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=-14.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham 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 DDA59C2D0C0 for ; Fri, 6 Dec 2019 02:08:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AA99D2245C for ; Fri, 6 Dec 2019 02:08:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726184AbfLFCI0 (ORCPT ); Thu, 5 Dec 2019 21:08:26 -0500 Received: from foss.arm.com ([217.140.110.172]:55216 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726065AbfLFCI0 (ORCPT ); Thu, 5 Dec 2019 21:08:26 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 4448A31B; Thu, 5 Dec 2019 18:08:20 -0800 (PST) Received: from localhost.localdomain (unknown [10.169.40.54]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 834003F718; Thu, 5 Dec 2019 18:08:16 -0800 (PST) From: Jia He To: Marc Zyngier , James Morse , linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu Cc: Julien Thierry , Suzuki K Poulose , linux-kernel@vger.kernel.org, Jia He , Ard Biesheuvel Subject: [PATCH] KVM: arm: remove excessive permission check in kvm_arch_prepare_memory_region Date: Fri, 6 Dec 2019 10:08:02 +0800 Message-Id: <20191206020802.196108-1-justin.he@arm.com> X-Mailer: git-send-email 2.17.1 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org In kvm_arch_prepare_memory_region, arm kvm regards the memory region as writable if the flag has no KVM_MEM_READONLY, and the vm is readonly if !VM_WRITE. But there is common usage for setting kvm memory region as follows: e.g. qemu side (see the PROT_NONE flag) 1. mmap(NULL, size, PROT_NONE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0); memory_region_init_ram_ptr() 2. re mmap the above area with read/write authority. Such example is used in virtio-fs qemu codes which hasn't been upstreamed [1]. But seems we can't forbid this example. Without this patch, it will cause an EPERM during kvm_set_memory_region() and cause qemu boot crash. As told by Ard, "the underlying assumption is incorrect, i.e., that the value of vm_flags at this point in time defines how the VMA is used during its lifetime. There may be other cases where a VMA is created with VM_READ vm_flags that are changed to VM_READ|VM_WRITE later, and we are currently rejecting this use case as well." [1] https://gitlab.com/virtio-fs/qemu/blob/5a356e/hw/virtio/vhost-user-fs.c#L488 Cc: Ard Biesheuvel Suggested-by: Ard Biesheuvel Signed-off-by: Jia He --- virt/kvm/arm/mmu.c | 9 --------- 1 file changed, 9 deletions(-) diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c index 38b4c910b6c3..a48994af70b8 100644 --- a/virt/kvm/arm/mmu.c +++ b/virt/kvm/arm/mmu.c @@ -2301,15 +2301,6 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm, if (!vma || vma->vm_start >= reg_end) break; - /* - * Mapping a read-only VMA is only allowed if the - * memory region is configured as read-only. - */ - if (writable && !(vma->vm_flags & VM_WRITE)) { - ret = -EPERM; - break; - } - /* * Take the intersection of this VMA with the memory region */ -- 2.17.1