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=-13.2 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_SANE_1 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 EA356C43603 for ; Fri, 6 Dec 2019 08:29:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C77CB24677 for ; Fri, 6 Dec 2019 08:29:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726621AbfLFI3J (ORCPT ); Fri, 6 Dec 2019 03:29:09 -0500 Received: from foss.arm.com ([217.140.110.172]:35650 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726088AbfLFI3J (ORCPT ); Fri, 6 Dec 2019 03:29:09 -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 94BCC31B; Fri, 6 Dec 2019 00:29:08 -0800 (PST) Received: from localhost (e113682-lin.copenhagen.arm.com [10.32.145.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 76F653F718; Fri, 6 Dec 2019 00:32:18 -0800 (PST) Date: Fri, 6 Dec 2019 09:29:06 +0100 From: Christoffer Dall To: Jia He Cc: Marc Zyngier , James Morse , linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, Ard Biesheuvel , linux-kernel@vger.kernel.org, Julien Thierry , Suzuki K Poulose Subject: Re: [PATCH] KVM: arm: remove excessive permission check in kvm_arch_prepare_memory_region Message-ID: <20191206082906.GA2749@e113682-lin.lund.arm.com> References: <20191206020802.196108-1-justin.he@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191206020802.196108-1-justin.he@arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Dec 06, 2019 at 10:08:02AM +0800, Jia He wrote: > 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 Reviewed-by: Christoffer Dall > > 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 > > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel