct vm kvm_pfn_t *p_pfn) { unsigned long pfn; + pte_t *ptep; + spinlock_t *ptl; int r; - r = follow_pfn(vma, addr, &pfn); + r = follow_pte_pmd(vma->vm_mm, addr, NULL, NULL, &ptep, NULL, &ptl); if (r) { /* * get_user_pages fails for VM_IO and VM_PFNMAP vmas and does @@ -1512,14 +1514,19 @@ static int hva_to_pfn_remapped(struct vm if (r) return r; - r = follow_pfn(vma, addr, &pfn); + r = follow_pte_pmd(vma->vm_mm, addr, NULL, NULL, &ptep, NULL, &ptl); if (r) return r; + } + if (write_fault && !pte_write(*ptep)) { + pfn = KVM_PFN_ERR_RO_FAULT; + goto out; } if (writable) - *writable = true; + *writable = pte_write(*ptep); + pfn = pte_pfn(*ptep); /* * Get a reference here because callers of *hva_to_pfn* and @@ -1534,6 +1541,8 @@ static int hva_to_pfn_remapped(struct vm */ kvm_get_pfn(pfn); +out: + pte_unmap_unlock(ptep, ptl); *p_pfn = pfn; return 0; }