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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 D657FC433E0 for ; Sat, 30 May 2020 19:14:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B9C78206F0 for ; Sat, 30 May 2020 19:14:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729294AbgE3TOa (ORCPT ); Sat, 30 May 2020 15:14:30 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54750 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728998AbgE3TOa (ORCPT ); Sat, 30 May 2020 15:14:30 -0400 Received: from ZenIV.linux.org.uk (zeniv.linux.org.uk [IPv6:2002:c35c:fd02::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 352F5C03E969; Sat, 30 May 2020 12:14:30 -0700 (PDT) Received: from viro by ZenIV.linux.org.uk with local (Exim 4.93 #3 (Red Hat Linux)) id 1jf6w4-000YbD-9X; Sat, 30 May 2020 19:14:24 +0000 Date: Sat, 30 May 2020 20:14:24 +0100 From: Al Viro To: Linus Torvalds Cc: Paolo Bonzini , Linux Kernel Mailing List , linux-fsdevel , KVM list Subject: Re: [PATCH 8/9] x86: kvm_hv_set_msr(): use __put_user() instead of 32bit __clear_user() Message-ID: <20200530191424.GR23230@ZenIV.linux.org.uk> References: <20200528234025.GT23230@ZenIV.linux.org.uk> <20200529232723.44942-1-viro@ZenIV.linux.org.uk> <20200529232723.44942-8-viro@ZenIV.linux.org.uk> <20200530143147.GN23230@ZenIV.linux.org.uk> <81563af6-6ea2-3e21-fe53-9955910e303a@redhat.com> <20200530183853.GQ23230@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, May 30, 2020 at 11:52:44AM -0700, Linus Torvalds wrote: > > It really isn't. > > Your very first statement shows how broken it is: > > > FWIW, the kvm side of things (vhost is yet another pile of fun) is > > > > [x86] kvm_hv_set_msr_pw(): > > arch/x86/kvm/hyperv.c:1027: if (__copy_to_user((void __user *)addr, instructions, 4)) > > HV_X64_MSR_HYPERCALL > > arch/x86/kvm/hyperv.c:1132: if (__clear_user((void __user *)addr, sizeof(u32))) > > HV_X64_MSR_VP_ASSIST_PAGE > > in both cases addr comes from > > gfn = data >> HV_X64_MSR_VP_ASSIST_PAGE_ADDRESS_SHIFT; > > addr = kvm_vcpu_gfn_to_hva(vcpu, gfn); > > if (kvm_is_error_hva(addr)) > > return 1; > > Just look at that. You have _zero_ indication that 'adds" is a user > space address. It could be a kernel address. > > That kvm_vcpu_gfn_to_hva() function is a complicated mess that first > looks for the right 'memslot', and basically uses a search with a > default slot to try to figure it out. It doesn't even use locking for > any of it, but assumes the arrays are stable, and that it can use > atomics to reliably read and set the last successfully found slot. > > And none of that code verifies that the end result is a user address. kvm_is_error_hva() is return addr >= PAGE_OFFSET;